Hum in sub caint be ground loop, can new reciever be bad? - AVS Forum
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post #1 of 13 Old 11-28-2012, 07:50 PM - Thread Starter
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I hve this problem with my subwoofer humming whe reciever is turned off. After changing recievers, but same subwoofer and cables, i get this humming from my sub when i turn my reciever off, humming also stops when disconnect LFE cable. could i have a bad reciever? I also have a wireless blu-ray player put in at time i replaced reciever. Sub has two prong power cord so it caint be ground loop. original sub cable, so i know thats not bad. any ideas?
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post #2 of 13 Old 11-28-2012, 07:59 PM
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I'm no expert,but I had a similar problem. I replaced the sub cable with
One that was shielded and heavier duty. Solved the problem.
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post #3 of 13 Old 11-28-2012, 08:00 PM
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Quote:
Originally Posted by shogun1964 View Post

I hve this problem with my subwoofer humming whe reciever is turned off.
When the receiver is off its output impedance goes from low to high, and that's the source of the noise.The noise level will be proportional to the square of the cable length, so it should be as short as possible. The simple cure is to turn the sub off too.

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post #4 of 13 Old 11-29-2012, 06:20 AM - Thread Starter
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it wasn't humming before i replaced reciever. before i could leave sub on after turning reciever off. now i do have to turn it off. same sub amd cable.
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post #5 of 13 Old 11-29-2012, 06:35 AM
 
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Originally Posted by shogun1964 View Post

I hve this problem with my subwoofer humming whe reciever is turned off. After changing recievers, but same subwoofer and cables, i get this humming from my sub when i turn my reciever off, humming also stops when disconnect LFE cable. could i have a bad reciever? I also have a wireless blu-ray player put in at time i replaced reciever. Sub has two prong power cord so it caint be ground loop. original sub cable, so i know thats not bad. any ideas?

Technically, it can be ground loop as plugs use neutral returns which are the same as ground. If your neutrals are on different legs of the service box, there can be a difference in the feeds between the receiver and the sub power, my understanding, hence the loops are they're trying to find equalization between the two grounds.

Is your subwoofer cable shielded? Could the something you added to the equipment rack be picked up by the subwoofer cable and you need a better shielded subwoofer cable?

In truth, it's a wire-way nightmare behind our entertainment center. Cables coming out and going all over everywhere. But making sure of using teflon coated speaker wires and shielded cables, as much as one can expect is being rejected from being picked up by the speaker/subwoofer cables.

In the case of outlets, I had a couple of four-plex outlet boxes added so no plug strips. Everything has a wall plug of it's own.

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post #6 of 13 Old 11-29-2012, 07:02 AM
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Originally Posted by shogun1964 View Post

it wasn't humming before i replaced reciever.
Obviously your old receiver didn't have the same behavior when turned off. Your only option other than turning the sub off is to transformer isolate the receiver output from the sub cable. That will probably fix it.

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post #7 of 13 Old 11-29-2012, 07:24 AM
 
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Originally Posted by Bill Fitzmaurice View Post

Obviously your old receiver didn't have the same behavior when turned off. Your only option other than turning the sub off is to transformer isolate the receiver output from the sub cable. That will probably fix it.

What's the most efficient manner in which to effect your above fix suggestion?

When I post "the most efficient manner", I'm not saying the cheapest but a manner/fashion that corrects the possible problem, with the least amount of user interface complications; plug-n-play if you will.

(Yes, I understand your suggestion may not fix the OP's problem.)
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post #8 of 13 Old 11-29-2012, 07:40 AM
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Quote:
Originally Posted by shogun1964 View Post

it wasn't humming before i replaced reciever. before i could leave sub on after turning reciever off. now i do have to turn it off. same sub amd cable.
There could be a problem with the sub out port on the receiver. Mine did the same thing. It worked fine and then one day I took the cable off of the receiver. When I put it back on I was twisting the cable to get it all the way on and heard a "crack". Something inside the receiver had broken. The sub would hum terribly until I twisted that cable back and forth at the port until I found a sweet spot. As long as I didnt touch it again then it was fine. And yes it would even hum when the receiver was off.

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post #9 of 13 Old 11-29-2012, 03:34 PM - Thread Starter
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the only thing other than the reciever is a wireless blu-ray player.
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post #10 of 13 Old 11-29-2012, 04:44 PM
 
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Originally Posted by shogun1964 View Post

the only thing other than the reciever is a wireless blu-ray player.

Does your AVR have any pass through and wireless does use radio signals. I don't recall you mentioning if your subwoofer cable was shielded.
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post #11 of 13 Old 11-29-2012, 06:59 PM - Thread Starter
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sorry about that, yes i believe the cable is shielded. the ends look like a rca cable but made for a sub.
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post #12 of 13 Old 11-29-2012, 08:06 PM
 
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Originally Posted by shogun1964 View Post

sorry about that, yes i believe the cable is shielded. the ends look like a rca cable but made for a sub.

Not trying to be pointed. Do you know for a fact if the cable is shielded or are you guessing? It does make a difference in how the cable does or does not pickup RFI.
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post #13 of 13 Old 11-29-2012, 09:21 PM
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Never hurts to try a new one any way. I had a sub cable that worked fine on my Yamaha RX-V1 but had a hum when I switched to an Onkyo. Also doesn't hurt to have a backup. Especially since they are so cheap from monoprice.
If it works fine, if not your only out a few bucks and have an extra.

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