Hi All

I received my 990/7700/LMF/SMS equipment last week and got everything hooked up. It sounded great, but I had a hum coming through my speakers. I read the directions to the 7700 related to ground loops. I unhooked the cable box and the hum went away. The instructions suggest calling the cable company and have them insert a ground loop isolator. I know almost nothing about electricity. So that I don't sound like an idiot on the telephone, can anyone describe to me what I should be asking for from the cable company?

The problem is that the cable service isn't grounded quite the way it is supposed to be (as you might have guessed from the 7700's manual, it's quite common). You can tell the cable company that you have a ground loop hum coming from your speakers, that you've determined that it's being caused by your cable service (specifically, unhooking the cable from the box causes the hum to disappear), and that you would like them to provide a ground loop isolator to resolve the problem. Odds are probably 50-50 that the teir 1 customer service rep will understand the issue, but the service guy they send out should be familiar with the issue.

ground loop isolation - Parts Express


gound loop isolator - Rat Shack

Both of those are good suggestions for a "do it yourself" way of solving the problem - the cable company will use a device just like one of these. You could pick one of them up and save the hassle of dealing with your cable company, or save the $10 or $20 bucks and make the cable company provide the part. Either approach should solve the ground loop problem.

I'll run by Radio Shack after work. Thank you for the help.

I have a motorola 6200 cable box, i hooked it up via optical to get rid of my hum. I tried a jensen isolator, but the hum was still there (much reduced, but i could still hear it)

These ground loop isolators work great for cable hum but is there anything you can do for hum caused by satellite Tivo receivers?

This could still be a ground loop hum. If disconnecting the sat cable or unplugging the that sat box fixes the problem, you're not grounded somewhere, I would guess.

I tried the ground loop isolator-no luck. Called the cable company. We'll see if they can fix it.

In the meantime, to read up on the topic, here's a goundloop link

I solved my ground loop hum coming from cable box by installing the isolator from Parts Express several months ago. It was suggested by gonk and it works great. No more noise from the speakers.

I installed the ground loop isolator from Parts Express as well. It's made by Dayton. The "buzz" is gone however, I have a problem with my HD signal when the isolator is installed. It degrades the signal enough that I lose a couple of HD channels and a couple of others break up. I originally thought this might just have been a bad night for the cable company as we have had a lot of windy weather here, but as soon as I took the isolator out of the system the picture was fine. I may have to try the more expensive Jensen Tranformer piece to see if that keeps from degrading the video signal. The Dayton part did get rid of the "buzz" but I obviously don't want to lose video quality as a result.

I used the Jensen to eliminate the ground loop caused by my cable. I have HD service and there was no loss of video quality with the Jensen.

It sounds like you are on the edge of not having a strong enough signal at your box. I've had numerous problems with that at our current house, mainly affecting the cable modem. The best bet is to contact your cable company and get them to either fix whatever is causing the drop in signal quality or add a booster at the box.