Axiom Home Page Forums General Discussion Home Theater EP500 Hum

Hello all.
Yesterday I received the ep500 and was pretty anxious to see what this thing could do compared to the ep350 it will be replacing. However, I ran into an unexpected humming noise as soon as everything was connected and powered up. I tried removing the "loop screw" per instructions. This reduced the humming by half, but still very audible. I played with the crossover settings on the sub and found I can eliminate the hum by setting it to 40. Nice but not desirable. I switched cables and used a higher quality audio cable. This lowered the hum. Unscrewed the "loop screw" again and it lowered more but still audible.

Any suggestions? I plan on calling Axiom for additional help and will also start unplugging all equipment to see if one of them is the culprit.

Thanks!

Check the ground on the cable TV connection by disconnecting it from the TV (as well as anything else in your system that it might plug into). See if that eliminates it.

Michael_A:
I would not have believed it had I not tried it. I just came back from an errand and decided to disconnect the cable from the TV first thinking I would eliminate that item first. Once I did it I connected the sub and turned everything one. Huge HUM! I mean huge. Louder than before. I freaked. Then I realized the "loop screw" was out. When I put it back in I tried it again. This time with the sub volume set way down. I slowly increased volume. Pure silence.

Thanks for suggesting the cable!

Now on to how to resolve the cable issue.

One of the great reasons I hang out here is the vicarious pleasure I get when other people's problems get solved.

This will resolve the cable issue.

Just a quick update. Had the cable company out most of the afternoon yesterday trying to determine if they were at fault. Its funny how they operate. When the guy first arrived he ask what the problem is and I tell him. He takes what I say and then proceeds to explore. When he can't solve it right away, he calls the manager for help. After that, he's not quite the same and now is in defense mode, out to prove its my stuff. He tried isolating my house, the noise went away. He bypassed my house and connected directly to the main line. The noise remained. He tried this and that and could never find the root cause. Next he did something smart. He ran the line upstairs to another suround system with an old Sony sub. No hum. We moved the 500 upstairs, please don't try this at home, and the hum returned. His prognosis was that it must be the sub. He packed up and left. Now I am sure they are going to stick me with a bill of some sort as they proved they are not at fault. It just didn't fit in my mind - cable disconnected, no hum; cable connected, hum. After he left, I did some quick research on ground loop issues and learned something interesting. According to what articles I read, no one really is at fault. It seems to be something that can be tamed when it arises but not truely prevented in the real world. Cable is grounded. House is grounded. But not exactly in the same fashion. The addition of the 500, with its sophistication, either picked up the hum or helped creat the loop. In either case, the easiest solution was to break the loop at the cable tv. A trip to RS for parts 15-1140 and 15-1253, put it on and poof, no more hum.

With that said, I am going to ground any cable splices just to be on the safe side.

In reply to:

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Cable is grounded. House is grounded. But not exactly in the same fashion.

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Hence the loop. All the fool needed to do was ground the cable to the same ground that the main electrical panel uses. The reason that there is a loop is because there is a diffenence in resistance between the 2 grounds. Hook them to the same place, and the only possible difference between the 2 grounds would be caused by the wiring inside the house. This would be the electrical ground wires from the breaker to the outlet and the shield of of the cable TV coax back to the grounding block, plus the piece of wire from there to the actual ground.

In reply to:

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The addition of the 500, with its sophistication, either picked up the hum or helped creat the loop.

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It was probably the latter. You didn't by chance happen to plug the sub into an outlet on a different circuit than the reciever and/or TV, did you?

I'm glad it all worked out. I think the cable guy should have fixed it for you. If you know any electricians in the area, ask them what the code is for cable TV grounding. In my county, they are required to ground to the same ground as the electrical panel. If they don't, they are breaking the law. It is a "safety" issue. If they try to bill you, let them know that you heve decided not to notify the public utilities commission, but would appreciate some credit on your account to compensate you for properly grounding their connection.

If you don't know any electricians, drive by some of the gentlemen's clubs around 4:30 on any weekday, and look for the company vans in the parking lot. They wear names on their shirts, so they're easy to find once you are inside. I'll bet you can get your answer for the price of a highly overinflated beer.

DJM, you may have to call your power company or an electrician - sounds like you have a bad ground. My next house, I want to be there when the electricians are doing their work - they never seem to bother to ground outlets, and generally perform as low bidders.

M-
Yeah, I plugged it into a different outlet. After reading the information on ground loops, I purchased a power strip for all devices except the sub. The sub has been placed on at different wall. I may move it, oh back pain, closer and plug into the stip next week to see what that does.

As for the cable co., I'll first print out some info for them on ground loops. This will at least let them know I've done some homework on the issue.

Thanks for your advice!