tag:blogger.com,1999:blog-34802284034034352662024-03-26T04:57:24.020-07:00QRP HomeBuilder - QRPHB -Celebrating 28 years on the web! Scratch analog electronic design — radio & audio. Join us on the bench as we learn & measure home-built, analog electronic circuitsVasily Ivanenkohttp://www.blogger.com/profile/17387516134063150119noreply@blogger.comBlogger80125tag:blogger.com,1999:blog-3480228403403435266.post-41010732760718355302024-02-25T21:29:00.000-08:002024-02-25T21:29:11.470-08:00The 50 Ω audio preamplifier that goes after a diode ring product detector in DC receivers - Part 1<p> I posted my longest video to date:</p><div class="separator" style="clear: both; text-align: center;"><iframe allowfullscreen="" class="BLOG_video_class" height="405" src="https://www.youtube.com/embed/8e7U6gObfiY" width="487" youtube-src-id="8e7U6gObfiY"></iframe></div><p></p><p><br /></p><p>I'll post a few images from the video in the days ahead. Making such a big video felt pretty exhausting.</p><p>Best to you<br /></p><p><br /></p>Vasily Ivanenkohttp://www.blogger.com/profile/17387516134063150119noreply@blogger.com1tag:blogger.com,1999:blog-3480228403403435266.post-87936560490878886342024-01-04T18:02:00.000-08:002024-01-06T13:44:03.251-08:00Audio Frequency Return Loss Bridge — 50 Ω —<div class="separator" style="clear: both; text-align: center;"><br /></div><div class="separator" style="clear: both; text-align: left;"><br /></div><div class="separator" style="clear: both; text-align: left;"> <iframe allowfullscreen="" class="BLOG_video_class" height="363" src="https://www.youtube.com/embed/deEfGZkoVNY" width="437" youtube-src-id="deEfGZkoVNY"></iframe></div><p></p><div class="separator" style="clear: both; text-align: center;"><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjeW2SwvccVcJhsqtgFX7dAAbRmuyAa3TgNsDJFJXZ6pZDT2sRQXVdURLQW1THFHuQvxjn5XJ8gW1vuH5j7mk6pijjm4_kbkf8PKltwWZaxk4T8LH5KZSZ-U8rwagPxyefaYarNEZw3vQjD7f9__xkMNTIcm6TtOx607tPw0clg2l9LXTn_pFjf0yS_IjNX/s934/v8.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="576" data-original-width="934" height="394" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjeW2SwvccVcJhsqtgFX7dAAbRmuyAa3TgNsDJFJXZ6pZDT2sRQXVdURLQW1THFHuQvxjn5XJ8gW1vuH5j7mk6pijjm4_kbkf8PKltwWZaxk4T8LH5KZSZ-U8rwagPxyefaYarNEZw3vQjD7f9__xkMNTIcm6TtOx607tPw0clg2l9LXTn_pFjf0yS_IjNX/w640-h394/v8.jpg" width="640" /></a></div></div><p>Above — +/- 15 VDC input and ground ports on die cast chassis.<br /></p><p> <a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEivGKbLbDjtqCqEys7KqxjA9sGT4V__gp46MZ68P9Xo4VCKVoCEAhTFw3cDtORTQvN8ur8GXOdbz3fbCNLegfU5HVFHLuQiqC-0c-rxI0TUjJgqzxrYs9FlMNqZRzUIDbFMKPTPlJQ1Ie6TUIIKKUf_vkDkeS4j2gHHDrOjKE2ViG4fcawtDB9eU4331ZRz/s656/v6.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="640" data-original-width="656" height="624" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEivGKbLbDjtqCqEys7KqxjA9sGT4V__gp46MZ68P9Xo4VCKVoCEAhTFw3cDtORTQvN8ur8GXOdbz3fbCNLegfU5HVFHLuQiqC-0c-rxI0TUjJgqzxrYs9FlMNqZRzUIDbFMKPTPlJQ1Ie6TUIIKKUf_vkDkeS4j2gHHDrOjKE2ViG4fcawtDB9eU4331ZRz/w640-h624/v6.jpg" width="640" /></a><br />Above — Side view showing all the input and output ports.<br /></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEicMSgQvBFlbRCykvIRqboP4_4Jk0Lx65Na9BehNFyf5YIGMZ9Kv-s1heRYT_MIrpkNQS9kkZTmFFKSbaogvjimFsCSb7Rv3BIavEc1r8bQQO42O544Os9b4huxM0wSVw7K4a7DRKTMyNciUu67IRcuWWaUL-dDS6xWquBqHpI55To53uWrAhi19_8WtNWK/s989/RL%20Bridge.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="564" data-original-width="989" height="364" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEicMSgQvBFlbRCykvIRqboP4_4Jk0Lx65Na9BehNFyf5YIGMZ9Kv-s1heRYT_MIrpkNQS9kkZTmFFKSbaogvjimFsCSb7Rv3BIavEc1r8bQQO42O544Os9b4huxM0wSVw7K4a7DRKTMyNciUu67IRcuWWaUL-dDS6xWquBqHpI55To53uWrAhi19_8WtNWK/w640-h364/RL%20Bridge.png" width="640" /></a></div><br /><p>Above — Schematic of 50 Ω differential bridge assembly. I employed a split DC supply to boost headroom and simplify op-amp biasing.I use the moderate power BD139/140 for the filter transistors: a sturdy part with low flicker noise -- no apologies.<br /></p><p></p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjyCkYP6m396O9UTXlz9WPv3c7MiyCGxeb5pH-ZvhCIzA8fcKrnbwtaC2cyX3ZXh4jFynZ37wTAcDeCA4UTvOxhITFc_qeDmr-SBMPRBySWKfTvuAT5X8az34UZCJHRwqOUZnQ-9jXTzDNcqcwoPC7BtXCSCOAeK3K4L1maHYm3IHBLxWuNRcsc_Ae4i2kE/s785/v2.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="564" data-original-width="785" height="460" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjyCkYP6m396O9UTXlz9WPv3c7MiyCGxeb5pH-ZvhCIzA8fcKrnbwtaC2cyX3ZXh4jFynZ37wTAcDeCA4UTvOxhITFc_qeDmr-SBMPRBySWKfTvuAT5X8az34UZCJHRwqOUZnQ-9jXTzDNcqcwoPC7BtXCSCOAeK3K4L1maHYm3IHBLxWuNRcsc_Ae4i2kE/w640-h460/v2.jpg" width="640" /></a></div><p><br />Above — Input ports.<b> Left:</b> DC input (direct with a wire) using an SMA connector. <b>Middle:</b> AC coupled port with RCA jack. Built in 220 µF coupling cap allows testing of 50 ohm input Z audio amplifiers with no worries about the bridge causing a DC disturbance of the biasing or current.<br /><b>Right:</b> 50 Ω audio signal generator input with a BNC connector.</p><p> </p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgUptMiNpa8inkyozDTIZAeUYxxM_PUyGo2GVnYGB3IQ7SRyZ5aQd8cnMCLWysBHY3NEFznZfc7OXhGWCNfmFdIBFFGlNmawAKF5dgVEdbcm4_i8FKL-X4aK9RGEkZc0_mfPBdPmBX79T-yXwVtLj-3AVjkNbpVjFpEP_AQrtLgNXIyfnsPAe3O8rSBuwfY/s951/v4.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="617" data-original-width="951" height="416" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgUptMiNpa8inkyozDTIZAeUYxxM_PUyGo2GVnYGB3IQ7SRyZ5aQd8cnMCLWysBHY3NEFznZfc7OXhGWCNfmFdIBFFGlNmawAKF5dgVEdbcm4_i8FKL-X4aK9RGEkZc0_mfPBdPmBX79T-yXwVtLj-3AVjkNbpVjFpEP_AQrtLgNXIyfnsPAe3O8rSBuwfY/w640-h416/v4.jpg" width="640" /></a></div><p></p><p>Above — The output of the instrumentation amp U1 gets buffered by the U2a follower. Low impedance output to use a 50 Ω terminated DSO as the detector. <br /></p><p> </p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi9WCL2KyzfVeJhpnY-KaBLqJxXZ_UHFQZBHFlQYQT-SY2DQxpqdpVL-v33EV3vv0eQBjuSOLcYVwAg2xnVPvibA-KtrdrAy2UTpF0CySIDjd67lmA009U5HXrW8SMt-6YMfYwEPpfNLjBzYDx_YNXKPZgEPXLKSFoYtLZxWCBB4aZ0S6w67qbGdtDjDcvJ/s708/ZIF%20receiver.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="351" data-original-width="708" height="318" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi9WCL2KyzfVeJhpnY-KaBLqJxXZ_UHFQZBHFlQYQT-SY2DQxpqdpVL-v33EV3vv0eQBjuSOLcYVwAg2xnVPvibA-KtrdrAy2UTpF0CySIDjd67lmA009U5HXrW8SMt-6YMfYwEPpfNLjBzYDx_YNXKPZgEPXLKSFoYtLZxWCBB4aZ0S6w67qbGdtDjDcvJ/w640-h318/ZIF%20receiver.png" width="640" /></a></div><p></p><p>Above — In analog output direct conversion or superhet receivers that use a diode ring product detector, we often employ a simple post product detector network that some refer to as a diplexer. It's not quite a diplexer, although, it does provide a 50 Ω termination to a narrow band of RF frequencies. <br />You might sweep this network at AF and RF with return loss bridges to study the input match versus frequency.<br /></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiN2yTDtqsAMWutWvTjtU9nOCFSbZ56Y8sLHhlufUeFJ3gfXgFQBte6mGDg1jy9DeEvji6BmiPiNcK_pi4xqFH-9N0phf9Z6ElS_n6CnepqHoWGRlEq6_5pKbWjz-7EXyEyi01agITw0iTI_HXY8ztXXThFpFZpviavrW3ctgBBk-YgjRpKABUZh0lNgqmN/s524/return%20loss.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="448" data-original-width="524" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiN2yTDtqsAMWutWvTjtU9nOCFSbZ56Y8sLHhlufUeFJ3gfXgFQBte6mGDg1jy9DeEvji6BmiPiNcK_pi4xqFH-9N0phf9Z6ElS_n6CnepqHoWGRlEq6_5pKbWjz-7EXyEyi01agITw0iTI_HXY8ztXXThFpFZpviavrW3ctgBBk-YgjRpKABUZh0lNgqmN/s16000/return%20loss.png" /></a></div><p style="text-align: left;"></p><p>Above — My current post product detector network with part values chosen to <b>try </b>and match from 200 Hz to 200 MHz. This proved very difficult with such a simple network because the bandwidth is huge and really this calls for 2-3 networks to get it done. However, in simple receivers, this basic network works OK. The impedance match looks terrible from ~ 1 to 4 MHz, however, trying to fix this worsened the match elsewhere.</p><p>I performed the above AF measurements with my old audio return loss bridge built in 2010. It failed recently -- and that failure prompted me to design and build this new AF return loss bridge.<br /> <br />Compromise is a key term in simpler RF design. The network components shown gave me the best overall input Z match from 200 Hz to 200 MHz. This network also provided decent low-pass filtration of the RF lurking in the product detector's audio output. A 220 µF (or higher value) audio coupling capacitor helps keep the input noise down in the AF preamp. <br /></p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiFqTuJIQKbfePLVfU1oxk0OEz97WOQwVSv7WXgObNgkOzKlqn6wgkSS5NgjotHo1UVEXuuxIEzBo_aFp5ldiIy3W45CBLY4VnoiqVj7tgTch7QTaki6rZ9KihoYdmPIhJE6679y0UGzYk3kVEHisv-yxH1PWDSy9KBGmdmpPFNl2wm_aEpAuiTjklUUwk9/s695/pMnetworkSweep.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="475" data-original-width="695" height="438" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiFqTuJIQKbfePLVfU1oxk0OEz97WOQwVSv7WXgObNgkOzKlqn6wgkSS5NgjotHo1UVEXuuxIEzBo_aFp5ldiIy3W45CBLY4VnoiqVj7tgTch7QTaki6rZ9KihoYdmPIhJE6679y0UGzYk3kVEHisv-yxH1PWDSy9KBGmdmpPFNl2wm_aEpAuiTjklUUwk9/w640-h438/pMnetworkSweep.png" width="640" /></a></div><br />Above — A 50 MHz wide sweep of the post product detector network in a tracking generator-spectrum analyzer. The 220 µF capacitor was removed for this RF measure.<br /><p></p><p></p><p> <a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEit3IXH-AE5d5oPTPhoTAMCYn0WvktT2PRRlygWl2qoVKVd_xmUyO100Hc_94Shvbp1reVySGOqMN7y4rfGCfWareDi9z65sXqdjgsuBqmIEAbImiVkw9UgQBZuP_8988FWsO_Zx3V20UQI5PKXcpRLxJ8fR0RLc26bqgKQqSU7zRTQo9GFFUP9pfumaiO_/s930/v12.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="597" data-original-width="930" height="410" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEit3IXH-AE5d5oPTPhoTAMCYn0WvktT2PRRlygWl2qoVKVd_xmUyO100Hc_94Shvbp1reVySGOqMN7y4rfGCfWareDi9z65sXqdjgsuBqmIEAbImiVkw9UgQBZuP_8988FWsO_Zx3V20UQI5PKXcpRLxJ8fR0RLc26bqgKQqSU7zRTQo9GFFUP9pfumaiO_/w640-h410/v12.jpg" width="640" /></a></p><p>Above — Testing gear used in the video: a 50 Ω Mini Circuits SMA terminator + barrel connector to 50 Ω coax -- and an RCA jack with a 2K potentiometer.<br /></p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjK5lrprz2o3ai-SkK_RsoUUW_juKH7S3U6xDkxat5x_kN7Zmw4OcqJ37DDmbkItIMa1YB7mENjK9ENw8AJ5BzvjyV0dXtSdfCL72OOP_UsEflw-wDP9MiBlaB04RtnAHocOSx6XVNGYygt-hlKRl5yO0cPZhqJjs3QDT1LplSzrn9vR2kSeYG-93Ggxx1H/s835/v7.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="624" data-original-width="835" height="478" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjK5lrprz2o3ai-SkK_RsoUUW_juKH7S3U6xDkxat5x_kN7Zmw4OcqJ37DDmbkItIMa1YB7mENjK9ENw8AJ5BzvjyV0dXtSdfCL72OOP_UsEflw-wDP9MiBlaB04RtnAHocOSx6XVNGYygt-hlKRl5yO0cPZhqJjs3QDT1LplSzrn9vR2kSeYG-93Ggxx1H/w640-h478/v7.jpg" width="640" /></a></div><br /> Above — It's always fun to acquire more test gear.<br /><p></p>Vasily Ivanenkohttp://www.blogger.com/profile/17387516134063150119noreply@blogger.com0tag:blogger.com,1999:blog-3480228403403435266.post-40427338482963914552023-11-01T12:39:00.016-07:002023-11-15T13:26:01.692-08:0050.1 MHz VFO + Hybrid Combiner for 2 Tone VHF Testing<p> <iframe allowfullscreen="" class="BLOG_video_class" height="395" src="https://www.youtube.com/embed/pUVYrSkOmSo" width="475" youtube-src-id="pUVYrSkOmSo"></iframe></p><p></p><p>Above — This blog post supports the video shown above</p><p></p><p><b>[1] SIGNAL GENERATOR</b></p><p></p><p>Steve AA7U & Everett N4CY, built gear -- plus a procedure to test Intermodulation Distortion (IMD) on a loop amplifier using a Siglent SDG2042X generator and SSA3021X spectrum analyzer. <a href="https://siglent.co.uk/inter-modulation-distortion-imd-testing" target="_blank">Click on this hyperlink</a> to read about it. I'm a fan of Siglent test equipment.<br /></p><p>My strategy employs a 50.0 MHz crystal oscillator-based signal generator plus a 50.1 MHz VFO as the second signal source. My VFO tunes from about 49.6 to 51.8 MHz via a front panel air variable capacitor. <br /></p><p><b>My 50.1 MHz VFO</b></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjYIgmxaUoRWM89liJOo8sXDq_ak3neZwkNehpXD6LdFBsE2661GJ9ooT1NsT-4kkhoikw2Pt3DoCrE7J1c_bYbqrJl_JveNYZWd38Q8uvrp2GRXnDSABowS7sDgP-CJ19-A6oKoDC7KJjyJONJC3gzjsksvBy-GFt4s4zB-LqGnMOeEppwhpP_N0LlzzVi/s792/LO-final.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="579" data-original-width="792" height="468" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjYIgmxaUoRWM89liJOo8sXDq_ak3neZwkNehpXD6LdFBsE2661GJ9ooT1NsT-4kkhoikw2Pt3DoCrE7J1c_bYbqrJl_JveNYZWd38Q8uvrp2GRXnDSABowS7sDgP-CJ19-A6oKoDC7KJjyJONJC3gzjsksvBy-GFt4s4zB-LqGnMOeEppwhpP_N0LlzzVi/w640-h468/LO-final.png" width="640" /></a></div><br /><p></p><p></p><p><b></b></p>Above — VFO schematic. Although I had worked out the low-pass filter L and C values, I built this VFO without a schematic and perhaps would build it differently if I needed to make another. I might consider tuning the output of the differential amplifier buffer for more output power and less harmonic energy.<p></p><p>I thought mostly about temperature drift when making this -- I started with JFET amp as the oscillator and struggled to make it work. This would be wise since a JFET offers better temperature drift over a BJT and gives a cleaner output signal with lower phase noise. However, I only had 1 day for this entire project and got frustrated. I deployed a common base PNP BJT local oscillator (LO) that never fails for me.</p><p>Both the LO and its buffer get regulated, well filtered DC. The LO gets temperature compensation/separation from the 8.2 volt Zener diode-based voltage regulator by way of 2 R C low-pass filters. I applied several C0G caps to resonate the tank and ran 2 air variable trimmer capacitors -- 1 as the main board frequency trimmer, the other as the front panel tuning control.</p><p>The LO gets lightly coupled via 1 pF to a differential amplifier emitter fed 10 mA with a current source. Differential amps offer strong reverse isolation, plus a reduced 2nd harmonic if the BJT balance is OK. The BC546 pair offer reasonable balance right out of the bin (without matching) & the BC546C serves as my go-to differential amp BJT from DC to ~ 100 MHz. The 10 mA current source, plus the 21 mA current in the final feedback amp provide heat for my temperature compensation scheme.</p><p>Low-pass filters built using T30-10 toroids worked OK. This was a board cram -- so the inductors are not spaced apart as much as when more board space is available. The 22 gauge air inductor measured ~ 374 nH & seems well anchored to the main 1-sided board with J-B Weld epoxy, plus the grounded coil lead soldered to the main board. The main board = 1/16″ (1.60 mm) Half Ounce 500 Series Copper Clad Board from MG Chemicals.<br /></p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhAWRIOPCzPcqEOiEZDMw_ZqqH-j0s8jgHap0Q3D4JqNBulqB8ziHTcl35GBjmfD74N8IxCAUcNNMAxKHDT_ClEjLxIRX37LDm5JJwgHw-ETT0hErqPHeIgcRocXbrnSCbRNjPoiCQbd18q7zyoNgt6KJvYpLvITeEvMdDvSxLU07oN1pNI4hgoYk3DlY4E/s1092/goo1.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="578" data-original-width="1092" height="338" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhAWRIOPCzPcqEOiEZDMw_ZqqH-j0s8jgHap0Q3D4JqNBulqB8ziHTcl35GBjmfD74N8IxCAUcNNMAxKHDT_ClEjLxIRX37LDm5JJwgHw-ETT0hErqPHeIgcRocXbrnSCbRNjPoiCQbd18q7zyoNgt6KJvYpLvITeEvMdDvSxLU07oN1pNI4hgoYk3DlY4E/w640-h338/goo1.jpg" width="640" /></a></div><br />Above — Copper board under test. To simulate the front panel capacitor, I've got the air variable front panel tuning cap in a small bracket that I got from a local Builders merchant. I have several for holding caps, jacks and potentiometers during test phase circuit development. Mine are all pre-drilled with the proper sized holes to fit pots jacks, or air-variable trimmer caps.<br /><p></p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjb1ewo9M3fkDKcvvI7AGlUlt71q7buaRPnZPfJQXL48IxDuu8y6DOcNLnYP4fJ8J2PmZ0N2Ne2dPwOJ-2Ysj41VyBf7MWKU1EblZ0bl9vAe7lCWiYngBOuDsGOz_-CJ8Pt9g1Th_rz3-lrtii_HMEN-364dynmZEcz3xPQpsMWIRmdLt_l3ypXM33d8Wjz/s1145/g77.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="603" data-original-width="1145" height="338" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjb1ewo9M3fkDKcvvI7AGlUlt71q7buaRPnZPfJQXL48IxDuu8y6DOcNLnYP4fJ8J2PmZ0N2Ne2dPwOJ-2Ysj41VyBf7MWKU1EblZ0bl9vAe7lCWiYngBOuDsGOz_-CJ8Pt9g1Th_rz3-lrtii_HMEN-364dynmZEcz3xPQpsMWIRmdLt_l3ypXM33d8Wjz/w640-h338/g77.jpg" width="640" /></a></div><p>Above — Close up of the tank coil secured with a messy application of epoxy.<br /></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEir1mc49qo9scDioMqsOBz68JBt2fTVHFutdpHXZNTtdvBP24Efjb5MHBLiELTiCNGsIOBZcWpfKUxT-3nz-IBNrft8Qvd8oicqu-fvjwruU9da7xm_O5wNc_tWMw14r2tho0Y7AwrOIn_ckvETxRTYFqSHYzt3qq5NB-vRBxcWSoTbSguMyvJhVViSgiu_/s1133/g56.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="624" data-original-width="1133" height="352" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEir1mc49qo9scDioMqsOBz68JBt2fTVHFutdpHXZNTtdvBP24Efjb5MHBLiELTiCNGsIOBZcWpfKUxT-3nz-IBNrft8Qvd8oicqu-fvjwruU9da7xm_O5wNc_tWMw14r2tho0Y7AwrOIn_ckvETxRTYFqSHYzt3qq5NB-vRBxcWSoTbSguMyvJhVViSgiu_/w640-h352/g56.jpg" width="640" /></a></div><p></p><p>Above — Side view. The actual front panel capacitor leads were this long to allow slack to put on the herring tin cover. The Herring Tin lid added much difficulty with temperature compensation and construction tactics -- but I got it done! The idea of the herring tin cover came from <a href="https://soldersmoke.blogspot.com/2023/10/bringing-faulty-herring-aid-5-receiver.html" target="_blank">this blog post</a><br /></p><p></p><div class="separator" style="clear: both; text-align: center;"></div><div class="separator" style="clear: both; text-align: center;"></div><div class="separator" style="clear: both; text-align: center;"></div><div class="separator" style="clear: both; text-align: center;"></div><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhYf_odqCG7FWx8UmhA-BflPG5Tb2WNPh1HHN0Jlq3pYyjQx1Ud5huCewwQL0ApdRfKleIjJKinsl0QIp8aIjrCcwxD_rNmxRLnLKB3j31GN73mNU9P3BaAfITKJZmq-MsPPKCfSAs9MfgPE0pnav6h_nVHTYmiUhyphenhyphenG_0LL6UMD8IgCVY1Ac219unXM-KOs/s902/f11.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="526" data-original-width="902" height="374" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhYf_odqCG7FWx8UmhA-BflPG5Tb2WNPh1HHN0Jlq3pYyjQx1Ud5huCewwQL0ApdRfKleIjJKinsl0QIp8aIjrCcwxD_rNmxRLnLKB3j31GN73mNU9P3BaAfITKJZmq-MsPPKCfSAs9MfgPE0pnav6h_nVHTYmiUhyphenhyphenG_0LL6UMD8IgCVY1Ac219unXM-KOs/w640-h374/f11.jpg" width="640" /></a></div><p>Above —View for the VFO showing the DC input port ( an RCA connector ) plus the SMA RF output port. 2 bolts hold the tin to the copper clad board.<br /></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgWfd4RgTJwULwhdpHV9H49kswI_rFhlEizVQh4Lvk11NIsWo4-VwW5bDMfQembTVHmDm9-StbfWbPw15V8SjN0eeWnlsIzqqpj8wPJOfvGKh8FfDZhqxU9utjrDLiMYzUbwDnRJG6b5p0zjzdvpsSpeXouBE-SC_uBkwmRKLg2btzG6afVFznlFbD_qIUJ/s578/f5.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="562" data-original-width="578" height="622" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgWfd4RgTJwULwhdpHV9H49kswI_rFhlEizVQh4Lvk11NIsWo4-VwW5bDMfQembTVHmDm9-StbfWbPw15V8SjN0eeWnlsIzqqpj8wPJOfvGKh8FfDZhqxU9utjrDLiMYzUbwDnRJG6b5p0zjzdvpsSpeXouBE-SC_uBkwmRKLg2btzG6afVFznlFbD_qIUJ/w640-h622/f5.jpg" width="640" /></a></div><p>Above — My 50.0 MHz xtal based oscillator next to the Herring made VFO. Ready for 2 tone testing. The front panel tuning capacitor is front left. The front panel bolt just fills in a hole I drilled by mistake.</p><p>If I want to drive a DUT such as a high IP3 amp -- or say a diode ring mixer ( I rarely use them anymore), I'll chain up 1 of 3 separate, sealed up wide band amplifiers that range from 12 dB to 26 dB gain (up to 150 MHz or so). I also have a plethora of low-pass and band-pass filters in sealed Hammond cases that go from 5 MHz to microwave if needed.<br /></p><p></p><p><b>[2] 6 dB HYBRID COMBINER</b><br /></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEif__CFCeKc2gHThOJHgWOLRA3V7gyaXUdX1B7tgqody_uhxm1elhYXhyuTmIMwqhi5WNAdlqyOaVSX2RAnJAFeCSdrjPsaj6NAKs0pDu7vojF3pFfGNK7m4PI7AxquKuaOoUE1Jv0mZdLeRIChUohDm1maathojjGh9oOazI6l7X5zUmrPAERmimgA2FQH/s612/combiner.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="612" data-original-width="480" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEif__CFCeKc2gHThOJHgWOLRA3V7gyaXUdX1B7tgqody_uhxm1elhYXhyuTmIMwqhi5WNAdlqyOaVSX2RAnJAFeCSdrjPsaj6NAKs0pDu7vojF3pFfGNK7m4PI7AxquKuaOoUE1Jv0mZdLeRIChUohDm1maathojjGh9oOazI6l7X5zUmrPAERmimgA2FQH/w502-h640/combiner.png" width="502" /></a></div><p>Above — The VHF targeted hybrid combiner is also a return loss bridge and vice versa. No experimenter bench should likely be without a return loss bridge or 3. I built with standard 1/4 watt 1% metal film resistors and tried several different coils as the transformer. After many versions, I settled with 3 stacked BN61-2402 ferrites with 4 total turns of lightly twisted wire. I twisted the wires only enough so they would stay together during winding. Because of only 4 turns, I was able to use 28 gauge wire. I measured 43 dB port isolation at 50 MHz.<br /><br /></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjyBCRyapcYWVNKXDS-zGrOvNAk7WL6Vt5kUvE8w5GV19b-nkZz9cDpyL8ITeAftajLMekXo_i8ZzdLvV2UEwr4QNmeHCW6d9XdYHp66tzZ4_tVCVrlQddlebqxeG6Th7RmXBIFLo_CujyuPmMvzdtYR90DVgE9R6nB4j439Lak-OFRT1i1faPuaGQmjMIw/s570/F3.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="311" data-original-width="570" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjyBCRyapcYWVNKXDS-zGrOvNAk7WL6Vt5kUvE8w5GV19b-nkZz9cDpyL8ITeAftajLMekXo_i8ZzdLvV2UEwr4QNmeHCW6d9XdYHp66tzZ4_tVCVrlQddlebqxeG6Th7RmXBIFLo_CujyuPmMvzdtYR90DVgE9R6nB4j439Lak-OFRT1i1faPuaGQmjMIw/s16000/F3.jpg" /></a></div><p></p><p>Above — The applied transformer.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhypmrG_M7Cx7wTf5TZiuxY_jl-K0tWeRkny1PZgDv12NW6BocayTHySqASeBU3RlqeBRaLedmpaP4xrLIBYy7O0ki36bu8oSiLBSNn2z9fgZJd4-NSFjVzDCzuSnTli69UmwJxTXXlmiiRjTCbcSrwneM6HFCjNelR04OCImpRZe8UDHXHcQX1oAFdquXF/s863/f1.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="621" data-original-width="863" height="461" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhypmrG_M7Cx7wTf5TZiuxY_jl-K0tWeRkny1PZgDv12NW6BocayTHySqASeBU3RlqeBRaLedmpaP4xrLIBYy7O0ki36bu8oSiLBSNn2z9fgZJd4-NSFjVzDCzuSnTli69UmwJxTXXlmiiRjTCbcSrwneM6HFCjNelR04OCImpRZe8UDHXHcQX1oAFdquXF/w640-h461/f1.jpg" width="640" /></a></div><p></p><p>Above — Boxed up combiner/return loss bridge with a Mini-Circuits Lab 50 Ω SMA resistive load attached.<br /></p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg3KQQ30sABMC6M3FfaNYh-MLyRcDfo4gvU6_K9C6DHrhfUykLdsfESZbcL06sHK0znndCK4ffbXszNZlbNlQS3AE5LNvZEyJd5eduFMsd8-5LmwFjjPfhLB1gnehDYc1MXT-Qk10dK4nc88MoDJaU6Hi_1TmyDAKFC7_OV1GnnMeHX_Pj25_HCodurQiGY/s691/f2.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="507" data-original-width="691" height="470" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg3KQQ30sABMC6M3FfaNYh-MLyRcDfo4gvU6_K9C6DHrhfUykLdsfESZbcL06sHK0znndCK4ffbXszNZlbNlQS3AE5LNvZEyJd5eduFMsd8-5LmwFjjPfhLB1gnehDYc1MXT-Qk10dK4nc88MoDJaU6Hi_1TmyDAKFC7_OV1GnnMeHX_Pj25_HCodurQiGY/w640-h470/f2.jpg" width="640" /></a></div><p></p><p>Above — Another view of the hybrid coupler<br /><br /></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiYUIngDdnJHtQaWmIft2lwIbdLHh9F35C-Bik2SlCwNb5fQ6vsBhi4mNzDmQqw9ZJ7LTWj8XHPzVN4i7BumR9rsNz1IAmtoCnpXkmd6Z5JxFZngOLHpUSvKWcFvNiLnFAX-CrjeDnnnTeo8ZaB9SddGYwXlri9lRkGr_sGDj8AURRifEy5Nu66dT3hgJqf/s657/tods.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="503" data-original-width="657" height="490" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiYUIngDdnJHtQaWmIft2lwIbdLHh9F35C-Bik2SlCwNb5fQ6vsBhi4mNzDmQqw9ZJ7LTWj8XHPzVN4i7BumR9rsNz1IAmtoCnpXkmd6Z5JxFZngOLHpUSvKWcFvNiLnFAX-CrjeDnnnTeo8ZaB9SddGYwXlri9lRkGr_sGDj8AURRifEy5Nu66dT3hgJqf/w640-h490/tods.png" width="640" /></a></div><br />Above — My favourite design project of 2014: a wide band return loss bridge with directivity >= 30 dB from 5 MHz to 1.5 GHz. You may read more about it in the old site pops.net archive: Topics 2012 - 2014 : Caitlyn 310 — UHF Beginnings : 3. Return Loss Bridge Experiments : Bridge #4Vasily Ivanenkohttp://www.blogger.com/profile/17387516134063150119noreply@blogger.com3tag:blogger.com,1999:blog-3480228403403435266.post-63580158390166717992023-10-24T14:24:00.074-07:002023-10-29T11:10:31.201-07:00Popcorn QRP Audio PA for Receivers and Projects<p>Greetings! For 2-3 years, I’ve received emails from readers seeking a simple “popcorn” discrete transistor PA to substitute for the LM386 part in their DYI projects. Readers wanted 3-4 transistors maximum & no differential amplifiers with current sources — and hopefully low distortion up to 1 watt with a ~12 VDC single supply. </p><p>That seemed a tall order, but I did it (more or less). I’ll define ‘popcorn’ to mean that at maximum clean signal power, all harmonics are down to -50 to -55 dBc. This amp behaves well until driven to about 1.3 Watts. <i><span style="color: #2b00fe;"> I made a video that lies in the last section.<br /></span></i></p><div class="separator" style="clear: both; text-align: center;"><i><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEghPNVETJaIzKK4vN53MdS8bxmv4EF7w0BqavFa9zpoq99cB4PxEtXyESM5WxE1xUqJVrUyoOd_FHaGhF7MAzBRINiAts3JSSmPUFhIiqBYhv7rakoV2x-V88WQoW0QNIz3LR3-6Dn3fToVxFBp5BqXbMy8gXrPJV_7oHmCIrOAuU_4cl3xFTep65lYoMRU/s697/PA%20High%20PowMAIN.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="560" data-original-width="697" height="514" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEghPNVETJaIzKK4vN53MdS8bxmv4EF7w0BqavFa9zpoq99cB4PxEtXyESM5WxE1xUqJVrUyoOd_FHaGhF7MAzBRINiAts3JSSmPUFhIiqBYhv7rakoV2x-V88WQoW0QNIz3LR3-6Dn3fToVxFBp5BqXbMy8gXrPJV_7oHmCIrOAuU_4cl3xFTep65lYoMRU/w640-h514/PA%20High%20PowMAIN.png" width="640" /></a></i></div>Above — The final Popcorn QRP PA. 4 transistors. Voltage gain = 28. Quiescent current = 73.5 mA.<br />This is a power amp designed to cleanly drive a speaker even at loud volumes. To reduce distortion + boost stability, I applied ample local + global feedback which lowered gain. I suggest readers consider building up their AF signal voltage with low noise, low distortion, feedback-containing voltage amplifiers -- and not rely on their PA stage to make all the voltage + power gain. Getting most of your voltage gain in your PA adds too much noise into your AF chain. <p></p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhHEgY5WrWYNViZ7ju6ROZ_5DFCUD-HAwEVM4Sojfwqb9NFhYsJoc7Y6el_l35p13X1wVKGT_p3nWcOIb1VI37COzB7QQUYLcP5PAysZRgIhrT8UE0ykrmosJu6X0ox6fBDNcwMMzpVf9qzo8EHrv4nXfZarOX-TTd1zpM4JoRkoBLQem1rYZ3ON7iTaiPm/s800/H-1Watt.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="431" data-original-width="800" height="344" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhHEgY5WrWYNViZ7ju6ROZ_5DFCUD-HAwEVM4Sojfwqb9NFhYsJoc7Y6el_l35p13X1wVKGT_p3nWcOIb1VI37COzB7QQUYLcP5PAysZRgIhrT8UE0ykrmosJu6X0ox6fBDNcwMMzpVf9qzo8EHrv4nXfZarOX-TTd1zpM4JoRkoBLQem1rYZ3ON7iTaiPm/w640-h344/H-1Watt.png" width="640" /></a></div>Above — An FFT of the Popcorn AF PA driven to exactly 1 Watt output power. The load = a 7.9 Ω “resistor” consisting of 3 two watt resistors in parallel. The second harmonic lies ~53 dB down. <a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh1O-yfKdtVJ7wajvPo2VrPsLxYWP_52US8EWQN9i0nU1tftvDZZLUS7rR7BbQqYOX6quVmRKFI6Ja5H-I1Mv-truu_YGhDq1jGdp797cKHcR1-KWIz-lbTefh0suLYGdDJPAtJmPL2WNeaR2XC6UOUgesgeYzZbCcSSmdsj1lI1oL4z5Lel7hZyKSWQQ1M/s800/lm386G40-feedback.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="409" data-original-width="800" height="328" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh1O-yfKdtVJ7wajvPo2VrPsLxYWP_52US8EWQN9i0nU1tftvDZZLUS7rR7BbQqYOX6quVmRKFI6Ja5H-I1Mv-truu_YGhDq1jGdp797cKHcR1-KWIz-lbTefh0suLYGdDJPAtJmPL2WNeaR2XC6UOUgesgeYzZbCcSSmdsj1lI1oL4z5Lel7hZyKSWQQ1M/w640-h328/lm386G40-feedback.png" width="640" /></a><br /><p>Above — LM386 driven to 808 mW. This is the only LM386 scope trace I had where the voltage gain = 40 plus I had applied a good negative feedback network. Therefore, this practice seems a reasonable head-to-head test against the most venerable LM386. The Popcorn PA makes less distortion at 1 Watt, than the LM386 does at 0.81 W. At 1W power, the LM386 begins compressing into a square wave.</p><p>I promote bench experiments – and developed this amp on my bench. I began with a lower power version using 2N4401/2N4403 complimentary emitter followers to drive the speakers. Push- pull drive as opposed to a single-ended PA driver seems the best way to go for decent output power. You might substitute any number of small signal BJTS such as the 2N3904 for the 2N4401 (or the PNP equivalent) in this project.<br /><br />Let’s start where I began. I’ll show the development of the Popcorn AF PA and give ideas to consider in your own experiments.<br /><br /><span style="color: #2b00fe;"><b>TABLE OF CONTENTS</b></span></p><p><span style="color: #2b00fe;"><b>[ SECTION 1 ] LOW POWER DEVELOPMENT VERSION<br />[ SECTION 2 ] OUTPUT STAGE BIAS<br />[ SECTION 3 ] FULL POWER VERSION<br />[ SECTION 4 ] VIDEO</b></span></p><p><b>---- [ SECTION 1 ] LOW POWER DEVELOPMENT VERSION ----</b><br /><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhnk7LJLUdh_S4u9yeJjroOlYtJF_bfIoVwj7upoftlEj43RYSdZpVxKO2eKYTnJTx9rHjZZuwVO3pEqwDAdr7NcIMma-fZCAHv6kJO3Nnn7k6WW0x5zfGQJQcWTcVizxbbsUKyIZbTGunvIMNKBjEWU9oTWIiL2aNaHlFz0xbtY3vubFhKLzvGPYpmraaB/s641/PA%20LOW%20power%20main.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="500" data-original-width="641" height="500" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhnk7LJLUdh_S4u9yeJjroOlYtJF_bfIoVwj7upoftlEj43RYSdZpVxKO2eKYTnJTx9rHjZZuwVO3pEqwDAdr7NcIMma-fZCAHv6kJO3Nnn7k6WW0x5zfGQJQcWTcVizxbbsUKyIZbTGunvIMNKBjEWU9oTWIiL2aNaHlFz0xbtY3vubFhKLzvGPYpmraaB/w640-h500/PA%20LOW%20power%20main.png" width="640" /></a></p><p>Above — The schematic of the initial & fledgling Popcorn PA using paired 2N4401/2N4403 as the complimentary emitter followers. In 1956 while working for RCA, H.C. Lin developed the first transistor power amp that didn’t use an output transformer. By around 1968, output transformers in solid state AF power amps had all but disappeared in professional designs. <br /><br />Audio transformers suffer from non-linearity and in the case of the tiny transformers employed in cheap transistor radios of lore — these gave distortion, poor bass response -- plus very low output unless run in push-pull fashion. I suggest there are < 2 coherent reasons to use AF output transformers for solid state designs in 2023.<br /> <br /><b>Input Stage</b><br /><br />Without a differential pair as the input stage, I chose a PNP for the Q1 input amp with global negative feedback coming from the output rail going back to the Q1 emitter. The Q1 emitter also gets local feedback -- AC degeneration through the 330 Ω resistor. Because of all the feedback on Q1, Q2 provides most of the voltage gain and gets around double the collector current.<br /><br />In all PA versions, Q1 bias gets set by a potentiometer (20K here). The pot proves necessary since all of us use a slightly different DC power supply voltages. The potentiometer allows you to optimize the Q1 bias for the lowest possible distortion with whatever DC power supply you use. When satisfied, you may remove the pot, measure it, and replace it with 1 -- or 2 series or parallel resistors to try to get as close as possible to the measured pot value. Alternately, you hard wire in a 20 – 25K trimmer potentiometer. <br />In the final Popcorn PA version, I show a fixed Q1 bias resistor and a procedure how to set this value<br /><br />The Q2 “stack” includes Q2 & all the parts connected to the Q2 collector going straight up to the positive DC power supply rail. Q2 serves as the main voltage amplifier. I placed a 10 Ω emitter resistor as local negative feedback to stabilize the stack against HF during development. I have not found any HF instability in the Popcorn PA with or without that 10 Ω resistor.<br /><br />With the 2K Q2 collector resistor, the stack draws ~ 2.5 mA. Let’s look at some DSO outputs:<br /></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiqbZX4U94qn4Y89t63JY0BMLgcdoBY0zMMvIL8yj22xEVBujGDyI6oL5xNFgwwhAioWKUW8nuxciDz_W1P7Xg96-KrPAwTZKw267ZHwtZrWHgUDjRCSPZMWLu46DcPnKuWKNiwwRst3fp9xqWSW4Qu7H2uuCLAF7EF20mXwQ1NKbsnavLuBEuevuxPlOer/s799/plainLP2.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="425" data-original-width="799" height="340" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiqbZX4U94qn4Y89t63JY0BMLgcdoBY0zMMvIL8yj22xEVBujGDyI6oL5xNFgwwhAioWKUW8nuxciDz_W1P7Xg96-KrPAwTZKw267ZHwtZrWHgUDjRCSPZMWLu46DcPnKuWKNiwwRst3fp9xqWSW4Qu7H2uuCLAF7EF20mXwQ1NKbsnavLuBEuevuxPlOer/w640-h340/plainLP2.png" width="640" /></a></div><p>Above — DSO time domain output. The first draft PA driven to 2.01 volts peak-peak. Lovely sine wave. Power = 64 mW. <a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjywTDgxeR1GltpWLYX_dF8kNfZjjf1iSjRhHblzS8GJZ53FzCn5Ki8yBWLfHC9yKQ8rgKZ5aJw_jaHrpCZjLKUY1I9MEks9eEqV5eKUPNROuek0yYZVFdiBos7oeIgkCZM-dYZlmHEyWcQB7dX1uoXwWkE95QUO9mmKA-_d6IedcNY5jyKe9FqAyqwPMaJ/s800/plainLPsine.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="405" data-original-width="800" height="324" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjywTDgxeR1GltpWLYX_dF8kNfZjjf1iSjRhHblzS8GJZ53FzCn5Ki8yBWLfHC9yKQ8rgKZ5aJw_jaHrpCZjLKUY1I9MEks9eEqV5eKUPNROuek0yYZVFdiBos7oeIgkCZM-dYZlmHEyWcQB7dX1uoXwWkE95QUO9mmKA-_d6IedcNY5jyKe9FqAyqwPMaJ/w640-h324/plainLPsine.png" width="640" /></a></p><div class="separator" style="clear: both; text-align: left;">Above — The FFT of the PA driven to 2.01 Vpp or 64 mW into a 7.9 Ω load. <br /></div><div class="separator" style="clear: both; text-align: left;"></div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj19lvIBrusQvCQ-I1WgW6uCnYU05h7tdOJTyElj8UDO-MBZmvzHvJ0sbSIRmeWLaolVqn3jyCXBXF4KJc8N9BN47syPVOlyHVBiJTHIxZt5W-YPSDUcGPgUaRoTbZFu_6I74UuKlCGSlNj8FNGe8ZnQ3GUDTvcHmKj2zeLzecjU_Nz6nRv-j1FqimdJQ0P/s781/both4-and%205Vpp.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="359" data-original-width="781" height="294" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj19lvIBrusQvCQ-I1WgW6uCnYU05h7tdOJTyElj8UDO-MBZmvzHvJ0sbSIRmeWLaolVqn3jyCXBXF4KJc8N9BN47syPVOlyHVBiJTHIxZt5W-YPSDUcGPgUaRoTbZFu_6I74UuKlCGSlNj8FNGe8ZnQ3GUDTvcHmKj2zeLzecjU_Nz6nRv-j1FqimdJQ0P/w640-h294/both4-and%205Vpp.png" width="640" /></a></div><p>Above — Left PA driven to 4 Vpk-pk [ 253 mW ] and 5 Vpk-pk [ 396 mW ]. Only the fundamental 2nd,3rd and 4th harmonics shown. The 3rd harmonic tone starts to rise as the amp is driven to 4 Vpp. You can see the limitations of a single pair of TO-92 transistors such as the 2N4401/2N4403. <br /><br />We’ve already exceeded the harmonic distortion goal for a popcorn PA amplifier. That is --- all harmonics must be down 50-55 dB at the maximum clean power</p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhIqnjff81V6bHlFw2rreyibSig_AzpNaqsgpn9jtDo8iZLG5SdCuS9HQ16swo1wtMuNqY-e8ujmouUbNY7-mqvLDN7W_JuxVpI7JH5gsWnsqKscA4hDTZrY5LdD-ck28kjDB8-wBEb82Hoavngo0WhIr5nDuRwFppNuXTHjmDyyhie6OLLOL04dzRzNfg8/s800/sixplain.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="421" data-original-width="800" height="336" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhIqnjff81V6bHlFw2rreyibSig_AzpNaqsgpn9jtDo8iZLG5SdCuS9HQ16swo1wtMuNqY-e8ujmouUbNY7-mqvLDN7W_JuxVpI7JH5gsWnsqKscA4hDTZrY5LdD-ck28kjDB8-wBEb82Hoavngo0WhIr5nDuRwFppNuXTHjmDyyhie6OLLOL04dzRzNfg8/w640-h336/sixplain.png" width="640" /></a></div><p>Above — FFT with PA driven to 6 Vpk-pk or 570 mW. The 3rd harmonic is only 27-28 dB down. These TO-92 transistors are getting hot and starting to stink. Some of this distortion might be Beta droop from the high collector current plus heat. <br /><br />Regardless, this seems like unacceptable distortion. You could easily hit power level this high on a strong Morse code (CW) station. <br />At this point, the 2N4401/4403 emitter followers seem only good enough for headphone level listening. <br /><br />What can we do to try boost their linearity?<br /> </p><p><b>Technique One — Bootstrapping</b></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgt0NjI79yz2o4gCT8_eEO4AGrZDfFtnOcfmi3-jmxd46cCzSsPnwzw6OmjPSxwd5Hj860H34Xt1ZALuWEgZabRz8Bzjg5f4s2TzwTtCesSeUylDfEjwSmFHnAW4y5jQ2jVbH04GgzSbuaS1EVjREWfHQqT_TuMsxPs6H6w4e81FlWbZWcUV3WbLkbo1lZL/s692/PA%20bootstrap%20lopower.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="511" data-original-width="692" height="472" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgt0NjI79yz2o4gCT8_eEO4AGrZDfFtnOcfmi3-jmxd46cCzSsPnwzw6OmjPSxwd5Hj860H34Xt1ZALuWEgZabRz8Bzjg5f4s2TzwTtCesSeUylDfEjwSmFHnAW4y5jQ2jVbH04GgzSbuaS1EVjREWfHQqT_TuMsxPs6H6w4e81FlWbZWcUV3WbLkbo1lZL/w640-h472/PA%20bootstrap%20lopower.png" width="640" /></a></div>Above — Boot strapping Q2.<br /><br />Q2’s 2K collector resistor gets split to make a tap for a 330 µF bootstrap capacitor that provides positive phase feedback from the output rail to the collector. This raises collector impedance and reduces the loading effects of the Q2 collector resistance on the input of our 2 complimentary emitter followers. The positive feedback lowers Q2 signal drop.<br /><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg_PtzSbBT5vLyPgNraLTdj-4PDl77lP7t68MCjbXXxWoZ2vhajtA4j-BEcW8la4Swnn3LALDua5QV1JrKuuph0JbD2oCE6NatiJvsJuPsrt6v-SMu5hOrR3lN9LaR0h2fMmvfl_drOiIOyq0_4ysPJE_P8EM6EFhTx9eYPYQtrKjL9VscK17TDR91gEVMb/s786/bootstrap2.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="402" data-original-width="786" height="328" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg_PtzSbBT5vLyPgNraLTdj-4PDl77lP7t68MCjbXXxWoZ2vhajtA4j-BEcW8la4Swnn3LALDua5QV1JrKuuph0JbD2oCE6NatiJvsJuPsrt6v-SMu5hOrR3lN9LaR0h2fMmvfl_drOiIOyq0_4ysPJE_P8EM6EFhTx9eYPYQtrKjL9VscK17TDR91gEVMb/w640-h328/bootstrap2.png" width="640" /></a></div><p>Above — The FFT of the PA driven to 2.0 Vpp or 63 mW into a 7.9 Ω load. If anything, the 3rd harmonic is about the same while the rest are a bit worse. Bootstrapping is not helping here.</p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh4Txk2fhaWR2R0eIJY3oWrvQLG4-FNfGHfaCO0afC2xUChH4G19c2KeD-_K6uo8SRZ1CT99IHF_m9B5cEDvOYlTPQs4yNH4PWp3YfpFyP0ftvRtrtw2-ksmO_xQePvVmQPqeN6TLaMQAz81Hfdw6vAh45X4kvaIbhWpuX_p01q4jkdNccMrVhOo1hevAim/s800/bootstrapped4.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="421" data-original-width="800" height="336" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh4Txk2fhaWR2R0eIJY3oWrvQLG4-FNfGHfaCO0afC2xUChH4G19c2KeD-_K6uo8SRZ1CT99IHF_m9B5cEDvOYlTPQs4yNH4PWp3YfpFyP0ftvRtrtw2-ksmO_xQePvVmQPqeN6TLaMQAz81Hfdw6vAh45X4kvaIbhWpuX_p01q4jkdNccMrVhOo1hevAim/w640-h336/bootstrapped4.png" width="640" /></a></div><br />Above — The FFT of the PA driven to 4 Vpk-pk or 253 mW . The third harmonic is about the same without bootstrapping, while the other tones look a bit worse.<p></p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhByjBst6Mab_kW1iegEFZ1YIY82G2Itcmxss1hBwXSqvkyBKV0OH8SqKznfpAI0QfNZ2NZdZTlLPaka06IcZsK4VS2aT9UO0A249Fe-_8mZpIiZtwh2yfq1VhqyAR_wxtflcuVlpdCGS-2n70u4NCGhMc-N03M-wnXeYWV2eRgaqx7AJTs0VOJBLZ4iX0w/s797/bootstrapped6.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="400" data-original-width="797" height="322" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhByjBst6Mab_kW1iegEFZ1YIY82G2Itcmxss1hBwXSqvkyBKV0OH8SqKznfpAI0QfNZ2NZdZTlLPaka06IcZsK4VS2aT9UO0A249Fe-_8mZpIiZtwh2yfq1VhqyAR_wxtflcuVlpdCGS-2n70u4NCGhMc-N03M-wnXeYWV2eRgaqx7AJTs0VOJBLZ4iX0w/w640-h322/bootstrapped6.png" width="640" /></a></div><p>Above — FFT of the PA driven to 6.03 Vpp or 753 mW. In this case, the harmonic distortion has improved. For example the 3rd harmonic improved by about 7 dB. But overall, the net distortion exceeds our harmonic distortion goal.<br /><br />Theoretically, bootstrapping may help and often works as well as driving the Q2 stack with a current source. However, it doesn’t seem to work in this simple amplifier with a 2N4401/2N4403 pair.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjsm1ApJxRuAIAe7eQioqRCmtWgdHIWLPtjLNRj0TupgYFIM-TwRpvV9WPk0OPESG8ZZL5AHRgQ_nb1HtTz3naupSfasAYkBhW7D9Clm2QeTQEJYotYky2qGVAOYeDGNdRMHKWPjTAS0mQHD6OWkgckiftW3TO3bkKwudvZ8SdeThXdWjSryzhQcPHg_qLu/s798/bootstrap8.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="420" data-original-width="798" height="336" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjsm1ApJxRuAIAe7eQioqRCmtWgdHIWLPtjLNRj0TupgYFIM-TwRpvV9WPk0OPESG8ZZL5AHRgQ_nb1HtTz3naupSfasAYkBhW7D9Clm2QeTQEJYotYky2qGVAOYeDGNdRMHKWPjTAS0mQHD6OWkgckiftW3TO3bkKwudvZ8SdeThXdWjSryzhQcPHg_qLu/w640-h336/bootstrap8.png" width="640" /></a></div><p>Above — A fun FFT of what happens when you submit the 2N4401/2N4403 pair to 1 Watt power. Lots of compression, square waves & those emitter followers are smoking hot + stinking up the room.</p><p><b>Technique Two — Current Source</b></p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiJhX7Hu0X1-JeGvrc4mduyrKW4nXqkmro7qOrzTCbVtGEc7SzOOGYJKEGU2nMn4C4G2yqBAY_3_PR9N88JK_calZUi0eWjnSwVIHgH1hyphenhyphen0azvi73EFCc2-NRDxmYVOMnEGNJCGXgdKMBre3T3_393Dtj3v-VYZgoaHpItzvU1vJuXRCls_jvLdJmjGL2kB/s438/current%20source.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="438" data-original-width="414" height="400" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiJhX7Hu0X1-JeGvrc4mduyrKW4nXqkmro7qOrzTCbVtGEc7SzOOGYJKEGU2nMn4C4G2yqBAY_3_PR9N88JK_calZUi0eWjnSwVIHgH1hyphenhyphen0azvi73EFCc2-NRDxmYVOMnEGNJCGXgdKMBre3T3_393Dtj3v-VYZgoaHpItzvU1vJuXRCls_jvLdJmjGL2kB/w378-h400/current%20source.png" width="378" /></a></div>Above — I biased a single PNP to function as a current source. I set the output current as close as possible to that of the Q2 stack with the 2K collector resistor (limited by standard value resistors). The current source provides high impedance drive to the emitter follower pair. I won’t show any tracings because the current source, like the positive feedback, didn’t reduce distortion --- and in for some tones, worsened it. I went back using a collector resistor.<b><br /><br />Technique Three — Reducing the 2K collector resistor to 1K Ω</b><br /><br />With the 2K collector resistor, the stack current measured ~ 2.5 mA. I measured the Q2 stack current at 4.83 mA when reducing the 2K Ω resistor in half. The results seemed unimpressive.<br /><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiOD1unUmf59dNb6frB-bdRflOsop6zm9N3ax516sykLYS7wiJtgJ_B331iHH9_F4CNIUeFt9gstRjdjLsDA84ZxwE1SxIJ8BlHNx9ov5cK6MSEtW4EavmDe46Uh6gCBN_7jt89bH7SHGixXEgDEaj2XZdZr-jzNdMWBObQgzsLO8cgapRm4Xv9NWpGgaXp/s797/S2Kresistor.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="423" data-original-width="797" height="340" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiOD1unUmf59dNb6frB-bdRflOsop6zm9N3ax516sykLYS7wiJtgJ_B331iHH9_F4CNIUeFt9gstRjdjLsDA84ZxwE1SxIJ8BlHNx9ov5cK6MSEtW4EavmDe46Uh6gCBN_7jt89bH7SHGixXEgDEaj2XZdZr-jzNdMWBObQgzsLO8cgapRm4Xv9NWpGgaXp/w640-h340/S2Kresistor.png" width="640" /></a></div><p>Above — For reference, With the 2K collector resistor driven to 3 Vpp. [142 mW power] <br /><br /> <a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhwPqd_s9mV7I_R9Bgr1H5ErQiGfHO6Ii7s-7OKeKdxpnLz-2DX0n-hC3gY-zBklKhwVLyFMqJnKAvHiCZ3rkQvI7oLdakEZr0AQ192nogSesU7zx0d0PHg1RRQrXTkGoIUwGq9BoTrKKsP-mO8pUp52ZEuGv9VmRvKPQFF2UaWRW27l9C5UleBWPgGf2KO/s798/S1Kresistor.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="411" data-original-width="798" height="330" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhwPqd_s9mV7I_R9Bgr1H5ErQiGfHO6Ii7s-7OKeKdxpnLz-2DX0n-hC3gY-zBklKhwVLyFMqJnKAvHiCZ3rkQvI7oLdakEZr0AQ192nogSesU7zx0d0PHg1RRQrXTkGoIUwGq9BoTrKKsP-mO8pUp52ZEuGv9VmRvKPQFF2UaWRW27l9C5UleBWPgGf2KO/w640-h330/S1Kresistor.png" width="640" /></a>Above — With 1K Q2 collector resistor driven to 3 Vpp. The 2nd harmonic improved by ~ 5 dB and the 3rd by about 4 dB. At higher power like 500-600 mW, , the distortion was still too high for my liking. Further, the increase in amplifier quiescent current for the net reduction in harmonic content wasn’t worth it.<br /><br />I’ve gone as far as I can with the simple 2N4401/2N4403 emitter followers. I’ve got to add some current gain and get some proper power followers. </p><p>Before, we go to Section 3, the high power version of the Popcorn QRP PA -- Section 2 quickly covers output stage biasing:</p><p><!--[if gte mso 9]><xml>
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</p><p class="MsoNormal"><span lang="EN-US" style="mso-ansi-language: EN-US;"><b>----<span style="mso-spacerun: yes;"> </span>[ SECTION 2<span style="mso-spacerun: yes;">
</span>]<span style="mso-spacerun: yes;"> </span>OUTPUT STAGE BIAS<span style="mso-spacerun: yes;"> </span>----</b><br style="mso-special-character: line-break;" />
</span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-ansi-language: EN-US;">2 diodes
produce a voltage drop of around 1.3 volts providing sufficient bias for the 2N4401/2N4403
output emitter followers. From reading & my own experiments, the output bias may affect
PA output distortion. The most obvious way is by giving crossover distortion.</span></p><p class="MsoNormal"><span lang="EN-US" style="mso-ansi-language: EN-US;"></span></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhaaPheRXpducwGYQuihyV305oPH8TnpwfPfwtH0PKdKa9Kr9_MOBYwL28K-ka13_jRuWaw4dtrUw7HF2-44gySz3X316nXxwxkK7vY8jlIDlnmSUW3P1QwPTWGGhnljmCRuRtCBUbt8c2ChIsO0nfuVZJFICX8CfKawSKrHD2qNsdsGfSlov9RCdfxr8oc/s799/crossOverDis.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="425" data-original-width="799" height="340" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhaaPheRXpducwGYQuihyV305oPH8TnpwfPfwtH0PKdKa9Kr9_MOBYwL28K-ka13_jRuWaw4dtrUw7HF2-44gySz3X316nXxwxkK7vY8jlIDlnmSUW3P1QwPTWGGhnljmCRuRtCBUbt8c2ChIsO0nfuVZJFICX8CfKawSKrHD2qNsdsGfSlov9RCdfxr8oc/w640-h340/crossOverDis.png" width="640" /></a></div><br />Above — DSO screen capture of the low-power Popcorn PA with only 1 bias diode across the emitter follower bases. You may easily see (and hear) crossover distortion.<p></p><p class="MsoNormal"><span lang="EN-US" style="mso-ansi-language: EN-US;"></span></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjo4WNiAo-6aul1D77V-nma3u64zLycsLLaPc7XsFp4T6Mtkl6NlRGdCFnmSbwHGZZddnmSuY86fRc-D2oOvyAVueIlkz-o542M2rX1gz8TIGxAnAJP_p2zDf8Pbeco_MqT6fa1arosiJ3THU3NjJutWWOXIst39NBP7ge7-KymWMncH8mpljpaGX4gyvqB/s798/S1diode.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="424" data-original-width="798" height="340" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjo4WNiAo-6aul1D77V-nma3u64zLycsLLaPc7XsFp4T6Mtkl6NlRGdCFnmSbwHGZZddnmSuY86fRc-D2oOvyAVueIlkz-o542M2rX1gz8TIGxAnAJP_p2zDf8Pbeco_MqT6fa1arosiJ3THU3NjJutWWOXIst39NBP7ge7-KymWMncH8mpljpaGX4gyvqB/w640-h340/S1diode.png" width="640" /></a></div><span lang="EN-US" style="mso-ansi-language: EN-US;"> </span><span lang="EN-US" style="mso-ansi-language: EN-US;"></span><p></p><p class="MsoNormal"><span lang="EN-US" style="mso-ansi-language: EN-US;">Above — An FFT of the 1 diode output bias with only the amp driven to 36 mW output power. The distortion dominates with odd order harmonics. </span></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh-a9cPAMtuJxWbD9eH5pYqbGuWb6sXqtLSK995t04WE-GcjrYH9JNq6IAvnjHqDlgZo86mTWzsVhWOe7c9sF-zvvTGVzLs5AzCFi6_LGSj0vGumNZijk5xWcsScDxIezTtae86l6hvm_TboO735uv4NF13iRZ06luVtdVAN7o7MWDHPbn7xrzmLzyZ7Z6E/s798/s2-diodes.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="427" data-original-width="798" height="342" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh-a9cPAMtuJxWbD9eH5pYqbGuWb6sXqtLSK995t04WE-GcjrYH9JNq6IAvnjHqDlgZo86mTWzsVhWOe7c9sF-zvvTGVzLs5AzCFi6_LGSj0vGumNZijk5xWcsScDxIezTtae86l6hvm_TboO735uv4NF13iRZ06luVtdVAN7o7MWDHPbn7xrzmLzyZ7Z6E/w640-h342/s2-diodes.png" width="640" /></a></div><p></p><p class="MsoNormal"><span lang="EN-US" style="mso-ansi-language: EN-US;">Above — FFT after adding back the 2nd output bias diode. This reduced the amplifier distortion shown above. Crossover plus output follower switching distortion pose factors we must live with. How far the output pair are biased from Class B towards Class A may also affect amplifier distortion. <br /><br />However, using 2 diodes, we don’t have much control over that. You may place a small value resistor in series with 1 diode instead of using 2 diodes -- or in series with 2 (or more) diodes to change the output bias. An alternate way is to remove the diodes and replace them with a transistor.</span></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgya_byDlhbJKhhPXKIsteaeGlSlOWf2y2LRm9FowfHui_aKJpLWjxQfZjutX-MwnTE3yiXO3c_mtXHYX9pZbl4cQfm_ica_-p3ewqotyNarsWtoBym6q0m_qiRQ6QWoI6UotrJkOttOP9qP7CxalF0Cnra9Zz3JD9hwrl-KaVNa2vaG4dDK3xrXu_n7as5/s717/PA%20LOW%20aMpDiode.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="494" data-original-width="717" height="440" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgya_byDlhbJKhhPXKIsteaeGlSlOWf2y2LRm9FowfHui_aKJpLWjxQfZjutX-MwnTE3yiXO3c_mtXHYX9pZbl4cQfm_ica_-p3ewqotyNarsWtoBym6q0m_qiRQ6QWoI6UotrJkOttOP9qP7CxalF0Cnra9Zz3JD9hwrl-KaVNa2vaG4dDK3xrXu_n7as5/w640-h440/PA%20LOW%20aMpDiode.png" width="640" /></a></div><br />Above — Schematic with the 2 diode bias replaced with an NPN referred to as an amplified diode or Vbe multiplier bias generator. Normally, this BJT has a trimmer resistor as R1 in the schematic for tweaking the voltage divider bias. The trimmer gets adjusted while watching the output in a test circuit to find the sweet spot of bias -– the setting that offers the lowest distortion in the output. <br /><br />I normally temporarily make R1 a trimmer pot, set the bias and then remove and measure the trimmer pot. Then I replace that with a fixed resistor such as the 1K8 Ω shown.<br /><br />Since this is the popcorn PA stage, we’ll stick to plain diode biasing of the output followers.<p></p><p class="MsoNormal"><span lang="EN-US" style="mso-ansi-language: EN-US;"><b><br />[ SECTION 3 ] FULL POWER VERSION</b></span></p><p class="MsoNormal"><span lang="EN-US" style="mso-ansi-language: EN-US;"></span></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjS9p-rfz9iSzSze7Lr61G_R_K_QQdVgNcOJ7StLjWlsxxw75NF476bAlYMgk0SjXCEsLwK7bBW_cdCJhTWWIDDwS_f-8qC-dh0jd30JU26jFDN6nSr3nwkRU2OKleT_xZeaOdtmdiMbmF6G-MAn7Wil7VnAi1Y2bPfMU1xVYY6OczPP4OYRxnOhZdAzu37/s893/DUT1.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="561" data-original-width="893" height="402" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjS9p-rfz9iSzSze7Lr61G_R_K_QQdVgNcOJ7StLjWlsxxw75NF476bAlYMgk0SjXCEsLwK7bBW_cdCJhTWWIDDwS_f-8qC-dh0jd30JU26jFDN6nSr3nwkRU2OKleT_xZeaOdtmdiMbmF6G-MAn7Wil7VnAi1Y2bPfMU1xVYY6OczPP4OYRxnOhZdAzu37/w640-h402/DUT1.jpg" width="640" /></a></div>Above —
Device under test. The best part about bench building is getting to use your
test equipment. Glory and fun on the bench. Since I usually make 22 – 50 watt PAs, my electrolytic
capacitor collection are all rated 50 volt to 100 volts. They look quite large
in the Popcorn PA.<p></p><p class="MsoNormal"><span lang="EN-US" style="mso-ansi-language: EN-US;"></span></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgbxgjT8uktsVpeWSJ9yXdLAx0jb8AOx2G0GDhOUGiRHQqId_ua9W-r4mPL9lmP6kRF_fYLu3E7nXJJdMr3QjcnKDjRsMKbkj8wvwNlTYwoHM9RmAO8Dte7CpQKWFM5RGtVM_r4TxLcrr4BC12FtIs3Y31Mh3qWdwewK0gMF2GYvcqJckPrzRqcNGxmQo2n/s717/PA%20High%20PowDCV.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="538" data-original-width="717" height="480" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgbxgjT8uktsVpeWSJ9yXdLAx0jb8AOx2G0GDhOUGiRHQqId_ua9W-r4mPL9lmP6kRF_fYLu3E7nXJJdMr3QjcnKDjRsMKbkj8wvwNlTYwoHM9RmAO8Dte7CpQKWFM5RGtVM_r4TxLcrr4BC12FtIs3Y31Mh3qWdwewK0gMF2GYvcqJckPrzRqcNGxmQo2n/w640-h480/PA%20High%20PowDCV.png" width="640" /></a></div>Above — Popcorn PA with DC voltages. Q1 shows fixed bias. I’ll give the bias procedure soon. The 10 Ω Q2 emitter resistor got dropped since this adds 1-2 dB of lower tone harmonic distortion under heavier drive. <br /><br />I didn’t bother with the standard Zobel network in parallel with the speaker as seen in most AF PAs. This series cap + 10 Ω resistor across the speaker serves to lower the Q of the resonant peak of the speaker’s peak impedance at somewhere between 80 and 130 Hz. While important for crossover design + function, I’ve left it out. You may need it with some speakers perhaps.<br /><p></p><p class="MsoNormal"><b>Power Followers</b><br /> </p><p class="MsoNormal"></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjEC-2oowq1qDtooJY5_RNySm4LR3TU8IhcUr5TDFyaHNCzz7sqBPMMgg1HZy2RPr5jBCnEPTgOhZ48AoLOIUwi2TWV6UOah5-IKsfqY9UGt7dhdGj2s9Di9Fq2XJnUY08qaw8ZCwn1JcQHy6HhdAzRGGHNlGANdNffzzEIYVSFJSYCChNqvXGK3KpkThhj/s410/tip127-122.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="410" data-original-width="359" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjEC-2oowq1qDtooJY5_RNySm4LR3TU8IhcUr5TDFyaHNCzz7sqBPMMgg1HZy2RPr5jBCnEPTgOhZ48AoLOIUwi2TWV6UOah5-IKsfqY9UGt7dhdGj2s9Di9Fq2XJnUY08qaw8ZCwn1JcQHy6HhdAzRGGHNlGANdNffzzEIYVSFJSYCChNqvXGK3KpkThhj/s16000/tip127-122.png" /> </a></div><div class="separator" style="clear: both; text-align: left;">Above — I swapped out the TO-92 finals for some big boots. In many lower power amps, to get current gain you’ll keep the TO-92 followers and then drive another set of power followers such as the BD139/BD140 pair. This works well and is recommended, however; we’re going full on popcorn on this project.<br />Thus, we’re keeping the emitter follower driving an emitter follower theme, but combining both in a packaged Darlington pair. This keep the parts count down -- plus provide the high Beta and current we seek to drive our speaker with room filling, low distortion loudness.<br /><br />The TIP122/127 pair are only 1 example of packaged Darlington current amplifiers. I’ve got 3-4 other in my parts bins such as the BD94C/93C or TIP142/147 pairs – but again, usually I build higher power amps.<br /><br />I bought the TIP122/127 pair for $2.30 Canadian dollars & they look husky and tough. You don’t even need to heat sink them for 12 VDC power. If you need to heat sink them, then it's easy to do. Some readers emailed me to say they had smoked countless 2N3904/2N3906 pairs in their PA building adventures. Some soldered several in parallel to make a "power follower", etc.. <br /><br />While purists may dislike a packaged Darlington pair – they seem perfect for popcorn PA stages and practice guitar amps alike. We have to add 2 more diodes to properly bias both Darlington transistors.<br /><br />I added the Q2 boot strap back in. For this version, it significantly helped boost linearity from low to high power.<br /><br />I kept the 1 Ω emitter resistors of the low power version. In pro audio, these are usually 0.1 or 0.22 Ω but of course, those amps are making some serious power. <br />In the past, I placed two or three quarter watt 1 Ω resistors of 1% tolerance in parallel to get the maximum possible output power. I left the popcorn emitter resistors at 1 Ω to ensure this project is stable for anyone choosing to experiment with it. <br /></div><p></p><p>Play with every resistor value on the test bench. You’ll probably make a better PA than I did.<br /><br />Let’s go through some FFT’s of the Popcorn PA at various drive levels:</p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhEzSazjFLBYCzMRKlOqzLzmALATG9vNvEn9uSWDSn5K1YGiV4ijDLYxDp2Hfb502hGsdXh7-pNbfgSlCkLuwo_PHXZ-efZwPmAzyzykBHwRMXrR_Sp83AufAMmqQPB6fu7YMtnlbKcJwCyhvU8KjCnYhwflPTRYa-FfXo8zy449Ne_T60rqbCGynpFN8kN/s798/h3.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="423" data-original-width="798" height="340" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhEzSazjFLBYCzMRKlOqzLzmALATG9vNvEn9uSWDSn5K1YGiV4ijDLYxDp2Hfb502hGsdXh7-pNbfgSlCkLuwo_PHXZ-efZwPmAzyzykBHwRMXrR_Sp83AufAMmqQPB6fu7YMtnlbKcJwCyhvU8KjCnYhwflPTRYa-FfXo8zy449Ne_T60rqbCGynpFN8kN/w640-h340/h3.png" width="640" /></a></div><br />Above — FFT at 3 Vpp. This proved the lowest 2nd harmonic tone measured @ -56 dBc. You could further experiment with the output bias, add a current source, or perhaps make other tweaks, if chasing a lower 2nd harmonic tone is your goal. <br /><p></p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiAehtmgAZuE7lJDUlqJCx5AOOh4Ihxe2Ou4E3AMm4VksK0v3fua6FOJjhYfUgwPyXsEB-iQWh5-I8uIA58_4vV2Txrr17Rp7VHA39aUfMLoAzjOidPyJzZqyyv1wZBjfGuO5dqnGQ1jI4TYZ5-aFAUe8gXbvFPtppRFES5ftPMBZf3VkJi5olHL5JL_EsY/s798/h6.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="425" data-original-width="798" height="340" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiAehtmgAZuE7lJDUlqJCx5AOOh4Ihxe2Ou4E3AMm4VksK0v3fua6FOJjhYfUgwPyXsEB-iQWh5-I8uIA58_4vV2Txrr17Rp7VHA39aUfMLoAzjOidPyJzZqyyv1wZBjfGuO5dqnGQ1jI4TYZ5-aFAUe8gXbvFPtppRFES5ftPMBZf3VkJi5olHL5JL_EsY/w640-h340/h6.png" width="640" /></a></div><br />Above — FFT with the Popcorn PA driven to 6 Vpp or 570 mW. Looks about the same as with 3 Vpp.<p></p><p></p><div class="separator" style="clear: both; text-align: left;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj7m3egOOMrWyFi34oIfh4iKq57CsdtQwt4FqhPhE7XQHnJBkcbPX0W6r5UAekmHIHwv7DKb9U9jXu65Zx6NDyLYQ2b9hPpkHlCecwLIcjws-U2N6vGte7YdTnz4pL7ABihKRo0z-n_GIG3_6QOzgqOj8TGRKy8OD7kUAYctb92gZte-gSCc4fjfj9DaQAE/s797/h7-5.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="420" data-original-width="797" height="338" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj7m3egOOMrWyFi34oIfh4iKq57CsdtQwt4FqhPhE7XQHnJBkcbPX0W6r5UAekmHIHwv7DKb9U9jXu65Zx6NDyLYQ2b9hPpkHlCecwLIcjws-U2N6vGte7YdTnz4pL7ABihKRo0z-n_GIG3_6QOzgqOj8TGRKy8OD7kUAYctb92gZte-gSCc4fjfj9DaQAE/w640-h338/h7-5.png" width="640" /></a><br /><br />Above — FFT at 7.5 Vpp. Again it look similar to the Vpp = 3 or 6 FFTs.</div><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgW_4EcAVNL_67v5JWLRp9Vda8cL43ZlWn6lzSszrcgokrTxQUTBYW06EeARjVhPNlDb0CI-Vu6W-RTnXYVE8QjLqVgo9OX6aUWvsdQxiwaIuxXCv8373xRVC0C0XOnwqkeC0wkvsUqRuaMzM-T4KHbmADMUe8aB8daHL7tNSIH4SFgbeFUSTQysr4A2SIB/s797/H8-39.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="418" data-original-width="797" height="336" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgW_4EcAVNL_67v5JWLRp9Vda8cL43ZlWn6lzSszrcgokrTxQUTBYW06EeARjVhPNlDb0CI-Vu6W-RTnXYVE8QjLqVgo9OX6aUWvsdQxiwaIuxXCv8373xRVC0C0XOnwqkeC0wkvsUqRuaMzM-T4KHbmADMUe8aB8daHL7tNSIH4SFgbeFUSTQysr4A2SIB/w640-h336/H8-39.png" width="640" /></a></div><p>Above — Cranking up the drive! FFT while driven to output 8.39 or 1.11 Watts. Still meets our popcorn goal of all tones down 50-55 dB at maximum clean power.</p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhjdHaCXkc7Pl3XlboevyYsNcni784WNIH21SsiEnZVNDa4e_Fc_GOfQj7F5RNos238LidX6fnFhYV4ZDPjbnQUsTQf0gEkZAoarhKTDrtZi1SxjgxJv5HAJiWrj4dayZztezRGi9G1Vt98j0z-7giMwW6tz_LF1yPLeXMqwfHHxzJnUAwJattmS15rGr-C/s800/H9-18.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="425" data-original-width="800" height="340" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhjdHaCXkc7Pl3XlboevyYsNcni784WNIH21SsiEnZVNDa4e_Fc_GOfQj7F5RNos238LidX6fnFhYV4ZDPjbnQUsTQf0gEkZAoarhKTDrtZi1SxjgxJv5HAJiWrj4dayZztezRGi9G1Vt98j0z-7giMwW6tz_LF1yPLeXMqwfHHxzJnUAwJattmS15rGr-C/w640-h340/H9-18.png" width="640" /></a></div>Above — FFT while driving the PA to 9.18 Vpp. The harmonic tones are starting to rise!<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh8AbN5LsKEWaNeL2dHvclgKu4QEKGK5Tkl37Cq67PPcAdNU_fTbV2ALVgaZIHP5ff_TxPJMyOuYWNfJZ5K1X96eqfLTX69QtS2EEKbMX_CBmuFcEO8tpAwdMfqe_5gNZT9Kj_7wFqCAFM0nKwoLlPVM8AGfXKUlniLTIFdKUy0gmrGn52h9FJIy8SkWQIs/s796/H9-21.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="423" data-original-width="796" height="340" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh8AbN5LsKEWaNeL2dHvclgKu4QEKGK5Tkl37Cq67PPcAdNU_fTbV2ALVgaZIHP5ff_TxPJMyOuYWNfJZ5K1X96eqfLTX69QtS2EEKbMX_CBmuFcEO8tpAwdMfqe_5gNZT9Kj_7wFqCAFM0nKwoLlPVM8AGfXKUlniLTIFdKUy0gmrGn52h9FJIy8SkWQIs/w640-h340/H9-21.png" width="640" /></a><p>Above — FFT while driven to 1.34 Watts. Things are falling apart. Ok, let’s finish up.</p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjrT5xwn74JJ5Wf33_S6VjjX8GtFZ9d0ald1lkWfsos3MICLeTqYQkW1MX4l_Wr7QC8DiHzP1gZhpekZjwtNV1s0n18582yOE8hIJLNvNe5EpkYA4-QAC6cILjf8UWgCU_lMhrMG7kiFt9S3R0VuNk5xd8LhSq2KORb0VoXiUt6HV_aDW52PwKiwbWNvorN/s825/PA%20High%20PowDCAdjust.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="481" data-original-width="825" height="374" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjrT5xwn74JJ5Wf33_S6VjjX8GtFZ9d0ald1lkWfsos3MICLeTqYQkW1MX4l_Wr7QC8DiHzP1gZhpekZjwtNV1s0n18582yOE8hIJLNvNe5EpkYA4-QAC6cILjf8UWgCU_lMhrMG7kiFt9S3R0VuNk5xd8LhSq2KORb0VoXiUt6HV_aDW52PwKiwbWNvorN/w640-h374/PA%20High%20PowDCAdjust.png" width="640" /></a></div>Above — Set up schematic. If your power supply is close to 12 VDC, then consider just building the fixed Q1 bias version shown earlier. However, bigger is better in PA stages. If you’ve got 13.8 or 14 VDC, then your maximum clean output power will go up. You may choose to optimize Q1 bias for a different DC supply.<br /><br />In big power PA’s the DC rails are often unregulated. Fortunately, most of our ~ 12 VDC single power supplies are regulated which makes setting up the Popcorn AF PA a snap.<br /><br />Terminate the output with a 10 ohm or lowish value resistor – or your bench 8 Ω load. Do not connect anything to the input. Preset to maximum resistance, connect a 10 - 25K pot from the DC power supply rail to the Q1 base. Clip your positive voltmeter probe to the output rail and tweak the pot until your measured DC = your DC supply voltage divided by 1.82. Remove the pot and measure. Substitute the nearest standard value or place 2 in series or parallel to get close to this voltage. <br /><br />If the output rail voltage lies between VCC/1.82 & VCC/2 you’ll be fine. Of course, you may experiment to find the optimal Q1 bias for your particular build -- that serves as the best way to optimize linearity.<br /><br /><b>[ SECTION 4 ] VIDEO</b><br /><br />I made a short video so you can hear the Popcorn PA in action. I connected it to a CD player plus my 8 inch guitar speaker and cranked it loudly to show its linearity under heavy audio drive.<br /> <br />I sampled at 44.1 KHz into mono using a Lewitt LCT 440 large-diaphragm condenser mic --- the same mic I use for my voice overs. I like the LCT 440 since it offers a flat bandwidth + very low added noise at a reasonably low cost.<br /><p></p><div class="separator" style="clear: both; text-align: center;"><iframe allowfullscreen="" class="BLOG_video_class" height="372" src="https://www.youtube.com/embed/dSDp43ADrno" width="448" youtube-src-id="dSDp43ADrno"></iframe></div><p>Above — It seems better to watch this video on YouTube directly.<br /></p><p><b>Addendum:</b><br /></p><p>To clarify, I think the LM386 is an awfully good part. Imagine if your design team made a linear IC that went into hundreds of thousands of projects or products? I'm a fan of the LM386 and the designers left us IC pins to add negative feedback with. <br /><br />I cover this in the following blog post:<br /></p><p><a href="https://qrp-popcorn.blogspot.com/2022/11/another-look-at-lm386.html" target="_blank">Link to my LM386 Experiments from November 2022</a></p>Vasily Ivanenkohttp://www.blogger.com/profile/17387516134063150119noreply@blogger.com3tag:blogger.com,1999:blog-3480228403403435266.post-35834895065042855392023-10-09T20:35:00.017-07:002023-10-10T22:08:55.779-07:00That 0-degree Phase Difference in Oscillators<p></p><p>This blog post arose from emails exchanged with a reader in 2015. The reader Frédéric — a newbie, sought to understand how the various sinusoidal oscillators worked in his circuits. He wanted explanations with little math & physics. Answering back, I realized how poor my basic oscillator theory teachings skills were. I studied up and wrote him a series of emails based on simple bench experiments. This Fall, I enhanced that content and even repeated many of the experiments. With joy and generosity, I present this content.<br /><br /><b>Introduction</b><br /><br />Oscillators form the heart of radio frequency design & building. When you read oscillator papers written by genius electronics professionals, they might go something like this: They start off with the Barkhausen criterion & equations (of course). Then, they may veer straight into a series of equations using vector algebra complete with upper and lower case Greek letters; radians + total admittance in rectangular coordinates and perhaps more — all mixed in gruesome equations. Then comes the inevitable root locus plot, the showing of loop gain via a third-order voltage transfer function, and then finally they may go off into byzantine filter theory using complex conjugate poles. Absolutely fabulous stuff if you’re an engineer or physics major – and yes, I do exaggerate for fun. <br /> </p><p>All fun aside, understanding oscillator best practices ranks as problematic for some pros and amateurs alike since oscillators are non-linear circuits with linear aspects. You’ll find seemingly endless schematics to puzzle over. I’ve read that there are 18 or more variants of the Colpitts oscillator alone — spanning LF to terahertz.</p><p>Design & analysis of oscillators usually involves 3 basic methods:<br /><br />[1] Negative resistance method using the +/-R & jX operators. <br />[2] Reflection amplifier method using scattering parameters & reflections (S11 and/or S22).<br />[3] Positive feedback loop method. This seems the easiest way for newcomers — I’ll only discuss concepts from the positive feedback loop method. <br /><br />The 2 minimal conditions according to the Barkhausen conditions:<br />To oscillate + sustain: the input & output phase difference must be zero; and the whole loop gain must = 1 or greater than 1.<br /><br />These are important minimal requirements. Real oscillator designers strive to achieve other goals that may include biasing for the best amplifier operating point, boosting resonator Q, lowering phase noise, and/or enhancing temperature + amplitude stability. They may work to reduce loading effects on the frequency determining circuit by the gain stage, or, perhaps, to fit the oscillator into a very tiny footprint. We’ll ignore all that stuff.<br /><br />Let’s begin our minimum math discussion with the table of contents:</p><p><span style="color: #2b00fe;"><b>[ SECTION 1 ] Phase Difference<br />[ SECTION 2 ] Feedback & Function<br /><br />[ SECTION 3 ] B E N C H E X P E R I M E N T S<br /> via 3 basic types of frequency determining feedback networks<br /> a. Transformer<br /> b. Pi phase shifter<br /> c. Tuned input and output<br /></b></span></p><p><span style="color: #2b00fe;"><b>[ SECTION 4 ] Conclusion<br />[ SECTION 5 ] References</b></span></p><p><!--[if gte mso 9]><xml>
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<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Continue 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Continue 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Message Header"/>
<w:LsdException Locked="false" Priority="11" QFormat="true" Name="Subtitle"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Salutation"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Date"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text First Indent"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text First Indent 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Note Heading"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text Indent 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text Indent 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Block Text"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Hyperlink"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="FollowedHyperlink"/>
<w:LsdException Locked="false" Priority="22" QFormat="true" Name="Strong"/>
<w:LsdException Locked="false" Priority="20" QFormat="true" Name="Emphasis"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Document Map"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Plain Text"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="E-mail Signature"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Top of Form"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Bottom of Form"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Normal (Web)"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Acronym"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Address"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Cite"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Code"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Definition"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Keyboard"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Preformatted"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Sample"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Typewriter"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Variable"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Normal Table"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="annotation subject"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="No List"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Outline List 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Outline List 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Outline List 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Simple 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Simple 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Simple 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Classic 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Classic 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Classic 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Classic 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Colorful 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Colorful 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Colorful 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Columns 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Columns 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Columns 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Columns 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Columns 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 6"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 7"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 8"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 6"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 7"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 8"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table 3D effects 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table 3D effects 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table 3D effects 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Contemporary"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Elegant"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Professional"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Subtle 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Subtle 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Web 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Web 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Web 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Balloon Text"/>
<w:LsdException Locked="false" Priority="39" Name="Table Grid"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Theme"/>
<w:LsdException Locked="false" SemiHidden="true" Name="Placeholder Text"/>
