Quad pre ground loop noise lead channels only ?

[Paul Secondino]

Hi
I have a quad that was sitting for about 6 months .Used to be fairly quiet but now I am getting a ground loop somewhere.Only on Lead 1 and 2 though. So I:

-Changed out each of the preamp tubes

-Flipped the ground on off switch (no change)

-Cleaned the input / output jacks

-Tapped lightly on most of the components on the pcb (no changes)

And I am sure that all the cables are good as they don't make any noise in my other amps.

Thanks
8)

 

[ToneAddictJon]

Try running it into a power conditioner or different outlet.

 

[RobertH]

Hey Paul, is it racked? I had a problem with my 2:90 some years back when my band mates loaded my rack. When I hooked up all of a sudden I had this major hum that would not go away, I called Mesa and they had no idea. I eventually yanked it out of the rack, problem solved, the rack ears on the amp lost some paint and grounded to the rail. I isolated the rails and never had that problem again.

 

[disassembled]

I use "hum frees" rack isolation tabs but two rubber washers would do the trick nicely if it is indeed a ground loop and not some internal circuitry failure.


Greg

 

[Paul Secondino]

It was already isolated but I took it out of the rack but no change. Also, I tried going to a different power outlet but no change there either.

I'm kind of baffled why the 2 lead channels are humming but not the rhythm channels. I own a 2nd quad preamp and it is very very quiet. No hum at all.

 

[disassembled]

It was already isolated but I took it out of the rack but no change. Also, I tried going to a different power outlet but no change there either.

I'm kind of baffled why the 2 lead channels are humming but not the rhythm channels. I own a 2nd quad preamp and it is very very quiet. No hum at all.

Sounds like something failed inside and probably needs to be checked over by a tech.


Greg