Strange Sound on Last 2 Gain Settings

[Black Magic]

Just finished my D11, N72, and A12 with an sc10. The first two builds went perfectly, but the A12 is having an issue.

It sounds fine on the lower gain settings, but on the highest to gain settings there is a sort of sizzle distorted squeel which changes pitch as I adjust the the fine-gain fader. It only happens on the last two gain settings though.

Also the A12 breaks up a lot sooner than the N72, is this normal?

[Black Magic]

when it is on the last 2 settings, or when I hear the squeel I get a inconsitent voltage around 0.008V, It changes with the sound. This is the SC10 at +/-24v.

edit: when I switch from the third to last gain setting to the second to last gain setting there is a pop, and U1 pin 4 to pin 6 goes from .090V to -.008V which also creates a squeal which changes pitch as the voltage drops. I tried adjusting the Bias so that on the problem gain settings the op amp output voltage was 0V, but it still makes a squealing sound.

The unit also makes buzzing/crackling sounds when I touch/wiggle its stepped atten, or the knobs of other modules in the same chassis. Almost like some kind of grounding issue.

Could it be the Opamp? Is there a way to test the opamp?

[Black Magic]

Audio Clip of Noises: A12 pops and squeel
Photos (not sure if this will be helpful, but what the hell):

[Black Magic]

Is this forum completely dead? I'm getting no tech support whatsoever. I feel like I'm being left out in the cold here.

Tim, I sent you a couple emails to sales@seventhcircleaudio.com please get back to me asap. I'm not sure if it is the opamp or not, but I've got some gar2520's on their way. So if no one responds to me by then I guess I will find out...

[jmettam]

Hey Black Magic,

Hang in there, Tim will reply eventually. They are a small operation and you are looking for support over a holiday weekend so who knows life's logistics on the other end.

It sounds to me like you may have a cold solder joint either on the pins of SW1 or on a resistor or two (R1 - R13). It would be worth taking the time to reheat your joints just to be sure.

- John

[Black Magic]

So, Just replaced the SC10 with a gar2520. And... IT WORKS!

So it appears the problem was with the SC10, Terrific!