<w:LsdException Locked="false" Priority="1" QFormat="true" Name="No Spacing"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading"/>
<w:LsdException Locked="false" Priority="61" Name="Light List"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 1"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 1"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 1"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 1"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 1"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 1"/>
<w:LsdException Locked="false" SemiHidden="true" Name="Revision"/>
<w:LsdException Locked="false" Priority="34" QFormat="true"
Name="List Paragraph"/>
<w:LsdException Locked="false" Priority="29" QFormat="true" Name="Quote"/>
<w:LsdException Locked="false" Priority="30" QFormat="true"
Name="Intense Quote"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 1"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 1"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 1"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 1"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 1"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 1"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 1"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 1"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 2"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 2"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 2"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 2"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 2"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 2"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 2"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 2"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 2"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 2"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 2"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 2"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 2"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 2"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 3"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 3"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 3"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 3"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 3"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 3"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 3"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 3"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 3"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 3"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 3"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 3"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 3"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 3"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 4"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 4"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 4"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 4"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 4"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 4"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 4"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 4"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 4"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 4"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 4"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 4"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 4"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 4"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 5"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 5"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 5"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 5"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 5"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 5"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 5"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 5"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 5"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 5"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 5"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 5"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 5"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 5"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 6"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 6"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 6"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 6"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 6"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 6"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 6"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 6"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 6"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 6"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 6"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 6"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 6"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 6"/>
<w:LsdException Locked="false" Priority="19" QFormat="true"
Name="Subtle Emphasis"/>
<w:LsdException Locked="false" Priority="21" QFormat="true"
Name="Intense Emphasis"/>
<w:LsdException Locked="false" Priority="31" QFormat="true"
Name="Subtle Reference"/>
<w:LsdException Locked="false" Priority="32" QFormat="true"
Name="Intense Reference"/>
<w:LsdException Locked="false" Priority="33" QFormat="true" Name="Book Title"/>
<w:LsdException Locked="false" Priority="37" SemiHidden="true"
UnhideWhenUsed="true" Name="Bibliography"/>
<w:LsdException Locked="false" Priority="39" SemiHidden="true"
UnhideWhenUsed="true" QFormat="true" Name="TOC Heading"/>
<w:LsdException Locked="false" Priority="41" Name="Plain Table 1"/>
<w:LsdException Locked="false" Priority="42" Name="Plain Table 2"/>
<w:LsdException Locked="false" Priority="43" Name="Plain Table 3"/>
<w:LsdException Locked="false" Priority="44" Name="Plain Table 4"/>
<w:LsdException Locked="false" Priority="45" Name="Plain Table 5"/>
<w:LsdException Locked="false" Priority="40" Name="Grid Table Light"/>
<w:LsdException Locked="false" Priority="46" Name="Grid Table 1 Light"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark"/>
<w:LsdException Locked="false" Priority="51" Name="Grid Table 6 Colorful"/>
<w:LsdException Locked="false" Priority="52" Name="Grid Table 7 Colorful"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 1"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 1"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 1"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 1"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 1"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 1"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 1"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 2"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 2"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 2"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 2"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 2"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 2"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 2"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 3"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 3"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 3"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 3"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 3"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 3"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 3"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 4"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 4"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 4"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 4"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 4"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 4"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 4"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 5"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 5"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 5"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 5"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 5"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 5"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 5"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 6"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 6"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 6"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 6"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 6"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 6"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 6"/>
<w:LsdException Locked="false" Priority="46" Name="List Table 1 Light"/>
<w:LsdException Locked="false" Priority="47" Name="List Table 2"/>
<w:LsdException Locked="false" Priority="48" Name="List Table 3"/>
<w:LsdException Locked="false" Priority="49" Name="List Table 4"/>
<w:LsdException Locked="false" Priority="50" Name="List Table 5 Dark"/>
<w:LsdException Locked="false" Priority="51" Name="List Table 6 Colorful"/>
<w:LsdException Locked="false" Priority="52" Name="List Table 7 Colorful"/>
<w:LsdException Locked="false" Priority="46"
Name="List Table 1 Light Accent 1"/>
<w:LsdException Locked="false" Priority="47" Name="List Table 2 Accent 1"/>
<w:LsdException Locked="false" Priority="48" Name="List Table 3 Accent 1"/>
<w:LsdException Locked="false" Priority="49" Name="List Table 4 Accent 1"/>
<w:LsdException Locked="false" Priority="50" Name="List Table 5 Dark Accent 1"/>
<w:LsdException Locked="false" Priority="51"
Name="List Table 6 Colorful Accent 1"/>
<w:LsdException Locked="false" Priority="52"
Name="List Table 7 Colorful Accent 1"/>
<w:LsdException Locked="false" Priority="46"
Name="List Table 1 Light Accent 2"/>
<w:LsdException Locked="false" Priority="47" Name="List Table 2 Accent 2"/>
<w:LsdException Locked="false" Priority="48" Name="List Table 3 Accent 2"/>
<w:LsdException Locked="false" Priority="49" Name="List Table 4 Accent 2"/>
<w:LsdException Locked="false" Priority="50" Name="List Table 5 Dark Accent 2"/>
<w:LsdException Locked="false" Priority="51"
Name="List Table 6 Colorful Accent 2"/>
<w:LsdException Locked="false" Priority="52"
Name="List Table 7 Colorful Accent 2"/>
<w:LsdException Locked="false" Priority="46"
Name="List Table 1 Light Accent 3"/>
<w:LsdException Locked="false" Priority="47" Name="List Table 2 Accent 3"/>
<w:LsdException Locked="false" Priority="48" Name="List Table 3 Accent 3"/>
<w:LsdException Locked="false" Priority="49" Name="List Table 4 Accent 3"/>
<w:LsdException Locked="false" Priority="50" Name="List Table 5 Dark Accent 3"/>
<w:LsdException Locked="false" Priority="51"
Name="List Table 6 Colorful Accent 3"/>
<w:LsdException Locked="false" Priority="52"
Name="List Table 7 Colorful Accent 3"/>
<w:LsdException Locked="false" Priority="46"
Name="List Table 1 Light Accent 4"/>
<w:LsdException Locked="false" Priority="47" Name="List Table 2 Accent 4"/>
<w:LsdException Locked="false" Priority="48" Name="List Table 3 Accent 4"/>
<w:LsdException Locked="false" Priority="49" Name="List Table 4 Accent 4"/>
<w:LsdException Locked="false" Priority="50" Name="List Table 5 Dark Accent 4"/>
<w:LsdException Locked="false" Priority="51"
Name="List Table 6 Colorful Accent 4"/>
<w:LsdException Locked="false" Priority="52"
Name="List Table 7 Colorful Accent 4"/>
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</p><p class="MsoNormal"><span lang="EN-US" style="mso-ansi-language: EN-US;"><b>---------- [ SECTION 1 ] Phase
Difference ----------<br /></b></span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-ansi-language: EN-US;">Phase
difference is the time interval between a discrete event occurring on 2 or more
wave forms. The discrete event occurring at a point in time may be the positive
peak of a sine wave, or perhaps the rising edge of a square wave, or something
else. In electronics, 1 way to express time (phase) difference is in degrees. </span></p>
<div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjmvN_ADTb0Vq_ZDg_t5ZDjpXjm4NvUo33xdjywMdEkowNjBd606n3NnhLw2Dmu8hCavQZTRWvHmXWDWxbEQs6HTej0gUe8FvD_Me1Vrd_IdODHIOuMVJMhGCm46HiXUFlMEBDzzye_9IcYi4lJTQtY7aRGmXdNOvZwY9iFEljg0ijCYZ9ZnfdsGDYCbo0k/s773/phase%20difference.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="466" data-original-width="773" height="386" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjmvN_ADTb0Vq_ZDg_t5ZDjpXjm4NvUo33xdjywMdEkowNjBd606n3NnhLw2Dmu8hCavQZTRWvHmXWDWxbEQs6HTej0gUe8FvD_Me1Vrd_IdODHIOuMVJMhGCm46HiXUFlMEBDzzye_9IcYi4lJTQtY7aRGmXdNOvZwY9iFEljg0ijCYZ9ZnfdsGDYCbo0k/w640-h386/phase%20difference.png" width="640" /></a></div><p>Above — Two identical frequency sine waves. The discrete event in time is the positive peak of the sine wave. Wave A leads wave B. You might also say that B lags A. The time difference of these 2 events relates to the phase difference between the 2. This figure shows a very simple formula to help beginners. </p><p>Phase difference = the time difference between the discrete event in A and B divided by the total time of 1 complete cycle. That value gets multiplied by 360 to convert it to degrees. Thus, when total time = 1 second; if the time difference = .25 seconds, the phase difference = 90 degrees. If the time difference = 0, then the phase difference is 0 — & the 2 waves are said to be in phase.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhrWmml2J2iMJxp-6CQQQ2CD1Wy79aNryPOoDYNc7RF74XEJwEj62Xi6KHiE2J2ooGykZtnxcBOOo_ZHqS-FD_bxJraSXBoYMQ-QhNEiRlyHW74IbZFhiH-KqfB_pQDbIvtFUdpcaD_7riVycKdAPXfN5BaZ3Zm66Om8Gxnc0OnTgjk-5vBc4s-OimQl4uR/s702/Experiment1.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="315" data-original-width="702" height="288" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhrWmml2J2iMJxp-6CQQQ2CD1Wy79aNryPOoDYNc7RF74XEJwEj62Xi6KHiE2J2ooGykZtnxcBOOo_ZHqS-FD_bxJraSXBoYMQ-QhNEiRlyHW74IbZFhiH-KqfB_pQDbIvtFUdpcaD_7riVycKdAPXfN5BaZ3Zm66Om8Gxnc0OnTgjk-5vBc4s-OimQl4uR/w640-h288/Experiment1.png" width="640" /></a></div>Above — I built a simple pi filter designed to give a 90 degree phase difference at 3.58 MHz when comparing the output to the input or vice versa. A signal generator set to 3.58 MHz with a 50 Ω output impedance was connected to the filter. The filter output got terminated in the 50 Ω input of my DSO. I placed a 10X probe on the filter input to give 2 channels. The DSO output shows a 90 degree phase difference between the 2 waves at 3.85003 MHz. <br /><br />I had to tweak the frequency a little to account for real-world variances of the L C parts. We might say that the output was phase shifted 90 degrees compared to the input. The terms leads or lags with respect to 2 travelling waves might help firm up the concept of a time difference between the 2 signals in your mind. <br /><br />In more advanced analysis with math, the phase difference gets characterized by a measured quantity known as a phase angle.<br /><p><b>---------- [ SECTION 2 ] Feedback and Function ----------<br /></b></p><p><b>Feedback</b><br /><br />A portion of the output signal (either a voltage or a current) is connected to, or “fed back” to the input. We'll focus on voltage feedback in this presentation.<br /><br /><b>Negative feedback </b></p><p>The fed back output signal has a 180 degrees phase difference with the input signal. This is called anti-phase, or inverted phase. Negative feedback bucks or subtracts from the input signal and gets called degenerative feedback. </p><p><b>Positive feedback</b><br /></p><p>The fed back output signal is identical in phase to the input signal. This is called in-phase or a 0 degree phase difference (it may also be 360 degrees, or multiples of 360 degrees). Positive feedback adds to the input signal — it sums with the input voltage causing the output to increase and gets called regenerative feedback.<br /><br />To sustain oscillation, the feedback must be positive since apart from power supply DC, an oscillator lacks an external input signal. The oscillator amplifier output goes to a buffer for external circuitry, plus, some portion of the output goes through a frequency determining network and back to the input with no net phase difference at the oscillation frequency. E.g., a positive feedback loop at 1 frequency.<br /> <br />A proper oscillator produces a repetitive output waveform. This output waveform may be sinusoidal (sine wave) or non-sinusoidal. We’ll focus on sinusoidal or near-sinusoidal RF oscillators that use LC inductor/capacitor circuits.<br /><br /><i>The oscillator as a filtered noise amplifier</i></p><p>Some impulse(s) must trigger the loop circuit to start oscillating. This might be turn-on noise, plus random noise from loop parts such as transistor thermal noise. That bit of noise loops around from output to input and starts the ball rolling.<br /><br />Initially, positive feedback will cause the signal amplitude to build up and the active device will operate in it’s undistorted linear region. Eventually the rising linear oscillation amplitude will push the device into saturation and gain becomes nonlinear (distorted) & clipping + compression occurs. In its saturation region, amplifier gain tends to decrease as the signal amplitude moves towards the DC power supply voltage. At some point, the amplitude will reach steady state with stabilized or “limited” amplitude. The final amplitude depends on complex factors that may include the amplifier non-linear device characteristics and how deep into non-linear operation the gain stage goes.<br /><br />Thus, at the loop frequency determined by the frequency determining circuitry, where the input and output phase difference is 0, a signal will arise having fundamental, harmonic and noise energy. <br /> <br />The loop gain criterion >=1 does not imply the amplifier voltage gain is 1 or 0 dB. The amplifier must provide enough gain to overcome circuit losses, plus have enough gain for start up — and to sustain oscillation in a variety of conditions such as adverse temperature or load changes. Further, losses may vary with the type of resonator circuit. A crystal or SAW resonator will give more insertion loss than an LC tank or pi filter at resonance.<br /><br />Finally, the oscillator output harmonic distortion and stability is affected by the Q of the frequency determining network. A high Q circuit filters more sharply, so signals fall off from the resonant frequency more quickly than a low Q circuit. A high Q network also incurs less losses than a low Q circuit at resonance. The Q may also affect stability since non-linear amplifier function may vary with the degree of filtration offered by a given frequency determining network. <br /><br /><b>---------- [ SECTION 3 ] B E N C H E X P E R I M E N T S ----------<br /></b><br /> via 3 basic types of frequency determining feedback networks<br /><b> [ 3a ] Transformer</b><br /></p><p style="text-align: left;"> <a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgUJ1IESa-znj5lBesKpxkTF2kbEZnNHfxiAHX6iPMA3D7P6sqoTLkslOVhNSs5sfVNMdhE4-pbET0_hHgrS-kYkIlY1kypmgS84Dts7vMsP9lZg8iWQ973v9_eeJZe4VQnFrDJ3VjzRlwpUk8R5bLnWs2i3xHbfQRhK_Ebhl4lc3JmRyljYx7clku9bhez/s432/feedback%20osc%20common%20base.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="323" data-original-width="432" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgUJ1IESa-znj5lBesKpxkTF2kbEZnNHfxiAHX6iPMA3D7P6sqoTLkslOVhNSs5sfVNMdhE4-pbET0_hHgrS-kYkIlY1kypmgS84Dts7vMsP9lZg8iWQ973v9_eeJZe4VQnFrDJ3VjzRlwpUk8R5bLnWs2i3xHbfQRhK_Ebhl4lc3JmRyljYx7clku9bhez/s16000/feedback%20osc%20common%20base.png" /> </a> </p><p style="text-align: left;">Above — A common base BJT oscillator using transformer feedback. For the Section 3 experiments, I show minimalist, biased & functioning circuits at 1 frequency. By going with split DC supply, we enjoy a reduction in bias circuitry to allow a clear view of the frequency determining feedback network and amplifier. Each circuit employs a 10K resistor connected to the negative DC rail to provide a current source. All the circuits run between 0.8 to 1.3 mA DC current for easy comparison. To measure the emitter/collector current measure the voltage drop across either 100 Ω resistor and use Ohm’s Law to calculate current.<br /><br /><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjRJsGKyUYWIuRpFTy4TqE7ArF39JYobtHANmRHAeXXMG0ySndJRdwJhMC9NIh1oFMW0I_yPpYDLcxGopaZPsg7T2LRmTuSk7RpjZd747OnSR4MR1QRWok-8slygmPVaUOlj_eyP1l4fDdF0cq0LSDa9ECAU9IgQ1B1XWwa6-w2a1W-PHN2LftpoViv6EIK/s1064/probe.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="402" data-original-width="1064" height="151" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjRJsGKyUYWIuRpFTy4TqE7ArF39JYobtHANmRHAeXXMG0ySndJRdwJhMC9NIh1oFMW0I_yPpYDLcxGopaZPsg7T2LRmTuSk7RpjZd747OnSR4MR1QRWok-8slygmPVaUOlj_eyP1l4fDdF0cq0LSDa9ECAU9IgQ1B1XWwa6-w2a1W-PHN2LftpoViv6EIK/w400-h151/probe.jpg" width="400" /></a><br />Above — To sample the output in my DSO, I placed 1 turn of wire through the T68-2 toroid & grounded 1 end. A 10x probe is connected to the hot end. Normally, we use a linear buffer with oscillators. Again, my approach is minimalist, so the basic oscillator circuit gets emphasized. <br /></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjH2P37ql2MMkwWe0vbfm03VVDgz3N1OMpY-EYaB1393O42MrgYP1sVnx15wEEBS9LfhzX3ERp8OWWl0QiHTWm_TlaRpCHYTxyq6YpAdD-ld5CSKGgeJB-3bA456tXBi0XFJDy-BLXFJM-0FuLQcJ63D1LAZGjH_1JcbmfWmx3JA6gt8cCy3x31vc5ITYPt/s1036/ex3%20combined.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="264" data-original-width="1036" height="163" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjH2P37ql2MMkwWe0vbfm03VVDgz3N1OMpY-EYaB1393O42MrgYP1sVnx15wEEBS9LfhzX3ERp8OWWl0QiHTWm_TlaRpCHYTxyq6YpAdD-ld5CSKGgeJB-3bA456tXBi0XFJDy-BLXFJM-0FuLQcJ63D1LAZGjH_1JcbmfWmx3JA6gt8cCy3x31vc5ITYPt/w640-h163/ex3%20combined.png" width="640" /> </a></div><div class="separator" style="clear: both; text-align: left;">Above — Output wave forms of the common-base BJT oscillator with no 8K2 shunt resistor [left] and as shown in the schematic [right]. In most basic oscillator circuits amplitude regulation gets achieved by the BJT going into clipping — clipping maybe minimized if the BJT gain is just high enough to maintain oscillation, but you need enough gain to start oscillation and sustain it with temperature changes. In the right sided DSO tracing, the 8K2 shunt resistor reduces transistor gain and thus clipping. The only thing that stabilizes oscillation amplitude is the non-linear activity of the BJT. The powdered iron inductor measured 4.67 uH.</div><p></p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEia2Nxic18abfDKgtX66jmNAjPVM9Hwk1-6Ab3s2-4mFY0hx-ktfVolNNtWHld0kLIuTDNFD5WMVn62K_K6tMHM0jQhu6cJqnJAo5YVM0kBE9ILFlwRa4YVOiCqAO4hHZ8PLd5invW2MowCWR9QiDzpxEfqYy2e4YR85O4I1mAfAjksK-0fIXJjDkd6o4F4/s412/feedback%20osc%20common%20gate.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="292" data-original-width="412" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEia2Nxic18abfDKgtX66jmNAjPVM9Hwk1-6Ab3s2-4mFY0hx-ktfVolNNtWHld0kLIuTDNFD5WMVn62K_K6tMHM0jQhu6cJqnJAo5YVM0kBE9ILFlwRa4YVOiCqAO4hHZ8PLd5invW2MowCWR9QiDzpxEfqYy2e4YR85O4I1mAfAjksK-0fIXJjDkd6o4F4/s16000/feedback%20osc%20common%20gate.png" /></a></div><p>Above — A common gate version of the above oscillator.</p><p></p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgK1q1dCwdswgOtBvHktGzLHMinKTZpCBugX3VJn1jyk_WLwwVIbbmYm-Cb8NOQcuz755FL1mQ5s6EeP8SmPB4IXiwJFEKkh0YAq7TzBTbql6abhSJVA7PN8iKDMAl19nh8QnIL3ssvLSw07q4inPfZbzv7cbZXBjogGddmyZ-zL6JccpG8qFKF4vT5FB5G/s800/output1.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="400" data-original-width="800" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgK1q1dCwdswgOtBvHktGzLHMinKTZpCBugX3VJn1jyk_WLwwVIbbmYm-Cb8NOQcuz755FL1mQ5s6EeP8SmPB4IXiwJFEKkh0YAq7TzBTbql6abhSJVA7PN8iKDMAl19nh8QnIL3ssvLSw07q4inPfZbzv7cbZXBjogGddmyZ-zL6JccpG8qFKF4vT5FB5G/w640-h320/output1.png" width="640" /></a></div><p></p><p>Above — The DSO output of the common gate oscillator with lower distortion than the BJT equivalent. In general, like with tubes, JFET oscillators go into gain compression more gradually than a BJT, so oscillation amplitude regulation occurs with less distortion. Further, FETs offer quicker + better temperature stability, plus less heat dissipation into nearby circuitry compared to BJTs.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgiS9gHHRuGJuvp85NtFutqwmzHVo4jjVKKWrKB64-ypu7UWpO7ZAo7UIwlVQEAWKpTikwi758r719DolVBH5qJvDOHChNEoan3a8PDeeCLpwbhYb6kbBWs96o0j8BLZe50gxcjXjKEfLoW1pqBVtfxWIq7-wScqXvXB29JAsCHlrTH4AwoxAtXpBWRrm72/s794/FFT.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="396" data-original-width="794" height="320" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgiS9gHHRuGJuvp85NtFutqwmzHVo4jjVKKWrKB64-ypu7UWpO7ZAo7UIwlVQEAWKpTikwi758r719DolVBH5qJvDOHChNEoan3a8PDeeCLpwbhYb6kbBWs96o0j8BLZe50gxcjXjKEfLoW1pqBVtfxWIq7-wScqXvXB29JAsCHlrTH4AwoxAtXpBWRrm72/w640-h320/FFT.jpg" width="640" /></a></div><p></p><p></p><p>Above — An FFT of the common gate oscillator. The 2nd harmonic lies ~ 44 dB down. I found that the feedback coupling cap could go as low as 100 pF before it ceased to oscillate. From 100 to 200 pF the amplitude varied directly with the capacitor value. Above 200pF it made little difference to the amplitude up to 1000 pF ( the maximum value I tried with the coupling capacitor). This capacitor mainly serves to block the negative DC voltage flowing directly to ground through the secondary winding — AC coupling. In many oscillators, capacitors are used to AC couple circuits, but may also be part of the frequency determining network.<br /><br /><b>Discussion</b><br /><br />Shown above is the classic Armstrong transformer feedback oscillator (also called the Meissner oscillator). The feedback gets coupled via an untuned secondary winding on the LC parallel “tank” resonator. The secondary gets called a tickler by some. Feedback networks maybe manipulated to provide the correct amount of feedback, provide a phase shift and also to impedance match the input to the output.</p><p>A common base/common gate amp runs a low input impedance and quite a high output impedance which the transformer turns ratio reflects. <br /><br />The common base/common gate amp provides zero phase shift from the transistor input to output. In order for the phase difference at the oscillator amplifier input to be 0, the frequency determining network must also provide zero phase shift as shown by the phasing dots on the transformer primary and secondary. The tank, a parallel resonant circuit, is 1 all experimenters should know about. In summary, at resonance, XL = XC and the impedance is maximal (considered a pure resistance). </p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi_-W_eiOVElNX0Aw-lGRboRTNfFgjK_7l2dggwtNE-z-krOzDFgBp-0II_Tc4Ca0ZDGNVwhzydmXkAcFq8GKen5ZvjqSv3TrcWttoL5Kz_Y4emceL5QdcJtwSSUG61ffGvXaKoKCQTbS2EEq6apneGDnHSq57EkJJt89YUOlah0qiF7W7QpBh3M5UhzN8j/s710/combinedEX5.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="325" data-original-width="710" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi_-W_eiOVElNX0Aw-lGRboRTNfFgjK_7l2dggwtNE-z-krOzDFgBp-0II_Tc4Ca0ZDGNVwhzydmXkAcFq8GKen5ZvjqSv3TrcWttoL5Kz_Y4emceL5QdcJtwSSUG61ffGvXaKoKCQTbS2EEq6apneGDnHSq57EkJJt89YUOlah0qiF7W7QpBh3M5UhzN8j/s16000/combinedEX5.png" /></a></div><p> Above — The oscillator circuit with a common emitter (A) and common source (B) amplifier.<br /></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhXcSygmqz5p6w_6qPZuwtPxvNjsDHcxELF2rgArN6e7zgNxRfE1402slxiU1pfF_5b3lNj7qpEYG9C7Mu4A6nwaKU7-7DI4jAMKMh62fyM0px37IkUazQpZJ1C1QpWtjwmA90xcoMagpGzqC0EJ5mKSL_2RqS-wM6_RGkg7q7mVaqK5jFkq8CMzjJWllQ9/s800/ex5OUTcombined2.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="345" data-original-width="800" height="276" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhXcSygmqz5p6w_6qPZuwtPxvNjsDHcxELF2rgArN6e7zgNxRfE1402slxiU1pfF_5b3lNj7qpEYG9C7Mu4A6nwaKU7-7DI4jAMKMh62fyM0px37IkUazQpZJ1C1QpWtjwmA90xcoMagpGzqC0EJ5mKSL_2RqS-wM6_RGkg7q7mVaqK5jFkq8CMzjJWllQ9/w640-h276/ex5OUTcombined2.jpg" width="640" /></a></div><p>Above — DSO output wave forms for the (A) BJT and (B) FET oscillators. These amplifiers invert the phase of the signal from input to output (180 degree phase shift). Thus, the frequency determining network must also invert the phase. The parallel tank itself has 0 phase shift, so the secondary winding of the tank is where we perform this phase inversion. Note the polarity or phasing dots on the transformers.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhKiEA39mJv-HPJBN1EdMlZLf7nn6nlqkJj-wU8ViP0IWhapKJyKEGSceeyXtS7ZIA9XD8CG1dsF_gXXXYzHhBgaAF2tlcUjzRHh1_0fhyphenhyphenJbSSQQqVXf7OcIF_2cCSdg7BPFPzHlhghpBY8HM6qI7o2Z_VmcsCsrf4eNkGU_xOWse9Z5vxk6lRFQ17AljVV/s600/invert2.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="447" data-original-width="600" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhKiEA39mJv-HPJBN1EdMlZLf7nn6nlqkJj-wU8ViP0IWhapKJyKEGSceeyXtS7ZIA9XD8CG1dsF_gXXXYzHhBgaAF2tlcUjzRHh1_0fhyphenhyphenJbSSQQqVXf7OcIF_2cCSdg7BPFPzHlhghpBY8HM6qI7o2Z_VmcsCsrf4eNkGU_xOWse9Z5vxk6lRFQ17AljVV/s16000/invert2.jpg" /></a></div><p>Above — For newcomers to decode oscillators, a good place to start is to know whether your amplifier(s) invert the phase from input to output. A and B are op-amps shown in the inverting and non-inverting forms. When using logic gates biased as “linear amplifiers” we often employ inverters (a dead giveaway whether phase inversion happens). D shows the 3 equivalent BJT + FET circuits and whether they invert from input to output. This is something to memorize. If the oscillator contains 2 BJTs or FETs like in the Franklin oscillator, you identify whether each device inverts or not — and then trace the signal path though the loop.</p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiMCFD-C8mkHru0w5mLPq6g_AfjFB5dGWWhtEamMRBxzLYoAabi4Id69tNC6YIc3hW_hneCKuMSDEF0Gk4sKggpjN8XMJpMshaYM5AjvL5mkzPNAIMoEX4SGBHKjLVXsnKHH9OmnD8SrokoJJLQiuseEuUdCic5Y3tVprejUNUDx2m0wAGYcydMEWGR5FuA/s612/poops%20out.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="311" data-original-width="612" height="326" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiMCFD-C8mkHru0w5mLPq6g_AfjFB5dGWWhtEamMRBxzLYoAabi4Id69tNC6YIc3hW_hneCKuMSDEF0Gk4sKggpjN8XMJpMshaYM5AjvL5mkzPNAIMoEX4SGBHKjLVXsnKHH9OmnD8SrokoJJLQiuseEuUdCic5Y3tVprejUNUDx2m0wAGYcydMEWGR5FuA/w640-h326/poops%20out.png" width="640" /></a></div><p>Above — I built a version of the common emitter oscillator with too few secondary windings and the DSO results lie above. The oscillator starts, but then poops out because positive feedback voltage was too low in amplitude to sustain life.<br /><br />On the other hand, if you make the feedback voltage too high in amplitude; depending on the amplifier type plus other factors, you may incur some bad side effects. This might include affecting amplifier input impedance and bias stability, loading the frequency determining network — or squegging. Squegging is more common in some oscillator topologies and/or oscillator amplifier types than others. <br /><br />Essentially — undesirable parallel oscillations arise. A great example is motor boating in an AF power amplifier. Too much signal amplitude excessively charges the feedback coupling capacitor and this changes the bias of the amplifier in repetitive bursts. Keeping the feedback coupling capacitor value down as low as possible is an easy way to crush squegging in oscillators where squegging might occur. <br /><br />Let’s move to the second type of frequency determining feedback networks: the pi network.<br /><br /><b> [ 3b ] Pi Phase Shifter</b><br /><br />The humble ¼ wave pi network, whether made from L + C parts, or a transmission line such as coax or microstrip line serves as a fundamental building block in RF design. ¼ wavelength pi networks may function as impedance matcher, filter, phase shifter, frequency determining network, frequency controller, or a line balance converter just to name a few of its possible functions.<br /><br />Those who work with antenna designs will get this — a ¼ wave coaxial matching transformer or stub can match a high impedance to a low impedance e.g. a capacitive reactance at 1 end may appear as an inductive reactance at the other.<br /><br />The pi phase shifter is a representative feedback network for a bunch of famous oscillators. A high Q LC pi network at resonance (at its cutoff frequency peak) will function similarly to a bandpass filter. Studying the pi feedback network in the oscillators that follow may boost your insight into understanding many of the popular oscillators that are named after their inventor.<br /></p><p>The frequency determining network of a Colpitts oscillator uses capacitive feedback, the Hartley uses inductive feedback, while the Vackar uses capacitive feedback plus a parallel LC tank. Further, these circuits may employ tapped capacitors or inductors to establish the correct feedback level at the oscillator’s amplifier input.<br /> <br />In a feedback loop, apart from the resonator components in a feedback loop, any stray inductance or capacitance from loop parts becomes part of the network. Of particular concern is the internal capacitances of the amplifier. Both FETS and BJTS have internal capacitances that vary directly with temperature — If temperature goes up so do these capacitances. The end result is frequency drift as temperature goes up and down. <br /><br />Designers may work to minimize this drift by various mechanisms ranging from carefully regulated DC voltage to putting the oscillator in an oven chamber. With respect to our feedback network, they might try to reduce the impact of amplifier internal capacitance by absorbing or swamping this C with external capacitors in the feedback network. The aim is to minimize the effect of device internal capacitances in determining the oscillation frequency. For example, place a large capacitor in parallel with a nearby internal capacitance to absorb it.<br /><br />I’ve read that from a frequency spectrum of DC to daylight, the theoretical phase shift range for a pi network is 0 to 270 degrees. So far, I’ve only built them with a phase shift from 0 to just over 180 degrees.<br /><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh2W09LibSjF0naml7lzq6aRJHOgtnZxjLRVWFfHKpj0_ghwgcpRwJOyfiBokYbTEgL7Zp5j7TSnl_olivOXLHW23sc6QT0ZzOaJRdA0bmO2b-aHg2fKGZ9ajvmW9xa8nI5UaGOG5QGAWhZ4Ap4T739x4_xQOcFK8TYKp0WXhLyBYsHcZSIxOkpYsyDoL0P/s843/feedback%20osc%20common%20emitterLP.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="354" data-original-width="843" height="268" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh2W09LibSjF0naml7lzq6aRJHOgtnZxjLRVWFfHKpj0_ghwgcpRwJOyfiBokYbTEgL7Zp5j7TSnl_olivOXLHW23sc6QT0ZzOaJRdA0bmO2b-aHg2fKGZ9ajvmW9xa8nI5UaGOG5QGAWhZ4Ap4T739x4_xQOcFK8TYKp0WXhLyBYsHcZSIxOkpYsyDoL0P/w640-h268/feedback%20osc%20common%20emitterLP.png" width="640" /></a></p><p>Above — A low pass form pi network phase shifter is added to a common emitter oscillator amplifier at A. I changed to using a 5 pF capacitor AC coupled to a 100K resistor as a load to measure across with my 10x probe (B). The RFC was just a random 1 mH epoxy-coated choke that was lying on my bench. I measured it at 920 µH. This choke serves only to prevent the collector AC output from passing though the 0.1 µF capacitor to ground and the value isn’t critical. </p><p>The CE transistor amp inverts the signal, so the feedback determining network must also invert the signal. The low pass form pi network serves as a metaphor to the Colpitts oscillator. I experimented with the feedback capacitor by placing a 5-450 pF air variable cap in its place and settled on 47 pF because it gave stable and sustained oscillation. Going below 40 pF ceased oscillation. If you change any value of capacitor or the inductor value, the output frequency will change. <br /></p><p>The most common direct example of a low-pass pi style network phase shifter is that of the Pierce crystal oscillator shown as the inverting gate oscillator in an earlier diagram. The phase shift/frequency determining network includes a crystal functioning as the resonator. The entire feedback network also includes the output resistance of the gate.<br /><br />Some logic ICs such as the 74HC4060 ripple counter; or any number of microcontrollers include an inverter gate so you may wire up an RC or crystal Pierce oscillator.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiYvzW7ikODKL6ZHInv-XV8Ve7pO1QlhRmEJyR6wNqZ8Hl3X9esoNjIgSbkAs203bcycyKBGdu2u_WpcciAZuoZOoAJ2jySnIqWtvsIZx55GyR4RbAPDuDs2JXoiQkk5uWMFNgpR8iSfXyAVfviLX1_PyBPXTO7V93KxMdaU3vuBqsNUVTZz5IjPMrFN6aH/s799/lpPI1.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="404" data-original-width="799" height="324" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiYvzW7ikODKL6ZHInv-XV8Ve7pO1QlhRmEJyR6wNqZ8Hl3X9esoNjIgSbkAs203bcycyKBGdu2u_WpcciAZuoZOoAJ2jySnIqWtvsIZx55GyR4RbAPDuDs2JXoiQkk5uWMFNgpR8iSfXyAVfviLX1_PyBPXTO7V93KxMdaU3vuBqsNUVTZz5IjPMrFN6aH/w640-h324/lpPI1.png" width="640" /></a></div>Above — the DSO time domain waveform of the pi low-pass oscillator.<br /><p></p><div class="separator" style="clear: both; text-align: center;"></div><div class="separator" style="clear: both; text-align: center;"></div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh9OQNEvWw2G9IT81JGWUOnabD0z3Y-SvtdCnHXT-CdVeaphyWm6NKvQ27nEngrSZqhtjvRP6TZaicuWTjyNTigFM6QpBNUHXFUBZQHd72k9BvNt3ZyatIrmM0jsBrSmCfwcf9LBZGUpC7FlenJvi9X4t1Zz72SaO4Rvt4PS0Xf1GY-SYPgr2KUTKwrLYZb/s848/feedback%20osc%20common%20emitterHP.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="348" data-original-width="848" height="262" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh9OQNEvWw2G9IT81JGWUOnabD0z3Y-SvtdCnHXT-CdVeaphyWm6NKvQ27nEngrSZqhtjvRP6TZaicuWTjyNTigFM6QpBNUHXFUBZQHd72k9BvNt3ZyatIrmM0jsBrSmCfwcf9LBZGUpC7FlenJvi9X4t1Zz72SaO4Rvt4PS0Xf1GY-SYPgr2KUTKwrLYZb/w640-h262/feedback%20osc%20common%20emitterHP.png" width="640" /></a></div><p>Above — Schematic and DSO measured output of a common emitter + high pass form pi network phase shifter. The network required an additional 0.1 µF AC coupling capacitor to prevent a DC short to ground through the left hand inductor. The series resonant frequency of that 0.1 µF cap = 6.6 MHz, so it provides a low impedance to the 7.35 MHz signal.<br /> <br />The high pass pi network version provides a metaphor to the Hartley oscillator. At their resonant frequency, many popular oscillator frequency determining networks resemble the circuitry & function of the pi phase shifter circuit in some form.<br /><br /></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj7F6CzK1QGp6FtqjqFDhBaNnE0cZLY6djgQi-jOOzXDqxNcgX0vNhBclWUj3a-k3UJxQ-XnFIDzgOZgiUwYWkXctNJk456RGfIcCw7yA6awgE-zxHQvPqkDdLi4piBM2N8Sy14xHmMsIW5tIIcEmUIBoxRFY3ofHD2agr9N6gS0bAY-5fDMYeRMWyl8fo0/s363/Experiment2a.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="275" data-original-width="363" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj7F6CzK1QGp6FtqjqFDhBaNnE0cZLY6djgQi-jOOzXDqxNcgX0vNhBclWUj3a-k3UJxQ-XnFIDzgOZgiUwYWkXctNJk456RGfIcCw7yA6awgE-zxHQvPqkDdLi4piBM2N8Sy14xHmMsIW5tIIcEmUIBoxRFY3ofHD2agr9N6gS0bAY-5fDMYeRMWyl8fo0/s16000/Experiment2a.png" /></a></div><p>Above — A sidebar experiment using standard value series 100 pF capacitors that match a parallel tank to 50 Ω input & output Z at 7 MHz.<br /></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj70tttZzxhPbDI1B7KJ0kAfvTadJnxpJRVizTjopJXE0gGb6pfOENWJwBPXjuYkiauRdnKSQNDcCC4xtJeyFbaPuOn88RSqM3DJRJN7zycJcQ5mKcviYZHZNXOcysC8In7RPpL2jhr8R1Ea8saizz4ckJBxlbbdbwjCJb2f7jN6-uWaWBbqIBOTHVLtaXu/s800/Ex2Outcome.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="480" data-original-width="800" height="384" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj70tttZzxhPbDI1B7KJ0kAfvTadJnxpJRVizTjopJXE0gGb6pfOENWJwBPXjuYkiauRdnKSQNDcCC4xtJeyFbaPuOn88RSqM3DJRJN7zycJcQ5mKcviYZHZNXOcysC8In7RPpL2jhr8R1Ea8saizz4ckJBxlbbdbwjCJb2f7jN6-uWaWBbqIBOTHVLtaXu/w640-h384/Ex2Outcome.png" width="640" /></a></div><p><br />Above — A DSO trace of the above schematic showing a phase inversion. I had to tweak the frequency slightly to allow for L C variations from the design to get 180 degrees. The key point = RF filters using various topologies exhibit phase shift that changes with frequency within their pass-band, stop-band and roll-off frequency range in accordance with filter reactances & topology. <br /><br />Applying L C networks, you may manipulate filter network impedances & reactances to get a desired phase shift at a particular frequency or frequency band.<br /><br />Most oscillator’s seen in amateur literature are copies of someone else’s oscillator that’s kept exactly, or perhaps scaled to another frequency. This works fine in many cases. You may also figure lots out by performing experiments on your bench, or by pursuing computer-aided design & simulation.<br />Actually designing oscillators for specific goals requires math + measurement that goes beyond the scope of this blog post.<br /><br /></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiZDZlMuHgH4bq4l4qIf5JeFRnahGpiUiXPABHd9DXdfsf1h5LKaqEh38pvZ7Y_k8TbRnvbUsS4Dtz7iL7r6eOb-wOjXOPVLdCrhYo9WzH2rTZSZSld5o2fPBOhaFe3-IsQfls2nvnVeen1K96wF6-d0zEpYfbSl2bhm8-wkSwum90i3xTxNcI9yEJh7Gnf/s723/feedback%20osc%20common%20drain2.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="284" data-original-width="723" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiZDZlMuHgH4bq4l4qIf5JeFRnahGpiUiXPABHd9DXdfsf1h5LKaqEh38pvZ7Y_k8TbRnvbUsS4Dtz7iL7r6eOb-wOjXOPVLdCrhYo9WzH2rTZSZSld5o2fPBOhaFe3-IsQfls2nvnVeen1K96wF6-d0zEpYfbSl2bhm8-wkSwum90i3xTxNcI9yEJh7Gnf/s16000/feedback%20osc%20common%20drain2.png" /></a></div><div class="separator" style="clear: both; text-align: center;"><br /></div><div class="separator" style="clear: both; text-align: left;">Above — Frédéric pointed out I had not made a common drain nor common collector type oscillator, so I built the very simple Colpitts design shown above. It’s your job to figure out the phase shifts. Does the common collector/common drain amplifier invert the signal from input to output?</div><p>Let’s wrap up and go to the 3rd and final basic type of frequency determining feedback networks you might see in your travels.<br /><br /><b> [ 3c ] Tuned input and output</b></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjsNgFEyC6jddQlbiM6mn-ehs5P-k57xwfbKn-CyenNZMh_BVNBchg_whelwMp2ADCCzpugCcMJvYZdvhysaB4VkwRDrHPPF3a_zGAVmC-oUcpxb2XpWPhGY_OBakqIzpIuihIrgGBNbKRpvdrISQJRK5nZMRN7mM021FNQX90oa2vfCs-n6JnATXHJM1M8/s567/TITO1.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="385" data-original-width="567" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjsNgFEyC6jddQlbiM6mn-ehs5P-k57xwfbKn-CyenNZMh_BVNBchg_whelwMp2ADCCzpugCcMJvYZdvhysaB4VkwRDrHPPF3a_zGAVmC-oUcpxb2XpWPhGY_OBakqIzpIuihIrgGBNbKRpvdrISQJRK5nZMRN7mM021FNQX90oa2vfCs-n6JnATXHJM1M8/s16000/TITO1.png" /></a></div><p>Above — A tuned input + tuned output oscillator or TITO oscillator with a common source amp. I had to tune the gate tank since its pretty difficult to match up 2 L C tanks without at least 1 variable capacitor. <br />The common source JFET amp inverts the signal. The TITO uses a bandpass filter phase shift network to invert the feedback signal back to 0 phase difference at the JFET input. The bandpass filter (called a 3 element pi section in my old ARRL handbook) gives the needed 180 degree phase shift.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgn23bCHxQaBK95dWJlqFJpMGNLEqY9f-RgajNIu1H5uocQPXcA-DPRle6451CX-G9QaUQSvDJviFY27_SBb9giPZEIyyH4nielqRLP49LxaJ-wntQ0PSNJ-uMc2_pVogASmkHOq4u_QpzaaSwdnocUvNk6AWkRtfx-PNrI4of5t67-30V0RqTBjhaJjJGc/s700/titoOUTdso1.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="358" data-original-width="700" height="328" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgn23bCHxQaBK95dWJlqFJpMGNLEqY9f-RgajNIu1H5uocQPXcA-DPRle6451CX-G9QaUQSvDJviFY27_SBb9giPZEIyyH4nielqRLP49LxaJ-wntQ0PSNJ-uMc2_pVogASmkHOq4u_QpzaaSwdnocUvNk6AWkRtfx-PNrI4of5t67-30V0RqTBjhaJjJGc/w640-h328/titoOUTdso1.png" width="640" /></a></div><p>Above — The DSO tracing for TITO. <br /><br /><b>[ Section 4 ] Conclusion ----------</b><br /><br />I provided a basic, non-math introduction to RF oscillators using simple but functioning designs. The same principles apply to oscillators that use a crystal, SAW, coaxial, or MEMS resonator instead of an L C type circuit.<br /> <br /><b>[ Section 5 ] References ----------<br /></b><br />The Oscillator as a Reflection Amplifier, an Intuitive Approach to Oscillator Design,” by John W. Boyles, Microwave Journal, June 1986, pp. 83–98<br /><br />Lindberg, E. (2013). Oscillators - a simple introduction. In Proceedings of ECCTD 2013 IEEE<br /><br />M. Gottlieb, Practical Oscillator Handbook, Butterworth-Heinemann, London, 1997<br /><br />R.W. Rhea, Oscillator Design and Computer Simulation, 2nd Edition, Noble, 1995<br /><br />Yasuda, T., Uchino, K., Izumiya, S., Adachi, T., & Senanayaka, S. S. (2013). 433 MHz wide-tunable high Q SAW oscillator. 2013 Joint European Frequency & Time Forum & International Frequency Control Symposium (EFTF/IFC), 744–746</p>Vasily Ivanenkohttp://www.blogger.com/profile/17387516134063150119noreply@blogger.com4tag:blogger.com,1999:blog-3480228403403435266.post-1336825327219344812022-12-04T14:28:01.120-08:002023-03-16T22:50:41.216-07:00Suzu 12 — All Discrete Component Guitar Amplifier for 2023<div style="text-align: left;">In January & February 2023, I built 4 smaller size versions of the GAA -12 Practice Guitar Amp that we call Suzu. My design goals included fresh & unique circuitry, all discrete components, all split supply amplifiers plus a clean & simple signal path. I'll show my 4th and best version. Serving as my upstairs guitar practice amp, I specifically designed it for the T-style or Fender Telecaster ™ guitar and a 10 inch speaker.</div><div style="text-align: left;"> </div><div style="text-align: left;">The overall tone flavor of this amp harkens the Gibson GA-50. I avoided a mid range tone control and deep middle frequency scooping. If you boost the bass and treble controls, you do create some mid scooping but it's low Q and quite subtle compared to old black panel Fender guitar amps of lore.</div><div style="text-align: left;"><i><br /></i></div><div style="text-align: left;"><i>Note this was originally published as an update on Dec 4, 2022. I added much new content and then re-published it on Feb 20, 2023.</i><br /></div><div style="text-align: left;"><br /></div><div style="text-align: left;"><i style="color: #2b00fe;">— C O N T E N T S —<br /></i><br /></div><div style="text-align: left;">1. Preamplifer 1</div><div style="text-align: left;">2. Preamplifier 2 + design spreadsheet to download<br /></div><div style="text-align: left;">3. Power supply</div><div style="text-align: left;">4. Power Amp - PA -</div><div style="text-align: left;">5. Speaker</div><div style="text-align: left;">6. Miscellaneous Photos<br /><br /></div><div style="text-align: left;"><a href="https://qrp-popcorn.blogspot.com/p/guitar-related-index.html" target="_blank">Click here</a> for my <b>Guitar-Related Index</b> <br /></div><div style="text-align: left;"> </div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiYzoocpN2lyP5ZzqSFEJRkE7CD4CgzWdTpJuDbRZvnrCD1Kr-UQHXOGYZvA2qkLsRfwGEc2TtgJTRtIfwiIl4mf9lLOGHXJUInRxrdDtr_UUMfSZp_GC8OjRx__2sv7Awtd71gDdI97CF6bsvRIzD9cZFr9Ww4ne28ltKV0ixnWCRozbMCLEmGvEUaQA/s973/ss1.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="571" data-original-width="973" height="376" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiYzoocpN2lyP5ZzqSFEJRkE7CD4CgzWdTpJuDbRZvnrCD1Kr-UQHXOGYZvA2qkLsRfwGEc2TtgJTRtIfwiIl4mf9lLOGHXJUInRxrdDtr_UUMfSZp_GC8OjRx__2sv7Awtd71gDdI97CF6bsvRIzD9cZFr9Ww4ne28ltKV0ixnWCRozbMCLEmGvEUaQA/w640-h376/ss1.jpg" width="640" /></a></div><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh6wVLEKGXbJFnPlo3QMkLxL31L3ylwR10SWvec4vH1qfDLeSIB5jBuNsnP4x4KWqIF8JZ4TDRk9YT6-BgtA3tU_64gZedJPZfJdTIgs23FuYRhUaf2LXXn6nG5gDwXGdTXKQSufbqOdLxqqVvF7XqzbhVPYEekYLBMUmHGQPBPLecEtS6-bncovkXibA/s839/Q1.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="625" data-original-width="839" height="297" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh6wVLEKGXbJFnPlo3QMkLxL31L3ylwR10SWvec4vH1qfDLeSIB5jBuNsnP4x4KWqIF8JZ4TDRk9YT6-BgtA3tU_64gZedJPZfJdTIgs23FuYRhUaf2LXXn6nG5gDwXGdTXKQSufbqOdLxqqVvF7XqzbhVPYEekYLBMUmHGQPBPLecEtS6-bncovkXibA/w400-h297/Q1.jpg" width="400" /></a></div><div style="text-align: left;"></div><div style="text-align: left;"></div><h3 style="text-align: left;"><br />1. Preamplifer 1<br /></h3><h3 style="text-align: left;"><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgA4Mhf8J2bFfxortZ_DmbcJSMQx-RjpDyOXlOdlp3qtqycHnjguIes2tk5Dvh_7Cswr48XEzraiGrIhk7i0JZ7AvoWK-b2SBYmR55bIiGM83uugeqQDbUyZImiwtQQUNVzPVqjS8I_S-tNtTlfGMPaEIWfUSbhXd74doAxmkWeD0hJ5NVzmhe8ZfrvFg/s796/Feb%2019-A%20%20.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="600" data-original-width="796" height="482" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgA4Mhf8J2bFfxortZ_DmbcJSMQx-RjpDyOXlOdlp3qtqycHnjguIes2tk5Dvh_7Cswr48XEzraiGrIhk7i0JZ7AvoWK-b2SBYmR55bIiGM83uugeqQDbUyZImiwtQQUNVzPVqjS8I_S-tNtTlfGMPaEIWfUSbhXd74doAxmkWeD0hJ5NVzmhe8ZfrvFg/w640-h482/Feb%2019-A%20%20.png" width="640" /></a></div></h3><div style="text-align: left;">Above — First preamplifier schematic. Preamp 1 and 2 connect directly to the main DC power supply with no voltage regulation to get the maximum possible rail to rail AC guitar signal. To subdue power supply ripple and to isolate the preamplifier from the PA supply, a ripple filter feeds the preamp stages DC. I employed further RC low pass filtration on each stage to enhance ripple & noise rejection in this single coil pickup purposed guitar amplifier.<br /></div><div style="text-align: left;"> </div><div style="text-align: left;">The input 12K stopper resistor and capacitor form a low-pass filter to prevent AM radio detection. Eleven volt zener diodes clamp excessive signal amplitude from popping the input. This cold/dry Winter [coldest temperatures every recorded here in 2022] caused a lot of electrostatic buildup and discharge. Shocking. Sadly, empirically, I learned that static discharge can easily blow up front end circuitry & that <i>all </i>guitar amps need input protection.</div><div style="text-align: left;"><br /></div><div style="text-align: left;">A low-noise JFET with 1 megohm gate resistance provides a high input Z to the guitar pickup(s) and drives an emitter follower so the following stage tone circuit sees a low output impedance. The JFET voltage gain is set to about 3.3 with the 2K7 gain setting, source degeneration resistor. I normally set my maximal input stage voltage gain between 3 and 5. The JFET source current = 1.3 mA. The emitter follower collector current = 2.4 mA. When AC coupled to a 1K resistor load, the JFET + emitter follower can pass a 1 KHz signal with a magnitude of ~8.6 Vpp before it starts to clip. Lovely.<br /><br /></div><div style="text-align: left;">I prefer to bias each preamp block with a signal generator and DSO running and temporary resistor load AC connected. I strove to run the lowest possible current for each stage along the signal path. I chose the FET drain resistor value by temporarily substituting in a 10K potentiometer while adjusting it to get the highest clean signal swing at my bias point and then swapped in the nearest standard 1% metal film resistor. Almost every resistor is a 1% metal film and I happily grew my metal film resistor collection this Winter.<br /><br /></div><div style="text-align: left;"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhNJuEDgYRxuRklMAmGana5E1-Sox_9dwaKzMk-mcEblyLv5fZEPkrr8gYvl-7WW0qij17l-vWLiYLitiBZ8l3AKZuEPODIDPCjS9zpLo4q01RFfweg27iuyaWx3RiaxGkfGq0_pWTneAiksUFOI7N3_McxnwLbwuRfQwtWr-YncLHPe08Oo6B7UCPJ4A/s766/ss4.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="661" data-original-width="766" height="345" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhNJuEDgYRxuRklMAmGana5E1-Sox_9dwaKzMk-mcEblyLv5fZEPkrr8gYvl-7WW0qij17l-vWLiYLitiBZ8l3AKZuEPODIDPCjS9zpLo4q01RFfweg27iuyaWx3RiaxGkfGq0_pWTneAiksUFOI7N3_McxnwLbwuRfQwtWr-YncLHPe08Oo6B7UCPJ4A/w400-h345/ss4.jpg" width="400" /></a></div><h3 style="text-align: left;"> <br />2. Preamplifer 2<br /><br /></h3><div style="text-align: left;">Preamplifer 2 functions as the heart of my amplifier. I spent a month on this stage alone. Most of my discrete circuit designs resembled op-amps: For example, differential input, a voltage amp, plus a low Z output, however, but I found it wasn't necessary since I was not pursuing a ultra-linear preamp design. Some guitar amps built with op-amps and careful local + global feedback are said to sound sterile or too HiFi. Perhaps this rings true? <br /><br /> I did not get hung up on an ultra-linear signal path, rather tried my best while avoiding the emitter-coupled pairs found in op-amps plus many other analog ICs. It's fun to bias discrete transistors, calculate & measure things like input impedance, or the feedback values needed to get a particular gain and so forth. I miss this stuff. Old school electronics for analog dinosaurs like me. </div></div><div style="text-align: left;"><div style="text-align: left;"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiL9T3wWwqc4fzhbfaNuTMrPJ_WarYnJdWaw57sg9hovYLut1bhGsz6jZGe-BTNYf-zT2pyE-i8jg7jYgnx8HYBzIPvv0vlutz9Sv1l5NrAzi3H3jsepxyDbydFdef2h6Z93bA140K1G2DMDYhoxXea1QzKzTJBey6smh_Y398R6Y_5b-d2lSGOctkVqw/s916/Feb%2019-B.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="614" data-original-width="916" height="428" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiL9T3wWwqc4fzhbfaNuTMrPJ_WarYnJdWaw57sg9hovYLut1bhGsz6jZGe-BTNYf-zT2pyE-i8jg7jYgnx8HYBzIPvv0vlutz9Sv1l5NrAzi3H3jsepxyDbydFdef2h6Z93bA140K1G2DMDYhoxXea1QzKzTJBey6smh_Y398R6Y_5b-d2lSGOctkVqw/w640-h428/Feb%2019-B.png" width="640" /></a></div>Above — Second preamplifier schematic. The 22 µF input capacitor gets driven by emitter follower Q4 from Preamp 1. Preamp 2 voltage gain = 17.7 <br /></div><div style="text-align: left;"><br />The Baxandall tone circuitry time constants reflect that T-style guitars generally sound bright. For the classic 100 Hz / 10 KHz Bass + Treble 3 dB turnover tone section, you might wish to run 100 nF and 15 nF for the capacitors respectively. The 50K bass potentiometer works well since I tend to 'pump the bass' & this prevents the impedance from getting too low at the extreme wiper setting seen when when boosting hard.<br />The treble and bass are fairly independent and the boost / cut is just over 10 dB. Clearly op-amp tone controls boost and cut with more amplitude, but this work OK and proved very simple. The emitter of Q6 provided a convenient node for negative feedback into the tone circuit.<br /></div><div style="text-align: left;"> </div><div style="text-align: left;">The two 100 µF coupling capacitors help boost the low end for bright T-style guitars.</div><div style="text-align: left;"> </div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhJXOB15uaSupS4BoHMdCaPq1CVQw98byWOjmqQ-nMn2lU3MLRtI_A_fPJKE9MSxtvRuSihXCMZQAM_0JFodibDEAV4zrTqA1UqQ_wJCcQmeGQ7BjAMXsydRMdztrW3BMa3px83ECH3G9L14uWeKhRWOuUTUSu45e9LRCYSMz5_Hn_Zg6jfpaBg5Zn9Jw/s799/scope_9.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="501" data-original-width="799" height="402" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhJXOB15uaSupS4BoHMdCaPq1CVQw98byWOjmqQ-nMn2lU3MLRtI_A_fPJKE9MSxtvRuSihXCMZQAM_0JFodibDEAV4zrTqA1UqQ_wJCcQmeGQ7BjAMXsydRMdztrW3BMa3px83ECH3G9L14uWeKhRWOuUTUSu45e9LRCYSMz5_Hn_Zg6jfpaBg5Zn9Jw/w640-h402/scope_9.png" width="640" /></a></div>Above — A DSO trace of the Q6-Q7 feedback amp probed at the 22K load resistor. I measured 26 Vpp output clean signal voltage — at 26.1 Vpp, the lower half started to clip. This image shows a virtue of split DC supply for making amplifiers: better headroom. Not nearly as good as an op-amp, but pretty good headroom all the same.<br /><br /></div><div style="text-align: left;"><br /></div><div style="text-align: left;"><b>Feedback Amp Notes</b><br /></div><div style="text-align: left;"><br /></div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgcOR_FU-VJ8tuGDoH2pJpbbDO-9Bt6TLt9VGHF4TR8ugpVjvAQKQTyiG8GM8zigzMezxWcEIDrm9J3O8p_8w9UCpeL6iCgkdNleKXEecRE4jnMe2uKVB630gdAXFDFSmtKnQ05P3yM-d_w4Yr2eEL1OOnl-F-BT59RlajBnsuCcdY0TKzX990xamv1Cg/s492/FBA1.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="293" data-original-width="492" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgcOR_FU-VJ8tuGDoH2pJpbbDO-9Bt6TLt9VGHF4TR8ugpVjvAQKQTyiG8GM8zigzMezxWcEIDrm9J3O8p_8w9UCpeL6iCgkdNleKXEecRE4jnMe2uKVB630gdAXFDFSmtKnQ05P3yM-d_w4Yr2eEL1OOnl-F-BT59RlajBnsuCcdY0TKzX990xamv1Cg/s16000/FBA1.png" /></a></div><div style="text-align: left;">Above — This is my favourite AF feedback amp in single DC supply. In Suzu version 4, I employed this particular feedback amp for Preamp 2 with a split DC supply. Simplicity, wide bandwidth, stability — and medium to higher voltage gain make this a favourite amp for me. It goes well after a follower since the input impedance is relatively high and won't load down a source or emitter follower. I use a VCC from 3 to 28 volts DC in my single supply design work and whatever I can muster from my power supply in my split DC supplies. Of course, you have to watch the transistor collector to emitter breakdown voltage. I stock (hoard) high voltage BJTs knowing they are getting scarce and more expensive.<br /></div><div style="text-align: left;"><br /></div><div style="text-align: left;">In late 2021, retired EE Ken Kuhn suggested that I learn to make every discrete amplifier in split DC supply. (Paraphrasing) Ken wrote ... "any circuit can be biased to operate on single or split supplies and split supplies do not have to be symmetrical (i.e. +5, -12). All that matters is the total supply voltage."</div><div style="text-align: left;"><br /></div><div style="text-align: left;">To that end, I learned to make all the common configurations such as common emitter, emitter/source followers and differential amplifiers with both BJTs and JFETs at various total supply voltages. I struggled with some feedback amps as the calculations seemed tricky and I had no example circuits to inform my own designs. I sent Ken the above 19 volt single DC supply feedback amp requesting help to convert it to split DC supply. <br /></div><div style="text-align: left;"><br /></div><div style="text-align: left;">To my delight, Ken made a spreadsheet that did all the calculations and allowed the user to change supply voltages with the ability to adjust the gain to a desired value (combination of RE1 and RF).<br />Big thanks Ken! You may change parameters like VBE -- it might be best to measure VBE and input that value, however, if not, the spreadsheet gets you close and offers a great learning tool.<br /></div><p></p><p>Spreadsheet taken down for re-location to another server. <br /></p><div style="text-align: left;"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhXAMSm72lYWAsxcDVgaU5tf-MEZefkZhmXpH4vy_ZoWLEAQJTsCklOyCMChf-hNQVRqEJYzQKsuW-_dbsYdFyIUcmkJc2OeNQIbOAv55mZNaczb3L4hxbOSkC7q5lzix6MkO0CpCEZcAvfiOOEIXHAQPz0SdT9_dBqMNPephHmmvfOkpas_iGgPSBCkw/s682/ken1-scrn.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="604" data-original-width="682" height="566" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhXAMSm72lYWAsxcDVgaU5tf-MEZefkZhmXpH4vy_ZoWLEAQJTsCklOyCMChf-hNQVRqEJYzQKsuW-_dbsYdFyIUcmkJc2OeNQIbOAv55mZNaczb3L4hxbOSkC7q5lzix6MkO0CpCEZcAvfiOOEIXHAQPz0SdT9_dBqMNPephHmmvfOkpas_iGgPSBCkw/w640-h566/ken1-scrn.png" width="640" /></a></div><br />Above — A screen capture from the spreadsheet manipulated to fit this image file. This shows an example of using the tool to run the calculations for my single DC supply amp shown earlier. Note that the feedback resistor idealized value = 510 Ω, not 560. I adjusted RF using standard resistor values so that the 2 values VC2 center and VC2 actual were as close together as possible -- in this case 0.16 volts.<br /></div><div style="text-align: left;"> </div><div style="text-align: left;"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjU9SlTuJONKqPYs7FbwoUMueHDCv5Tid8j9Wra1IY7ZDHP0Kcd1cWJXKEgL4wu_EfatGHKmr7LljsHbGUvMnKl5Dk5gW5cykW7nmgTw7FnGtP06J1ZftgB8yZHRvcGOtXfaKkTQppIRtFNWDxM2h7XPi1VmfTxLJyzNna4J-o1YsLkUHCwLzixADGC1g/s525/ken2-scrn.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="250" data-original-width="525" height="304" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjU9SlTuJONKqPYs7FbwoUMueHDCv5Tid8j9Wra1IY7ZDHP0Kcd1cWJXKEgL4wu_EfatGHKmr7LljsHbGUvMnKl5Dk5gW5cykW7nmgTw7FnGtP06J1ZftgB8yZHRvcGOtXfaKkTQppIRtFNWDxM2h7XPi1VmfTxLJyzNna4J-o1YsLkUHCwLzixADGC1g/w640-h304/ken2-scrn.png" width="640" /></a></div><br />Above —My actual single DC supply amp with RF = 560 Ω. The difference between VC2 center and VC2 actual is only 0.6 volts, so well within the +/- 2V specified by Ken's spreadsheet. Notice the unloaded voltage gain rose by .91 . In reality my measured voltage gain was 11.7 -- the spreadsheet gets you close. You can manipulate RF and RE1 within reason to target more or less gain. The spreadsheet has a split DC supply example design defaulted into it. Between that example and my single supply examples here, the spreadsheet should prove easy to use if you ever build this feedback amp.</div><div style="text-align: left;"><br /></div><div style="text-align: left;">Within Suzu, RB1 can be made from parallel and/or series values, although my collection of resistors over 100K seems quite limited. To provide the Baxandall tone circuit with a higher input Z, I increased RB2 to 10K and made RB1 from two parallel 120K 5% resistors placed in series with a 150K 1% metal film resistor. I measured 208K from this resistor block -- it worked perfectly.<br /><br />You may also stick a temporary pot for RB1 [ I used a 250K potentiometer] to find the exact center for the Q1 bias on the test bench. With a 1 KHz signal generator and DSO probe on the 22K resistor, I drove the amp just into soft clipping and tweaked the pot to find the sweet spot for a perfect bias voltage. I removed the pot and measured just over 208K. Do not leave a regular potentiometer or trimmer pot in the actual circuit as it may add noise and potential for oscillations. </div><div style="text-align: left;"> </div><div style="text-align: left;">The feedback amp also provides a soft start and silent power off for the guitar amp. <br /></div><div style="text-align: left;"><br /></div><div style="text-align: left;"><b>Output Filter</b></div><div style="text-align: left;"><br /></div><div style="text-align: left;">Preamp 2 contains a crude RC low-pass filter on the output. Some of my 10 inch speakers sound shrill -- and this switchable low-pass filter tames that down. Further, the added stopper resistor(s) changes the dynamics of the power amp. I like the 2nd or middle position switch a lot, as it seems to make the guitar sound more “woody”.</div><div style="text-align: left;"><br /></div><div style="text-align: left;">I did make some active low-pass filter using FETs and BJTs and found they did not better,my tone. In the end, I preferred the RC filters since the added stopper resistors, plus the shunt caps provide me 2 additional practice tones to enjoy. <br /><br /></div><div style="text-align: left;"></div><div style="text-align: left;"><h3 style="text-align: left;">3. Power Supply</h3><div style="text-align: left;"> <a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhTbrEYNYRQrzYOafQ7zmHvsRk0NELvGa7msDSlQNQWzX3pFtPL48w2exrVO04ZUEISdPzbdC2HzJthc0ELf9nTOhfYThD_nebbP_xeNpO7heCgjSceCzpz39144LFfGqYhM7XutyElji0OOb07K1K1-NE1fYF40SCJdIIvD6J_0RMmcmqRw6Kiy7DgUg/s730/Feb%2020%20PSW.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="463" data-original-width="730" height="406" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhTbrEYNYRQrzYOafQ7zmHvsRk0NELvGa7msDSlQNQWzX3pFtPL48w2exrVO04ZUEISdPzbdC2HzJthc0ELf9nTOhfYThD_nebbP_xeNpO7heCgjSceCzpz39144LFfGqYhM7XutyElji0OOb07K1K1-NE1fYF40SCJdIIvD6J_0RMmcmqRw6Kiy7DgUg/w640-h406/Feb%2020%20PSW.png" width="640" /></a>Above — A basic power supply. The different green and orange LED resistors try to equalize their relative brightness on the front panel. 1 LED for each DC rail.<br /></div><h3 style="text-align: left;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhUwkGxxRUa4zN-LoV4jo9XJpj9REzf1iw_ieyet5XJaCwKgkcBds971ZAWtszzM8g7ZOYSU8ibvP-XLNDGVwItsx7M-rZAFGPGU_B1gO2urDhrhwWG_P3dy9l3G27lkXkkmVEJFmOMC-pGG8ENdEfcWjI4AU9XArPiJcL_UUVuKRBV18UUz4fllVGvwg/s735/rectifier.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="320" data-original-width="735" height="278" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhUwkGxxRUa4zN-LoV4jo9XJpj9REzf1iw_ieyet5XJaCwKgkcBds971ZAWtszzM8g7ZOYSU8ibvP-XLNDGVwItsx7M-rZAFGPGU_B1gO2urDhrhwWG_P3dy9l3G27lkXkkmVEJFmOMC-pGG8ENdEfcWjI4AU9XArPiJcL_UUVuKRBV18UUz4fllVGvwg/w640-h278/rectifier.png" width="640" /></a></h3></div><div style="text-align: left;"></div><p></p><div class="separator" style="clear: both; text-align: center;"></div><p></p><p>Above — For the first time ever, I'm using a commercial grade bridge
rectifier and will also apply this part in my high powered amps. You may
heat sink the GBUE2560 for high power amplifiers. <br /></p><p></p><p></p><p><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhs_75NAGTZaWkj4TMlFsm7xxkCEQZxYpd5PiErVl4cufMeMHfB66Uf8-EcouRSkYmFTgnUNd4pGuud3c6ATC5jTB2VPTe72qWXolm67Wdw_oTYqSQyptYCfrmIze9wyI6jvyiwoF5gQhwxWe65x0RCS-y80_1wALL3C0y8QETyELQi-j7jPujPnhRnJQ/s719/decamp4.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="521" data-original-width="719" height="464" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhs_75NAGTZaWkj4TMlFsm7xxkCEQZxYpd5PiErVl4cufMeMHfB66Uf8-EcouRSkYmFTgnUNd4pGuud3c6ATC5jTB2VPTe72qWXolm67Wdw_oTYqSQyptYCfrmIze9wyI6jvyiwoF5gQhwxWe65x0RCS-y80_1wALL3C0y8QETyELQi-j7jPujPnhRnJQ/w640-h464/decamp4.jpg" width="640" /></a></p><p>Above — Rectifier and 2 gorgeous reservoir caps for the DC power supply.</p><p><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhRwx8T79IUWpcX15FoOXRt_IVvKQnODkiv5nHQLOAS82IFMDU5MVW6AMRr56aO7OjW1L-KfhGhOtYtqRCN3AemSaoJof9Mci8spgFriWeUpnHXf4RMvsDQyVwmk-06AWGeU6G3MesFcOweRieU671MPeJxVmIvUlJ0TKyeetyZ9w-iKq6Un1F35BLxMQ/s933/decamp2.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="628" data-original-width="933" height="430" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhRwx8T79IUWpcX15FoOXRt_IVvKQnODkiv5nHQLOAS82IFMDU5MVW6AMRr56aO7OjW1L-KfhGhOtYtqRCN3AemSaoJof9Mci8spgFriWeUpnHXf4RMvsDQyVwmk-06AWGeU6G3MesFcOweRieU671MPeJxVmIvUlJ0TKyeetyZ9w-iKq6Un1F35BLxMQ/w640-h430/decamp2.jpg" width="640" /></a></p><p> </p>Above
— The power supply transformer just sitting in the chassis prior to
wire shortening and mounting.The Hammond 166L25 gives 12 watts out,
while the166L20 gives about 8 watts clean output power. Further, if you
regulate the op-amp DC supply with the 166L20, this means running +/-12
volts split as the unregulated DC voltage sags downs to less than 14 VDC
on each rail when driven hard. <br /><br />I also tested a larger
transformer with 29 VDC unregulated on each rail & for awhile, Suzu
was running at 27 Watts output power. The Hammond 166L25 and 166L20 have
identical dimensions. In the end,<i> </i>I opted with the 166L25, since
its higher output DC voltage allows running the preamplifier rails at 17-18
volts DC unregulated to get maximum headroom.<p></p><p><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhnF443Fnedr-Dkb_7On-vonMRWZgMD6ExqhguQBBCSgAlMph5DqUseKQkDnzFJF_WFExuNVPVq60EXckieL539okJd6dMDgcTnc8QGC5oMIzUG5PPk9tKUb2KlhPQRUZkHmgzQBvfoFeV--qTRsN2jHnKsFSI8n_xzhcPFx9X1mX4_g--U3_mTjM9Pjw/s1138/decamp5.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="734" data-original-width="1138" height="412" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhnF443Fnedr-Dkb_7On-vonMRWZgMD6ExqhguQBBCSgAlMph5DqUseKQkDnzFJF_WFExuNVPVq60EXckieL539okJd6dMDgcTnc8QGC5oMIzUG5PPk9tKUb2KlhPQRUZkHmgzQBvfoFeV--qTRsN2jHnKsFSI8n_xzhcPFx9X1mX4_g--U3_mTjM9Pjw/w640-h412/decamp5.jpg" width="640" /></a></p><p> Above — The power supply section mounted and tested. </p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiQXxVfot5_fRswRtRPQINM4KXNzJ4NiAAEk3HtudDBs7Wzta0yrSbwmMhykXNky9vgxUOR5I3Y5NgrPDHdKV7aD8tB7V_Ci3tTbYpaMZ-pqaLgXz6nY4JgTRLzWUvAmMeW5TexnX-Y8Rw-xhgneLS3Wx_I9lK9nwxxt51E0HwsM2n-ea6NtjHN66uGMA/s768/Q2.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="581" data-original-width="768" height="485" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiQXxVfot5_fRswRtRPQINM4KXNzJ4NiAAEk3HtudDBs7Wzta0yrSbwmMhykXNky9vgxUOR5I3Y5NgrPDHdKV7aD8tB7V_Ci3tTbYpaMZ-pqaLgXz6nY4JgTRLzWUvAmMeW5TexnX-Y8Rw-xhgneLS3Wx_I9lK9nwxxt51E0HwsM2n-ea6NtjHN66uGMA/w640-h485/Q2.jpg" width="640" /></a></div><p></p><p>Above — My downstairs Telecaster ™ with a Seymour Duncan Phat Cat single coil pickup in the neck slot and his Alnico 2 Pro™ in the bridge position. I added my newly designed, switchable treble bleed circuit in February 2023. <b> </b></p><p><b> 4. Power Amplifier — P A —</b><b></b></p><div class="separator" style="clear: both; text-align: center;"><b><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgRIuZdzvOzv2L_98-4g3Ivb3zPgZl-dxAtEu9zP-SPHwDH4N1aYtyHfALVAbaP5nMCLVPvYGR3wNgt34cdrNDRykw4uJXpmmX5HTyOY3aV_TYxKSDqYypZQZ_8dY1Iz70Ftpgh8ba6rDTFLNzseaLhOuw5BrzcVpotyqNYL2FjltPM3wzD_GiywgpPfQ/s911/PA%20Dec%203.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="608" data-original-width="911" height="428" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgRIuZdzvOzv2L_98-4g3Ivb3zPgZl-dxAtEu9zP-SPHwDH4N1aYtyHfALVAbaP5nMCLVPvYGR3wNgt34cdrNDRykw4uJXpmmX5HTyOY3aV_TYxKSDqYypZQZ_8dY1Iz70Ftpgh8ba6rDTFLNzseaLhOuw5BrzcVpotyqNYL2FjltPM3wzD_GiywgpPfQ/w640-h428/PA%20Dec%203.png" width="640" /></a></b></div><p></p><p>Above — PA schematic. I chose different transistors for the input
emitter coupled pair and also for the finals compared to the original GAA -12 Practice Guitar Amp. Further, I sank a little
more current in the emitter coupled pair and the VAS/driver stack. At
this point, I only plan to run voltage feedback in the global feedback
loop, although, I can easily add current feedback if desired.</p><p>I
measured a β of 540 for BC546B matched pair. The whole BC54-X- series
seem an incredible BJT collection offering low noise figure plus high β
and, of course, is long obsolete. I've got 30 pieces of the über low NF
BC549 in my parts bins for future 12 volt single-supply, discrete,
low-noise AF amplifiers.<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgwUlqXAdTHxNCo_CcoscQQOlPNE6z2X0IjVoGbQy234My18hmY2jI1mziLJNrL1lTMKibgehOwByAOCsOxLZUSoxFqQyr9qK83oNRE7b5Rukjq0Ku4QhUfDz1KAABg-KBkkG00D_pw8NVUzDrXI8-XjqT5h7b8yvdoHWfUihLyyyEqj3Bb6gQM4LCfVw/s704/BDW93C%20-%20end-of-likfe.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="536" data-original-width="704" height="488" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgwUlqXAdTHxNCo_CcoscQQOlPNE6z2X0IjVoGbQy234My18hmY2jI1mziLJNrL1lTMKibgehOwByAOCsOxLZUSoxFqQyr9qK83oNRE7b5Rukjq0Ku4QhUfDz1KAABg-KBkkG00D_pw8NVUzDrXI8-XjqT5h7b8yvdoHWfUihLyyyEqj3Bb6gQM4LCfVw/w640-h488/BDW93C%20-%20end-of-likfe.png" width="640" /></a></p><p>Above — Notice from Mouser. The day after I installed the power
Darlington complimentary finals, I got this notice by email.
