Originally Posted by bmrowe
Thanks. Loudest ground loop I've heard. The receiver is in a media closet about 70 ft away so using the same outlet isn't an option. Are you saying just ground the amp and cleanbox to each other?
It's best to start with the basics first.
It you're plugged in to two different outlets, first make sure that the polarity is correct at the outlets.
An outlet should be wired such that the HOT lead is connected to a specific side of the outlet, and the neutral lead to the other. This is done for safety reasons. Switches on the things you plug into the outlet will open and close the HOT side, so when the switch is off, there will be no voltage inside the device.
The HOT side, should be the smaller of the two openings on the outlet. The neutral will be the wider of the two. Cords where it matters will have one of the prongs wider so the neutral side and hot side line up correctly.
How can you tell? Use a voltmeter, and check the voltage between the narrow opening and the ground opening. It should measure about 110-125V. Measure the voltage between the wider opening and the ground. It should be zero. If your readings are reversed, your polarity is reversed.
If you have reversed polarity at one of the outlets, you'll get a ground loop hum.
If you find that the outlets are correct, try reversing the plug on either the Denon or the Peavey and the Art Cleanbox Pro. You can also try a "cheater plug adapter" to lift the ground.
Since the problem is not present with the Art Cleanbox Pro out of the connection path, I suspect the problem is in the XLR connection termination, i.e. shield/ground pin connection.
BTW, based on the input sensitivity of the Peavey (1.84v) and the 1.2v output of the Denon, I'm not sure there is a significant benefit or need to use the Art Cleanbox Pro. The difference is 3.7dB and I doubt that you will hear any significant difference without it.