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power grid issues?

Hi  Agoners. By chance, are there any bright EE around who may have an answer to this? I get "grid hum" on my Balanced Audio Technology tube amp. It is irregular, happens for different intervals and different lengths of time. I have check my house system by shutting evert appliance of during these "hum intervals" and I do know it is not my house systems that are creating this noise, or fluctuation. I had PG&E check their system. They used a neutral detector and said that their neutral to the source is good. The power is stable. This morning the hum, which is audible in the transformer, was a wave. on off on off on off, for a good hour. then it stopped. Yesterday it was just a straight hum for a period of time. no fluctuations at all. What is going on? 
Thanks for any input!
Greg
greg22lz

Showing 3 responses by erik_squires

erik_squires
15,805 posts
 
@theaudiotweak is confusing ground loop issues with DC.

Ground loop issues cause hum out the speakers, and digital jitter which may or may not be audible. 
Mechanical humming from transformers is not caused by this.

Best,
E
erik_squires
15,805 posts
 
I found this article, and it seems to be pretty comprehensive:

https://www.pooraudiophile.com/2015/03/how-to-fix-dc-offset-and-transformer.html
erik_squires
15,805 posts
 
It sounds like the age-old issue of having DC on the line.  This will cause mechanical vibration in the transformer.

I would not just turn off appliances, I'd turn off all the breakers to see if it's something in your home. Usual suspects are digital supplies, as well as LED or high efficiency light bulb supplies. Hair dryers, and dimmer switches.

The permanent fix for this is to use a balanced power conditioner. Furman, Equitech, Torus, etc. will eliminate this completely.

There are also smarter, less expensive devices like this from Emotiva, which I have not tried:
https://emotiva.com/products/cmx-2

Best,
E
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