Obsolescence might be the central story of my electronic hobbyist career
? Happily, I've got enough <i>genuine</i> power follower pairs -- both standard and Darlington style to last me for a long time.</p><p> <a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjRs-fKqLZoCZ7ScZsO9xQ9yfgSrdjTxIDqCcetGELLfR5uFKJJkj1g0d-oCqx3QaupuyWoKefbqhs61_-uBLUJFDnJLJ_S-fmp7XCBz1w944BeUUToaTRVdJ2fB28yNz95hl1nG0zblb2P6Yvt_xTTKFf954glOyblFB_kNVIqJlaXejooKjURIiB0Eg/s1018/hs1.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="485" data-original-width="1018" height="304" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjRs-fKqLZoCZ7ScZsO9xQ9yfgSrdjTxIDqCcetGELLfR5uFKJJkj1g0d-oCqx3QaupuyWoKefbqhs61_-uBLUJFDnJLJ_S-fmp7XCBz1w944BeUUToaTRVdJ2fB28yNz95hl1nG0zblb2P6Yvt_xTTKFf954glOyblFB_kNVIqJlaXejooKjURIiB0Eg/w640-h304/hs1.jpg" width="640" /></a></p><p>Above —The finals mounted in their heat sinks. Once again a hack saw helped fashion DYI heat sinks.</p><p> <a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhG5BTAumZsQB7xK81ec2kXGhGcXBYpA3dnDksDkR5Z6JfVHwaB1XZE3yJkG9Q1q_fsH_HOJdGngxhk3FHGeh1j6gePNuAyRpxsJGl1ThPsldS0Z4U5cQEY5HibnGjq0Y2Gpu0HBUfGrZUTr6q_-qFwf150YOVy8MSSH_G8mt9v12P4hn_it5_jLu1H8A/s937/decamp3.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="622" data-original-width="937" height="424" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhG5BTAumZsQB7xK81ec2kXGhGcXBYpA3dnDksDkR5Z6JfVHwaB1XZE3yJkG9Q1q_fsH_HOJdGngxhk3FHGeh1j6gePNuAyRpxsJGl1ThPsldS0Z4U5cQEY5HibnGjq0Y2Gpu0HBUfGrZUTr6q_-qFwf150YOVy8MSSH_G8mt9v12P4hn_it5_jLu1H8A/w640-h424/decamp3.jpg" width="640" /></a></p><p>Above — The finals and PA mounted in the "cake pan". The power
transformer sat unmounted in this photo. Suzu with it smaller chassis and will go upstairs in our living room to serve as my main practice amp. The
downstairs GAA -12 amp serves as my main transcription amplifier. I
spend time downstairs transcribing horn solos. I rarely
listen to guitarists other than if a guitar happened to be on the song of the
horn player whom I'm transcribing. <br /><br /><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi8fZ9HKdXruZQK1AcbYuIh_-Mbw0f_dpTEQiIgGBgerWLrXYSKgw0YSGfqKjU2x77xiC5sejCyhyaH6KybbwRLbBwHmiRSEr1GRX6WscxR4Ozp770fBOVucRQS-6jqZpD1hjk9NaNA6SrmXv3PgunX-FyU_hxiP6LGHBi6z_RJDZ7Xr5FRVpgP8i9g8w/s797/suzu.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="417" data-original-width="797" height="334" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi8fZ9HKdXruZQK1AcbYuIh_-Mbw0f_dpTEQiIgGBgerWLrXYSKgw0YSGfqKjU2x77xiC5sejCyhyaH6KybbwRLbBwHmiRSEr1GRX6WscxR4Ozp770fBOVucRQS-6jqZpD1hjk9NaNA6SrmXv3PgunX-FyU_hxiP6LGHBi6z_RJDZ7Xr5FRVpgP8i9g8w/w640-h334/suzu.png" width="640" /></a></p><p>Above — Suzu's PA offers low distortion. I'm very happy with this PA
stage. The matched input pair have obliterated the 2nd harmonic and I
believe what's left are crossover + some intermodulation products from
interactions with my outboard circuit, test leads, clips and probes. </p><h3 style="text-align: left;"> <b>5. Speaker</b></h3><p>I chose the Eminence Legend 1058 speaker for my upstairs practice amp.</p><p>Fortunately, many kind YouTube posters have uploaded head-to-head trials with various 10 inch guitar speakers for comparison. I tend to favour Alnico magnet 10 inch speakers, however, dislike their cost. My "non Alnico" preference seemed to the the Legend 1058 in several videos. So I bought one and found it well suited my purposes. — and the added bonus, it's not expensive.<br /></p><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjd8v8QvBaxPUeNbRmhOAFCNHxRNr3-wG7MlgIPQfJdbdn1pPWJU9r9raTUgNs0K5XOLViXQEg0JYZfPlmdIz6YIs8xXbQAQpTioVyonMad1DqQVGqg_JoYXpYJgN56SneblDB8P1StvSH_ZNaCi9p0ro_10JW31WSfR3q6lc2dcc2eqqeStdGi3Xul6A/s925/spk2.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="730" data-original-width="925" height="506" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjd8v8QvBaxPUeNbRmhOAFCNHxRNr3-wG7MlgIPQfJdbdn1pPWJU9r9raTUgNs0K5XOLViXQEg0JYZfPlmdIz6YIs8xXbQAQpTioVyonMad1DqQVGqg_JoYXpYJgN56SneblDB8P1StvSH_ZNaCi9p0ro_10JW31WSfR3q6lc2dcc2eqqeStdGi3Xul6A/w640-h506/spk2.jpg" width="640" /></a></div><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEijDgrFCHyOrMhv62y7lkWL5UYofc7rnmU18cHpqKzSNlu6wW_KZq7EunPbOlovV_2N9BYMuj0GRRtnfOzlQkv3iL8JZ-1NaYoVJ_3CUyb9ERzxsVGQ5fVG3KiSj31GC_cI-8qfsGneedNSLHztcG5NFfF0AXLcenFmVYmyOYZzBDMr3Xp7MN_aT6g-Sg/s933/spk3.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="648" data-original-width="933" height="444" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEijDgrFCHyOrMhv62y7lkWL5UYofc7rnmU18cHpqKzSNlu6wW_KZq7EunPbOlovV_2N9BYMuj0GRRtnfOzlQkv3iL8JZ-1NaYoVJ_3CUyb9ERzxsVGQ5fVG3KiSj31GC_cI-8qfsGneedNSLHztcG5NFfF0AXLcenFmVYmyOYZzBDMr3Xp7MN_aT6g-Sg/w640-h444/spk3.jpg" width="640" /></a></div><p>Above — The large dust cap makes the speaker look bigger than 10 inches in diameter. This speaker is a gem. Ferrite magnet and weighs 2 Kg.<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEikLy7NdfCt5VNTc3n89Esu80ExS4lpcs0ymKKJjpOFl9vz7KF85zdvQxsB_uCDpOEqi5IEWGpVhGBhhnWr1QkUWqKKip5OsckC567s4Vg7FGk0qeXQpAo-rUn-tPOu10kgXHZr__SLa5dZZbcRaxSyoUBCs87iqvqDx9WCAuaiXGQ_svCHL7bOuJ4jlQ/s781/Legend%20105b8.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="458" data-original-width="781" height="376" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEikLy7NdfCt5VNTc3n89Esu80ExS4lpcs0ymKKJjpOFl9vz7KF85zdvQxsB_uCDpOEqi5IEWGpVhGBhhnWr1QkUWqKKip5OsckC567s4Vg7FGk0qeXQpAo-rUn-tPOu10kgXHZr__SLa5dZZbcRaxSyoUBCs87iqvqDx9WCAuaiXGQ_svCHL7bOuJ4jlQ/w640-h376/Legend%20105b8.png" width="640" /></a></p>Above — Transfer function of the Legend 1058 from Eminence. It directly connects to what I hear with actual playing tests. In a cube shaped cabinet with my preamp circuit, the bass is OK while lower middle response sounds a little scooped. There is 1 "sharp" peak at ~2700 Hz, but the treble response starts to fall down a cliff at around 5 KHz. Perhaps a good fit for a Fender Telecaster ™ through a 10 inch speaker? I prefer scooped lower mids for rhythm, but stronger lower mids for lead playing. There is no 'ideal' speaker for me it seems. <br /><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh8CzDCVIGunquVGe0Wq3N8NwnrZRYVr6EgfqIe1EfbPsMcg1Qva72ZfV-l-ReaccRRMXndBC3VfPOso5oay2FnnYr7xD8DsZVfdxV_jcyMTMFGZOsCN9rHn9WUxVtRkBOFDt8GXi5DJ_e3suxejrOARupSDVTMj5UD1Os6nH69dm-v0g-h-0EpmBFwEQ/s1100/speakBox1.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="765" data-original-width="1100" height="446" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh8CzDCVIGunquVGe0Wq3N8NwnrZRYVr6EgfqIe1EfbPsMcg1Qva72ZfV-l-ReaccRRMXndBC3VfPOso5oay2FnnYr7xD8DsZVfdxV_jcyMTMFGZOsCN9rHn9WUxVtRkBOFDt8GXi5DJ_e3suxejrOARupSDVTMj5UD1Os6nH69dm-v0g-h-0EpmBFwEQ/w640-h446/speakBox1.jpg" width="640" /></a></div><p>Above — My wife designed & built a prototype cabinet from a plank of 12 inch wide, 3/4 inch thick pine. The final specs are 12 inches <i>depth</i> x 12 inches <i>height</i> x 14 inches <i>width</i> [ or 30.48 cm deep x 30.48 cm height X 35.56 cm width ]. I stuffed some fibreglass pink insulation in the cavity to dampen any reflecting waves. The back is partially open with a 2 inch gap across the top end. This keeps out cats (protects the speaker), keeps in the insulation and gives punchy bass tones with <i>some</i> room audio fill through he back of the speaker cabinet.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjcQXJS3TIMDISOqGNvwli2yNRVJVuVhvgT8f0s_57L0SWXF_8Yn6nP5T3CiaKTy9O08EfxExHd0rpkpAJFT4cIea0VlGctLJfXUFKEiFFZLjsccs8XzDlpCjJYKTtBA95OablQQ7fEWwhYQHZR4YN12ZhtPjN4eOuI91uyyRlaixcnfJ8CcyVSCbi3LA/s843/mod10-35.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="683" data-original-width="843" height="518" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjcQXJS3TIMDISOqGNvwli2yNRVJVuVhvgT8f0s_57L0SWXF_8Yn6nP5T3CiaKTy9O08EfxExHd0rpkpAJFT4cIea0VlGctLJfXUFKEiFFZLjsccs8XzDlpCjJYKTtBA95OablQQ7fEWwhYQHZR4YN12ZhtPjN4eOuI91uyyRlaixcnfJ8CcyVSCbi3LA/w640-h518/mod10-35.jpg" width="640" /></a></div><p>Above — I've got a Jensen Mod 10-35 in another identical cabinet at the moment. I like the strong mids for neck pickup solos better when compared to the 1058, however, it sound quite bright. It's best to listen to a speaker for many months before you write in in or off.</p><h3 style="text-align: left;">6. Miscellaneous Photos<br /></h3><p></p><p></p><h3 style="text-align: left;"></h3><p></p><p></p><p></p><p></p><p></p><p></p><p> <a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEji0H1AKIvwoz5NuAbPhF8gz0_hK65eIrNEky_2rquADWODbKVDp1nHHHTPPvW4RO5G6_n33lwxALv6CxSYjM3MDlFulPy1seWxoemGQXeYhqw1rsztxr5SvOAb7_rHxDM8WCGSIqGrGpX9Y7J2tlSv1fEySZX9Kuz607LRRrGQng4sTbIZ_hKDWxtxAg/s891/spkr1eef1.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="597" data-original-width="891" height="428" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEji0H1AKIvwoz5NuAbPhF8gz0_hK65eIrNEky_2rquADWODbKVDp1nHHHTPPvW4RO5G6_n33lwxALv6CxSYjM3MDlFulPy1seWxoemGQXeYhqw1rsztxr5SvOAb7_rHxDM8WCGSIqGrGpX9Y7J2tlSv1fEySZX9Kuz607LRRrGQng4sTbIZ_hKDWxtxAg/w640-h428/spkr1eef1.jpg" width="640" /></a></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhOd5gDy56UNBl8dKAD9hoYAEb4kf9BngB1uOXAODMXb3Qkmpps-jm-f8hM2-m8jYYuDiyk4AYj0YF_zJesHcIa-HH0wZjPK2jBmI7jgU8NKxFX-oRuvNePPfemf9YWuieGg7wQzBvUMXst62T6PN6JuVJq3UFRh7XJC1sVmRSwpBYdbwuAUMrHwF-u2A/s913/barseee1.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="674" data-original-width="913" height="472" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhOd5gDy56UNBl8dKAD9hoYAEb4kf9BngB1uOXAODMXb3Qkmpps-jm-f8hM2-m8jYYuDiyk4AYj0YF_zJesHcIa-HH0wZjPK2jBmI7jgU8NKxFX-oRuvNePPfemf9YWuieGg7wQzBvUMXst62T6PN6JuVJq3UFRh7XJC1sVmRSwpBYdbwuAUMrHwF-u2A/w640-h472/barseee1.jpg" width="640" /></a></div><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgvNvTOBuvQBZ7OBcMuL-SsIrandbugi7uiMuoGK8f3q-p7d0YwKV_LUeRT3gLsqeLDDyhZksa8XXkZIx9Kwl0uxhdedwmgCmCIQnk80M81pd3Sj6dLeN8l3OVjidHdWG0W_kK-hhbp-r1X-0z6W6kK80acLEH9bKqt1nOBltgWLVJkK4ryP93IwNNsLg/s901/bars33s.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="611" data-original-width="901" height="434" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgvNvTOBuvQBZ7OBcMuL-SsIrandbugi7uiMuoGK8f3q-p7d0YwKV_LUeRT3gLsqeLDDyhZksa8XXkZIx9Kwl0uxhdedwmgCmCIQnk80M81pd3Sj6dLeN8l3OVjidHdWG0W_kK-hhbp-r1X-0z6W6kK80acLEH9bKqt1nOBltgWLVJkK4ryP93IwNNsLg/w640-h434/bars33s.jpg" width="640" /></a></div><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhexJkvpNb8gu0I-yHScLm_zJtTnZYkITA_-gya3VRvOLG4o0324eSgGpEAAvaGAYrs6R8VHKm2qgsjGPK_vb2U9NXbLoFp4HFPvJXo37M2Ouhb7pwK-NZiGsDlNAbGayEYAjp5O-E3OMyryMCuEIFrZ_h_FvUg1IdN418cxhkbyxfFN4yvnZfSeNgCBg/s629/kot4.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="629" data-original-width="519" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhexJkvpNb8gu0I-yHScLm_zJtTnZYkITA_-gya3VRvOLG4o0324eSgGpEAAvaGAYrs6R8VHKm2qgsjGPK_vb2U9NXbLoFp4HFPvJXo37M2Ouhb7pwK-NZiGsDlNAbGayEYAjp5O-E3OMyryMCuEIFrZ_h_FvUg1IdN418cxhkbyxfFN4yvnZfSeNgCBg/w528-h640/kot4.jpg" width="528" /></a></div><div class="separator" style="clear: both; text-align: center;"></div><p></p><p>Best regards! <a href="https://qrp-popcorn.blogspot.com/p/guitar-related-index.html" target="_blank">Click here</a> for my <b>Guitar-Related Index</b></p><p><b></b></p><div class="separator" style="clear: both; text-align: center;"><b><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiH4FJvfscRVvEVuXYDyLrmhphHHOx2vbYYDYR2CkthJb7_bvzwaKe0UUuTHFT6-7_DmZOmXXnILarVMUTF6DgewzRz6Hck226w4P0BYUifjdr24FTMsdbqZpda85RVbCRwvWG8sHIiV6f06buwmW0mL7OEAFHxGGk05_eWiGVU1jyhaSjfm5pfZ81cuA/s879/Feb%2012%20preamp%20C.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="614" data-original-width="879" height="448" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiH4FJvfscRVvEVuXYDyLrmhphHHOx2vbYYDYR2CkthJb7_bvzwaKe0UUuTHFT6-7_DmZOmXXnILarVMUTF6DgewzRz6Hck226w4P0BYUifjdr24FTMsdbqZpda85RVbCRwvWG8sHIiV6f06buwmW0mL7OEAFHxGGk05_eWiGVU1jyhaSjfm5pfZ81cuA/w640-h448/Feb%2012%20preamp%20C.png" width="640" /></a></b></div><p></p><div style="text-align: left;">Above — 1 of the Preamp 2 designs I explored, but later discarded.<b><br /></b></div><p><b> </b><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhmk6Yypad8wHkcRzgMMWd0aYX8542a5ErFKCHSFaAqj3Bimq604qyfktOGRhKOznWH7DvqcLAcYgcsgL3LkZmBfIu7fDejeEJctg7hJ9I4KhnsSnFJe3A8s_JDhiCdvdBclClNKzaNjVuE93b5KuYHwWavhQm7xb1wbbAWSP9AwBsL2Gv6O6UmAcmL8Q/s1080/ss5.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="645" data-original-width="1080" height="382" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhmk6Yypad8wHkcRzgMMWd0aYX8542a5ErFKCHSFaAqj3Bimq604qyfktOGRhKOznWH7DvqcLAcYgcsgL3LkZmBfIu7fDejeEJctg7hJ9I4KhnsSnFJe3A8s_JDhiCdvdBclClNKzaNjVuE93b5KuYHwWavhQm7xb1wbbAWSP9AwBsL2Gv6O6UmAcmL8Q/w640-h382/ss5.jpg" width="640" /></a></p>Vasily Ivanenkohttp://www.blogger.com/profile/17387516134063150119noreply@blogger.com1tag:blogger.com,1999:blog-3480228403403435266.post-5063795729604231162022-11-22T18:34:00.011-08:002022-11-23T18:17:41.467-08:00Another Look at the LM386<p>On a whim, I took another look at the LM386-4 one cold Sunday afternoon this November. My focus was to drive a loud speaker and not headphones. I won’t personally use the LM386 for a headphone amp as we enjoy so many better options. For example, an op-amp driving a pair of TO-92 followers, or perhaps placing 2 NE5532 op amps in parallel as the headphone PA stage.<br /><br />Since the mid 1970’s the LM386 has enjoyed popularity amongst hobbyists for low to flea power AF power amplification. The NE612 mixer IC plus the LM386 have literally formed the basic building blocks of innumerable radio receivers amongst Hams and hobbyists for decades.<br /><br />Although, imperfect like all other linear ICs, the LM386 design team delivered a simple, flexible, low power AF amp with reasonably low distortion.<br /> <br />This part is noisy though. The input noise density = ~ 50 nV/√(Hz) — about 10X that of an NE5532 op amp. So. if you use this part in high gain mode [with a gain of 100 to 200] and drive it with a low-level audio signal, you’ll really hear the noise (hiss) in your speaker.<br /><br />Others online have provided detailed analysis about each stage of the LM386, so I won’t bother. However, I will comment about why it might be noisy. Normally, in modern AF power amps. the differential input pair emitters get 50 - 100 ohms of degeneration to boost linearity at the expense of noise. Other than that, in the IC only current sources connect to the emitters (and usually active loads to the collectors -- i.e. no resistors), However, the LM386 input pair get multiple large value resistors connected to their emitters. This translates into lots of Johnson noise from thermal agitation within conductors, plus related high-level input current noise that all gets amplified by the NPN voltage amp and delivered to the output stage.</p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh_zcFTvQ9LMqNOMWpZsoTQLM0x_DY6rthrM8PIztNLJI_oHTPQdwY1M0cqOkFK1BZBcmqH2TZK2FjnwegJXqt1S0SFdN03fHpmDpuNOGHikl578e2HsdfmHmtjiftP3ln7nMab-3iz6qH_SCHfQcql4EYPr07iDwp8WlkFwDlOUaw8zvLNFgJt4gXg5w/s711/lm3data.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="421" data-original-width="711" height="378" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh_zcFTvQ9LMqNOMWpZsoTQLM0x_DY6rthrM8PIztNLJI_oHTPQdwY1M0cqOkFK1BZBcmqH2TZK2FjnwegJXqt1S0SFdN03fHpmDpuNOGHikl578e2HsdfmHmtjiftP3ln7nMab-3iz6qH_SCHfQcql4EYPr07iDwp8WlkFwDlOUaw8zvLNFgJt4gXg5w/w640-h378/lm3data.png" width="640" /></a><br /></div><div class="separator" style="clear: both; text-align: left;">Above — My basic test setup superimposed on the internal schematic of the LM386. I RC low-pass filtered the 12.24 VDC and ran two 1 Watt resistors in parallel as my resistive load. The measured load resistance for my power calculations = 8.4 ohms. I AC coupled a 1 KHz, ultra low distortion signal generator with a gain control to the input and watched the output in a DSO containing a stalwart FFT with 12-bit sampling. </div><div class="separator" style="clear: both; text-align: left;"><br /></div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh6VZS2lnVFX-7U_aVs0uoN4LpHMcKXo5BkT5ioOmWsYcpzaJnZBNREE0XemhtxsDeI_rISt1c9AgWBdnV7b4o36D7g_7sWT4WkiI59zHMOnAV4vrONZDgE6ZmN8-2xBjXnc4V3Z7eZ7ZzvvXAqPwWt5w6K084-gT-9NIYppKTOMJ9dAoHWxPZxYYkBNw/s1066/lm386-11.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="609" data-original-width="1066" height="366" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh6VZS2lnVFX-7U_aVs0uoN4LpHMcKXo5BkT5ioOmWsYcpzaJnZBNREE0XemhtxsDeI_rISt1c9AgWBdnV7b4o36D7g_7sWT4WkiI59zHMOnAV4vrONZDgE6ZmN8-2xBjXnc4V3Z7eZ7ZzvvXAqPwWt5w6K084-gT-9NIYppKTOMJ9dAoHWxPZxYYkBNw/w640-h366/lm386-11.jpg" width="640" /></a></div><br />Above — An early photo during my initial bread boarding for these experiments. The non-inverting input resistor was changed to 10K for my experiments.<br /><p></p><h3 style="text-align: left;">Index of this blog post</h3><p>1. Gain = 20 Mode<br />2. Bass Boost and More<br />3. Gain = 50 Mode<br />4. Gain = 200 Mode -- plus lifting and AC bypassing Pin 2</p><p>I'm avoiding math in 2022, as data shows that my blog readers don't care for it. <br /></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjy3mpCYMP4mwewM1ueacDfmZMoYYS9tKRi3ypmsHzK_ABCoq31-bApYxs-pk8Ul56pQxPPKBk9DOcT8pcDVQ-GySUvuaLaeW6FfBihiGs1ggbUv-zc_doB7mm1teQYCAduhCBk28GDNZvewTx9P0FNr3xMMsPe4ki_fwIvdURHP_WcW3m5bExgmMLboA/s1124/b2.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="688" data-original-width="1124" height="392" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjy3mpCYMP4mwewM1ueacDfmZMoYYS9tKRi3ypmsHzK_ABCoq31-bApYxs-pk8Ul56pQxPPKBk9DOcT8pcDVQ-GySUvuaLaeW6FfBihiGs1ggbUv-zc_doB7mm1teQYCAduhCBk28GDNZvewTx9P0FNr3xMMsPe4ki_fwIvdURHP_WcW3m5bExgmMLboA/w640-h392/b2.jpg" width="640" /></a></div><p></p><div style="text-align: left;">Above —For comparison and contrast, here is the FFT of a discrete guitar PA pushing 3.4 Watts in this photo. The 2nd harmonic lies ~ 64 dB down.<br /><br /></div><h3 style="text-align: left;">1. Gain = 20 Mode<br /><br /></h3><div class="separator" style="clear: both; text-align: left;"><h3 style="text-align: left;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhLg8hd5STKU7M-FeFgLFPQW7xWIkxEvOoLw2j7CVOLKWAiNCzeriHDPU1byRdruyTE-RIK7qCEpzwO5VACJssqNMTNN2YO65B4kMhsEi8cLIiZaoihdUr6q9nVap4dCIa1O-MpuQmBXzj85kcL1Uu7noS_fyXBpkfkOBW65nz75s03FRy1uX8A_w7wng/s397/gain%20=%2020b.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="271" data-original-width="397" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhLg8hd5STKU7M-FeFgLFPQW7xWIkxEvOoLw2j7CVOLKWAiNCzeriHDPU1byRdruyTE-RIK7qCEpzwO5VACJssqNMTNN2YO65B4kMhsEi8cLIiZaoihdUr6q9nVap4dCIa1O-MpuQmBXzj85kcL1Uu7noS_fyXBpkfkOBW65nz75s03FRy1uX8A_w7wng/s16000/gain%20=%2020b.png" /></a></h3><div style="text-align: left;">Above — The data sheet suggested amplifier with Gain = 20, using minimal parts. </div><div style="text-align: left;"><br /></div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjrsUkgaNl_jU-pZQNA6-MxS76RgIECWRIjwaaVznRZ6MPoRR4T2yo3-CdJ8vOv8VH6Bba90LSDw8tulea2UkQYDUZRkc1imsxQg41iTnQOdubWpm5VpoyF31OMrIDv08Ms5wKDoIhLSDYTo5wGmGjR_glxs27pZT4Up2AiU7guhQSBvL_ZYO0pGAd1Zw/s798/20%20MODE-no%20pin%207%20bypass.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="411" data-original-width="798" height="330" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjrsUkgaNl_jU-pZQNA6-MxS76RgIECWRIjwaaVznRZ6MPoRR4T2yo3-CdJ8vOv8VH6Bba90LSDw8tulea2UkQYDUZRkc1imsxQg41iTnQOdubWpm5VpoyF31OMrIDv08Ms5wKDoIhLSDYTo5wGmGjR_glxs27pZT4Up2AiU7guhQSBvL_ZYO0pGAd1Zw/w640-h330/20%20MODE-no%20pin%207%20bypass.png" width="640" /></a></div><br /><div style="text-align: left;">Above — The FFT of the above schematic with the fundamental plus 4 harmonic tones showing. I'll show many traces with a "standardized" output voltage of 5 Vpp or 372 mW into my 8.4 Ω load. This allows comparisons of various circuits. Note the 2nd harmonic is only 46 dB down [ -46 dBc ].<br /><br /></div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjVY4A1jZCpvhcS9QwH0e_syIfnxnrIczPIHxTclbvWg9bTQjbCxNBzJ3EUKUa96b4YESu3KNdsZgmPy7nkWnB-vGV9fM5OdgILolqTXdccnyxEyNvWEH8UigI9dc1gwj_W9B4B2NpG8FTyyk5qYKY_R9zeZFu-nQnmjWuLxYs1D7nsrJMin_Ept3t41g/s795/20MODE-Add%20Pin%207%20bypass.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="423" data-original-width="795" height="340" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjVY4A1jZCpvhcS9QwH0e_syIfnxnrIczPIHxTclbvWg9bTQjbCxNBzJ3EUKUa96b4YESu3KNdsZgmPy7nkWnB-vGV9fM5OdgILolqTXdccnyxEyNvWEH8UigI9dc1gwj_W9B4B2NpG8FTyyk5qYKY_R9zeZFu-nQnmjWuLxYs1D7nsrJMin_Ept3t41g/w640-h340/20MODE-Add%20Pin%207%20bypass.png" width="640" /></a></div><br /><div style="text-align: left;">Above —FFT with only 1 change -- I bypassed pin 7 with a 10 µF capacitor. The 2nd harmonic decreased by ~ 9 dB. Always bypass Pin 7.</div><div style="text-align: left;"> </div><div style="text-align: left;"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh-JLhnBh8wOWcyqyrFxzgXvSWhsDhZOc_ExahvO7D7q7NjgDezE_pJ50Svgakg2KL06B9keYiZeI6T6lxB6tfTzijY1kilnumdBdAc2vSehkM9s8Jd3DJKg4YqCZ1mJLDXAUPG3dDn6pj1vP53O2lmojIY05qUI51OFse3sV-xcpGfO7Ma_zfw9RKxCA/s800/20%20MODE-really%20low%20level.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="418" data-original-width="800" height="334" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh-JLhnBh8wOWcyqyrFxzgXvSWhsDhZOc_ExahvO7D7q7NjgDezE_pJ50Svgakg2KL06B9keYiZeI6T6lxB6tfTzijY1kilnumdBdAc2vSehkM9s8Jd3DJKg4YqCZ1mJLDXAUPG3dDn6pj1vP53O2lmojIY05qUI51OFse3sV-xcpGfO7Ma_zfw9RKxCA/w640-h334/20%20MODE-really%20low%20level.png" width="640" /></a></div> </div><div style="text-align: left;">Above — Apart from the 2nd harmonic, this FFT shows very low distortion at low signal levels (20 mW) The clever 1/2 positive DC supply biasing scheme within the LM386 isn't perfect and the input pair are not perfectly balanced due to both variable AC and DC factors and this effects 2nd harmonic suppression. We also see some crossover distortion in the output. Don't get me wrong — I feel amazed by this design. Like you, I kind of like the humble LM386; plus have used it a lot over time.</div><div style="text-align: left;"> </div><div style="text-align: left;"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi1LFb2Ga6P0YA48c6WauBdsG5RMswSrp9uwhTPZWYlO4izNWGWephQcJrmBjJXqY1jZZ3gpXcvswvknyCBhWCfii3TblRh1hoPqk2rtBk_TxBc6hl_cXOFsHlVi4OnZFD6IBJk60LTyt9gUMSgBEDmLy9-RcDdJUj8QSdJ3qOgJXJZP6lvQqQ5qe3cug/s797/MODE%2020-sine.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="426" data-original-width="797" height="342" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi1LFb2Ga6P0YA48c6WauBdsG5RMswSrp9uwhTPZWYlO4izNWGWephQcJrmBjJXqY1jZZ3gpXcvswvknyCBhWCfii3TblRh1hoPqk2rtBk_TxBc6hl_cXOFsHlVi4OnZFD6IBJk60LTyt9gUMSgBEDmLy9-RcDdJUj8QSdJ3qOgJXJZP6lvQqQ5qe3cug/w640-h342/MODE%2020-sine.png" width="640" /></a></div><br />Above — This is the cleanest sine wave I can drive before clipping using my eyeball. This is 725 mW output power.</div><div style="text-align: left;"></div><div style="text-align: left;"><br /></div></div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjf_HxEVfk1V9-nJK8DY2AD7xTHQZ7lJdLyr4bCWos7AETqMaTbRehwhE0eQnTvZ9KKlcMORfj4tR9UDQxHjEzSqvMrRhOrJjKy2ms5ldB1jLt5Hlit4SOydntUvhGudrGcCyB7AOuKeKfK8IQNxesqG7OXnXhssmVikLQEz97tfy1MaSjXzvjJYMbewg/s800/MODE20-top%20clipper.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="414" data-original-width="800" height="332" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjf_HxEVfk1V9-nJK8DY2AD7xTHQZ7lJdLyr4bCWos7AETqMaTbRehwhE0eQnTvZ9KKlcMORfj4tR9UDQxHjEzSqvMrRhOrJjKy2ms5ldB1jLt5Hlit4SOydntUvhGudrGcCyB7AOuKeKfK8IQNxesqG7OXnXhssmVikLQEz97tfy1MaSjXzvjJYMbewg/w640-h332/MODE20-top%20clipper.png" width="640" /></a></div><p>Above — I kept advancing the gain knob until clipping appeared on the top half.</p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhkpZNm5j7zrAcLi0cwu7b9ljBwTix5Miju_pOEa5IItit04VN7e7pYq8Ym2WpdWRQtJFPh-7HpAj06moUFNQ49-KcCL00SETewEIibzxtl8t7aLIf2-hBRD0FVWs_EaKwFmBHLI_m_RC2Yf9maGb6Cwbd_QukgHAkWdte987SeLsytrX9PggrwGQ_Ipw/s796/MODE20-FFT%20of%20clip.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="417" data-original-width="796" height="336" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhkpZNm5j7zrAcLi0cwu7b9ljBwTix5Miju_pOEa5IItit04VN7e7pYq8Ym2WpdWRQtJFPh-7HpAj06moUFNQ49-KcCL00SETewEIibzxtl8t7aLIf2-hBRD0FVWs_EaKwFmBHLI_m_RC2Yf9maGb6Cwbd_QukgHAkWdte987SeLsytrX9PggrwGQ_Ipw/w640-h336/MODE20-FFT%20of%20clip.png" width="640" /></a></div><p>Above — Switch to FFT mode, although you can still see the yellow coloured sine wave. At this point, the tones are almost level and 45 - 47 dB down. You may easily hear distortion at this level.</p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiqNJ9EzgnHFpdvOTHQxNg4-kv5_GUs8IVC_CwC-S7S-OC0NIeGLmY8XAg1nheUTAUGK5-0gNePh26k25dwSmuV3-f-Ghj4AbNCvZjcURQSRw8Zore_KnNSQZxCDm2snm2_FuCDBGaq5yKwQk28yqb3-GAqd8pvgIly5FQtw_Q3RXXfpQ3FIONfmUP68Q/s798/MODE20-hard%20clipping.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="426" data-original-width="798" height="342" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiqNJ9EzgnHFpdvOTHQxNg4-kv5_GUs8IVC_CwC-S7S-OC0NIeGLmY8XAg1nheUTAUGK5-0gNePh26k25dwSmuV3-f-Ghj4AbNCvZjcURQSRw8Zore_KnNSQZxCDm2snm2_FuCDBGaq5yKwQk28yqb3-GAqd8pvgIly5FQtw_Q3RXXfpQ3FIONfmUP68Q/w640-h342/MODE20-hard%20clipping.png" width="640" /></a></div><br />Above — I kept advancing the signal generator gain knob until the tones look really strong. You can see the sine wave is now both bottom and top clipped. These FFT screen shots and my notes serve as the basis of what follows. I learned a lot doing these experiments and hope you like them.<p></p><h3 style="text-align: left;">2. Bass Boost and More <br /><br /></h3><div style="text-align: left;"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg19ndexCKq0YTigmWs9au8CBdQItGB90yAUO4I-xlLOgsi-18iNeAIRWZGqwnpSmvIYK9YgdXzebgJNmYrX3M6NndkVAS8IPzr1hUjkQ7neuurwoDHvZjTqtOPYfwWGiMRxrptNUnLwJ6Ab1KNZ9Afs94dJXex2HKQHQm5NYWynIZmuxyBTq57P5nScA/s405/bass-boost-shematic.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="258" data-original-width="405" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg19ndexCKq0YTigmWs9au8CBdQItGB90yAUO4I-xlLOgsi-18iNeAIRWZGqwnpSmvIYK9YgdXzebgJNmYrX3M6NndkVAS8IPzr1hUjkQ7neuurwoDHvZjTqtOPYfwWGiMRxrptNUnLwJ6Ab1KNZ9Afs94dJXex2HKQHQm5NYWynIZmuxyBTq57P5nScA/s16000/bass-boost-shematic.png" /></a></div> Above — The data sheet suggested schematic for Amplifier with Bass Boost.<br /></div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg4RTwYr2-eSK815-EExwGvyVhMKpdWKlR0exm7I-4hupK1QttrgcMyYYUYKVujradboI5qEF_W6nhCVSstm8_clkHS0msnq_Zg0HARrUVAmJrt62XpF2F82R7qx28zSfD__SkNAVZ0INdh0NQblflhzjEaBkH9NMOi5wFtE6b-59NmYEIK1fv7qXyvNw/s406/bass-boost-graph.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="398" data-original-width="406" height="392" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg4RTwYr2-eSK815-EExwGvyVhMKpdWKlR0exm7I-4hupK1QttrgcMyYYUYKVujradboI5qEF_W6nhCVSstm8_clkHS0msnq_Zg0HARrUVAmJrt62XpF2F82R7qx28zSfD__SkNAVZ0INdh0NQblflhzjEaBkH9NMOi5wFtE6b-59NmYEIK1fv7qXyvNw/w400-h392/bass-boost-graph.png" width="400" /></a></div><div style="text-align: left;">Above — Voltage gain versus frequency graph showing the 6 dB peak at ~ 90 Hertz. In the LM386, both AC and DC feedback runs back from the output to the non-inverting input emitter. Pins 1 and 5 allow us nodes on either side of this 15K resistor so we may provide additional AC feedback in parallel with it. The bass boost example provides us insight into possible feedback strategies: a 10K resistor + 33 nF cap form a network to boost the bass and also low-pass filters the frequencies out to ~ 5 kilohertz. <br /></div><p>If you listen to this amplifier with music through a speaker, it sounds muffled and somewhat lacks the important mid frequencies for both voice and music. The hiss is definitely attenuated though. Further, the voltage gain goes from 20 without feedback down to around 8 with the 10K + .033 µF network added. There are other potential side effects to with such heavy feedback which I'll show soon.<br /></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjKK2yyWgzCJg6zt8Hqwkr1_ptKqxc7Rm_zry9cgAaLDPlUq23kmeheM9T8KRYetIGSkUZDktJddzNYRvLDwUwwDhg3qcjgelfm9wACvYt2CwHyvupnbZRFW-oNGH7_8ElqV74faOyxLyVsEL1XCJe4D69JVTNu0HHqRSPyeTm_p5YDVYRrOOYbOLSdQQ/s797/Bassboost-at%205vpp.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="418" data-original-width="797" height="336" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjKK2yyWgzCJg6zt8Hqwkr1_ptKqxc7Rm_zry9cgAaLDPlUq23kmeheM9T8KRYetIGSkUZDktJddzNYRvLDwUwwDhg3qcjgelfm9wACvYt2CwHyvupnbZRFW-oNGH7_8ElqV74faOyxLyVsEL1XCJe4D69JVTNu0HHqRSPyeTm_p5YDVYRrOOYbOLSdQQ/w640-h336/Bassboost-at%205vpp.png" width="640" /></a></div><br />Above — FFT with fundamental + 8 tones of the bass boost circuit driven to output 5 Vpp. The feedback has suppressed the 2nd plus all other harmonics effectively. Feedback certainly holds promise in reducing harmonic distortion in the LM386.<br /><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjHTTC6mlSu_mXhzC3PA-w622PPylJo8w2ILveElUAUfTZsnD2wJSo5LpW9BKvHkAxBoXNFdUnn9OCv7CKQ5-MMAkHJf3cbynUXRKhVDPfXjBaGG3buxfy0Pmj0dTXo_zGrhHA-5tj041KmDDA2numdfHMLxxmvBDgiuAulEdFm-PTrFMMsEFAXS3Nd8g/s797/BASSbOOST-sine%20clipweird.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="419" data-original-width="797" height="336" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjHTTC6mlSu_mXhzC3PA-w622PPylJo8w2ILveElUAUfTZsnD2wJSo5LpW9BKvHkAxBoXNFdUnn9OCv7CKQ5-MMAkHJf3cbynUXRKhVDPfXjBaGG3buxfy0Pmj0dTXo_zGrhHA-5tj041KmDDA2numdfHMLxxmvBDgiuAulEdFm-PTrFMMsEFAXS3Nd8g/w640-h336/BASSbOOST-sine%20clipweird.png" width="640" /></a></div><p>Above — The bass boost circuit<i> may</i> produce weird distortion when driven hard in some circuits. The bottom half of the sine wave clips initially.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEheBvm4A740zYY_cZfnojooyeiRIX8E1NEiuTqGyCVGUQXosTasDWaxBqmYqzB1shm17Qgbg-kPzpJ5HeTfq6xSOE-IiWIx2VeCxWSWLq898rCnBINY7l4buxMhiPrqaU1sS6t0EeZu3Bv6XKajRSDxvl21E-Hku2gP7YlpCa77pJaseJ1Oy6Nauxzvhw/s795/BASSBOOST-weird%20clippingFFT.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="422" data-original-width="795" height="340" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEheBvm4A740zYY_cZfnojooyeiRIX8E1NEiuTqGyCVGUQXosTasDWaxBqmYqzB1shm17Qgbg-kPzpJ5HeTfq6xSOE-IiWIx2VeCxWSWLq898rCnBINY7l4buxMhiPrqaU1sS6t0EeZu3Bv6XKajRSDxvl21E-Hku2gP7YlpCa77pJaseJ1Oy6Nauxzvhw/w640-h340/BASSBOOST-weird%20clippingFFT.png" width="640" /></a></div><br />Above — The FFT of the above DSO tracing when pushed a little harder. This looks and sounds terrible.I do not recommend people use the bass boost circuit, or if you do, please check for instability. <br /><p>Let's adjust the feedback network and perhaps find something that works better. <br /></p><p>In a classic PA with a differential transconductance input pair, 1 BJT base serves as the input stage while the other base receives the negative voltage feedback. The transconductance pair subtracts that negative feedback from the input and passes the difference voltage onto the voltage amplifier stage that follows. This doesn't happen in the LM386 -- negative feedback goes to the non-inverting BJT emitter which is often also the input side of the input emitter coupled pair. <br /><br />Negative feedback also affects an amps gain, bandwidth, frequency response, plus its input and output impedance (although the output impedance is just fractions of an ohm). When we add AC feedback between pins 1 and 5, our network is in parallel with the 15K resistor and may be affected by other amplifier parameters including the gain and input impedance.</p><p>From the data sheet, In low gain mode, we should strive to keep the amplifier's closed loop gain 10 or greater which happens with the 10K resistor in our R C network. It's quite easy to turn your LM386 into an oscillator with too much feedback. I've noticed that feedback networks that look OK in SPICE simulations may actually oscillate in real life bench work -- especially with higher gain and/or drive.</p><p></p><p>I took the bass boost circuit example, kept the 10K resistor, and tried different capacitor values. If you lower the 10K resistor, you'll have to watch for oscillations at input drive levels high enough to cause distortion. This also may also reduce the LM386 voltage gain considerably.<br /></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhfZbOvzRMH8l5qkB0GamH5SgqyI38eDmb5NuAAcpJhnkEcDPdj-h3w5ocGsCCG7danyd3vCB7uhm_k-ZTsaFxy9fcHaMym9xIW7Ra7NAruiWOada8dmvm4dYxHdF-0P1iN2i9ABRqR3KOrj90y_nyH-iVwH1IfWenevRJaCQ9yWTkGxXwParcJf9WV7A/s397/gain%20=%20FB.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="271" data-original-width="397" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhfZbOvzRMH8l5qkB0GamH5SgqyI38eDmb5NuAAcpJhnkEcDPdj-h3w5ocGsCCG7danyd3vCB7uhm_k-ZTsaFxy9fcHaMym9xIW7Ra7NAruiWOada8dmvm4dYxHdF-0P1iN2i9ABRqR3KOrj90y_nyH-iVwH1IfWenevRJaCQ9yWTkGxXwParcJf9WV7A/s16000/gain%20=%20FB.png" /></a></div><p>Above — Our base schematic to evaluate different values of C1 and view the resultant FFT and voltage gain.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj0_0O2p0zHkL0V478J4EZOvHECm8uSiVtSky15xluNuWAPZRW6vJkjkWhHOOFUQsEe-USjHrY7DDr6wS-Vjtkg7s-0IbwkN0wgkYn6t5yvWRTnOyoCJ8QhOzAFfeJugcvUiNIEgT7_Zy6wTTz5lxhZiMhyda1-evg7FDkUC4QRGgKC9bdMByZhK-glZw/s795/Oh1-5vpp.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="410" data-original-width="795" height="330" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj0_0O2p0zHkL0V478J4EZOvHECm8uSiVtSky15xluNuWAPZRW6vJkjkWhHOOFUQsEe-USjHrY7DDr6wS-Vjtkg7s-0IbwkN0wgkYn6t5yvWRTnOyoCJ8QhOzAFfeJugcvUiNIEgT7_Zy6wTTz5lxhZiMhyda1-evg7FDkUC4QRGgKC9bdMByZhK-glZw/w640-h330/Oh1-5vpp.png" width="640" /></a></div><p>Above — FFT at 5 Vpp where C1 = 0.01µF. Outstanding results! This turned out to be the best feedback capacitor of the few I tried. The LM386 voltage gain dropped to just under 11 with that particular capacitor value for C1.<br /></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjpsTgdorrm8POolDYx9OUn-Li7ydvmvuGY24RCCbd9oN0kWwe82Vxc8Xz_XmfTIZFiOrOatncpBtSI4BHGR6QjPf2W3O6ckknef2W3jljIBKXeueb6Ls4p9_q3t3aBU_wL0ffiLBpr9UjGDPnO1eFGTMMqYnbVtuCcBLoveQ3XDEG0Sf7Z0zww2AQdTw/s798/OH1-6.47.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="406" data-original-width="798" height="326" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjpsTgdorrm8POolDYx9OUn-Li7ydvmvuGY24RCCbd9oN0kWwe82Vxc8Xz_XmfTIZFiOrOatncpBtSI4BHGR6QjPf2W3O6ckknef2W3jljIBKXeueb6Ls4p9_q3t3aBU_wL0ffiLBpr9UjGDPnO1eFGTMMqYnbVtuCcBLoveQ3XDEG0Sf7Z0zww2AQdTw/w640-h326/OH1-6.47.png" width="640" /></a></div><p></p><p>Above — Driving it as little harder to give 623 mW output power. Still fairly clean compared to other tracings.<br /></p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEie5jhmPDBCr0OJnk2FeE33JqYb3ZRayeGtzx4eyMR430H7UyLbhAPVVFv6Qta8hEvsC6ijHg4cY2ecPOzE_6r8NU86h_2X0ABdwi0SxwAVxstIkoLYboDBslrvxLakDJEHDjXv5xrdNxQDDiWvjCTRm4_xRGqppbQd_MWOtxKYlL_nptDu7uoEhGEewg/s797/OH1-7.03vpp.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="411" data-original-width="797" height="330" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEie5jhmPDBCr0OJnk2FeE33JqYb3ZRayeGtzx4eyMR430H7UyLbhAPVVFv6Qta8hEvsC6ijHg4cY2ecPOzE_6r8NU86h_2X0ABdwi0SxwAVxstIkoLYboDBslrvxLakDJEHDjXv5xrdNxQDDiWvjCTRm4_xRGqppbQd_MWOtxKYlL_nptDu7uoEhGEewg/w640-h330/OH1-7.03vpp.png" width="640" /></a></div><br />Above — FFT with the top just starting to clip. 3rd harmonic re-emerging. 735 mW output power.<br /><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgdlntrVLvx_gZh9gnpLuz9KtkCn_b5SszNeUCL2rv-Jlcg9K9q749P34PWQSIGFxeAVBDhpgLriT2CcN8_nt2XC9aj0Goe_l-7Gyrs-rqC9nxbxd_vdHm0DeJbZQY1qNPZu-sHYQ5nPWZwXvlJqNOjIp-gXR6SXOTJChQ6fxv7mjMNzREsMBnym--jIQ/s800/OH1-7.15vpp.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="409" data-original-width="800" height="328" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgdlntrVLvx_gZh9gnpLuz9KtkCn_b5SszNeUCL2rv-Jlcg9K9q749P34PWQSIGFxeAVBDhpgLriT2CcN8_nt2XC9aj0Goe_l-7Gyrs-rqC9nxbxd_vdHm0DeJbZQY1qNPZu-sHYQ5nPWZwXvlJqNOjIp-gXR6SXOTJChQ6fxv7mjMNzREsMBnym--jIQ/w640-h328/OH1-7.15vpp.png" width="640" /></a></div><p>Above — Pushed a little harder to 761 mW. Things are getting ugly. C1 still = 10 nF. Let's decrease the C1 value by a decade to 1 nF:<br /></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjGYQC3x8o3reU0JXfUf5Dwr8QrO6E6bHeJcv-3Fj4po3GO9Zs8my1MdbOvdbsEZ-92Ple3Y0oNlMpqBt21mx00WvORRU-XFkfXr2bloJgAHBTETuGvVtrB8_EBkOeRDhoeYrOXVBllCoTS47x6M-7jYPeAIu9FRWf7xGRVsIiURfilgmYEj89ezlezeQ/s794/OO1-5vpp.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="426" data-original-width="794" height="344" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjGYQC3x8o3reU0JXfUf5Dwr8QrO6E6bHeJcv-3Fj4po3GO9Zs8my1MdbOvdbsEZ-92Ple3Y0oNlMpqBt21mx00WvORRU-XFkfXr2bloJgAHBTETuGvVtrB8_EBkOeRDhoeYrOXVBllCoTS47x6M-7jYPeAIu9FRWf7xGRVsIiURfilgmYEj89ezlezeQ/w640-h344/OO1-5vpp.png" width="640" /></a></div><p></p><p>Above — FFT at 5 Vpp where C1 = 0.001µF. While not as impressive as when C1 = 10 nF, it's still quite good and the LM386 voltage gain is around 19.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgL0z6SVrkMW-qkQYf7p0gdOLmCI6kh8f_wChfUk3JOW52a56QvsyZr0r-q5xA3LfLo7t-upIxU4vIhCnD8ZoJ14igMSHxYefat2F-bvVGTncGw8ZPyRWZkZCgAUTdnq-GkkAexIcPjkyOij1w0tbLy0sJyfuWuPLhE6aPgPM0NGJkBD4lmGhyCX0Tt3Q/s795/OO1-7.15vpp.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="416" data-original-width="795" height="334" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgL0z6SVrkMW-qkQYf7p0gdOLmCI6kh8f_wChfUk3JOW52a56QvsyZr0r-q5xA3LfLo7t-upIxU4vIhCnD8ZoJ14igMSHxYefat2F-bvVGTncGw8ZPyRWZkZCgAUTdnq-GkkAexIcPjkyOij1w0tbLy0sJyfuWuPLhE6aPgPM0NGJkBD4lmGhyCX0Tt3Q/w640-h334/OO1-7.15vpp.png" width="640" /></a></div><p>Above — FFT at 7.14 Vpp or 759 mW output power, The second harmonic is somewhat better than the case where C1 = 0.01uF. <a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh46Eu9q1XXtyjuRvN1kCE0YDD-4kYSHsZ0BmfPG1DSH48cZWko-HnPlRgDDbaHJw2cGXTRkingsFjDsB39FpA_bd09MMNF5wh9un2kWHmgHfAdIAF1cTQR_PEz7Lgt0SywVzJChsRbj5U2ZP25eJtBjfqSRNA5Ds4IkFybPq0h1cIK6jeSn8EYEoxuXg/s796/For70-5vpp.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="428" data-original-width="796" height="344" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh46Eu9q1XXtyjuRvN1kCE0YDD-4kYSHsZ0BmfPG1DSH48cZWko-HnPlRgDDbaHJw2cGXTRkingsFjDsB39FpA_bd09MMNF5wh9un2kWHmgHfAdIAF1cTQR_PEz7Lgt0SywVzJChsRbj5U2ZP25eJtBjfqSRNA5Ds4IkFybPq0h1cIK6jeSn8EYEoxuXg/w640-h344/For70-5vpp.png" width="640" /></a></p><p>Above — FFT at 5 Vpp where C1 = 470 pF. Another favourable reduction of harmonic distortion when the LM386 amp is running at reasonably high, unclipped power levels. I measured no loss in voltage gain with a 470 pF cap + 10K resistor.<br /></p><p>I also tried a 220 pF cap - it worked somewhat, but the harmonic suppression started to fall off at this point. The overall best unclipped harmonic suppression occurred where C1 = 0.01 µF in my experiments, albeit with 45% voltage gain loss. <br />To decide on a C1 value, it's important to listen to it to with actual audio to ensure that any frequency peaks, or more importantly, the low pass effects caused by the network doesn't wreck the audio you listen to.</p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi7gRmp1TFEZmjlD6FDYw0sNnGv61BIdceDKpXRl0Lu6gQ-auzwzCmRFMRwhuvWYJV8e8x4R7FOYLztnWQADTTXyFwzeRgjGQYXpJHSoIuaCGjFikCxAY6znri_w-2X4F7toAktm4Sr01rfgQ8uadhZYNAykQrbkDQMbbe-ZtIroJyA1An6OzbDrlPDcQ/s893/speaker8.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="603" data-original-width="893" height="432" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi7gRmp1TFEZmjlD6FDYw0sNnGv61BIdceDKpXRl0Lu6gQ-auzwzCmRFMRwhuvWYJV8e8x4R7FOYLztnWQADTTXyFwzeRgjGQYXpJHSoIuaCGjFikCxAY6znri_w-2X4F7toAktm4Sr01rfgQ8uadhZYNAykQrbkDQMbbe-ZtIroJyA1An6OzbDrlPDcQ/w640-h432/speaker8.jpg" width="640" /></a></div><br />Above — Listening to monaural jazz from my CD player into the LM386 and then into my 8 inch lab speaker. Although C1 = 0.01 µF gives the best reduction in harmonic energy, it rolls off too much high frequency audio for my tastes. I usually start at 0.001 µF and work up in capacitance. To my tastes, a 0.0018 or 1.8 nF cap sounded best. We've entered subjective territory. Variables may include personal taste, your hearing + age, your AF signal source overall tone, speaker size -- and perhaps whether the speaker is mounted in a cabinet, etc.. You might consider choosing a feedback cap between 0.01 µF and 470 pF according to your needs and wants.<br /><p></p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjjBRITBABGLaA8jPYg7UiHEeeKIb0D9mmhALHHP8eKB8362rkujOg0sJzG08odZ-uNrn-3F_yjxpENtrRUyJWlcNWlzL3YQ0YOaLQz_0FA0fjxnKBmyXj4eaJHv3YnIJoBqFEYavp9m6ErBcQkb5pmnVvOxVVPeBPxOWyw7bi8Ut0hYo6K0uZBhDr0gg/s659/speaker6.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="563" data-original-width="659" height="546" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjjBRITBABGLaA8jPYg7UiHEeeKIb0D9mmhALHHP8eKB8362rkujOg0sJzG08odZ-uNrn-3F_yjxpENtrRUyJWlcNWlzL3YQ0YOaLQz_0FA0fjxnKBmyXj4eaJHv3YnIJoBqFEYavp9m6ErBcQkb5pmnVvOxVVPeBPxOWyw7bi8Ut0hYo6K0uZBhDr0gg/w640-h546/speaker6.jpg" width="640" /></a></div><br />Above — Listening through my 6 inch lab speaker. My C1 preference = .0039 µF for this speaker.<br /><p></p><h3 style="text-align: left;">3. Gain = 50 Mode<br /><br /></h3><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjXR4Hq_CZBCdtEC3yaAb7P0V48DYjrNDMuxQH20BE5QTmX0DQ0eUwjgQ__M-Ktp2pi9q1bNCLziEzjKmhOfNHxO9BxdkoK9DD0NDO2syaNRleSvKv7v_fPhTnwoj1WOQfDlA4a0nLtUanl21_7dxg7MGsScgC_aqNAmFwEDm3QUpKEyCxBxbosq6USpQ/s393/gain%20=%2050.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="250" data-original-width="393" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjXR4Hq_CZBCdtEC3yaAb7P0V48DYjrNDMuxQH20BE5QTmX0DQ0eUwjgQ__M-Ktp2pi9q1bNCLziEzjKmhOfNHxO9BxdkoK9DD0NDO2syaNRleSvKv7v_fPhTnwoj1WOQfDlA4a0nLtUanl21_7dxg7MGsScgC_aqNAmFwEDm3QUpKEyCxBxbosq6USpQ/s16000/gain%20=%2050.png" /></a></div>Above — Datasheet example: Amplifier with gain = 50<br /><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi7n50UstdDi3m08sb8am0bjPs0gFI1pyXmH_JN64SGGRJRdxRyxUy8QzCeVRqXIE0uHIop2nakahyljKHR2wZF4YcH_RczVvpRoaTIoyVOEHWxwYRN5SrSdqdpiT-nPIBzflp20i3XV4W1Rw8cOcr45dxgz2XE5nWdK2U_hOHwa38db7BYXKSPWMMEYQ/s796/Gain50-5vpp.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="414" data-original-width="796" height="332" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi7n50UstdDi3m08sb8am0bjPs0gFI1pyXmH_JN64SGGRJRdxRyxUy8QzCeVRqXIE0uHIop2nakahyljKHR2wZF4YcH_RczVvpRoaTIoyVOEHWxwYRN5SrSdqdpiT-nPIBzflp20i3XV4W1Rw8cOcr45dxgz2XE5nWdK2U_hOHwa38db7BYXKSPWMMEYQ/w640-h332/Gain50-5vpp.png" width="640" /></a></div><p>Above — FFT at 5 Vpp with a 1K2 and 10 µF cap between Pins 1 and 8. Although we see the 2nd harmonic at about 52 dB down, it's still OK for the LM386. Signal noise will appear louder compared to the "Bass Boost" feedback variants with the same output power.</p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiaxn0B8_HywoxaJZBV6EDZeVmI3DiSJyo4KafJcjnGVvI_md4bBnfJNQ94LYHumKsWvuA4ZfDV0UGZtW3wVE1DezPpY1OU36gRvWUIwMpieiKR4J3OoIjnWgQlxBebrOl93HcXv2i8_l2czO4KDfc-9NpcCgK0eBIF-uCE9QjmN3ATCb6xDPraWsw0pg/s797/Gain50-hardClip.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="423" data-original-width="797" height="340" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiaxn0B8_HywoxaJZBV6EDZeVmI3DiSJyo4KafJcjnGVvI_md4bBnfJNQ94LYHumKsWvuA4ZfDV0UGZtW3wVE1DezPpY1OU36gRvWUIwMpieiKR4J3OoIjnWgQlxBebrOl93HcXv2i8_l2czO4KDfc-9NpcCgK0eBIF-uCE9QjmN3ATCb6xDPraWsw0pg/w640-h340/Gain50-hardClip.png" width="640" /></a></div><br />Above — I pushed it hard to 7.39 Vpp or 813 mW output power. This is the nastiness you'll hear on loud signal peaks.<p></p><h4 style="text-align: left;">4. Gain = 200 Mode -- plus lifting and AC bypassing Pin 2</h4><p>Last section. Here's the famous schematic used by millions to make simple DYI audio projects:</p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgus0O-vqh3AcBM7lS0Ahum6ArGi1_bhQgYf_1DXbMm56bqrRlKM8W9CAwzCCZIVtrM6fsWRt_Fe4qb8dJ2AYWDmEfqbeKwuWQO11KSTtctxoOAwyCfWWBIQyKUzXzvdeaxyZ4vQFKpmDYijKC3kApFSsqBcGhYADsHKlK92gF_trr4rgjPZEvwkojULg/s393/gain%20=%20200.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="250" data-original-width="393" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgus0O-vqh3AcBM7lS0Ahum6ArGi1_bhQgYf_1DXbMm56bqrRlKM8W9CAwzCCZIVtrM6fsWRt_Fe4qb8dJ2AYWDmEfqbeKwuWQO11KSTtctxoOAwyCfWWBIQyKUzXzvdeaxyZ4vQFKpmDYijKC3kApFSsqBcGhYADsHKlK92gF_trr4rgjPZEvwkojULg/s16000/gain%20=%20200.png" /></a></div><br /><p>Connecting Pins 1 and 8 AC bypass a 1.35K emitter resistor in the input pair -- and unleash the hounds. We get a full menu of gain, noise, and potentially harsh sounding distortion.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgbOuC6dKqVUqe5Rgr_RuRZF1Opx3NTuq8Q43l7TDUazwBgkorGcp0iXarcweNBCxm1nfORGlhY7OO8yEiCWlsZELOJwzdNwqleqkCaKoSdlX6TvnnjJ27FjCZ3P8vRaf-HBTtBxv8zu1w5InZZgLV1nEQ8MN-A8yl2dateezGyvNQYarpkudH4uZxL7A/s798/Gain=200-square%20waves.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="416" data-original-width="798" height="334" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgbOuC6dKqVUqe5Rgr_RuRZF1Opx3NTuq8Q43l7TDUazwBgkorGcp0iXarcweNBCxm1nfORGlhY7OO8yEiCWlsZELOJwzdNwqleqkCaKoSdlX6TvnnjJ27FjCZ3P8vRaf-HBTtBxv8zu1w5InZZgLV1nEQ8MN-A8yl2dateezGyvNQYarpkudH4uZxL7A/w640-h334/Gain=200-square%20waves.png" width="640" /></a></div><p>Above —In this separate experiment to showcase the worst-case scenario, I've manipulated & then pushed this particular amp into raucous distortion. Note the strong 3rd and 5th harmonics relative to the 2 even harmonics. This is worst case fuzz box stuff. While this might sound bad with your ears, it's great fun to see it on a DSO.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEizZ25ArVr3S9emiNPH47iS5vo3L347OIR67HCytzB-bvW-c_g-1ZBDqXWzc_PQpiqJb9HKw0B9stOKU8WtnXFaMWF7W9gq3QkZ64VcLFKWP2Zc1oWQF2piuBupZ1RTonPvj08H2Ie_2ekJBYA1fcxZ9Lm8SD-0tiYeULT8nAl7ivSX6AATUhilH-qDPQ/s798/Gain200-5vpp.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="424" data-original-width="798" height="340" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEizZ25ArVr3S9emiNPH47iS5vo3L347OIR67HCytzB-bvW-c_g-1ZBDqXWzc_PQpiqJb9HKw0B9stOKU8WtnXFaMWF7W9gq3QkZ64VcLFKWP2Zc1oWQF2piuBupZ1RTonPvj08H2Ie_2ekJBYA1fcxZ9Lm8SD-0tiYeULT8nAl7ivSX6AATUhilH-qDPQ/w640-h340/Gain200-5vpp.png" width="640" /></a></div><p>Above — Back to the main experiments using the schematic shown above... The FFT at 5 Vpp or 372 mW output power. The 2nd harmonic lies at -46 dBc.The various tones do not go down much at lower input signal levels.</p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh4P34JwjEujHpQgapX9cBDLwKt51XaGvD8SOUMnJJHoxsIktR-_WjjTYAon_NxpKKYZtaS0DcBzD-wZ2HSJO5uX2jSsu0-_DcCQMKUTk1BvWd9-bTML63FjMMqIcVHgtbSGLhyEAquXwyRF0PAqOl614muVk-Qg4las-Pb-ka6o5qUblkhK7NiEIuh_Q/s798/Gain200-7.02vpp.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="420" data-original-width="798" height="336" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh4P34JwjEujHpQgapX9cBDLwKt51XaGvD8SOUMnJJHoxsIktR-_WjjTYAon_NxpKKYZtaS0DcBzD-wZ2HSJO5uX2jSsu0-_DcCQMKUTk1BvWd9-bTML63FjMMqIcVHgtbSGLhyEAquXwyRF0PAqOl614muVk-Qg4las-Pb-ka6o5qUblkhK7NiEIuh_Q/w640-h336/Gain200-7.02vpp.png" width="640" /></a></div><br />Above — Increasing the signal generator output to push the amp into clipping. The 3rd harmonic looks ready to break open.<br /><p></p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEghU4O7CRHRMAQkC85sgnPn41FtoumgC9nCyQHREof7jFDVm6I9Fmd38oDRqHxHwhzwrYF5V2WTyg4ndmnn9-xclSdfU4QHqztBhvP3bUoNKH8E1aIqT7ATvZE5xtagGv6TrnC3U3D_e6Y1kF_3oPv4EyKrllfMbjY4qwxuoMoqIWHOx3eU6GOI2JtS_Q/s794/Gain200-7.09vpp.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="420" data-original-width="794" height="338" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEghU4O7CRHRMAQkC85sgnPn41FtoumgC9nCyQHREof7jFDVm6I9Fmd38oDRqHxHwhzwrYF5V2WTyg4ndmnn9-xclSdfU4QHqztBhvP3bUoNKH8E1aIqT7ATvZE5xtagGv6TrnC3U3D_e6Y1kF_3oPv4EyKrllfMbjY4qwxuoMoqIWHOx3eU6GOI2JtS_Q/w640-h338/Gain200-7.09vpp.png" width="640" /></a></div><p></p><p>Above — A slight increase from 7.01 to 7.09 Vpp. The 3rd harmonic is about 41 dB down.When in full gain mode, the LM386 tends to offers more odd harmonics <br /></p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEio6kL9eodP0cwjvFj_yA7ZKMoxeA5NPVaQZO8jJ1AaTDHxSQp_YCnNqoAZCynZwVNKYadPytR91x8r0aOLG7jbzZLmuVMS8KlbD3-vKZu8uU-n3T-sP5Xg531YBRhOYklfxC3AIm1HFXcqRMZ-IHrfET3i_qz5GbpATnxu1d2vMt9xm_LrjrMLyUdzxQ/s800/GAIN200-7-35vpp.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="430" data-original-width="800" height="344" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEio6kL9eodP0cwjvFj_yA7ZKMoxeA5NPVaQZO8jJ1AaTDHxSQp_YCnNqoAZCynZwVNKYadPytR91x8r0aOLG7jbzZLmuVMS8KlbD3-vKZu8uU-n3T-sP5Xg531YBRhOYklfxC3AIm1HFXcqRMZ-IHrfET3i_qz5GbpATnxu1d2vMt9xm_LrjrMLyUdzxQ/w640-h344/GAIN200-7-35vpp.png" width="640" /></a></div><p>Above — Top and bottom sine wave clipping translates into wretched distortion.<br /><br />My question -- will feedback similar to what we used in the Bass Boost variants lower the harmonic distortion?</p><p></p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEix2Pr2a_t3dephbzFwmNNlBcq_utmrbz_Re3T38eSt8zQrn6w2KfXBMBd-EUWunCQJmeJzt6D9iXvFqLUaddZiCtIbVUu5lk_unTNztqXkYCEJ33MWk9eD3SKrGMJqePcR3EkTddxUh51UelWWOdjjbyXyU8a4ZKFAmNWfMOI2d1rSr4Veo33m78zfoQ/s794/OH1-5vpp2.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="415" data-original-width="794" height="334" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEix2Pr2a_t3dephbzFwmNNlBcq_utmrbz_Re3T38eSt8zQrn6w2KfXBMBd-EUWunCQJmeJzt6D9iXvFqLUaddZiCtIbVUu5lk_unTNztqXkYCEJ33MWk9eD3SKrGMJqePcR3EkTddxUh51UelWWOdjjbyXyU8a4ZKFAmNWfMOI2d1rSr4Veo33m78zfoQ/w640-h334/OH1-5vpp2.png" width="640" /></a></div><p>Above — At our standard of 5 Vpp, the affects of feedback leap out at us. [ 10K plus 0.01 µF cap ] Feedback is our friend? However, the gain dropped to around 100 and you will hear lots of high frequency roll off.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgyyag_dNiR6JuZ5oarjSHiu20bcPI_yM10AI85GgpjIFgebNejdSBhIDxkReKU3YgwKN4D9S3r8i4tYApZr1I9RXV0xNBs0jknrv8vMlRh4v8d53j8poE0BvnESAKF3d9NZ2HKyp3FGFKbXsPriMIoVEPNQFi7R0SxeBLmvLhjqjmA-j1XLsbm1h8BJQ/s798/ThousPF-5vpp.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="417" data-original-width="798" height="334" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgyyag_dNiR6JuZ5oarjSHiu20bcPI_yM10AI85GgpjIFgebNejdSBhIDxkReKU3YgwKN4D9S3r8i4tYApZr1I9RXV0xNBs0jknrv8vMlRh4v8d53j8poE0BvnESAKF3d9NZ2HKyp3FGFKbXsPriMIoVEPNQFi7R0SxeBLmvLhjqjmA-j1XLsbm1h8BJQ/w640-h334/ThousPF-5vpp.png" width="640" /></a></div><p></p><p>Above — Vpp = 5 with a feedback network consisting of a 10K + 0.001 µF cap. The response is lack luster compared to 10K + 0.01 µF capacitor. The drop in voltage gain was only 2%. The 2nd harmonic is maybe 1-2 dB better than without the feedback network?</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj_XR51-Zd9fSCpejgzxDWxAudFC0QhWnO4T0oNVcfiuSxNkrwhbEkyr-oFZnHGEbTWjx51pf-Dq8PN7DUmjyK-u_2qFwHr2wwCVr18ptGAVt0LgIHCFS5w5PrpXnAaTG7_NjnEjrcrPXYtxILHMLn-ss1RrMfmTagdNXalIfjWN310rf726-1IQJb0ZQ/s798/Two20PF-Vpp-5.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="423" data-original-width="798" height="340" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj_XR51-Zd9fSCpejgzxDWxAudFC0QhWnO4T0oNVcfiuSxNkrwhbEkyr-oFZnHGEbTWjx51pf-Dq8PN7DUmjyK-u_2qFwHr2wwCVr18ptGAVt0LgIHCFS5w5PrpXnAaTG7_NjnEjrcrPXYtxILHMLn-ss1RrMfmTagdNXalIfjWN310rf726-1IQJb0ZQ/w640-h340/Two20PF-Vpp-5.png" width="640" /></a></div><br />Above — Vpp = 5 with a feedback network consisting of a 10K + 220 pF capacitor. Interesting FFT ! The 2nd harmonic is now -50 dBc where without the network it measured -46 dBc.. Some of the tones dropped around 4 or 5 dB too. No change in voltage gain by adding this network.<p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiJUtefGG0UZzqS_kMXOaP0VGQHMGdFuK1tU9NOetRs1hWPZAc99LiszyRpBwxOVME0n8ek1BIUpVrbau-C99EckWB6QR_J50wd1Pm3jtsG6KRHz8MV5tuC7a3TfMUwLM1lPMbDyG9R15_iYavEHGGSKuuSwTlY22znl8MUFVpUYjQLX6MgIPS4DnxkBw/s393/lift-pin2.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="250" data-original-width="393" height="255" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiJUtefGG0UZzqS_kMXOaP0VGQHMGdFuK1tU9NOetRs1hWPZAc99LiszyRpBwxOVME0n8ek1BIUpVrbau-C99EckWB6QR_J50wd1Pm3jtsG6KRHz8MV5tuC7a3TfMUwLM1lPMbDyG9R15_iYavEHGGSKuuSwTlY22znl8MUFVpUYjQLX6MgIPS4DnxkBw/w400-h255/lift-pin2.png" width="400" /></a></div><p>Above — There's an old trick left to try. Normally, most builders will ground Pin 2 like I did throughout this blog post. What if we AC couple Pin 2 to ground through capacitor C2?. This may help to better DC balance the input pair bases ( may reduce DC offset ) and perhaps even bypass some portion of the distortion to ground.</p><p>Does this work?<br /> <br /></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEixGjszIj0Bl9ufDfv4F592g5-MtO1q_dHAQdmFczCil5OOdLSl8Ysjo0cAcJ5LZhWYGCI0f5xALMwC0TykMJ5DVxgVqrMHqYInvI4ffk9yElHz8JXnTuambyloguWxbDVSSapo0wmnHlSJ8NpimJg8Ae0Qif4rE96F5qgf0AIAHBc-FNThUlag7rfx3g/s629/dB%20improvement%20with%20cap.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="414" data-original-width="629" height="422" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEixGjszIj0Bl9ufDfv4F592g5-MtO1q_dHAQdmFczCil5OOdLSl8Ysjo0cAcJ5LZhWYGCI0f5xALMwC0TykMJ5DVxgVqrMHqYInvI4ffk9yElHz8JXnTuambyloguWxbDVSSapo0wmnHlSJ8NpimJg8Ae0Qif4rE96F5qgf0AIAHBc-FNThUlag7rfx3g/w640-h422/dB%20improvement%20with%20cap.png" width="640" /></a></div><br />Above — The FFT tracing shown above is with C2 in place showing that C2 does decrease distortion in certain cases. I could not superimpose 2 FFTs, so I made a red line above each of the 4 harmonic tones.<br /><p></p><p>The bottom of the red line is the exact peak of the each tone with Pin 2 shunted to ground. Above the red line is the measured improvement for that particular tone caused by C2. I installed a switch across the C2 capacitor to make comparisons. . C2 = 0.01 µF in this particular experiment.<br /></p><p>In my experiments with a gain of >=150 and no feedback network, when the LM386 is pushed into harmonic distortion, C2 lowered the harmonic tones by 4 to 8 dB. I tried C2 values of 0.01 to 0.27 µF<br />and changing the value of C2 within that range seemed to make no significant difference. Replacing C2 with a resistor of any value did not work to lower distortion.<br /></p><p>C2 seemed to have less of an effect when the LM386 gain was lower than 150. At Gain = 20 with no feedback, I observed a maximum 2-3 dB maximal improvement in any 1 tone. With feedback, the effect diminished a little further, however, results were inconsistent. C2 does not appear to lower the harmonic distortion when the audio signal is unclipped -- rather, it seems to reduce distortion due to clipping when it happens. </p><p>I performed other experiments such as bringing the feedback to Pin 2 with Pin 2 connected to ground via a resistor or resistor + capacitor (like what you do with an op-amp or discrete AF amplifier). I also tried lowering the feedback 10K resistor value at various gain levels. Often enough, the result was that the LM386 would go into a writhing spasm when pushed into distortion. <i>See below.</i></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiIogTZXsVXISTraJKVT6QTrXySu_1TnDlpiPPGovIA8UUFXwxSd0ZTeZHONsBHFjrFiK1rHw8s370IVneWcO24qPtaLa-nBYf_2Ua2_MXsYkK-tEB6CWDpEENF5tT4nJlzLt969RERk2dOlWUNUwAio9YqoHPBke0R61CW1W2PbEVY9ysqaTNULINUyw/s797/scene%203%20-%20spasm.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="421" data-original-width="797" height="338" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiIogTZXsVXISTraJKVT6QTrXySu_1TnDlpiPPGovIA8UUFXwxSd0ZTeZHONsBHFjrFiK1rHw8s370IVneWcO24qPtaLa-nBYf_2Ua2_MXsYkK-tEB6CWDpEENF5tT4nJlzLt969RERk2dOlWUNUwAio9YqoHPBke0R61CW1W2PbEVY9ysqaTNULINUyw/w640-h338/scene%203%20-%20spasm.png" width="640" /></a></div><p>Above —Fancy feedback experiments often resulted in the above tracing. It seemed better to explore simpler ways to lower distortion. <br /></p><h3 style="text-align: left;">Conclusion</h3><p>Wow, this was a lot of work, but proved fun. I encourage you to perform your own experiments with the LM386. While no panacea, and a little long in the tooth, the LM386 reflects a simpler, mostly analog time for many of us home builders.</p><p>I suggest you consider using the LM386 with lower gain and build up your audio signal voltage with a low noise preamp using an op-amp like the NE5532. </p><p>Further, consider adding feedback [ 10K plus some value of C1 ] from Pins 5 to 1 and also AC coupling Pin 2 to ground. I did both of these tricks in my 2 photographed bench CD player listening tests shown in Section 2. <br /></p><p></p><p>とてもいい </p><p><br /></p>Vasily Ivanenkohttp://www.blogger.com/profile/17387516134063150119noreply@blogger.com7tag:blogger.com,1999:blog-3480228403403435266.post-2244995240856964702022-11-06T19:54:00.099-08:002022-11-27T20:46:08.369-08:00GAA-12 Practice Guitar Amp<p> <a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh57zbBfUeIEShtzbImRtgET_bScsKEQbOOKGBhkUFJRL2HHzPwHttWlyOI7Wud2L5lbkwha81zcaHD3EFxea0CKrVozjYONVLpqDiPeloalOpdriW_sP_4EAGYjRW53NM409Q4tOmzdAqn08DCR53XiGrgSfFBgTzP_vocDeob-VFD9smBZEOZbSqDBw/s1131/amp5667.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="580" data-original-width="1131" height="328" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh57zbBfUeIEShtzbImRtgET_bScsKEQbOOKGBhkUFJRL2HHzPwHttWlyOI7Wud2L5lbkwha81zcaHD3EFxea0CKrVozjYONVLpqDiPeloalOpdriW_sP_4EAGYjRW53NM409Q4tOmzdAqn08DCR53XiGrgSfFBgTzP_vocDeob-VFD9smBZEOZbSqDBw/w640-h328/amp5667.jpg" width="640" /></a></p><div class="separator" style="clear: both; text-align: left;"><!--[if gte mso 9]><xml>
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<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="page number"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="endnote reference"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="endnote text"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="table of authorities"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="macro"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="toa heading"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Bullet"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Number"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Bullet 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Bullet 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Bullet 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Bullet 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Number 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Number 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Number 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Number 5"/>
<w:LsdException Locked="false" Priority="10" QFormat="true" Name="Title"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Closing"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Signature"/>
<w:LsdException Locked="false" Priority="1" SemiHidden="true"
UnhideWhenUsed="true" Name="Default Paragraph Font"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text Indent"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Continue"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Continue 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Continue 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Continue 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Continue 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Message Header"/>
<w:LsdException Locked="false" Priority="11" QFormat="true" Name="Subtitle"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Salutation"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Date"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text First Indent"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text First Indent 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Note Heading"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
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<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text Indent 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Block Text"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Hyperlink"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="FollowedHyperlink"/>
<w:LsdException Locked="false" Priority="22" QFormat="true" Name="Strong"/>
<w:LsdException Locked="false" Priority="20" QFormat="true" Name="Emphasis"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Document Map"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Plain Text"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="E-mail Signature"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Top of Form"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Bottom of Form"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Normal (Web)"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Acronym"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Address"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Cite"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Code"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Definition"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Keyboard"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Preformatted"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Sample"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Typewriter"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Variable"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Normal Table"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
