Could a Ground Loop Blow a Mixer's Phantom Power?


Feb 7, 2010
I recently moved to a new apartment and since that day, there's been an awful hum coming from my mixer. Low enough to filter out using software, so I kept using it as it was. It came to a head recently when I tried to use my Phantom Powered condenser mic. The hum was about the same as normal, except when I touched the microphone with my hands, or if my lips came in contact with it, the noise would become terrible.

So I decided to move the mixer into another room on another circuit and the humming went away as expected, however I seem to be having continuing problems with my Phantom Power. My dynamic mics and Electret condenser mics all work just fine, but my phantom power seems to be all messed up.

Firstly, it doesn't even come on every time. I sometimes have to flip the switch about 10 times before I get the light. When it does work, it only works for low audio; background audio sounds perfect, no noise at all, but when I get close to the mic and make a loud noise, it cuts out, like it's drawing too much juice and the mixer just can't keep up. Sometimes after a long period of making loud noises directly into the microphone, everything will get crazy for a few moments (tons of pops, clicks and buzzing and humming), and the settles back to normal after a bit.

My basic understanding of electronics leads me to think some kind of capacitor is blown, because it's kinda like the mixer can provide enough power only if the microphone is not drawing too much at any one time.Could this have been caused by the aforementioned ground loop, or is it just some unfortunate coincidence?

Also, what could I possibly do, or where could I take my equipment to get it repaired?

Thanks for your help.



If the mixer has a three prong power plug, then the rest of the equipment must have the power ground (third prong) lifted. Do this by purchasing two prong to three prong power plug adapters at the hardware store. Make sure that there is only ONE three prong power plug, and the rest are lifted off the third power prong. If you have more than one ground going to the building power, it causes a ground loop and hums.
Another source of hum is a cable TV connection to any part of the audio system. Test this by totally disconnecting the cable TV wire from any unit connected to the audio system. If the hum goes away, you will need a cable TV isolation transformer. It is designed to lift the cable ground, allowing the cable signal to pass through.
Is the phantom mic powered by an external supply? Does the external supply have a three prong power plug?
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