Behringer ADA-8000 owners: PLEASE READ!!!

[Matador]

It may not be a ground loop, it may be that the current draw of multiple units drag down the secondary voltage enough that the regulators drop out of regulation, which will indeed turn them into 120Hz (100Hz) hum generators.

A voltmeter across pins 1-3 of the positive regulators (or 2-3 of the negative ones) will tell you if this is happening: these regulators need 2-3V worst case across them minimum in order to stay in regulation.

 

[kike]

If this is the case, what is the cure?

 

[Matador]

If this is the case, what is the cure?

I would confirm that's what's happening first! It's pretty easy to test if you have a VOM.

 

[kike]

The pins on 15v regulators gives approximately 9V when all three units plugged, 10V when only one

The pins on 5v regulators gives 2V when all three units plugged, 2.7V when only one.

I have oscilloscope, can I check something with that?

Edit:

I have played with an oscilloscope.
Don't know what I am doing but still...

The voltage on 15V regulators is flat but on 5V regulator has a small oscillation when i plug all three units


The input stage of 074 opamps output pins doesn't do anything