March 16, 2008
by: jovial_cynic

Back in November, I built up the Little Gem audio amplifier, and toyed around with it for a little while before I listed it on Craigslist to see if I could make a few bucks on it. Before it sold, somebody in my area saw the ad and contacted me to see if I'd be interested in a Peavey amp head that stopped working. He couldn't get it to work, and after replacing a fuse in it, he said it "started smoking," so he didn't want to mess with it anymore. I took it, figuring that at best, I'd be able to fix it and sell it, and at worst, I'd have a bunch of nice knobs and components that I could scavenge and use for future projects.

Not wasting any time, I plugged in to see what would happen. No smoke. Good. Next, I tried the pre-amp line to see if the unit was sending any signal at all, and sure enough, the pre-amp side of the unit successfully shaped the signal, which meant that I had reverb, equalizer, and a couple other miscellaneous features.

Curious about why the power-amp side of the amp head didn't work, I cracked the case open and found this:

At the center of that wasteland stands three prongs that used to be a transistor (possibly the power transistor), and all around it were burnt out resistors.

I have no interest in trying to replace every burnt component, only to have them fizzle out again because of the short in the circuit that caused the problem in the first place. Instead (thanks to the suggestion of a friend), I decided to try to run the pre-amp side to another unit I had handy:

This is a JVC tuner/stereo-amp that I've had for years. For a while, I've been using it for my computer audio, but recently picked up a set of good computer speakers and subwoofer, so I didn't really have much use for it. The tuner has a few bugs... some of the buttons don't respond, and the volume control is really finicky. However, it does amplify audio just fine.

I tore out the power-amp transformer (I'm sure it still works; I'll use it for another project later...), relocated the reverb chamber to the top of the case, and threw the JVC tuner into the Peavey casing. I had to remove the JVC's feet to make it fit, but it worked.

Here's how it looks without a face board to clean it up.

Here's the rear. It's handy that the JVC has a switched outlet, allowing me to plug the Peavey into the JVC, and then run the JVC to the wall outlet. Additionally, the JVC is a 220watt 2-channel system, so I can threw multiple speakers onto the system and have it crank out a lot of noise. I can also attach an antenna to the system and listen to the radio through it as well, although the radio won't go through the amp head. It's too bad, because I was thinking about building a little wireless FM transmitter and turning the system into a wireless amp.

I'm sure I could rig something up to make it work...

Anyhow, here's a clip. I play it first through a Yamaha distortion pedal, and then play it straight. Since the tuner is a stereo amp, the audio is very clean coming through the speakers.

This time, my two-year old gets in on the action. She seems me through the baby-gate and goes around and then realizes she can see me playing through the view-finder on the camera. The whole time she's talking, she's talking to the camera. Cute.

Also, I stuck my toe on the audio plug because there's some kind of grounding issue with my mandolin that causes a terrible buzz. My toe provides a good grounding point.


Dan said:
NICELY DONE!!!! Now, make it FM compatible..
March 16, 2008

jovial_cynic said:
I'll see if I can get the tuner working... there's an antenna that came with the tuner that might have gotten lost. If I can get the tuner working, my next electronic project may be to build a wireless FM transmitter. But if not, I've always got the baby monitor...
March 16, 2008

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