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How Much DC is OK on a Power Line?

The other night my Classe amplifiers started producing a substantial mechanical hum. Classe told me that it was likely from DC on the power line. The hum was there even when the preamp was switched to standby, and even when I plugged the amps into different sockets.

My questions:

1) how much DC on the powerline does it take to cause problems with audio equipment?

2) How does DC get into the AC signal on the power line?

3) Do the power companies have any spec they need to acheive for maximum DC?

4) Or is it more likely appliances within my house causing the DC.

Thanks, Peter
peter_s
jea48
4,789 posts
 
Ralph,

I am not dismissing what you are saying about odd harmonics. They can and do play havoc on AC power systems.

They can cause the secondaries of power distribution transformers to run hotter than normal. And yes be mechanically noisier than normal.
sbrownnw
717 posts
 
Gbart, could you make a dc line filter / blocker for me? If so, can you email me at: white 78 911 at hotmail dot com
jea48
4,789 posts
 
Harmonics.

http://www.fluke.com/fluke/twen/solutions/pq/troubleshooting-power-harmonics.htm

http://www.psihq.com/iread/harmonic.htm

Is DC offset the product of harmonics?
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psag
518 posts
 
My balanced power conditioner (Isoclean) was humming/buzzing loudly, sometimes for hours, sometimes for days, with no predictable pattern, and this was on a dedicated line. I put the Channel Islands XDC-2 between the wall outlet and the Isoclean unit, and the problem immediately and permanently disappeared.
sbrownnw
717 posts
 
Forgot to post that @Gbart built me a very nice custom DC blocker that allowed me to not only address my transformer hum in my preamp but also use the outlet I wanted, which is one of Al Porter's Ports.

Great service and product all around. :)

Scott
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