Identify this hum, please

It's not the amps. I hooked my iPod up to the amp and listened and there's no problem. It's both the preamp and the phono stage since when I unplug the phono stage/turntable (which is powered by the same DC power supply -- WT Simplex and a Dynavector P75) much of the hum goes away but there's still a buzz so that's the Lighter Note LDR preamp that I'm using. So the question is: Is there anyway to isolate the preamp side from the amp side? Putting the mono amps on a different circuit doesn't help at all. Same exact issues. It's a 60 year old house with some interesting wiring issues. The thing is, every other amp I've ever had was not a problem. Thanks everyone for the help.

It sounds to me as if you have a ground loop. This is likely caused by poor wiring practice in both the amps and the preamp working in tandem.

The wiring problem has to do with how the units are grounded through the power cable. Although Minorl is correct in his admonishment to not lift the safety grounds, I do understand the temptation to do so.

Here is my recommendation:

Go to the hardware store and get some of those ground cheater plugs. You are going to do a test to find out where the problem is.

Start by using the cheater on the preamp.

If hum goes away you have two solutions:
1) send the preamp back for repair to the ground
2) get an isolation transformer for it

Second, plug the preamp into the wall normally and put the cheater on the amps.

if hum goes away you have the same two solutions as listed above.

DO NOT use the cheater otherwise! It represents a shock/fire hazard should anything go wrong.

Alternative approach using a Digial VoltMeter (DVM):

Set the meter to ohms scale. Measure from the ground pin of the power cord to the ground of the RCAs.

If you read near zero ohms, follow the solutions above. If you read significantly higher than zero ohms (25 ohms or more), the unit is off the hook.

I agree with Atmasphere's approach.

Many ground hums are caused by Cable TV. Do you have any type of cable TV connection into any of your equipment?

I did all the ground lifting and measuring and in the end it's not the amp. It's the preamp. I replaced the passive with an old Advent 300 receiver (using it's preamp out) and the hum is gone. That Advent actually sounds WAY better than it should. I've always been a passive guy but I've heard that my amps (Joule-Electra Stargate SET) rather like a regular preamp. After hearing even the Advent I can see why. These are great amps by the way. Any preamp suggestions :)

Thanks to everyone for their help!