Ampeg VH 140C Reverb problem

[BKLZ]

Hello Everyone.
I just bought an Ampeg 140 and there is an issue with the Reverb. If you turn it up the audio output progressively dies out, and it produces more buzz(which might be somewhat normal, but I would like to reduce the buzz if there is a known easy fix, like shielding of some kind). Anybody have any ideas? Maybe a simple fix?

[The Dude]

Schematic is here:

https://ampeg.com/support/files/Sche...Schematics.pdf

[BKLZ]

Thanks. Any ideas on what might be happening? Could it be as simple as a potentiometer? I only have the most basic understanding of whats going on in these things. I could replace caps or something but really cant troubleshoot without assistance.....

[The Dude]

............If you turn it up the audio output progressively dies out, and it produces more buzz......

Can you explain that a little better. By turn it up, what do you mean by "it" - the reverb, volume? When you say it dies out, do you mean the overall volume, just the reverb level, etc.?

[BKLZ]

When Im playing and the reverb knob is dialed up the overall sound output is reduced significantly. Maybe by 75 or more percent if the reverb is dialed to 10. Some buzz remains, and increases a bit as you dial up the reverb.

[The Dude]

I'd check the obvious/easy things first. Are the tank wires good? Check the tank input and output and make sure the transducers aren't open. If you turn up the reverb and smack the tank, do you hear the reverb "crash". If all is good there, there are test points on the schematic for the reverb circuit. I'd trace signal through the circuit and see if something doesn't jive.

[BKLZ]

Thanks. If I remember right, as the reverb was dialed up it did produce reverb. but the overall volume decreased. I am on the road and in a hotel so cant get to it right now. Testing may be beyond my pay grade. Seems I have to input 1kh signal, maybe have an oscilloscope, which I have no idea how to use. What does p-p mean in the test point chart??? Thanks

[BKLZ]

The guy I bought it from said that the reverb just started doing this, and after playing for a while it will start working normally. I can't confirm this as I only played through it for a couple minutes and it was completely screwed up for me. Sounds awesome and is loud as hell anyway

[BKLZ]

Just a bump hoping someone might have ideas, and know what p-p means on the tea point chart. Point to point????? I’m a total newb.

[glebert]

Just a bump hoping someone might have ideas, and know what p-p means on the tea point chart. Point to point????? I’m a total newb.

Vp-p is Volts peak-to-peak. This is a measurement of an AC voltage, as opposed to a DC voltage. The other common way to measure AC voltages is with an RMS (root-mean-square) value. Usually it is easier to measure Vp-p on an oscilloscope and Vrms on a multimeter (even if it isn't a "true" RMS measurement, which is a huge argument that won't help anyone in this thread).

[Helmholtz]

1Vrms = 2.83Vp-p with sine signals.

[BKLZ]

Thank You