Newly built house: Ground Loop Hum in Left Rear Speaker - Page 2 - AVS Forum
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post #31 of 49 Old 04-05-2013, 04:42 PM
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Quote:
Originally Posted by Ratman View Post

Never said I was an expert. But just looking at the obvious. Most power companies don't/won't come out to diagnose a hum in one channel of an audio system. Maybe they do that in Hungary.... but not in America. (Unless you want to pay).

After 40+ years with A/V and I/T experience, I can make better suggestions than just
"call the power provider" tongue.gif.

Most? Not all of them? Have you ever called any of them with such a problem? Come on, what's the problem with giving them a call, huh? biggrin.giftongue.gif
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post #32 of 49 Old 04-06-2013, 05:05 AM
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Originally Posted by mogorf View Post

Have you ever called any of them with such a problem?
No. Have you? (You'll probably say yes rolleyes.gif )
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Come on, what's the problem with giving them a call, huh?
No problem. Give 'em a call! As soon as they stop laughing, they will tell you to call a licenced electrician. And... that won't be free.
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post #33 of 49 Old 04-06-2013, 06:00 AM
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Can you temporarily disconnect the ground wire that goes to the cable coax on the side of your home and see what happens? Does your home have aluminum siding? I saw a problem once where the cable coax grounding block mounted on aluminum siding was causing hum. Taking the grounding block off the home made the hum go away. Can't remember the permanent fix though.

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post #34 of 49 Old 04-08-2013, 12:46 AM
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So, if you pick up and move speakers, but leave the wires, the new speaker at the same wire location will hum. But if you leave the speakers and switch the wires at the receiver, the hum disappears?

Essentially, then, the interference only occurs if a wire is connecting one particular receiver connector and one particular physical location?

That makes no sense as a ground loop issue even if you look past the "only on one output" question, unless the ground loop is caused by the location of the speaker somehow.

Is it possible you have mounted the speaker to a conductor, either a pipe or wire run or metal stud and it's now conducting power from either the coax or power strip through the speaker transducer and wall? Most speaker housings are not conductive, I know. (Also, this answer doesn't explain why the hum doesn't jump receiver outputs to whatever speaker is at that location unless you also have an AVR fault)

Do you have an oscilloscope? You could monitor signal from each AVR output and confirm it still happens even when no speaker is plugged into the humming output and/or confirm it's really 60hz and a ground/power issue and not some other interference.
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post #35 of 49 Old 04-08-2013, 07:17 PM
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Quote:
Originally Posted by rritterson View Post

So, if you pick up and move speakers, but leave the wires, the new speaker at the same wire location will hum. But if you leave the speakers and switch the wires at the receiver, the hum disappears?

Essentially, then, the interference only occurs if a wire is connecting one particular receiver connector and one particular physical location?

That makes no sense as a ground loop issue even if you look past the "only on one output" question, unless the ground loop is caused by the location of the speaker somehow.

Is it possible you have mounted the speaker to a conductor, either a pipe or wire run or metal stud and it's now conducting power from either the coax or power strip through the speaker transducer and wall? Most speaker housings are not conductive, I know. (Also, this answer doesn't explain why the hum doesn't jump receiver outputs to whatever speaker is at that location unless you also have an AVR fault)

Do you have an oscilloscope? You could monitor signal from each AVR output and confirm it still happens even when no speaker is plugged into the humming output and/or confirm it's really 60hz and a ground/power issue and not some other interference.

Sounds like a possible compromised speaker wire? like it has a staple through it or a nail, drywall screw, etc... somewhere along it's length?

If possible do a temp run of wire straight from the offending channel to the speaker. Sometimes installers staple the wires in and compromise the insulation jacket on the speaker wire, or heaven forbid the electrical cable in the wall. I doubt the OP's power runs are damaged since that is typically checked on inspection during cunstruction, but the low voltage cables like speaker wire, phone, Ethernet and coax can get overlooked and are very easy to effectively break by damaging the jacket.

