Monday, 15 March 2021


Clean Jazz Guitar Amp Builder Notes — Part 4: Pre Amplifier Notes

Part 1 lies here
Part 2
lies here

Part 3 lies here

Click for my Guitar-Related Index

Preamplifier notes from March 7, 2021 until present

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 .

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.

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.

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?

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.  

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.

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.

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, who I've referenced in Parts 1 and 2.

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.

I lined up multiple new circuits to try and will present them over the next few months. Stay tuned.

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!

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