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<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="No List"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Outline List 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Outline List 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Outline List 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
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<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Simple 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Simple 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
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<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
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<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Classic 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Classic 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Colorful 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Colorful 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Colorful 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Columns 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Columns 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Columns 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Columns 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Columns 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 6"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
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<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
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<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
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<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
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<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
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<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
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<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
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<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 8"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table 3D effects 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
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<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table 3D effects 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Contemporary"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Elegant"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Professional"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Subtle 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Subtle 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
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<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
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<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Web 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Balloon Text"/>
<w:LsdException Locked="false" Priority="39" Name="Table Grid"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
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<w:LsdException Locked="false" SemiHidden="true" Name="Placeholder Text"/>
<w:LsdException Locked="false" Priority="1" QFormat="true" Name="No Spacing"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading"/>
<w:LsdException Locked="false" Priority="61" Name="Light List"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 1"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 1"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 1"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 1"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 1"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 1"/>
<w:LsdException Locked="false" SemiHidden="true" Name="Revision"/>
<w:LsdException Locked="false" Priority="34" QFormat="true"
Name="List Paragraph"/>
<w:LsdException Locked="false" Priority="29" QFormat="true" Name="Quote"/>
<w:LsdException Locked="false" Priority="30" QFormat="true"
Name="Intense Quote"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 1"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 1"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 1"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 1"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 1"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 1"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 1"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 1"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 2"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 2"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 2"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 2"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 2"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 2"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 2"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 2"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 2"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 2"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 2"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 2"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 2"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 2"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 3"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 3"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 3"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 3"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 3"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 3"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 3"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 3"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 3"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 3"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 3"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 3"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 3"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 3"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 4"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 4"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 4"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 4"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 4"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 4"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 4"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 4"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 4"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 4"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 4"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 4"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 4"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 4"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 5"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 5"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 5"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 5"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 5"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 5"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 5"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 5"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 5"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 5"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 5"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 5"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 5"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 5"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 6"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 6"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 6"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 6"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 6"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 6"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 6"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 6"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 6"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 6"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 6"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 6"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 6"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 6"/>
<w:LsdException Locked="false" Priority="19" QFormat="true"
Name="Subtle Emphasis"/>
<w:LsdException Locked="false" Priority="21" QFormat="true"
Name="Intense Emphasis"/>
<w:LsdException Locked="false" Priority="31" QFormat="true"
Name="Subtle Reference"/>
<w:LsdException Locked="false" Priority="32" QFormat="true"
Name="Intense Reference"/>
<w:LsdException Locked="false" Priority="33" QFormat="true" Name="Book Title"/>
<w:LsdException Locked="false" Priority="37" SemiHidden="true"
UnhideWhenUsed="true" Name="Bibliography"/>
<w:LsdException Locked="false" Priority="39" SemiHidden="true"
UnhideWhenUsed="true" QFormat="true" Name="TOC Heading"/>
<w:LsdException Locked="false" Priority="41" Name="Plain Table 1"/>
<w:LsdException Locked="false" Priority="42" Name="Plain Table 2"/>
<w:LsdException Locked="false" Priority="43" Name="Plain Table 3"/>
<w:LsdException Locked="false" Priority="44" Name="Plain Table 4"/>
<w:LsdException Locked="false" Priority="45" Name="Plain Table 5"/>
<w:LsdException Locked="false" Priority="40" Name="Grid Table Light"/>
<w:LsdException Locked="false" Priority="46" Name="Grid Table 1 Light"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark"/>
<w:LsdException Locked="false" Priority="51" Name="Grid Table 6 Colorful"/>
<w:LsdException Locked="false" Priority="52" Name="Grid Table 7 Colorful"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 1"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 1"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 1"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 1"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 1"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 1"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 1"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 2"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 2"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 2"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 2"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 2"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 2"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 2"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 3"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 3"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 3"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 3"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 3"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 3"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 3"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 4"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 4"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 4"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 4"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 4"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 4"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 4"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 5"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 5"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 5"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 5"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 5"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 5"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 5"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 6"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 6"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 6"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 6"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 6"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 6"/>
<w:LsdException Locked="false" Priority="52"
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<p class="MsoNormal"><span lang="EN-US" style="mso-ansi-language: EN-US;">Greetings! This Fall, I built the first of 2 planned practice amps. Inspired by simple
1950’s tube guitar amps I too kept it simple. In those Golden-era amplifiers, you plug the
guitar in 1 jack, the speaker in the other and hit the switch. Modern
solid state guitar amplifiers with effect loops, frequency compensating gain control stages and features
galore may just complicate things in the guitar - amp - player interface. While perhaps cool and fancy, these added stages may carry high-value
resistors that boost op-amp input current noise and also increase resistor-related
Johnson noise too.</span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-ansi-language: EN-US;">My goal =
make a low noise jazz / clean guitar amp as opposed to a low distortion,
high-fidelity practice amplifier. I remember having to turn the volume pot on
my Stratocaster to 0 between songs in my Marshall 50 - 100 Watt amp days of lore.
The amp sounded great, but was super noisy unless the rest of the band was
playing loudly to drown the amp noise out. At my age, a quiet amp seems desirable.</span></p><p class="MsoNormal"><span lang="EN-US" style="mso-ansi-language: EN-US;"><span style="color: #800180;">Note, I completely redesigned the preamp on November 15th after first posting this amplifier on November 6, 2022. Two things changed to trigger that : [ 1 ] I moved to 10 inch speakers [ 2 ], I moved to playing Fender Telecaster guitars 95% of the time instead of an arch top. With my back and wrist pain, the Telecaster proves much easier to play --- and also it's Leo Fender's gift to humanity. Such a joy to play. Thus, I re-designed my practice amp around playing a Telecaster through a 10 inch speaker. The result is a basic preamp with few AC coupling capacitors in the signal path.</span><br /><br /></span></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg1ePB6Y0ri-hs6AL4U216SQ3_RZAlDaKLN5xE9BzGfvjin7u_TD_pFnYjh0HFvw9GG-KQy19nlsRamQMVWzNcu8l3umXwVAq9b0oAWbvPW94m0VW9fNOCNNyleUvceAcG0LNo1ZBooH-0JJ2UvhWraMdaqergE1hMFR77jR7VFjJ6T5rfX8rYJOlnfRQ/s824/block-out.gif" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="359" data-original-width="824" height="278" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg1ePB6Y0ri-hs6AL4U216SQ3_RZAlDaKLN5xE9BzGfvjin7u_TD_pFnYjh0HFvw9GG-KQy19nlsRamQMVWzNcu8l3umXwVAq9b0oAWbvPW94m0VW9fNOCNNyleUvceAcG0LNo1ZBooH-0JJ2UvhWraMdaqergE1hMFR77jR7VFjJ6T5rfX8rYJOlnfRQ/w640-h278/block-out.gif" width="640" /></a></div><br /><p></p><div class="separator" style="clear: both; text-align: left;"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhqDGJ8QpnnGeyB_mowMkAeKq_RMlK221HtXvJLAFVZgmsPwCdir2f2voce_CZPT5moAZjA3THmvdgdZPZLxtiov5m4-C2htStg2kfurg0XrT2_WFC2hl8BnNeQzMf4LD6XnWrjsGvWS3iVyoABii044I4Np2FvcqPv-nlSiurZrqvRtv4rPgqQGs4IJA/s1055/amp11.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="717" data-original-width="1055" height="434" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhqDGJ8QpnnGeyB_mowMkAeKq_RMlK221HtXvJLAFVZgmsPwCdir2f2voce_CZPT5moAZjA3THmvdgdZPZLxtiov5m4-C2htStg2kfurg0XrT2_WFC2hl8BnNeQzMf4LD6XnWrjsGvWS3iVyoABii044I4Np2FvcqPv-nlSiurZrqvRtv4rPgqQGs4IJA/w640-h434/amp11.jpg" width="640" /></a></div> <br /><h3 style="text-align: left;"><b>Project Index<br /><br /></b></h3></div><div class="separator" style="clear: both; text-align: left;"><h2></h2></div><div class="separator" style="clear: both; text-align: left;">1. Preamplifier and Tone stages<br />2. Power Amp<br /></div><div class="separator" style="clear: both; text-align: left;">3. Power Supply</div><div class="separator" style="clear: both; text-align: left;">4. Miscellaneous Bench Notes</div><div class="separator" style="clear: both; text-align: left;">5. Video Links (only 1, but more coming later)<br /><br /><h3> 1. Preamplifier and Tone Stages<br /> </h3><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEif8TUijpofFM90WIUxuOCoNJ6Oc29OTWnWY24ZFeA-SrRG2OGcuWWs0Z81igvIpbaQNvf0EKCMmrVWmVZ6VwIau5NB-r-JbEJz4MRewlFiu4hNkBFcvYXfVF98JqJZLFxNI5JpG274mwJ2SnPKsH0PB84VrOMitjuOx7wZAr7oa7A2MGK9WH8t02ihWQ/s915/input.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="551" data-original-width="915" height="386" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEif8TUijpofFM90WIUxuOCoNJ6Oc29OTWnWY24ZFeA-SrRG2OGcuWWs0Z81igvIpbaQNvf0EKCMmrVWmVZ6VwIau5NB-r-JbEJz4MRewlFiu4hNkBFcvYXfVF98JqJZLFxNI5JpG274mwJ2SnPKsH0PB84VrOMitjuOx7wZAr7oa7A2MGK9WH8t02ihWQ/w640-h386/input.png" width="640" /></a></div><div style="text-align: left;"><span style="font-weight: normal;">Above — Input stage also showing ground loop reduction techniques to eliminate 60 cycle hum.</span></div><div style="text-align: left;"><span style="font-weight: normal;"></span></div><div style="text-align: left;"><span style="font-weight: normal;"><br />In tube amps, we employ our quietest 12AX7 or alternate preamp tube in V1 -- or the first preamp position, since all arising noise gets boosted down the signal chain. Same for solid state design. We seek to input the guitar signal, filter off radio frequency interference, plus control & boost signal amplitude while adding minimal noise and hum. <br /></span></div><div style="text-align: left;"><span style="font-weight: normal;"></span></div><div style="text-align: left;"><span style="font-weight: normal;"></span></div><div style="text-align: left;"><span style="font-weight: normal;"></span></div><div style="text-align: left;"><span style="font-weight: normal;"><br /></span></div><div style="text-align: left;"><span style="font-weight: normal;">I prefer a </span><span style="font-weight: normal;">12 K Ω</span><span style="font-weight: normal;"> input resistor for Telecaster guitars and I didn't have any in metal film, so placed two 22 </span><span style="font-weight: normal;">K Ω resistors in parallel got get the 11K </span><span style="font-weight: normal;"> Ω</span> shown.<span style="font-weight: normal;"> For picofarad level caps, I use MLCC types with C0G temp compensation in all of my projects from AF to microwave. Both the positive and negative op-amp DC voltage pins get a 100 nF capacitor shunt to ground as close to the op-amp package as possible. It's OK if the temperature compensation of those particular 100 nF MLCC caps is X7R from my experiments.<br /><br /></span></div><div style="text-align: left;"><span style="font-weight: normal;">An active gain control keeps the noise down. Like in tube amps, many solid state guitar amp input systems maximally boost the signal in the input stage(s) and then immediately attenuate it using a volume pot. This functionally works OK, but when a stage is operating at maximal gain, it’s also making maximum noise and today we may choose to apply noise - reducing active gain circuits with our op-amp & transistor design work.</span></div><div style="text-align: left;"><span style="font-weight: normal;"><br />I chose a warm, jazz guitar amp voicing inspired by the lovely Gibson amps of the 1950’s. </span></div><div style="text-align: left;"><span style="font-weight: normal;"> </span></div><div style="text-align: left;"><span style="font-weight: normal;">The above schematic also shows 1 ground loop prevention strategy to consider. Each stage including the power supply and PA are electrically isolated from the chassis by carving away copper around the mounting bolts + nuts. A single, insulated ground wire from each isolated board goes to the master star ground node located on the power supply board. Classic star grounding.</span></div><div style="text-align: left;"><span style="font-weight: normal;"> </span></div><div style="text-align: left;"><span style="font-weight: normal;">At the guitar input jack, the chassis becomes connected to the input jack bolt ground lug when you tighten the bolt. An insulated wire from the input jack ground lug runs to the EARTH ground on the AC receptacle. The non-grounded input jack lug coax centre runs to the op-amp input, however, the braid of the coax at this end goes to the star ground system as shown. The chassis gets connected to the star ground system only through the coaxial braid at the guitar input end of the coax. The result is no hum. I use RG-174, but any coax or shielded wire may work OK. No other coaxial cable are used in this guitar amplifier.</span></div><div style="text-align: left;"><span style="font-weight: normal;"> </span></div><div style="text-align: left;"><span style="font-weight: normal;"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj8FVwtnraOx7zwZs-mcJxirF9XDIP0_wrSR4zccb6-hStOuG0bxdR7pgIUcmVqb7hh74bmvMYdIwQa98FN_HkKhUg98FqBlaHhx2_dJeK1tMlqHOGaVoHSF-CKqbvtiY1K1Pi4-VOWrdNLGNWxrIee0brxyvCQlCtzdv8hDAxJbvR73TXrkivYWiJmdw/s1047/ts1.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="777" data-original-width="1047" height="474" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj8FVwtnraOx7zwZs-mcJxirF9XDIP0_wrSR4zccb6-hStOuG0bxdR7pgIUcmVqb7hh74bmvMYdIwQa98FN_HkKhUg98FqBlaHhx2_dJeK1tMlqHOGaVoHSF-CKqbvtiY1K1Pi4-VOWrdNLGNWxrIee0brxyvCQlCtzdv8hDAxJbvR73TXrkivYWiJmdw/w640-h474/ts1.jpg" width="640" /></a></div> <br /></span><span style="font-weight: normal;">Above — The entire preamp went onto this board. This photo shows an earlier iteration. I place some local DC filter</span><span style="font-weight: normal;"> capacitors on each board in my projects. On this board, 100 µF and 100 nF were placed. The blue and white wires move DC to the op amps positive and negative terminals. A guitar signal flows down copper wires along with its DC supply.<br /></span></div><div style="text-align: left;"><span style="font-weight: normal;"><br />I employed genuine Texas Instruments brand NE5532s with a typical input noise density of 5nV/√Hz for the 2 op-amps that make the preamp. I enjoy this lovely, quiet part.<br /><br /></span><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhjoexY1oaRtPrALFbV81efZOq54TbFtdAHWpUW1eWmBfMgdhbKDE7CWQ7S2h-zz2cn2CaBoHF1ISw--wPJgCWlTLuvOLiy_M17dUZG9vXtN4AF71-EWEmkI5Gc8S9woJw3nTMNzYTC7heRfXb7ioliOC7F70qcWTeIbdvQRPjl271SWcgzGVdUAaQWDg/s960/Tone%20Stack.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="428" data-original-width="960" height="286" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhjoexY1oaRtPrALFbV81efZOq54TbFtdAHWpUW1eWmBfMgdhbKDE7CWQ7S2h-zz2cn2CaBoHF1ISw--wPJgCWlTLuvOLiy_M17dUZG9vXtN4AF71-EWEmkI5Gc8S9woJw3nTMNzYTC7heRfXb7ioliOC7F70qcWTeIbdvQRPjl271SWcgzGVdUAaQWDg/w640-h286/Tone%20Stack.png" width="640" /></a></div></div><div style="text-align: left;"><span style="font-weight: normal;"><br />Above — The tone stack, buffer, plus final preamp stage with master volume control. This board uses a hybrid approach to tone control — a passive 1960's tone stack for bass, middle and treble -- plus active bass with a </span><span style="font-weight: normal;">Baxandall circuit</span><span style="font-weight: normal;">. A regular Fender/Marshall style passive tone stack cuts too much bass for my needs. The active bass control turnover frequency is 80 Hertz and offers ~ 15 dB cut or boost. <br />I kept the impedance higher to allow hard boosting with no distortion or noise. This amp with a 10 inch speaker gives more bottom end than many solid state guitar amps with a 12 inch speaker.<br /></span></div><div style="text-align: left;"><span style="font-weight: normal;"> </span></div><div style="text-align: left;"><span style="font-weight: normal;">The scaled to nearest standard value capacitor, classic Fender tone stack RC network use relatively low value potentiometers plus higher capacitance to reduce noise. With the active bass, this tone circuitry offers a wide variation in tone control. Fender / Marshall et al. tone stacks work best driving a high impedance, thus it drives a nJFET follower with 1.7 mA source current. This, in turn, drives the Baxandall circuit with a preferable low impedance.The FET drain is RC low-pass filtered and connected to the regulated, positive op-amp supply rail.<br /></span></div><div style="text-align: left;"><span style="font-weight: normal;"> </span></div><div style="text-align: left;"><span style="font-weight: normal;">The master volume active gain stage uses the topology from first preamp stage — the additional resistor ( 1K here ) causes the 10K pot to change gain in a more linear fashion. As you age, your near vision worsens --- and also when playing, room light is often poor, so you might just adjust volume knobs “by ear”. This amp sounds very loud for 12.4 Watts and when cranked up, vibrates the walls in my den at low frequencies with a 10 inch speaker.<br /><br /></span><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhhk8Mcm4ayFJSqAO9hzvqZEa_JPfDVyo3emfe1I0BMv0RTV_wNpOlc4ggsn2addP4Jo4Y1lIv83qlZ4zmGKd4b7bpLHmFkFfzroUGBGgMN5PxjzEkdMdHUUM8ncbHYGzoo0hWXupLCQW6g2Z8VCR5z7p6J172bjQw3Rpzk3fQp-Yzs2ja_0woMC_HLHw/s971/preamp1c.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="667" data-original-width="971" height="440" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhhk8Mcm4ayFJSqAO9hzvqZEa_JPfDVyo3emfe1I0BMv0RTV_wNpOlc4ggsn2addP4Jo4Y1lIv83qlZ4zmGKd4b7bpLHmFkFfzroUGBGgMN5PxjzEkdMdHUUM8ncbHYGzoo0hWXupLCQW6g2Z8VCR5z7p6J172bjQw3Rpzk3fQp-Yzs2ja_0woMC_HLHw/w640-h440/preamp1c.jpg" width="640" /></a></div><span style="font-weight: normal;"> </span></div><div style="text-align: left;"><span style="font-weight: normal;">Above —The complete preamp board with some test wires and a temporary 1/4 inch input jack for bench testing.<br /><br /></span><h3 style="text-align: left;">2. Power Amp<span style="font-weight: normal;"><br /><br /></span><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi69Nt2iJ36wKZ0y38tOVB05lr9lLrw8Q-VPY5iYj_WSmUa0gGCrTcyur-w01l8p9LC10QfeaZjMhnJRjSf3iWTuvcb5oARH7ZEhTK2BoMKLIG6doLvLqITDiHSvyLUuDdL-deZvaUA5-21yXnQn20lKK35P-X-6SKKXJccv7vzBW1QC2AfPpafE55D3A/s949/PA%20Nov%2013.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="608" data-original-width="949" height="410" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi69Nt2iJ36wKZ0y38tOVB05lr9lLrw8Q-VPY5iYj_WSmUa0gGCrTcyur-w01l8p9LC10QfeaZjMhnJRjSf3iWTuvcb5oARH7ZEhTK2BoMKLIG6doLvLqITDiHSvyLUuDdL-deZvaUA5-21yXnQn20lKK35P-X-6SKKXJccv7vzBW1QC2AfPpafE55D3A/w640-h410/PA%20Nov%2013.png" width="640" /></a></h3></div><div class="separator" style="clear: both; text-align: left;">Above — The PA schematic. </div><div class="separator" style="clear: both; text-align: left;"> </div><div class="separator" style="clear: both; text-align: left;">Since this is a low DC voltage amp with plus/minus ~ 20.85VDC (unloaded) on the rails, common, low-voltage transistors such as the 2N4401 emitter coupled pair shown will work in the transconductance amp. All resistors = 1% metal film types as possible. Most are rated at ¼ watt. The emitter couple pair get degenerated with 49.9 Ω resistors to boost linearity. Some designers leave them off, however, PA distortion will increase dramatically. I think 49.9 Ω is a reasonable value for guitar PA transconductance amplifiers.<br /></div><br />The pair get sunk by a current source biased for 1.48 mA. Even a simple current source design like I used greatly surpasses old-school long tail resistor biasing since the high collector resistance helps boost differential balance to reduce noise and distortion. For my current sources, I opted to use cheap BD139 transistors instead of small signal TO-92 types.<br /><br />This PA lacks any protection circuitry for when something goes wrong. Thus, I overbuild to keep it running when something does go wrong. Guitar amps may suffer lots of punishment including when you are building and testing them. I feel that the current sensing and limiting protection circuits found in many commercial PA circuits move away from the spirit of the 1950’s style amplifiers where simplicity proved a key feature. After all, if my PA fries a transistor or 2, I can fix it.</div><div class="separator" style="clear: both; text-align: left;"><br />The voltage amp or VAS = a genuine NXP brand BD-140 PNP job. I tried 5 PNP BJT’s in this slot: the venerable high voltage classic KSA-1381, a BF-423, a BD-238, the BD-140 -- and a suspect bootleg MJE-350. The MJE-350 gave poor gain and went in the garbage. The KSA-1381 offered the most gain but seemed a bit overkill -- and the others provided similar gain and PA clean signal power with bench testing. <br />In the end, the BD-140 seemed the logical choice for a practice amp. Since I wanted this PA to offer good gain, I only degenerated the VAS emitter by 10 ohms which may lead to instability in some designs. You’ll commonly see resistor values of 33-47 ohms used in some commercial designs. Increasing emitter degeneration boosts stability plus noise while the lowering the PA gain. The measured PA voltage gain = 56.<br /><br /></div><div class="separator" style="clear: both; text-align: left;"></div><div class="separator" style="clear: both; text-align: left;">The most sensitive part of the entire PA is the collector of the VAS
transistor. I found a strange phenomenon. When I put the 'standard' 68 to 120 pF cap
between its collector and base, HF oscillations occurred and I saw
distortion of the PA output when looking in my PA in a DSO with low
levels of 1 KHz signal generator input. I actually remembered to save
these image files as an FFT and a sine wave:<br /><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgemtPKys5pJjsHDGYo0SlZHpELaHPFHwO-kSfebbgggAat-ZRjYzUlJUEFXWXyWqRVnTfxRU_Q4nCkff4f0cNpD1beFgZgvLXpS6l9KFePTGJjb7ngJwesSTFRY4WmeUXxXRFcEboBSXoCKKMRAan8SyHmeRBXD9mMXDfJvRyL7H8fsYJ1N32tv40VdQ/s791/distortion.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="542" data-original-width="791" height="438" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgemtPKys5pJjsHDGYo0SlZHpELaHPFHwO-kSfebbgggAat-ZRjYzUlJUEFXWXyWqRVnTfxRU_Q4nCkff4f0cNpD1beFgZgvLXpS6l9KFePTGJjb7ngJwesSTFRY4WmeUXxXRFcEboBSXoCKKMRAan8SyHmeRBXD9mMXDfJvRyL7H8fsYJ1N32tv40VdQ/w640-h438/distortion.jpg" width="640" /> </a></div><div class="separator" style="clear: both; text-align: center;"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEihTpBpxmNkM6tGc-VmVaJEFC0ruwutZTLQbJwFQuwGHyj5NOs5Mq6y4vcFSt7ZbBsAza593YVLfx2F6tuf6_oJPCMErQpIDnQfDmOr0sCY8cNn5wYG9MbFVHfODuDpAEyw7U5QqxI2p7KEOVMkXgMZvHpdxSQtrCxRu5wQEmh9hizNR-OQlotzFyl7KA/s799/VAS%20distortion.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="465" data-original-width="799" height="372" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEihTpBpxmNkM6tGc-VmVaJEFC0ruwutZTLQbJwFQuwGHyj5NOs5Mq6y4vcFSt7ZbBsAza593YVLfx2F6tuf6_oJPCMErQpIDnQfDmOr0sCY8cNn5wYG9MbFVHfODuDpAEyw7U5QqxI2p7KEOVMkXgMZvHpdxSQtrCxRu5wQEmh9hizNR-OQlotzFyl7KA/w640-h372/VAS%20distortion.png" width="640" /></a></div></div>Above — Distortion caused by the VAS feedback capacitor that went away when I cranked the input signal up above 10 Vpp. When I removed the cap, no distortion appeared at low levels, but re-emerged at high levels of input drive. I left out the 120 pF feedback cap and instead installed a 10 Ω resistor plus 56 pF shunt capacitors on each arm driving the Darlington complementary power followers. This eradicated all instability at all input signal levels.<br /><br />Sadly, when I built the master volume gain control circuit and connected that up to the PA and then my signal generator to its input, the distortion problem re-emerged! Thus, I added back the 120 pF feedback capacitor and the PA stabilized at all signal levels. Likely, increasing the VAS emitter degeneration would have helped, but I can live with 3 small capacitors stabilizing my PA. I find it best to add stabilizing capacitors after you build and look at your PA with a dummy load, signal generator and DSO (‘scope). Then decide what capacitors you need add to remove HF oscillations. <br /></div><br />Continuing on ... a similar current source biased for 1.77 mA sinks the VAS & output driver stack. I stopped using diodes for biasing the output followers in my PA stages – rather, I prefer to run a single BD-139 with fixed bias for simplicity. The 1K5 resistor going from collector to base gets soldered in. Then, I temporarily solder in a 5K pot between the base and emitter nodes and tweak the pot until the crossover distortion disappears. The pot is then removed and measured with an ohmmeter. <br />A nearest standard value resistor ( in this case 2K7) gets substituted for the pot and then a final check is done with a DSO with or without an FFT as you can see easily crossover distortion in a sine wave on your 'scope. You might even further check this by ear into a speaker while playing single notes on the thicker guitar strings. The voltage across the power follower biasing NPN transistor is just over 2.1 VDC.<div class="separator" style="clear: both; text-align: left;"><br /></div><div class="separator" style="clear: both; text-align: left;">For guitar amp PAs, I now prefer using complimentary Darlington style transistors like the TIP142/147 pair. It simplifies design and works well. Other transistors I may evaluate in the future include the BDX33C/BDX34X, BDW93C/BDW94C and the TIP 127/TIP 122.<br /><br /></div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhiaypGdbTorqzN_mfuPDE5rLpBcZ_n0v58xTgelmvY97985jQ-UkkqxPg7WfTimLYpVuWYYXaiEplQ2uq1bbtYw5lQleSyA559Uv5ALwGZZdyuA9E6qLn8kCdizuczP0vp8bhsw5CJXaHHxSJcfP7LWyDQjnmeH2L1xmr1Yg11mL52SDqSE43uqScfcg/s796/Power%2012-4%20Watts.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="449" data-original-width="796" height="362" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhiaypGdbTorqzN_mfuPDE5rLpBcZ_n0v58xTgelmvY97985jQ-UkkqxPg7WfTimLYpVuWYYXaiEplQ2uq1bbtYw5lQleSyA559Uv5ALwGZZdyuA9E6qLn8kCdizuczP0vp8bhsw5CJXaHHxSJcfP7LWyDQjnmeH2L1xmr1Yg11mL52SDqSE43uqScfcg/w640-h362/Power%2012-4%20Watts.png" width="640" /></a></div></div><p>Above — The maximum clean signal power into a dummy load with all harmonics < 60 dBC. Very happy.</p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgqZTnLuG7blO-f0dRy4ItWxXy7Xca0cuLN7kpLwX81kjzOBreFlCqHwCw6isffYA7Ppua3ooO3adOJbFqmFDlM8faYwefSRq1Ubr01YPpBM8ezeLFZ-pculDKwxDL_IwQMrfj9GG4Mu1vUT9aEKTaZrJaP23ttiQ1hIGm_tG7lCcUgrySTSReGG6Vg8w/s618/r7.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="595" data-original-width="618" height="385" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgqZTnLuG7blO-f0dRy4ItWxXy7Xca0cuLN7kpLwX81kjzOBreFlCqHwCw6isffYA7Ppua3ooO3adOJbFqmFDlM8faYwefSRq1Ubr01YPpBM8ezeLFZ-pculDKwxDL_IwQMrfj9GG4Mu1vUT9aEKTaZrJaP23ttiQ1hIGm_tG7lCcUgrySTSReGG6Vg8w/w400-h385/r7.jpg" width="400" /></a></div><br />Above — Heat sinks fashioned for the TIP 142/147 power follower pair. I ran the amp in test mode with signal generator + dummy load at 10 Watts for 30 minutes and the PA temperature measured ~29 degrees C. Hulky 10 amp transistors on big heat sinks in a low power guitar amp should last a long time.<br /> <p></p><h3 style="text-align: left;"><b>3. Power Supply<br /></b><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj5NusvxMEtaBROiyaPWf2yLCjJW8uiHup0y83_foyLUYXGcZG0RpFo0VS8lUomVx-D6Ps_ya9wfNQGBCPHRo24K4A8AxFW1U1m3x_E40Uu8KBb1lcqinyg_iRYHsqdIsT0iHtUWqvUQGUfsX5l51RZHoe6BcFWj8F0F0q-s9lKWVoge79XwjSuJ69WLg/s730/Oct%2013%20PSW.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="463" data-original-width="730" height="406" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj5NusvxMEtaBROiyaPWf2yLCjJW8uiHup0y83_foyLUYXGcZG0RpFo0VS8lUomVx-D6Ps_ya9wfNQGBCPHRo24K4A8AxFW1U1m3x_E40Uu8KBb1lcqinyg_iRYHsqdIsT0iHtUWqvUQGUfsX5l51RZHoe6BcFWj8F0F0q-s9lKWVoge79XwjSuJ69WLg/w640-h406/Oct%2013%20PSW.png" width="640" /></a></div></h3><div style="text-align: left;"><span style="font-weight: normal;">Above — The split DC voltage power supply. I employ no switch as my amps AC plug into a certified, high-grade, commercial power bar that is turned off and then unplugged when the amp is not in use. Power supplies involve voltage + current that may cause injury, death or fire. Only work on power supplies and/or amplifiers if you are a certified to do so. You incur all liability arising from all electrical equipment problems, accidents, or mistakes. Safety. Safety. Safety.<br /></span></div><div style="text-align: left;"><span style="font-weight: normal;"> </span></div><div style="text-align: left;"><span style="font-weight: normal;">LED apparent brightness is adjusted by the current limiting resistor to each. 1 LED monitors each rail in my designs. Orange = positive is my personal standard. If your PA is self-oscillating, you might even see an LED flicker.<br /><br /></span><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgDo1sz8Fd3r3jBl6_fRfnAov7WYHgrlR6GpArbUC2etvf6wwsO1DNMYH7D5XR3T1k-Jyp-_VP68jbCnsPv-2HLa3Cy8tvB7rbI7d5wNtuFsZbqBRqHMMmxnsoHC5hyCYTfrt-sq-ZiDZskZKS_BZ7bKMsLEP6GRfENCMq12A8e3Sr_oLKHpyab9ndsvg/s586/trans1.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="586" data-original-width="421" height="400" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgDo1sz8Fd3r3jBl6_fRfnAov7WYHgrlR6GpArbUC2etvf6wwsO1DNMYH7D5XR3T1k-Jyp-_VP68jbCnsPv-2HLa3Cy8tvB7rbI7d5wNtuFsZbqBRqHMMmxnsoHC5hyCYTfrt-sq-ZiDZskZKS_BZ7bKMsLEP6GRfENCMq12A8e3Sr_oLKHpyab9ndsvg/w288-h400/trans1.png" width="288" /></a></div><br /></div><div style="text-align: left;"><span style="font-weight: normal;">Above — Twins! I purchased these 2 light, low power transformers for my 2 practice amps. The 25 VAC RMS centre-tapped transformer [1L6625] went into the GAA-12 amp. The 20 VAC RMS transformer will go in an even smaller practice amp for our living room. It will hide it on a bookshelf and drive a 10 inch speaker.<br /><br /></span><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi4rKF28OvQGvSYmpAbF7hfskvmTv6ldgo7mb6ET-Qlanu-ecNAWDHNAe52j3KthlLgFSQLaHJ4o60H-zavoNETSFrRfkyqO2JdTtmcgX00FlUwFglzCh751Wiv49ovp2g9yGXl0FCio42o_znSX5aCKoYpj_Mr2_X0Ve87YoWBYt-aYINOOA5dkJdckw/s559/caps%2033.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="559" data-original-width="481" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi4rKF28OvQGvSYmpAbF7hfskvmTv6ldgo7mb6ET-Qlanu-ecNAWDHNAe52j3KthlLgFSQLaHJ4o60H-zavoNETSFrRfkyqO2JdTtmcgX00FlUwFglzCh751Wiv49ovp2g9yGXl0FCio42o_znSX5aCKoYpj_Mr2_X0Ve87YoWBYt-aYINOOA5dkJdckw/w550-h640/caps%2033.png" width="550" /></a></div><br /></div><div style="text-align: left;"><span style="font-weight: normal;">Above — The genuine Nichicon brand capacitors that went on the power supply board to filter. We now have to worry about bootleg transistors, capacitors, power resistors, linear ICs and more. Such as pain! Caveat emptor.<br /></span></div><div style="text-align: left;"><span style="font-weight: normal;"> </span></div><div style="text-align: left;"><span style="font-weight: normal;">Finally, the op-amp voltage regulators went on their own small PC board:<br /><br /></span></div><div style="text-align: left;"><span style="font-weight: normal;"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj57RhggvKSpXtNhvLVyjrS79bVuvcxH2eHVW9eKMjZ7q11MMvynDTgrAO6GtGHq6BjWVYC3mz9x8AKdBocsBiZG6KJwM_yPGsN1T38Vc1iiaB-eY8OYk2zIyhsc9qkYv_lARQb5atFVCSgBDoRsT0NXh0G3Tx_2AzlCgxOShnUvuy5q0yvxlJO-wJqUA/s645/Op-amp%20power%20supply.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="270" data-original-width="645" height="268" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj57RhggvKSpXtNhvLVyjrS79bVuvcxH2eHVW9eKMjZ7q11MMvynDTgrAO6GtGHq6BjWVYC3mz9x8AKdBocsBiZG6KJwM_yPGsN1T38Vc1iiaB-eY8OYk2zIyhsc9qkYv_lARQb5atFVCSgBDoRsT0NXh0G3Tx_2AzlCgxOShnUvuy5q0yvxlJO-wJqUA/w640-h268/Op-amp%20power%20supply.png" width="640" /></a></div> </span></div><div style="text-align: left;"><span style="font-weight: normal;"> <div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhdaX2ze25Zu4nQklrLqAto2Cc_FuFKMQE7AWC8UUwHmJuospRutxDUX3ho2ODzj4R9e0qgXVTOYd_fdYzzffLDKx0nzQf0h_Yvt4Bnt8p9ySX0h5izjJrLgEe1babH_rjMHS1X-OCSEcgJhJlO_MU5LO8mz5wr6klsWaf96D7neYAO2cYi_nBcRt7Yvw/s871/psw%201.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="657" data-original-width="871" height="482" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhdaX2ze25Zu4nQklrLqAto2Cc_FuFKMQE7AWC8UUwHmJuospRutxDUX3ho2ODzj4R9e0qgXVTOYd_fdYzzffLDKx0nzQf0h_Yvt4Bnt8p9ySX0h5izjJrLgEe1babH_rjMHS1X-OCSEcgJhJlO_MU5LO8mz5wr6klsWaf96D7neYAO2cYi_nBcRt7Yvw/w640-h482/psw%201.jpg" width="640" /></a></div><br />Above — Parts for the op-amp voltage regulators. Again, I overbuild. These hulky, slow transistors will last longer than I will -- and provide extra stiff voltage regulation.</span></div><div style="text-align: left;"><span style="font-weight: normal;"><br /></span></div><div style="text-align: left;"><span style="font-weight: normal;">Continuing on... a couple of the latest amp chassis photos I call the passive tone stack 'bass', the fat control:<br /></span></div><div style="text-align: left;"><span style="font-weight: normal;"> <div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhdvxydwkqY5-jLn1dptXUwp2EDOHe895qod49EZEdqzop295tqe-TZ5dg7Pjd2dimztOdEk-65Na2lSfy9y4bYfBm7QUneGpPYXkKJ5l_cdA9LHt6obRF8GBp4TLizrmqYAbXpr7ZNihPXr6BabVFVF_meYFZNVmayPNOXJpjbw1_s5Dn-2TtBwPs7Mw/s997/amp122.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="661" data-original-width="997" height="424" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhdvxydwkqY5-jLn1dptXUwp2EDOHe895qod49EZEdqzop295tqe-TZ5dg7Pjd2dimztOdEk-65Na2lSfy9y4bYfBm7QUneGpPYXkKJ5l_cdA9LHt6obRF8GBp4TLizrmqYAbXpr7ZNihPXr6BabVFVF_meYFZNVmayPNOXJpjbw1_s5Dn-2TtBwPs7Mw/w640-h424/amp122.jpg" width="640" /></a></div></span></div><div style="text-align: left;"><span style="font-weight: normal;"> </span><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi_cNZcdYOu2WRPGXRiZ3vEI7YPr_Z3enHiT1sHGNPlzwF5lCsDJQKANudnIRNmj9F4Fec2uFcvkLid7HW2r41EbD-a039malUjZeSpqfBL4_lDZVserlYdvh-RXlmHlvO7Jvl3mJA0d1uKSGNTOuphJothYulthD9GrDjvyK8sMJsu0qIv2t9CgMZvpQ/s964/newA2.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="403" data-original-width="964" height="268" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEi_cNZcdYOu2WRPGXRiZ3vEI7YPr_Z3enHiT1sHGNPlzwF5lCsDJQKANudnIRNmj9F4Fec2uFcvkLid7HW2r41EbD-a039malUjZeSpqfBL4_lDZVserlYdvh-RXlmHlvO7Jvl3mJA0d1uKSGNTOuphJothYulthD9GrDjvyK8sMJsu0qIv2t9CgMZvpQ/w640-h268/newA2.jpg" width="640" /></a></div><br /></div><div style="text-align: left;"><span style="font-weight: normal;"></span></div><div style="text-align: left;"><h3 style="text-align: left;"><span style="font-weight: normal;"><b>4. Miscellaneous Bench Notes<br /><br /></b></span></h3><div style="text-align: left;"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh3Z1YSCKdbRlmhECQVVjxbArfGIJvv7enIM4oiWQjwBbajEW1vV0g5KPxcoQa-ZVZmjWTjPqQiSxGe19ehTZWQI6-j_argLxc54URtbzpYvCLNRbDJj7UjrObXHjV_EDXV3VFAOSzeLvUSUdiyGX41RSaDlqFBDUHPJRZXNYJ_3LNNhoV3E7n9TfRTgQ/s697/r4.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="445" data-original-width="697" height="408" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh3Z1YSCKdbRlmhECQVVjxbArfGIJvv7enIM4oiWQjwBbajEW1vV0g5KPxcoQa-ZVZmjWTjPqQiSxGe19ehTZWQI6-j_argLxc54URtbzpYvCLNRbDJj7UjrObXHjV_EDXV3VFAOSzeLvUSUdiyGX41RSaDlqFBDUHPJRZXNYJ_3LNNhoV3E7n9TfRTgQ/w640-h408/r4.jpg" width="640" /></a></div></div><div style="text-align: left;"> </div><div style="text-align: left;">Above — A bench test jig that contains a TIP 142 and TIP 147 pair that I use for PA board development.</div><div style="text-align: left;"><br /><span style="font-weight: normal;"><b></b></span></div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiE3mUGDp7KfP3N7x3XH_mbf3WZ6kD12Vr_bnBOYP9tMLdUJo1JXMrtG7BO4hAKdZlCVeSnLfuLF5zlX8CWQh8jdk-x6QEp9i6_vOLD9MTWaaz3W6ybgrqha2zq32OYV8JxlIVz3llYfaQWG0zOm7bYLOoEO7cRgPq1spWrqwFJMUj7fbQrESmy_N9JGw/s609/r-1.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="362" data-original-width="609" height="380" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiE3mUGDp7KfP3N7x3XH_mbf3WZ6kD12Vr_bnBOYP9tMLdUJo1JXMrtG7BO4hAKdZlCVeSnLfuLF5zlX8CWQh8jdk-x6QEp9i6_vOLD9MTWaaz3W6ybgrqha2zq32OYV8JxlIVz3llYfaQWG0zOm7bYLOoEO7cRgPq1spWrqwFJMUj7fbQrESmy_N9JGw/w640-h380/r-1.jpg" width="640" /></a></div></div><div style="text-align: left;"><div style="text-align: left;"> </div>Above — The reverse view of the PA test jig seen from the opposite angle. It contains a pair of 0.22 Ω resistors, a Zobel network and an isolated speaker jack. The yellow wire passes through to the 0 volt centre rail. <br /><br /></div><div style="text-align: left;"></div><div style="text-align: left;"></div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhfp3wiKeotTtAQ4dbdUs1NvhTMKLalLZWlbP-E3oIbh3ycQ2HYwwuKRj5HlRRU-1Lm6-LxkSJZNjtoPi2gCkKt9EVaVyTk1gTgwJfi5Lr0XyCbT99ZBvTOP3EoCVL8Qlr1ia4N15xjLcjDxq6Q3mlh7CxLz9Qjn9J6fIDiZ7sBhwQVqm3rbax221vr9A/s1041/r6.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="815" data-original-width="1041" height="502" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhfp3wiKeotTtAQ4dbdUs1NvhTMKLalLZWlbP-E3oIbh3ycQ2HYwwuKRj5HlRRU-1Lm6-LxkSJZNjtoPi2gCkKt9EVaVyTk1gTgwJfi5Lr0XyCbT99ZBvTOP3EoCVL8Qlr1ia4N15xjLcjDxq6Q3mlh7CxLz9Qjn9J6fIDiZ7sBhwQVqm3rbax221vr9A/w640-h502/r6.png" width="640" /></a></div><br /><div style="text-align: left;">Above — The GAA -12 PA board under test with 1 or 2 temporary parts attached. Since the PA transistors are normally mounted in heat sinks in your amp chassis & connected with wire or PC board paths to the rest of the PA circuitry, this test jig mimics them well. You can instant tell if you made a mistake or parts are broken etc.. </div><div style="text-align: left;">When I mounted the PA board in the amp chassis and the PNP transistor did not work, I knew it was not the PA board at fault. It turns out that the 0.22 Ω power resistor connected to the PNP follower inside the amp chassis was open circuit. I didn't have any more, so, then changed both to 0.1 Ω emitter resistors as I had several of these in stock. From now on, I'm sticking with Vishay brand wire wound resistors as bootleg power resistors have sadly made their way into our parts bins. I prefer 0.22 Ω emitter resistors to boost stability in the power follower pair.<br /></div><div style="text-align: left;"> </div><div style="text-align: left;"><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgAQmeZ_eei7hOGDpZEfq3zXY83LCnZmWTnq6YZatvKGYce0BDyWEYXpFsG8lvnD2pkNEnjTSwiQsj9HkAjl4PonQTRtsQtJATwnQiQCzPmagh90e4AQyiAYnXg1qYhDlxz4RksCQsu2NtNhpILuZGN0KuHXBc6LAszkn0klh1eHzjxq-io05Tf2GDGHQ/s1147/v%20reg1.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="783" data-original-width="1147" height="436" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgAQmeZ_eei7hOGDpZEfq3zXY83LCnZmWTnq6YZatvKGYce0BDyWEYXpFsG8lvnD2pkNEnjTSwiQsj9HkAjl4PonQTRtsQtJATwnQiQCzPmagh90e4AQyiAYnXg1qYhDlxz4RksCQsu2NtNhpILuZGN0KuHXBc6LAszkn0klh1eHzjxq-io05Tf2GDGHQ/w640-h436/v%20reg1.jpg" width="640" /></a></div></div><div style="text-align: left;"></div><div style="text-align: left;"><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjdSUXL-HSQ4KAOhJHjQy1E-dm_nmt9JoFFteZsEqUfTdnUVgWCTUtpJ1UZpQMZFGtZdhBvpIaqBlXYntCESLbxIo_JOgY9nl0DyjJHRJhI3YUTbSYvsihF8BG7jTdZIBc-IQDuGp_V5YM6xDiKKs9wuoKoD7qndkuCZkMi9L_bQNpHnnv5Dm8HNPwuZA/s1007/vREG%202.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="753" data-original-width="1007" height="478" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjdSUXL-HSQ4KAOhJHjQy1E-dm_nmt9JoFFteZsEqUfTdnUVgWCTUtpJ1UZpQMZFGtZdhBvpIaqBlXYntCESLbxIo_JOgY9nl0DyjJHRJhI3YUTbSYvsihF8BG7jTdZIBc-IQDuGp_V5YM6xDiKKs9wuoKoD7qndkuCZkMi9L_bQNpHnnv5Dm8HNPwuZA/w640-h478/vREG%202.jpg" width="640" /></a></div> <br /></div><div style="text-align: left;">Above 2 pictures — The transformer and power supply, input, master volume/ DC regulator & PA boards -- plus the heat sinks all mounted in the chassis. The guitar amp input is as far away from the power supply as possible.</div><div style="text-align: left;"><br /></div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhNVVUcUK0QZ19YSAwWYfxx0YGbjM5GP5LhUmNzl12yBdt-rJGXRzjnm1rd1XCtx9NcCWI5fTK_32BbAYJntU0eFkG4yz1tpNkzpKN35E0NnBmk_XrilSHCgUnakQiQ7-ZRSilG7EUtM1f2SMQ25butCNpLg-rccNHqM0Cl1it8913JRnMwIUfvVkK78g/s911/ts2.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="357" data-original-width="911" height="250" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhNVVUcUK0QZ19YSAwWYfxx0YGbjM5GP5LhUmNzl12yBdt-rJGXRzjnm1rd1XCtx9NcCWI5fTK_32BbAYJntU0eFkG4yz1tpNkzpKN35E0NnBmk_XrilSHCgUnakQiQ7-ZRSilG7EUtM1f2SMQ25butCNpLg-rccNHqM0Cl1it8913JRnMwIUfvVkK78g/w640-h250/ts2.jpg" width="640" /></a></div><br /><div style="text-align: left;">Above — Reverse view of the the entire preamp module under development. This likens a blank canvas with 2 op amps plus all the potentiometers installed. It's now up to you to install the right combination of resistors + capacitors to make a nice guitar amp. It's really that simple in 1 aspect. This entire module goes into the amp chassis and the pots line up with the holes drilled in the metal chassis.<br /><br /></div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh8E6p1Ejaf4N3G8Fqipo7A5KoL-iTzD2pI12kfUqBQu5kjtzXVtXc5LPnlpp54ZRAggjwSsZv9pwWMg4siwvC3yXxtYXQlJ4UzajK4aXnOrIrO73bvLkHW9o3qbA6J5uM7QuzMK3t9ANG_TaNYJnIv-2n4MMivBMCkygyrVIOyKtxbn2D_fwc73QVJeg/s1019/guitar%201.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="783" data-original-width="1019" height="492" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh8E6p1Ejaf4N3G8Fqipo7A5KoL-iTzD2pI12kfUqBQu5kjtzXVtXc5LPnlpp54ZRAggjwSsZv9pwWMg4siwvC3yXxtYXQlJ4UzajK4aXnOrIrO73bvLkHW9o3qbA6J5uM7QuzMK3t9ANG_TaNYJnIv-2n4MMivBMCkygyrVIOyKtxbn2D_fwc73QVJeg/w640-h492/guitar%201.jpg" width="640" /></a></div><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEix0dnEXFjHKAWdDQIIEvST1p52uLmEghKJ9zSAxm8jlfgjoxZCDq0xSuf71Y-vWniqLmNulRGqBhO1YCcpZ39GGvfSQIeBHgqmuww2Hp8hAVF-qdf3VYIpaAs3iDwcnieLhkheMluhs9sfITHzQlH1_3JRoo9GOfWdg5Ymk4rNdQlgOi_BsjywZ-TsVQ/s1001/newAmp2.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="783" data-original-width="1001" height="500" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEix0dnEXFjHKAWdDQIIEvST1p52uLmEghKJ9zSAxm8jlfgjoxZCDq0xSuf71Y-vWniqLmNulRGqBhO1YCcpZ39GGvfSQIeBHgqmuww2Hp8hAVF-qdf3VYIpaAs3iDwcnieLhkheMluhs9sfITHzQlH1_3JRoo9GOfWdg5Ymk4rNdQlgOi_BsjywZ-TsVQ/w640-h500/newAmp2.jpg" width="640" /></a></div><p></p><div style="text-align: left;"></div><div style="text-align: left;"></div><div style="text-align: left;"></div><div style="text-align: left;"><h3 style="text-align: left;"><b>5. Video Links </b>(only 1, but more coming eventually later)<br /></h3><div style="text-align: left;"><span style="color: #2b00fe;"><span style="font-weight: normal;">My videos look better on YouTube proper</span></span></div><div style="text-align: left;"><span style="color: #2b00fe;"><span style="font-weight: normal;"> </span></span><br /></div>The only video so far is this short 1 already posted on Oct 22, 2022 <br /></div><div style="text-align: left;"> </div><div style="text-align: left;"><div class="separator" style="clear: both; text-align: center;"><iframe allowfullscreen="" class="BLOG_video_class" height="354" src="https://www.youtube.com/embed/E6uRSB0CJyw" width="426" youtube-src-id="E6uRSB0CJyw"></iframe> </div><div class="separator" style="clear: both; text-align: center;"> </div><div class="separator" style="clear: both; text-align: left;"> </div><div class="separator" style="clear: both; text-align: left;">My YouTube Page : <a href="https://www.youtube.com/channel/UC_QonLhYyvpBoD-Pz1wnnqA" target="">QRPHB YouTube</a><br /></div><div class="separator" style="clear: both; text-align: left;"><br />My Guitar-related Index : <a href="https://qrp-popcorn.blogspot.com/p/guitar-related-index.html" target="_blank">Click</a></div></div><div style="text-align: left;"> </div><div style="text-align: left;">Ciao!<br /></div><br />Vasily Ivanenkohttp://www.blogger.com/profile/17387516134063150119noreply@blogger.com0tag:blogger.com,1999:blog-3480228403403435266.post-28480203966231339542022-10-10T14:49:00.017-07:002022-10-10T16:27:00.132-07:00QRPHB Check In<p>Despite my rare posts — and sadly lacking much time for QRPHB, this blog enjoys reasonable traffic and I gratefully enjoy email from readers all over the world. Thank you !</p><p>Although home brew radio electronics remains a passion for me, component-level hobbyist radio electronics lies past its prime. Digital devices pushing ever higher frequencies = the new frontier as hardware plus software radio excites newer generations of builders. Craving simpler times, where we get to bias transistors and perhaps implement long-obsolete parts, some of us enjoy more nostalgic creativity — and prefer making radio gear from solid state parts. </p><p>Although I enjoy them all, it seems that many nostalgic ‘transistor plus resistor’ or tube RF circuits enthusiasts rarely seem to move beyond their comfort zone of LF - HF? I recall reading many wonderful VHF and UHF hardware projects in Ham Radio-related magazines in the 1980s into the 2000s. Where did this interest go? I do feel inspired by the modern-day Low Frequency Experimental Radio buffs who “get it done” despite the many challenges they face.<br /><br />Perhaps ironically, we modern time solid-state builders enjoy an abundance of cheap, digital-based bench test equipment like never before. <br /></p><p>QRPHB promotes hobbyist diversity and seeking knowledge. Like you, I’ve got many geeky ideas and interests and have way more questions than answers. We also champion inclusiveness – tribalism is tearing apart society. Whoever you are, whatever your hobby interests — this is a safe space to read, think and to question for all.<br /> <br />Lately, guitar amplifier-related hits dominate the blog. Please see a snippet of data from the past week below: <br /></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiizX9heXlRxctlHzYjhC0XXdYOTN1oOiBZt77_ErumxkAUZ1zNLR66ZHYz3I2JjKednhpMO7Yd1DX7HmfivOJOp-30Hk6oC0PupOjXmWmG0zn1lPgA2JFynAYlu6Zz1JsR_wahUQYOeKRM90RHc0Xuig3XfYkwW8xGLqhcCWGw_WCsKDp3cbXEhqSrGA/s696/blog%20data.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="470" data-original-width="696" height="432" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiizX9heXlRxctlHzYjhC0XXdYOTN1oOiBZt77_ErumxkAUZ1zNLR66ZHYz3I2JjKednhpMO7Yd1DX7HmfivOJOp-30Hk6oC0PupOjXmWmG0zn1lPgA2JFynAYlu6Zz1JsR_wahUQYOeKRM90RHc0Xuig3XfYkwW8xGLqhcCWGw_WCsKDp3cbXEhqSrGA/w640-h432/blog%20data.png" width="640" /></a></div>Above — Unique visits to QRPHB plus the 2 topped rank blog posts from Oct 3 to today, Oct 10 (well most of today). Guitar amplifier interest beats out RF by far. I only got 2 comments, but garnered 18 emails. I answer all emails and enjoy engaging with others about our geeky hobby pursuits.<br /><p></p><p>I’ve got many ideas to share and also much to learn about making jazz guitar amplifiers.<br /> <br />Here, once again, a small group of enthusiasts choose to make solid-state analog devices in a very tube dominated, plus digital guitar amp world. I think the best future home brew jazz guitar amps will involve digital, plus analog circuitry (and perhaps might include a single 12AX7) to give you that boss, sweet, bluesy guitar tone! In the distant future, after learning how, I will add sound bites on YouTube so you can hear my amps in action.<br /> <br />Behind the scenes at QRPHB live some amazing family members doing some cool but very geeky things. 1 particular area of interest for us is indoor air quality — specifically using data to test the effectiveness of our indoor air quality interventions such as filtration. </p><p></p><div class="separator" style="clear: both; text-align: center;"></div><div class="separator" style="clear: both; text-align: center;"></div><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgsBzvbVwMh4Po4WNuT1S9HOrC5EVJHUiCq_4xcqjEtYnFbSdmS08pAm9mE2X9ETqV56HL0U5Z8aW206PfqeYvFvHqEArga3yT8n6WBAAV6rCCx0J83-PsvRpnYNxnacnB44WhXd8YsDPwo3RhCRqR5HrxqqLvQBz80-61Ei90u-OHZq408k6_3S1QMgA/s2384/start1.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1162" data-original-width="2384" height="312" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgsBzvbVwMh4Po4WNuT1S9HOrC5EVJHUiCq_4xcqjEtYnFbSdmS08pAm9mE2X9ETqV56HL0U5Z8aW206PfqeYvFvHqEArga3yT8n6WBAAV6rCCx0J83-PsvRpnYNxnacnB44WhXd8YsDPwo3RhCRqR5HrxqqLvQBz80-61Ei90u-OHZq408k6_3S1QMgA/w640-h312/start1.png" width="640" /></a></div><p>Above — Stuart's air quality system lying on the sand with a local admirer. Not many builders get wildlife inspecting their projects.<br /></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhrXdnhNdtH91EKpPi99NG-CkbzGni9ruMRy2_UXceegUg5dw2q94QTakE_Xn1jxiNSkZbKZ0vaoL21JZ4C1yWRl8huRps7u5OeC_IzVQRlNI3Izo_X7o6yZL3v5Uxxzfnob1wCgYjXamkRP0CgzryiDHq7WOxA-TBK9WzOq7-eJ8hhvsUK5yyWlGMzBQ/s2386/start2.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1918" data-original-width="2386" height="514" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhrXdnhNdtH91EKpPi99NG-CkbzGni9ruMRy2_UXceegUg5dw2q94QTakE_Xn1jxiNSkZbKZ0vaoL21JZ4C1yWRl8huRps7u5OeC_IzVQRlNI3Izo_X7o6yZL3v5Uxxzfnob1wCgYjXamkRP0CgzryiDHq7WOxA-TBK9WzOq7-eJ8hhvsUK5yyWlGMzBQ/w640-h514/start2.png" width="640" /></a></div><p>Above — A close up of Stuart's indoor air quality monitoring system. I feel amazed that we can measure particles below 5 microns --- let alone 0.3 µ</p><p>Here are a couple of URLs:</p><p><a href="https://www.waveshare.com/wiki/Pico-Environment-Sensor">https://www.waveshare.com/wiki/Pico-Environment-Sensor</a><br /></p><p><a href="https://www.adafruit.com/product/4632">https://www.adafruit.com/product/4632<br /></a><br />I’m also interested is radio astronomy and space weather. I like and support the GRAPE project:</p><p>SPACE WEATHER<br /><br />Grape Version 1: First prototype of the low-cost personal space weather station receiver<br /><br />pdf file for free download at<br /><a href="https://www.sciencedirect.com/science/article/pii/S2468067222000347">https://www.sciencedirect.com/science/article/pii/S2468067222000347</a><br /></p><p><b>ABSTRACT</b><br /><br />Crowd sourced data collection among the international community of amateur radio operators and shortwave listeners has great potential for addressing problems of under-sampling in the geospace system. <br /><br />Quantitative Doppler measurements of high frequency (HF) time standard stations, used in bottom side ionospheric sensing, have been accomplished using existing radio hardware belonging to volunteers in distributed campaigns. However, typical shortwave receivers cannot be put to ordinary use while these measurements are being taken, do not have standardized signal chains, and are generally too expensive to be purchased for the sole purpose of taking Doppler measurements. <br /><br />Here, we provide documentation for a low-cost intermediate frequency receiver, the Grape Version 1, which is designed specifically for measurements of North American time standard stations. Grape receivers can be easily constructed and deployed by amateur scientists in order to gain a deeper understanding of variations in radio propagation in their local environment. When compared over long periods and across distributed networks of stations, the resulting data yield insights on greater spatial and time scales. At the time of writing, several of these receivers have been deployed across the United States and are actively collecting data. These receivers form the first iteration of the Low-Cost Personal Space Weather Station network.<br /><br />Gibbons, J., Collins, K., Kazdan, D., & Frissell, N. (2022). Grape Version 1: First prototype of the low-cost personal space weather station receiver. HardwareX, 11. https://doi.org/10.1016/j.ohx.2022.e00289<br /></p><p><br /></p>Vasily Ivanenkohttp://www.blogger.com/profile/17387516134063150119noreply@blogger.com1tag:blogger.com,1999:blog-3480228403403435266.post-52789700691352752452022-10-08T13:21:00.039-07:002023-11-20T12:07:28.702-08:00Some Analog IC Gilbert Cell Mixer Notes<p><span style="font-size: medium;"> <b><span style="color: black; mso-themecolor: text1;">Introduction</span></b></span></p><p><span style="font-size: small;"><span style="color: red; mso-themecolor: text1;">Updated April 2, 2023 </span><span style="color: red; mso-themecolor: text1;">— scroll to the bottom for addendum</span></span>
</p><p class="MsoNormal"><span style="color: black; mso-themecolor: text1;">I love
working with analog ICs. For example, op-amps, sensors, audio PA chips — and of
course the parts we apply as modulators/demodulators and mixers for frequency
translation. Analog ICs using BJTs or MOS devices tend to contain 3 main
components: [1] differential amplifiers [2] various types of emitter or source
followers [3] constant current sources. In the case of bipolar transistors (which I'll write about), I use
the terms emitter-coupled pairs (ECPs) and differential pairs interchangeably in
this blog post. <br /></span></p>
<p class="MsoNormal"><span style="color: black; mso-themecolor: text1;">Let’s focus
on frequency translation with the so-called four quadrant analog multiplier
that many refer to as the Gilbert cell mixer. Others may call it the
Jones-Gilbert mixer since H.E. Jones had patented a similar layout prior to B.
