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#424368 - 03/23/17 02:26 PM Amplifier hum
JBrad Offline
hobbyist

Registered: 03/23/17
Posts: 20
Hello all. Just need some advice on a possible DC offset situation. I have 2 separate amps in my system. One amp is connected to my front LFR 1100's and VP180HP. The other is connected to 4 QS8's. I have a hum coming from both amps that is audible when turned on and without any source being played. Has anyone had this problem and what was your fiix? Emotiva has an inexpensive device,CMX-2, that may help. Any thoughts would be appreciated.

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#424375 - 03/23/17 05:18 PM Re: Amplifier hum [Re: JBrad]
cb919 Offline
connoisseur

Registered: 02/17/09
Posts: 1165
Loc: Ottawa, Canada
Welcome JBrad,
Sounds like you may have a ground loop hum. Does it happen when only one amp is on? What other equipment is connected? Best to try and identify and eliminate the voltage differential at the source if possible and could be the cheapest solution as well. Test one component then one connection at a time then figure how best to deal with it. Why spend $120 on a CMX-2 when it may not be needed at all?

I had this issue a long time ago and it turned out to be my coaxial cable from my cable provider. With a $2 cable ground part to my main house ground the issue was gone.

Cheers,
_________________________
Dan
On-Wall M5HP LCR, QS8 & EP500 in 7.1

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#424377 - 03/23/17 07:23 PM Re: Amplifier hum [Re: cb919]
JBrad Offline
hobbyist

Registered: 03/23/17
Posts: 20
Thanks Dan. I don't believe it's a ground loop problem as I've tried everything with the same plug in. Then again I may be wrong. I have 4 dedicated 15 amp circuits to the breaker box and 1 20 amp. I have tested 1 component at a time and the hum may be a little less noticable with only my front amp connected. I have an Arcam BDP 300, LFR100 DSP, PS3, SVSSB13 sub, Arcam P777 amp, Arcam P1000 amp, Marantz 7701 pre/pro, and a 60" plasma TV in the loop. If the hum was coming from the speakers instead of the amps themselves would that be a ground loop issue? Thanks again.. Also, I know power conditioners don't do jack with these problems but I have 3 in the loop as well.


Edited by JBrad (03/23/17 07:37 PM)

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#424379 - 03/23/17 07:47 PM Re: Amplifier hum [Re: JBrad]
Mojo Offline
connoisseur

Registered: 01/21/07
Posts: 4613
Temporarily install a cheater plug to see if the problem goes away.

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#424380 - 03/23/17 07:49 PM Re: Amplifier hum [Re: JBrad]
JBrad Offline
hobbyist

Registered: 03/23/17
Posts: 20
Thanks Mojo. The cheater plug you mean is 2 prong into the wall and 3 to the component?

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#424381 - 03/23/17 08:15 PM Re: Amplifier hum [Re: JBrad]
Mojo Offline
connoisseur

Registered: 01/21/07
Posts: 4613

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#424383 - 03/23/17 09:04 PM Re: Amplifier hum [Re: JBrad]
JBrad Offline
hobbyist

Registered: 03/23/17
Posts: 20
Thanks again Mojo.

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#424385 - 03/23/17 09:22 PM Re: Amplifier hum [Re: JBrad]
Mojo Offline
connoisseur

Registered: 01/21/07
Posts: 4613
Also try progressively disconnecting each source at the receptacle AND its downstream connection (eg. Receiver).

You'll hear ground loop hum in your speakers and not electronic components.

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#424391 - 03/23/17 10:13 PM Re: Amplifier hum [Re: JBrad]
JBrad Offline
hobbyist

Registered: 03/23/17
Posts: 20
Have done Mojo. I think I'll buy the Emotiva tweak. If it doesn't work I'm only out the return shipping. It might be something I want in my loop anyway. I can hear something from my LED pot lights...

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#424393 - 03/23/17 11:18 PM Re: Amplifier hum [Re: JBrad]
Gr8_White_North Offline
connoisseur

Registered: 07/12/09
Posts: 2144
Loc: Whitehorse YT
How old is your home. You may want a respected electrician to inspect your outside ground rod. I lived in an old house and i solved my hum issue's by plugging an extension cord into a receptacle down the hall on a different circuit to run some of my equipment along with a cheater plug. Some old houses have some messed up wiring issues. As stated before, cable vision can cause issue's you may want to t install a baluns on your cable.
_________________________
DOG is GOD spelled backwards.
What others think of me is none of my business.
M80 V3 MY GLOSS Cherry

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