Peavey Nashville 112 reverb noise

[Prattacaster]

I've got a Nashville 112, the reverb is noisier as you turn up the reverb pot. With the reverb pot at max you get a healthy dose of white noise. Is this inherent in the 112's?

I was troubleshooting with nothing plugged into amp. Reverb tank unplugged did not affect noise, maybe slightly. C35 is installed backwards according to the attached schematic, however the schemo indicated C35 is part # 1A50NP. Does the NP stand for non-polar? If so the stock C35 cap is not a non-polar cap. I'd really like to reduce the background noise the reverb injects into the circuit. Components and voltages check out with the possible exception C35. Should a replace the BA4560 Op-Amp with a quieter one? Thanks.



NASHVILLE_112.pdf

[Enzo]

Peavey has been using that same reverb circuit for over 25 years. Doesn;t matter what model it is in.

If it is noisy, try a new op amp.

[Prattacaster]

Thanks Enzo, any thoughts regarding C35? It was mounting backwards on the PCB according to the schematic. It doesn't seem like the typical place for a non-polar either.

[Enzo]

How can a non-polar cap be backwards? The whole point of one is that it is non-polar, has no polarity.


C35? One end is at ground potential through R46. The other end is on a signal pin of the op amp. The op amp runs on split supplies and so signal pins sit at zero. The signal can then go positive or negative from zero, meaning the cap can have a positive or negative voltage across it at any instant. Hence non-polar cap.

Look on the cap, does it say NP or BP right on the cap?

[Prattacaster]

The cap did not appear to be Non-polar, the schemo indicates polarity, but there is a coding (1A50NP). My question was whether or not the coding signified non-polar. Of course you cant put a non-polar in backwards!

The cap says BPTK - Illinois cap. I could not see the BPTK until I uninstalled it. Its physical shape is identical to a normal polarized cap, that's what threw my off.

I, by chance, had a OPA2134PA sitting around, I replaced the stock op amp and it was a marked improvement. Still a little noisy, but purely white noise. With the stock op amp, there was a low freq. accompanying the noise, that is now gone with the Burr-Brown OPA2134PA.