I have a Yamaha receiver from 4 years ago that has been serving me reasonably well. I'm setting up for a system in a new house that has a very large "great room", and I wound up getting less efficient speakers. Since the speakers are less efficient, and the room is much bigger, I found a used seperate Amp (Marsh Sound Design HT-500s) to drive the front three speakers.
With the 3 speakers plugged into the Yamaha, there is no buzz regardless of what is connected. With them plugged into the Marsh, there is. I read the FAQ on buzz/hum/ground loop problems, and tried unplugging everything from the wall (power and cable box) except the Yamaha and the Marsh. The buzz went away. Reconnected the cable TV coax and the buzz started again, even without anything (including the cable box) plugged into power except the two amps.
At this point I was sure I had a completely standard ground loop problem with the cable that was going to be easy to fix. Just to be sure I disconnected the cable TV and plugged everything (a computer, game systems, cable box) back into the power, without turning them on. The buzz came back, perhaps not as pronounced as when the cable TV was connected to the wall jack, but it was easy to hear anywhere near the speakers.
With a little testing I have found that plugging in either a computer monitor or my plasma into the same power strip as the two amps causes the hum (probably more stuff as well, I did not try everything). The monitor was connected to a computer (unplugged) which had a RCA L/R pair going to the Yamaha. When this RCA jack was unplugged the buzz stopped (monitor plugged in, but no longer connected to the amps in any way, so no buzz).
So presumably this is some variant of the standard ground loop problem. The thing that seems odd to me is that with everything plugged into the same surge protector it should all be sharing the ground. Figuring that maybe it would help if I tried plugging the Marsh in somewhere else I ran an extension cord to the kitchen (just for testing). With the Marsh and the Yamaha the only things plugged into the wall (kitchen and belkin respectively), no buzz. Add the computer monitor to the belkin (without turning it on, and with the computer unplugged) buzz
.
I tried different interconnects between the Yamaha and the Marsh, no change. I figured maybe the Yamaha was introducing the problem, so I had tried plugging the computer soundcard out directly into the Marsh (skipping the Yamaha), this also buzzed. This makes it seem like there is an issue on the Marsh's end, but when the Yamaha and the Marsh are the only things plugged in there is no buzz, and I can play test tones from the Yamaha and hear them just fine.
Any thoughts? Since I am moving in a month or two I can just plug the speakers into the Yamaha for now, and see if the problem replicates in the new house. But if anyone has had something similar happen and there is something I am overlooking (e.g. better power strip with line conditioning of some kind) I'd feel better fixing it now.
Thanks in advance for reading this rather long post, and any ideas would be much appreciated.
--Matt
