Help! Subwoofer background humming driving me insane!

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Aug 10, 2019
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For reference: my amp has a single phono output for the subwoofer and my subwoofer has a L and R input.

When I plug my subwoofer into power with no cable to the amp, and turn the volume right up, I get silence. This is good.

When I connect the double-shielded phono cable from the amp to the sub (into either L or R) the sub starts humming.

If I turn the amp off, the humming gets quieter, but still exists at 50% the volume is was originally at.

I have tried a different cable, I have tried plugging the amp into the same power lead as the amp itself, and I have tried putting one of those magnetic clamps around the power cable at the sub end to stop any power interference.

If the sub remains connected to the amp, with the sub plugged into power and turned on, but the amp has no power whatsoever (i.e. it's unplugged) I still get the same level of humming as when the amp is plugged in and simply turned off (i.e. 50% of original volume).

So... does anyone have any advice??

This humming means I must have the sub volume turned down so low for general use that it's almost not worth having it...

Thanks in advance
 

Dan Turner

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Jul 9, 2007
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It sounds like you have a ground loop. you could try getting an rca-rca ground loop isolater and putting that between one end of your interconnect and either the amp or the sub. I got one for about £3 on ebay
 

Andrew17321

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Nov 12, 2008
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Yes, a ground loop.

Try using the same mains wall socket for the sub and amp. If that fails, simply disconnect the earth wire in the mains plug for the sub. At your own risk, of course. If this worries you, instead you can disconnect the earth connection with the interconnecting cable and its plug at the sub end. You might be able to get away with using insulating tape at the input plug to allow the centre pin to connect but the outer sleeve to not connect. Cost £0.

The idea is to have only one earth connection: either through the mains, or the interconnect, but not both.

(I had the same problem and disconnected the earth in the mains plug. Problem solved.)
 

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