How Much DC is OK on a Power Line?

DC can come from your neighbors on the same feed as you....I notice my transformer will hum only occasionally at different times of the day...has to be from something my neighbors are running...have tried DC removal devices and none ever worked

The PS Audio Humbuster III is working well in my system. It's main goal is to eliminate as much DC as possible coming into the system.

My system isn't humming.

Peter, what model Classe amp do you have ? A lot of later production CA-XX0 series amps have DC blocking circuitry, and for earlier production models that did not have it, the DC blocker circuit board was available as a retrofit.

A couple hundred millivolts of DC is all it takes to cause transformer hum. Abnormal high voltage and harmonic distortion can also cause hum. DC blockers will not eliminate hum caused by harmonic distortion.

DC can be caused by a variety of devices, including but not limited to light dimmers, appliance speed or temperature controls, washing machine motors, refrigerator and air conditioner compressors, etc.

The PS Audio Humbuster and Channel Islands XDC-2 AC filter should eliminate most transformer noise caused by DC. There is also the DIY option. I've done DC blockers for a few Audiogon members at a fraction of the cost of the "big boys".

As mentioned above, DC can come from a neighbor's house. It can also be generated in your own house. I would investigate in-house sources before looking for a solution. Look for possible sources, shut off all breakers and see if the noise goes away.

I don't know of any power company DC spec.

whould a power regenerator (Purepower, PS audio) remove the hum/buzz caused by the DC on the line?

Thanks Gbart. I'm using Classe Omega amplifiers. I just measured my outlet for DC, and am seeing about 200 mv. I had an air compressor plugged in that night, and maybe it went on and the motor increased my outlet DC?