Krell KAS amplifier hum

OP,

I assume you are hearing the hum from the left and right channel speakers.

Hum is probably caused by a ground loop.

Are you using balanced ICs or SE ICs?

How are you feeding 120V power for the preamp and the connected front end equipment?
Another dedicated circuit?
Or an existing 15 amp convenience outlet branch circuit?

Update,  I unplugged the 6m long XLR from each amp.  Then, I powered on both amps.  There was no hum at all. 

@jea48 
All instruments are plugged into a Silver Circle audio, "pure power one 5.0, which is plugged into an existing outlet. 

Pre = ARC Ref 3
Phono = DSA
Tuner = McIntosh MR 67
Transport = ML No31
Dac = ML 36s
TT = Final audio VTT-1 
Tonearms = Talea and Kuzma 4pt

Best,
Jose

This means @jea48 is correct - you have a ground loop hum. I still had my hum with only speakers plugged into amp and no other components connected. You need to go through through a process of elimination adding one component at a time to see which is causing the hum.

@ jg2077

There is a good chance the existing 120V 15 amp convenience outlet branch circuit safety equipment ground is causing the ground loop hum. There is a good chance there is a difference of potential, voltage, between the convenience outlet safety equipment ground and the equipment grounds of the two 20 amp dedicated branch circuit outlets, for the power amps.

For a test try this.

Unplug all front end equipment ICs from the input jacks of the preamp. Including any phono ground wire.
All you want is the preamp connected to the two amps. Nothing else.

Check for ground loop hum through speakers. No hum? Post back.


If you still have the hum, for a test, connect a ground cheater between the plug of the preamp power cord and the wall outlet. Check for the hum. (Make sure the cheater plug ground wire, or lug, is isolated, insulated, from contacting the screw that holds on the wall outlet cover plate).
You can also use a 2 wire IEC power cord if you have one instead of using your existing preamp power cord. You won’t need a ground cheater then.


Check for hum.... If the hum is gone post back.

All was unplugged from the back of the pre, I still have "hum".

I ran a ground wire from the pre power cord (plugged into the back of the power distributor) to the ground of wall outlet the power distributor is plugged into; the hum remains...??

Many thanks for all advice given, 
Jose