Unusual scratchy gain control problem

[Gaz]

When you take it off standby, are there filter caps after the switch?

If so, that is why the voltage jumps for a bit.

Do you have the open side of the chassis shielded?

9 out of 10 times when a new build has problems, it is a wiring error or bad ground or both.

There are no errors I can find, and I have rebuilt the whole front end searching... Also, shield does not help with the static-y noise, but now I'm more focused on the DC on the pot on startup, which I'm beginning to think is not actually out of the ordinary at all.

I've observed the same thing on another amp, and now am thinking I just never noticed at before because I was not so focused on the turning the gain knob with nothing plugged into the amp as soon as it comes on... if that makes sense.

But yes, the standby is after the SS rectifier, and before the main resovoir. I just tried switching the SB to after the first cap, but the DC spike on the gain pot stays the same. Again, what happens is when the amp comes off standby, there is a little surge to about 1.2V max on the gain pot before bleeding off. Is this just coupling cap(s) "charging up?" My electronics knowledge is too limited to really understand what's happening here.

[pdf64]

I think that the transient conditions at start up are a red herring; you're probably just measuring the audible thump that normally occurs when a circuit is energised.
Back to the scratchy pot, do the Vdc levels of the surrounding stages change, either as the pot is operated, or at various pot settings?

[Gaz]

I think that the transient conditions at start up are a red herring; you're probably just measuring the audible thump that normally occurs when a circuit is energised.
Back to the scratchy pot, do the Vdc levels of the surrounding stages change, either as the pot is operated, or at various pot settings?

I agree, the DC voltage spike and bleed that happens on start up occurs on every one of my amps here (champ, Twin, and this new one), and I think it was just something I never noticed before. I'd like to know what's actually happening here, because my non-technical guess is "coupling caps charging" or something equally as dumb sounding


As far as the static-y sound, it's very hard for me to measure anything now because it's intermittent. Sometime I'll get static, then it's gone. It is relatveily quiet compared to DC being on the pot. I have not monitored the DC levels at that stages plates while I turn the control, but I will next time it's static-y. Thanks for the idea.