I also work in IT plus do installs sometimes and this doesn't sound like a ground loop from the potential difference between the CATV live to the TV because running the coax through a power strip did seem to affect it but it could be the HDMI back-feeding somehow, I just never hear that happen to a single channel on a amp.

The OP could test the ground on the tv with a cheater plug if it is a 3 prong power cord but after a point disconnecting grounds get dangerous for either your equipment or yourself if somehow a components chassis gets energized so I don't recommend disconnecting the CATV ground over getting a pro over with test equipment to take a look.
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post #36 of 49 Old 04-09-2013, 04:37 AM - Thread Starter
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^^^ Thanx for the advice. I will try the seperate run of speaker wire... Unfortunately we just moved into a newly built home and the wife says there are more important things to work on than my home theater at this point. I can't really argue with her considering she is 8.5 months pregnant and we want to have the house in order before the new baby.

So when I get around to it I will dive into this problem deeper. FYI I ran all the speaker wire when the house was just studded out, not that I couldn't have messed up the wire myself so I'll have to see.

Shawn
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post #37 of 49 Old 04-09-2013, 06:49 AM
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Quote:
Originally Posted by flickhtguru View Post

I ran all the speaker wire when the house was just studded out, .
How did you run the speaker wires? Front of studs, center of studs or behind the studs?
Did you run the speaker wires before or after the electrical "rough in"?
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post #38 of 49 Old 04-09-2013, 08:40 AM - Thread Starter
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I ran them about in the center of the studs. After electrical rough in, But there was some electrical done afterwards. The wire is 14AWG monoprice in-wall rated speaker cable and I tried to be careful as I pulled it thru the holes in the studs. I also ran the wires as far as possible away from the 120VAC house wiring.

Shawn
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post #39 of 49 Old 04-09-2013, 12:12 PM
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Good that you ran away from AC wiring. But, did you use these to protect your wiring from nails/screws when they put up the drywall?
LIke this?
http://www.garvinindustries.com/electrical-junction-boxes/cable-protection/cable-protection-plates/sp-3
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post #40 of 49 Old 04-10-2013, 04:48 AM - Thread Starter
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No I didn't use those, I guess I should have tho... Hopefully this weekend I'll get to dive into the problem.

Shawn
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post #41 of 49 Old 04-10-2013, 10:05 AM
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You could also try connecting the speaker to a different output on the avr. The speaker channel in the avr could be damaged. I have an older onkyo avr that has a hum in one of the front channels.
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post #42 of 49 Old 04-10-2013, 10:23 AM
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One more thing you can do is find out every receptacle and light on the circuit and make sure all your grounds are good. Then unplug everything except your home theater and see if the hum goes away. If you have a security system on the same circuit it might not be grounded properly.
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post #43 of 49 Old 04-10-2013, 03:05 PM
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You might try connecting a new set of Left Rear wires to that speaker, not the ones running through the wall. If you have no hum then move those speaker wires near the path that the inwall wires are and see if you pickup hum. It seems a little strange that you could induce enough hum signal into a set of speaker wires terminated on an 8 ohm speaker as the impedance is really low. Its easy to induce a signal into a high impedance line but not so easy with a low impedance line. The other thing you can do is to take a small transistor radio tuned to an empty AM frequency and move it around the room to see if the signal might be an RF signal getting into your system. Poor connections can act like a diode and detect the AM signal and introduce it into your system. This would most likely be on one of the inputs to your AVR which are all high impedance inputs.
I have to agree with Ratman about the Power Company. They are concerned with safety and over/undervoltage conditions and not with your home theater. You can easily determine if you have unsafe ground voltages between components with an AC voltmeter and it sounds like you have the skill to run those tests.
From an ideal standpoint, a Star ground system is what you want. All components referenced off of the same ground. From the discussion so far, your Plasma sounds to me like it might be one of the suspicious boxes.

Ground loops are why there are all of those switches on Band electronics to lift the ground leads.

"So many tweeks....So little time!"
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post #44 of 49 Old 04-10-2013, 03:21 PM
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I re read the thread a couple times.

