2. amps-preamps
  3. 184310-3592

Krell KSA 200s ground hum

I picked up this amp a week ago and I REALLY like it. When I first plugged it in with nothing attached except speakers it was silent. Like small hiss from an inch away but one of the more silent pieces I have had. As soon as I hooked up an rca from my preamp there it was. Loud ground hum. So right now I have floated the ground with cheater plugs on everything in the chain. Silence all is good with the cheater plugs and the system sounds great. If I take the cheater plug off of any of the 5 pieces in the chain it’s back! All same outlet and dedicated 10 gage line. I mean I’m “ok” with the cheater plugs if need be but…….. any ideas? 

mofojo
mofojo OP
2,203 posts
 

No it’s at least 2 ft away from the closest component. 

jea48
4,320 posts
 

Are you using the OEM power cord that came with the Krell Amp?

Is there a ground loop hum with only the preamp connected to the Krell amp? (Nothing connected to any of the inputs on the preamp. No other type of ground wire(s) connected to the preamp either.

If yes there is hum with only the preamp connected to the amp, (nothing connected to any preamp inputs. No external ground wires connected to the preamp... For a test install a ground cheater on the power cord of the Krell amp only. Hum should be gone... Yes?

 

Just curious are the shorting jumpers, pins, installed on the XLR inputs?

CAUTION:Use only one input to the amplifier at a time. The KSA is shipped
with shorting pins in the XLR inputs. These pins should remain in the XLR
inputs if you are operating the KSA in the single-ended mode. When the
shorting pin is inserted, pin 1 and pin 3 are shorted together. The shorting
pins must be removed to connect the KSA for balanced operation.

.

gs5556
1,218 posts
 

A common way of wiring the RCA jack on amplifiers is to connect the RCA ground to both the signal ground and the chassis. The chassis ground connection is isolated through a filter with low value cap. The problem then could be the RCA jack is touching the chassis (a worn insulator) or the coupling cap from RCA ground to chassis has shorted. Try gently moving the RCA cable at the amp input and see if the hum changes or goes away.

mofojo OP
2,203 posts
 

@jea48 

“Are you using the OEM power cord that came with the Krell Amp?

Is there a ground loop hum with only the preamp connected to the Krell amp? (Nothing connected to any of the inputs on the preamp. No other type of ground wire(s) connected to the preamp either.

If yes there is hum with only the preamp connected to the amp, (nothing connected to any preamp inputs. No external ground wires connected to the preamp... For a test install a ground cheater on the power cord of the Krell amp only. Hum should be gone... Yes?

 

Just curious are the shorting jumpers, pins, installed on the XLR inputs?”

 

Not using the power cord that came with the Krell. It did not come with it unfortunately. Using an older large gage probably 1 grand cable from its time. Can’t recall the brand offhand and it’s worked flawlessly with other amps. 
 

shorting pins were not connected, again I did not get them. I did buy some XLR cables to go from dac to preamp and from preamp to amp and same thing. 
 

Preamp with nothing connected to it causes same issue. 
 

thanks

ieales's avatar
ieales
1,201 posts
 

Verify that XLR pin 1 is connected to the line earth. It may have a low value resistance like 10Ω if there is a loop break.

In recording studios we used twin screen, connected RCA pin to +ve, and -ve & screen to the shell at the source. At the amp XLR, +ve to +ve and -ev ONLY to -ev. Screen unconnected at amp.

If that does not work, there is an issue with the source earth.

If you are going to use cheaters plugs, ground the amp and lift everything else.

 

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