Fixing Ground Loop Hum/Buzz

[Kevinicus]

So, I'm nearing completion on my new theater and I started to connect some equipment and do some testing.

In my previous theater, I had a 7.1.4 setup. That included three mains, two side surrounds, two rear surrounds, four ceiling speakers, and two subs (same channel). All of the speakers, with the exception of two ceiling speakers used the AVR (Yamaha A3050) for amplification. The other two speakers used the pre-outs from the AVR and were powered by a stereo amp (Audiosource AMP100VS). The subs went from the AVR sub output to a Behringer Ultragain mic 220 pre-amp, and then through a Crown XLS 5000 amp. The equipment was on one 20A circuit, and the sub pre-amp and amp were on a separate 20A circuit.

I had/have a WattBox surge protector/conditioner, and an APC J25B UPS that was used for connections on the main equipment.

I never had any issues with humming.

For my new theater, I'm adding a 2nd pair of side surrounds for the 2nd row of seating. So, I purchased a new amp (OSD XMP500) to power the surrounds, using the pre-out from the AVR.

Aside from that, everything else is the same. Separate circuits for the equipment and the sub pre-amp/amp.

Now, I get the buzz/hum from my side surrounds, and only the side surrounds. The rest of the speakers are still perfectly quiet.

I've done a lot of testing to try and diagnose the issue and find a solution.

First, there is very little connected to the AVR. I only had one input/output connected, and have disconnected both of those and get the same buzz/hum.

I've tried disconnecting all of the other speakers except those attached to the new amp - no success.
I have tried connecting different speakers to the amp, and that just moves the hum to those speakers.
I've tried using a different pre-out from the AVR - still buzzes.

There are a few things that do remove the buzz...

1. If I disconnect the input coming from the AVR, the buzz goes away.
2. If I disconnect the subwoofer out from the AVR, the buzz goes away.
3. If I plug the equipment into the same circuit as the sub pre-amp/amp, the buzz goes away.

Even when the buzz/hum is gone, the speakers connected to the amp still hiss. That I'm assuming is just the amp itself.

I have checked the breaker panel, and both circuits would appear to be on the same phase.

I'm not really clear on what my next steps should be, and would appreciate any help troubleshooting.

[dontpokethebear3893]

I also have ground hum using my AVR Pre-outs, but only the pre-outs! Interesting...