Audio breakup after gain stage 10?

[rhythminmind]

Ok last T15 problem.
Channel 8 of my 8 T15 channels breakups/distorts after gain stage 10. Everything visibly seems fine. It works fine up until stage 11. Any ideas?

[tpryan]

Make absolutely sure you have the right resistors installed at R19 and R20.

Re-flow the solder joints at those resistors and at the rotary switch.

If that doesn't do it, measure the voltages at U2, pins 1 and 7 while the distortion is occurring. Are the voltages stable, or are they changing rapidly?

Let us know what you find.

[rhythminmind]

Ok re flowed the joints, nothing.

So at full gain&trim
U2 pin 1 is unstable. Its currently -2.2 and counting down. Now it's -4.
pin 7 = 0.003

at gain stage 9
U2 pin 1 = -0.105 (stable)
pin 7 = 0.002

[tpryan]

Is this with a mic connected?

What happens if you terminate the input with a 150 ohm resistor, or short pins 2 and 3?

Does switching phantom off make a difference?