Sure sounds like the problem is the difference in ground potential between the Cable Coax and your system ground. Disconnect the cable Coax and measure the AC voltage between that loose piece of Coax attached to the Cable Box and your system ground.
Then unplug your Cable box from the power line and measure the voltage again between the loose Coax and your system ground.
Keep in mind that the coax from you Cable Modem is also running off to somewhere else from that splitter to your router in another part of the house and it may involved also.

Not sure why you mention disconnecting the negative line of the speaker. Clearly if you disconnect the speaker there should be no sound coming out of it.

You also mention no hum with 7.1 mode. Are you running 7.1 with left and right backs as well as left and right rears?

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post #45 of 49 Old 04-10-2013, 03:36 PM
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Quote:
Originally Posted by DoyleS View Post

I re read the thread a couple times.

Sure sounds like the problem is the difference in ground potential between the Cable Coax and your system ground. Disconnect the cable Coax and measure the AC voltage between that loose piece of Coax attached to the Cable Box and your system ground.
Then unplug your Cable box from the power line and measure the voltage again between the loose Coax and your system ground.
Keep in mind that the coax from you Cable Modem is also running off to somewhere else from that splitter to your router in another part of the house and it may involved also.

Not sure why you mention disconnecting the negative line of the speaker. Clearly if you disconnect the speaker there should be no sound coming out of it.

You also mention no hum with 7.1 mode. Are you running 7.1 with left and right backs as well as left and right rears?

To the OP, read the Hum FAQ again...please! smile.gif
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post #46 of 49 Old 04-11-2013, 07:59 AM
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Originally Posted by mogorf View Post

To the OP, read the Hum FAQ again...please! smile.gif

In regard to your recommendation(s).... one can read the FAQ and/or call the power company, but.... can you be positive the problem in one channel of a 7.1 sound system is absolutely a "ground loop" problem? And if so, explain why, how and your recommendation to resolve the problem. wink.gif

Maybe the speaker wire runs next to a crappy dimmer switch in the wall. tongue.gif
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post #47 of 49 Old 04-11-2013, 08:34 AM - Thread Starter
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I will say this currently I'm not positive it is a ground loop problem. It may have been a wiring mistake of mine. Also I know its not a dimmer switch or anything like that cuz we don't have any dimmers in our house and plus the switches that are in that room aren't on the same wall as these wires. I'm thinking it could be my mistake somewhere in the wiring because now sometimes i have the hum and sometimes I don't. And I checked with the timing of the hum, it doesn't correspond to anything like the frige or freezer kicking on or the clothes washer or dryer or anything like that. But from last evening at like 8:30 thru when I left this morning at 6:30 I had no hum.

Like I said I need to just take some time and trace out the problem but I just didn't have the time to do that yet.

Shawn
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post #48 of 49 Old 04-11-2013, 09:41 AM
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Quote:
Originally Posted by flickhtguru View Post

I will say this currently I'm not positive it is a ground loop problem. It may have been a wiring mistake of mine. Also I know its not a dimmer switch or anything like that cuz we don't have any dimmers in our house and plus the switches that are in that room aren't on the same wall as these wires. I'm thinking it could be my mistake somewhere in the wiring because now sometimes i have the hum and sometimes I don't. And I checked with the timing of the hum, it doesn't correspond to anything like the frige or freezer kicking on or the clothes washer or dryer or anything like that. But from last evening at like 8:30 thru when I left this morning at 6:30 I had no hum.
You could simply have a bad amplifier channel. That readily creates a "hum." Wiring problems would not introduce hum on and and off as you describe. But it is very probable for an amp to have hum that comes and goes.

Take a hair dryer and blow hot air into the set and see if it accelerates it doing it. If it does, then for sure you have a bad amp channel.

I think are too focused on electrical issues where the symptoms do not match that other than the sound you are hearing. Keep your perspective broader and you may be able to find it smile.gif.

Amir
Founder, Madrona Digital
"Insist on Quality Engineering"

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post #49 of 49 Old 04-11-2013, 10:39 AM - Thread Starter
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^^^ Thanks. The main thing I don't get is the hum is only there when the receiver is off or when it's not in a 7 channel mode.

Shawn
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