Originally Posted by Newbie789
First I tried the same outlet and/or tripp lite lc1200 combinations. No luck, but I did notice that the marantz has no grounding plug.
Then I tried disconnecting all wires from the Marantz except the amp interconnects, but the hum did not stop.
Next tried disconnecting everything except speaker wires from the amp, hum got better but didn't stop.
That's when I grounded the reciever to the amp, based in advice from this forum.
The hum got much much better after i ran a 12ga speaker wire from the Marantz ground to a screw in the Rotel RMB-1585 case.
Now I have a hum only when putting my ear to the tweeter, which is the same as what best buy has in their showroom.
I would think for an amp as expensive as Rotel that there would be absolutely zero hum...but maybe with a 200watt / channel amp it's normal?
Also my speaker wire runs are between 50-75 feet from my AV closet to the living room, crossing lights and ceiling fans. Maybe using ferrite on the speaker wire will help?
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In general it is harder to resolve ground loop hum when there is a ground pin than it is on polarized equipment (no ground pin). All of the newer AVRs and processors are polarized rather than grounded for this reason. It is better to remove grounds (break the loops) than add grounds and try to get everything at the same potential when trying to resolve ground loops but when you have a mix of equipment adding grounds may be the only option.
The polarized receivers/amplifiers/etc are however designed to be polarized rather than grounded. Polarized equipment will normally have a switch on the hot wire so that when it is turned off there is no power to the device. Other precautions to ensure that a fault won't allow electricity to flow to the metal case also have to be taken. Less precautions are required on grounded equipment because a short of the hot wire to the case would connect the ground pin to the hot wire and trip a breaker.
If you want to check to see if it is really a ground loop or just amplifier hum you can TEMPORARILY lift the ground pin. I do not recommend running with the ground pin lifted for anything other than testing the unit and care must also be taken to ensure that you don't run AC current through your amplifier chassis an into your body while doing this.
Also be sure that it is still polarized correctly while doing this test or you could potentially damage yourself or your equipment. Most importantly don't electrocute yourself...
If the hum goes away when you temporarily lift the ground then it is likely a ground loop issue and not the amplifier.
BTW the other reason to run everything on the same outlet (assuming that your power requirements are met by one outlet) is that it guarantees that you are powering everything on the same phase. A house actually has two 120V inputs that are 180 degrees out of phase. Anything running 240V is using both phases to make 120+120=240. There could be some extra noise if you cross phases even though it probably doesn't matter in most practical cases....
Also disconnect your cable/satellite connection. That is actually the most common source of ground loop hum.
I did have an adcom amplifier with excessive hum once even when not grounded and it turned out to be some weak capacitors on the amplifier DC power rails. Ground loops aren't really inhernet to high power amplifiers but they are somewhat inherent to grounded amplifiers.
The moral of the story is that lots of issues can cause humming.