Help with Peavey amp repair
Solid state Peavey Mark 3 Series Bass head
Bought it used in 91, copyright is 1978 so it was manufactured some time between those years
I haven't played through this amp for about 8 years but now my son wants to use it. It is putting out some kind of electrical sound. The sound is difficult to explain: not quite a buzzing sound. Only happens (most noticeably) while playing A thru D. Sounds similar to a blown speaker or something loose in the cabinet. It is faint, lower dB than the actual signal, but still noticeable. It is not the cabinet or the cables or the bass, I verified all on other systems. I cleaned, then checked all inputs and the sound is equal in all (also both outputs, and for the hell of it, tried on/off switch in both directions). I also adjusted every pot but the noise only lessened when i dropped the lows out of the eq (50-250hz) I took the amp apart to check for anything obvious (loose wire, burned cap, resistor, transistor, etc) but nothing stood out. I am at the point of removing everything from the board and testing individually but I was hoping someone might have some insight before I started that task. All help is appreciated
Have you tried it through different cabs?
Any amp circa 1978 is probably due a cap job. Those big old filter caps love to bulge, leak, dry up and cause all sorts of mess. A quick clean of all the pots is probably in order as well. Sliders are trickier to clean, but worth it as well. I would do all of this before you rip it all down and start testing individual components.
If the filter caps are dried up, the low A (especially) can sound weird and flabby. That's where I'd start, well that and putting it on a scope to see how it's doing.
In other words, time to have the amp get a little service done. Take it to a tech or replace the caps yourself if you have some basic electronic expertise.
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