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See if you can "predict" a future ground loop hum?

I was hoping someone could perhaps shed some light on whether or not I may be in trouble regarding ground loop hum....here's the situation:

I'm about to move into a newly built custom home that we designed with a music/library. I had the electrician wire 2 20 amp dedicated lines: 1 at the front of the room for a McIntosh MC 402 and 1 on the side wall for the other components, Classe preamp/Rega & NAD M5 CD players. No video will be on this system. The entire system will be balanced except the Rega Apollo and the REL storm subwoofer.

We're still currently in my "old" home with no special wiring. Last evening, I decided to hook up the MC 402 like I'll have it in the new home to test it out (I just recently purch. it and hadn't tested it yet). When I powered it on plugged into a socket in the front of the room (apart from the other components), there was an audible hum coming from the speakers. I then grabbed an extension and tried different outlets, and of course the one which had no noise was the outlet where the rest of the equipment is plugged into.

Now I'm scared to death that we'll move in to this nice room that I designed and could have the same problem. My question is will the dedicated lines (assuming they're wired correctly) solve this problem or could the same thing happen as in the old home that has no special wiring consideration?
audioguy3107
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stonedeaf
101 posts
 
Wouldn't get too exercised about this potential problem just yet.Your new home was wired by a electrician who understood what you were looking to do with this room? He should have been careful to get the grounding right.
Don't know how old the existing home is - but in general - older wiring ( especially if you are not the only tennat during the home's history) is always a crap shoot - hidden hot boxes or my favourite - three wire receptacles that aren't hooked up to anything on the third wire are always fun.
And for reasons I really don't understand - the number of wire nuts I've had just plain fall off of 3rd. wire (safety grounds) when i pull receptacles out of wall boxes is just plain crazy.There's a reason they're called crafts unions - problem is like any other profession - there's a percentage of don't give a damm slobs wearin the same hats.
How WELL your AC wiring is done really does matter.
bundy
127 posts
 
Finished my basement.
Put in 3 dedicated 20amp outlets.
Had hum as preamp and amp into different sockets.
Removed ground pin on amps cord.
Hum gone.

10 years of happy operation.

I think that as long as there is a gound somewhere in the circuit, you are fine. Mine is through the preamp.
tfkaudio
591 posts
 
As I understand it, the safety issue is real in theory, but not in practice. If, for instance, you have a gound loop and use a cheater plug to lift the ground on the amplifier power cord, this is ok because the amp is still grounded via the interconnects to the preamp (assuming the pre-amp is grounded via a 3-prong power cable).

Now, let's say you make the foolish mistake of removing the interconnects to the amp with the amp turned off but still plugged in. You now have a REAL safety issue because you've just removed the component's path to ground.

So, as I said, it's not a safety issue in pratice because you generally wouldn't leave an amp in the plugged-in-but-not-connected state for very long (usually only while making component changes).

However, as any component manual will tell you, unplug ALL affected components before removing interconnects. Follow this rule 100% of the time and you will be fine.

Cheers.
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