Friday, 30 November 2018

New Lab Speaker

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.

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.

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.

I ordered a replacement speaker on Amazon -- an 8 inch ceramic Jensen guitar speaker rated at 20W peak @ 8 Ω.

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.

Above — Front view of the new speaker.  You can see the cone seam at about the 5:30 position.

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.

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
bigger power amp stages. I ordered some rubber feet and a top handle for the speaker cabinet.

All is well in my lab once again.

Oh look, my 8 inch speaker just got a baby sister:

My Guitar Related Index

Sunday, 18 November 2018

Kostas' Mini - VFO

Kostas, SV3OR does it again.  Please view his mini VFO project

 I'll build 1 in the new year.

Currently I'm making a guitar equalizer -- and in November, built power amps, multiple tone circuits, effects loops, balance line outs  -- a plethora of guitar related stuff.  Hope to post in December. Until then, a few photos lie below:

Into a 4 ohm load -- that's 23 Watts clean average power