Acoustic Model 109 (G60-112) help

[fspa8724]

I have an Acoustic Model 109. (Early version of the G60-112) Channel 1 volume is very low, while the drive volume is loud. I have had it in to several repair shops, and each time some one works on it new problems occur. Any one have suggestions on the problem.
Much appreciated

[Steve L]

Acoustic 109

I have repaired quite a few Acoustic amps, especially in the early 80's when there were a lot more of them around, however I don't recall a 109 model.
Nonetheless, if the preamp was designed like most G60 and other Acoustic preamps were, the problem(s) should be very easy to find.

Given your description of new problems arising everytime you bring it somewhere, it very likely has several cold solder joints in various places.
That was/is a very common problem with Acoustic amps back then as well as any other manufacturer.
I would suspect that you will find it at, or somewhere near the channel 1 volume pot. There is not much circuitry there, especially if channel 2 is good.

As long as you can solder well, go in and touch up every suspect solder joint on the board, especially all of the potentiometer connections. Clean the pots as well with a good cleaner. It will be quicker to fix it this way first than going in with a scope. You can do that later if you did not find the bad solder joint.

Steve

[52 Bill]

...if the preamp was designed like most G60 and other Acoustic preamps were, the problem(s) should be very easy to find.

As I recall, the Acoustic design added gain stages to the clean channel for the overdrive. If the overdrive channel works, then at least parts of the clean channel circuitry are working. The problem may be in the switching circuitry. Maybe a bad coupling cap or or a bad optoisolator (if this one uses them).

[fspa8724]

Thank you. I will retouch the solder joints, and check the caps