Why Do I Have Feedback on My Home Theater System?

Question

I recently installed a home theater system. I have a nice 50" plasma on the wall. All the wiring is hidden. I have 5 infinity speakers all wall mounted. I have a Denon AVR receiver, and I utilize Cable TV through Comcast.

No matter what I try, there's still a constant buzzzzzz or some might call it a hummmmmmm coming through my speakers. Most of the time you don't hear it because there's programming coming through on the TV. But if the TV gets quiet, it's there.

I have maximized the settings. I have the TV sound all the way down. The Comcast Cable Box sound all the way down. And I use the AVR sound as my main sound and that helps a lot, but the buzz is still there in the background. I've been told it's because I'm using Comcast Cable and there's nothing that can be done about it, but surely there's some kind of electronic silencer I can use to take that buzz out.

Answer 1

Sounds like you have a ground loop problem, where your cable TV system isn't properly grounded to your home's electrical supply. I had this problem after remodeling my home. I had gutted the house out to the studs and ran all of the cable outlets in the house to an equipment panel in the back of a closet. I also installed a distribution amplifier to boost the signal to each outlet.

When I hooked up the TV and surround receiver, I got a constant 60-cycle hum from the speakers. Since the wiring was new, I figured the ground system would be correctly attached. So, the problem had to be that the cable system was improperly grounded.

To fix the problem, I ran a ground wire (about 12-gauge) from the body of the splitter where the cable came into the equipment panel to a s***w on the chassis of the distribution amplifier. This put the cable ground at the same potential as the electrical system and the hum went away.

Answer 2

It sounds like a ground loop problem.

Try to put all your electronics on the single phase of your wiring. Connect the ground wires as required. Keep the power cables clubbed together and if possible through a power line filter.

Keep the speaker cables away from power line and if they must cross, cross them at 90 degrees.

Try changing the orientation of your plugs. One way is usually quiter than the other.

Most important thing among the tips that I have listed above is to ground your system properly.

Answer 3

When they delivered and hooked mine up, I found that they had the wires wrong and that fixed it for me.

Answer 4

Have you tried using a power/line conditioner?

http://www.amazon.com/8-OUTLET-Line-Cond...

Answer 5

There are 3 common ways hum gets into your system:

A) CATV coax

B) Ground loop with a self-powered sub

C) 60hz AC noise getting into the wiring.

Here is how you can test some of these:

A) Turn the system on and turn up the volume so the hum is noticeable. Un-s***w the main CATV coax cable. If the hum stops, contact your CATV company and have them come out and ground the coax just outside your house.

B) Get the system to generate the hum and un-plug the subwoofer. If this hum stops you have 2 ways to solve the problem:

- Get a 2-prong to 3-prong adapter and put it on the Subwoofer power cord.

- Get a "Subwoofer" cable with little arrows. This RCA cable does not connect the shield at both ends. This breaks the ground loop.

C) We are now left with wires running too close to AC power cords and this is injecting noise into the system.  You basically have to try disconnecting some of the interconnects in  a trial-and-error attempt to see if any one wire is causing the problem.  The other source could be the speaker wires (are these in-wall?).  Once again - try one at a time test to see which wires are causing the problem.  

I hope one of these techniques help track down the problem.

EDIT:

This is rare - but it could happen: Look at the back of your equipment rack.  Are the AC power cords separated from the interconnect and speaker wires?

You really want 3 separate bundles of wires that stay separated: AC power cords, Speaker wires, Interconnects.

Make sure your AC power cords are not bundled tightly with the other wires.