Amp Noise

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ElectricianJeff

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Running a couple of new circuits next week to a music room. Thought I run a MWBC because the basement I need to cross is semi-finished and extremely cluttered with 60 years of stuff. The homeowner is having problems with noise on his guitar amplfiers from what we suspect to be from the old K & T circuits.

Any problems with the shared neutral causing noise problems on these circuits? Having second thoughts.
 
When it comes to audio systems and AC power, I always reference the following papers:

The Bill Whitlock of Jensen Transformers Seminar paper
http://www.jensen-transformers.com/an/generic seminar.pdf

The Jim Brown of Audio Systems Group white paper
"Power and Grounding for Audio and Audio/Video Systems"
http://www.audiosystemsgroup.com/SurgeXPowerGround.pdf

"Power White Paper" from Middle Atlantic.com
http://www.middleatlantic.com/pdf/PowerPaper.pdf

or a different version of the same paper

"The TRUTH" from ExactPower of Middle Atlantic Products
http://www.exactpower.com/elite/assets/pdfs/theTRUTH.pdf
 
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Moving on:

The only audio system that I would wire as a MWBC, is one with 2 or more very powerful audio amplifiers. With the amps on breakers on both legs the Neutral currents for a large part will cancel out.

Some guitars are very sensitive to electrical fields.

A similar problem, but much of it is from a musician's point of view.
http://www.gearslutz.com/board/stud...ying-humming-static-noise-guitar-pickups.html

When I read about this type of problem, I first think about "lost neutrals" or in the case of "K&T" that the Hot and Neutral are taking very different paths.
 
Actually K&T should be free of ground noise unless some bootlegged a ground in somewhere along the circuit.

First thing I try, is utilizing a UPS to feed the amp once operating unplug the UPS and see if the noise clears up. If it does clear up it is electrical, if noise is still present it is the amp.

Next move the amp to a grounded plug somewhere near the new source or run an extension cord, see if this clears the issue up.
 
masterinbama said:
All of my amps go to 11


View attachment 7640
Click to expand...
:D "I don't think the problem with the show was that the band was down, I think the problem with the show was we had a Stonehenge that was perfectly capable of being trampled by dwarfs."

I also don't don't think MWBC cause audio buzzes, I have used them with no trouble. Bad wiring does, unless it is the equipment, and Brian's trick for checking that is a good one.
 
So the thread starter is somewhere between K&T and MWBC, everything else others have added. With K&T the EGC doesn't come into play unless it was added as an after thought. With a MWBC, I wouldn't be happy unless I had complete control of the circuit. Lots can go wrong with creative MWBC wiring. Most audio system don't need but one 20A circuit. The exceptions are real big power amps and real big video projectors.
The big problem with K&T was lack of discipline when installing it 70 years ago. Any handy Neutral was used, so the Hot could go on direction and the Neutral the other, now connect a noisy light dimmer or a SMPS and we have a big antenna system broadcasting interference all over the place.
 
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masterinbama said:
I installed some of these on a high powered (500 watt I believe) PA system at a NASA test facility. They reduced audio hum quite a bit.
http://www.apc.com/products/apcav/products/index.cfm?action=model&id=323&ISOCountryCode=us&tsk=g843v
Click to expand...

So it's an Audio/Video Power Filter.
This is Bill Whitlock's view on the matter.

In reality, many of the benefits often ascribed to ?power treatment? schemes are simply
due to plugging all system equipment into the same outlet strip or dedicated branch
circuit. For obvious reasons, this is always a good idea!

http://www.jensen-transformers.com/an/generic seminar.pdf
 
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