On one leg or two legs?

Hanaleimike,
I'm a little late to this discussion, but anyway, here is a question for you:
When you said: " I would think that if each receptacle has it's own run via a 12/3 wire , all the way back to the panel on a separate ground bar in the panel, that there couldn't be any ground loops. I think the ground pin in the receptacle runs back to the panel, and the receptacle itself is grounded to the metal box. It sure made a difference sound wise too."
Specifically " separate ground bar in the panel"- did you mean, that there is supposed to be a separate ground bar for each dedicated line?
I understand, there is only one ground bar in the panel. Could you please explain that in more details?
I always been somewhat confuzed about the term "isolated ground"- isolated exactly how?
The reason I'm asking is this;
I have licenced electrician to install separate panel with five dedicated lines connected to it:
One for digital,
one for analog,
two for power mono blocks,
and one for video projector
He used Romex 12/3 wire, and to my understanding, at least, that's how I asked him to do it, ground wire from each receptacle (actually there are two receptacles on each run of wire) is connected to a ground bar in the panel, and the ground bar is connected to a copper ground rod right next to the panel, and to a common house ground elsewere.
Still, I have a ground loop problem somewhere.
Even when just a power amps connected to the speakers, and nothing else connected to the amps, and with grounds lifted on both amps with a cheater plugs, still I hear faint hum (much louder with no cheater plugs).
I have tried everything:
Unplugged every piece of equipment, and turned off all circuit breakers,
Lifted grounds on every single piece,
There is no cable, or TV on the same circuits,
Disconnected copper ground rod, installed along with the new lines, from the panel-
still, there is ground loop somewhere.
Now, I suspect, there is something wrong with how the ground wires from the dedicated lines are connected to the panel.
Unfortunately, I don't know of any audiophile electrician in my area, who could sort out the problem, and my "regular" electrician apparently has no clue.
Please, could somebody explain how to correctly ground my five dedicated lines, and how exactly "isolated grounds are created?"
Thanks in advance.

Are they all on the same leg in the circuit breaker box?

They are probably on both legs.
Try plugging everything into one outlet and see if the hum goes away...

I have learned alot from this thread.
I found that my 3 dedicated circuits were not only on the 2 legs, but one of the grounds, neutrals were put on opposite sides of thier hot wire.

So, I moved everything to the same side in the breaker panel, including grounds and neutrals.

Ozzy,
They are physically on both sides of the panel, I'm not sure it electrically corresponds to an opposite legs, or not. I will have to check that later tonight.
I tried to plug it into one outlet, stll hums.

I have licenced electrician to install separate panel with five dedicated lines connected to it:

A sub panel fed from the main electrical panel.
By chance do you know what size wire he used to feed the sub panel?

I assume the electrician fed the sub panel from a 2 pole breaker in the main panel. Look on the breaker handle of the breaker what is the number? 40, 50,60, ect?

Because you have a sub panel the panel will have a separate ground bar. The equipment grounding conductors that are part of the dedicated branch circuits that feed the receptacles will terminate on this bar. The ground bar will have an equipment grounding conductor, wire, that goes backs and connects to the main electrical panel ground bar. No exception....per NEC.

He used Romex 12/3 wire, and to my understanding, at least, that's how I asked him to do it, ground wire from each receptacle (actually there are two receptacles on each run of wire)......

A dedicated circuit feeds two duplex receptacles? Is that correct?
Why did you use 12/3 with ground? Is the ground bar in the sub panel an isolated ground bar? There by isolated from the panel's metal enclosure?

...... is connected to a ground bar in the panel, and the ground bar is connected to a copper ground rod right next to the panel, and to a common house ground elsewere.

More than likely here is your problem. Just bet you have a difference of potential, voltage, between the equipment ground at the receptacles and the neutral, the grounded conductor.

Per NEC the feeder equipment grounding conductor shall be installed in the same cable, or raceway, as the feeder current carrying conductors. And the equipment grounding conductor shall terminate in the same panel the feeder is fed from.
http://www.aes.org/sections/pnw/pnwrecaps/2005/whitlock/whitlock_pnw05.pdf

Jea 48,
Sub panel is connected to the main one with 4 AWG wire, with Black, White, Red and naked copper ground conductors.
Breaker in the main panel, feeding the sub panel is 60.
The wire he used for dedicated circuits has Black, White and naked copper ground conductors, so I guess, I mistakingly called it 12/3.
All five dedicated circuits feed 5 duplex receptacles, that is correct.
I don't think, that the ground bar in the sub panel is isolated from the panel metal enclosure.
Yes, sub panel ground bar IS connected to the main panel ground bar.
Also main panel ground bar is connected to an additional
copper rod, installed at the same time, as the sub panel.
And one more thing: I noticed, that a small connector box with TV and Internet cables, has a ground wire, connected to the main panel ground bar.
I have two questions:
1. When evrybody says "isolated ground" does it mean ground bar in the panel isolated from the metal enclosure?
And, if it's not isolated from the panel (like in my case, it seems), would that be a problem causing ground loop?
2. You'd have to forgive me, but I'm not entirely clear about the last part of your post;
"More than likely here is your problem. Just bet you have a difference of potential, voltage, between the equipment ground at the receptacles and the neutral, the grounded conductor.

Per NEC the feeder equipment grounding conductor shall be installed in the same cable, or raceway, as the feeder current carrying conductors. And the equipment grounding conductor shall terminate in the same panel the feeder is fed from".
And how exactly should I correct this problem?
Thanks a lot for taking your time- it's really priceless.