Ground Loop?

I want to thank everyone for their input. It’s not 20 gauge now that I think more about it, it was done 12 years ago and the 10 gage sounds more familiar. The wire was made for this application. I had an electrician install the wire, breakers and receptacles to code. The run is only about 10-15 feet at most. Even so I plugged 1 at a time into a regular receptacle, 1 in the dedicated line and 1 in the regular socket then both with no change. So, I don’t think it’s in the dedicated receptacle and another regular outlet do the same thing. I’ll get my neighbor to check ground and stuff, he knows more about A/C than I do.

I’m so glad! When I read 20 awg, my heart sank. If you used audio receptacles, check the ground requirements. If interconnects are running to a device on a different ground, this may be the source of the ground loop. Hope you figure things out. Have a great weekend!

I was pretty sure the OP meant 20A wiring, so I just skipped right over that. :) 

I had similar problem with a preamp. The solution was purchasing an isolation transformer. 

Perhaps run a temporary drop cord from another outlet to the phono preamp. Costs nothing and maybe the problem goes away? If the problem remains, it’s one more resolution to scratch off the list.