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
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....
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
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
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/
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
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).]
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.
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.
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.
If Pauluk and Big Jims suggestions don't work you may want to check the rest of the outlets on that circiut for any shorts between the neutral and the ground. This could cause the ground to be carrying some of the circiut current. Also check the circiut for any "harmonic producing equipment", lighting and dimmers have been discussed, but "electronic equipment" has not. However I think Pauluk "hit the nail on the head" (the outlet is not grounded properly at the outlet or the panel or somewhere inbetween)
Personaly i wouldnt worry about it to much, most high wattage amps generate a hum, you will probably find once the music is on you cant hear it.
worked in night clubs for about 5 years, then worked for a national company called Stage Electrics,, who hire out everything, and stage events etc..
there PA rigs hummed.. so long as your are confident all the connections tight and nothing is short circuited, i wouldnt worry too much.
we used to pick up the local taxi company through the sound system at the last night club i worked in.
Just check the socket outlet is grounded, etc or are the speaker cables running close to any mains cables.
[This message has been edited by PaulCornwall (edited 10-23-2003).]
Along the lines of Paul C's reply, I was going to mention the "Open Loop" noise of a typical Amplifier.
By this I am referring to the signal input loop being open (no connection to equipment), and not "driven to ground" as is done through a volume pot on the equipment being amplified.
Best example is a Guitar Amp(and most specific - a Non-Humbucking pickup!).
Without touching the strings, the Amp will be picking up all the stray 60Hz noise that's present.
Pull the patch cord's male 1/4" phone end from the Guitar, then place a finger across Tip and Ring; funky noise will be Amplified.
The volume pot on the Guitar will drive the power amplifier's preamp input stage to ground as the volume level is decreased (via it's internal resistance). At the end of the taper (turns), the preamp is driven to ground through a resistance of something like 250KOhms.
If the Amplifier in question DOES have its signal input connected properly and is driven to ground level, then verify the input line (signal level) is solid and hot!
Look into power quality issues only after verifying the signal input(s) are proper - as that's where the noise is coming from!
Scott35
What is driving the amplifier? Is it a microphone or an audio feed? Some balanced mic cords may have what is called a pin 1 problem where pin one is jumpered to the shell of the connector. This could cause hum. Also, any other equipment connected to this amplifier should be plugged in the same outlet to avoid any loop problems. Another thing to consider is the gain stucture of the system. There is alot of info on this thread to consider. Check some of the audio message boards like Pro Sound Web
http://www.live-audio.com/board.shtml Blessings, Mark
I went out to the club to check on the circuit that causes the huming in the speaker. And here is what i found.
H-N= 119.6 Volt
H-G= 119.6 Volts
N-G= 0.4 Volts
This receptacle makes the amplifier hum. However, when i used the three prong adapter with out the ground the noise went away.
Then i checked the extension cord that client plugs in the amplifier that DOES NOT create a hum in the speaker and here is what i found.
H-N= 120.5 Volts
H-G= 66.5 Volts
N-G= 48.2 Volts
What would cause these voltages?
And why does the amplifier/speaker hum in the receptacle that measure a good voltage and NOT hum in the extention cord that hasa the weired voltages?
Thank you
Edward
It sounds as though the receptacle from which the amplifier is run with the extension cord might be missing its ground connection.
The 48 and 66V readings are likely caused by capacitive coupling (if you're using a high-impedance meter) and/or filter components connected from line to ground in the amplifier.
The fact that deliberately lifting the ground (with the adapter) removes the hum seems to suggest either a ground loop of some kind or that the building ground is carrying a lot of noise.
The hum is still there with no inputs connected to the amplifier and the input gain controls all turned to minimum, right?
Is there a possibility that you have a ground on the speaker wiring somewhere?
[This message has been edited by pauluk (edited 11-05-2003).]
MVRANDAZZO asked a good question. What is driving the amplifier?(C.D. player, mixing console, microphone or house system?) How is it connected? (XLR, RCA or 1/4" jacks?). A "stand alone" speaker/amplifier that is supplied by one of the receptacles that you have described and is being driven by mixing console (or etc) that is pluged into the other receptacle that you have described, and are interconneccted by RCA or 1/4" or improperly terminated XLR will produce the noise you have described. The solution to the problem is "most likely""fix the defective circiut and this will eliminate the ground loop".