Gilbert’s 1968 paper [Reference 1].<span style="mso-spacerun: yes;"> </span></span></p><p class="MsoNormal"><span style="color: black; mso-themecolor: text1;">It’s
called 4 quadrant because in addition to 2 outputs, there are 2 inputs (X and Y)
with 4 possible differential signal combinations: +X, +Y;<span style="mso-spacerun: yes;"> </span>-X, +Y ;<span style="mso-spacerun: yes;">
</span>-X, -Y and +X, -Y<span style="mso-spacerun: yes;"> </span>where +/-
refers to the polarity of the AC waveform at the LO and RF inputs. A mixer switching
transistor switches to an open or closed state by the polarity of the AC LO
signal applied to its base.</span></p>
<p class="MsoNormal"><span style="font-size: medium;"><b><span style="color: black; mso-themecolor: text1;">Gilbert Cell
Pros/Advantages</span></b></span></p>
<p></p><ul style="text-align: left;"><li><span style="color: black; mso-themecolor: text1;">RF to IF Conversion
gain with double balance ( the main reason to use them )<br /></span></li><li><span style="color: black; mso-themecolor: text1;">May have wide
bandwidth in newer design monolithic ICs</span></li><li><span style="color: black; mso-themecolor: text1;">Eliminates
common mode noise</span></li></ul><p>
</p><p class="MsoNormal"><span style="font-size: medium;"><b><span style="color: black; mso-themecolor: text1;">Gilbert Cell
Cons/Disadvantages</span></b></span></p>
<p></p><ul style="text-align: left;"><li><span style="color: black; mso-themecolor: text1;">More flicker
noise than passive ring topology mixers which typically offer better low
frequency noise performance </span></li></ul><p></p><p class="MsoNormal" style="margin-left: 40px; text-align: left;"><span style="color: black; mso-themecolor: text1;">
Devices including semiconductors exhibit low frequency noise that is inversely
proportional to frequency that’s called 1/f, flicker, or contact noise. 1/f literally
means flicker noise is greater when frequency is lower. In the case of BJTs, this
low frequency voltage fluctuation (noise) likely gets produced when base
current flows through the rbb or base spreading resistance of the mixer ECPs
and interacts with microscopic contact + surface imperfections in the
substrate.<br />
<br />
Flicker noise adds to the mixer noise figure and proves even more vexing with
direct conversion architectures since these mix down to audio frequency — and any low
frequency base band noise (such as flicker noise) gets amplified in the audio signal chain. Flicker noise is
worse in Metal Oxide Semiconductor (MOS) transistors than in BJTs [Reference 2].</span></p>
<p class="MsoNormal" style="margin-left: 40px; text-align: left;"><span style="color: black; mso-themecolor: text1;">Modern
Gilbert cell mixer engineers toil relentlessly to reduce flicker noise / mixer noise figure at very
high frequencies.</span></p><p class="MsoNormal" style="margin-left: 40px; text-align: left;"><span style="color: black; mso-themecolor: text1;"><i>Gilbert Cell Cons/Disadvantages continued...</i></span><span style="color: black; mso-themecolor: text1;"> <br /></span></p>
<p></p><ul style="text-align: left;"><li><span style="color: black; mso-themecolor: text1;">A narrow
bandwidth in earlier monolithic ICs.</span></li><li><span style="color: black; mso-themecolor: text1;">Lower dynamic
range than passive ring topology mixers</span></li><li><span style="color: black; mso-themecolor: text1;">Many of the
older and now obsolete designs ran low power [low DC voltage(s) and/or current]
— so they suffer from low IP3 and dynamic range. There were exceptions such as
the venerable Plessey SL6440. </span></li></ul><p>
</p><p class="MsoNormal"><span style="color: black; mso-themecolor: text1;">I do not make
superheterodyne receivers and instead focus on the direct conversion
architectures of zero-IF or low-IF<i>.</i> Thus, an IC such as the SA612 would make
a poor choice for me on the Ham bands since I like to listen to CW pileups on contest
weekends where in amongst weak signal clusters lie abundant strong signals that
would invariably overload my low power IC product detector(s) and make me feel
sad.<span style="mso-spacerun: yes;"> </span></span></p><p class="MsoNormal"><span style="color: black; mso-themecolor: text1;">Then, too, an analog Gilbert cell IC might be OK for use
in a DC receiver used to study the atmosphere or listen to decametric emissions
from Jupiter.</span></p><p></p><p class="MsoNormal"><span style="font-size: medium;"><span style="color: black; mso-themecolor: text1;"> </span><b><span style="color: black; mso-themecolor: text1;">Double
balanced</span></b></span>
</p><p class="MsoNormal">The Gilbert cell mixer is double balanced for LO and RF so,
ideally there should be no LO or RF leakage into the outputs. In reality, port
isolation isn’t perfect and factors including BJT matching and single-ended
versus balanced LO & RF inputs may affect port isolation along with other mixer parameters
such as IP3. However, the Gilbert cell
mixer does not just rely on transformers to give balance; therefore, it still
functions as a double-balanced mixer whether you use single-ended or
differential inputs on the LO and RF ports</p><p class="MsoNormal">Mixer balance affects port to port isolation and more. When unequal currents flow in an ECP, overall cancellation
is reduced. Symmetry is everything in balanced mixers — common mode noise, input signals & even order
harmonics alike get reduced in amplitude through precise 0 to 180 degree phase shift cancellations within the ECPs of the Gilbert cell mixer.<span style="font-size: medium;"><b><span style="color: black; mso-themecolor: text1;"> </span></b></span></p><p class="MsoNormal"><span style="font-size: medium;"><b><span style="color: black; mso-themecolor: text1;">Going…
going… Gong!</span></b></span></p>
<p class="MsoNormal"><span style="color: black; mso-themecolor: text1;">Many classic
Gilbert cell monolithic IC mixers lie obsolete. These include the MC1496,
MC1595, IAM-81028, SL6440, µPC1037, SOP42, TL-442 and AN612. The NE/SA 602 or 612 chip is
still available but must be circling the drain at this point. Still in
production IC packages range from the simple HFA3101BZ96 to the ADL5801-5802,
ADL5380 (I/Q demodulator), MAX2680-MAX2681-MAX2682, SMA5101 and many others.</span></p>
<p class="MsoNormal"><span style="color: black; mso-themecolor: text1;">Like they say — “if you like an analog part now, buy some today because they might not be
around in the days past tomorrow”.</span><span style="color: red;"> </span><span style="color: black; mso-themecolor: text1;">It's worth reflecting that industry
needs dictate the rise & lifespan of parts. Hams and hobbyists latch on to
certain parts while in production and well after they turn obsolete —but it was
never about home brew electronics.</span></p>
<p class="MsoNormal"><span style="color: black; mso-themecolor: text1;">Modern
builders have employed Gilbert multiplier cell mixers into mm-waves in industry
or research. Apart from BJT and MOS devices, in microwave you might see m</span>onolithic
microwave integrated circuit<span style="color: black; mso-themecolor: text1;"> (MMIC)
implementations in InP HBT, SiGe HBT, GaAs HBT and pHEMT high speed technology.<br />
Modern Gilbert cell mixers typically employ low DC voltage, low to moderate
current and very high speeds.</span></p>
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</p><p class="MsoNormal"><span style="font-size: medium;"><b><span style="color: black; mso-themecolor: text1;">Predistortion
and improving linearity in the ECP</span></b></span></p>
<p class="MsoNormal"><span style="color: black; mso-themecolor: text1;">Barry
Gilbert’s version of the 4-quadrant analog multiplier predistorted the LO input
signal of the switching transistors by essentially using diodes to compress the
signal logarithmically. From his 1968 paper describing his experiments, the
terms Gilbert cell or Gilbert mixer arose to popularity [Reference 1]. </span></p>
<p class="MsoNormal"><span style="color: black; mso-themecolor: text1;">For amateur
radio buffs, we may eliminate his linearizing predistortion circuitry plus any DC
offset balancers since as a RF mixer we employ high Q, tuned band-pass circuitry
to remove unwanted frequencies — and as a product detector we use a low-pass
filter network to remove any residual carrier and other RF garbage that leaks
through to the zero-IF or low-IF output(s).</span></p>
<p class="MsoNormal"><span style="font-size: medium;"><b><span style="color: black; mso-themecolor: text1;">The
4-quadrant multiplier proves a versatile analog workhorse circuit</span></b></span></p>
<p class="MsoNormal"><span style="color: black; mso-themecolor: text1;">The versatile
4-quadrant multiplier may be set up to function as a squarer/multiplier, divider/square
rooter, frequency doubler, balanced modulator or demodulator for AM or SSB, an
FM quadrature detector and a variable gain control amongst other tasks. A true
analog workhorse circuit.</span></p>
<p class="MsoNormal"><span style="font-size: medium;"><b><span style="color: black; mso-themecolor: text1;">Gilbert
Cell Mixer Function</span></b></span></p>
<p class="MsoNormal"><span style="color: black; mso-themecolor: text1;">Let’s examine
basic mixer function.</span></p>
<p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhxu0QRoxmoIFNo2lTbaR3hHJQcXL2rEkLi4X6_IQMizokkOJc4VGZEpy34l6vbUYL-fm9yXVkVPCrtSM9fWHKwIGBNTSywvs0kIGbj91IphCszp3ixrEsfcA6CfT4JaTNmY0pQ8c24IkFkw9HZGTRluDp9mVyOcG87eAjHFK9tbnKmqa43iQ3kG_Hf-g/s540/FIG1.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="448" data-original-width="540" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhxu0QRoxmoIFNo2lTbaR3hHJQcXL2rEkLi4X6_IQMizokkOJc4VGZEpy34l6vbUYL-fm9yXVkVPCrtSM9fWHKwIGBNTSywvs0kIGbj91IphCszp3ixrEsfcA6CfT4JaTNmY0pQ8c24IkFkw9HZGTRluDp9mVyOcG87eAjHFK9tbnKmqa43iQ3kG_Hf-g/s16000/FIG1.png" /></a></div><p><!--[if gte mso 9]><xml>
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<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="toa heading"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Bullet"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Number"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Bullet 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Bullet 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Bullet 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Bullet 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Number 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Number 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Number 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Number 5"/>
<w:LsdException Locked="false" Priority="10" QFormat="true" Name="Title"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Closing"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Signature"/>
<w:LsdException Locked="false" Priority="1" SemiHidden="true"
UnhideWhenUsed="true" Name="Default Paragraph Font"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text Indent"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Continue"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Continue 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Continue 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Continue 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Continue 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Message Header"/>
<w:LsdException Locked="false" Priority="11" QFormat="true" Name="Subtitle"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Salutation"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Date"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text First Indent"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text First Indent 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Note Heading"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text Indent 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text Indent 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Block Text"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Hyperlink"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="FollowedHyperlink"/>
<w:LsdException Locked="false" Priority="22" QFormat="true" Name="Strong"/>
<w:LsdException Locked="false" Priority="20" QFormat="true" Name="Emphasis"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Document Map"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Plain Text"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="E-mail Signature"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Top of Form"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Bottom of Form"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Normal (Web)"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Acronym"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Address"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Cite"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Code"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Definition"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Keyboard"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Preformatted"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Sample"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Typewriter"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Variable"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Normal Table"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="annotation subject"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="No List"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Outline List 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Outline List 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Outline List 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Simple 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Simple 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Simple 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Classic 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Classic 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Classic 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Classic 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Colorful 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Colorful 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Colorful 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Columns 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Columns 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Columns 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Columns 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Columns 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 6"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 7"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 8"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 6"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 7"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 8"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table 3D effects 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table 3D effects 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table 3D effects 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Contemporary"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Elegant"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Professional"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Subtle 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Subtle 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Web 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Web 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Web 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Balloon Text"/>
<w:LsdException Locked="false" Priority="39" Name="Table Grid"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Theme"/>
<w:LsdException Locked="false" SemiHidden="true" Name="Placeholder Text"/>
<w:LsdException Locked="false" Priority="1" QFormat="true" Name="No Spacing"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading"/>
<w:LsdException Locked="false" Priority="61" Name="Light List"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 1"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 1"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 1"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 1"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 1"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 1"/>
<w:LsdException Locked="false" SemiHidden="true" Name="Revision"/>
<w:LsdException Locked="false" Priority="34" QFormat="true"
Name="List Paragraph"/>
<w:LsdException Locked="false" Priority="29" QFormat="true" Name="Quote"/>
<w:LsdException Locked="false" Priority="30" QFormat="true"
Name="Intense Quote"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 1"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 1"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 1"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 1"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 1"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 1"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 1"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 1"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 2"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 2"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 2"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 2"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 2"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 2"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 2"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 2"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 2"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 2"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 2"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 2"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 2"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 2"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 3"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 3"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 3"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 3"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 3"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 3"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 3"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 3"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 3"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 3"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 3"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 3"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 3"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 3"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 4"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 4"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 4"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 4"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 4"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 4"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 4"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 4"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 4"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 4"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 4"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 4"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 4"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 4"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 5"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 5"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 5"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 5"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 5"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 5"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 5"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 5"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 5"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 5"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 5"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 5"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 5"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 5"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 6"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 6"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 6"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 6"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 6"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 6"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 6"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 6"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 6"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 6"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 6"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 6"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 6"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 6"/>
<w:LsdException Locked="false" Priority="19" QFormat="true"
Name="Subtle Emphasis"/>
<w:LsdException Locked="false" Priority="21" QFormat="true"
Name="Intense Emphasis"/>
<w:LsdException Locked="false" Priority="31" QFormat="true"
Name="Subtle Reference"/>
<w:LsdException Locked="false" Priority="32" QFormat="true"
Name="Intense Reference"/>
<w:LsdException Locked="false" Priority="33" QFormat="true" Name="Book Title"/>
<w:LsdException Locked="false" Priority="37" SemiHidden="true"
UnhideWhenUsed="true" Name="Bibliography"/>
<w:LsdException Locked="false" Priority="39" SemiHidden="true"
UnhideWhenUsed="true" QFormat="true" Name="TOC Heading"/>
<w:LsdException Locked="false" Priority="41" Name="Plain Table 1"/>
<w:LsdException Locked="false" Priority="42" Name="Plain Table 2"/>
<w:LsdException Locked="false" Priority="43" Name="Plain Table 3"/>
<w:LsdException Locked="false" Priority="44" Name="Plain Table 4"/>
<w:LsdException Locked="false" Priority="45" Name="Plain Table 5"/>
<w:LsdException Locked="false" Priority="40" Name="Grid Table Light"/>
<w:LsdException Locked="false" Priority="46" Name="Grid Table 1 Light"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark"/>
<w:LsdException Locked="false" Priority="51" Name="Grid Table 6 Colorful"/>
<w:LsdException Locked="false" Priority="52" Name="Grid Table 7 Colorful"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 1"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 1"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 1"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 1"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 1"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 1"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 1"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 2"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 2"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 2"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 2"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 2"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 2"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 2"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 3"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 3"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 3"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 3"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 3"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 3"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 3"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 4"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 4"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 4"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 4"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 4"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 4"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 4"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 5"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 5"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 5"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 5"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 5"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 5"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 5"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 6"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 6"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 6"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 6"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 6"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 6"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 6"/>
<w:LsdException Locked="false" Priority="46" Name="List Table 1 Light"/>
<w:LsdException Locked="false" Priority="47" Name="List Table 2"/>
<w:LsdException Locked="false" Priority="48" Name="List Table 3"/>
<w:LsdException Locked="false" Priority="49" Name="List Table 4"/>
<w:LsdException Locked="false" Priority="50" Name="List Table 5 Dark"/>
<w:LsdException Locked="false" Priority="51" Name="List Table 6 Colorful"/>
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</p><p class="MsoNormal">Above — The basic structure of the Gilbert cell mixer. LO is
applied to the X ports and RF to the Y ports.</p>
<p class="MsoNormal">The switch quad (sometimes called the mixer core) Q1- Q4
multiply the linear current from Q5 and Q6 with the switched LO signal.<span style="mso-spacerun: yes;"> </span>Q5 and Q6 provide +/- RF current and Q1 and
Q4 switch alternately to provide normal or inverted output to the Q1 load
resistor while Q2 and Q3 switch alternately to drive the Q4 load resistor with
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</p><p class="MsoNormal"><b>Switch quad [ Q1-Q4 ]</b></p> 2 cross-coupled, parallel, differential BJT pairs form a quad switch<br /><p></p><ul style="text-align: left;"><li>Q1 & Q4, then Q2 & Q3 function as differential pairs within the quad<br /><br /></li><li>The 4 upper transistors go either fully ON or fully OFF in response to LO polarity at each half-cycle of the LO waveform<br /> <br /></li><li>The quad switches multiply the current from each collector of Q5 & Q6 by +1 or -1. Multiplying the RF signal by +1 transfers it to the output with no phase change, while multiplication by -1 inverts the output 180 degrees in phase<br /><br /> </li><li>When the LO signal goes positive in polarity, Q1/Q4 turn ON and Q2/Q3 turn OFF. This flip flops when the LO cycle goes negative in polarity. No change in current occurs in Q5 and Q6. Due to their symmetry, the 2 current arms I-1Y and I +1Y lie equal and opposite — and thus cancel out<br /><br /></li><li>1 collector output node will always receive the negative of the current value at the other output node<br /><br /></li><li>The ideal drive for the upper transistors is a differential square wave of about 0. 9 Vpp. If fed with a sine wave, then Vpp should run about double or triple the 0.9 Vpp square wave amplitude to create a switch quad conductance waveform that mimics a square wave<br /><br /></li><li>In short, ensure that you apply enough LO amplitude to switch the upper transistors ON and OFF quickly<br /><br /></li><li>Ideally feed the quad switch from a low-impedance LO signal source, although that’s not critical. A virtue of the Gilbert cell mixer is that it’s not as fussy about port impedance as a diode ring mixer. You may require quad switch base termination resistors to allow stable drive from your LO signal source. For example; with a single-ended LO input </li></ul><p><b>Transconductance pair [ Q5, Q6 ]</b><br /></p><ul style="text-align: left;"><li>The 2 lower transistors operate linearly like standard differential amplifiers on the RF input signal to convert the RF input voltage into current for the commutating switch quad above</li></ul><p></p><ul style="text-align: left;"><li>For the RF signal path to the lower pair, any base termination such as low-value resistor bias resistors may take away RF signal power from the lower ECP. Base bias resistor values should generally only be as low as required to insure a stable DC bias voltage </li></ul><p></p><ul style="text-align: left;"><li>In IC data sheets, you’ll observe bias resistor values from 120 to 3K3 Ω in single DC supply designs, while several thousand Ω resistors may go from base to ground in split DC supply designs. Experiments and simulation may help you choose your ideal resistor values. Some designs match the lower RF pair input impedance to their RF source Z to boost conversion gain. </li></ul><p></p><p><!--[if gte mso 9]><xml>
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</p><p class="MsoNormal"><span style="font-size: medium;"><b><span style="color: black; mso-themecolor: text1;">Simple bias
resistor versus constant current source</span></b></span></p>
<p class="MsoNormal">The ideal current source offers a <i>fixed </i>current
level, a high output resistance, & low noise. <b><span style="color: black; mso-themecolor: text1;"></span></b></p>
<p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiy1vm_OVuDT0dKSJ4rxLVb9mJDutFMwZtKfmwvRtz-KFWKHqxj7h_tW_vz7vDcILjCQWBE5Q-6gmSxs-B-S6QIDbRe6-fFzcP7-Dtfy4Pcr2vHISYNQ957PhNprwshMxLnCiQkx7VLKiubDEqOpEVmPL0cSe9dY5tDstVyDxtFN_e_Cr8lmSARbF4Iqg/s957/FIG2.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="731" data-original-width="957" height="488" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiy1vm_OVuDT0dKSJ4rxLVb9mJDutFMwZtKfmwvRtz-KFWKHqxj7h_tW_vz7vDcILjCQWBE5Q-6gmSxs-B-S6QIDbRe6-fFzcP7-Dtfy4Pcr2vHISYNQ957PhNprwshMxLnCiQkx7VLKiubDEqOpEVmPL0cSe9dY5tDstVyDxtFN_e_Cr8lmSARbF4Iqg/w640-h488/FIG2.png" width="640" /></a></div>
<p class="MsoNormal"><b><span style="color: black; mso-themecolor: text1;">Figure 2 for
Discussion<span style="mso-spacerun: yes;"> </span><span style="mso-spacerun: yes;"> </span></span></b><span style="color: black; mso-themecolor: text1;">Figures</span><span style="color: black; mso-themecolor: text1;"> A to D show the (lower 2) simple differential amps with a split DC
supply for clarity.</span></p>
<p class="MsoNormal"><span style="color: black; mso-themecolor: text1;">For maximum real-world
performance, IC designers use ECP’s matched for VBE and hFE (Beta). That’s much
easier to do when the transistors come from the same substrate. If you choose to build a Gilbert cell from discrete BJTS — indeed, you should match the discrete transistors that
make up your ECPs. </span></p><p class="MsoNormal"><span style="color: black; mso-themecolor: text1;">With some ICs,
you'll decide whether to use a plain old emitter resistor to provide ‘constant
current’ to your mixer, or to employ a constant current sink device: a
transistor biased with resistors and/or diodes, or used to mirror a separate reference
current.</span></p>
<p class="MsoNormal"><span style="color: black; mso-themecolor: text1;"><b>In Figure A,</b> RE
is a simple resistor and the current flowing through the ECP is determined by
-VEE and RE. The sum of the currents flowing through each ½ of the ECP should ideally
be fixed or constant. In order for that to happen, RE must be a large value
resistor to drop a significant voltage across it. </span></p><p class="MsoNormal"><span style="color: black; mso-themecolor: text1;">This means the corresponding
DC voltage must also be large. Typically, most builders run lower DC voltages
such as 5 to 12 volts with a single power supply rail. Thus, RE falls short as
a constant current source whether running single or split DC supply. It might
be perfectly OK to run RE in bench design work, for low complexity radios, and/or
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</p><p class="MsoNormal"><span style="color: black; mso-themecolor: text1;"><b>Figure B
</b>shows RE replaced by a transistor Q3. We assume that the collector to emitter
current of Q3 is equal to the base to emitter current X the current gain of the
transistor & its current gain is independent of the collector to emitter
voltage. <b><br /><br />Figure C</b> shows Q3 fully biased from the negative rail with included diodes
to boost temperature stability. Since the diodes get fabricated from the same
wafer, they thermally track the ECPs and offset temperature-related current
changes.</span></p>
<p class="MsoNormal"><span style="color: black; mso-themecolor: text1;">
While Figure C is OK, some constant current sources are better than others. A
basic, better-grade and popular constant current source biased with positive DC
is shown in <b>Figure D</b>. This circuit is known as a current mirror and a ‘diode-connected’
BJT (Q3) forms the current mirror. Just like ECP’s, both current mirror
transistors need matching for best results.<br />
<br />
Various forms of improved current mirrors exist and include for example, the
Wilson and Widlar current mirror designs. You may see emitter resistors on both
transistors to help with transistor matching and to raise the effective
collector resistance. Finally, please refer to <b>Figure E</b> to see cascaded current
mirrors in use with a Gilbert cell mixer. An example of this lies in the MC1496.</span></p>
<p class="MsoNormal"><span style="color: black; mso-themecolor: text1;">Input signals
common to both differential amplifier inputs (common mode signals) such as
noise, or stray voltages that drive both inputs will not get amplified since
this is a difference amplifier. In effect, the differential pair rejects common
mode signals — and the better this rejection, the better the balance of the
differential stages are in the amplifier or mixer. Thus, DC current through mixer
ECPs should ideally remain fixed <i>no matter what</i>— and a constant current
source helps achieve this. Other Gilbert cell mixer constant current source benefits
might include improved output linearity, boosted port isolation &
potentially reduced power rail noise.</span></p>
<p class="MsoNormal"><span style="color: black; mso-themecolor: text1;">Thus, a
constant current source marks a big improvement over the plain old resistor RE.
Summarized --- For an ECP, the higher the resistance of its current source, the
lower the common mode gain + the better the common mode rejection ratio.</span></p>
<p class="MsoNormal"><span style="color: black; mso-themecolor: text1;">I have merely
scratched the surface about constant current sources. Abundant constant current
source info lies in books on differential amplifiers + constant current sources
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</p><p class="MsoNormal"><span style="font-size: medium;"><b><span style="color: black; mso-themecolor: text1;">Balanced
or unbalanced input and/or output</span></b></span></p>
<p class="MsoNormal"><span style="color: black; mso-themecolor: text1;">We’ve got
decisions to make. Considering the external RF or LO stages that drive our Gilbert
cell mixer – plus whatever stage is going to receive the mixer’s output, we’ve
got the following choices:</span></p><div style="margin-left: 40px; text-align: left;">[1] LO and RF Mixer Input Ports <br /></div><div style="margin-left: 40px; text-align: left;"><ul style="text-align: left;"><li>single ended LO and RF output to single ended mixer LO and RF input</li><li>single ended LO and RF output to differential mixer LO and RF input</li><li>differential LO and RF output to differential mixer LO and RF input </li><li>a hybrid combination – different drive strategies for the LO and RF ports</li></ul></div><div style="margin-left: 40px; text-align: left;">A lot of choices! Once again, you’ll decide how you feed your LO and RF ports. Single ended inputs ranks as very popular with home builders. Myself, I prefer differential LO & RF drive using a balun transformer with the primary to secondary turns ratio providing the input match to the RF and LO single-ended signal sources. The SA612 and ilk data sheet has a wonderful section showing the various ways to input signals into a Gilbert cell mixer. I recommend you download this data sheet along with the data sheets of the other IC mixers I have mentioned in this blog post. Data sheet study remains a proven way to learn more about electronic devices + circuitry.<br /></div><p></p><p style="margin-left: 40px; text-align: left;">[2] Mixer Output Ports<br /></p><ul style="text-align: left;"><li>single ended output off 1 collector</li><li>differential output using both collectors to either a single ended or differential post- mixer input stage</li><li>collector resistors versus transformer for the output whether single ended or differential output</li><li>broadband versus tuned collectors if using an output transformer</li></ul><p style="margin-left: 40px; text-align: left;">I favor differential output using a center-tapped transformer which doubles your output power over a single ended output. However, then you’ve got to make or purchase a center tapped transformer that will also step down the high collector impedance to something close to your post transformer device input impedance. This might even involve you winding a trifilar transformer on a ferrite toroid. Many experimenters evidently suffer an inflammatory disease known as TTA [ Trifilar Transformer Allergy]. For them, a trifilar transformer crosses the line.<br /><br />Wouldn’t it be easier to just apply a simple resistor to convert that collector current into a voltage and then not have to mess with a transformer? Yes. There are always trade-offs — plus your needs may vary. What are you using the mixer for? If it’s just a transmit mixer, I may just use a resistor and feel OK with dropping my conversion gain by half. But that might not be OK for a receiver. Since a major reason to employ a Gilbert cell mixer is to get mixer conversion gain, I tend to go with differential output to either a single ended or differential input next stage in my receivers. Your needs may vary.</p><p style="text-align: left;"><span style="font-size: medium;"><b> Datasheet Studies</b></span><br /></p><p style="text-align: left;"><!--[if gte mso 9]><xml>
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<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Date"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text First Indent"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text First Indent 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Note Heading"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text Indent 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text Indent 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Block Text"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Hyperlink"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="FollowedHyperlink"/>
<w:LsdException Locked="false" Priority="22" QFormat="true" Name="Strong"/>
<w:LsdException Locked="false" Priority="20" QFormat="true" Name="Emphasis"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Document Map"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Plain Text"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="E-mail Signature"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Top of Form"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Bottom of Form"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Normal (Web)"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Acronym"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Address"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Cite"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Code"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Definition"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Keyboard"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Preformatted"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Sample"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Typewriter"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Variable"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Normal Table"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="annotation subject"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="No List"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Outline List 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Outline List 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Outline List 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Simple 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Simple 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Simple 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Classic 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Classic 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Classic 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Classic 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Colorful 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Colorful 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Colorful 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Columns 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Columns 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Columns 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Columns 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Columns 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 6"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 7"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 8"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 6"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 7"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 8"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table 3D effects 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table 3D effects 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table 3D effects 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Contemporary"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Elegant"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Professional"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Subtle 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Subtle 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Web 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Web 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Web 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Balloon Text"/>
<w:LsdException Locked="false" Priority="39" Name="Table Grid"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Theme"/>
<w:LsdException Locked="false" SemiHidden="true" Name="Placeholder Text"/>
<w:LsdException Locked="false" Priority="1" QFormat="true" Name="No Spacing"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading"/>
<w:LsdException Locked="false" Priority="61" Name="Light List"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 1"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 1"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 1"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 1"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 1"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 1"/>
<w:LsdException Locked="false" SemiHidden="true" Name="Revision"/>
<w:LsdException Locked="false" Priority="34" QFormat="true"
Name="List Paragraph"/>
<w:LsdException Locked="false" Priority="29" QFormat="true" Name="Quote"/>
<w:LsdException Locked="false" Priority="30" QFormat="true"
Name="Intense Quote"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 1"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 1"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 1"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 1"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 1"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 1"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 1"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 1"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 2"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 2"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 2"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 2"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 2"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 2"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 2"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 2"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 2"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 2"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 2"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 2"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 2"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 2"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 3"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 3"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 3"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 3"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 3"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 3"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 3"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 3"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 3"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 3"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 3"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 3"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 3"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 3"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 4"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 4"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 4"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 4"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 4"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 4"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 4"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 4"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 4"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 4"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 4"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 4"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 4"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 4"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 5"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 5"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 5"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 5"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 5"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 5"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 5"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 5"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 5"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 5"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 5"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 5"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 5"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 5"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 6"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 6"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 6"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 6"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 6"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 6"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 6"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 6"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 6"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 6"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 6"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 6"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 6"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 6"/>
<w:LsdException Locked="false" Priority="19" QFormat="true"
Name="Subtle Emphasis"/>
<w:LsdException Locked="false" Priority="21" QFormat="true"
Name="Intense Emphasis"/>
<w:LsdException Locked="false" Priority="31" QFormat="true"
Name="Subtle Reference"/>
<w:LsdException Locked="false" Priority="32" QFormat="true"
Name="Intense Reference"/>
<w:LsdException Locked="false" Priority="33" QFormat="true" Name="Book Title"/>
<w:LsdException Locked="false" Priority="37" SemiHidden="true"
UnhideWhenUsed="true" Name="Bibliography"/>
<w:LsdException Locked="false" Priority="39" SemiHidden="true"
UnhideWhenUsed="true" QFormat="true" Name="TOC Heading"/>
<w:LsdException Locked="false" Priority="41" Name="Plain Table 1"/>
<w:LsdException Locked="false" Priority="42" Name="Plain Table 2"/>
<w:LsdException Locked="false" Priority="43" Name="Plain Table 3"/>
<w:LsdException Locked="false" Priority="44" Name="Plain Table 4"/>
<w:LsdException Locked="false" Priority="45" Name="Plain Table 5"/>
<w:LsdException Locked="false" Priority="40" Name="Grid Table Light"/>
<w:LsdException Locked="false" Priority="46" Name="Grid Table 1 Light"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark"/>
<w:LsdException Locked="false" Priority="51" Name="Grid Table 6 Colorful"/>
<w:LsdException Locked="false" Priority="52" Name="Grid Table 7 Colorful"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 1"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 1"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 1"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 1"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 1"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 1"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 1"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 2"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 2"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 2"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 2"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 2"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 2"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 2"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 3"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 3"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 3"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 3"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 3"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 3"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 3"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 4"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 4"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 4"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 4"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 4"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 4"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 4"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 5"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 5"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 5"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 5"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 5"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 5"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 5"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 6"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 6"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 6"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 6"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 6"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 6"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 6"/>
<w:LsdException Locked="false" Priority="46" Name="List Table 1 Light"/>
<w:LsdException Locked="false" Priority="47" Name="List Table 2"/>
<w:LsdException Locked="false" Priority="48" Name="List Table 3"/>
<w:LsdException Locked="false" Priority="49" Name="List Table 4"/>
<w:LsdException Locked="false" Priority="50" Name="List Table 5 Dark"/>
<w:LsdException Locked="false" Priority="51" Name="List Table 6 Colorful"/>
<w:LsdException Locked="false" Priority="52" Name="List Table 7 Colorful"/>
<w:LsdException Locked="false" Priority="46"
Name="List Table 1 Light Accent 1"/>
<w:LsdException Locked="false" Priority="47" Name="List Table 2 Accent 1"/>
<w:LsdException Locked="false" Priority="48" Name="List Table 3 Accent 1"/>
<w:LsdException Locked="false" Priority="49" Name="List Table 4 Accent 1"/>
<w:LsdException Locked="false" Priority="50" Name="List Table 5 Dark Accent 1"/>
<w:LsdException Locked="false" Priority="51"
Name="List Table 6 Colorful Accent 1"/>
<w:LsdException Locked="false" Priority="52"
Name="List Table 7 Colorful Accent 1"/>
<w:LsdException Locked="false" Priority="46"
Name="List Table 1 Light Accent 2"/>
<w:LsdException Locked="false" Priority="47" Name="List Table 2 Accent 2"/>
<w:LsdException Locked="false" Priority="48" Name="List Table 3 Accent 2"/>
<w:LsdException Locked="false" Priority="49" Name="List Table 4 Accent 2"/>
<w:LsdException Locked="false" Priority="50" Name="List Table 5 Dark Accent 2"/>
<w:LsdException Locked="false" Priority="51"
Name="List Table 6 Colorful Accent 2"/>
<w:LsdException Locked="false" Priority="52"
Name="List Table 7 Colorful Accent 2"/>
<w:LsdException Locked="false" Priority="46"
Name="List Table 1 Light Accent 3"/>
<w:LsdException Locked="false" Priority="47" Name="List Table 2 Accent 3"/>
<w:LsdException Locked="false" Priority="48" Name="List Table 3 Accent 3"/>
<w:LsdException Locked="false" Priority="49" Name="List Table 4 Accent 3"/>
<w:LsdException Locked="false" Priority="50" Name="List Table 5 Dark Accent 3"/>
<w:LsdException Locked="false" Priority="51"
Name="List Table 6 Colorful Accent 3"/>
<w:LsdException Locked="false" Priority="52"
Name="List Table 7 Colorful Accent 3"/>
<w:LsdException Locked="false" Priority="46"
Name="List Table 1 Light Accent 4"/>
<w:LsdException Locked="false" Priority="47" Name="List Table 2 Accent 4"/>
<w:LsdException Locked="false" Priority="48" Name="List Table 3 Accent 4"/>
<w:LsdException Locked="false" Priority="49" Name="List Table 4 Accent 4"/>
<w:LsdException Locked="false" Priority="50" Name="List Table 5 Dark Accent 4"/>
<w:LsdException Locked="false" Priority="51"
Name="List Table 6 Colorful Accent 4"/>
<w:LsdException Locked="false" Priority="52"
Name="List Table 7 Colorful Accent 4"/>
<w:LsdException Locked="false" Priority="46"
Name="List Table 1 Light Accent 5"/>
<w:LsdException Locked="false" Priority="47" Name="List Table 2 Accent 5"/>
<w:LsdException Locked="false" Priority="48" Name="List Table 3 Accent 5"/>
<w:LsdException Locked="false" Priority="49" Name="List Table 4 Accent 5"/>
<w:LsdException Locked="false" Priority="50" Name="List Table 5 Dark Accent 5"/>
<w:LsdException Locked="false" Priority="51"
Name="List Table 6 Colorful Accent 5"/>
<w:LsdException Locked="false" Priority="52"
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</p><p class="MsoNormal"><span style="color: black; mso-themecolor: text1;">Let’s dive
in.<span style="mso-spacerun: yes;"> </span>I’ll briefly show 3 data sheet
examples that illustrate single supply DC biasing with or without constant
current sources and various mixer input and output strategies.</span></p>
<p class="MsoNormal"><span style="color: black; mso-themecolor: text1;">Recall that
the RF enters via a differential transconductor with their output currents
commutated by a quad of LO switches. The top switch quad operates in the
saturation region while the bottom ECP are biased in their linear region.</span></p>
<p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjGWYKwbB2Uyc4xbLwOJ9Oo8chFwEpYF0D2kKVo_Cs0jURVCSmC03sUYvRVshyQh2W3hzffuCyuTJLq6Wp1Vou9bWpAVpx2vp_uf_-4suy97-EHjTcq1dQDGh3bu1519ctZQ9kQarI8vlTO3chGR14QfUW-9u_1vEM6BYqATCpRyycXv3p298o7UbmVlQ/s679/FIG3.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="576" data-original-width="679" height="542" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjGWYKwbB2Uyc4xbLwOJ9Oo8chFwEpYF0D2kKVo_Cs0jURVCSmC03sUYvRVshyQh2W3hzffuCyuTJLq6Wp1Vou9bWpAVpx2vp_uf_-4suy97-EHjTcq1dQDGh3bu1519ctZQ9kQarI8vlTO3chGR14QfUW-9u_1vEM6BYqATCpRyycXv3p298o7UbmVlQ/w640-h542/FIG3.png" width="640" /></a></div>
<p class="MsoNormal"><span style="color: black; mso-themecolor: text1;">Above — The
data sheet schematic of the S042P Gilbert cell IC.<span style="mso-spacerun: yes;"> </span>No constant current source. Typical current
consumption = 2.15 mA. No internal switch quad collector resistors are provided.
