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Joined: Dec 2002
Posts: 308
E
Edward Offline OP
Member
One of my dance club clients complains when they plug in a amplifier/speaker in the outlet on the stage the amplifier/speaker makes a loud humming noise. this is when the music is off. Wht is the cause of this problem?

Edward


Thanks
Edward
Joined: Aug 2002
Posts: 1,691
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Member
Could be a ground loop?

This is sort of a dangerous suggestion but you can try it just to prove to yourself.

Do these amps have grounded plugs?

If so, try using one of those "cheater" plugs (a grounding adapter plug made for plugging in 3-pin plugs into two-pin outlets) to see if the hum goes away.

Also, if you use a non-polarized cheater plug, you may be able to reverse the plug in the socket.

Sometimes that helps....

Joined: Dec 2002
Posts: 308
E
Edward Offline OP
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SvenNYC,
What is a ground loop? And what is the cause of it? And what else could be the cause beside the ground loop?

Thank you


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Edward
Joined: Mar 2002
Posts: 86
S
Member
Edward,

Could be that the amp is pluged into the same circuit as a dimmer switch.

Is there any dimmer switches around to dim the lights? If so you will need to plug into a different circuit.

Tev

Joined: Aug 2002
Posts: 1,691
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Ground loop is basically when you've got interconnected devices that are not connected to a common ground.

This website explains it better. http://www.epanorama.net/documents/groundloop/index.html

So does this one: http://www.smr-home-theatre.org/Ground-Loops/

Joined: Dec 2002
Posts: 308
E
Edward Offline OP
Member
Tev,
we do not have any lighting on that circuit.

How can i check the quality of the voltage at that receptacle? Is there any other way without using the expensive power quality analyzer?

Edward


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Edward
Joined: Nov 2001
Posts: 745
M
Member
Hi Edward: got a few questions for you: 1) Is the hum you describe actually a hum, such as a 60 cycle sound, or does it have a raspy, buzzy quality to it...some cheaper grades of electronic light dimmers inject this kind of noise into circuits that sound equipment will easily pick up (and may not necessarily be on the same circuit as the equipment, but on the same phase or hot leg in the breaker panel...they will also cause some lamp filaments to "sing")... 2) Is the equipment used by the client a piece of stand-alone gear, such as a guitar amplifier, or is its output connected to a P.A. system through a microphone input or a direct box (which could lead to the ground loop scenario mentioned), ... 3) if it is a stand-alone unit, does it hum when powered up with nothing else connected to it (possibly indicating bad filter capacitors in its power supply), and 4) Does the piece of equipment hum if it is connected to a different outlet, if one is available?

In many theaters, especially ones that attract road touring groups, a separate electrical service to the stage is provided for use with sound equipment, fed from a separate transformer from that which feed the stage lighting service. The transformer serves as a device to "decouple" or isolate the sound equipment from the stage lighting dimmers.

Just thinkin...

Mike (mamills)

[This message has been edited by mamills (edited 10-22-2003).]

[This message has been edited by mamills (edited 10-22-2003).]

Joined: Dec 2002
Posts: 308
E
Edward Offline OP
Member
Mamils,
It is stand alone unit. When it is pluged-in it makes that noise. So they are using an extension cord from another outlet which does not make the speaker HMM.
They have other speakers and amplifiers but is that only unit that hums in that receptacle.

Edward.


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Edward
Joined: Aug 2001
Posts: 7,520
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Member
Many possibilities have already been mentioned, but another springs to mind.

If the amplifier has a 3-wire cord, there's always the chance that the receptacle on the stage is simply missing its ground connection.

Depending upon the design of the amp and the EM fields present in the area, a missing ground on the chassis and shielding could result in some background 60Hz hum.

Joined: Jul 2003
Posts: 394
B
Member
Ideas:
(obvious) Is the outlet wired correctly?
Is that circuit on the same phase as the one where it operates correctly?
Some older amps (especially tube) have a polarity reversing switch, usually near the power cord. If this one has one, try flipping it and see if things improve.

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