Odd Busses on Soundcraft 8000

The odd (1,3,5,7) busses on my 8-buss Soundcraft 8000 suddenly started to act as white noise generators. Like, LOUD, white noise. 2,4,6 & 8 are dead quiet and work fine. All input strips work fine, master and aux strip works fine.

The problem doesn't travel w/ the strip, pans left and right, and when I'm going at it with my scope, I can see that it starts before the first op-amp in the buss strip. So I'm assuming some kind of power issue. However, all of the op amps are getting their +/- 17vdc at the correct pins.

My question is, what sounds like white noise? DC getting somewhere it shouldn't? Excessive ripple on one of the DC rails? I'm kind of a beginner at troubeshooting issues w/ this board, I feel like I would have an easier time tracking this down if I knew what I was hearing.

A short to ground on a bus could cause the noise but this doesn't seem likely on all odd buses.

What is common to all?  Does the master have a slate tone or talkback to bus that possibly connects to all?

Is there a common power supply or circuitry to all odd bus amps?

JR

JohnRoberts said:

A short to ground on a bus could cause the noise but this doesn't seem likely on all odd buses.

What is common to all?  Does the master have a slate tone or talkback to bus that possibly connects to all?

Is there a common power supply or circuitry to all odd bus amps?

JR

Click to expand...

Thanks JR.

Turns out it was a short to ground at the meter pcb. Bad resistor.

It was a vexing one tho, because all busses get their +/-17vdc from the same rail. If just one odd bus strip was hooked up, it was silent, but if another one was added it made the ground loop and caused the white noise.