The resistors and diodes shown above are contained in the substrate. <span style="mso-spacerun: yes;"> </span>The builder supplies external bypass/signal
capacitors, gain setting resistor(s) for the transconductance pair current — and
AC connections through coils for the RF, LO and output in typical applications.</span></p>
<p class="MsoNormal"><span style="color: black; mso-themecolor: text1;">This DIP-14 IC
mixer offered by Siemens Semiconductors (Infineon) ran a maximum DC voltage of 15v
and went to 200 MHz. <span style="mso-spacerun: yes;"> </span>It featured an
optional built-in oscillator. The data sheet shows a NF of 7 dB. They also
offered a round, leaded, metal case version called the SO42E. You’ll see this
IC in many European home brew gear, including the projects of LF and VLF
enthusiasts in more recent times. The oldest schematic I could find using the S042P
was dated 1979.</span></p>
<p class="MsoNormal"><span style="color: black; mso-themecolor: text1;">Using an 8K2
instead of an 8K resistor, I show the upper quad plus lower ECP DC bias
voltages using a bench DC supply of 12.18v. The entire bias stack consumes 1.2
mA. The wafer fabricated bias diodes are thermally matched to the ECPs in this
IC for temperature compensation. This data sheet shows an archetypical way a builder
may bias a discrete transistor Gilbert cell mixer. Each diode in the bias stack
drops ~ 0.61 VDC.</span></p>
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Name="List Number"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Bullet 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Bullet 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Bullet 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Bullet 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Number 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Number 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Number 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Number 5"/>
<w:LsdException Locked="false" Priority="10" QFormat="true" Name="Title"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Closing"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Signature"/>
<w:LsdException Locked="false" Priority="1" SemiHidden="true"
UnhideWhenUsed="true" Name="Default Paragraph Font"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text Indent"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Continue"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Continue 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Continue 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Continue 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="List Continue 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Message Header"/>
<w:LsdException Locked="false" Priority="11" QFormat="true" Name="Subtitle"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Salutation"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Date"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text First Indent"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text First Indent 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Note Heading"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text Indent 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Body Text Indent 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Block Text"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Hyperlink"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="FollowedHyperlink"/>
<w:LsdException Locked="false" Priority="22" QFormat="true" Name="Strong"/>
<w:LsdException Locked="false" Priority="20" QFormat="true" Name="Emphasis"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Document Map"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Plain Text"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="E-mail Signature"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Top of Form"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Bottom of Form"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Normal (Web)"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Acronym"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Address"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Cite"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Code"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Definition"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Keyboard"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Preformatted"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Sample"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Typewriter"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="HTML Variable"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Normal Table"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="annotation subject"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="No List"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Outline List 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Outline List 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Outline List 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Simple 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Simple 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Simple 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Classic 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Classic 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Classic 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Classic 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Colorful 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Colorful 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Colorful 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Columns 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Columns 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Columns 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Columns 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Columns 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 6"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 7"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Grid 8"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 4"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 5"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 6"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 7"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table List 8"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table 3D effects 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table 3D effects 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table 3D effects 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Contemporary"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Elegant"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Professional"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Subtle 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Subtle 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Web 1"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Web 2"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Web 3"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Balloon Text"/>
<w:LsdException Locked="false" Priority="39" Name="Table Grid"/>
<w:LsdException Locked="false" SemiHidden="true" UnhideWhenUsed="true"
Name="Table Theme"/>
<w:LsdException Locked="false" SemiHidden="true" Name="Placeholder Text"/>
<w:LsdException Locked="false" Priority="1" QFormat="true" Name="No Spacing"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading"/>
<w:LsdException Locked="false" Priority="61" Name="Light List"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 1"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 1"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 1"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 1"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 1"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 1"/>
<w:LsdException Locked="false" SemiHidden="true" Name="Revision"/>
<w:LsdException Locked="false" Priority="34" QFormat="true"
Name="List Paragraph"/>
<w:LsdException Locked="false" Priority="29" QFormat="true" Name="Quote"/>
<w:LsdException Locked="false" Priority="30" QFormat="true"
Name="Intense Quote"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 1"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 1"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 1"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 1"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 1"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 1"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 1"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 1"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 2"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 2"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 2"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 2"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 2"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 2"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 2"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 2"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 2"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 2"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 2"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 2"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 2"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 2"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 3"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 3"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 3"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 3"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 3"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 3"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 3"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 3"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 3"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 3"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 3"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 3"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 3"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 3"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 4"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 4"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 4"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 4"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 4"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 4"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 4"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 4"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 4"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 4"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 4"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 4"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 4"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 4"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 5"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 5"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 5"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 5"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 5"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 5"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 5"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 5"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 5"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 5"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 5"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 5"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 5"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 5"/>
<w:LsdException Locked="false" Priority="60" Name="Light Shading Accent 6"/>
<w:LsdException Locked="false" Priority="61" Name="Light List Accent 6"/>
<w:LsdException Locked="false" Priority="62" Name="Light Grid Accent 6"/>
<w:LsdException Locked="false" Priority="63" Name="Medium Shading 1 Accent 6"/>
<w:LsdException Locked="false" Priority="64" Name="Medium Shading 2 Accent 6"/>
<w:LsdException Locked="false" Priority="65" Name="Medium List 1 Accent 6"/>
<w:LsdException Locked="false" Priority="66" Name="Medium List 2 Accent 6"/>
<w:LsdException Locked="false" Priority="67" Name="Medium Grid 1 Accent 6"/>
<w:LsdException Locked="false" Priority="68" Name="Medium Grid 2 Accent 6"/>
<w:LsdException Locked="false" Priority="69" Name="Medium Grid 3 Accent 6"/>
<w:LsdException Locked="false" Priority="70" Name="Dark List Accent 6"/>
<w:LsdException Locked="false" Priority="71" Name="Colorful Shading Accent 6"/>
<w:LsdException Locked="false" Priority="72" Name="Colorful List Accent 6"/>
<w:LsdException Locked="false" Priority="73" Name="Colorful Grid Accent 6"/>
<w:LsdException Locked="false" Priority="19" QFormat="true"
Name="Subtle Emphasis"/>
<w:LsdException Locked="false" Priority="21" QFormat="true"
Name="Intense Emphasis"/>
<w:LsdException Locked="false" Priority="31" QFormat="true"
Name="Subtle Reference"/>
<w:LsdException Locked="false" Priority="32" QFormat="true"
Name="Intense Reference"/>
<w:LsdException Locked="false" Priority="33" QFormat="true" Name="Book Title"/>
<w:LsdException Locked="false" Priority="37" SemiHidden="true"
UnhideWhenUsed="true" Name="Bibliography"/>
<w:LsdException Locked="false" Priority="39" SemiHidden="true"
UnhideWhenUsed="true" QFormat="true" Name="TOC Heading"/>
<w:LsdException Locked="false" Priority="41" Name="Plain Table 1"/>
<w:LsdException Locked="false" Priority="42" Name="Plain Table 2"/>
<w:LsdException Locked="false" Priority="43" Name="Plain Table 3"/>
<w:LsdException Locked="false" Priority="44" Name="Plain Table 4"/>
<w:LsdException Locked="false" Priority="45" Name="Plain Table 5"/>
<w:LsdException Locked="false" Priority="40" Name="Grid Table Light"/>
<w:LsdException Locked="false" Priority="46" Name="Grid Table 1 Light"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark"/>
<w:LsdException Locked="false" Priority="51" Name="Grid Table 6 Colorful"/>
<w:LsdException Locked="false" Priority="52" Name="Grid Table 7 Colorful"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 1"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 1"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 1"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 1"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 1"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 1"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 1"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 2"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 2"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 2"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 2"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 2"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 2"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 2"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 3"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 3"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 3"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 3"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 3"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 3"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 3"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 4"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 4"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 4"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 4"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 4"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 4"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 4"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 5"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 5"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 5"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 5"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 5"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 5"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 5"/>
<w:LsdException Locked="false" Priority="46"
Name="Grid Table 1 Light Accent 6"/>
<w:LsdException Locked="false" Priority="47" Name="Grid Table 2 Accent 6"/>
<w:LsdException Locked="false" Priority="48" Name="Grid Table 3 Accent 6"/>
<w:LsdException Locked="false" Priority="49" Name="Grid Table 4 Accent 6"/>
<w:LsdException Locked="false" Priority="50" Name="Grid Table 5 Dark Accent 6"/>
<w:LsdException Locked="false" Priority="51"
Name="Grid Table 6 Colorful Accent 6"/>
<w:LsdException Locked="false" Priority="52"
Name="Grid Table 7 Colorful Accent 6"/>
<w:LsdException Locked="false" Priority="46" Name="List Table 1 Light"/>
<w:LsdException Locked="false" Priority="47" Name="List Table 2"/>
<w:LsdException Locked="false" Priority="48" Name="List Table 3"/>
<w:LsdException Locked="false" Priority="49" Name="List Table 4"/>
<w:LsdException Locked="false" Priority="50" Name="List Table 5 Dark"/>
<w:LsdException Locked="false" Priority="51" Name="List Table 6 Colorful"/>
<w:LsdException Locked="false" Priority="52" Name="List Table 7 Colorful"/>
<w:LsdException Locked="false" Priority="46"
Name="List Table 1 Light Accent 1"/>
<w:LsdException Locked="false" Priority="47" Name="List Table 2 Accent 1"/>
<w:LsdException Locked="false" Priority="48" Name="List Table 3 Accent 1"/>
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<![endif]-->The diode pairs may be replaced by fixed resistors and biasing via resistor voltage dividers plus the 2K2 and 3K3 decoupling resistors remains common in home brew BJT Gilbert cells built today. <br /><br />Since the transistor fT’s were high (probably >=1 GHz), VHF oscillations often occur. They suggest a 10-50 pF capacitor between the LO inputs to prevent VHF parasitic oscillations. Other builders implemented low value series resistors on the ECP base inputs as well. <a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg2GFWI6H15H3jnoITxo3caKpQU3OaD_EbO_8QHPYLvnOMIhKWDnhkxPBF_VPF7NUxDW-qGOG1Sdc70pCjASETMD81_Hq1JfQvK9pKqfoPWhm8F7UfOG1ytBe2HuzOC-k7SjbTiS7SHNTyPmusDGPOb2nb4lLDH2mDge7WrqImnYMOA-C_XBvKiVgtCLA/s1025/FIG4.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="538" data-original-width="1025" height="336" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg2GFWI6H15H3jnoITxo3caKpQU3OaD_EbO_8QHPYLvnOMIhKWDnhkxPBF_VPF7NUxDW-qGOG1Sdc70pCjASETMD81_Hq1JfQvK9pKqfoPWhm8F7UfOG1ytBe2HuzOC-k7SjbTiS7SHNTyPmusDGPOb2nb4lLDH2mDge7WrqImnYMOA-C_XBvKiVgtCLA/w640-h336/FIG4.png" width="640" /></a><br /></p><p style="text-align: left;">Above — A data sheet schematic of the HFA3101 Gilbert cell IC with some DC bias values added by me. No constant current source. Absolute maximum current consumption = 30 mA. This is just a very fast transistor array with a small PC board footprint. The builder supplies all biasing resistors, capacitors, & current setting + degeneration resistors for the transconductance pair — and AC connections through resistors, caps, and/or coils for the RF, LO and output.<br /><br />This SOIC-8 IC mixer offered by Renesas specifies an fT of 10 GHz. It’s tiny and fast using BJTs! A review of the data sheet proves fascinating. This part appears well characterized for 50 Ω use and the circuit examples give clues how we can set up our own discrete or IC mixers using single-ended inputs and outputs. The singled-ended LO + RF input penalty of reduced port isolation is acknowledged in the data sheet and it well shows the trade-offs builders must consider.<br /><br />At high frequencies such as UHF, they specify that the LO must be matched to the switch quad input to avoid parasitic oscillations. RF port matching also proves important for conversion gain. Clearly a mixer operating as a upconverter @ 825 MHz is a whole different animal from a HF Gilbert cell mixer. The design examples show very low value biasing resistors — again this is for UHF and I estimate the low values may provide stable bias, low noise, low input impedance and decreased potential for parasitic oscillations. My added notes show a VCC of 2.96 VDC. I swapped a 120 Ω resistor for the 110 Ω resistor shown. DC bias voltages are shown for the upper quad and lower ECP — the total current draw of the bias stack alone = 4.4 mA due to the low value bias resistors.<br /><br />The RF capacitor values shown don't make sense. The series resonant frequency of the 0.01 µF caps shown seems too low for UHF applications. <br /></p><p style="text-align: left;">Also mentioned in the data sheet, when a (single-ended) output tuned coil is shunted with a 2K resistor, this improves the third order intercept while somewhat decreasing gain. E.g. less distortion products are generated while stability is enhanced. This would be something to try at HF on your test bench if you’ve got the test gear and want to run a tuned, single ended output.</p><p style="text-align: left;">You really go to school by reading this data sheet. What a fabulous IC that doesn’t use MOS transistors — so we can relate to it a bit better.<br /></p><div style="text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgUY9kQJoNUOOrybtSQlJ6VzhDfmJNN7172Db-nFQSWpOG59bBQHF8fZ8WBN6SUQZ9_JGgAdDNj5MR3Yjroy75eM5TnKvBHx2mIlViTXk7cGximbosgnr3NK-_6Zep9wEBYi4T4q7EZfjIBcq3vFLjjpIPT5DTbisi9ok113z6fu0pcXPL1uzSYmOdp1A/s624/FIG5.png"><img border="0" data-original-height="336" data-original-width="624" height="344" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgUY9kQJoNUOOrybtSQlJ6VzhDfmJNN7172Db-nFQSWpOG59bBQHF8fZ8WBN6SUQZ9_JGgAdDNj5MR3Yjroy75eM5TnKvBHx2mIlViTXk7cGximbosgnr3NK-_6Zep9wEBYi4T4q7EZfjIBcq3vFLjjpIPT5DTbisi9ok113z6fu0pcXPL1uzSYmOdp1A/w640-h344/FIG5.png" width="640" /></a></div><p>Above — The schematic of the silicon BJT MMIC IAM81008 Gilbert cell IC offered in the past by Hewlett Packard (Keysight Technologies). Single polarity bias supply of 4 to 8 VDC [ most often builders would use 5 volts which would draw a maximum DC current of 12 mA. SSB NF = 17 dB. RF and LO ports = 50 Ω. 8 dB RF to IF conversion gain from 0.05 - 5 GHz with an IF output from DC to 1 GHz.<br /><br />This is a great historical example of a complete, active mixer that required minimal off-chip parts to get it operating at VHF to UHF -- plus it also featured an interesting on-chip bias circuit. You just need to AC couple in your RF plus LO signals with appropriate value capacitors -- and then provide a VCC and ground. Pretty amazing active 5 GHz IC mixer in that day in time.<br /><br />As such, this double-balanced mixer was used with single-ended LO + RF and output ports. A built-in emitter follower reduced loading effects on the output port, The current sources schematic numbered 1,2 and 3 show the evolution from a typical on-chip current mirror to something much more sophisticated. <br /><br />This mixer seemed popular for VHF and UHF work in Europe for experimenters and while it suffered from a relatively high NF (lots of transistors + resistors) and low dynamic range, it worked OK as second mixer in a typical receiver -- or perhaps as a transmit or PLL mixer.<br /><br />Many writers have covered the SA-612 and ilk, so I won’t. For me, a measured SSB NF of <= ~8 dB at <= 45 MHz made that part special when it came out. However, modern Gilbert cells ICs offer a much improved dynamic range plus a higher upper frequency limit — although they’re not as easy to use for HF to lower VHF home brew experiments as the popular SA612. </p><p><span style="font-size: medium;"><b>Home brew Gilbert cell Mixers</b></span><br /></p><p>Although this blog post covers analog ICs, I'll write a few comments about making home brew versions with discrete transistors. I've built at least 6 discrete BJT home brew Gilbert cell mixers and each of them suffered strong parasitic oscillations between 110 to 430 MHz. Whether using single-ended or differential inputs or output, they oscillated. When running higher currents such as > 12 mA to get a better input intercept, parasitic oscillations tended to worsen. Some mixers were stable with 1 set of LO and RF input frequencies, but then became unstable when used with different LO and RF input frequencies. Quite vexing.<br /><br /> I had to spend a lot of time adding series resistors, bypass capacitors and so forth to swamp out these VHF-UHF oscillations. The whole process proved time consuming and frustrating. With commercial, analog IC versions, I did not suffer these problems, or they were easily fixed if parasitic oscillations happened to arise.<br /><br />I can make a simple, stable, active, transformer-balanced home brew mixer with 2-4 FETs or BJTs that will outperform any of my discrete transistor Gilbert cell mixers with far less parts and stress. Thus, I tend to use commercial IC Gilbert cell mixers.You may have better luck! Perhaps, I'm doing something wrong?</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiJP-3V-OvYYa-tOFq6RDrsj_9gMppq56SA86xKGjMAIgYq7Nln9rwU9KlXUMyyG22VZdY0T-BCKZtRr5h0vh7ui2Ot450DLurd4uDmy-kjBQkKshpWUb6IBn2cjexNoiRCmjhkR_Sa7W-VmCCpzUIX-WnwJ74uZmycT-fAjrer9Kix3uGoNNZ39QtDVw/s697/figure%206.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="479" data-original-width="697" height="440" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiJP-3V-OvYYa-tOFq6RDrsj_9gMppq56SA86xKGjMAIgYq7Nln9rwU9KlXUMyyG22VZdY0T-BCKZtRr5h0vh7ui2Ot450DLurd4uDmy-kjBQkKshpWUb6IBn2cjexNoiRCmjhkR_Sa7W-VmCCpzUIX-WnwJ74uZmycT-fAjrer9Kix3uGoNNZ39QtDVw/w640-h440/figure%206.png" width="640" /></a></div><p>Above — A spectrum analyzer screen shot of the output of 1 of my better home brew Gilbert cell mixers. RF = 14.08 MHz @ 0 dBm input, LO = 9.98 MHz @ 0 dBm input. This was for a down conversion mixer to a 4.06 MHz IF. RF conversion gain = 16.35 dB. I've measured as much as 19 dB conversion gain in my home brew Gilbert cells once parasitic oscillations were stifled. The LO and RF signals are down ~ 32 dB which shows pretty good balance for a home brew Gilbert cell mixer. You can see other strong tones in this image, but those are pretty standard in RF mixers. This was an OK mixer.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg7ENDCIF7HhCK0d7k2LVo37ooUemMv614tI3qMQ_4OL5cCG7oOo-6t3IC_fup6hsNw2RAhXDdQN-sbczRjFrdWY3TiUkv8YkL8MlgUGe77cBOJvx88sdaHS8m_WbpuIsoiGRzK2eQw8wqPKcC4Zk6NarsMRSln3G3Jz8-mkB0bKRHngOmsZVX-1jZK7g/s649/FIGURE%207.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="454" data-original-width="649" height="448" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEg7ENDCIF7HhCK0d7k2LVo37ooUemMv614tI3qMQ_4OL5cCG7oOo-6t3IC_fup6hsNw2RAhXDdQN-sbczRjFrdWY3TiUkv8YkL8MlgUGe77cBOJvx88sdaHS8m_WbpuIsoiGRzK2eQw8wqPKcC4Zk6NarsMRSln3G3Jz8-mkB0bKRHngOmsZVX-1jZK7g/w640-h448/FIGURE%207.png" width="640" /></a></div><p>Above — The spectral output of a Mini Circuits Level 7 diode ring mixer for comparison. Conversion loss = ~ 6 dB at 4 MHz. Beautiful suppression of the LO and RF input signals. In my home brew diode rings, I usually get only about 35 - 40 dB RF and LO suppression due to mismatches in my diodes + transformers, and from layout asymmetry.</p><p><b>Update April 2, 2023 - - Discrete BJT mixer - -<br /></b></p><p>I developed a very stable Gilbert cell mixer that uses no transformers in March 2023. I've run it from 2 MHz up to ~120 MHz with no VHF-UHF parasitic oscillations.<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhfoRCHcIZOrzB3NGzL3FPW6edZnmZb8QP9Tm6EjtGWoQtaBJaVNy9NC3Av3BdGX1obyx_EbxTXG_ocYS_krCuMbFC7Jzmp96I_HKWYIgUTkdvnbS8zbyKjXvFjWcLZ2d2A3NKX3CMmVaVj-j0C2ViQwX9i50-p3RtYvfYw5FTzkiUfU_TQr5VjrWAOYpVX/s698/march%2019.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em; text-align: center;"><img border="0" data-original-height="668" data-original-width="698" height="612" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhfoRCHcIZOrzB3NGzL3FPW6edZnmZb8QP9Tm6EjtGWoQtaBJaVNy9NC3Av3BdGX1obyx_EbxTXG_ocYS_krCuMbFC7Jzmp96I_HKWYIgUTkdvnbS8zbyKjXvFjWcLZ2d2A3NKX3CMmVaVj-j0C2ViQwX9i50-p3RtYvfYw5FTzkiUfU_TQr5VjrWAOYpVX/w640-h612/march%2019.png" width="640" /></a></p><div class="separator" style="clear: both; text-align: left;">Above — An avionics band (119.6 MHz RF test frequency) mixer. Conversion gain = 10.1 dB. Despite 0 transformers, the LO was 22.9 dB down from the IF output conversion gain -- and the RF was 25 dB down from the IF conversion gain.</div><p>The input LO and RF are well defined at VHF and = 50 Ω. The output impedance is low and easily matched to 50 ohm input devices with a resistor or pi match. The Q4 collector resistor at 1.5K gave the best conversion gain, but this value may go as low as 1K Ω. </p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjxIKjnk9FZudKY2oVhBsTkJu9XeWwtR1wZfH4LMYpDg4l5nc5tyshDWudVG-kRIa8Z1tl9SxfW2wqj_Dz-EhktUyn466kodp-ShUHa3_JlF_9Y0KYT96lMQQz4Mf3m_HUCFxBwgRtCnx3C_mNlA73ytHvV4Behs1qyPjhmjCifNfLcXc0JdTEF3LMxqQ/s641/blog3-3.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="458" data-original-width="641" height="458" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjxIKjnk9FZudKY2oVhBsTkJu9XeWwtR1wZfH4LMYpDg4l5nc5tyshDWudVG-kRIa8Z1tl9SxfW2wqj_Dz-EhktUyn466kodp-ShUHa3_JlF_9Y0KYT96lMQQz4Mf3m_HUCFxBwgRtCnx3C_mNlA73ytHvV4Behs1qyPjhmjCifNfLcXc0JdTEF3LMxqQ/w640-h458/blog3-3.png" width="640" /></a></div><p>Above — The IF output at 10.7 MHz. I used the <a href="https://www.mouser.ca/c/?q=BC547-CTA" target="_blank">BC547 CTA</a> transistor for the emitter coupled pairs. This transistor consistently gives <i>outstanding balance</i> despite not matching my differential transistor pairs.<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEja3shtc-GpNhe57K-OY4iGQ8oZVB6ubuhTDOUIif_TaZ7LUmw7MM45P1TbTDI7qWtroQAsQeXrjIg7_Mjo2b3qtGSBcoPTj-2EEsK4sX_H50lKk8EZwX6P3lhhQC2lYFX_SrIwmEPt2YFtqYhScTpGKK_bU5zbm4HjAWQGvWmq3vp7h1nH7HIgby0U8Vfq/s698/march%2019bb.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em; text-align: center;"><img border="0" data-original-height="668" data-original-width="698" height="612" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEja3shtc-GpNhe57K-OY4iGQ8oZVB6ubuhTDOUIif_TaZ7LUmw7MM45P1TbTDI7qWtroQAsQeXrjIg7_Mjo2b3qtGSBcoPTj-2EEsK4sX_H50lKk8EZwX6P3lhhQC2lYFX_SrIwmEPt2YFtqYhScTpGKK_bU5zbm4HjAWQGvWmq3vp7h1nH7HIgby0U8Vfq/w640-h612/march%2019bb.png" width="640" /></a></p><p>Above — My experimenters Gilbert cell mixer showing the variables such as capacitor choice versus frequency, setting up the 2 voltage divider bias networks, choosing mixer current & emitter degeneration to affect the input intercept. The BC547C specifies an fT of 300. Thanks.</p><div class="separator" style="clear: both; text-align: left;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh9PNbwcgrRSawnvLR4Wml1fIxNRVQtKTJdscBqAw5p_Nxhb8j-RbXyTLRA_HhGfRMZYVqlsf2fc20XUZMu2koTAbbMdkD-n53fbg2T_NOXYASZjk9CyH5XMn5FgpTUYAvD8GhG5uPEq03hU9chBrf5twzfKBC9mS6hb0kJ2OVIWfWXrRR8XfCsfajlC5-d/s618/version%203.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="602" data-original-width="618" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh9PNbwcgrRSawnvLR4Wml1fIxNRVQtKTJdscBqAw5p_Nxhb8j-RbXyTLRA_HhGfRMZYVqlsf2fc20XUZMu2koTAbbMdkD-n53fbg2T_NOXYASZjk9CyH5XMn5FgpTUYAvD8GhG5uPEq03hU9chBrf5twzfKBC9mS6hb0kJ2OVIWfWXrRR8XfCsfajlC5-d/s16000/version%203.png" /></a><span style="text-align: left;">Above — Yet another experimenters circuit for HF.</span></div><p></p><p style="text-align: left;"><span style="font-size: medium;"><b>References</b></span><br /><br />[1] B. Gilbert, “A precise four-quadrant multiplier with sub nanosecond response,” IEEE Journal of Solid State Circuits, Vol. 3, No. 4, December 1968, pp. 365-373.<br /><br />[2] Syu, J.-S., Meng, C., & Wang, C.-L. (2013). A 2.4-GHz Low-Flicker-Noise CMOS Sub-Harmonic Receiver. IEEE Transactions on Circuits & Systems. Part I: Regular Papers, 60(2), 437–447<br /><br /></p><p></p>Vasily Ivanenkohttp://www.blogger.com/profile/17387516134063150119noreply@blogger.com7tag:blogger.com,1999:blog-3480228403403435266.post-40827302924784230532022-09-24T18:51:00.010-07:002022-09-27T19:16:44.717-07:00 QRPHB Bench Tour <p></p><p></p><div class="separator" style="clear: both; text-align: center;"></div><br /><div class="separator" style="clear: both; text-align: center;"><iframe allowfullscreen="" class="BLOG_video_class" height="377" src="https://www.youtube.com/embed/smK1PA2ZnO0" width="454" youtube-src-id="smK1PA2ZnO0"></iframe></div><div class="separator" style="clear: both; text-align: center;"> Above —Unedited video. Poor audio. But all I have time for at the moment. Cheers !!</div><p></p><div class="separator" style="clear: both; text-align: center;"><iframe allowfullscreen="" class="BLOG_video_class" height="329" src="https://www.youtube.com/embed/C2evswYFmWA" width="396" youtube-src-id="C2evswYFmWA"></iframe></div><p>Above — Our 2 lab supervisors<br /></p><p><a href="https://www.youtube.com/channel/UC_QonLhYyvpBoD-Pz1wnnqA/featured" target="_blank">My YouTube Channel</a></p><p>Please subscribe. Going forward, I'll rely more on videos as people like them.<br />The resource I lack the most is time.</p><p><b>— Update —</b></p><p>I sincerely thank you for your support! <br />Over 90 QRPHB Bench Tour video views in 2 days and 52 YouTube subscribers.</p><p>I feel amazed as I really have not posted much content in the past few years --- and do not promote QRPHB whatsoever. Best to you!<br /></p><p><br /></p><p></p>Vasily Ivanenkohttp://www.blogger.com/profile/17387516134063150119noreply@blogger.com5tag:blogger.com,1999:blog-3480228403403435266.post-81262832352629925302022-09-04T21:51:00.022-07:002022-09-05T21:30:40.959-07:00QRP HomeBuilder — Season 24 —<p>For Season 24, after a hiatus from RF, I plan to share some radio projects beginning in late October.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhP8Jx-aEQ69A3UMDjpUvtox_fx9_czwAupONQK-twdw5wcd5TFjWoWrJPXLNyBVTL9tk1nxvcYS31oNL1-ELafT_Og41czH-JvB2b7yOM9kfgwx51gWafOFPvSbIqdHNoYAwlgS34s_XU77hiKSJlSepuBffuDphmEJygLGSSHPlLJeOO-CWhcpZZy3g/s844/QRPHB.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="577" data-original-width="844" height="438" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhP8Jx-aEQ69A3UMDjpUvtox_fx9_czwAupONQK-twdw5wcd5TFjWoWrJPXLNyBVTL9tk1nxvcYS31oNL1-ELafT_Og41czH-JvB2b7yOM9kfgwx51gWafOFPvSbIqdHNoYAwlgS34s_XU77hiKSJlSepuBffuDphmEJygLGSSHPlLJeOO-CWhcpZZy3g/w640-h438/QRPHB.jpg" width="640" /></a></div><p>Above — I've cleaned up my bench and began ordering some RF parts so they'll be here for Fall experiments. This summer, countless people have emailed me and requested some RF content, so I'll oblige. After a few years away from RF experiments, I feel reinvigorated. I've kept up my reading, but not RF bench experiments --- plus I'll have to brush up on my lab procedures.<br /></p><p>In addition, I just got a modern camera to add some video content to my blog posts. Therefore, I've got to learn V logger stuff and choose plus learn how to operate some video-editing software. That will take time. Time is the 1 resource I lack the most and I'm jealous of those retired experimenters who have time to work on stuff at their leisure. My experiments occur late at night with a push-through-to-the-end philosophy.</p><p>Until then, here is a gardening topic. I'm an avid gardener and for me it's served as my mental health re-constructor over the past ~ 3 years.</p><p><b>Single Dahlias</b></p><p>I Iove Dahlias and so do the pollinators around our place. We have more solitary bees than honey bees and I’ve taken measures to provide them a variety of spaces to nest in and around our property.<br />I mostly grow single row Dahlias for these pollinators and actually the so-called "single row" collection can be divided into Anemone, Collarette, Orchid, Orchette, Single, Micro-Peony and Species (non-hybrid) Dahlias. Unlike the fancy modern hybrids that people grow for weddings and for beauty, "single rows" have just 1 basic row of petals and their private bits are exposed so pollinators can easily access their pollen and nectar. <br /><br />2 examples of species plants include Dahlia merckii and Dahlia apiculate. I grow the latter.<br /></p><p>I wanted to share my adventures with an Anemone hybrid that I’ve worked with for 2 years. My basic plan is to get a variety of seeds, germinate them in late February under lights, grow them indoors until the frost is gone and then plonk them in our gardens. If the plant performs well, then continue that line by saving the tuber, and perhaps growing-on some cuttings for next season.<br /><br />I’ve noticed that all my "single row" Dahlias struggle in the scorching sun of late June to middle August. I planted some in a shady garden and the flowers plus foliage stays much nicer during the record setting, super-hot summer sun we got in both 2021-2022. In that shady garden, flowers get about 6-7 hours of sunlight then dappled shade to full shade. <br /></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjr8NX7aZFYc0mxN8oreLx9X0JyL-9hJBA134JfL2vgD-JIFOJyMWArqe3x3oCXVDWij9x8HNI-kmbq-nvZ1Dj0gdbIwvXVVdXAqo52qXduAEOi0l9GetdOsSIG62EDaIzgf0vkNBR3Q4IDgNdofOpFTU6mcZdd2CbH4hGJ9YD3ZLTuRrrlC3hKr6uGHQ/s961/dahlia1.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="624" data-original-width="961" height="416" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjr8NX7aZFYc0mxN8oreLx9X0JyL-9hJBA134JfL2vgD-JIFOJyMWArqe3x3oCXVDWij9x8HNI-kmbq-nvZ1Dj0gdbIwvXVVdXAqo52qXduAEOi0l9GetdOsSIG62EDaIzgf0vkNBR3Q4IDgNdofOpFTU6mcZdd2CbH4hGJ9YD3ZLTuRrrlC3hKr6uGHQ/w640-h416/dahlia1.jpg" width="640" /></a></div>Above — The anemone style Dahlia that blew us away this season. <br /><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh-e5Kp3wNEJSwE9X79dQd0DjxCyt3XPlzW7RpUzf2mdh4hpSsrQSPKbN1yaI1VSjoek--mOqA3BbClubiU9ozexxyUCCInLjJkXpuwn1yJS9o_InW_vsVvE1z7bUXSi1X0NLE5Y6uUKBNy7CJYaz0x0w-cldA8USZIVcDZU82JzYmjXKg2vLVnMARl2w/s3383/seedlings2-Feb%2028-22.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="3383" data-original-width="2585" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEh-e5Kp3wNEJSwE9X79dQd0DjxCyt3XPlzW7RpUzf2mdh4hpSsrQSPKbN1yaI1VSjoek--mOqA3BbClubiU9ozexxyUCCInLjJkXpuwn1yJS9o_InW_vsVvE1z7bUXSi1X0NLE5Y6uUKBNy7CJYaz0x0w-cldA8USZIVcDZU82JzYmjXKg2vLVnMARl2w/w490-h640/seedlings2-Feb%2028-22.jpg" width="490" /></a></div><p>Above — The seedlings on Feb 28, 2022. The largest seedling is the flower I'm describing. I had to re-pot it twice before planting in in our full sun front garden on May 17th. It started blooming in the house while sitting in a south facing window.<br /></p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhHTrZyY2TpSlnE62-PCNdFbigrGE89CKPy8Hm80NMec6Ow5jQKlkJvOMlhHR2BHPC8TQcAGyBviXb0hjWcohoNcxLJusK7wv1whfT1hsAzbwmu7pc28tJFH6ffWJ3qgmauWXkzuAUPnSfRP_dtPMkpu-PTiQ9RMRLtIHX639X-tCbmdNkkhlu4jm0sAQ/s1000/DSC_4017.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="665" data-original-width="1000" height="426" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhHTrZyY2TpSlnE62-PCNdFbigrGE89CKPy8Hm80NMec6Ow5jQKlkJvOMlhHR2BHPC8TQcAGyBviXb0hjWcohoNcxLJusK7wv1whfT1hsAzbwmu7pc28tJFH6ffWJ3qgmauWXkzuAUPnSfRP_dtPMkpu-PTiQ9RMRLtIHX639X-tCbmdNkkhlu4jm0sAQ/w640-h426/DSC_4017.jpg" width="640" /></a></div>Above — We endured a cool, wet Spring and most plants grew slowly. I took this photo on July 10 and by this time, despite the Spring weather, this plant was a "flower machine". Note how green the foliage looks.<br /><p></p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiJE5kYxla6KDG7iIO1Cc2fQmDwIvAZuOb3OzoEq3G-cCL31SRM75AVt-LuAA8SFrvSAeaDt20sZjqNuww6iCFBXCMtHgOWktKR9Nl6qvP7auDpoiLNrJF_ZCnrc7Ahz9vKjUHzkMMUBFZIPEt6EJ3Go3T8DSyUET7zYrwnJIpzb-AfpJlJdSZUxCYd7g/s982/dahlia2.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="649" data-original-width="982" height="422" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiJE5kYxla6KDG7iIO1Cc2fQmDwIvAZuOb3OzoEq3G-cCL31SRM75AVt-LuAA8SFrvSAeaDt20sZjqNuww6iCFBXCMtHgOWktKR9Nl6qvP7auDpoiLNrJF_ZCnrc7Ahz9vKjUHzkMMUBFZIPEt6EJ3Go3T8DSyUET7zYrwnJIpzb-AfpJlJdSZUxCYd7g/w640-h422/dahlia2.jpg" width="640" /></a></div><p>Above — Photo taken today, Sept 4, 2022. In late July into middle August, the leaves got scorched by the blazing hot sun during our heat wave. Many of the flower buds "cooked". They did not flower, rather they were burnt & turned black. I cut off these dead buds. This was not due to lack of water and a good mulch at the base of the plant — our hot weather has been brutal for the past 2 years. For awhile, there were very few flowers on this plant.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhSBYV0Mw8d5kE3T6JESFPxrN0Mtu2Z_Q16ukAly8TKn6z6ufiU_sDKJV32kEXyW4kXaWHHm73O15zbCIMKXSxrbeOWTRYrcN7Sv79cwngbkK9pEG1XAJtWS79cxcGVRBL7jVoiLlcUJonWUDLbzg4tsNeUOcuDQ9YInITe4zEW0PvuHc1GuA_zza0xJQ/s842/dahlia3.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="638" data-original-width="842" height="484" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhSBYV0Mw8d5kE3T6JESFPxrN0Mtu2Z_Q16ukAly8TKn6z6ufiU_sDKJV32kEXyW4kXaWHHm73O15zbCIMKXSxrbeOWTRYrcN7Sv79cwngbkK9pEG1XAJtWS79cxcGVRBL7jVoiLlcUJonWUDLbzg4tsNeUOcuDQ9YInITe4zEW0PvuHc1GuA_zza0xJQ/w640-h484/dahlia3.jpg" width="640" /></a></div><p>Above — The plant continues to recover and once again transformed into a flower machine. In addition, these flowers last longer than other "single row" dahlias in our gardens. This 1's a keeper and serves as a bee magnet. Grown from 1 seed this year, it out performs our other tuber-grown Dahlias in terms of bud production. Last year, we had the first frost kill of our Dahlias on November 3rd.<br /></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjHhJPBGjhp20FDj7zW3uukAeNGOPj8aJUdplY6Y1Ds_FNMLH-HXSgOz4Z4adcDTeDTTtf96BS1CFEDCTGvFrodoKwVWGQ04aZzXaZxasrFcscgcSnzbPbf75B39-95jtsc3KOqnfgzWJwk5fkLOsXQVoNyFd9HXQE5SNL-g2Vtx-CEgejIP0cTDGwxKw/s980/dahlia4.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="648" data-original-width="980" height="424" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjHhJPBGjhp20FDj7zW3uukAeNGOPj8aJUdplY6Y1Ds_FNMLH-HXSgOz4Z4adcDTeDTTtf96BS1CFEDCTGvFrodoKwVWGQ04aZzXaZxasrFcscgcSnzbPbf75B39-95jtsc3KOqnfgzWJwk5fkLOsXQVoNyFd9HXQE5SNL-g2Vtx-CEgejIP0cTDGwxKw/w640-h424/dahlia4.jpg" width="640" /></a></div><p>Above — Take care of yourself. Connect with nature. It will help clear your mind so you can do some serious electronics. Best to you!</p>Vasily Ivanenkohttp://www.blogger.com/profile/17387516134063150119noreply@blogger.com2tag:blogger.com,1999:blog-3480228403403435266.post-72810704666100229412022-08-06T22:37:00.007-07:002022-08-07T08:57:49.619-07:00Mini-Circuits Labs TC1-1-13M+ balun transformer - quick evaluation<p>I quickly evaluated a MCL or Mini-Circuits Labs TC1-1-13M+ transformer as a balun. Although we live in a single-ended dominant RF world (single-ended LNAs, IF amps, bandpass filters, low-pass filters, VFOs, VCOs, etc.) there are times when you want differential output. That’s 2 outputs inverted, or 180 degrees apart with hopefully equal amplitude in each arm. </p><p>It’s easy to make a homebrew balun, but I wanted to see how the MCL part compares to my home-built stuff which might be 4 or 5 twisted turns of #28 AWG on a FB-43-2402 binocular core, or something like that.</p><p>The MCL part looks tiny and its small footprint [ 3.81mm X 1.65 mm ] would well suit my hybrid SMT/through-hole build style using Ugly Construction with a few carved copper islands for the SMT parts and AC input/outputs, or DC inputs. I prefer my homebrew projects to be as small as possible. </p><p>MCL specs this part at 50 Ω port impedance from 4.5 to 3000 MHz. An amazing wide band response. I measured the inductance of each arm at 21.6 µH. This is about the same as 4 turns through a FB-43-2402 balun I had lying around in my ready-made transformer tray. Some of these transformers are really sketchy and have been soldered in out of quick bench experiments in some cases for over decades.<br /><br />My current interest is for lower HF, and in particular, ~7 MHz. </p><p>URL for the TC1-1-13M+ data sheet: <a href="https://www.minicircuits.com/pdfs/TC1-1-13M+.pdf" target="_blank">https://www.minicircuits.com/pdfs/TC1-1-13M+.pdf</a><br /><br /></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhBgyA3sAulUPayNfnaza533ExxEGoChR7YsTtmsLTpDF9aBZ7rXLBe_XodyVz3VRK6mwzKJlkfIukXUO6izlVT2boccg31BemQkK3FBQan90JOt6LHo0JYjPxI1szUYihc2qtCJjbSOGrmBo5cxSJ4MD3Kx1e_A7oEbXuV6FdMLL1YmENaiBbJJQbI0Q/s599/rig2.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="201" data-original-width="599" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhBgyA3sAulUPayNfnaza533ExxEGoChR7YsTtmsLTpDF9aBZ7rXLBe_XodyVz3VRK6mwzKJlkfIukXUO6izlVT2boccg31BemQkK3FBQan90JOt6LHo0JYjPxI1szUYihc2qtCJjbSOGrmBo5cxSJ4MD3Kx1e_A7oEbXuV6FdMLL1YmENaiBbJJQbI0Q/s16000/rig2.png" /></a></div><p>Above — The schematic of my testing jig.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEghDILPjTbksHmZPR6LimM7XYQ2taqym7ZDXRZRvc3LGxOexRx543edPw9x-I1gelBOxGm7UwQaPtk1AfaXx-eY0-6rlvNbAA9-UUUYED7yUf7IfMrPPNGU0dRTq_nGUyRIN_Au4pwJyZQcmxzSIK26_cf85Oxj6knQtgsq-l6XzbXCbG2Ht7PYveUe1g/s800/MCL%20balun%20best.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="537" data-original-width="800" height="430" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEghDILPjTbksHmZPR6LimM7XYQ2taqym7ZDXRZRvc3LGxOexRx543edPw9x-I1gelBOxGm7UwQaPtk1AfaXx-eY0-6rlvNbAA9-UUUYED7yUf7IfMrPPNGU0dRTq_nGUyRIN_Au4pwJyZQcmxzSIK26_cf85Oxj6knQtgsq-l6XzbXCbG2Ht7PYveUe1g/w640-h430/MCL%20balun%20best.png" width="640" /></a></div><p>Above — The MCL output into both 50 Ω terminated channels of my DSO with a 7.039 MHz signal applied. The phase difference is perfect as shown and lies in spec at all frequencies I tested -- really amazing. The amplitude difference isn't as good at HF but was within spec at lower VHF and all the way to ~3 GHz.</p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjlFdzG7atWlahC9qhCR8jzzataRQtASxDTHVFjZPrhbaX9lH1jq8G2WiAcHb9Yj-UNzvit9rGqGYd2u8QgkrFCKp3p0p006CJlRh09hXJMaKDImoP_FND6F4m7D4MELjDx53J3ekukwIp61NW33QKIBQxnxqkOOwMhhVzQCE6uPrL1Ug_khcxCQ7sN_w/s800/My%20balun.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="525" data-original-width="800" height="420" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjlFdzG7atWlahC9qhCR8jzzataRQtASxDTHVFjZPrhbaX9lH1jq8G2WiAcHb9Yj-UNzvit9rGqGYd2u8QgkrFCKp3p0p006CJlRh09hXJMaKDImoP_FND6F4m7D4MELjDx53J3ekukwIp61NW33QKIBQxnxqkOOwMhhVzQCE6uPrL1Ug_khcxCQ7sN_w/w640-h420/My%20balun.png" width="640" /></a></div>Above — My homebrew balun [4t #28 wire, twisted in a FB43-2402 ferrite] into the DSO. Amplitude difference looks better than the MCL at 7.039 MHz. The phase difference looks unimpressive. I will pay more attention to physical symmetry in my layout when I make actual new baluns for my Fall project.<p></p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjDWtnmu3OrSFs4L2jtEoy6qBBBAgJgjuKuWDPEowcqHXOHJrD1yheC-sG-biggQA4Jb9QKXvQqdNLyUeOAp01S7dTG8slzB1wnf9O3zR51FtYVQf1exRal8rDJTIk4tb2cL16hX1JnziU3YRpLinn78rzjxKr24s1D7Ez_repn20WO7eCe10Ps_AY6VA/s800/mcl%20balun%20sweep.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="480" data-original-width="800" height="384" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjDWtnmu3OrSFs4L2jtEoy6qBBBAgJgjuKuWDPEowcqHXOHJrD1yheC-sG-biggQA4Jb9QKXvQqdNLyUeOAp01S7dTG8slzB1wnf9O3zR51FtYVQf1exRal8rDJTIk4tb2cL16hX1JnziU3YRpLinn78rzjxKr24s1D7Ez_repn20WO7eCe10Ps_AY6VA/w640-h384/mcl%20balun%20sweep.png" width="640" /></a></div><br />Above — Tracking generator plus spectrum analyzer sweep. I terminated 1 output port with a 50 Ω RF terminator and swept the other output port. This screen shot is just an HF sweep starting at the lower limit of the MCL part @ 4.5 MHz. It's pretty flat and insertion loss is on spec on this and on wider sweeps. I'm impressed with this low insertion loss across a huge bandwidth from my measures.<p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjNChSa8kOdpvmqFEjflVafIfr-joIXfQiN-tX36RhqkdwQ1dyyxY-eImU6cJuUkUC22LUAQjnZAXQ8dhMprvVuCee2AGQ6e-ymPKbndwRS4evrumyU2QizyKKpimCz_54Qp4lplGAsTQxl4iN_Ehti7KDM96w4ZHzM5_c6kYFjre8OiOiKmTLyWbmtjA/s800/My%20balun%20home.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="480" data-original-width="800" height="384" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjNChSa8kOdpvmqFEjflVafIfr-joIXfQiN-tX36RhqkdwQ1dyyxY-eImU6cJuUkUC22LUAQjnZAXQ8dhMprvVuCee2AGQ6e-ymPKbndwRS4evrumyU2QizyKKpimCz_54Qp4lplGAsTQxl4iN_Ehti7KDM96w4ZHzM5_c6kYFjre8OiOiKmTLyWbmtjA/w640-h384/My%20balun%20home.png" width="640" /></a></div><p></p><p>Above — The sweep of my balun with identical settings.The #43 mix ferrite material rears its ugly head. ~ 3 dB insertion loss that gets worse as you move up into VHF and above. I've only got #61 and #43 material ferrites for making transmission line transformers. C'est la vie!</p><p>It's fun and humbling to compare your homebrew parts against premium industry components. </p><p>Ciao<br /></p><p><br /></p><p><br /></p>Vasily Ivanenkohttp://www.blogger.com/profile/17387516134063150119noreply@blogger.com2tag:blogger.com,1999:blog-3480228403403435266.post-24839118783657253852022-07-03T20:10:00.010-07:002022-07-11T21:16:43.597-07:00Reading Material 2022<p>In 2022 I l stopped most of my subscriptions to magazines and journals. I've got 2 left:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjEXeCk3GgAeyY26Epe71_t_i66sttRU6lZLefUe3Hf9T7FpgieUaVLVskHmQXPiNv_rage1SFWZ5tnTcWzj2BkVJsQk32xmchf73my-oJPhdSH9JPYMAhEdCOQseFZ0MhIkPhIsl9Y3xONo529_hD2vFAPu9_0nMbj4qppCD1O_M_F83ZhQaYw5NlKyg/s889/RAC1.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="889" data-original-width="685" height="640" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjEXeCk3GgAeyY26Epe71_t_i66sttRU6lZLefUe3Hf9T7FpgieUaVLVskHmQXPiNv_rage1SFWZ5tnTcWzj2BkVJsQk32xmchf73my-oJPhdSH9JPYMAhEdCOQseFZ0MhIkPhIsl9Y3xONo529_hD2vFAPu9_0nMbj4qppCD1O_M_F83ZhQaYw5NlKyg/w494-h640/RAC1.jpg" width="494" /></a></div><p></p><p>Above — I've belonged to Radio Amateurs of/du Canada for over 3 decades. The quality of our <a href="https://www.rac.ca/" rel="nofollow" target="_blank">RAC </a>journal 'The Canadian Amateur' has grown — and the build + technical articles rank as first class.</p><p> <a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjFE-Od-F7jz6gT1-mrlnzeRg2qpoGLX9DZuezIorZUy0Z_fF9rbJd3pQqkBI5Y3LrdP-o3JFF39aUuMu6K56BVgxzt89KH-hOmd2HObTkJUwvrygZA_VYuzazYExxMwRLD56ev6AHx_bhMQOw1bb268KyJAZfIv5XHgI1iYclYfHKLP9HrswXp0n4hzw/s782/NV1.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="681" data-original-width="782" height="558" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjFE-Od-F7jz6gT1-mrlnzeRg2qpoGLX9DZuezIorZUy0Z_fF9rbJd3pQqkBI5Y3LrdP-o3JFF39aUuMu6K56BVgxzt89KH-hOmd2HObTkJUwvrygZA_VYuzazYExxMwRLD56ev6AHx_bhMQOw1bb268KyJAZfIv5XHgI1iYclYfHKLP9HrswXp0n4hzw/w640-h558/NV1.jpg" width="640" /></a><br /></p><p>Above — Having subscribed to Nuts and Volts for many years, I still enjoy reading each new issue online. It helps keep me up-to-date with the hobbyist forefront. My interests aren't confined to amateur radio; they include a spectrum of electronics-related topics and general sciences.</p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiuJFvyZ0PrVGZAfKhweScLDrsagYNOepzP_KvdGOgkiFqwrr3P8hi25QYkQgVjfSYeseE8JowGx3EdVGBcICn29GMINKcciLMS52Ro5E4RJA3KcY8fA7baGf-UdiLXjqUTvyzOdIcpblJl4plH5s-IE8z5K4k1qmE-JBDgPFRfQ1kG7QpEDbA339lM3A/s777/journals.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="652" data-original-width="777" height="538" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiuJFvyZ0PrVGZAfKhweScLDrsagYNOepzP_KvdGOgkiFqwrr3P8hi25QYkQgVjfSYeseE8JowGx3EdVGBcICn29GMINKcciLMS52Ro5E4RJA3KcY8fA7baGf-UdiLXjqUTvyzOdIcpblJl4plH5s-IE8z5K4k1qmE-JBDgPFRfQ1kG7QpEDbA339lM3A/w640-h538/journals.jpg" width="640" /></a></div><br />Above — I still scan professional EE journal databases and read abstracts on topics I favour. Some articles are open-source and free. Occasionally I purchase articles of great interest to me.<p></p><p>My main hobby in Spring|Summer:</p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgSVP2o1HjL4PCb_gqMD6y7DRriR6R_FIvsSg3BM3fA8SAmZtQDQvYsW3eEkPxwe-NQu7V6o3Xo4UxNZn4HzZRnFbwf-R1jO3_ucQZcCJBX1MW67tak2Vpe6womKe2o0VfuAxlGLAeiEWFhuHqrswc75_JifljxDOpJSutl6U6VZlHwUwjep_XZ4u7niQ/s1000/DSC_3866.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="665" data-original-width="1000" height="426" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgSVP2o1HjL4PCb_gqMD6y7DRriR6R_FIvsSg3BM3fA8SAmZtQDQvYsW3eEkPxwe-NQu7V6o3Xo4UxNZn4HzZRnFbwf-R1jO3_ucQZcCJBX1MW67tak2Vpe6womKe2o0VfuAxlGLAeiEWFhuHqrswc75_JifljxDOpJSutl6U6VZlHwUwjep_XZ4u7niQ/w640-h426/DSC_3866.jpg" width="640" /></a></div><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhENWQ01RRMhGGr3S_7r8gYwD63FiQDB4kOwkTs934seyKjalXkgoEs8S6NZEHU0z-6X3_QcgjDiIFQVpffeHtYpHCxJeRMI2YnOTOSxguCjuU2OazJ9Uh_hpfMrReNRJBczeVBFXOdlRfp2N5sXY51KXdDQzF4efHAwG9H3W8YzxqdPp5dI_T9VCqeRQ/s1000/DSC_3853.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="665" data-original-width="1000" height="426" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhENWQ01RRMhGGr3S_7r8gYwD63FiQDB4kOwkTs934seyKjalXkgoEs8S6NZEHU0z-6X3_QcgjDiIFQVpffeHtYpHCxJeRMI2YnOTOSxguCjuU2OazJ9Uh_hpfMrReNRJBczeVBFXOdlRfp2N5sXY51KXdDQzF4efHAwG9H3W8YzxqdPp5dI_T9VCqeRQ/w640-h426/DSC_3853.jpg" width="640" /></a></div><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjr8omfJ0ospqUesjvnZUVp1GJ8CoJd2HOgrk56fNrpQjKPmEh442wod9n4M_SPr0SlqWEO7ifbff866czypgoRJmB0MHKvpsBPAAIuSC_3qC7Z4wqxnMBTzMi-Bp6uA3-lDd4zxWDJIA9cnxdMEhE9zK7PVHEjCZqQPh4Kxhk_hPJXtV8PPTW7WyV_vQ/s1000/DSC_3792.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="665" data-original-width="1000" height="426" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjr8omfJ0ospqUesjvnZUVp1GJ8CoJd2HOgrk56fNrpQjKPmEh442wod9n4M_SPr0SlqWEO7ifbff866czypgoRJmB0MHKvpsBPAAIuSC_3qC7Z4wqxnMBTzMi-Bp6uA3-lDd4zxWDJIA9cnxdMEhE9zK7PVHEjCZqQPh4Kxhk_hPJXtV8PPTW7WyV_vQ/w640-h426/DSC_3792.jpg" width="640" /></a></div><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj-y_k18YMAerjwVHSegTfzFmdVshJ7pCFcShaiuO6BPVXYYeM5ei43p1zFa2ZDZccNrcdak7MeQY1_Ya1BTmTCrv-nFKSUu3N19zfN8HFi6qwYt6TbuC8qS6mc8nJs2jszYqwaXZjO7W7rWdwacvwk5ExFBgLqoI55VBmnA3K2jz53TrwxYW23V86IRw/s1000/DSC_3856.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="665" data-original-width="1000" height="426" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj-y_k18YMAerjwVHSegTfzFmdVshJ7pCFcShaiuO6BPVXYYeM5ei43p1zFa2ZDZccNrcdak7MeQY1_Ya1BTmTCrv-nFKSUu3N19zfN8HFi6qwYt6TbuC8qS6mc8nJs2jszYqwaXZjO7W7rWdwacvwk5ExFBgLqoI55VBmnA3K2jz53TrwxYW23V86IRw/w640-h426/DSC_3856.jpg" width="640" /></a></div><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjLxPEqaKsqvYznCWRExKB8z9yQzssFX0qKC0S-ubzw_wqIa1y368pT3a6jXB190gz75Kk7uiJTnVXoni4wY1mQcvS5anIghb8duJQi32eEOS180W6Yc4gZS0uxDOUbgzrHcXvxevYgMsa4Y7d8QmGFCC76GrFs8fuRpl6AYJG2EupNHo340nW2F3p5jQ/s1000/DSC_4017.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="665" data-original-width="1000" height="426" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjLxPEqaKsqvYznCWRExKB8z9yQzssFX0qKC0S-ubzw_wqIa1y368pT3a6jXB190gz75Kk7uiJTnVXoni4wY1mQcvS5anIghb8duJQi32eEOS180W6Yc4gZS0uxDOUbgzrHcXvxevYgMsa4Y7d8QmGFCC76GrFs8fuRpl6AYJG2EupNHo340nW2F3p5jQ/w640-h426/DSC_4017.jpg" width="640" /></a></div><p></p><p></p><p></p><p></p><p></p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhDbgSM88MfMTMqJrHlkwVkbwavv6X50dRWVsRlXA_6ALwq9zwvHzAVbHaMRXUmAzdepuxmyTzdPOihTM38b6y1RrI1_7Zf3U7XmGzzOFIWY1erUQNep2pxkXiG5Hq9FTGV6D7HLI7vNoc4I8hU2Vdy0ceg9PprL3c-bsIiBR9ai9TF6MIKMm8Ql1HN1w/s1000/DSC_4023.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="665" data-original-width="1000" height="426" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhDbgSM88MfMTMqJrHlkwVkbwavv6X50dRWVsRlXA_6ALwq9zwvHzAVbHaMRXUmAzdepuxmyTzdPOihTM38b6y1RrI1_7Zf3U7XmGzzOFIWY1erUQNep2pxkXiG5Hq9FTGV6D7HLI7vNoc4I8hU2Vdy0ceg9PprL3c-bsIiBR9ai9TF6MIKMm8Ql1HN1w/w640-h426/DSC_4023.jpg" width="640" /></a></div><br /> <div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgrdoQLYoTW7iNWODENYJpnT-9gtzGJ-g-gKYqbH3VBDfujQUc7RnKG-LN2fEGRhyW_7-O8CwtlXNg6qF31b9_IiN2_csDOxL1z9xp0pscgtgdKlCsZcMRfdVW4WJta8BZ9KDtTxLbuR3Jlwa1WSWE1GdUOjW92GiJTycTWQJFZFbtYYl0S2T2qs7SVwQ/s1000/DSC_3944.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="665" data-original-width="1000" height="266" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgrdoQLYoTW7iNWODENYJpnT-9gtzGJ-g-gKYqbH3VBDfujQUc7RnKG-LN2fEGRhyW_7-O8CwtlXNg6qF31b9_IiN2_csDOxL1z9xp0pscgtgdKlCsZcMRfdVW4WJta8BZ9KDtTxLbuR3Jlwa1WSWE1GdUOjW92GiJTycTWQJFZFbtYYl0S2T2qs7SVwQ/w400-h266/DSC_3944.jpg" width="400" /></a></div><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhUVC4tYynwT-qjl1QU0CprSncG2VbwARerGFXEtj7k6VVMc3BN9sOEMmT6uxPK3Vnm-BqxggjU1QYnH8vsUPgr_1xVozhPY0rXAOLysIwjCL4zAmXsICja8WFfEle-nCzAtNS_8VHEEg-FmXoPI2rGhRi3CoqxQU_j1oHwS41StU3y-4bHeF57hwpe5Q/s1000/DSC_3942.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="665" data-original-width="1000" height="266" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhUVC4tYynwT-qjl1QU0CprSncG2VbwARerGFXEtj7k6VVMc3BN9sOEMmT6uxPK3Vnm-BqxggjU1QYnH8vsUPgr_1xVozhPY0rXAOLysIwjCL4zAmXsICja8WFfEle-nCzAtNS_8VHEEg-FmXoPI2rGhRi3CoqxQU_j1oHwS41StU3y-4bHeF57hwpe5Q/w400-h266/DSC_3942.jpg" width="400" /></a></div><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjcZflC3-8PIhZoXxC1d3bAoxmq2uPayg5TiVU1TXID09tg620tG6AFQGEH3kEC6dbro7y5vy--Yfh4h00kW4ZFy2Swy4j3PPr7a8vWLZxB6BeXIFX7GAzix8_2Yp2Nmx__rhfbRbBZJ3JO5_CcEc-Q2qyYQnfNJkqG-kQb1Y-vtL_5LxDAyZkhH2mVYg/s1000/DSC_3943.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="665" data-original-width="1000" height="266" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjcZflC3-8PIhZoXxC1d3bAoxmq2uPayg5TiVU1TXID09tg620tG6AFQGEH3kEC6dbro7y5vy--Yfh4h00kW4ZFy2Swy4j3PPr7a8vWLZxB6BeXIFX7GAzix8_2Yp2Nmx__rhfbRbBZJ3JO5_CcEc-Q2qyYQnfNJkqG-kQb1Y-vtL_5LxDAyZkhH2mVYg/w400-h266/DSC_3943.jpg" width="400" /></a></div><p><br /></p>Vasily Ivanenkohttp://www.blogger.com/profile/17387516134063150119noreply@blogger.com0tag:blogger.com,1999:blog-3480228403403435266.post-45285486114550472672022-06-06T21:16:00.004-07:002022-06-06T21:17:41.387-07:00Obsolete parts for an obsolete hobbyist?<p>The story of life as a hobbyist builder --- you get this email from a vendor from whom you buy parts:<br /></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiyH1H9ykUAfN5Op-BkIqih1To5iyEd4V5oQDTfRq8sJgRu5Z4GB6csGQCYoRHUfvUZ9PccLgQB0b9hZharrm8YFHXx4mUXNArCrE97czicglZ2H8wHPt51Jg9BaBAH1WcNkHeWaGMKTzJCkh-Cwxodtnh2Ia6se_9-jwS88XBlV7yDvs9DMyos1EtvLw/s830/mpsa56%20goes%20obsolete.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="531" data-original-width="830" height="410" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEiyH1H9ykUAfN5Op-BkIqih1To5iyEd4V5oQDTfRq8sJgRu5Z4GB6csGQCYoRHUfvUZ9PccLgQB0b9hZharrm8YFHXx4mUXNArCrE97czicglZ2H8wHPt51Jg9BaBAH1WcNkHeWaGMKTzJCkh-Cwxodtnh2Ia6se_9-jwS88XBlV7yDvs9DMyos1EtvLw/w640-h410/mpsa56%20goes%20obsolete.png" width="640" /></a></div><br /><p><br /></p>Vasily Ivanenkohttp://www.blogger.com/profile/17387516134063150119noreply@blogger.com2tag:blogger.com,1999:blog-3480228403403435266.post-13116507530800322102022-02-07T20:55:00.008-08:002022-02-08T18:33:03.440-08:00Jazz Guitar Amp Experimenters Series — Definitely Not Your Father's Tone Stack<p><b><span style="color: red;"><span style="font-size: medium;"><span style="color: black;"></span></span></span></b></p><p style="text-align: left;"><span style="font-size: medium;">Hey gang </span><b><span style="font-size: medium;">! </span></b></p><div style="text-align: left;"><p><span style="font-size: medium;">Let's further examine some guitar amp tone control circuitry. I'll show you results from a few of my Winter 2021-2022 experiments. </span>Our c<span style="font-size: medium;">ontext = clean, jazz guitar-focused amplifiers</span><b><span style="font-size: medium;">.</span></b></p></div><div style="text-align: left;"><p><span style="font-size: medium;">After publishing <a href=" https://qrp-popcorn.blogspot.com/2021/12/ga-50-inspired-guitar-preamplifier.html" target="_blank">Gibson GA-50 Inspired Guitar Preamplifier Tribulations</a> <br />I improved the basic tone circuit to reduce resistor shot noise and show the schematic below:<br /></span></p></div><p><b></b></p><div class="separator" style="clear: both; text-align: center;"><b><a href="https://blogger.googleusercontent.com/img/a/AVvXsEgVE47uaGxcEL6WM2-Y7pGfWqQ9scjo_Si9_IqJ22yCDnQWWiylMBIiaMN3m-tM7ThSgxOiiJ3X5NY_5Ah180CY1MV9kRWpFoKyDiQc_M_cs058Rf9U3AJkBlL4a8T8fGbSXh_HljYb4rK-cSuSBxbO35A4jNlucWEnaeWtvsQSyHgUYUw9rJBJXr6iXw=s1066" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="821" data-original-width="1066" height="492" src="https://blogger.googleusercontent.com/img/a/AVvXsEgVE47uaGxcEL6WM2-Y7pGfWqQ9scjo_Si9_IqJ22yCDnQWWiylMBIiaMN3m-tM7ThSgxOiiJ3X5NY_5Ah180CY1MV9kRWpFoKyDiQc_M_cs058Rf9U3AJkBlL4a8T8fGbSXh_HljYb4rK-cSuSBxbO35A4jNlucWEnaeWtvsQSyHgUYUw9rJBJXr6iXw=w640-h492" width="640" /></a></b></div>Above —<b> </b><span style="color: red;"><span style="color: black;">The evolved schematic of the adjustable low and high frequency shelf guitar preamplifier. Calculating the 3 dB high + low frequency turnover frequencies gets done by the standard formula Frequency = 1 / (2 pi * R * C ) with each potentiometer set to its minimum and maximum frequency for the low and high shelf.<br /></span></span><p></p><p>Although enjoyable, after experimenting with different capacitor values in the 2 shelving circuits, I abandoned this basic circuit. Why? Too much knob fiddling; plus I found I only liked a single 3 dB cutoff frequency for both the high and low shelf. Why bother with all this circuitry when a fixed high and low shelf frequency will do? I also wanted to focus on middle frequency circuits.</p><p></p><p>I learned that I prefer shelving tone equalizers over peaking or resonant types for both the low and high frequency. For mid range control, I seem to prefer peaking type albeit only if the resonant circuit Q is less than ~1.5</p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/a/AVvXsEg_7P1CVskz69RPfOKz5mY0aVy8Br-NDKxVUWY9n15_krOcuXXEdFQGo4id8ZT1sWT5qo1xjnnbBhmmpX2nYb0gdmH3WjFPsQ2R0XnOMjLiT7EYvU9vRvgbjbnBIrMz1cVE4uPzwc1_XUk1Z5L6Ugsro3i_2xIzB1X3SCMaMLvC8rnTo8BUgDoEuTQATg=s720" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="393" data-original-width="720" height="350" src="https://blogger.googleusercontent.com/img/a/AVvXsEg_7P1CVskz69RPfOKz5mY0aVy8Br-NDKxVUWY9n15_krOcuXXEdFQGo4id8ZT1sWT5qo1xjnnbBhmmpX2nYb0gdmH3WjFPsQ2R0XnOMjLiT7EYvU9vRvgbjbnBIrMz1cVE4uPzwc1_XUk1Z5L6Ugsro3i_2xIzB1X3SCMaMLvC8rnTo8BUgDoEuTQATg=w640-h350" width="640" /></a></div>Above — Two basic fixed-frequency shelving tone controls. These often are combined a single op-amp stage plus/minus isolation resistors. Those 2 circuits follow the familiar Baxandall topology and prove easy to design, build and use. <p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/a/AVvXsEi79qJPvZDurkmjejl6VCTgdvUB6193Q19ihBX3TZKmxL-c5YHKPTfr4oN-2dTd2B0TEyYZp-jrV5YMzsiOAqhUbA55e_4Q1100GNrqZHApj8wakEJq1egE2HhlbI5htSplpCsR9z198cjh-GopVbbZp7k88Ra7y_oOSFlLLYjOZj4ziJAFLeDhW7QcRg=s647" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="481" data-original-width="647" height="476" src="https://blogger.googleusercontent.com/img/a/AVvXsEi79qJPvZDurkmjejl6VCTgdvUB6193Q19ihBX3TZKmxL-c5YHKPTfr4oN-2dTd2B0TEyYZp-jrV5YMzsiOAqhUbA55e_4Q1100GNrqZHApj8wakEJq1egE2HhlbI5htSplpCsR9z198cjh-GopVbbZp7k88Ra7y_oOSFlLLYjOZj4ziJAFLeDhW7QcRg=w640-h476" width="640" /></a></div><p>Above — A bass, middle, treble tone circuit taken from the out of production Carvin Sx-2000 preamp. The trio of equalizers use a single, unity-gain inverting op-amp stage and all 3 are peaking types. Please view the series capacitor(s) coming off each tone control potentiometer's wiper. </p><p>Thus each active tone circuit uses 2 signal capacitors that convert it from shelving to peaking. The design formulae for peaking tone equalizers gets considerably more complex than shelving designs, however 1 capacitor establishes a 3 dB point <u>below</u> and the other <u>above</u> a centre frequency which give the bell shaped response of a band-pass filter.<a href="https://blogger.googleusercontent.com/img/a/AVvXsEhkek1VLwxehPCXnjg-YM9cLb2dl51I-gV9zs7hp-4hv_a96oH_CGZ18yMts31UOKudlJlzNlOpFdwe7pN7hStHvH0cZ5HR-gAWK2fS8e421RvsfZk1Fs57EwZe3FfNnpPBe2BhY7UTFRRay_lfbyAgDfuKwFMjJvvAJ7XFxUIm2AD7amRk9jjo4GxS3g=s643" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="458" data-original-width="643" height="456" src="https://blogger.googleusercontent.com/img/a/AVvXsEhkek1VLwxehPCXnjg-YM9cLb2dl51I-gV9zs7hp-4hv_a96oH_CGZ18yMts31UOKudlJlzNlOpFdwe7pN7hStHvH0cZ5HR-gAWK2fS8e421RvsfZk1Fs57EwZe3FfNnpPBe2BhY7UTFRRay_lfbyAgDfuKwFMjJvvAJ7XFxUIm2AD7amRk9jjo4GxS3g=w640-h456" width="640" /></a></p><p>Above — Another circuit that provides a peaking equalizer response; the Wien bridge design. This particular design offers a different time constant for each half of the Wien band-pass filter. You'll see this often in guitar amps since it allows the potential of a slightly higher Q (and a sharper response). I really enjoyed the 753 Hz 3 dB frequency version as a low middle control on my bench test guitar amp. All 3 scaled designs use standard value caps and the 3 dB frequency may also be manipulated by tweaking the 22K resistor value.</p><p>Guitar amps often feature a single middle frequency tone control; or perhaps bling out and offer 2 middle frequency tone controls such as low and high midrange. Which middle frequencies should I choose vexes many amplifier designers. This is likely the reason we may go with adjustable midrange frequencies, however as aforementioned, I want to move away from that. I built a guitar preamp with 2 separate Wien tone circuits and painfully tried many different time constants to see what worked best for me.</p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/a/AVvXsEjAZaCf7Tm0jznyoeuy3g2sSVnzKtWzdguPkrgIOufYZhVqa1zxV5lM-fp8imdCjbeIpacFoKSes-9-6AHTtZN-xKv40OV2_QrPKMEtk1Ip8OHGm-yTk-2-ik09L4tdFPeXvRD4m39BvZ-XP6J0Asv7ovNM_eN0Dn2W_QDCpLqE8rH5RWksa8i_bYuAyA=s880" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="670" data-original-width="880" height="488" src="https://blogger.googleusercontent.com/img/a/AVvXsEjAZaCf7Tm0jznyoeuy3g2sSVnzKtWzdguPkrgIOufYZhVqa1zxV5lM-fp8imdCjbeIpacFoKSes-9-6AHTtZN-xKv40OV2_QrPKMEtk1Ip8OHGm-yTk-2-ik09L4tdFPeXvRD4m39BvZ-XP6J0Asv7ovNM_eN0Dn2W_QDCpLqE8rH5RWksa8i_bYuAyA=w640-h488" width="640" /></a></div>Above — My current experimental guitar tone circuitry. I absolutely love this circuit and it's now my benchmark to compare new designs against. I drive this circuit with a single op-amp voltage amplifier affair identical to U1a and U1b shown in the first schematic on this blog entry. <br /><br />To avoid potentiometer interdependence, each tone stage gets its own op-amp. You'll occasionally see this in high-end console mixers. Since most of us are just making 1 home brew guitar amp and not a production run where a higher parts count costs your company money, perhaps we can afford to bling out and put in as many op-amps stages as we choose?<p></p><p>To keep design simple, I chose identical time constants for the low-pass and high-pass circuits of each Wien band-pass stage. Thus, the standard <span style="color: red;"><span style="color: black;"><i>Frequency = 1 / (2 pi * R * C ) </i>formula is in play.</span></span></p><p><span style="color: red;"><span style="color: black;">1 design consideration = what order do I put the bass middle treble circuits in? I did some experiments and with active tone circuits ,you may simple choose what sounds best to your ears. Some amps, however, run the middle, then low + high frequency circuits in order and this worked OK in my experiments.</span></span></p><p><span style="color: red;"><span style="color: black;"><b>Lower Middle 883 Hz </b><i>Peaking</i><br /></span></span></p><p><span style="color: red;"><span style="color: black;">My middle frequencies were chosen for standard value capacitors. To my ears, choosing a low middle of 800-900 Hz offers the optimum single frequency to tailor the lower midrange. Using a Fender Telecaster + a Gibson ES-175 as my test guitars, I preferred the low middle frequency slightly scooped on the neck + bridge pick up combination; or with the treble pickup alone -- and slightly boosted when playing the front/ neck pickup alone. <br />I tested this board through my <a href="https://qrp-popcorn.blogspot.com/2022/01/guitar-amp-experimenters-bench-pa-12.html" target="_blank">Popcorn PA</a> with 3 different 8 Ω speakers: A 10 inch speaker in open-back mounting, a 12 inch speaker in a open-backed cabinet + another 12 inch speaker in a closed-back, ported cabinet.<br /></span></span></p><p><span style="color: red;"><span style="color: black;"><b>Higher Middle 1540 Hz </b><i>Peaking</i><br /></span></span></p><p>I seem to prefer a higher middle frequency between 1200 and 1600 Hertz. Most often, I tended to boost this frequency in my listening tests, but occasionally left it flat. 1540 Hz is still low enough in the spectrum to adds some punch to your sound while avoiding the nasal sounding (when boosted) 1 KHz frequency. Boosting around 1500 Hz added some grit to my neck position humbucker<b> </b>pickup guitars, although too much boost sounded a little tinny, but not especially, since the Q only lies around 1.5 at maximal boost. <br /></p><p><b>Low and High Tone Controls </b><i>Shelving</i><br /></p><p>Simple shelving circuits boost or cut the low and high frequencies. The low-pass filter uses the familiar topology of the low-pass variable frequency shelving stage shown in the first schematic of this blog post. Bass response rolls on & off smoothly and capacitor values of 0.39, 0.47 and 0.56 µF were tested. I prefer the really low 72 Hz turnover frequency at this point in time. You may also tweak the 3K9 resistor value slightly, or put in a temporary trimmer resistor to find your dream low frequency 3 dB point.</p><p>Chosen for a 12 KHz 3 dB turnover, the high-pass circuit follows the standard Baxandall design & added considerable shimmer to my guitar tone when boosted. Some builders may prefer a 10 KHz cutoff. Build and test stuff! You're the King on your bench.<br /></p><p>On most of my experiments, I ran factory original Texas Instruments 5532 op-amps. On the low and high tone circuits, the 1.0 K end-stop resistors may be changed to limit the boost or cut as you prefer. They don't have to be symmetrical. </p><p>The 20K pots could easily be 10K potentiometers to lower resistor shot noise, however, at extreme settings of 10K control pots distortion <i>may</i> arise & you may have to increase your end-stop resistor values. As it goes, Baxandall circuits offer low input Z when boosting hard and heavy loading via the negative feedback path when cutting hard. Evidently, the 5532 performs better than many other popular op-amps in these extreme situations.</p><p>Further, conventional wisdom purports we use FET input op-amps since DC flows through our tone control pots.The TL072, or OPAx134 series come to mind. Bipolar input op-amps may drop noise and boost distortion performance if you don't mind adding a few DC blocking capacitors.<br /></p><h2 style="text-align: left;"><span style="color: #2b00fe;"><b>Other Experiments<br /></b></span><br /></h2><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/a/AVvXsEgFGzsF22mGc_Ua38SVm1UzdEUqVD6vSSwUIw-_oL9H8ktBD4d-_Y0Q5BOavZC5UfdO42INzKcFsAuFkd5N2YjWXfGeKFjUUe10HmwfaAkWwN_WnXkwjrgdf2NopUgJPzjaG0vY5QX9pLDiuIKMfKhafN6KYxKrtfsfySzRxUsRtEN9W7OVppKTIcER9g=s900" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="586" data-original-width="900" height="416" src="https://blogger.googleusercontent.com/img/a/AVvXsEgFGzsF22mGc_Ua38SVm1UzdEUqVD6vSSwUIw-_oL9H8ktBD4d-_Y0Q5BOavZC5UfdO42INzKcFsAuFkd5N2YjWXfGeKFjUUe10HmwfaAkWwN_WnXkwjrgdf2NopUgJPzjaG0vY5QX9pLDiuIKMfKhafN6KYxKrtfsfySzRxUsRtEN9W7OVppKTIcER9g=w640-h416" width="640" /></a></div><p>Above — An active equalizer with all stages centred at 500 Hz with 4 different Q factors to allow listening tests. I also performed this maneuver at 190 Hz and 1.6 KHz. I placed 2 or more capacitors in parallel to get as close to each non-standard value design capacitance as possible.</p><p>I felt amazed how differently the same frequency band sounded when changing its Q. Obviously, moving between a Q of 0.85 and 1.0 wasn't staggering, however, I heard a clear difference. I liked a Q of 1 and 1.7 best. However, between these 2 values, I preferred a Q of 1 better as a boost and liked a Q of 1.7 better as a cut. I never imagined such a observation. LTSPICE did not inform me about my preferences either — gotta do listening tests. When Q = 5.1, my boosted or cut tone sounded unnatural @ 500 Hertz.<br /></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/a/AVvXsEgS_OgQ6r163KcgfW1eSh79OQbVupnPkBQW14fUrVc0L3EAMIjmoRINs87o4rE1WufK3ViZM5v3BXEU_YCfkAAlJKSr6BfbWS6ajuU8IUicpHj4CLBziy7qMvGeyiQQSloag2N5bU_e-wFLFhiRld4hvfcOn353IW0gMsZqKICTS284x-cYRkZmNHKecA=s643" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="365" data-original-width="643" height="364" src="https://blogger.googleusercontent.com/img/a/AVvXsEgS_OgQ6r163KcgfW1eSh79OQbVupnPkBQW14fUrVc0L3EAMIjmoRINs87o4rE1WufK3ViZM5v3BXEU_YCfkAAlJKSr6BfbWS6ajuU8IUicpHj4CLBziy7qMvGeyiQQSloag2N5bU_e-wFLFhiRld4hvfcOn353IW0gMsZqKICTS284x-cYRkZmNHKecA=w640-h364" width="640" /></a></div><p>Above — A simple middle range Baxandall design. I've shown capacitor values for 3 frequencies, but I also scaled the cap values to test at 350, 400, 573 and 4000 Hertz. I preferred the Wien bridge middle range circuits over Baxandalls for midrange when both are centred on the same frequency. Likely, peaking sounds better than shelving to my ears for middle tones. Admittedly, by adding a capacitor to any Baxandall frequency band you may convert it to a resonant filter. The math poses a little more difficult than a Wien circuit, but its definitely an option for you to consider. <br /></p><p>I think this might prove useful in a bass-middle-treble tone circuit sharing a single op-amp stage. You could make the low and high shelving, and then add a series cap to convert the middle control to a peaking type.