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#148580 - 10/01/06 10:15 PM New Amp Humm / Noise
Juggernaut850 Offline
newbie

Registered: 10/01/06
Posts: 4
Hello,

I am hoping one of you guys or girls can help me out with a problem.

I just purchased a new set of NAD components, the T163 and T973 but now have what I beleive to be a ground loop problem. I have read much about the issue, though I feel that perhaps I may have something a bit more complex.

The problem exists even when I have nothing connected to the pre except the amp and speakers. The noise is evident from the front towers in stereo mode, and in multichannel selection it gets extremely loud in all channels. The sub adds to the problem (EP500) when it is connected, though it is not the only source of the issue.

What I do not understand is that the noise does not exist when just the amp is plugged into power and connected to the speakers, however when the pre is attached and powered on the noise is evident. So this means it has something to do with the pre & amp, though the pre is a two prong and the amp is three. All of the components are connected to the same power source, and line conditioners have not worked. I can get the buzz to lower by lowering the gains on the back of the amp, though this effects sound quality and level.

My old sony receiver had none of these problems and it was attached in the same maner.

Please if anyone has any ideas I would appreciate them.

(I posted a similar thread on AVS forums and have had some very nice people attempt to help me)

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#148581 - 10/01/06 10:19 PM Re: New Amp Humm / Noise [Re: Juggernaut850]
bridgman Offline
axiomite

Registered: 08/25/04
Posts: 5381
Loc: Bowmanville, Ontario, Canada
This is a faint hope, since normally 2 prong plugs and sockets are all polarized these days, but is it possible to reverse the 2-prong plug ? If you can reverse it, that might help.

Now the dumb question -- have you hooked up a good audio source to validate how far you are turning up the gain controls ? I remember once worrying about hum with nothing connected until I realized that the volume settings I was using would have played a real audio signal at about three billion dB


Edited by bridgman (10/01/06 10:20 PM)

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#148582 - 10/01/06 10:24 PM Re: New Amp Humm / Noise [Re: Juggernaut850]
Wid Offline
axiomite

Registered: 06/22/03
Posts: 6720
Loc: The Peoples Republic of Il.

Try a different set of interconnects from the pre to the amp.
_________________________
Rick


"A fear of weapons is a sign of retarded sexual and emotional maturity." Sigmund Freud


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#148583 - 10/02/06 12:46 AM Re: New Amp Humm / Noise [Re: Juggernaut850]
BrenR Offline
connoisseur

Registered: 12/10/03
Posts: 3602
Loc: Winnipeg MB Canada
Quote:

I just purchased a new set of NAD components


Thank you for not saying you just purchased a set of NADs. :P

Quote:

I can get the buzz to lower by lowering the gains on the back of the amp, though this effects sound quality and level.


Yeah, that'll mess up your gain staging.

The first thing I'd do to check for ground differential would be to bind the grounds... that is, run a wire from a bare metal spot on the pre toa bare metal spot on the amp, this will put both grounds on the same plane. If this solves the problem, them look at your grounds as the issue... if it doesn't - I'd look more towards the connections, your wires, sources of interference and making sure (sheepishly) that you're connecting the right outputs to the right inputs.

Bren R.

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#148584 - 10/02/06 10:36 AM Re: New Amp Humm / Noise [Re: Juggernaut850]
alan Offline
connoisseur

Registered: 01/29/02
Posts: 3187
Loc: Toronto/New York/Dwight
Hi Juggernaut,

Try connecting the AC cord for the EP500 to a different circuit in your room than the one supplying the other components. Read my step-by-step instructions to eliminating ground loops here:
http://www.axiomaudio.com/tips_eliminate_hum.html

If you have a cable-TV set-top box (or a satellite TV tuner box) connected in any way to your NAD gear, that's almost always the likely source of the ground loop. Disconnect the video feed to see if the hum goes away.

Try unscrewing the ground-lift screw on the rear panel of the EP500.
_________________________
Alan Lofft,
Axiom Resident Expert

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#148585 - 10/02/06 08:40 PM Re: New Amp Humm / Noise [Re: alan]
Juggernaut850 Offline
newbie

Registered: 10/01/06
Posts: 4
Guys, thanks for the input but I am still fighting the good fight.

I have moved the sub to a different outlet, and have read your step guide without any luck (thanks Alan).

At one point I had a ground wire running from the amp to th pre to the sub with still no luck. Is there anyway that I can test cables for problems, or rather can cables be at fault?

At this point I am hoping that it is something that I have done to creat the problem. All the pre to amp interconnects are new Belkin RCA's......

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#148586 - 10/02/06 08:42 PM Re: New Amp Humm / Noise [Re: Juggernaut850]
Juggernaut850 Offline
newbie

Registered: 10/01/06
Posts: 4
I also tried removing the ground loop screw from the back of the EP500 but then the sub started to humm so I went back...

Another question that may or may not be related. At one point I had the sub cable in my hand and the other end plugged into the sub, when I touched the loose RCA end it sent a signal to the sub, is that normal?

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#148587 - 10/03/06 10:49 AM Re: New Amp Humm / Noise [Re: Juggernaut850]
alan Offline
connoisseur

Registered: 01/29/02
Posts: 3187
Loc: Toronto/New York/Dwight
Hi,

It's fairly rare for RCA cables to be inherently faulty, but you can check each one by first, setting the volume control on your preamp to a moderate level, then selecting each source you have connected. Grasp the cable where it enters the RCA plug at each end and gently wiggle it back and forth. If you suddenly hear a big increase in hum, then that RCA plug is likely intermittent or defective.

Yes, it's normal to get a sudden increase in hum if you touch the hot terminal (the center one on a male RCA plug) when the other end of the RCA cable is connected to a sub or an amplifier or your preamp.

So is this a stereo setup or do you have any video source, including a TV monitor, connected in any way to the system?

One more thing: does the preamp have a headphone jack? If it does, then disconnect all your sources from the preamp, set the volume mid-way through the range of the control and plug in a set of headphones. Does the preamp by itself have audible hum? If so, then get it repaired under warranty.

If there is no hum (it should be silent), then one by one, connect each source, turn the source on, and listen to each one. If there is suddenly audible hum, then you know that source is the culprit. So try running that source from a different AC outlet or reverse its plug if possible.

I'd also remove the line conditioner totally from your system and connect each source individually to the wall outlet while you listen for hum.
_________________________
Alan Lofft,
Axiom Resident Expert

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#148588 - 10/03/06 07:54 PM Re: New Amp Humm / Noise [Re: alan]
Juggernaut850 Offline
newbie

Registered: 10/01/06
Posts: 4
Alan,

Thank you for your advice.

First, the noise exists without any video hooked up to the system. The noise exists when only the amp and pre are attached together before I get a chance to attach any other peripherals.

The pre amp does have a head phone jack and with nothing attached to the pre amp besides the power cable and the head phones I have noise. It sounds similar to the humm from the speakers but not quite as intense. It is independent of the volume control, however if I turn the volume right off then all noise goes away, if I turn it up all the way the humm stays but is mixed in with a good amount of white noise.

So does this definitively mean that the pre is bad? I will be calling for the location of the nearest service center tomorrow.

Thank you very much!!

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#148589 - 10/03/06 07:57 PM Re: New Amp Humm / Noise [Re: Juggernaut850]
Wid Offline
axiomite

Registered: 06/22/03
Posts: 6720
Loc: The Peoples Republic of Il.

Does your old Sony reciever have preouts ?
_________________________
Rick


"A fear of weapons is a sign of retarded sexual and emotional maturity." Sigmund Freud


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