Axiom Home Page Forums General Discussion Technical Questions Huuummmmmmm....

...Annoying ground loop hum!

Here is my config:

Pioneer receiver driving QS8s and an AX1.5 (rear surround)
Bryston 3B driving M60 mains
Thomas Patterson 120W amp driving VP150 and POS passive sub.

Last week I added a PVR, and got a ground loop hum through both amps (not the surrounds). Went out and bought shielded RCA cables. This eliminated the problem on the Bryston, and reduced it on the other amp. Still pretty annoying

The hum is there even with all equipment turned off (except for the amps!).

All equipment is plugged into the same powerbar.

Could it be a problem with the 2nd amp?

Any suggestions?

As with any ground loop problem. Disconnect all of the equipment from the system. Cept your amps. And then recconect one peice at a time. This means disconnecting ALL connections to and from it. Even if it is turned off you can still get ground problems. Seems somewhat strange that buying sheilded cables would cure a grounding problem. Perhaps you've got a loose connection and that had moved it.


I dunno what a PVR is but if the problem came after you added it then that could be it. Seems like you have more of an EMI type interference than a groundloop

PVR = personal video recorder, hard-drive based

I had a ground loop that got introduced into my system when my cable was installed too. Comcast gave me a PVR and immediately thereafter, I got a hummmmm....

I fixed it with two items from Radio Shack, for less than $10. Someone else can maybe jump in here and help me identify what I bought, but essentially, the cable now goes from the wall, to an adaptor that you would use to hook up a cable line to an older, non cable ready tv (you know, with the little wires terminating in small spade plugs). This then gets hooked up to another adaptor that turns that signal back into a regular cable signal.

My hum is gone, but the reception is pretty poor on some channels, and I have a ghosting issue on the big broadcasts that can be pretty annoying - but it is less annoying than hum.

edit: I just found this thread from the past that might provide some answers.

I also got a hummm as soon as I hooked up cable tv and a vcr to the receiver. I discovered it was a cable grounding issue and simply installed a cable ground connection and grounded it to the big a$$ grounding cable in the fuse box.

You might want to check if this is your problem (although, given you had some limited success installing shielded RCA cables sounds like something else might be the problem).

It sure sounds like you introduced a ground loop with that new piece of equipment. One accepted way of getting rid of ground loops is to have a common point ground. Sounds like you sort of tried with the common power bar. But, are the cable and/ or phone lines tied to this ground point, somehow?

You might want to look at a Trip-Lite Isobar Home Theater Surge Suppressor Model: HTPOWERBAR10. It has fixtures for cable TV and phone suppression as well as the standard AC outlets. I haven't opened up the ones I have, but I believe there is a common ground tie point. If someone knows otherwise, I would appreciate a comment.

For What Its Worth.

The Rat.