Audio Systems/Electronic organ

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Expert: - 12/13/2008


Question
Hello,
I own a 30 year old electronic organ that I am completely restoring.  Despite my best efforts, there remains a hum in the speakers.  All filter caps and grounds etc. have been replaced and painstakingly checked.  No ground loops exist, but the hum still remains.  I suspect there may be a short in the power transformer.  The instrument is not normally connected to an earth ground.  When I connect a multimeter from the organ chassis to an earth ground, with the organ 'on' I get an AC reading of aprox 67 volts, and aprox 150 millivolts AC with the organ OFF.  Grounding the organ chassis to earth has NO effect whatsoever on the hum.
Do I have a short in the transformer?

Answer
No, it is not the transformer.

You might try reversing the power cord; 30 years ago they did not always follow today's convention for wiring.

Also, try grounding the chassis and the electronic circuit grounds together.

Let me know if these tactics do not solve the problem.

C  

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Cleggsan

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Audio Design Engineer; systems, loudspeakers, cd/dvd players, etc. I am knowledgeable in all high end audio equipment and installations. MAKE SURE YOU GIVE A MAKE AND MODEL NUMBER AND CAR IF IT IS AN AUTO QUESTION. Note: I am getting some who ask good questions that take a lot of time to research but then the questioner fails to read the answer. Please don't ask questions unless you are seriously looking for an answer. If you find an answer to your question otherwise then let me know with your reply. Thank you.

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Have been associated with audio design, standards, testing and component systems for over 40 years.

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Life Fellow Member of Audio Engineering Society Life Senior Member of Institute of Electronic and Electrical Engineers

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Review technical manuscripts for IEEE Spectrum Write occasionally for high-end audio publications

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BSEE/MSCS/MBA

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Past Employee/advisor to several well known audio products manufacturers

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