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Speaker Hum with Krell amp?  

post #1 of 7
10/25/03 at 9:38pm
Thread Starter 
I have put a new Krell TAS 5 channel amp into my HT system and am getting humming in all five speakers. The hum goes away if I disconnect the processor from the amp (connected using unbalanced cables).

What is confusing to me is that if I put back my old 5 channel amp (ATI) I get no hum if the processor is connected but do get a hum if I disconnect the processor, i.e. the exact opposite of the Krell. (Although at least I can play music and films without the hum)

I also have a two channel Krell KAV300il and using that as just an amp I do not get any hum either with the processor connected or disconnected.

Any ideas????

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post #2 of 7
10/25/03 at 9:51pm
Do you have the U shaped jumper connected between pins 1 and 3 of the XLR input connectors? If not, you might want to do and it'll help reduce the hum/buzz noise.

Rich
post #3 of 7
10/26/03 at 4:15am
It's all about input impedence.

Krell amps have quite high imput impedences. This makes the amps require little current and be very easy for a preamp to drive.

In addition, all of the usual culprits causing hum in a system- like ground loops and EMI, will affect this amp more than the ATI (note- I'm don't know the input impedence of your ATI amp, but I bet it's much lower than the Krell).

Try these things

1. Short the XLR connections, like Rich suggested. Krell usually supplies shorting pins for this purpose.

2. Disconnect the CATV/SAT/Ant cable from the wall. This is the most likely culprit for a ground loop. If this fixes the problem then you either need a "ground loop breaker" or you need to ground your CATV to your main house ground.

3. Disconnect the inputs from the amp. If this fixes the hum, it's probably an internal problem in the amp.

4. One by one add each component into the system and figure out at what point you hear the hum..
post #4 of 7
10/26/03 at 7:07am
If the amps power cord has a 3 prong plug, try using a 2 prong adapter. I've had this same problem with any amp that had a 3 prong power cord and this has always cured it. I'm now using a Monster Power HTS 2500mk2 to plug the amps into and this cures my hum problems also. The HTS also has 12 volt remote turn on. If it's your cable tv causing the problem, a Mondial Magic Box will cure that.
post #5 of 7
10/26/03 at 7:58am
Thread Starter 
Thanks to all. I have borrowed the Krell from a dealer to try out and don't have XLR cables, just RCA. I have disconnected and removed all my equipment. The hum occurs when I connect the processor to any of the five inputs of the Krell with an RCA cable. Based on Bill's #3, looks like the problem may be with the amp itself. I get no hum at all with the ATI or my two channel Krell after all. The main thing that confused me was that I do get hum with the ATI if I don't have it connected to the procesor.
post #6 of 7
10/26/03 at 10:25am
If the amp doesn't hum when there is nothing connected to it, it's not an amp problem.

If it hums as soon as you connect one of the inputs, you very likely have a ground loop.

I had the same problem. When I upgraded from my BEL1001 to the Krell FPB300 my system went from no hum to hum. After I grounded the CATV ground to my main house ground- hum eliminated.

I've never heard the Krell you have, but they make amazing amps. Once I eliminated the hum, I could never go back to the BEL- and it was excellent.
post #7 of 7
10/26/03 at 2:57pm
Quote:
Originally posted by Bill Lummus

Krell amps have quite high imput impedences. This makes the amps require little current and be very easy for a preamp to drive.

In addition, all of the usual culprits causing hum in a system- like ground loops and EMI, will affect this amp more than the ATI (note- I'm don't know the input impedence of your ATI amp, but I bet it's much lower than the Krell).
FWIW Krell states 100K, and ATI states 28K respectively.
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