Acoustic G20-110

[RWood]

This is the early '80s solid state amp. Schem has proven difficult to find.

Any help?

RWood

[Jazz P Bass]

This guy has one
$20.00
Link: Acoustic Schematics

[RWood]

Thanks JP.
I was able to fix the amp without the need for a schematic.
RW

[Jazz P Bass]

Glad to hear it.
Probably a pretty basic circuit at 20Watts output.
Was the output discrete components or a TDA 2050 something?

[RWood]

Take a look - I didn't note the designation because the output was functioning fine. Looks like it had been replaced at some point though,

This amp's symptoms were in the preamp, oscillation that kicked in at about 7 on the low gain setting, and almost immediately in hi gain mode.
Also the channel volume pot was static-y any time i would tap it, even after having been cleaned.

Care to take a stab at the fix?

[Jazz P Bass]

Faulty coupling cap?
Opamp power rails ripply?
Is that a stereo amp?
I see two of everything in the output section.

[RWood]

I thought it would be bad coupling cap and expected to see DC on the pot, but there was none. I just re-flowed the vol pot connections on the pcb, and most of the others around it, and then cleaned out the pot again. Tried it out, better but still not all the way. Cleaned it out again and that did the trick. Must have been some serious shazz in there - my next step was going to be dismantling the pot body.

It is a mono amp, but this note (on the speaker!) might address the 'two of everything':

CAUTION
This is a bridged type power amp
do not reference output leads
to ground potential

[Jazz P Bass]

Thanks for the info.
Mono Bridged. Huh!
I like the dirty pot description.
"serious shazz"