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33 posts


#22238 21-May-2008 11:15
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Hey all

I have bought the Onkyo 605 and a Mission M Cube and love it except for the nasty sub hum caused by a ground loop.

I was able to fix this by wiring a length of cable to a chassis screw on the receiver and connecting the other end to a chassis screw on the Sub.

Is this fix safe?  (please dont laugh, this is my first home theatre setup)

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  #132349 21-May-2008 16:07
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Sounds like your sub cable is faulty (ie missing its shield/ground) wire, whilst there is nothing unsafe about your fix I suggest you fix the real fault. Have you tired another cable.



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  #132358 21-May-2008 16:40
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The cable I bought (SUB-X by Audioquest) has ground leads on it for just that purpose.  I haven't hooked it up yet, but the guy in the shop seemed to think they were seldom necessary.  Sounds like it does just what your solution does though.


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  #132454 22-May-2008 07:32
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I tried both the sub cable that comes attached to the umbilical for the M Cube and also a brand new Monster Sub cable. Both had the same result.

Is it anything to do with the Receiver having a 2 pin plug and the M Cube having a 3 pin plug?

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  #132494 22-May-2008 10:12
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manjina: I tried both the sub cable that comes attached to the umbilical for the M Cube and also a brand new Monster Sub cable. Both had the same result.

Is it anything to do with the Receiver having a 2 pin plug and the M Cube having a 3 pin plug?

That could be part of reason though you can get "ground loop" paths on both the neutral and earth circuits. If you have the receiver plugged into a different wall outlet from the sub that could also contribute.

Having that wire between the chassis of both is your best bet. That provides an alternative path for the current and thus reduces the noise on the signal return line. You could try a ground loop isolator on the sub line but I've had mixed results with them.

Usually you don't have many problems with subs but yours goes up to higher than normal frequencies to cover the satelites so this may be why you are hearing it. When you get ground noise most of it actually comes from the tweeters with a bit from the midrange. The ground potential/current means the signal return line acts like an antenna and picks up noise. I suspect there's not enough energy in the low frequency noise to drive output on the lower frequencies.

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  #132915 23-May-2008 22:39
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Ground loop will be because the receiver is connected to a TV, which has an antenna which is connected to the chassis of other gear. Pull the antenna and/or sat dish connection and it will prob come right. Its affecting the sub since its grounded and nothing else is.

Your fix has allowed the ground leakage to leave one device to the other away from the input circuitry so there is less noise introduced, but there will still be some.

Get a power strip with a antenna and sat surge protector in it, that will common all the grounds, then run everything off that power strip.

This is the exact reason that unbalanced shoddy RCA interconnects have no place in home theater, sadly the marketeers decide that balanced XLR connections are a premium feature so you have to pay the earth for it.


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