Krell KAS amplifier hum

jea48 said:

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.

That won’t work..... The male ground pin on the IEC inlet on preamp would be in the way.

jg2077 OP41 posts

12-11-2019 7:52pm

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,

That won’t work.  Adding a parallel ground path will solve nothing.

Use a ground cheater on the ARC preamp power cord plug. (Nothing connected to the inputs of the preamp. Again just the preamp and the 2 amps. Nothing else)
You need to lift, float, the equipment ground from the chassis of the ARC preamp. That will break the ground loop circuit.

By chance do the Krell amps have a ground lift switch on the rear panel? If so the switch will lift the signal ground of the amps from the safety equipment grounded chassis.
Just a note. At this point I am hoping the problem is the equipment ground of the 15 amp convenience outlet circuit. The ground cheater on the ARC preamp power cord will tell us that for sure if it breaks the ground loop and hum.

Take both mono block out of the circuits, connect a headphone amp to the ARC ref3 output and listen if hum still exist?

In some case, hum is caused by upstream equipment.

Is there a "conditioner" I can use to minimize/eliminate the mechanical hum

Beautiful amps BTW.

There is no conditioner I know of that can take idle current plus music playing current into MBLS’s of a pair of KAS Krell monoblocks and not be near it’s limit.

If your hearing hum through the speakers.
KAS Monoblocks can give hum by their very nature of being mono blocks, they should BOTH be plugged into the same heavy duty mains outlet to stop any earth loops through the house wiring.

Also use some "earth cheater plugs" on the preamp and source/s so they get the earth from the Krells through the interconnects, this way you stop any more earth loops through the house wiring.

Cheers George

georgehifi Said:

If your hearing hum through the speakers.
KAS Monoblocks can give hum by their very nature of being mono blocks, they should BOTH be plugged into the same heavy duty mains outlet to stop any earth loops through the house wiring.

jg2077 OP41 posts12-11-2019 5:54pmUpdate, I unplugged the 6m long XLR from each amp. Then, I powered on both amps. There was no hum at all.

@georgehifi ,
Yes I do realize the test above isolated the two amps from one another therein breaking the connection of the two amp’s power supply’s interactions (circuit ground/signal ground) but probably more importantly the two amp’s dedicated safety equipment grounding conductors.
Also worth mentioning is how did the designer of the Krell KAS amplifier connect the circuit ground/signal ground to the chassis of the amp where the AC mains safety equipment ground is bonded, connected to.



georgehifi Said:

Also use some "earth cheater plugs" on the preamp and source/s so they get the earth from the Krells through the interconnects, this way you stop any more earth loops through the house wiring.

Exactly.

Though there may be other factors at play. Process of elimination. The OP has to start somewhere. If we are assuming the hum is caused by a ground loop, imo, we need to isolate the 120V 15 amp wall outlet convenience outlet branch circuit safety equipment grounding conductor from the equation.

Why I picked the 15 amp convenience outlet circuit is because to me it has the highest probability for causing the ground loop hum.

Factors to consider?
Total length of the branch circuit wiring from the electrical panel to the wall outlet.
How many outlet boxes are in the run.
How were the equipment grounding conductors spliced together. (Wiring method used)
What other electrical loads are connected to the branch circuit. Possible small leakage currents from the hot line to equipment grounding conductor that may produced/caused by a connected load/s.


@ jg2077

ground cheater

https://www.homedepot.com/p/Commercial-Electric-15-Amp-Single-Outlet-Grounding-Adapter-Gray-U-09/203...

Put a piece of tape on the bottom side of the ground tab/lug, or over the outlet cover metal support screw, so it can not touch, contact, the equipment grounded receptacle metal screw that supports the outlet cover plate.