</p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhFqevsNH_GSCCaPVCQ2I189dO_SYoBNnv-Mrm3i7c6nQByDr6Y1qA0Tx-a4ArSeLliIqvZ-85GPuyCUbnOs-L176IavMV6l-YGqalKdQJz_flxnuH27V2atuVXwDnJQxOTyLfZ181e1APDsIOPzL2SSKUAzXrvO8qQQ9ZLfDqAYJOMrXmmF48EFALHFg/s518/contour-original.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="518" data-original-width="445" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhFqevsNH_GSCCaPVCQ2I189dO_SYoBNnv-Mrm3i7c6nQByDr6Y1qA0Tx-a4ArSeLliIqvZ-85GPuyCUbnOs-L176IavMV6l-YGqalKdQJz_flxnuH27V2atuVXwDnJQxOTyLfZ181e1APDsIOPzL2SSKUAzXrvO8qQQ9ZLfDqAYJOMrXmmF48EFALHFg/s16000/contour-original.png" /></a></div>Above — The Carvin contour control for scooping the low mids (or not). No boost. Somehow this circuit, a modified Wien bridge, fascinates me. I ran it in a practice amp for about 1 year and simmered a love-hate relationship with it. I scaled it to reduce shot noise with lower value resistors and a 20K control pot. Very creative circuit.<p></p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgvigQCNM2H_jvvJL5LGXQ0fawGQ2XoWkDEA3KODxGCJ9_LWYZRflPM4b9Re__80D1l-o5KOORhWGxdTV0_JLkFrWtIjdXHBQ5lMF1hxNBlLnDeNwHrLbxZDdhxJoa9BwxTAxrb-UM1RwZI2qXZPP2ckpvTieVJo_amTaeJdoOaW9ae0R4ZbvnFnyNBRA/s569/laney scooper.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="480" data-original-width="569" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEgvigQCNM2H_jvvJL5LGXQ0fawGQ2XoWkDEA3KODxGCJ9_LWYZRflPM4b9Re__80D1l-o5KOORhWGxdTV0_JLkFrWtIjdXHBQ5lMF1hxNBlLnDeNwHrLbxZDdhxJoa9BwxTAxrb-UM1RwZI2qXZPP2ckpvTieVJo_amTaeJdoOaW9ae0R4ZbvnFnyNBRA/s16000/laney scooper.png" /></a></div>Above —A Laney scooper. Another fixed frequency, Wien inspired, player defeatable, low middle frequency scooper. The Wien bridge circuit has spawned much cool circuitry and certainly Max Wien sits in the pantheon of electronic designers. Mid scooping circuits feature heavily in guitar distortion circuits and often serve as "mud cutters". <p></p><p><br /> <a href="https://qrp-popcorn.blogspot.com/p/guitar-related-index.html" target="_blank">Click here</a> for my Guitar-related index</p>Vasily Ivanenkohttp://www.blogger.com/profile/17387516134063150119noreply@blogger.com1tag:blogger.com,1999:blog-3480228403403435266.post-90118220830119859332022-01-01T22:02:00.013-08:002022-10-21T11:46:45.388-07:00Guitar Amp Experimenters Bench PA — 12 Watt Popcorn PA<p> </p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/a/AVvXsEjWb0T5IjfqIkVC3DJ3gR1LtzzSw7Qbnwayni6uy7cIZVo90EhD4yGeXYWbXsBesuYTo_RST02Wa3EOj40VDHuBjRAQy6fC-GEhXc7JuZAM7GmpxPOSksNPnSRPFDmZrFPRbBRgfNLNNnDSN7GE6Vrc_TDnAeqKBzdjvpEB6bfU0NCIpon_7KvmJ9xSng=s1200" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="904" data-original-width="1200" height="482" src="https://blogger.googleusercontent.com/img/a/AVvXsEjWb0T5IjfqIkVC3DJ3gR1LtzzSw7Qbnwayni6uy7cIZVo90EhD4yGeXYWbXsBesuYTo_RST02Wa3EOj40VDHuBjRAQy6fC-GEhXc7JuZAM7GmpxPOSksNPnSRPFDmZrFPRbBRgfNLNNnDSN7GE6Vrc_TDnAeqKBzdjvpEB6bfU0NCIpon_7KvmJ9xSng=w640-h482" width="640" /></a></div><p></p><p>I sought a low power bench audio PA to use for guitar preamplifier development. This brick measures ~ 18 x 11 x 8 cm and delivers 12 clean Watts power into an 8 Ω load. On the front panels 3 RCA jacks provide regulated +/- 17 VDC plus a signal ground connection. Additionally, the signal input jack lies on the front panel. The rear panel sports a speaker jack, fuse and the AC mains input. <br /> <br /></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/a/AVvXsEjE3Pm2CDCZsHfZ51xFyA3qwRfsfdnSJVAEQAkl17u0bYNlQ0lMFt4dkCa696X8bK3E4n5gFzpX9UJODDybcHcQWcaDzIfv1Gknr5FWHDVsqyuf5n5ri7uUghOcv30dfb_eemONL2pjNHtIfwJ-qUtVsD2rw_c_PKvHzrCT9Zkc4VDgaTep3w58LixrYw=s1200" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="798" data-original-width="1200" height="426" src="https://blogger.googleusercontent.com/img/a/AVvXsEjE3Pm2CDCZsHfZ51xFyA3qwRfsfdnSJVAEQAkl17u0bYNlQ0lMFt4dkCa696X8bK3E4n5gFzpX9UJODDybcHcQWcaDzIfv1Gknr5FWHDVsqyuf5n5ri7uUghOcv30dfb_eemONL2pjNHtIfwJ-qUtVsD2rw_c_PKvHzrCT9Zkc4VDgaTep3w58LixrYw=w640-h426" width="640" /></a></div>Above — A PA is built around a power supply transformer. This tall, heavy & old Hammond transformer has sat in my lab for decades: Although the label shows 25v CT, the AC voltages on each side measured 13.8 VAC under no load. Rectified and filtered this transformer provided +/- 18.89 VDC under a heavy load with no sag until pushed to the extreme. Thus it will function as a 10 -12 W guitar amp power supply — good for my purposes.<br /><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjqqT02jVQTewG7BOMJ3nG8Zb0LxK9IcVgkqTD8aGijQBofUu66bMo073Z69U01k51IU2GcuPbfcl1H0KVy8x8bqQ0g1RoaVveaXQCx8oCYRg6_hfSZEgLq7TEhwTA_u03ZTaCF8zTWghiQm_ODEVSliaBPrMa3NcJ7fKbKFycY8l_2hpZglbjamwmRLw/s640/Op-amp%20power%20supply.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="273" data-original-width="640" height="274" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEjqqT02jVQTewG7BOMJ3nG8Zb0LxK9IcVgkqTD8aGijQBofUu66bMo073Z69U01k51IU2GcuPbfcl1H0KVy8x8bqQ0g1RoaVveaXQCx8oCYRg6_hfSZEgLq7TEhwTA_u03ZTaCF8zTWghiQm_ODEVSliaBPrMa3NcJ7fKbKFycY8l_2hpZglbjamwmRLw/w640-h274/Op-amp%20power%20supply.png" width="640" /></a></div><p></p><p>Above — The +/- 17 volt rail regulator/filter circuits. My rectifier included a full wave bridge and the main reservoir capacitors = 4700 µF. I re-purposed The main Hammond chassis from some old project and this entire project falls under the low cost category since most of the parts were ancient specimens from my collection.<a href="https://blogger.googleusercontent.com/img/a/AVvXsEgQR3OeTOdY0BH1ij9BYLpy_4rSHxyk0UJ_BAsF8XKhJU95dUfFHNTq6MvWay79UFlg5KXVujEfsRSq806KD_hj30EDM3HmsYpx9d9b8egBjDtW51xYHOEj_uYm5nCq6rhNeEYd-X8lrWOkAmwmd6RAVlUlZ84lHAfMEpG-9jW8HNpqXZOZQNav_PZOiw=s855" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="650" data-original-width="855" height="486" src="https://blogger.googleusercontent.com/img/a/AVvXsEgQR3OeTOdY0BH1ij9BYLpy_4rSHxyk0UJ_BAsF8XKhJU95dUfFHNTq6MvWay79UFlg5KXVujEfsRSq806KD_hj30EDM3HmsYpx9d9b8egBjDtW51xYHOEj_uYm5nCq6rhNeEYd-X8lrWOkAmwmd6RAVlUlZ84lHAfMEpG-9jW8HNpqXZOZQNav_PZOiw=w640-h486" width="640" /></a></p><p>Above — Popcorn PA schematic. This is a slightly tweaked version of <a href="https://qrp-popcorn.blogspot.com/2021/11/clean-jazz-guitar-amp-experimenters.html" target="_blank">this</a> Polytone-inspired PA. I recommend this PA over my original version since it offers way less distortion.</p><p>The small signal transistors = 2N4401/2N4403 - a pretty decent general purpose BJT I use from DC to HF. The input pair feature some emitter degeneration via a 100 Ω trimmer potentiometer. If you lack a trimmer pot, place a 49.9 to 68 Ω resistor on each BJT emitter instead. </p><p>I ran out of BD140s plus sought a VAS with an fT of > 150 MHz, a low Cbe and a hfe as high as possible. VAS transistor choice seems to shrink every decade. Gone are the luscious high voltage, high current, high beta offerings from companies such as Toshiba or Sanyo. For example, the KSA1381/KSC3503 or 2SC2911/2SA1209. Yes, these are still available from online auction sellers, but they seem very expensive and the whole bootleg part worry looms heavy. The BD139-140 seem the only low cost, readily available choice for a low budget PA like mine. The BD139/140 pair specs also widely varies - and some are just garbage. I now get mine from Digi-Key and test a couple to confirm they are OK.<br /></p><p>In the end, I placed two 2N4403 BJTs in parallel with 10 Ω current sharing resistors for the VAS. This worked OK. Guitar amps are generally not hifi amplifiers giving ultra low distortion. Some might classify as hifi, but that is the exception. I avoided current sources, driving the VAS with a emitter follower and other distortion lowering techniques. </p><p>The virtue of this PA = easy to build, easy to debug and sounds very good for the parts count. If you scratch build a complicated HiFi PA, you suffer a high probability of failure. Especially when current limiting circuitry and 2 current sources that work together with negative feedback go into your circuit. Often enough, your first sign something is wrong comes in the form of smoke; and by the time you figure out why, you may have destroyed some parts. </p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/a/AVvXsEj6bHzL-ehCELc1ida8svGLhumylHXN2XRJBYXDzQFPplxsY4buLVT4WM-SSzjTflfPlIwd0DSw6PQqLpm6neiOTt4GMgVAj9otiXu7NWyOxM0j2AlbTNssCYS7NFBxVVwyKyQ7Tg3f9m4KfJr3WA-q-Kq1W9rgq6pzgQo_pLx12cqcoA0rmvu7eKyqUQ=s798" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="438" data-original-width="798" height="352" src="https://blogger.googleusercontent.com/img/a/AVvXsEj6bHzL-ehCELc1ida8svGLhumylHXN2XRJBYXDzQFPplxsY4buLVT4WM-SSzjTflfPlIwd0DSw6PQqLpm6neiOTt4GMgVAj9otiXu7NWyOxM0j2AlbTNssCYS7NFBxVVwyKyQ7Tg3f9m4KfJr3WA-q-Kq1W9rgq6pzgQo_pLx12cqcoA0rmvu7eKyqUQ=w640-h352" width="640" /></a></div><p></p><p></p><p>Above — FFT of the Popcorn PA. All harmonics are down at least 70 dBc. I tweaked the input pair 100 Ω trimmer to crush the second harmonic. Some of this spurious output comes from IMD in the TIP142/147 pair. In a PA, distortion can arise from many points along the signal path. I'm quite happy how this particular PA turned out.</p><p>Across the base inputs of the Darlington final pairs, I measured 2.064 VDC. Three rectifier diodes seemed to eliminate any detectable crossover distortion ( a dominant source of distortion in many PAs).</p><p>If you listen to a guitar amp that lacks enough forward PA base bias and suffers crossover distortion, you'll hear a faint, fuzzy sideband sound along with your main guitar sound. You really hear this when playing single, sustained note phrases. This popcorn PA sounds clean & punchy with no hum except with single coil pickups.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/a/AVvXsEiOm0dNvgtjdqmHfYEdMS1P_J2rp5UqtCpJepzc4KDu5p7L3yjXDwIz4PIKHVuYmPykI0x4M_k04PUiArv5FKa0uSkhs9wBblBrHjzWHT5yW5dbsgJG_JGeDvbvtnX4ZNOgnsXL8mRiS9IGs62fnfxmYjYnavLboNcjNLPoW0qCZIeQ5nHwqUGaeYiB_Q=s862" style="clear: right; float: right; margin-bottom: 1em; margin-left: 1em;"><img border="0" data-original-height="626" data-original-width="862" height="464" src="https://blogger.googleusercontent.com/img/a/AVvXsEiOm0dNvgtjdqmHfYEdMS1P_J2rp5UqtCpJepzc4KDu5p7L3yjXDwIz4PIKHVuYmPykI0x4M_k04PUiArv5FKa0uSkhs9wBblBrHjzWHT5yW5dbsgJG_JGeDvbvtnX4ZNOgnsXL8mRiS9IGs62fnfxmYjYnavLboNcjNLPoW0qCZIeQ5nHwqUGaeYiB_Q=w640-h464" width="640" /></a></div><p></p><p>Above — I built this version of my PA first. The BD-139/140 emitters get 120 Ω resistors so they don't need a heat sink and hopefully won't burn up if I made a mistake. I measured DC voltages, calculated current by voltage drops across selected resistors — and also tested it with a signal generator and dummy load. Only 2 diodes drops are needed to properly bias the BD139/140 pair.</p><p>With the amp working well, I then pulled the BD139/140 off the main board and wired up the chassis mounted TIP142/147 after adding 1 more diode to set the correct PA idling base bias. Finally, I added the current feedback loop. I chose the 7K5 Ω resistor during listening tests. <br /></p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/a/AVvXsEirSxKTWB0TYir538B2_LCmYkJ9-MHMNHmoEFGTnnD9IrwMuspXgzcTI67DdmS27K6azVGH2MnBgwvakMLx-qKX-rLfjOyRtNHIOAgbr0B09eDBaCBvEE5hrQiAXzyEzkK22RXw1r0UOiXh6Zpdq-yC235uqeWcO-c5e3CzAdz55IekXdJx5qWCO_vQ-g=s800" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="503" data-original-width="800" height="402" src="https://blogger.googleusercontent.com/img/a/AVvXsEirSxKTWB0TYir538B2_LCmYkJ9-MHMNHmoEFGTnnD9IrwMuspXgzcTI67DdmS27K6azVGH2MnBgwvakMLx-qKX-rLfjOyRtNHIOAgbr0B09eDBaCBvEE5hrQiAXzyEzkK22RXw1r0UOiXh6Zpdq-yC235uqeWcO-c5e3CzAdz55IekXdJx5qWCO_vQ-g=w640-h402" width="640" /></a></div>Above — FFT of the circuit shown in the schematic above (with the BD139/140). The distortion is about as low as I can measure with my DSO. All that is needed = a set of complimentary finals and a good PA might arise. A decent LoFi popcorn PA for guitar amps.<br /><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/a/AVvXsEi4Kxxc-MAtWBe6xJNKiPve8I6y-mZ0X6F8rhcLpDHQaFMMw5lOuLMxaPOF4E0WqtNKKmsQxALibN789qBT2TOTLXE4KdUNrLSIbxocBYs1RugbU6Cm4CIJZ9NxkjddwDw687k92tszVIJoXhF8dvFhjV06J_TpWzkekELJO0IE0BcOHTigQcWRjpIZbA=s1200" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1148" data-original-width="1200" height="612" src="https://blogger.googleusercontent.com/img/a/AVvXsEi4Kxxc-MAtWBe6xJNKiPve8I6y-mZ0X6F8rhcLpDHQaFMMw5lOuLMxaPOF4E0WqtNKKmsQxALibN789qBT2TOTLXE4KdUNrLSIbxocBYs1RugbU6Cm4CIJZ9NxkjddwDw687k92tszVIJoXhF8dvFhjV06J_TpWzkekELJO0IE0BcOHTigQcWRjpIZbA=w640-h612" width="640" /></a></div>Above — The "brick". The Popcorn PA lies on 2 boards with carved islands for the positive, negative and 0 volt rails - and to anchor the rectifier diodes. After taking this photo, I screwed on the cover plate to seal it for safety against the pile of wires and other mess on my bench. This amp is not connected to AC mains unless I am using it and does not have an on/off switch since all my audio test equipment goes on a dedicated switched AC mains power bar. <br /><br /><div class="separator" style="clear: both; text-align: center;"><a href="https://blogger.googleusercontent.com/img/a/AVvXsEjnkabqT3KNg_UZ_HiJzo2UtB9vhp9VoLpR5Z_bbugrq4FMNMEHa-pN47s9XIQVr95YtrQ5t-GSQmpztMYBs3_z-GR_V3T5yCkveMtK55L8-n9udnuXgtTR42MwSJL-uOSJnEj-5gCwX8sYEXsex9_z8QyLv2ekjCu59kKegMFMyxp60AD1j7ZgW32-cg=s1200" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="799" data-original-width="1200" height="426" src="https://blogger.googleusercontent.com/img/a/AVvXsEjnkabqT3KNg_UZ_HiJzo2UtB9vhp9VoLpR5Z_bbugrq4FMNMEHa-pN47s9XIQVr95YtrQ5t-GSQmpztMYBs3_z-GR_V3T5yCkveMtK55L8-n9udnuXgtTR42MwSJL-uOSJnEj-5gCwX8sYEXsex9_z8QyLv2ekjCu59kKegMFMyxp60AD1j7ZgW32-cg=w640-h426" width="640" /></a></div>Above — Rear view of the Popcorn PA. I'll start work on my next preamplifier circuit tomorrow and audio test it using this PA. I really like the small bench footprint this brick offers. I place the preamp circuit just in front of the brick and have small cables built for the 17 volt rails and input.<br /><p>Click <a href="https://qrp-popcorn.blogspot.com/p/guitar-related-index.html" target="_blank">here</a> for my guitar related index.</p><p><br /></p>Vasily Ivanenkohttp://www.blogger.com/profile/17387516134063150119noreply@blogger.com0tag:blogger.com,1999:blog-3480228403403435266.post-86878560941590906542021-12-11T17:48:00.034-08:002022-12-16T19:08:18.996-08:00Gibson GA-50 Inspired Guitar Preamplifier Tribulations<p><b> Introduction</b></p><p>Like many, I enjoy the recorded sounds of — and feel inspired by the Gibson GA-50. That warm tone, full mid range and brown suitcase look epitomizes an American jazz guitar amp classic.<br />What do I like about the GA-50? Its simplicity, the non-mega-scooped mid range, and of course, the warm, thick low and lower middle tones. Feeling inspired by these attributes, I embarked on a design journey to make a GA-50 inspired preamplifier to go with my simple <a href="https://qrp-popcorn.blogspot.com/2022/01/guitar-amp-experimenters-bench-pa-12.html">experimenters PA</a> and its offspring such as <a href="https://qrp-popcorn.blogspot.com/2022/12/the-gaa-12-amps-little-sister-suzu-10.html">this PA</a>.<br /></p><p>I used JFETs & op-amps instead of octal tubes. Perhaps, now, even op-amps are getting outdated as digital algorithms simulating some old amp of lore push the bleeding edge of design. I’m not a fan of using tubes in jazz guitar amplifiers – give me solid state any day for clean signals. Perhaps 1 day, I'll possess the skills for digital amp design. <br />I’ve studied hundreds of solid-state, analog designs and it seems that many just copy someone else's solid-state guitar amp design. Most of the ingenuity in solid-state design seems to go into the distortion circuitry. I found a patent by someone who made a so called 'tube sounding' clipping circuit by putting zener diodes in the feedback loop of an op-amp. Really?!? They were doing this in the late 1960s albeit for other reasons such as op-amp voltage limiters or zero crossing detectors.<br /><br />It's more than the 'lack of tubes' that make some solid-state amplifiers sound poor. Design elements such as putting electrolytic caps in the signal path, along with brash, tinny-toned, picofarad coupling capacitors. Add in toxic sounding distortion — and not to mention the grinding noise from mega-high, tube-era, resistor values, and sometimes poor gain distribution that often compromises the noise performance and/or headroom.<br /> <br />The classic, passive Fender, Marshall et al. mid scooping bass/middle/treble tone stacks looms prevalent in solid state guitar amps. You will find them in countless guitar amps from as many different companies. While they do sound good in many designs, they depart from the desired GA-50 tonality and boy they exhibit loss.<br /><br />My whole adventure focused on the study and testing of tone circuitry. I will blog more about that in future posts, however, as much as I wanted to keep the passive tone circuit of the original tube GA-50, it performed with lackluster results in my solid-state versions. Yes, these simple tone controls work, but such passive tone circuits seemingly lack versatility for getting a consistently warm tone with different guitars, speakers and speaker boxes.<br /> <br />That left active tone control circuitry and about 3 things to play with: [1] shelving bass or treble circuitry (basically these are variable low-pass or high-pass tone controls respectively) [2] peaking/resonant circuits [3] choosing a Q for my tone control circuits that gives the natural sound you hear in amps like the GA-50.<br /><br />I spent ~6 weeks on the bench & computer working on my tone circuits along with the basic gain stages. I also studied non-linear design including distortion circuitry, switching, line-out circuits and speaker box emulation circuits for DI purposes. I filled 2 notebooks and learned much.<br /><br />I burnt thru 3 soldering iron tips and tons of parts on my tone quest. I’ll start by showing you my latest design as of Dec 11, 2021. I strove to keep my signal path resistor values down in value to reduce Johnson or thermal noise arising from these resistors.</p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://1.bp.blogspot.com/-D3rICjD91Ho/YbUNlGo8m7I/AAAAAAAAD4k/-S4eDzLf1_UqXt8gItoAa8NvuWEC5FbYgCNcBGAsYHQ/s1121/Mark%2B7.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="821" data-original-width="1121" height="469" src="https://1.bp.blogspot.com/-D3rICjD91Ho/YbUNlGo8m7I/AAAAAAAAD4k/-S4eDzLf1_UqXt8gItoAa8NvuWEC5FbYgCNcBGAsYHQ/w640-h469/Mark%2B7.png" width="640" /></a></div>Above — The complete preamplifier schematic. Click on the image for a better view since it's 1121 X 821 pixels with lossless compression. This is actually version 7 & sounds sweeter, plus uses less parts than the previous 6 versions. This design was built around the glorious 5532 op-amp. I measured no instability. <br /><p></p><p><b>Buffers. Isolation buffers lurk everywhere !<br /></b></p><p>In your lab, you're likely not making a cost-conscious design for the production line. Therefore, use as many op-amp buffers as you like to enhance stage isolation and to prevent the loading of your tone circuit at extreme settings of the potentiometer wipers. I love buffers and isolation — almost to a fault. Go ahead and remove some of these voltage follower buffers if you wish.</p><p>The input 10K resistor adds noise at a low level spot in the preamp. However, a series input resistor follows normal practices. My listening experiments yielded my personal preference for this resistor to lie between 10 and 12K ohms. That resistor and the 150 pF shunt cap are wired right on the input jack provide RF filtration in a critical spot.</p><p>The 47 nF input cap comes right from the GA-50 which uses a 50 nF cap. This capacitor value works perfectly as a high pass filter pole to attenuate the low frequency rumbling noises emitted from an arch top guitar. Further, it simplifies the design by allows readily available for a reasonable price 1 µF signal chain caps for DC blocking in a clean signal preamplifier design. My 1 µF caps = Panasonic metalized film polypropylene jobs — chosen for their low distortion.</p><p>Active volume and master volume controls help with noise and headroom management. In many solid state guitar amps you'll see a stage of massive voltage gain immediately followed by passive attenuation via a 100K or so volume potentiometer that's shunt to ground. That voltage gain stage runs at its maximum gain (and noise) all the time. Why boost — then right away attenuate the signal if you don't have to ? I tried to copy the GA-50 and just provide 1 volume control, however, found too much compromise in headroom and noise performance. Distributing the gain stages and adding an active master volume control improves the preamplifier and 1 extra volume pot on the front panel does not seem too onerous.<br /></p><p><b>Tone Circuitry</b><br /></p><p>I tried many tone control circuits for bass, treble, lower mid and high mid range. I made variable Q parametric stages; EQ style stages with an op-amp gyrator to simulate the inductor at Qs ranging from 0.7 to 5.1; Baxandall circuits with shelving and/or peaking; and also Wien bridge type treble and mid range circuits. Some of these Wien circuits were fixed while others went variable frequency. I also explored some passive circuitry like those found in Fender, Marshall, Hiwatt, Pignose .....etc. amplifiers as well as circuits from old hi-fi amps. I even copied an old Hughes and Ketner design that plys passive middle and treble controls, then an active, op-amp bass stage that worked pretty well.</p><p>After listening to these circuits over many weeks I came to a few conclusions in the context of a GA-50 inspired amplifier:<br /></p><ul style="text-align: left;"><li>I disliked EQ style tone controls. If the Q was 0.7 to 1, they seemed a bit more tolerable<br /></li><li>In general, circuits with a Q > than about 1.5 tend to sound unnatural and may trigger listener fatigue<br /></li><li>I'm not a big fan of deeply scooped midrange</li><li>Shelving bass and treble sounded better than peaking bass and treble, however, variable frequency shelving seems quite desirable for versatility<br /></li><li>Combining shelving low and high; plus peaking or resonant type mid-range controls is common in mixer boards and other professional gear and sounds OK. Again, when the Q is <= 1.5, the peaking/resonant mid range tone circuit seems more natural sounding to me<br /></li></ul><p>Based on my conclusions above, you now know why I went with the variable frequency shelving low and high frequency controls that forms the heart of my preamplifier. I struggled with potentiometer interdependence in early shelving circuits. When running both a high and low shelf, the low boost/cut pot may affect the high shelf and visa versa. Further, when the shelf frequency pot is rotated to lower resistance to get a higher frequency, distortion, weird behaviour, and/or noises might creep in a some settings of the boost/cut pots. Hence voltage follower isolation amps help make all that pain go away — and provides reasonable potentiometer separation. My chosen circuit still needs work.<br /></p><p>Having 2 low and high frequency pots allows you to find a sweet spot for each respective shelf with respect to the room, guitar and whatever speaker your running at the moment. <br /><br />Ultimately, I opted to not put in a mid-range peaking/resonant tone control for my GA-50 inspired amp. That just seems wrong. On the other hand, the 2 shelving frequency controls allows some alteration of the middle tones which boost versatility. Shelving networks exhibit a Q of less than 1 and subtly, gently alter your guitar's tone. I'll blog more about my tone controls circuit experiments in the future — I've got lots of interesting material to show you.<br /><br /><span style="color: #2b00fe;"><b>Choosing Time Constants</b></span></p><p>In many low + high frequency shelving circuits, the designer chooses the same capacitor value but up a decade for the low frequency network. For example, .0082 + .082 µF. This allows a bit of overlap between the 2 shelves. I opted to run my high frequency network a little higher and get some calculated response slightly above the 10 KHz zone with the 20K high-pass potentiometer set to 0 Ω. <br /><br />The standard calculation applies. Frequency = 1 / (2 pi * R * C ). So, for the low-pass network with the 20K pot set to maximum resistance: Freq = 1/ (6.28 * 22200 Ω * .082 E-6) = 1/.011432 = 87.4 Hertz. If you seek mega bass, try swapping in a 100 nF capacitor instead.<br /></p><div class="separator" style="clear: both; text-align: center;"><a href="https://1.bp.blogspot.com/-s0E6woBGh4I/YbUw7kqNZtI/AAAAAAAAD4w/rM9uw9pDQzIZHWGKLVNGRqBjQT1EXTomwCNcBGAsYHQ/s922/Mark%2B6b.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="697" data-original-width="922" height="484" src="https://1.bp.blogspot.com/-s0E6woBGh4I/YbUw7kqNZtI/AAAAAAAAD4w/rM9uw9pDQzIZHWGKLVNGRqBjQT1EXTomwCNcBGAsYHQ/w640-h484/Mark%2B6b.png" width="640" /></a></div><p>Above — An early version of my preamplifier using nJFETs as amplifiers. I found IMD and clipping on the output of the Q3 source follower. I later replaced it with an op-amp buffer, and perhaps another after the volume control before abandoning JFETs altogether. The low frequency shelf circuit is by Douglas Self in his book <a href="http://douglas-self.com/ampins/books/ssad3.htm" target="_blank">Small Signal Audio Design</a>. I've got 4 of his lovely books and Mr. Self is my favourite audio design book author. I noticed that in his latest version of Small Signal Audio Design, he's added a chapter on guitar amplifiers. Yay!<br /></p><p>This schematic includes my favourite simple passive treble network. The 20K pot is used to variably shunt high frequency to ground. I also added a "fatten" switch to roll off less low frequency for use in 10 inch and 8 inch speaker applications. I would normally switch this capacitor in or out using a front panel switch that remotely controls some DC voltage to a JFET switch using the J111 or PF5102.</p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://1.bp.blogspot.com/--t0IpzhHBmo/YbVCxr4HlPI/AAAAAAAAD5Y/6bU9036YajAngMJvaL1qhNykgBtH7u0nQCNcBGAsYHQ/s837/GA50%2Besq%2Btone%2Bstack-externded.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="570" data-original-width="837" height="436" src="https://1.bp.blogspot.com/--t0IpzhHBmo/YbVCxr4HlPI/AAAAAAAAD5Y/6bU9036YajAngMJvaL1qhNykgBtH7u0nQCNcBGAsYHQ/w640-h436/GA50%2Besq%2Btone%2Bstack-externded.png" width="640" /></a></div>Above — A whimsical idea that I tested and discarded when I tried to keep the original passive GA-50 tone circuit topology in my preamplifier. When I don't like the result of a circuit I write <span style="color: red;"><b>FAIL</b></span> on it so that I never make it again.<br /><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://1.bp.blogspot.com/-s3msh4DabC0/YbVDeCraP9I/AAAAAAAAD5g/nU7X_zllCgwCsx0wsZzpVn4WGjXFgW7tgCNcBGAsYHQ/s680/Gibson%2BG35.%2BRev%2BB.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="417" data-original-width="680" src="https://1.bp.blogspot.com/-s3msh4DabC0/YbVDeCraP9I/AAAAAAAAD5g/nU7X_zllCgwCsx0wsZzpVn4WGjXFgW7tgCNcBGAsYHQ/s16000/Gibson%2BG35.%2BRev%2BB.png" /></a></div>Above —A schematic excerpt from the solid-state Gibson G-35 guitar amp. This amplifier kept the basic topology of the GA-50 tone circuit. By that time, most of their solid state amps had abandoned this style of tone control circuit and were running a passive Baxandall tone stack instead.<br /><p></p><p><b>Modules</b></p><p>At first, I built my preamps on small boards that I lifted in and out of my experimental chassis to work on. I did not bolt them in — for they were just held in place by the DC voltage, ground and wires going to and from the various potentiometers. This worked OK, but soldering and unsoldering all those wires became tedious. Later, I moved to modules that sat in front of the chassis that contained integral pots. I only had to solder or unsolder just 3 wires: B+, B- and the ground wire. Much easier.<br /></p><div class="separator" style="clear: both; text-align: center;"><a href="https://1.bp.blogspot.com/-m3FC9fPnwh8/YbU1C_9P9rI/AAAAAAAAD44/6eCxS-xbzdMgmwDWJkmDQeJ6dLUaA5RVgCNcBGAsYHQ/s1000/DSC_3627.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="631" data-original-width="1000" height="404" src="https://1.bp.blogspot.com/-m3FC9fPnwh8/YbU1C_9P9rI/AAAAAAAAD44/6eCxS-xbzdMgmwDWJkmDQeJ6dLUaA5RVgCNcBGAsYHQ/w640-h404/DSC_3627.jpg" width="640" /></a></div><p>Above — 2 identical modules that contain all the circuitry from input to U1b pin 7 of the inverting amp in my Dec 11 schematic. The circuits were tested with a signal generator + DSO. Then I began installing the low frequency shelving network boost/cut potentiometer as shown in the closer or proximal module. </p><div class="separator" style="clear: both; text-align: center;"><a href="https://1.bp.blogspot.com/-6Gi_qeV0NGs/YbU3P4V0d1I/AAAAAAAAD5A/Tzcpez4Rhks9ROXtYbxD9yLVFXNzp5PmACNcBGAsYHQ/s1100/DSC_3634.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="683" data-original-width="1100" height="398" src="https://1.bp.blogspot.com/-6Gi_qeV0NGs/YbU3P4V0d1I/AAAAAAAAD5A/Tzcpez4Rhks9ROXtYbxD9yLVFXNzp5PmACNcBGAsYHQ/w640-h398/DSC_3634.jpg" width="640" /></a></div><p>Above — The completed Dec 11, 2021 module with the DC voltage and ground wires attached. An alligator clipped lead connects the output to the PA input. A Boss digital reverb permanently lives on my bench for testing circuits with reverb. I'm addicted to plate reverb. The speaker cable runs just to the left of the reverb pedal. I've currently got five 8 Ω speakers in my lab for amp testing.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://1.bp.blogspot.com/-c8lvb96qR8s/YbU4jK0mt_I/AAAAAAAAD5I/Gj9mCS4RMZ8v0IDVq6eUrhPI_50WNKKjwCNcBGAsYHQ/s1200/DSC_3628.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="939" data-original-width="1200" height="500" src="https://1.bp.blogspot.com/-c8lvb96qR8s/YbU4jK0mt_I/AAAAAAAAD5I/Gj9mCS4RMZ8v0IDVq6eUrhPI_50WNKKjwCNcBGAsYHQ/w640-h500/DSC_3628.jpg" width="640" /></a></div><p>Above — A closer photo of the final module. The master volume pot lies on the extreme right hand side. I chose a 2.2 µF output cap since it lies in series with a 1 µF capacitor that's soldered to the PA input. In my final, proper build, I would just likely use a single 1 µF capacitor. My 2.2 µF polypropylene caps are huge 630 volt jobs. I've got a few 100 volt caps @ 2.2 µF, but save these for final builds. Brand name capacitors are not cheap.<br /></p><p>
</p><p class="MsoNormal"><b><span lang="EN-US" style="mso-ansi-language: EN-US;">Speakers</span></b></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-ansi-language: EN-US;">No doubt
some of the sonic signature tones from the GA-50 come from the Alnico magnet 12-
and 8-inch speaker pair. I’ve learned that speakers and perhaps even more
importantly, the box they’re mounted in prove crucial to realizing your desired
guitar tone. <span style="mso-spacerun: yes;"> </span>I’ve tried 2 speaker pairings: 12 +
8 inch, 12 + 10 inch and 8 + 8 inch. The wide sound field somehow disturbed me.
The only combination I seemed to tolerate was the 8-inch pair, however, they need
to go in a box designed to boost the bass response for my taste. Thus, I just
use one 8-ohm speaker with this preamp + my PA.</span></p>
<p class="MsoNormal"><span lang="EN-US" style="mso-ansi-language: EN-US;">With my
preamplifier, if you drive a speaker mounted in a cabinet designed to give bass
extension, the available low-end response might amaze you. This is definitely a warm, low-end focused amp – lacking the brash high-mid & raunchy treble
response associated with some “transistor amps”. However, the high end is still
there. Sometimes it’s pleasant to put a bit of shimmering > 8 KHz treble
into your tone. </span></p>
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<![endif]--></p><div class="separator" style="clear: both; text-align: center;"><a href="https://1.bp.blogspot.com/-34k0WnnV5fk/YbVKBpnE6ZI/AAAAAAAAD5o/SKJU6K3UmAAeHUrNT6zJAiC2mbDoqyftQCNcBGAsYHQ/s1200/JFET%2Bcircuit.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="945" data-original-width="1200" height="504" src="https://1.bp.blogspot.com/-34k0WnnV5fk/YbVKBpnE6ZI/AAAAAAAAD5o/SKJU6K3UmAAeHUrNT6zJAiC2mbDoqyftQCNcBGAsYHQ/w640-h504/JFET%2Bcircuit.jpg" width="640" /></a></div><p>Above — An early breadboard using Ugly Construction. The power supply is a simple interface to my bench +/-15 volts regulated, 5 Watt power supply. Islands are carved out in the circuit board for temporary connection to the power supply when developing circuits prior to putting them in the guitar amp. I measured DC voltages, DC current, AC peak-peak voltages and usually hook up a signal generator and look at the FFT also. I use the grounding techniques shown on <a href="https://qrp-popcorn.blogspot.com/2019/01/clean-jazz-guitar-amp-builder-notes.html" target="_blank">this web page</a> so despite all this wire, I hear no hum unless I use a single coil pickup.<br /></p><p><b>Future Experiments</b><br /></p><p></p><div class="separator" style="clear: both; text-align: center;"><a href="https://1.bp.blogspot.com/-ByotsY6ISGQ/YbVLSlO5Q9I/AAAAAAAAD5w/7xHYS14PRj457G9cJxaab8uG9H3biZzKwCNcBGAsYHQ/s848/line%2Bout.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="421" data-original-width="848" height="318" src="https://1.bp.blogspot.com/-ByotsY6ISGQ/YbVLSlO5Q9I/AAAAAAAAD5w/7xHYS14PRj457G9cJxaab8uG9H3biZzKwCNcBGAsYHQ/w640-h318/line%2Bout.png" width="640" /></a></div>Above — Future things to add to my GA-50 inspired amplifier. Thanks to the books of Douglass Self and from studying many schematics, I've got confidence to work out ways to record my amp without speakers + a microphone and/or add software-based digital effects. The features found in many newer amps such as integral DI patching, speaker cabinet emulation and ground loop noise isolation circuitry will help take the GA-50 inspiration into new realms. I feel that if Gibson's Seth Lover and Ted McCarty were alive today they would embrace the latest technology including digital signal processing and of course, op-amps. <p></p><p>I'll continue to work on my basic GA-50 inspired guitar amp from time to time. I've got parts coming to make a small, complete low-power amp Dec 11 version for practice. I've already tweaked the improved Polytone inspired PA from my <a href="https://qrp-popcorn.blogspot.com/2021/11/clean-jazz-guitar-amp-experimenters.html" target="_blank">last posting</a> to lower its noise floor & distortion a little.<br /></p><p>I only wish I had more time to spend on the bench.<br /> </p><p>Click <a href="https://qrp-popcorn.blogspot.com/p/guitar-related-index.html" target="_blank">here</a> for my guitar-related index.<br /></p><p><br /></p>Vasily Ivanenkohttp://www.blogger.com/profile/17387516134063150119noreply@blogger.com4tag:blogger.com,1999:blog-3480228403403435266.post-32836314240711879902021-03-15T22:20:00.014-07:002021-03-18T21:07:21.537-07:00<p> </p><h3 class="post-title entry-title" itemprop="name">Clean Jazz Guitar Amp Builder Notes — Part 4: Pre Amplifier Notes</h3><h3 class="post-title entry-title" itemprop="name"><span style="font-size: medium;">Part 1 lies <a href="https://qrp-popcorn.blogspot.com/2019/01/clean-jazz-guitar-amp-builder-notes.html" target="_blank">here</a><span style="color: purple;"><span style="color: black;"><br />Part 2</span> <span style="color: black;">lies</span> <a href="https://qrp-popcorn.blogspot.com/2019/11/clean-jazz-guitar-amp-builder-notes.html">here</a></span><span style="color: purple;"><span style="color: black;"><br />Part 3 lies <a href="https://qrp-popcorn.blogspot.com/2020/11/clean-jazz-guitar-amp-builder-notes.html" target="_blank">here<br /><br /></a></span></span></span></h3>
<span style="font-size: medium;"><a href="https://qrp-popcorn.blogspot.com/p/guitar-related-index.html" target="_blank">Click for my Guitar-Related Index</a></span><h3 class="post-title entry-title" itemprop="name">Preamplifier notes from March 7, 2021 until present</h3><h3 class="post-title entry-title" itemprop="name"><span style="font-size: medium;"><span style="font-weight: normal;">Seeking my ultimate clean jazz guitar amplifier I continue on from my last posting with Part 4. Procrastination set in. I did zero on the bench for several months; however, gathered new guitar, bass plus steel guitar amp schematics, plus thought about the next steps on my journey to find my ideal jazz tone machine .<br /></span></span></h3><h3 class="post-title entry-title" itemprop="name"><span style="font-size: medium;"><span style="font-weight: normal;">Although I liked the bass and treble controls from my previous preamp circuit, after months of listening, dissatisfaction arose. A sort of cognitive-aural dissonance loomed. My amp wasn't making me happy anymore. When we hear soothing, ideal guitar tones , we transform — suddenly your playing feels inspired and we make up new phrases simply because your mind feels pleased from what your hearing roar from the speakers. It's difficult to describe this to non-musicians.</span></span></h3><h3 class="post-title entry-title" itemprop="name"><span style="font-size: medium;"><span style="font-weight: normal;">A good guitar or amp may inspire you. Sometimes, just something new gets you on track. Hence many players suffer from guitar (or amp) acquisition syndrome and the like.<br /></span></span></h3><h3 class="post-title entry-title" itemprop="name"><span style="font-size: medium;"><span style="font-weight: normal;">Back to the bench. The mid range frequencies provide the sonic heart of a guitar amplifier. Nailing the mid range — with versatility & deft finesse (all while feeling sonic bliss) proves no small task. Do you prefer the scooped lower mid range Fender sound, or seek to hear thick tones with just enough sparkle to quell the mud monster that lurks only a few dB below? Or perhaps you desire both? <br /></span></span></h3><h3 class="post-title entry-title" itemprop="name"><span style="font-size: medium;"><span style="font-weight: normal;">My previous Polytone-like bass + treble stack provided a pleasant enough tone, but lacked the ability to blast thick midrange tones when I sought them. e.g. 'twas a 1-trick pony. </span></span></h3><h3 class="post-title entry-title" itemprop="name"><span style="font-size: small;"><span style="font-weight: normal;"><span style="font-size: medium;">So i built a 4 frequency Baxandall tone circuit and then kept experimenting with a separate preamplifer board that I'll work on over the next year. </span><br /></span></span></h3><h3 class="post-title entry-title" itemprop="name"><span style="font-size: small;"><span style="font-weight: normal;"> <div class="separator" style="clear: both; text-align: center;"><a href="https://1.bp.blogspot.com/-WMvuPTM4pRQ/YFA8zMgzSLI/AAAAAAAADxU/XnHp5BwIi1wJ4UAAmMKRjjaBjt97rL01gCLcBGAsYHQ/s791/preamp-BLOK.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="418" data-original-width="791" height="338" src="https://1.bp.blogspot.com/-WMvuPTM4pRQ/YFA8zMgzSLI/AAAAAAAADxU/XnHp5BwIi1wJ4UAAmMKRjjaBjt97rL01gCLcBGAsYHQ/w640-h338/preamp-BLOK.png" width="640" /></a></div><span style="font-size: medium;">Above — Preamplifer block diagram. I kept the early stage preamplifer shown in Part 3 and added a new tone stack and post tone circuit amplifier.</span></span></span></h3><h3 class="post-title entry-title" itemprop="name"><span style="font-size: small;"><span style="font-weight: normal;"></span><div style="text-align: center;"><a href="https://1.bp.blogspot.com/-xUIFLmiRxkI/YFA9Uag9uYI/AAAAAAAADxc/nfmVmh-SQLUF2CDDhIJRbj0y2mz61hccQCLcBGAsYHQ/s1076/tone-stack-March%2B7-2021.png"><img border="0" data-original-height="661" data-original-width="1076" height="394" src="https://1.bp.blogspot.com/-xUIFLmiRxkI/YFA9Uag9uYI/AAAAAAAADxc/nfmVmh-SQLUF2CDDhIJRbj0y2mz61hccQCLcBGAsYHQ/w640-h394/tone-stack-March%2B7-2021.png" width="640" /></a></div><span style="font-size: medium; font-weight: normal;">Above — The new section 2 & 3 circuit with the simple post tone stack amplifier attached to the tone stack for clarity. This version borrows from the work of Doug Self</span><span style="font-size: medium;">, <span style="font-weight: normal;">who I've referenced in Parts 1 and 2.</span></span></span></h3><h3 class="post-title entry-title" itemprop="name"><span style="font-size: small;"><span style="font-weight: normal;"><span style="font-size: medium;">This is a transition circuit. It got me away from the Polytonic sound of my previous tone circuit and into the territory where thick, but clear mids blast beautifully. Still, though, this circuit does not produce sweet, musical scooped mid tones even though I can cut the low and high midrange controls.<br /><br />I lined up multiple new circuits to try and will present them over the next few months. Stay tuned.</span><br /></span></span></h3><h3 class="post-title entry-title" itemprop="name"><div class="separator" style="clear: both; text-align: center;"><a href="https://1.bp.blogspot.com/-MCKQDwDpzcg/YFA_mqUGTvI/AAAAAAAADxs/uYQniNxwWd4MXU1m_KOmvh1WHX2rx657ACLcBGAsYHQ/s1099/DSC_3400.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="658" data-original-width="1099" height="384" src="https://1.bp.blogspot.com/-MCKQDwDpzcg/YFA_mqUGTvI/AAAAAAAADxs/uYQniNxwWd4MXU1m_KOmvh1WHX2rx657ACLcBGAsYHQ/w640-h384/DSC_3400.jpg" width="640" /></a></div><br /><span style="font-size: small;"><span style="font-weight: normal;"><span style="font-size: medium;">Above — the current tone circuit in my jazz guitar amp. I love thick mid-range tones, but not all the time. Let's work to grab some versatility. To the bench for experiments. Thank you!</span><br /></span></span></h3><h3 class="post-title entry-title" itemprop="name"><span style="font-size: small;"></span><br /></h3>Vasily Ivanenkohttp://www.blogger.com/profile/17387516134063150119noreply@blogger.com0tag:blogger.com,1999:blog-3480228403403435266.post-5541060568379665132020-11-16T23:34:00.490-08:002021-03-18T21:00:24.552-07:00Clean Jazz Guitar Amp Builder Notes — Part 3: Pre Amplifier <p>This is part 3 of a series about a complete prototype guitar amp.<br /><br />
Part 1 lies <a href="https://qrp-popcorn.blogspot.com/2019/01/clean-jazz-guitar-amp-builder-notes.html" target="_blank">here </a><br />
<span style="color: purple;"><span style="color: black;">Part 2</span> <span style="color: black;">lies</span> <a href="https://qrp-popcorn.blogspot.com/2019/11/clean-jazz-guitar-amp-builder-notes.html">here</a><br /><span style="color: black;">Part 4 lies <a href="https://qrp-popcorn.blogspot.com/2021/03/clean-jazz-guitar-amp-builder-notes.html" target="_blank">here</a></span><br /></span></p><div style="text-align: left;"><span>My guitar-related Index is <a href="https://qrp-popcorn.blogspot.com/p/guitar-related-index.html" target="_blank">here</a>.</span></div><p><span style="color: purple;"><span style="font-size: medium;"><b><span style="color: black;">Part 3: Preamplifer from Nov 29, 2020 to March 7, 2021 </span></b></span><br /></span></p><p><b>Bench Notes:</b></p><p></p><p></p><p>I sought a low noise, clean amplifier. In the head of most jazz guitarists an ideal guitar tone sits —<br />it might be Jim Hall in 1965, or Tal Farlow in 1957, or Julian Lage in 2020. I've discussed this topic previously and it essentially defines subjectivity. Tube versus solid state? 12 inch versus 10 inch speakers? Single coils versus humbuckers? The microphone! Was EQ applied by the recording engineer? And so on. Let's glide past this dribble and assume the 'ideal guitar sound' in your head sounds as good as mine.</p><p>I chose to power 2 speakers bolted in an open back cabinet. I feel open back cabinetry sounds more natural and previously felt 100% confident that sealed, ported speaker cabinets were the only way to get my jazz tone. Bah non, t’as fait n’importe quoi. Thus my tone shaping lies orientated to driving an open-backed speaker cabinet while still getting some thumping bass response at low, practice-level volume if desired.<br /></p><p>First comes the DC power supply for the op-amps. For maximum op-amp headroom, I ran the split supply DC as high as I could safely manage by choosing 17 volt zener diodes.</p><p><br /></p><div class="separator" style="clear: both; text-align: center;"><a href="https://1.bp.blogspot.com/-paf7jpR1RLs/X7IkqNtw6XI/AAAAAAAADqo/Yxc3ccwcuhIGXbFhtGbjxtAwWPPsPQDHwCLcBGAsYHQ/s878/Op-amp%2Bpower%2Bsupply.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="375" data-original-width="878" height="274" src="https://1.bp.blogspot.com/-paf7jpR1RLs/X7IkqNtw6XI/AAAAAAAADqo/Yxc3ccwcuhIGXbFhtGbjxtAwWPPsPQDHwCLcBGAsYHQ/w640-h274/Op-amp%2Bpower%2Bsupply.png" width="640" /></a></div><p>Above — I built the voltage regulators on the Stage 1 preamp board. These hulky transistors seem excessive, but in an earlier version, a BD139 failed and smoked up my lab. Don't get me going about how bootleg parts have polluted our parts drawers and reduce some of the joy. These 20 year old, Motorola TIP BJTs won't fail now or ever. My original design had diode current limiters, but I dispensed with them when I hurriedly rebuilt the voltage regulators after the NPN part failure. BP is ground; please refer to Part 1 for details on how I grounded the various stages to avoid hum and reduce noise.<br /></p><div class="separator" style="clear: both; text-align: center;"><a href="https://1.bp.blogspot.com/-0OqopLMfYMI/X8R745snsaI/AAAAAAAADuo/jeM6fjhAkKcupfzPZNovPZ92AXSc8OEYQCLcBGAsYHQ/s795/preamp-BLOK.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="418" data-original-width="795" height="336" src="https://1.bp.blogspot.com/-0OqopLMfYMI/X8R745snsaI/AAAAAAAADuo/jeM6fjhAkKcupfzPZNovPZ92AXSc8OEYQCLcBGAsYHQ/w640-h336/preamp-BLOK.png" width="640" /></a></div><div class="separator" style="clear: both; text-align: left;">Above — Block diagram of the preamplifer. I'll present each stage
separately.</div><div class="separator" style="clear: both; text-align: left;"> </div><div class="separator" style="clear: both; text-align: left;"><h2 style="text-align: left;"><b>STAGE 1<br /><br /></b></h2><h2 style="text-align: left;"></h2><br /><h2 style="text-align: left;"></h2><div style="text-align: left;"><span style="font-weight: normal;">Above — First preamplifier stage. </span></div></div><div class="separator" style="clear: both; text-align: center;"><a href="https://1.bp.blogspot.com/-MSKKFC5u1q4/X8WfoJyGO_I/AAAAAAAADvs/H-V98ERuvGUVPuXy-3SEMv0x-Wb3Yew4ACLcBGAsYHQ/s1118/Preamp-Nov29.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="720" data-original-width="1118" height="412" src="https://1.bp.blogspot.com/-MSKKFC5u1q4/X8WfoJyGO_I/AAAAAAAADvs/H-V98ERuvGUVPuXy-3SEMv0x-Wb3Yew4ACLcBGAsYHQ/w640-h412/Preamp-Nov29.png" width="640" /></a></div><p style="text-align: left;">The 10K and the 220 pF shunt capacitor form a low-pass filter at 72 kHz which attenuates high frequency signals such as AM radio stations that might sneak into the amplifier input. You may go as high as 470pF if needed; or may raise the resistor value to boost HF filtration. </p><p style="text-align: left;">Ideally your entire preamp should lie in a sealed metal box to reduce capacitive pickup, however, I designed as I built and fell short with shielding. Any noise arising in the first preamp goes down the chain and Stage 1 sets your amp noise floor.<br /><br />The 10K input resistor also serves to protect the op-amp from large signal overload such as a static spike or a high amplitude signal. Further, 11 volt anti-parallel zener diodes clamp excessive amplitude signals. The diode value isn't critical, however, many engineers would avoid zeners rated below ~ 6.2 volts as they may conduct prior to signals reaching the zener or knee voltage — and this might cause signal distortion.</p><p style="text-align: left;">How much gain and how to distribute it proves a vexing design consideration. Running lots of gain often means lots of noise. Ideally, we want just enough preamp gain for the power amp to reach its maximum clean power, but not a drop more. Distributing some of the gain before and after volume controls is 1 way guitar amp engineers manage the noise. The main goal is to avoid amplifying noise at low volume control settings. I spend most of my practice time at low volume settings so I don't drive my family nuts with repetitive practice routines.<br /></p><p style="text-align: left;">Imagine if you built a 15 dB gain preamp stage and then placed a passive volume control pot after it. Your preamplifier stage is always running at 15 dB gain and its noise and the noise of the potentiometer will go down the preamp chain. If you put another fixed 15 dB gain stage after this potentiometer, then even at low volume control settings, the system noise after the pot is still amplified by 15 dB.<br /></p><p style="text-align: left;">Applying active volume controls (an inverting op-amp stage with the volume pot in the feedback loop) is 1 way to keep noise down at lower volume control settings. Your stage gain goes up & down with the series resistance of the volume control pot. You'll see this in countless guitar amplifiers as it avoids amplifying noise at low volumes while still affording decent headroom for the input.<br /><br />Over several decades, many of the guitar amplifiers I've played were high gain "rock star specials" and quite noisy. By noise I mean Johnson thermal noise, shot noise, flicker noise, plus voltage and current noise from amplifier stages. Crank your amp to maximum gain by turning all the pots to "ten"; unplug your guitar cord from the amp input, or turn the volume pot on your guitar to zero and listen in a quiet room. You'll hear the noise floor of your amp at it's worst. Advance the tone controls to boost and then cut. If 1 exists, rotate the reverb control from minimum to maximum and see what happens to the noise you hear in the speaker. </p><p style="text-align: left;">I liken this sound to frying electrons in a skillet. It reminds me of listening to galactic noise in an astronomy receiver. Pretty much, they are the same thing.<br /></p><p style="text-align: left;">Many home brew and some commercial guitar amps are really noisy. Reducing noise serves as a major design goal for me. In this amp, I tried to keep noise down by using low value resistors (as possible) , quiet op-amps, active volume control and hopefully wise gain distribution. Some noise inevitably arises in the tone circuitry and for me this is where most of my amp's noise gets generated. <br /><br />Currently my home brew amp offers less noise and louder maximum room volume than my Polytone Megabrute and my blackface Fender Reverb. I still want it quieter in future versions however.<br /></p><p>Referring to the stage 1 schematic, my first stage unity gain arrangement buffers the input from the 5K volume control pot. The buffer allows you to avoid the noisy 50 or 100K volume pot you often see in guitar amps. The Baxandall active gain stage perfected by Doug Self gets employed. I strongly recommend Doug Self's book: <u>Small Signal Audio Design</u>, now in 3rd edition. Self, an adroit author and wise clinician, plys measurement based advice that can't be found anywhere else.<br /></p><p>The U1B buffer allows use of quieter low value resistors in the parallel U2 op-amp stages. This amplifier exhibits very low noise on lower volume settings and the only downside is the volume control isn't perfectly logarithmic across the rotation of the knob. You get used to it however.<br /></p><p>I prefer to not go above a setting of "9" on the gain pot as the noise performance at "1-9" seems stellar. </p><p></p><p>Another big concern is tone shaping the input. The capacitors C1 and C2 achieve this; especially C1. I placed a pair of alligator clips and tried capacitors in the C1 slot ranging from 1 nF to 10 nF. I settled on 4.7 nF as shown. C1 sets how much of your guitar's low frequency you want to high pass filter. <br /><br />If you apply too low a value, your guitar may sound thin and tinny. To large a value for C1 might cause you guitar to lack highs. The effect maybe subtle, but still important. I agonized over choosing the correct C1 for 1 year — pick something and stick to it ( for awhile anyway). You may help fatten a bright guitar with your C1 and C2 choice.<br /></p><p>For C2, I've got a 1 µF cap in place currently. Between 1 and 2.2 µF seems ideal for me. This helps prevent a flabby bass response when playing loudly. If you play distorted guitar, your C1 and C2 choices would likely be very different than mine. Down the chain I use 4.7 to 10 µF signal capacitors. My small, mostly donated collection of signal capacitors are older, mostly metallized polyester film types rated at 200 volts plus, and thus are big and unwieldy. 1 day, I will order some smaller size caps.<br /></p><p>Guitarists hotly debate whether plastic film capacitors insulated with polyester, polypropylene, polystyrene or some other exotic dielectric material "are the best". It's quite laughable. Doug Self tackles this myth with gusto in his Small Signal Audio Design book. I just prefer caps that don't distort the signal, leak DC, nor break my bank account. <br /></p><p>Finally, I employed the lovely LM4562 op-amp in Stage 1. Without the 100 nF COG/NP0 bypass caps on pins 8 and 4, I've seen this part oscillate at between 3.5 and 4 MHz. The 5532 would also prove a solid op-amp choice.</p><p></p><h2 style="text-align: left;"><b>STAGE 2<br /><br /></b><div class="separator" style="clear: both; text-align: center;"><a href="https://1.bp.blogspot.com/-2vseNfm1JGA/X8Wf3YP6L2I/AAAAAAAADvw/ooiEGfXP2g83QOsjTOaTJAwm75KdklHPgCLcBGAsYHQ/s797/bass-treblel2020.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="708" data-original-width="797" height="568" src="https://1.bp.blogspot.com/-2vseNfm1JGA/X8Wf3YP6L2I/AAAAAAAADvw/ooiEGfXP2g83QOsjTOaTJAwm75KdklHPgCLcBGAsYHQ/w640-h568/bass-treblel2020.png" width="640" /></a></div></h2><div style="text-align: left;"><span style="font-weight: normal;">Above — Second and third preamplifier stages. </span><br /> </div><div style="text-align: left;">I combined both Stage 2 and 3 on this schematic as they share the same op-amp<b>; </b>the Texas Instruments OPA2134 which potentially offers less noise than the TL072<b>. <br /><br /></b>For ~ 1 year I had a 9 channel equalizer as the tone control control circuit in my amp. I grew to dislike it. Why? It sounded unnatural, caused listener fatigue and lacked a 'musical character'. On Nov 29, 2020, feeling discontented and a little melancholy , I cut all the wires and unbolted the copper clad board. I was done with that circuit. ( Archived in<i> Old Stage Two and Three Notes</i> below).<br /></div><div style="text-align: left;"><b><br /></b></div><div style="text-align: left;">What to replace it with ?<b> </b>I felt a Baxandall tone circuit would work fine. The next question was 2, 3 or 4 frequency bands?<b> </b>Remembering a jazz concert 35 + years ago triggered me to go with the simple bass + treble version shown in the Stage 2-3 schematic.</div><div style="text-align: left;"><b><br /></b></div><div style="text-align: left;">I remembered the guitar player playing a Gibson L5 through a Polytone 102 with a speaker extension cabinet attached. His tone amazed me. I remember visually checking out his amp and saw it had tremolo, reverb and just bass + treble tone controls. I also remember feeling surprised that it wasn't a tube amp. Polytone amps emit a spongy, warm, quite musical sound that comes from the Baxandall tone circuit, plus perhaps, a closed speaker cabinet stuffed with insulation.</div><div style="text-align: left;"><b></b></div><div style="text-align: left;"><b><br /></b></div><div style="text-align: left;">Many Polytone amps seem to follow a interesting gain distribution pattern.<b> </b>The first preamp has a gain of 6 dB<b> </b>followed by a switch that throws it in a bass boost, bass cut, or normal.<b> </b>These circuit modify the op-amp feedback loop and by viewing Polytone schematics, it easy to see how they work. </div><div style="text-align: left;"><b><br /></b></div><div style="text-align: left;">After the first op-amp stage is a Baxandall tone stack with either bass + treble or bass middle + treble<b> </b>controls<b>. </b> A volume pot follows the tone stack — passive gain control. From there, the signal may go to a reverb circuit, tremolo, or a distortion circuitry , however, all of these are summed with a final 20 dB maximal gain op-amp stage with active gain control.<br /><br /></div><div style="text-align: left;"><div class="separator" style="clear: both; text-align: center;"><a href="https://1.bp.blogspot.com/-DhGNeYbgnBc/X8SKJZrhBpI/AAAAAAAADvA/sYd17tbGmPsyvsrmMKoOUJyq0gnZ1hrpwCLcBGAsYHQ/s1527/pTone.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="741" data-original-width="1527" height="310" src="https://1.bp.blogspot.com/-DhGNeYbgnBc/X8SKJZrhBpI/AAAAAAAADvA/sYd17tbGmPsyvsrmMKoOUJyq0gnZ1hrpwCLcBGAsYHQ/w640-h310/pTone.png" width="640" /></a></div><br /><span style="font-weight: normal;">Above — An excerpt from the schematic that came with my Polytone Megabrute. R18 is actually a 100K pot. <br /><br /></span></div><div style="text-align: left;"></div><div style="text-align: left;"><b></b></div><div style="text-align: left;">With the fond remembrances from decades ago, I decided to put the 102's approximate bass + treble tone circuit plus the Polytone Megabrute's summing op-amp into my guitar amplifier.<b> </b>The Baxandall tone circuit was a standard HiFi circuit back in the day and perhaps even now.<b> </b>It seems almost antithetical to the Fender scooped lower mid range tone stack.<b> </b>However, if you turn up the bass and treble controls, you hear the scooped mid range response. Just a bit more subtle. <b><br /><br /></b></div><div style="text-align: left;">I dispensed with the reverb, tremolo, and the infamous Polytone distortion circuit while <b></b>lowering the resistor values as possible to reduce Johnson noise. The end result is what you see in the Stage2/3 schematic. My first op-amp offer much more available gain, and by far my amp has a very low noise floor. My power amp also generates lower harmonic distortion and noise than Polytone amplifiers.</div><div style="text-align: left;"><br /></div><div style="text-align: left;">The 100 pF capacitor from U1a pin 7 to 6 is mandatory. If you turn the treble pot to boost treble, at some point, the tone stack will burst into high amplitude HF oscillation without this cap. </div><div style="text-align: left;"><br /></div><div style="text-align: left;">I tried a few different values for the treble capacitor and settled on 3.9 nF. I also boosted the low frequency by hiking the bass caps to 150 nF. With an open-back cabinet, this provides a little more available bass boost if required. For a closed back speaker cabinet — for 10K pots: 100 nF seems a good choice for the bass caps.<br /><br /></div><div style="text-align: left;"><b></b></div><h2 style="text-align: left;"><b>STAGE 3<br /><br /></b></h2><div style="text-align: left;">Stage 3 = the simple U1b active gain controlled inverting op-amp. </div><div style="text-align: left;"> </div><div style="text-align: left;"><table align="center" cellpadding="0" cellspacing="0" class="tr-caption-container" style="float: left; margin-right: 1em; text-align: left;"><tbody><tr><td style="text-align: center;"><a href="https://1.bp.blogspot.com/-F7ap4J1pNs4/X8SQR14xJZI/AAAAAAAADvM/VedYxtSP2884zUnIBXtDNPGhF7glvrwyQCLcBGAsYHQ/s1100/DSC_3356b%2B%25281%2529.jpg" style="margin-left: auto; margin-right: auto;"><img border="0" data-original-height="634" data-original-width="1100" height="368" src="https://1.bp.blogspot.com/-F7ap4J1pNs4/X8SQR14xJZI/AAAAAAAADvM/VedYxtSP2884zUnIBXtDNPGhF7glvrwyQCLcBGAsYHQ/w640-h368/DSC_3356b%2B%25281%2529.jpg" width="640" /></a></td></tr><tr><td class="tr-caption" style="text-align: center;"><br /></td></tr></tbody></table><span style="font-weight: normal;">Above — My front panel now has many unused pots and switches. I've stripped out my line-out, effects loop and other circuitry </span><span style="font-weight: normal;"><span style="font-weight: normal;">— </span>regressed to a very simple preamplifier circuit with no frills. Sometimes less = more.</span><br /> </div><div style="text-align: left;"></div><div style="text-align: left;"></div><div style="text-align: left;"><b></b></div><div style="text-align: left;"><div class="separator" style="clear: both; text-align: center;"><a href="https://1.bp.blogspot.com/-Wxs2WMjlpPQ/X8SQ6szDz0I/AAAAAAAADvU/t3QpG5kpd9A3n_uol6dxvEMKNSVZfvkJgCLcBGAsYHQ/s1100/DSC_3364.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1100" data-original-width="897" height="640" src="https://1.bp.blogspot.com/-Wxs2WMjlpPQ/X8SQ6szDz0I/AAAAAAAADvU/t3QpG5kpd9A3n_uol6dxvEMKNSVZfvkJgCLcBGAsYHQ/w522-h640/DSC_3364.jpg" width="522" /></a></div><br /><b><span style="font-weight: normal;">Above — My amp on top of a home brew speaker cabinet. I'm no carpenter. This cabinet holds a 10 inch + 12 inch speaker. I'll comment about speakers in Part 4 of this amplifier series. With cats, cloth speaker grills are out. I fashioned mine from an aluminum vent cover. </span></b></div><div style="text-align: left;"><b><span style="font-weight: normal;"><br /></span></b></div><div style="text-align: left;"><b><span style="font-weight: normal;">I love playing through this amplifier. It has a Polytone-like warm, bouncy sound with crisp note definition.<br /> </span></b></div><div style="text-align: left;"><b><span style="font-weight: normal;"> </span></b></div><div style="text-align: left;"> -------------------------------------------------------------------------------------------------------- <br /><h2 style="text-align: left;"><b>Miscellaneous bench notes plus discarded circuitry<br /></b></h2></div><div style="text-align: left;"> <div class="separator" style="clear: both; text-align: center;"><a href="https://1.bp.blogspot.com/-LoNVQIu8hyU/X7No0-6GQwI/AAAAAAAADtM/1iBk9ap8UHs4fcnSu6rNYA9d24RJQBaqACLcBGAsYHQ/s751/16Volt-circuit.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="602" data-original-width="751" height="514" src="https://1.bp.blogspot.com/-LoNVQIu8hyU/X7No0-6GQwI/AAAAAAAADtM/1iBk9ap8UHs4fcnSu6rNYA9d24RJQBaqACLcBGAsYHQ/w640-h514/16Volt-circuit.png" width="640" /></a></div><div style="text-align: left;">Above — The voltage regulators with current limitation. The zeners shown
are 16 volt jobs. 1 diode compensates for the BE of the transistor,
while the other diode limits the voltage across the emitter resistor to
the diode ON voltage of around 0.6 volts. The current limit runs a bit
over 200 mA per rail.<br /><br /></div><h2 style="text-align: left;"><b>Old Stage Two and Three Notes <br /><br /></b></h2><h4 style="text-align: left;"><i>Below lies the Stage 2 and 3 circuitry used prior to Nov 29, 2020.</i></h4><h2 style="text-align: left;"><b><a href="https://1.bp.blogspot.com/-4Jx2bd205ZY/X7IqatlsQ1I/AAAAAAAADq8/kCK9gDAEU-UQ0Nw6iV5VObVm1u95xGFSQCLcBGAsYHQ/s795/preamp-Dec3.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="418" data-original-width="795" height="337" src="https://1.bp.blogspot.com/-4Jx2bd205ZY/X7IqatlsQ1I/AAAAAAAADq8/kCK9gDAEU-UQ0Nw6iV5VObVm1u95xGFSQCLcBGAsYHQ/w640-h337/preamp-Dec3.png" width="640" /></a></b></h2><p>I
spent a lot of time studying and testing tone circuitry. I'm still
uncertain what I'll eventually stick in my final amp version, however,
here's my circuit prior to Nov 29, 2020:</p><div class="separator" style="clear: both; text-align: center;"><a href="https://1.bp.blogspot.com/-o-HLiR0LFks/X7RXSEo1ogI/AAAAAAAADt0/2KjLOVdoDMIjfwkVyzOsDF3UeZjxU33jwCLcBGAsYHQ/s1625/Nov2020.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="924" data-original-width="1625" height="364" src="https://1.bp.blogspot.com/-o-HLiR0LFks/X7RXSEo1ogI/AAAAAAAADt0/2KjLOVdoDMIjfwkVyzOsDF3UeZjxU33jwCLcBGAsYHQ/w640-h364/Nov2020.png" width="640" /></a></div><span style="font-weight: normal;">Above — Second preamplifier stage. </span><p>As
you can see, it's an equalizer. I've had this in place for over 1 year
to learn what frequencies I seek to boost or cut. Upon reflection, it
seems I mostly like to cut lower middle frequencies. I grew up listening
to guitar amps with scooped lower mids and it's ingrained. </p><p>I
actually built a partial 1/3 octave equalizer (50, 63, 80, 100, 125,
160, 200, 250, 315, 400, 500, 630, 800, 1K, etc.) but stopped at 6.3 KHz
to
experimentally see what frequencies I like to adjust in a clean guitar
amp. The frequencies I seemed to care about are those I picked for the
Stage 2 equalizer.<br /> <br /></p><div class="separator" style="clear: both; text-align: center;"><a href="https://1.bp.blogspot.com/-XXDkRs5xWss/X7MWfhUua6I/AAAAAAAADr8/g0oToV6paZoPPVecA2ihygH7gPNV6MJJQCLcBGAsYHQ/s1000/DSC_2774-1.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="551" data-original-width="1000" height="352" src="https://1.bp.blogspot.com/-XXDkRs5xWss/X7MWfhUua6I/AAAAAAAADr8/g0oToV6paZoPPVecA2ihygH7gPNV6MJJQCLcBGAsYHQ/w640-h352/DSC_2774-1.jpg" width="640" /></a></div><div class="separator" style="clear: both; text-align: center;"><span style="font-weight: normal;"><a href="https://1.bp.blogspot.com/-st2Nex9_Ei8/X7NzLWskd3I/AAAAAAAADtY/0GXIm7o3tAMre6HmdSkUPMH-8-zspUcDwCLcBGAsYHQ/s1100/DSC_3330.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="670" data-original-width="1100" height="390" src="https://1.bp.blogspot.com/-st2Nex9_Ei8/X7NzLWskd3I/AAAAAAAADtY/0GXIm7o3tAMre6HmdSkUPMH-8-zspUcDwCLcBGAsYHQ/w640-h390/DSC_3330.jpg" width="640" /></a></span></div><span style="font-weight: normal;"><br />Above
2 photos — My temporary outboard equalizer with 12 possible pots ( 2 were missing
at the time of the top photo). On my guitar amp, I placed a line out
after the first preamp — and a line in going to the PA stage with a
bypass switch (if needed) so I could test various external tone
circuits. On the outboard EQ, I tested up to 12 frequencies at once. <br /></span><p>I'll discuss my final Stage 2 EQ, going from left to right; or low frequency to high starting with the bass boost. </p><p>My
speaker tests get covered in Part 4, however, occasionally, I practice
with 6 or 8 inch speaker mounted in open-back cabinets. A switchable,
low Q, 75-80 Hertz bass boost makes a huge difference for these 2
speakers. It's also good for low volume playing when you really wish a
super fat bottom end for a change in pace. A front panel switch enables
or kills this filter.</p><p>I really like the main bass control to be
wide (low Q) and centered at 125 Hertz. A center frequency of 150-160 Hz
is too high for me. A slightly lower bass center frequency sounds OK,
but since I have the bass boost at ~75 Hz , a 150 Hz bass control worked
well. <br /></p><p><b>Low mid range frequencies</b></p><p>For many, the
lower mid range tone shaping defines the guitar amplifier. Some of you
have studied the transfer function graphs of classic Fender, Marshall
and other famous amplifiers to see the importance of lower mid range
shaping to set the signature tone of an amplifier. <br /></p><p>From
making the partial 1/3 octave, EQ, I learned I strongly dislike 250 and
315 Hz. These along with 400 and 500 Hz (respectively to a lesser
degree) make up the so called mud (or mud range) frequencies to my
ears. Thus I fixed cut 250 and 315 Hz. I found that 400Hz should be
adjustable (to vary the cut) and that 500 Hz is OK, but should <i>never</i> get boosted from my experiences. <br /></p><p>800 Hz ranked important in my listening tests. Generally a little bit of cut helps my tone at this frequency. <br /></p><p>I
can't handle 1 KHz at all. For me, its a nasally, festering, fingers
down a chalkboard frequency. For some reason, 1.2 KHz seems a bit more
palatable. Depending on the room and guitar, I may slightly boost, set
neutral, or slightly cut this frequency. Since I favor the 1960's Jim
Hall sound, I added 2K and 3K2 Hertz but nothing higher in frequency.
The Hair control is more just a general treble boost or cut — very
subtle. Although I omitted 5 KHz, it might belong on some guitar amps. <br /><br />For
the lower mids and highs, a Q of 5.1 sounded better than lower Q
versions. I think I tested a Q of somewhere around 1.7 and then 0.85 for
some of these frequencies.</p><p>Since there is DC on the pots, I stuck to the format employed by
countless amp designers to avoid scratchy pot adjustments: I built with the TL072 op-amp ( 6 of them ). I
just ordered some OPA4134 for future exploration.<br /></p><p><b>Other tone circuits</b></p><p>In
jazz amplifiers, it seems that the Baxandall tone circuit reigns
supreme. A few older Fender solid state amps ran their classic R-C
passive tone circuit ( the Fender scooper ) plus later in the
preamplifier stage, a Baxandall type tone control circuit to keep the
classic Fender midrange but still allow some boost/cut of the bass and
treble etc.. <br /></p><p>I first built the old bass and treble control employed in the early Polytone amps such as the Mini Brute or Model 104. <br /></p><p>I
reworked it with 10K pots to lower Johnson noise plus op-amp current
noise in keeping with the solid advice and influences from Doug Self's
book:<a href="https://1.bp.blogspot.com/-f8PMS90FKWs/X7NSUqHZ21I/AAAAAAAADsI/n43out9yWBgJH3v23i62DZt9qGM6GV1aQCLcBGAsYHQ/s688/bass-treblel1.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="499" data-original-width="688" height="464" src="https://1.bp.blogspot.com/-f8PMS90FKWs/X7NSUqHZ21I/AAAAAAAADsI/n43out9yWBgJH3v23i62DZt9qGM6GV1aQCLcBGAsYHQ/w640-h464/bass-treblel1.png" width="640" /></a></p><p><span style="font-weight: normal;">Above
— The basic bass & treble tone circuit that reasonably keeps the
time constants of the early Polytone tone circuits. This stage works
well for all its simplicity. I've put a version of this circuit in
radio receivers, and a code practice oscillator. I prefer this circuit
over the bass, middle, treble Baxandall tone circuit employed by
Polytone in later amps including the Mega-Brutes.</span></p><p><span style="font-weight: normal;">You
will find countless versions of 3 Baxandall frequency tone circuits in
guitar amplifier service manuals. I built a few and found a 4 frequency
tone control suits me better than a 3 frequency circuit.</span></p><div class="separator" style="clear: both; text-align: center;"><a href="https://1.bp.blogspot.com/-Uk5NVc9jx7g/X7NWp7TlPXI/AAAAAAAADsU/gDPNUfWNPzkbGrjkQLWIspKHXZEB0-uxACLcBGAsYHQ/s865/tone-stack-final.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="546" data-original-width="865" height="404" src="https://1.bp.blogspot.com/-Uk5NVc9jx7g/X7NWp7TlPXI/AAAAAAAADsU/gDPNUfWNPzkbGrjkQLWIspKHXZEB0-uxACLcBGAsYHQ/w640-h404/tone-stack-final.png" width="640" /></a></div><span style="font-weight: normal;">Above
— My favorite 4 frequency tone circuit. 20K pots prevent the input
impedance going too low when boosting heavily, You find interaction
between some of the peaking filters, but this is pretty sweet for 1
op-amp. There are also scores of 4 frequency variants in guitar
amplifier service manuals that cut/ boost up to 20 dB.</span></div><div style="text-align: left;"><span style="font-weight: normal;"><br /></span><div class="separator" style="clear: both; text-align: center;"><span style="font-weight: normal;"><a href="https://1.bp.blogspot.com/-U8Gt0Dq4ktE/X7NW1LZvanI/AAAAAAAADsY/BjFxAmqUMeMEw54tkbhWA42saT7J9xYygCLcBGAsYHQ/s1000/DSC_2041-1.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="674" data-original-width="1000" height="432" src="https://1.bp.blogspot.com/-U8Gt0Dq4ktE/X7NW1LZvanI/AAAAAAAADsY/BjFxAmqUMeMEw54tkbhWA42saT7J9xYygCLcBGAsYHQ/w640-h432/DSC_2041-1.jpg" width="640" /></a></span></div><span style="font-weight: normal;"> </span><span style="font-weight: normal;"><br /></span><span style="font-weight: normal;">Above — The board I put the 4 frequency tone circuit in. I added gain controls and 5532 op amp to turn this </span><span style="font-weight: normal;">into a simple, complete jazz guitar preamplifer. It sounded pleasant.</span><p><span style="font-weight: normal;">Further,
from his aforementioned book — I built Doug Self's low noise, variable
frequency, variable Q, state variable, mid range parametric equalizer.
