Krell KSA 80 bias & dc offset check & adjust procedure - diyAudio
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Old 5th August 2007, 09:57 AM   #1
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Join Date: Aug 2007
Default Krell KSA 80 bias & dc offset check & adjust procedure

Hello to all.
First, I would like to apologise for my semi poor english. I am portuguese, 46 and sometimes I can't remember well the english tecnical terms.

I bought yesterday a Krell KSA 80 for fun, and in order to check up the unit would like very much to know about the bias and DC offset value & procedure. There are 4 trim pots (2 per side) and also 2 more adjustable pots at the rear marked R and L.

Is there any good soul out there that could teach me and possibly send a schematic.

My amp is giving 230mv on each resistor of the left side, and 270mv & 220mv on the right side resistors.
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Old 8th August 2007, 10:58 AM   #2
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Perhaps this link can help you further (technical details and schematics of this wonderful amp).
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Old 8th August 2007, 09:51 PM   #3
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Join Date: Sep 2001
Location: Salt Lake City
Krell info says to set the bias to 325mv as measured across the emitter resistors on the heat sinks... so yours is a little on the low side. There is a potentiometer in the servo circuit I can't read the R-number on the schematic but it looks like R-38 or 39. That 200 ohm pot is most likely used to adjust offset... I am not sure on the exact procedure on this one... you may have to disconnect the servio then set the offset then re-connect the servo.

PLease also refer to this thread....
Reverse engineering Krell KMA 160

Note that Member JWB built his own KSA-80 Clones and if you e-mail him he can probably shed some light on adjusting the servo properly. Or perhps he'll see this post.

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Old 9th August 2007, 09:39 AM   #4
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Join Date: Aug 2007
Thank you very much for the interest in my KSA 80B problem.
Because I am new, I still am not allowed to contact members directly. I have tried to contact the famous JWB not only for his excelent job on his KMA 160, but also for sharing with us all his tremendous experience on the restaoration.
Perhaps someone could could alert JWB for me ?

I also have tried to acess a link above from someone who did an excelent restoration of a KMA100 mk2 but my old Macintosh could not read that PC file.

In the meanwhile, I will wait for a good soul that could send or exibit here in the forum the right procedure of adjusting this beautifull amp.

Cheers to all.

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