Rubbersoul,

I left you a lengthy voice mail yesterday. Please check it for an update on my discussion with the engineer. He believes the power cord is serving as a filter for DC; the longer the extension cord, the lower your hum level. He's going to give me a method for properly measuring for DC on your AC line. There's a little more detail in the VM, and I'll be in touch again on Monday with more.

Scott

Based on what Scott said, a possible fix would be a one to one transformer between your receptacle and the amp. The DC would not pass the transformer. How DC is getting on your AC circuit is still a mystery.

Thanks Scott
I have not checked the my voicemail, sorry.
Thanks for listening and going the extra mile.
I hope you see this message Scott. I have a Drs. Appointment on Monday at 12;30. Please call me early or if that is not convenient...4pm.

Thanks again.

XM...I did what you said and there is nothing new to say. Hopefully Monday after talking to Scott the problem will be resolved.
Mystery is correct.

Fill me in XM. I know that AC means alternate current and DC means Direct current. Can you explain to me how this is affecting my system?

Thanks

The amps power supply is expecting AC which oscillates its signal at 60 hz. DC does not oscillate and may affect the amp because it adds noise to the circuit and some of the components respond differently to DC current vice AC current. I have seen AC get into a DC circuit because it can induce a current in wire but how DC gets into an AC circuit is beyond my electrical experience. EEMan may be better able to explain since I think he is an electrical engineer.

Thanks XM.
This issue is really disappointing to me that it has not been a quick fix. I have tried everything. The amp was serviced, the receptacles were doubled checked, I even took the cover off my circuit breaker panel and checked for lose wires, Checked the grounding rod outside the house, disconnected the balance cables and speaker wires as you suggested and the list goes on.
I spoke to two electricians and they both agreed that it is not a grounding issue. Unless my gauge was not working properly and even then he did not think a ground issue would not cause the hum in the amp but rather my speakers. Ground loop.

I hope when I speak to Scott on Monday there is a solution.

Thanks to everybody for their support and suggestions.

Ok 3:25pm EST
Turned the 990/7700 on to watch the NFC championship game between SF and Atlanta.

The amp is quiet as a mouse. No HUM.
Voltage, mild weather??!

I going to enjoy it today.

Here is an extensive article that might help explain how to test / correct for DC on the AC line -- http://sound.westhost.com/articles/xfmr-dc.htm#warn

Thanks renov8r,
On the road right now but will definitely check it out.
I am anxiously awaiting to hear what Outlaw's answer to the problem.

I have to say Scott is great with customer service.
Good man.

Most of the times what people are talking about is corruption of the 60Hz AC signal resulting in the average voltage being something other than 0 volts. Motors are prime corruption suspects. Why is this bad? Transformer core magnetization follows a curve called a hysteresis loop. If the AC signal stay symetrical around 0V then the loop stays centered around 0. If there is a DC offset on the AC signal then the loop will start moving away from zero towards saturation where buzzing is possible.
I never thought about this until this thread, but it makes a lot of sense and matches what I'm hearing in my system. I wonder if I need to invest in one of those power conditioners that output a pure 60Hz sine wave.

The hair dryer example in the link above is an interesting thought. I wonder if there are some devices in your home that do a similar thing with changing voltage in a similar way. A multi-speed blender, an eco friendly refrigerator or even a heat pump that varies speed based on load could be a culprit. Since the problem seems to be related to the time of year maybe your AC or heating system is causing an issue.