Of the 3 parametric EQs I built, his worked the best in terms of noise
performance and function. I just never feel parametrics work the mid
range the way I seek for a jazz guitar amplifier. <br /></span></p><p>I also tried some high-pass filter circuits. 1 stood out.</p><div class="separator" style="clear: both; text-align: center;"><a href="https://1.bp.blogspot.com/-PjEhfq93P4s/X7NczxElwJI/AAAAAAAADso/jF6Kf3mIkeI4Q133VB-4TvVi7EN-wErTQCLcBGAsYHQ/s742/High-pass%2Bfilter.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="427" data-original-width="742" height="368" src="https://1.bp.blogspot.com/-PjEhfq93P4s/X7NczxElwJI/AAAAAAAADso/jF6Kf3mIkeI4Q133VB-4TvVi7EN-wErTQCLcBGAsYHQ/w640-h368/High-pass%2Bfilter.png" width="640" /></a></div><p><span style="font-weight: normal;">Above
— A high-pass filter for guitar input. This filter works well and seems
to enhance bass frequency tightness. We have no use for frequencies
below 60 Hz. I built my guitar input stage from stage 1 right on the
first unity gain buffer.</span></p><p><b>Stage 2 Conclusion</b></p><p><span style="font-weight: normal;">After
using the Stage 2 equalizer for ~ 1 year, I learned that in a future
circuit, I will probably only place a quad FET op-amp and make a 4-band
equalizer for 150, 250, 315 and 400 Hz with 250 and 315 Hz in a fixed
cut. </span></p><p><span style="font-weight: normal;">Perhaps
I will add a separate 1 op-amp stage bass boost as well. The high mids
and highs will likely get handled with a single op-amp with a switchable
peaking/ shelving EQ circuit. Who knows? Only time and experiments will tell.</span></p><p><span style="font-weight: normal;"></span></p><h2 style="text-align: left;"><b>STAGE 3<br /></b></h2><h2 style="text-align: left;"><div class="separator" style="clear: both; text-align: center;"><a href="https://1.bp.blogspot.com/-fx515Sq6WY8/X7NivH4tzTI/AAAAAAAADtA/hoIqGevlQpUlkkphsSW8HYL8rKgt1dMXACLcBGAsYHQ/s1014/post-amp-Nov13.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="740" data-original-width="1014" height="468" src="https://1.bp.blogspot.com/-fx515Sq6WY8/X7NivH4tzTI/AAAAAAAADtA/hoIqGevlQpUlkkphsSW8HYL8rKgt1dMXACLcBGAsYHQ/w640-h468/post-amp-Nov13.png" width="640" /></a></div></h2><div style="text-align: left;">Above
— Third preamplifier stage. This is similar to the stage 1 input
amplifier section. The last buffer is made from the left-over TL072
op-amp stage on the equalizer.</div><div style="text-align: left;"> </div><div style="text-align: left;">The master volume pot dramatically lowers the noise when gain is reduced. <br /></div></div><div style="text-align: left;"> </div><div style="text-align: left;"><h4 style="text-align: left;">Miscellaneous Photos </h4></div><div style="text-align: left;"> </div><div class="separator" style="clear: both; text-align: center;"><a href="https://1.bp.blogspot.com/-i70JRzuCIP8/X7NzUtgbnWI/AAAAAAAADtc/Xb163zBMkPEAv-Eno8bprx97cISc4GgrgCLcBGAsYHQ/s1100/DSC_3341.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="722" data-original-width="1100" height="420" src="https://1.bp.blogspot.com/-i70JRzuCIP8/X7NzUtgbnWI/AAAAAAAADtc/Xb163zBMkPEAv-Eno8bprx97cISc4GgrgCLcBGAsYHQ/w640-h420/DSC_3341.jpg" width="640" /></a></div><p></p><p>Above and below — The amp chassis with equalizer during testing. No hum!<br /></p><div class="separator" style="clear: both; text-align: center;"><a href="https://1.bp.blogspot.com/-vWFHaf9n_Hs/X7Nzq081KqI/AAAAAAAADto/x9nw4SwBsh8GJnzzqjoUUGnfM-7EdQO2gCLcBGAsYHQ/s1100/DSC_3348.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="647" data-original-width="1100" height="376" src="https://1.bp.blogspot.com/-vWFHaf9n_Hs/X7Nzq081KqI/AAAAAAAADto/x9nw4SwBsh8GJnzzqjoUUGnfM-7EdQO2gCLcBGAsYHQ/w640-h376/DSC_3348.jpg" width="640" /></a></div><br /><div style="text-align: left;">The index for this project is on my guitar-related page. <a href="https://qrp-popcorn.blogspot.com/p/guitar-related-index.html" target="_blank">Click here</a>. </div>Vasily Ivanenkohttp://www.blogger.com/profile/17387516134063150119noreply@blogger.com0tag:blogger.com,1999:blog-3480228403403435266.post-75267182949131593332019-11-20T12:41:00.003-08:002021-03-18T21:01:02.392-07:00Clean Jazz Guitar Amp Builder Notes — Part 2: Power Amplifier <h3 class="post-title entry-title" itemprop="name">
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This is part 2 of a series about a complete prototype guitar amp.<br /><br />Part 1 lies <a href="https://qrp-popcorn.blogspot.com/2019/01/clean-jazz-guitar-amp-builder-notes.html" target="_blank">here </a><br />
<span style="color: purple;"><span style="color: black;">Part 2</span> <span style="color: black;">lies</span> <a href="https://qrp-popcorn.blogspot.com/2019/11/clean-jazz-guitar-amp-builder-notes.html">here</a><br /><span style="color: black;">Part 4 lies <a href="https://qrp-popcorn.blogspot.com/2021/03/clean-jazz-guitar-amp-builder-notes.html" target="_blank">here</a></span></span><br />
<span style="color: purple;"><br /></span>
<span style="color: purple;"> <b>Power Amp Stage Notes:</b></span><br />
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<span style="font-size: large;"><b>Section A The Final Amp | 21 Watt power amplifier for clean jazz guitar.</b></span><br />
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Above — Schematic of the final power amplifier developed for this series. Much of the design keeps the VAS + VBE multiplier, and ultimately the final output pair from instant destruction when things go wrong. For example, a speaker disconnection, or accidental bench experiment electrical short. Of course, we likely can't provide fail proof protection to sustained adverse events.<br />
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This amp includes an abundance of medium power transistors: BD139 | BD140 , plus current limiting in the VAS + the final drivers.<br />
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Most resistors outside of the input differential pair circuitry are 1/2 watt rated. Most caps are 50 VDC rated. In the schematic above, I've got the 1000 µF filter capacitors going to signal ground for clarity. Actually, they return to their own special ground @ the power supply as discussed in Part 1.<br />
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Above — 12-bit FFT of the maximum clean signal output | 21 Watts. With a beefier power supply , ( such as +/- 30 to 40 VDC on the rails), better heat sinks on the power follower, and slight adjustment of the 2 current source emitter resistors, this amp could work OK to <=50 Watts or so.<br />
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On the bench, I hooked it to my dummy load. I applied a 1 KHz tone and drove it to the brink of distortion as described in here on my <a href="https://qrp-popcorn.blogspot.com/2018/12/guitar-amp-builder-notes-af-power.html" target="_blank">Dummy Load</a> page. That's what you see in this FFT.<br />
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Above — PA board installed in the amp.<br />
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Above 2 photos — In chassis for testing. I'm using some of the installed rear panel jacks as temporary paths for input into the PA. This allows PA testing and real-world tests of the preamp + tone shaping stages. 2 speaker output jacks wired in parallel provide output possibilities.<br />
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I'll go through some notes:<br />
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I build circuits from DC to ~ 1.5 GHz on FR4 board using Ugly Construction. Evidently, this frightens some of my readers.<br />
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<b>Board Construction & Heat Sinking</b><br />
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I built the PA on 2-sided , 1 ounce copper clad board. Circuit paths, or islands were carved with a motorized tool while outdoors. I also isolated each board mounting hole so the board does not get connected to chassis ground when bolted in. I seek star grounding for each circuit board.<br />
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The PA board gets lifted off the chassis by spacers that prevent shorting the power BJT mounting bolts to the chassis [ recall that they're connected to each collector terminal]. This also allows air flow under the PA board for cooling.<br />
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Above —Heat sinking the power followers. I bent ~ 20 gauge aluminum with a brake to fashion crude heat sinks. Further, under each heat sink lies a small piece of 24 gauge copper sheeting and under that lies more 24 gauge aluminum stock.<br />
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The copper sheeting + aluminum heat sink is secured to the main board with the main power transistor mounting bolt plus an additional 6-32 bolt below each transistor. The additional bolt presses the heat sink & sheets firmly onto the main board — and lowered BJT temperature 3-4 degrees C more than without the extra bolt during tests.<br />
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For my 21 W amp, this crude heat sinking worked OK for this, my first solid-state guitar amp. In a test setup with a dummy load, I applied a 1 KHz signal to give 20 Watts output in the DSO & left it that way for 24 minutes ( a torture test ). The big NPN measured 47-49 degrees, while its PNP sister measured 54- 56 degrees C. My heat sink resistors measured 82 degrees C . When playing guitar at a comfortably loud bedroom volume, the transistors run around 23-24 degrees C. <br />
<br />
<b>Transistors</b><br />
<br />
For the small signal transistors, I call for the MPSA06 and MPSA56 BJTs, however, by this time, I'd run out of them and applied 2N4401/2N4403. My experiments showed that the MPSA series transistors are better matched from BJT to BJT and likely prove a better choice for the differential input pair at least. <br />
<br />
While I chose the very husky MLJ21194 + MLJ21193 as power followers, a 2SA1302 2SC3281 pair, or even the TIP 35C | 36C could work well. All of my parts were brand name & purchased from reputable American dealers. I saw a couple of cheap bootleg transistors let their smoke out during my several PA builds under heavier current.<br />
<br />
In previous versions of this amp,I employed T0-92 encased transistors for all but the finals and the
BD139-140 BJTs in earlier versions of this amplifier. This proved a big
mistake. With mishaps + during torture tests, the VAS transistor
quickly or progressively failed and the VBE multiplier died instantly. This led to a current surge and caused the fuses on my AC
transformer secondary side to blow.<br />
<br />
While T0-92
transistors provided a lovely high Beta, they led to a lot of
frustration. In audio amps, and in particular guitar amps,
"overbuilding" seems important. Thus, I used a lot of medium power
transistors — even for the current sources.<br />
<br />
<b>Current Sources</b><br />
<br />
For my build, I ran out of
BD140s, so I bolted two TIP42A's onto my circuit for the current sources transistors. I isolated their
mounting points and also sought them for mechanical rigidity — a needed
thing when you build using Ugly Construction. The current sources exhibited nearly 0 temperature drift once they ran for ~ 1 minute.<br />
<br />
I closely measured them in a variety of situations and placed some of this data in Table 1 on the schematic. The input pair get sourced with a lovely high impedance with a current that varies from 6.25 mA to 5.7 under test conditions. I sought around 10 mA for the VAS supply , and measured a range from 10.5 to 8.61 mA with the amp driven to a constant 3W, 5W , 10W and 20 W output. <br />
<br />
This shows what happens to my DC power supply under different amplifier power loads. I placed in DC measures in Table 2 below:<br />
<br />
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<br />
Since I'm only going with 1 pair of finals, the VAS current needs to
be high enough to fully drive the top half of the AC signal swing @
high output to a potentially low output impedance . For example, with two 8 Ω
speakers in parallel which doubles the current needed to drive a single 8 Ω
speaker. The emitter follower located before the VAS helps that cause
immensely.<br />
<br />
Ultimately, For lower current, distortion,
heat sinking requirements and DC ripple, I plan to stick to an 8 Ω load,
however, i plan to experiment with different speakers and all of mine
are currently 8 Ω speakers. If I find 2 speakers I like better
together than just a single 8 Ω unit, then I'll order these 2 speakers
in 16 Ω for a final future amp.<br />
<br />
<b>Amplifier Topology</b><br />
<br />
A basic 3 stage power amp that borrows heavily from the recommendations of Douglas Self. The classic differential transconductance pair serves as the input stage to subtract negative feedback from the input and drive an error voltage to the voltage-amplifier stage or VAS.<br />
<br />
In professional power amps, input differential stage emitter + collector resistors get replaced with high Z current sources + mirrors. Discrete transistor current mirrors improve the balance of the input pair across a wide frequency spectrum to cancel the 2nd harmonic. You'll see a variety of current mirrors used extensively within op-amps to boost linearity & reduce HF distortion.<br />
<br />
Some designers employ boot-strapped resistors to supply the VAS current and this evidently can also work very well. I went with a current source. <br />
<br />
The voltage-amplifier stage [ VAS ] provides all the voltage gain in a solid state power amp. I applied Douglas Self's recommendation of driving the VAS with an emitter follower to reduce distortion and garner more current drive for the followers. <br />
<br />
The VAS circuit also contains 2 small COG or NP0 ceramic RF caps to stop HF oscillations. The current limiting transistor helps protects the VAS in event of a catastrophe. <br />
<br />
When I first built the amp, I did not connect the final power transistor collector nor base node wires. Every other part was wired in however. Thus I had a small functional amp to test and measure with a signal generator, DMM, DSO or oscilloscope, plus a dummy load.<br />
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<br />
Above — Output of the amplifier with just the BD139-140 drivers in-situ with a +/-15 volt DC supply. I first test any PA circuit with my +/- 15 VDC bench supply before going to higher DC voltages.<br />
<br />
You won't get much power with the 100 Ω degenerative emitter resistors, but can fully test the amp without a lot of current flowing. By tweaking the 1K pot on the VBE multiplier, I also set the bias across points <b>a</b> and <b>b</b> at 1.2 VDC with no input AC signal applied. Thus the bias is at a good starting point for when you connect the power followers.<br />
<br />
Finally, connect the power followers and adjust the bias while looking at the output in a scope or DSO plus FFT. The quiescent current of the entire PA ran ~ 22.4 mA. At full clean signal power it will consume around 714 mA if you connect an ammeter between the supply and 1 of the DC rails.<br />
<br />
<b>Of negative feedback, folklore and tribalism</b><br />
<br />
This design applies mixed mode negative feedback: voltage and current negative feedback. Both provide series feedback to provide the same function -- to boost PA linearity. <br />
<br />
Negative feedback also affects an amps gain, bandwidth and frequency response, plus its input and output impedance (Z). Negative current or voltage feedback affect linearity + gain similarly, but with respect to output impedance, current feedback increases output Z by the size of the feedback factor, while voltage feedback decreases output Z by the feedback factor. To calculate the feedback factor for each type, a different equation gets applied and I won't go into the math.<br />
<br />
A classic HiFi solid state amp with just voltage feedback exhibits a very low output Z that is just fractions of an ohm. Delivered power decreases as the speaker Z rises. <br />
<br />
For decades, solid state guitar power amp designers have applied current plus voltage negative feedback. This leads some to suggest that the solid state amp is now behaving more like a transformer-coupled tube amp that offers a higher output Z while exhibiting a lower dampening factor. <br />
Some engineers who design audio amplifiers hotly debate current versus voltage source drive. See this brief <a href="https://www.edn.com/design/consumer/4423155/Loudspeaker-operation--The-superiority-of-current-drive-over-voltage-drive?utm_source=AspenCore&utm_medium=EDN" target="_blank">EDN article</a> by Esa Meriläinen who argues for driving speakers with current rather than a voltage source. I've got papers by respected authors who state the opposite. I'll stay out of this debate.<br />
<br />
In my PA, output current is sensed by measuring the voltage drop across a 0.22 Ω resistor in series with the output voice coil. This resistor senses a fraction of the output signal and feedbacks a small voltage to the input stage that is phase inverted and thus "negative feedback". The voltage drop across the 0.22 Ω resistor goes up or down proportionally to the output current. This variable voltage is fed to the 510 Ω emitter resistor in the 2nd half of the input differential pair, As the fed back voltage increases, amplifier gain decreases. E.g. increased voice coil current increases the voltage drop across the current sense resistor and this bucks the amplifiers input signal.<br />
<br />
The 10K resistor connecting the power follower collectors to 1/2 of the differential pair's base node provides the voltage feedback.<br />
<br />
<b>Output Impedance and Dampening Factor</b><br />
<br />
Going back to your electronics training, for example -- studying linear
power supplies. In current feedback, the circuit attempts to keep the
output current constant meaning that the output impedance has to be
high. For output voltage to be constant the output impedance has to be
low. Regardless, whether constant voltage, or constant current, the
power delivered is still a function of speaker impedance versus
frequency.<br />
<br />
Dampening factor is another term that may polarize some guitar amp lovers; especially by those who adore distortion. Dampening factor (aka dampening) = the ratio of loaded Z ( typically 16, 8, 4 Ω ) to the amplifier's output impedance. In guitar world, higher dampening is often considered a bad thing by the cognoscenti. A very low output Z solid state amp dampens the speaker more than a higher impedance transformer-coupled amplifier. This is true according to the arithmetic. <br />
<br />
Raising the amplifiers output Z reduces dampening, however, the most significant factor affecting dampening is the series resistance of the speaker voice coil. I once significantly changed the dampening on a friend's solid state amplifier with no soldering — I put in a different speaker with a much lower voice coil DC resistance. He loved the result.<br />
<br />
<b>How I chose the 820 Ω feedback resistor. <span style="color: magenta;"> Color you PA Tone</span></b><br />
<br />
The other board bolted in the amp chassis thus far contains a split-supply voltage regulator for the op-amps used in the preamp and tone shaping circuits, plus this board also houses the first preamp & it's connected to a 1K gain pot.<br />
<br />
I connected my guitar to the amp input and routed the output of the first preamp into the power amp input. It's interesting to listen to a guitar amp with no tone control circuit -- and just 1 volume control.<br />
<br />
I connected an 8 Ω 12 inch Jensen speaker to the amp and played through it. Instead of the 820 ohm resistor, I place a 1K 2 Watt potentiometer in the feedback loop and tweaked the pot as I played.<br />
<br />
I seemed to hear some changes in the bass & treble frequencies at different rotations of the pot. This aurally supports the claim that current feedback tends to boost lows and highs and thus provides a mid frequency scoop. Further, I seemed to prefer 1 particular setting on the pot. I removed the pot and measured it with an ohm meter.<br />
<br />
Continuing on, I tried 4 other 8 Ω speakers that I had on hand at the moment. I also tried different speakers in parallel. In most cases, the setting on the pot that I seemed to prefer was different. I also tried longer speaker wires ( 16 foot, 8 foot versus 3 foot ) -- this exhibited a small effect on 2 of the speakers but this in turn felt dependent on the pot setting. Speaker cable resistance can potentially exhibit an effect on dampening in a very low output Z power amp. Normally, I use a 3 foot ( 91 cm) speaker cable<br />
<br />
The 1 pot setting that worked as a compromise setting was then determined: 811 Ω, I soldered in a 820 Ω 1 Watt resistor in for now. When I finally complete the amp and decide which speaker(s) to use, I'll repeat my test with a potentiometer.<br />
<br />
The current feedback resistor allows for a potential change in the output impedance that can allow for some equalization of the speaker - power amp system in concert with the speakers frequency response + resonant frequency [<i> speaker resonance often lies somewhere between 75 - 120 Hz and varies from model to model ]. I </i>wonder if adjusting the pot allows you to enhance the resonant frequency of the speaker?<br />
<br />
This function paled in comparison to actually changing the speaker. Using speaker choice to dial in whatever desired guitar sound lurks in your head seems critical. Then you can try to tweak it with a current feedback resistor choice.<br />
<br />
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<br />
<span style="font-size: large;"><b>Section B Faux Amp</b></span><br />
<br />
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<br />
Above — Schematic for a faux amplifier I built for plus and minus 15 volts all on 1 PC board to investigate PA stages, plus different preamplifer circuits. Clean signal output = 9.5 Watts, as my bench split supply has a small transformer and normally gets used for developing small signal op-amp circuitry. This was my first split supply power amp and I learned a ton and gained some confidence.<br />
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<br />
Above — The finals were mounted directly on 2-side copper clad board. At under 10 W power, they did not get above 30C even during maximum power torture tests for 15-20 minute stints. <br />
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<br />
Above — RCA inputs used for connecting the +/- 15 volt split DC supply to this board. This is OK for a low power experimenter board, or for op-amp circuitry, but not recommended for real power amplifiers.<br />
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<br />
Above — Entire board. In the forefront lies an RCA jack connected to the PA input. <br />
<br />
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<br />
Above — Time domain. Compared to above, increasing the drive by 1 Vpp produces harsh clipping.<br />
<br />
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Above — I've connected a preamplifer module to the power amp. I'll cover several preamp schematics plus discussion in Part 3 of this series. <br />
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Above — Side view. You can see the power supply rails. Generally you want to keep them closer together, but this was my first go and gave me lots of building space.<br />
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Above — Output section. The emitters connect to their resistors through small holes. I wound the coil and held it together with tape. This OK for a temporary project. I connected the output jack to either my dummy load or speaker(s).<br />
<br />
I enjoyed this little amp and it sounded great. Surprisingly, a 9.5W amp cranked up proves quite loud in an electronic lab.<br />
<br />
<b>Miscellany</b><br />
<br />
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<br />
Above — This power amp featured parallel power followers to reduce current-induced Beta drop when driving 4 Ω loads into 60 W. I learned from this board that the most important stage in your entire amp = the power supply.<br />
<br />
To get desired a output power, your DC supply needs to provide the needed current without sagging too much under full load. Using transistors that are specified to have lower Beta drop, plus putting them in parallel does help the Beta drop issue. The BJTs = MLJ21194 & MLJ 21193. Heat sinking was provided by copper plating on the back side to the board.<br />
<br />
<br />Vasily Ivanenkohttp://www.blogger.com/profile/17387516134063150119noreply@blogger.com0tag:blogger.com,1999:blog-3480228403403435266.post-59469647864354588902019-11-01T23:22:00.000-07:002019-11-01T23:33:15.390-07:00Signal Generator for Bat Receivers<div class="separator" style="clear: both; text-align: center;">
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<br />
<div class="MsoNormal">
<b>Introduction</b><br />
<b><br /></b>
<b><br /></b></div>
<div class="MsoNormal">
</div>
<div class="MsoNormal">
In summer months, around dusk, I venture into our garden to
watch bats feast on flying insects. In my valley, bat research + conservation garners deserved attention. Bats prove an important
part of nocturnal insect control & also help cycle nutrients from
wetlands into forests.</div>
<div class="MsoNormal">
Bat detectors, or bat receivers input bat audio in the range
of ~15 -120 kHz and output AF into head phones, and/or give a Fourier transform
of the received waveform on a small screen, or, in some cases, also provide the bats vocalized frequency range. <br />
<br />
Bats frequency modulate ultrasonic audio
and rapidly sense the location of fixed and/or moving objects in 3-dimensional
space as they fly. I’ve watched bats sense and careen around my dipole antenna wires
on many occasions. They amaze me.</div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
Bat receivers seem to fall into 3 basic categories:</div>
<div class="MsoNormal">
</div>
<br />
<ul>
<li>Direct conversion; also call heterodyne, or zero IF</li>
<li>
Direct digital sampling </li>
<li>
Down conversion using logic IC division to move the frequency into a spectrum humans can hear</li>
</ul>
<br />
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
I plan to design and build my own bat receiver and to be
honest, this task seems fairly unremarkable for someone who on occasion, designs and builds radio
equipment. What you might lack is test equipment.</div>
<div class="MsoNormal">
<br />
In order to start, I sought, an ultrasonic signal generator
to help me design front ends, test mixers, and so forth. I wanted a very temperature stable signal
source that gave some outputs between 15 to 100 KHz. I sought a reasonably low distortion sine wave signal into
a well buffered output network with amplitude control. I require a sine wave
output to measure loss or gain in my filters, amplifiers and downconverters.</div>
<div class="MsoNormal">
<br /></div>
<div class="MsoNormal">
<b>Main Circuit Schematics </b></div>
<div class="MsoNormal">
<div class="separator" style="clear: both; text-align: center;">
<a href="https://1.bp.blogspot.com/-G7Ywb-ND7SQ/Xbz0ya5QBQI/AAAAAAAADdQ/wk8x-bRgOI0H4YlebysewvvZqPXf-PzBgCLcBGAsYHQ/s1600/Oscillator1.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="744" data-original-width="1015" height="468" src="https://1.bp.blogspot.com/-G7Ywb-ND7SQ/Xbz0ya5QBQI/AAAAAAAADdQ/wk8x-bRgOI0H4YlebysewvvZqPXf-PzBgCLcBGAsYHQ/s640/Oscillator1.png" width="640" /></a></div>
Above — Main oscillator with binary division + signal conditioning.<br />
<br />
The 74HC4060 14-stage ripple counter seems delightful. It offers a number of flip-flop bit counters, plus an inverter so you can hang an oscillator off this IC. For temperature stability and ease, I chose a crystal oscillator. I wanted an output of 200 KHz, so that gave many crystal choices — ultimately, I went with a 3.2 MHz crystal fashioned in the usual Pierce oscillator topology. Selecting output Q3 with Pin 7 gave divide by 16 and a 200 KHz output.<br />
<br />
<div class="separator" style="clear: both; text-align: center;">
<a href="https://1.bp.blogspot.com/-zk9KszvoZp8/Xbz-oy3Z41I/AAAAAAAADd0/FrzNHrr81GYv0w754f14DGk-qcWjHuPdgCLcBGAsYHQ/s1600/hf-out.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="481" data-original-width="800" height="384" src="https://1.bp.blogspot.com/-zk9KszvoZp8/Xbz-oy3Z41I/AAAAAAAADd0/FrzNHrr81GYv0w754f14DGk-qcWjHuPdgCLcBGAsYHQ/s640/hf-out.png" width="640" /></a></div>
<br />
Above — Inverter output of my 4060 clocked at 3.2 MHz.<br />
<br />
<div class="separator" style="clear: both; text-align: center;">
</div>
The 74HC193 4-bit synchronous binary up or down counter takes the 200 KHz signal and further divides it according to the 4-bit WORD set by data input pins 9, 10, 1 and 15. Pin 9 is soldered to ground and stays Low. Pins 10, 1 and 15 are preset High through the 22K resistors. Thus the function table shown in the schematic should <i>technically</i> have Low placed in front of the other bits. For example, divide by 7 = Low, High ,High, High.<br />
<br />
Pins 10,1 and 15 are set low as required by turning on a MOSFET switch. The 2N7000 is a lovely, inexpensive way to ground lower current components. I measured the <i>average</i> ON resistance on my board at 3.2 Ω for my 2N7000 trio.<br />
<br />
A front panel switch controls the data bits of the 74HC193. You could eliminate the front panel 7PST switch + FETS and just ply 3 SPST front panel switches, however, I prefer grounding data pins local to the counter IC — and not having to remember switch combinations to set the bits.<br />
<br />
Steering diodes keep the MOSFETs on or off as selected. Not all of them are technically needed, but they cost pennies and ensure stable performance.<br />
<br />
<div class="separator" style="clear: both; text-align: center;">
<a href="https://1.bp.blogspot.com/-9PejNCIS40k/Xb0HQ1Ua_cI/AAAAAAAADeA/J6wvb_VY43ULdU2g4lcjxm7DxDryV51xwCLcBGAsYHQ/s1600/a-scope_0.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="480" data-original-width="800" height="384" src="https://1.bp.blogspot.com/-9PejNCIS40k/Xb0HQ1Ua_cI/AAAAAAAADeA/J6wvb_VY43ULdU2g4lcjxm7DxDryV51xwCLcBGAsYHQ/s640/a-scope_0.png" width="640" /></a></div>
<br />
<br />
Above — Output of divide by 2 from the 74HC193 synchronous 4-bit binary up/down counter.<br />
<br />
Following the programmable counters, comes a 74HC74 D flip-flop. Nothing cleans up a digital pulse better than a flip-flop. As you switch through the 7 frequency channels, each output exhibits a 50% duty cycle and is well conditioned for low-pass filtration into a sine wave.<br />
<br />
Onto the low-pass filters and buffer stage:<br />
<br />
<br />
<div class="separator" style="clear: both; text-align: center;">
<a href="https://1.bp.blogspot.com/-L-3rYo63yi0/Xbz5H7rl9TI/AAAAAAAADdo/Xrhc-yeJ_oo_U_nghIz2v9HP2C2ZNWq0gCLcBGAsYHQ/s1600/Filters1.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="810" data-original-width="1084" height="478" src="https://1.bp.blogspot.com/-L-3rYo63yi0/Xbz5H7rl9TI/AAAAAAAADdo/Xrhc-yeJ_oo_U_nghIz2v9HP2C2ZNWq0gCLcBGAsYHQ/s640/Filters1.png" width="640" /></a></div>
Above — My low pass filter banks + the AF gain control and output buffer.<br />
<br />
All signal capacitors are polyester types such as polyester film, or metallised film etc..<br />
I employed the NE5532 op amp throughout. The 1 µF input connects the signal to a single order low-pass pole set for around 100 KHz and then into a unity gain buffer.<br />
<br />
All of the op-amps employ a gain of 1 which simplifies construction. The signal then passes through a cascade of second order low-pass filters that employ a Q of just under 1 ; Sallen-Key topology; and a Chebyshev response with a maximum ripple of 1 dB. <br />
<br />
All filters use the same capacitor values and you can see how changing the 2 resistor values affects the 3 dB response of each filter. I chose 5 filter outputs. The 20 + 25 KHz filter and 14.3 + 16.6 KHz get combined to save 1 op-amp + 4 capacitors + 5 resistors. Since these frequencies are fairly close together, attenuation of the higher of the 2 frequencies is minimal. You could actually make the whole board with just 3 filters: 50, 20 and 14.3 KHz, however, attenuation of some frequencies could be a deal breaker dependent on your needs.<br />
<br />
The worst filtration occurs at 100 KHz, where the 2nd harmonic is only 20 dB down. For me, that's OK since I don't plan to use this much and its still reasonable for measurement purposes.<br />
<br />
<div class="separator" style="clear: both; text-align: center;">
<a href="https://1.bp.blogspot.com/-UOlqdp_4h2M/Xb0QDeu7FbI/AAAAAAAADeM/_9Ixgp5KORQ-cuPXlPZS-EPKhIcPRrlbwCLcBGAsYHQ/s1600/Hundred.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="503" data-original-width="800" height="402" src="https://1.bp.blogspot.com/-UOlqdp_4h2M/Xb0QDeu7FbI/AAAAAAAADeM/_9Ixgp5KORQ-cuPXlPZS-EPKhIcPRrlbwCLcBGAsYHQ/s640/Hundred.png" width="640" /></a></div>
<br />
Above — The 100 KHz signal in Time Domain.<br />
<br />
<div class="separator" style="clear: both; text-align: center;">
<a href="https://1.bp.blogspot.com/-ap0khVdLnu4/Xb0RKGKyi7I/AAAAAAAADeY/kgGTxnp2enQF6G1eWlZsixBDb-AsQM93QCLcBGAsYHQ/s1600/fourier.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="481" data-original-width="799" height="384" src="https://1.bp.blogspot.com/-ap0khVdLnu4/Xb0RKGKyi7I/AAAAAAAADeY/kgGTxnp2enQF6G1eWlZsixBDb-AsQM93QCLcBGAsYHQ/s640/fourier.png" width="640" /></a></div>
<br />
Above — An FFT of the 20 KHz signal. The worst harmonic = 38 dB down from the fundamental tone. In an FFT of the 14.3 output, the worst harmonic is 43 dB down. Good results from simple low Q, low-pass filters with 10% parts.<br />
<br />
<div class="separator" style="clear: both; text-align: center;">
<a href="https://1.bp.blogspot.com/-ap860FO_Yws/Xb0UjhTHsXI/AAAAAAAADek/-fJlKCG6j74w1DZ00lVue1WObIz-QjPYwCLcBGAsYHQ/s1600/lowest.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="423" data-original-width="798" height="338" src="https://1.bp.blogspot.com/-ap860FO_Yws/Xb0UjhTHsXI/AAAAAAAADek/-fJlKCG6j74w1DZ00lVue1WObIz-QjPYwCLcBGAsYHQ/s640/lowest.png" width="640" /></a></div>
<br />
Above — A Time Domain DSO capture of the 20 KHz signal.<br />
<br />
The various filter outputs connect to a 5 pole switch ( I stock 7 pole switches so 2 lugs go unused).<br />
I can select the appropriate low-pass filter and may even "double down" by using the next lower frequency filter knowing that the signal will get attenuated.<br />
<br />
A 1 K pot allows a range of outputs from down a maximum somewhere between 5 and 7 volts peak to peak down to ~ 10 - 20 mV pk-pk.<br />
<br />
The output passes through 1 more unity gain voltage follower then to an AC-coupled RCA jack.<br />
I plan to drive circuits directly, or connect a piezo-electric transducer, or a MEMS ultrasonic transducer (CMUT) as needed.<br />
<br />
<b>Photographs and Final Notes</b><br />
<br />
<div class="separator" style="clear: both; text-align: center;">
<a href="https://1.bp.blogspot.com/-yzXi2wbXE6k/Xb0cbprzCWI/AAAAAAAADew/rWOhw3FBHisWbmqqwLetc8nelFPA1hhjgCLcBGAsYHQ/s1600/DSC_2655-1.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="665" data-original-width="999" height="426" src="https://1.bp.blogspot.com/-yzXi2wbXE6k/Xb0cbprzCWI/AAAAAAAADew/rWOhw3FBHisWbmqqwLetc8nelFPA1hhjgCLcBGAsYHQ/s640/DSC_2655-1.jpg" width="640" /></a></div>
<br />
Above — I designed this project on the bench and built it using Ugly Construction. I added a power on LED to the circuit.<br />
<br />
<div class="separator" style="clear: both; text-align: center;">
<a href="https://1.bp.blogspot.com/-o3_ZIyOi6Qw/Xb0cxK0MavI/AAAAAAAADe4/LiOfqbBiIAcsNPbTxOlKaLB3H3VdFXCmACLcBGAsYHQ/s1600/DSC_2649-1.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="629" data-original-width="1000" height="402" src="https://1.bp.blogspot.com/-o3_ZIyOi6Qw/Xb0cxK0MavI/AAAAAAAADe4/LiOfqbBiIAcsNPbTxOlKaLB3H3VdFXCmACLcBGAsYHQ/s640/DSC_2649-1.jpg" width="640" /></a></div>
<br />
Above — Photo of the 7 channel selector switch plus entire circuit board. I do not plan to put in a case. I'll use it like this over the next couple of years.<br />
<br />
<div class="separator" style="clear: both; text-align: center;">
<a href="https://1.bp.blogspot.com/-9XZs0VgaBoo/Xb0dIigbXII/AAAAAAAADfA/g5XSFMiCUEM23EbARrQoWyrVWR-svOVwACLcBGAsYHQ/s1600/DSC_2652-1-2.jpg" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="761" data-original-width="1000" height="486" src="https://1.bp.blogspot.com/-9XZs0VgaBoo/Xb0dIigbXII/AAAAAAAADfA/g5XSFMiCUEM23EbARrQoWyrVWR-svOVwACLcBGAsYHQ/s640/DSC_2652-1-2.jpg" width="640" /></a></div>
<br />
Above — Filter section knob, plus gain pot and output RCA jack. I'll trim off the unused copper board using aviation shears.<br />
<br />
<div class="separator" style="clear: both; text-align: center;">
<a href="https://1.bp.blogspot.com/-VYJUr76Tohs/Xb0ev5Jt8ZI/AAAAAAAADfM/8WLCmEI9-_ILgvpnYXkt0Uckr37FUxj5QCLcBGAsYHQ/s1600/unused%2BFL.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="285" data-original-width="643" src="https://1.bp.blogspot.com/-VYJUr76Tohs/Xb0ev5Jt8ZI/AAAAAAAADfM/8WLCmEI9-_ILgvpnYXkt0Uckr37FUxj5QCLcBGAsYHQ/s1600/unused%2BFL.png" /></a></div>
<br />
Above — Unused filters designed for 16.6 and 25 KHz.</div>
Vasily Ivanenkohttp://www.blogger.com/profile/17387516134063150119noreply@blogger.com4tag:blogger.com,1999:blog-3480228403403435266.post-12639078105324082922019-01-04T22:21:00.003-08:002021-03-18T21:02:44.104-07:00Clean Jazz Guitar Amp Builder Notes — Part 1: DC Power Supply<!--[if gte mso 9]><xml>
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<b>— D I S C L A I M E R —</b></div>
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The text, diagrams and images on this blog are presented for
information purposes only. You are entirely responsible for any damages, harm, or injuries that arise from any equipment you build, or from any experiments you perform. — Experiment and build at your own risk —</div>
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Building a power supply & audio frequency equipment <span class="st">poses a serious risk of
personal injury</span>, death, destruction of personal property and for fire. Safety first ! Always keep children and pets away from your bench. </div>
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Further, all home built equipment should never be connected
to your household Mains AC electric system when <i>not in use</i>. Connect your AC power
supply containing devices to a <b>suitably rated</b>, commercial switched power bar, or switch system
that is certified/approved in your Country. For example by the CSA Group, ANSI,
ASME, ASSE, ASTM, ASFE, UL, NSF etc.. Turn
your device AC supply on and off with this power bar/ switch system — <span style="mso-spacerun: yes;"> </span>or better yet, unplug it when it's not in use, or unattended. </div>
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Work safely! <span style="mso-spacerun: yes;"> </span>Prevent
accidents and fires. Keep an annually certified fire extinguisher in your home
shop, or lab at all times in case a fire starts.</div>
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<a href="https://4.bp.blogspot.com/-AMUX13sVxtg/XCmrAAb2TWI/AAAAAAAADSU/LmCM40mZ0QwBfwRW5Ehm_rlP60krh65ngCLcBGAs/s1600/DSC_2186-1.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="1000" data-original-width="466" height="400" src="https://4.bp.blogspot.com/-AMUX13sVxtg/XCmrAAb2TWI/AAAAAAAADSU/LmCM40mZ0QwBfwRW5Ehm_rlP60krh65ngCLcBGAs/s400/DSC_2186-1.jpg" width="186" /></a></div>
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Above — The fire extinguisher that hangs in my lab. We also have 2 others: 1 next to the electric clothes dryer & 1 in the kitchen. According to local fire officials, these 3 places are the most likely areas for a fire to start in a non-smoking home.</div>
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<b>A. Basic Power Supply Goals</b></div>
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[1] Electrical safety.</div>
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[2] Low ripple.</div>
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[3] No amplifier hum, or noise caused by ground loops, or inductively and/or capacitively coupled rectifier pulsations.<br />
[4] Manage heat and/or prevent expensive component damage from thermal runaway, or a catastrophic parts or design failure.</div>
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I'll show my pursuit of a split DC supply for a jazz guitar amplifier [ ~22-24 Watts into an 8 Ω load ]. I learned a ton making this power supply, and, of course, this knowledge will boost the success of obtaining the above 4 goals in future designs.</div>
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<b>B. Transformers </b></div>
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In 2018, I bought 2 suitable iron transformers: a toroidal + conventional frame type. Likely, the transformer is the most important plus <i>costly</i> object in your whole amplifier build. <br />
<br />
This blog will lean towards low power clean jazz guitar amps, however, all the same principles apply for higher power guitar amps. </div>
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I show how I measure my amplifier power ratings near the bottom of this blog page: <a href="https://qrp-popcorn.blogspot.com/2018/12/guitar-amp-builder-notes-af-power.html" target="_blank">Click here</a></div>
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<a href="https://3.bp.blogspot.com/-PzrVDUbSj7I/XCmz1OwnUWI/AAAAAAAADSs/sjuXL-ng0eAIwpjmAP3pT_PE2fsj4w89ACLcBGAs/s1600/DSC_2157-1.jpg" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="638" data-original-width="1000" height="408" src="https://3.bp.blogspot.com/-PzrVDUbSj7I/XCmz1OwnUWI/AAAAAAAADSs/sjuXL-ng0eAIwpjmAP3pT_PE2fsj4w89ACLcBGAs/s640/DSC_2157-1.jpg" width="640" /></a></div>
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Above 2 photos — My 2 transformers. I purchased the "Torel" toroidal unit on eBay from hansurmann from the Russian Federation. I purchased the Hammond 'heavy weight' locally & mainly because I got a very good deal on it. The heavy Hammond transformer will either go in a lab power supply, or perhaps a combo amp that never leaves the lab. It's a well built transformer that offers separate bobbins for the 2 windings eliminating the need for an electrostatic shield between the primary and secondary coils.<br />
<br />
Hammond Manufacturing also offers a good selection of Toroidal transformers to view and to learn more about them. <a href="http://www.hammondmfg.com/1182.htm" target="_blank">Click here.</a> </div>
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Transformer power rating isn't usually expressed in Watts; rather VA (Volts [RMS] and Ampere units). So my Hammond center-tapped transformer as shown is 30 VAC * 5 Amps = 150VA. This would work very well for a 4 ohm load guitar amp.<br />
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Your transformer's secondary AC voltage and rectified DC voltage varies with the diode type + rectifier topology, how you filter the pulsating DC into low-ripple DC voltage — and<i> the load</i> on the power supply . If you seek to make a 'specific' wattage guitar amp, this makes choosing your transformer output AC voltages a little more difficult than you might like. <br />
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Hammond Manufacturing offers a file with some math and rectifier circuits to make this job a little easier: <a href="http://www.hammondmfg.com/pdf/5c007.pdf" target="_blank">Click here</a><br />
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For a ~22 Watt 8 Ω jazz guitar amp. You'll roughly need +/- 23 to 24
volts on your power amp stage DC rails (under heavy load) to get that maximum
clean power.</div>
For this project, I do <b>not</b> regulate the DC supply going to the final power amplifier. Only the pre-amplifier stage op-amps get regulated DC. I think this is typical for guitar amplifier power stages. Unregulated DC on your PA rails offers a proven, reliable strategy, and of course, gives lower cost & complexity than when you put high power linear regulators on the power amp stage DC supply.<br />
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Unregulated, you won't achieve the somewhat theoretical doubling of maximum amplifier power when going from an 8 to 4 Ω load, since the current draw doubles and this results in a greater voltage drop in the DC supply system. This also may occur because of AC signal factors: mainly increased PA transistor beta drop which I'll discuss in Part 2. As aforementioned, you need to consider many factors when choosing what DC rail voltages you'll need to get a certain clean signal amplifier power.<br />
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When driving our PA stage, we suffer DC power losses from many factors. These include transformer winding resistance and leakage reactance, I squared R energy losses in your power supply system wires + any resistors including PA emitter degeneration resistors and so forth.<br />
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<a href="https://2.bp.blogspot.com/-mk2k_TfkOdc/XF-m4y0ty9I/AAAAAAAADWs/KpFvwFYGwAIEbiE-JS17LrHy1VCBG5fAgCLcBGAs/s1600/ripple-measures.png" style="margin-left: 1em; margin-right: 1em;"><img border="0" data-original-height="595" data-original-width="748" height="508" src="https://2.bp.blogspot.com/-mk2k_TfkOdc/XF-m4y0ty9I/AAAAAAAADWs/KpFvwFYGwAIEbiE-JS17LrHy1VCBG5fAgCLcBGAs/s640/ripple-measures.png" width="640" /></a></div>
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Above — A simple bench setup to measure AC + DC voltages on either of the DC supply rails. I'll use this to measure my positive DC rail voltages -- and later, peak-peak voltages [ AC ripple voltages ] on the positive rail.<br />
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Above — DC measure of the positive rail of my power supply that's connected as shown in Figure 1. The signal generator is switched off, or to 0 output. The unloaded positive rail measures + 27.1 VDC.<br />
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Above — DC measure of the power supply when connected to a PA driven to maximum clean signal power [ 23W ] by the 1 KHz signal generator.<br />
The unregulated positive rail has sagged to 23.1 VDC under this heavy load. We'll use the above measure when we calculate % ripple in Section E. Reservoir Capacitors and Ripple.<br />
<br />
You can't just casually order a transformer like you would some power resistors. Also, the cost may shock you; especially if you live in Canada. Making a power supply takes some thought & planning. Think about your transformer's VA, weight, mounting requirements, RMS AC output voltage, what maximum peak - peak signal voltage, you seek, plus other factors such as whether or not you plan to put the power supply right on the amp chassis, or sit it on the floor of a combo amp with patch wires connecting the power supply to DC power rails. </div>
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As you go up in amplifier power rating & apply bigger transformers that provide a larger split DC voltage with more current, your build increases in difficulty. Heat sinking requirements, I squared R losses, the need for thermal protection/current limitation circuitry -- and the potential for unwanted noises all go up. This is especially true if you wish to drive a 4 Ω load.<br />
<br />
No one showed me how to make a solid state guitar amplifier, that's why my blog
needs to be taken with a grain of salt. Experts and critics may just
lurk and smirk — however, I welcome constructive criticism from any readers who
know more than I. We all learn that way. </div>
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That's why I chose a roughly 23W into 8 Ω clean guitar amp for my first build. Keeping the power down hopefully will allow us to enjoy success in order build confidence, plus gain the skills we might apply to future higher power amps if so desired.<br />
<b> </b><br />
<b>C. Schematic</b><br />
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Above — Power supply schematic. For this project, I used the center-tapped Torel toroidal transformer that was listed as 50VA with + 18, 0, and -18 VAC RMS output. Mine measured 20 VAC peak -- and rectified + filtered under load, I get a nominal +/- 25 VDC output. The panel mounted fuse is connected to the <b>hot </b>polarized AC Mains plug. This power supply gets used in all experiments shown on this blog page.<br />
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Above — Measuring the positive DC rail with no load on a DVM. I built my power supply enclosure from 2 - sided copper clad board. The lid is off for testing and photography. Although toroidal transformers leak less magnetic flux than conventional frame types, they still require electrostatic shielding to prevent capacitive coupling to nearby circuitry. Sometimes moving or rotating them may reduce their hum field. In general, keep you power supply away from your signal path circuitry; and especially your pre-amplifier.</div>
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If you consider the wires that lead to and from the transformer, the rectifier diodes and the reservoir capacitors as a loop — the smaller the loop area, the better for EMI prevention. A loop potentially may inductively couple the transformer pulse currents into your nearby circuitry causing an annoying background AF buzzing noise that cannot be filtered off with bypass capacitors.</div>
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I'll go through the circuit starting with the Mains AC supply.<br />
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Years ago — for anything I make that uses AC mains electricity. I switched to only using an IEC320 C14 receptacle — plus a cord containing an IEC320 C13 appliance plug on 1 end, and a grounded NEMA 5-15P polarized plug at the other Since they're commonly used on personal computers in North America, you seemingly can always find a cord if you forget or misplace one.<br />
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Above — Another view of the power supply with the cover off. The IEC320 C14 receptacle contains a 10 amp DPDT switch. The 2-sided copper board is well soldered on both sides so it's technically RF tight around the transformer and mechanically solid to strongly support the AC receptacle and fuse.<br />
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Above — The IEC320 C14 receptacle with DPDT switch & the toroidal transformer mounting hardware.<br />
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<b>D. In Rush Current</b><br />
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When you turn on and energize a power transformer, an instantaneous surge of current gets drawn to charge up the reservoir caps and to magnetize the transformer. The magnitude of the in rush current is not related to the amplifier load, rather it's dependent on the point in the Mains AC wave cycle when the transformer is switched on. <br />
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On the (low resistance) primary coil side this puts potential strain on your switch and fuse -- some larger toroidal transformers will even snap off a house circuit breaker the odd time. Thus ensure you use a slow blow panel fuse, plus a well rated switch. For example, I used a 10 amp @120 VAC rated switch. Perhaps overkill for a small guitar amp, but you get the picture.<br />
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On the transformer secondary coil side, your rectifier diodes and reservoir caps get strained during any start up surge. Any rectifier diodes must be tough. I initially purchased a commercial 25 Amp rated diode ring that featured a heat sink and mounting hole. Sadly, this part tested defective. I looked in my rectifier parts drawer and saw about 40 Vishay brand 1N5822 3A Schottky barrier rectifier diodes and then studied their datasheet online. These should well handle my voltage, current needs and any brief inrush surge. They work well for my particular guitar amp. I have no idea when, or who I bought them from however.<br />
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I put a slow-blow fuse on each AC secondary to keep the transformer alive should the diode ring ever go shunt to ground. Currently, I've got a 2 Amp slow blow fuse in each slot. The X capacitors are to bypass any HF noise created by the switching diodes from going into the house wiring. <br />
I used hulky capacitors because in the presence of AC bias, some small size ceramic caps may not hold their capacitance value. These 1 kV caps are cheap and easy to find. Carefully check the datasheets for any parts you place in your power supply and consider avoiding 'no - name' parts. It's really sad when you fry a $50 transformer because you decided to save 50 cents by plying a, cheap no-name, part.<br />
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Above — The improvised diode ring. I'll shorten the wires even more. Sadly, I misplaced my 0.01 µF/ 1kV X capacitors and had to order more. No doubt, I'll locate them the day the fresh capacitors arrive. I'll shorten the diode ring wires when I install those X capacitors.<br />
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<b>E. Reservoir Capacitors and Ripple</b><br />
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The main question we all ask — how big should my reservoir capacitors be? Professor Ken Kuhn wrote a great pdf document for his students. <a href="http://www.kennethkuhn.com/students/ee351/power_supplies_filter_capacitor.pdf" target="_blank">Click here </a><br />
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I consider this document essential reading. Also check out his fantastic web site.<br />
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Some audiophiles get carried away with 'requiring" ultra low ripple at high power. From Ken's article, consider aiming for medium to low ripple and use the smallest capacitance that will achieve that goal. Higher capacitance increase surge current as Ken mentioned in his article. More capacitor = more dollars too!<br />
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Ripple is a nuanced number that's conditional and contextual. DC supply ripple increases in tandem with PA stage current draw. So ripple could be quoted with no power supply load, with the amp at 1/2 power, full power and so on. For a clean jazz guitar amplifier, the best case seems to be with no applied test signal and the worst case occurs when you apply the maximum test signal before the amplifier sine wave distorts. This is often quoted as the maximum signal drive where amplifier THD is under 1%.<br />
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On the web, you'll find a number of write ups and videos how to calculate percent ripple, or, the reservoir capacitor value you need to get a certain percentage ripple. Sometimes they lack precision and seem a bit theoretical. We amp builders need a practical, measurement-based way to evaluate ripple. I'll show some simple oscilloscope measurements and apply Professor Kuhn's formula below. It seems to work OK. It's also fun to actually view the ripple on your DC rails with various reservoir capacitor values and power supply loads. Visceral stuff.<br />
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Above — The formula taken from Professor Kuhn's document. To get data to calculate, you'll need a power supply, a signal generator, a PA stage, a dummy load and a oscilloscope or DSO. I've already shown how to measure rail DC with a 'scope DC coupled to your rail earlier in Figure 1. Again, I'll only show the positive rail.<br />
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I place additional ripple filtration capacitors on both my pre-amplifier and PA boards. We'll only consider the PA board. As shown in my power supply schematic, my main reservoir caps are 6800 µF. On my PA board lie additional capacitors and on my test 23 W power amplifier, I've got a 2200 µF /50 volt electrolytic capacitor on each of the DC supply rails. So per rail, that's a total of 9000 µF.<br />
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Above — DSO screen capture with an AC coupled 10X probe on the positive rail with <i>no</i> applied signal drive. This would be the "best case ripple", but seems totally unrealistic as the PA is drawing only 16 - 20 mA quiescent PA bias current from the power supply.<br />
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Above — A DSO capture of the AC signal on my positive DC rail using an AC-coupled 10X probe. The V peak-peak = 660 mV. This is 'worst case' ripple as my PA is drawing maximum current; a heavy load for the DC power supply.<br />
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Using Ken's formula, let's calculate the percent ripple from the data we've gleaned.<br />
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<span style="color: magenta;"><b>Ripple = 100 * RMS Ripple Voltage / Average DC Voltage</b></span><br />
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Your DSO may calculate and display the RMS ripple voltage, however, let's assume you've got a 25 year old oscilloscope with no math functions. We might simply just estimate RMS ripple voltage by taking the measured V peak-peak value and dividing it by 3. We bring the 'worst case' DC voltage from the earlier DC measurement of the positive PA rail.<br />
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<b>Ripple = 100 * (0.66 / 3) / 23.1 = 0.952%.</b><br />
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On a popular (but unnamed) jazz guitar amp I recently measured, the AC ripple signal was around 2 V peak-peak with maximum clean drive signal into a 8 Ω resistive load. So I did OK.<br />
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This simple method allows you to measure and crudely calculate ripple percentage to make comparisons with different capacitors in real time. So my 9000 µF of C in a low-power jazz guitar amp ranks as ultra-low ripple at 'worst case'. Of course, if you go for a 4 Ω load, it could be a game changer. More on that in Part 2 of this series.<br />
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Above — My 2 main reservoir capacitors. Installing them proved a little time consuming. I built my power supply using Ugly Construction on 2-side copper clad board. Since you can only solder their short, thick leads on the bottom side of the main circuit board, I had to improvise. I cut Cu islands for the DC rails and O volt pathways on the top side. <br />
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I also had to cut islands on the bottom side of the Cu board. I connected the positive, negative and 0V top islands to their respective capacitor leads below by joining the top and bottom carved islands with via wires. I drilled 5 via holes for each lead and soldered 20 gauge solid copper wire to join each appropriate top and bottom island. I'm used to doing this to provide a low impedance ground in UHF circuits, so it's not a big deal for me. After final testing with an ohmmeter, the 6800 µF caps were installed. I did the soldering with my 80W iron.<br />
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I installed the filter capacitors by drilling 1 hole for each cap lead into each of appropriate carved islands and then soldered each capacitor lead to the bottom copper board.<br />
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<b>F: Power Supply, Signal and Filter Capacitor Grounding Scheme</b><br />
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We ought to consider ground loop hum and reduce it by carefully placing our parts, rails and various types of ground wires to avoid contaminating our signal ground with charging currents from filter capacitors and other unwanted AC currents. You'll also need a scheme to connect your signal ground to chassis ground plus Earth.<br />
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A stellar reference for this topic and also my entire project = <br />
<b><u>Audio Power Amplifier Design by Douglas Self </u></b>. I can't recommend this book enough. <a href="http://www.douglas-self.com/ampins/ampins.htm" target="_blank">Click for Doug Self's web site</a><br />
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Doug Self's practical knowledge, writing skills and published experiment results provide game-changing insight into the world of audio design from small signal to PA stages. <br />
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Above — Grounding scheme. We've got multiple ground terms which gets confusing. On the power supply circuit board lies Reservoir Ground. Reservoir Ground is the 0 volt rail on the power supply and it's only connected to the transformer center tap and 1 node of each reservoir capacitor. Lots of pulsating charge current flowing here.<br />
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Signal, and Electrolytic Capacitor 0 Volt Grounds on any circuit boards are connected to the Reservoir Ground by wires. I made a tee off the Reservoir Ground rail and put an Electrolytic Capacitor Ground point at 1 end — and the Signal Ground point at the other end of this tee. <br />
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This separates pulsing capacitor charging currents from Signal Ground — and by way of the tee, keeps these 2 points confined away from the 2 main reservoir capacitors. Connecting Signal Grounds to 1 point on the Reservoir Ground rail by wires is commonly called star grounding.<br />
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Apart
from the power supply board, most circuit boards will have only Signal
Ground, or Electrolytic Capacitor Ground.<br />
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Signal Ground on any circuit board gets connected to the Star Point on the power supply board by a wire as shown.<br />
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Grind away any copper on the power supply, pre-amplifier, PA or any auxiliary circuit boards that your circuit board anchoring hardware passes through. This prevents you from connecting any type of circuit board ground to the chassis through any bolts, spacers, washers and nuts used to mount your various boards to the chassis.<br />
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In essence, the circuit boards are "floating" from the chassis. <i>They won't truly be floating since we'll connect these boards to the chassis by a special means that's described later.</i><br />
Consider the DC rails on the PA and pre-amplifier boards. At the
beginning of each positive and negative DC rail lies electrolytic
capacitor(s) that connect to a small 0 volt rail (Electrolytic Capacitor
Ground) that is separate from the Signal Ground on each board. On my
boards, I carve out a small island for the Electrolytic Capacitor Ground
rail. Run a copper wire from each Electrolytic Capacitor Ground island
back to it's proper grounding point on the power supply board as shown.<br />
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Auxiliary board 0 Volt
ground returns such as those that contain relays, thermal, or non-signal support circuitry get
connected to the their own special tee to Reservoir Ground on the power supply circuit board by a
copper wire. See the diagram.<br />
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Mains ground from now on is called EARTH. EARTH is the AC ground lug of the IEC320 C14 receptacle. Connect a thick, shielded copper wire from this EARTH lug to the guitar amplifier input <i>jack ground </i>lug. Thus, the amplifier input is EARTHED by this wire.<br />
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The 2 - sided copper clad board surrounding my transformer is also connected to EARTH lug of the IEC320 C14 receptacle. Since my power supply shielding box is "floating" from the chassis it will only be connected to the chassis by way of the single wire mentioned above.<br />
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Signal Ground is connected to Chassis Ground at 1 point. Some designers do this with a 10 Ω resistor. For example, you'll see this in the Fender Jazzmaster Ultralight guitar amplifier schematic.<br />
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Another way, I learned about from Doug Self, is through a shielded input cable from the guitar amplifier input jack to the first pre-amplifier stage.<br />
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The 1/4 inch guitar amp input jack's grounded sleeve body is usually automatically connected to the metal chassis because it's a conductor. Check it with an ohmmeter. If you use a plastic 1/4 inch amp input jack, you'll have to connect its ground lug with a short wire to a bolt on the chassis. Whatever you do, ensure you've got a solid, low impedance connection to the chassis from the amplifier input jack's <i>ground</i> node.<br />
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The ground braid or shield of the proximal input coaxial cable gets connected to the guitar input jack <i>ground lug</i>. However, recall that the jack ground lug ( and chassis ) is also EARTHED through a wire at exactly this point — providing strong ground loop immunity.<br />
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The distal end of the coaxial cable goes to your pre-amplifier input stage. The braid at this end goes to the star grounding point on the power supply circuit board as shown. So you now have connected your EARTH, Chassis and Signal Grounds to the Reservoir Ground in a manner which helps reduce grounds loops.<br />
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<b>G. Regulated DC for Your Pre-Amplifier Board</b><br />
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To garner maximum headroom, it's desirable to run op-amps like the NE5532 and/or TL072 with more DC voltage than the doldrum standard of +/- 15 VDC. You might go as high as 17 volts on the rails. Since, I've got an abundance of 16 volt zener diodes on hand, I opted to build my rail voltage regulators around these. The 17V 1N5247B zener diode might also prove a good choice.<br />
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Many builders just run linear regulators and adjust the rail voltages to somewhere between 15 and 17 VDC. <br />
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I chose the field-tested emitter-follower configured DC regulator with a gain of 1. The base-emitter voltage drop of this topology lays in series with the load, so load current changes will alter the regulator output voltage. Vout = V Zener – VBE: so the regulated voltage will be under 16 volts if you apply a 16 volt zener diode. Barring catastrophe, once the pre-amplifier board is connected, the DC voltages on each rail will hold steady.<br />
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The BJT base bypass capacitor value gets roughly multiplied by the transistor's current gain which boosts low-pass filtration of the stage to further scrub down rail ripple. The electrolytic capacitor and zener diodes 0V leads go to Electrolytic Capacitor Ground on the power supply board as discussed earlier.<br />
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Above — Pre-amplifier voltage regulators: one for each rail. I added diodes to limit the stage current to a maximum value somewhere above 200 mA. One diode compensates for the BE junction of the transistor, while the second diode limits the voltage across the emitter resistor to the diode ON voltage ( around 0.6 V ).<br />
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I'll show the actual capacitor values + my DC measures on the pre-amplifier boards later in this series of blog posts.<br />
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<b>H. Output Rail Notes</b><br />
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Above — Power Amp Output Rail diagram. This isn't really about the power supply circuitry, however, I don't know where else to put it. Your PA output rail receives all of the amplifier's power and some serious current is flowing here. Authors such as Doug Self recommend that we don't connect our 3 PA output rail networks at the emitter connection points. Make a tee as shown and then choose your 3 takeoff points. This confines the PA transistor emitter energy away from these 3 nodes.<br />
<br />This is part 1 of a multiple part series about a scratch home brew guitar amp.</div><div class="MsoNormal"> </div><div class="MsoNormal">Part 1 lies <a href="https://qrp-popcorn.blogspot.com/2019/01/clean-jazz-guitar-amp-builder-notes.html" target="_blank">here </a><br />
<span style="color: purple;"><span style="color: black;">Part 2</span> <span style="color: black;">lies</span> <a href="https://qrp-popcorn.blogspot.com/2019/11/clean-jazz-guitar-amp-builder-notes.html">here</a><br /><span style="color: black;">Part 3 lies <a href="https://qrp-popcorn.blogspot.com/2020/11/clean-jazz-guitar-amp-builder-notes.html" target="_blank">here</a></span><br /><span style="color: black;">Part 4 lies <a href="https://qrp-popcorn.blogspot.com/2021/03/clean-jazz-guitar-amp-builder-notes.html" target="_blank">here</a></span></span> <br /></div><div class="MsoNormal"><br />
<a href="https://qrp-popcorn.blogspot.com/p/guitar-related-index.html" target="_blank">Click for my Guitar-Related Index</a><br />
<br /></div>
Vasily Ivanenkohttp://www.blogger.com/profile/17387516134063150119noreply@blogger.com7tag:blogger.com,1999:blog-3480228403403435266.post-89619624803280820632018-12-10T22:02:00.004-08:002018-12-30T19:34:30.205-08:00Guitar Amp Builder Notes — AF Power Amplifier Dummy Load<br />
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I'll describe a simple 8, or 4 Ω dummy load to test your home brew guitar power amplifiers.<br />
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Low cost 16 Ω / 25W wire wound, aluminum shell, chassis mount resistors seem abundant. I got mine on eBay. Wire wound resistors vary in quality, design and tolerance. Some even exhibit low inductance by winding with an Ayrton-Perry bifilar technique. Resistor tolerances range from 10% down to ± 0.5 % + 0.05 Ω. Typical manufacturer power ratings are done at 25C, however, these devices are meant to sit on a heat sink when used and that's why the aluminum housing contains 2 relatively large mounting holes.<br />
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I crafted my heat sink from MG Chemicals Copper Clad Board, Double Sided, 1 oz Copper, 1/16" thick, FR4. My entire chassis serves as the heat sink. I come from an RF background and we builders use double sided board for enclosures, heat sinks, shields, and of course, for our circuit boards. I employed a clumsy 80W soldering iron to solder my boards together.<br />
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Above — Project schematic. My switch rating = 6A at 225 VAC. I opted to use a standard 1/4 inch speaker jack as the input. I connect it to my power amps under test via a short home brew patch cable.<br />
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Above — Front view of my dummy load. <br />
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Above —Side view. Each power resistor's ground wire passes through a hole drilled in a double sided Cu clad "vertical fin" board. The tip of each ground wire was bent flush against the copper fin board and soldered. The copper fin board is soldered to the main board on both sides providing a low impedance ground, plus some heat sinking. You can't well see it but I completely soldered the grounded resistor side of the copper fin board to the main board.<br />
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The input side of the power resistors connects to the input jack and switch via bare, solid core 22 gauge wire that's folded in half, twisted and then soldered together. <br />
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Above —Above, oblique view. You can see the vertical, ground wire "fin" copper board and a secondary vertical fin Cu board behind it for added heat sinking. <br />
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Above — I applied thermal grease to the bottom of each aluminum power resistor enclosure before bolting them down. I've enjoyed good results with MG Chemicals' super thermal grease II in many previous projects. Wear gloves and lay out some paper to prevent a messy bench + greasy hands.<br />
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Above —Bottom of main Cu board. The 2-sided board provides reasonable heat sinking, plus mechanical strength. The nuts and bolts connect the top and bottom board sides at DC & @ AC out to High Frequency. I placed 4 stick-on rubber feet for a sturdy base.<br />
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Above — The holes in my green power resistor aluminum enclosures were big enough (3.5mm/0.14inch) to allow the use of 6-32 hardware — you can really bolt them down securely to your heat sink. <br />
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Above — Close up photos of my particular power resistors. I purchased them for $2.59 CAD each including shipping and handling. Quite reasonable. <br />
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<b>RF Assessment </b><br />
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With a strong RF background, the term 'wire wound resistor' strikes a bit of fear in my heart. I measured my resistor's inductance, plus swept 1 in a tracking generator + spectrum analyzer from ~ 9Khz to 1.3 GHz.<br />
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Typical inductance of the couple of resistors I tested from my batch= 889 nanoHenries. My sweep revealed that the series resonant frequency (SRF) of 1 of my batch of resistors = ~ 109 MHz. The notch @ ~ 109 MHz isn't very deep; it's around 14 dB down from reference. <br />
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This fits with my lab experiences. I keep a good selection of wire wound chip inductors for building circuits in the 100 - 1200 MHz region. Every chip inductor I own has been swept and characterized — I keep a high Q, Coilcraft, wire wound, 880nH, size 0603, SMT inductor and its SRF = 104 MHz. In truth, a chip inductor & a power resistor compare poorly, but give the chip inductor gives a ballpark SRF reference of what to expect. <br />
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Of course, the SRF notch of my high Q SMT part is ~44 dB deeper than a lousy 16 Ω power resistor. Since the power resistor is low in resistance (and will go in parallel with other 16 Ω resistors), its a low Q inductor — and with a SRF above 100 MHz, it will work fine as an AF power resistor.<br />
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<b>Resistance and Temperature</b><br />
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Above — My 16 Ω resistors tolerance = 5%. With all 4 resistors in parallel I measured 4.28 Ω at room temperature with my DVM in high resolution mode. With the resistors at 48.9 degrees Celsius, my DVM measured 4.29 Ω, I will use 4.28 Ω as my "4 ohm" resistor value in all amplifier power calculations based on bench measures.<br />
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Above — With 2 resistors in parallel I measured 8.29 Ω and this rose to 8.3 Ω when the resistor's temperature rose to 50.6 Celsius. Resistor temperature coefficient =100 PPM / C . I'll use 8.29 Ω as my resistance when calculating power from measures made on the bench.<br />
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Above — An infrared temperature monitor proves invaluable for bench temperature measures. I measure the temp of my power resistors — and also project AF and RF final transistors temperature with this device.<br />
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I put my switch in the 8 Ω setting and ran a 1KHz signal generator into a small power amp with the dummy load connected. I set a measured 15W output power and let it run for 15 minutes unattended to heat up my dummy load. After 15 minutes, the peak temperature on the 2 power resistors in parallel = 50.6 C. This seemed @ steady state, as the temperature did not rise above 50.6 C.<br />
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Then I switched to the 4 Ω setting, drove the load for 15 W measured power and let it run for another 10 minutes or so . The peak temperature measuring on top of the resistors was 46.5 C. Distributed across the 4 resistors, my dummy load ran cooler than with the same output power into 8.29 Ω paralleled pair. All as expected.<br />
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During normal bench measurements of power, or when setting the bias on a tube amp; or adjusting the trimmer potentiometer to set DC voltage for the VBE multiplier on a solid state PA, it probably only takes < 5 minutes. Thus a continuous 1 KHz wave @15W for 15 - 25 minutes proved a bit of a torture test.<br />
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In 2019, I hope to build some guitar amps that exhibit a clean average peak power of 40W or so. I'll carefully measure my dummy load & update this posting when I've got some more temperature data. Clearly, if you want to torture test a load driven to 100W measured power, you'll have to consider increasing the heat sink area, apply more resistors, or perhaps, spawn a correct thermal resistance heat sink design using math and measures. <br />
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Mine is just a hack — and it operates within spec for my particular resistors and needs.<br />
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Above — the temperature of my concrete floor. It's already cold in my lab and we're barely into the Canadian winter. That's ~60 F for those who dwell in the USA.<br />
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Above — My previous home brew 8 Ω dummy load made sometime in the 1990s. The big resistors are 2W rated 1% tolerance resistors and this worked OK for the AF power amps I built up until the last couple of years.<br />
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<b>Power Calculation</b><br />
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It seem that some people quote a guitar amplifier's peak versus RMS power etc. This causes confusion.<br />
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For reference, here is how I calculate the maximum power for all the guitar amps I'll present over time. To measure power, we employ a signal generator ( often a 1 KHz sine wave, low distortion signal source ); an amplifier under test that contains a power amp stage; and finally a purely resistive load such as the dummy load I presented.<br />
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Above — Average power formula. We advance the signal generator gain until distortion appears on the oscilloscope output. Then we back it off slightly to re-establish an output free of distortion by viewing the sine wave on an oscilloscope; or the sine wave and/or FFT in a digital storage oscilloscope.<br />
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The oscilloscope peak to peak voltage gets divided by 2 to give the peak voltage.<br />
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The peak voltage is then squared. The peak voltage squared is then divided by 2X the load resistance. So if the dummy load is set to 8 Ω, we would divide by (2 times 8) which is 16 Ω.<br />
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For my particular dummy load, I'll use (2X 4.28 Ω) or (2X 8.29 Ω) for my load resistance.<br />
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<br />Vasily Ivanenkohttp://www.blogger.com/profile/17387516134063150119noreply@blogger.com1tag:blogger.com,1999:blog-3480228403403435266.post-40507131602237678812018-11-30T19:59:00.000-08:002018-12-10T20:01:37.920-08:00<b>New Lab Speaker</b><br />
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For the past 25 years, I've listening tested every audio amplifier I've built on a gifted 8 Ω speaker that's mounted in the home made box it came in. This ~7.5 inch speaker is at least 40 years old and is likely rated under 5 watts. Over time, the cone dried out and ripped. It certainly did not have the peak power rating I need for testing my newer audio amplifiers which typically range from 5 to 20 watts into an 8 Ω load impedance.<br />
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Above — Reverse view of my old, trusty lab speaker. Over many years, I've built hundreds of radio receivers and listened to each of their audio PA stages through this speaker.<br />
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Above — You can see 3 rips in the paper cone. Plus the surround had dried out. I could not re-cone this speaker even if I wanted to. Time for a fresh driver.<br />
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I ordered a replacement speaker on Amazon -- an 8 inch ceramic Jensen guitar speaker rated at 20W peak @ 8 Ω.<br />
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Above — The new speaker mounted perfectly in the plywood box. Delightfully, the speaker mounting holes lined up exactly with the baffle holes originally drilled for the old speaker. Serendipity. I secured it with the same hardware.<br />
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Above — Front view of the new speaker. You can see the cone seam at about the 5:30 position.<br />
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Above — I cut a scrap piece of 1/4 inch plywood and fashioned a back to this cabinet. There's quite a gap so the speaker can't compress, but the back does help forward projection a little and protects the rear of the speaker from my feet. This box normally sits under my bench.<br />
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I mounted a standard 1/4 inch jack, plus an RCA [ in parallel ] into a scrap piece of copper sheet metal. I'll use the RCA jack for bench testing small radio receivers and the 1/4 inch jack for my<br />
bigger power amp stages. I ordered some rubber feet and a top handle for the speaker cabinet.<br />
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All is well in my lab once again.<br />
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Oh look, my 8 inch speaker just got a baby sister:<br />
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<a href="https://qrp-popcorn.blogspot.com/p/guitar-related-index.html" target="_blank">My Guitar Related Index</a>Vasily Ivanenkohttp://www.blogger.com/profile/17387516134063150119noreply@blogger.com0