GV-22 Ch. 1 Low Volume

[Mr_bibbles]

Hello Y'all, I have a Gv-22 (https://ampeg.com/support/files/Sche...0Schematic.pdf) that has an issue- the first channel sounds good, but is too quiet!


Information so far:

1. Qualitatively, the channel sounds good, rich, and like a guitar amp should. It's just %60-%70 of the volume it should be, and I can compare it to another GV-22 to confirm this. Channel 1 is the tremolo and reverb channel.

2. I scoped the signal coming out of the tone stack on both channels and it is identical, so we know that the signal loss happens somewhere AFTER
the tonestack on CH. 1 and (Edit the summing point "Z"

Things I've tried;

1. Replacing all the caps (except the .002's since I have none) and verifying all the resistor values in the tremolo section.

2. Measuring for incorrect Voltages, but they are in line with those posted on the schematic, and swing with the foot switch on / off. as they should.

3. The tremolo and the Reverb work just fine.



Anyone ever experience this before, or have an idea of where the signal loss could be occurring? Happy to provide measurements, but again, voltages all match the schematic through that section.

Thanks!

P.S. So nice to see the forum up and running again!

[Helmholtz]

2. I scoped the signal coming out of the tone stack on both channels and it is identical, so we know that the signal loss happens somewhere AFTER
the tonestack on CH. 1 and the summing point "Z"

I guess you mean BEFORE point "Z" as otherwise channel 2 would be affected as well?

2. Measuring for incorrect Voltages, but they are in line with those posted on the schematic

Does that include all cathode and plate voltages?

[Mr_bibbles]

I guess you mean BEFORE point "Z" as otherwise channel 2 would be affected as well?




Does that include all cathode and plate voltages?

Thanks Helmholtz, AFTER the tone stack and BEFORE z, yes.

Yes, all cathode voltages and plate voltages accounted for. (I used the voltages posted from the filter caps to verify)

[Helmholtz]

The dry signal of CH1 is processed by V8, so I would concentrate on that section.

[Mr_bibbles]

The dry signal of CH1 is processed by V8, so I would concentrate on that section.

Thanks! That's what I had thought, I replaced the tremolo caps, but I havn't replaced the .001 and .002 yet due to not having one on hand. Those are coupling caps? They are such small values I'm not sure.

Additionally, could a half-bad tremolo unit (varistor assembly) cause this? I can bypass the resistor side with a jumper and get a *slight* volume increase, but it doesn't seem to bring it back to %100... any way to test this without purchasing an expensive unit from Fliptops?