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Large neon sign above a sound stage is causing noticable hum in the audio mix when turned on. The sign is wired on a seperate circuit from stage power. Sharing a common ground? Thank you.

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Marty McCann posted this on Peavey Tech notes about "Hum and pin #1 with common ground. It helped me on a hum problem in several places I've worked. I'm sending you the link to his note on this plus the link to other sound related problems. Hope you find this useful.
http://www.peavey.com/support/technotes/soundsystems/humandpin.cfm
http://www.peavey.com/support/technotes/

Posted on Oct 04, 2010

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How do I adjust the mixer to remove humming noise?


I used to be a hi-fi enthusiast many years ago.
A low frequency hum can be caused by inadvertently creating a "hum loop". This is when audio separates are earthed or grounded where they are plugged into the power outlets and then connected together using screened audio leads where the screening is connected to both plugs.
The situation can become worse when one of the separates is a type that isn't grounded.

Ineffective or insufficient power supply smoothing and/or shielding leaving an AC ripple on the DC also creates a hum or in the case of poor design or bad shielding can radiate AC magnetism into the high gain input stages of amplification.

Whatever the cause of the hum it can be aggravated by poor matching of separates with regard to input/output sensitivities and impedances. If the pre-amp stage gains have to be high to compensate for a low input signal the signal-to-noise ratio will always be poor through every stage. Small signals requiring large amounts of amplification requires low impedance circuitry and appropriate sensitivity.

Food for thought...

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I have Sansui G-9000, and its phono stages emit a buzzing/distorted sound even if a turntable is not connected. There is also no sound coming from the left speaker (I already tried switching the speakers,...


The Phono section has a very high level of amplification and so the audio input is very sensitive. So a possible faulty/loose grounding of the input can create a HUM which can be due to even a poor shielding of the input from stray AC factors. So you need to check for the these factors that can bring in the hum , you can confirm by isolating the phono circuit and working to the faulty stage.
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1 Answer

I have a pioneer xc-is21v .basically 2000 audio model which has a vcd player and amp with woofer . i get a humming noise in the speaker but not in the headphones pluged in amp.this is a low ?60hz hum...


It may be that your headphones just don't handle that frequency well enough for you to notice it. A hum at this level could be due to earth(grounding) problems caused by a double earth. If you have other devices (tv, laptop, CD player, games console and the like), plugged into your amp try unplugging them one at a time to try and identify the source of this hum. (I get this occurring with hum on my television if I leave my laptop plugged into my audio system - which the TV is also connected to - even if the audio system and laptop are powered off).
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2 Answers

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Proper level setting of the mixer is important. HOWEVER if the clipping is occuring at the speakers the only possible problem MIGHT be that you have a supersonic feedback that is saturating the speakers above your hearing range, Be sure you don't boost the highs too much with the EQ as this can cause the feedback that you can't hear. Also make sure that you power the speakers from the SAME receptacle as the mixer, even if it means running an extension cord to bring power to the mixer. This is to avoid a low frequency hum and common mode distortion/damage. A low frequency hum could cause the clipping.
It would be a good idea to get a sound meter to check the sound level. You should be able to reach 85 Db from this system without clipping. If you need more than that, you MAY need more speakers if the band instruments are too loud. Also if the band has amps that get into the vocal microphones that adds to the clipping level... make sure the mics don't "hear" the band instruments. Make sure your speakers are toward the audience from the mics to avoid the supersonic feedback problem. If the vocalists can't hear themselves with that configuration you need to set up seperate stage monitors.

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Hi and welcome to fixya.

To answer your question;
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It would be either with the large capacitors in the first stage of the supply(most likely) or with the regulation system that supplies +-15 volts to the preamp section.

If you are not familiar with electronic circuits you could still ask a repair shop to verify those large capacitors.

Hope this help and happy holidays.

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1 Answer

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Cheers and good luck.

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1 Answer

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