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Help I think my AC is polluted

After months of trouble shooting, I've come to the conclusion that my AC is the culprit of a very annoying hum. The thing that's odd is it only occurs every couple weeks, and only for two or three days at a time. The other thing that's strange is it happens on the weekend and ends usually by Monday night.

Let me give a few details about my system.
- I recently installed two dedicated 20 amp lines. This did not change the intermittent hum.
- I've tried cheater plugs during the hum and they had no effect.
- I'm in the process of auditioning two power conditioners. The Equi=tech Son of Q Jr. and the Furutech e-PT609. Niether of them has had any effect on the hum when it's happening.

I've put my ear right next to each component during the hum and found the Equi=tech transformer humming. I turned off all other components and the Equi=tech continued to hum, even in standby. When the hum is gone, the Equi=tech is dead quite. The hum doesn't change whether the powercords are plugged into the wall or either power conditioner.

I'm going to give the power company a call but I don't expect much help from them. I may try putting in an isolated ground and see if that helps. According to Equi=tech, balanced power should take care of most all ground loop issues, so I don't think an isolated ground will help much with this problem.

Has anyone else ever experienced this? Any ideas on a solution?

mootsdude
jea48
4,423 posts
 
Jmho excessive mechanical noise of a toroidal transformer is not due to low voltage. It is due to DC offset voltage on the AC power mains.

Here is a link for the industry standards for power companies. The nominal AC power voltage they should maintain to the customer shoud be within plus or minus 5%. Usually a + or - 10% range for equipment.
http://powerstandards.com/tutorials%5CVoltageRegulation.htm
stilljd
159 posts
 
All,

Thanks for the discussion and information. It points out a misunderstanding I had about causes of transformers humming - not low voltage - but DC offset voltage (see stilljd above, I started the low voltage stuff). Now I have to understand what DC offset voltage is.

Also explains why my Alpha 9's CDP transformer hummed occasionally at home but not at work.

Appreciate the information and I didn't mean to post erroneous info, just hoping to learn more myself. My apologies.

Best Regards,
Jim S.
oldears
386 posts
 
I seem to have a similar problem. Is there an easy way to measure DC offset on the AC line? I have access to a scope, but no skill in using one.
Also I discovered when I added dimmers to the dining room light that the electrician had not run a ground to the switches (single pole). I get hum even when the dimmer is off.
Any advice?
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