Noise in one channel of krell KSA-80

Deoreo · 30th March 2004, 01:05 PM

I have a problem with this amplifier that has
me stumped. If I have this amp plugged directly
into a dedicated 20 amp line, I get an "electrical" fuzzy
noise/buzz in the speakers that varies in level all by itself.
It is very audible across the room from the left channel, and
present in the right channel but not as loud.

Now the weird part - if I plug an 1800W voltage
regulator into the dedicated circuit, and then
power the amp from it - no noise.

I measured the wall voltage with an averaging
meter and get 116-117 volts out of the dedicated line
and I get 126 volts out of the voltage regulator
I also have 0.3 volt DC riding on the AC

Is there a part in the amp that may be failing, making
it sensitive to the line voltage, or is my wall
voltage too low?

Steve

Steven · 30th March 2004, 06:00 PM

That 0.3V DC on the mains might be the problem. It may saturate the transformer and cause nasty current peaks that radiate into the amplifier.
On this forum circuits circulate that remove the DC part of the mains. Some use just a few big diodes in anti parallel in series with the primary. Some add a big low voltage bipolar capacitor in parallel to these diodes. E.g. 2x 10.000u, 16V (in series, minus to minus) will make a nice bipolar cap. The diodes keep the voltage across the cap low, but you need a big capacitance to deal with the ripple current.

Steven

Deoreo · 30th March 2004, 06:22 PM

Steven,
Thank you for the reply,
The DC was my first suspect, too -
however, the DC is present at the
wall outlet, and at the output
of the voltage regulator. And the
amp is perfectly happy running off
of the voltage regulator, but not directly
from the wall outlet. I know running the
voltage regulator is the easiest answer,
however I think it is a band-aid to a
possible other problem, because all
of my other components have no problem
running with no voltage regulation.
I may send it to Krell service, but I wanted to
see if anyone had some ideas as to what is
causing this.

Steve

30th March 2004, 01:05 PM	#1
Deoreo diyAudio Member Join Date: Jan 2004 Location: North Canton, Ohio	Noise in one channel of krell KSA-80 I have a problem with this amplifier that has me stumped. If I have this amp plugged directly into a dedicated 20 amp line, I get an "electrical" fuzzy noise/buzz in the speakers that varies in level all by itself. It is very audible across the room from the left channel, and present in the right channel but not as loud. Now the weird part - if I plug an 1800W voltage regulator into the dedicated circuit, and then power the amp from it - no noise. I measured the wall voltage with an averaging meter and get 116-117 volts out of the dedicated line and I get 126 volts out of the voltage regulator I also have 0.3 volt DC riding on the AC Is there a part in the amp that may be failing, making it sensitive to the line voltage, or is my wall voltage too low? Steve

30th March 2004, 06:00 PM	#2
Steven diyAudio Member Join Date: Oct 2003 Location: The Netherlands	That 0.3V DC on the mains might be the problem. It may saturate the transformer and cause nasty current peaks that radiate into the amplifier. On this forum circuits circulate that remove the DC part of the mains. Some use just a few big diodes in anti parallel in series with the primary. Some add a big low voltage bipolar capacitor in parallel to these diodes. E.g. 2x 10.000u, 16V (in series, minus to minus) will make a nice bipolar cap. The diodes keep the voltage across the cap low, but you need a big capacitance to deal with the ripple current. Steven __________________ The Analog Art shows no sign of yielding to the Dodo's fate. The emergence and maturation of monolithic processing finesse has perhaps lagged a bit behind the growth of the Binary Business. But whereas digital precision is forever bounded by bits, there is no limit excepting Universal Hiss to the ultimate accuracy and functional variety of simple analog circuits. - Barry Gilbert, 1973

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30th March 2004, 06:22 PM	#3
Deoreo diyAudio Member Join Date: Jan 2004 Location: North Canton, Ohio	Steven, Thank you for the reply, The DC was my first suspect, too - however, the DC is present at the wall outlet, and at the output of the voltage regulator. And the amp is perfectly happy running off of the voltage regulator, but not directly from the wall outlet. I know running the voltage regulator is the easiest answer, however I think it is a band-aid to a possible other problem, because all of my other components have no problem running with no voltage regulation. I may send it to Krell service, but I wanted to see if anyone had some ideas as to what is causing this. Steve

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