DIYRE G Bus 202c VCA Weird Noise. Please Help.

[Clbraddock]

Ended up putting it all back together with the 202c vcas. Something I noticed: Originally, I had thoroughly cleaned the boards with 99% IPA they looked pretty clean to me, but unrelated to this projected I had randomly looked at the data sheet for my solder (Kester 26-6040-0027) and saw that it said IPA was ineffective for cleaning. After reassembly, I recleaned the boards with MG Chemicals 4140A) and they are definitely even cleaner now. As a side effect, THD is lower now both with CW and CCW threshold positions. With 202c VCA and threshold CW it bounces between .05-.08 and with CCW (10:1) it goes up to about .11 (before additional cleaning and with with stock vcas CCW was .19). So a pretty good improvement in distortion. Keep in mind this is with the 202c vcas, which (I assume) already have more distortion baked in than the stock vca. So, REALLY cleaning the boards seems important for this build.

Separately, something that I worry about is did I do any harm to the op-amps briefly running the G-Bus with the control boards disconnected when I was testing in this thread? I seem to recall in the GSSL thread it was mentioned that running the GSSL without control boards would potentially damage the op-amps (I cant find the post back though). Everything seems to be working, so they haven't outright failed, but I've heard that when damaged it sometimes just causes extra VCD on the op-amp outputs. Am I likely okay, or is it worth testing for that?

 

[Meathands]

Ended up putting it all back together with the 202c vcas. Something I noticed: Originally, I had thoroughly cleaned the boards with 99% IPA they looked pretty clean to me, but unrelated to this projected I had randomly looked at the data sheet for my solder (Kester 26-6040-0027) and saw that it said IPA was ineffective for cleaning. After reassembly, I recleaned the boards with MG Chemicals 4140A) and they are definitely even cleaner now. As a side effect, THD is lower now both with CW and CCW threshold positions. With 202c VCA and threshold CW it bounces between .05-.08 and with CCW (10:1) it goes up to about .11 (before additional cleaning and with with stock vcas CCW was .19). So a pretty good improvement in distortion. Keep in mind this is with the 202c vcas, which (I assume) already have more distortion baked in than the stock vca. So, REALLY cleaning the boards seems important for this build.

Separately, something that I worry about is did I do any harm to the op-amps briefly running the G-Bus with the control boards disconnected when I was testing in this thread? I seem to recall in the GSSL thread it was mentioned that running the GSSL without control boards would potentially damage the op-amps (I cant find the post back though). Everything seems to be working, so they haven't outright failed, but I've heard that when damaged it sometimes just causes extra VCD on the op-amp outputs. Am I likely okay, or is it worth testing for that?

Interesting about the flux! Good to know, thanks.

Looking through the circuit, I don't see any opamps where removing the control boards would result in open-loop gain, an excessive load or anything like that. So I don't see any cause for concern.