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In Reply to: RE: Major ground loop problems after construction on new house posted by M-B on August 24, 2014 at 21:17:38
I'd take a look at the subpanel wiring. The "safety" grounds should all be connected next to each other and preferably on the tail end of the bar away from the input so that power current doesn't flow across them.
If you need to move things around be very very sure to turn the breaker for the subpanel off in the main box first and check for voltages with a meter before unscrewing things.
Of course this assumes that you weren't having the problem before rewiring. I agree with the poster who says to see if it the cable connection is part of it.
Good luck, Rick
Follow Ups:
Cable tv coax is disconnected along with everything else except for the amp and preamp.
If you have a voltmeter and some wire you may be able to measure the various voltages between your grounds. I agree with Jea48 that voltage differentials are the rub, the question is why and where. Even a $10 meter from Harbor Freight will probably do the job. Their AC LSD is .1V and your audio signals are around 1V max so if the hum is loud it's prolly < 20 dB down.
Good luck, Rick
Cable tv coax is disconnected along with everything else except for the amp and preamp.
Did you disconnect the incoming CATV coax cable from the CATV receiver box? If not the CATV incoming coax cable would still be connected to the safety equipment grounding conductor of the power cord of the CATV receiver box to the wall receptacle the preamp is plugged into. That is if the CATV receiver box uses a 3 wire power cord and plug.
What you are looking for is a reason/source why there is a difference of potential, voltage, somewhere between the safety equipment grounds of your 4) 20 amp dedicated circuits.
Edits: 08/25/14 08/25/14
To reiterate, there are only 2 things plugged in at the moment. The amp on 1 circuit. The preamp on another circuit. The preamp only has a interconnect running between it and the amp.
To reiterate, there are only 2 things plugged in at the moment. The amp on 1 circuit. The preamp on another circuit. The preamp only has a interconnect running between it and the amp.
When you plugged the amp and preamp into the same duplex receptacle, where you did not have the ground loop hum, did you use the same long interconnects as was used when the equipment was separated plugged into two different power circuits? This is important to establish a common base line to start from.
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