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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
almarg's avatar
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almarg
8,673 posts
 
I think that all that can be said about lifting an ac safety ground on a piece of audio equipment is that the risk of a problem is small but is not zero.

But if you are saying that the sub is not on the same ac outlet as the preamp and the rest of the stack, and if the hum goes away when the sub is disconnected, I would certainly try connecting it to that same outlet.

Also, let us know whether the sub is connected via line-level or speaker-level.

Regards,
-- Al

xti16
1,495 posts
 
Lifting the ground would be like using a 2 to 3 prong ac adapter on the various power cords.
audioful
1 posts
 
Have used 3 to 2 prong plugs for several years. No problems. Have them plugged into conditioner/surge protecter which has 3 prong into wall plug. Good luck
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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
125 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.
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