Older Krell Schematics

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Oops!

It seems that I fell into the trap of mistaking 620 on a SM cap to mean 620pF rather than 62x10^0 or 62 pF. I should have spotted that 620 pF was way too much for the compesation. I will upload the corrected schematic for the KSA-100 MkII tonight.
There is no file in the link for the overall schematic of the amp because I had a problem with it as well. It should be loaded tomorrow.
 
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Hi lmaclean,
That's amusing. I've been away from the audio "business" for a number of years too, since I sold my shop. I'm in the telecomunications field now. I know exactly what you mean by audio "business".
I still keep a finger in by doing low volume service by appointment. At least now I get a chance to design and rebuild for pleasure.
-Chris
 
I saw too many good designers/engineers drop out of high end in frustration. When I was in school, all I was interested in was high end audio design. While I was working with the distributor, I got to meet a lot of interesting people from companies like Vandersteen, Bryston, Apogee, P.S. Audio, Belles, VSP, Spectral, AGI and of course Krell.
If you look at the list of who is left in the "business", it kind of tells you something. Somehow, most of the best have moved on to other things. At the time my girlfriend was working in the fashion business and I can assure you it is far less flakey!
 
lmaclean said:
I saw too many good designers/engineers drop out of high end in frustration. When I was in school, all I was interested in was high end audio design. While I was working with the distributor, I got to meet a lot of interesting people from companies like Vandersteen, Bryston, Apogee, P.S. Audio, Belles, VSP, Spectral, AGI and of course Krell.
If you look at the list of who is left in the "business", it kind of tells you something. Somehow, most of the best have moved on to other things. At the time my girlfriend was working in the fashion business and I can assure you it is far less flakey!
I guess one can make a whole lot more $$$$ in the fashion business if you are good at it.
:bigeyes:
 
please sir may I have more?

Hi,

I've been looking at your schematics, and I was wondering if you have a couple of other datapoints. A few of us are going to make a KSA50 and are debating rail voltages and bias current. These numbers are missing from the schematics you've posted, so if you have this info please let us know.

Thanks

Stuart
 
Re: please sir may I have more?

Stuart Easson said:
Hi,

I've been looking at your schematics, and I was wondering if you have a couple of other datapoints. A few of us are going to make a KSA50 and are debating rail voltages and bias current. These numbers are missing from the schematics you've posted, so if you have this info please let us know.

Thanks

Stuart


Sure, no problem.
The KSA 50 used supply rails of +/- 36.5 VDC and the bias was set to 620 mV DC across 0.68 ohm emitter resistors.
The KSA 100 used +/- 48-50 VDC (depending on vintage) supply rails and the bias was set to 575 mV across 1.0 ohm emitter resistors.
All early amps used EI core transformers and later amps used toroidal.

Lloyd
 
More info needed?

I have included my response off line to another member which may give additional answers to questions:

Be cautious of the source of the schematics you intend to use. I have seen several where the compensation capacitors are given as 10x the actual value (i.e. 390pF instead of 39pF). There is one on the internet that has added SOA protection to the outputs which is not necessary. All of the later vintages mount the bias transistor on the driver board, not the output stage. Because of the class "A" operation, this is possible. I have posted the correct schematics on my page:
http://home.ca.inter.net/~lloyd.maclean/Krell/Krell.htm
I drew these from actual amplifiers that I was working on.

The early Krell amps were very simple in design and contained no inovative circuitry. What made them desireable was:
1) They were one of the first to have the courage to build big amps with big powerful power supplies.
2) They ran in pure class "A" mode right up to full power into 8 ohms (a current probe and a scope is needed to verify this - which I did).
3) They were stable enough to drive low/complex impedances with ease when many contemporary amps had trouble.

If you build a "clone", you will only achieve these benefits if you meet all of the design criteria mentioned above. The same circuitry with a cheap power supply will sound exactly like a NAD 3020, but at a much higher cost.

ALL Krells of these series had fully independent channels right back to the line cord. 2 transformers - EI core in the early versions and toroidal later and in the MK II (Avel Lindberg or Holden & Fisher). The power supply was common to both the amplifier board and the output stages (seperate regulation came later). The KSA 50 had a DC supply of +/- 36.5 VDC. The KSA 100 used supply rails of +/-48-50 VDC (depending on vintage).

Good luck with your project. You will have difficulty sourcing devices that were used in the MK II version as they are no longer made. I'm sure others can be used but you have to research them first. Once you have everything, it should be pretty straightforward to build. Just keep in mind that you can find them on ebay from time to time for about $1000 USD for a KSA 100.

Regards,
Lloyd
 
KSA 50 photo

FYI:
A photo taken from a brochure of the KSA 50
 

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lmaclean :king:

WTG! :cool:

Thats! the best Krell related site on the WWW. :drool:
the presentation is just like the krells... Large, Pure and Simple ... The pictures combined with the schematics is far more informative compared to any "lets have some fun and mess up the Krell" tread :yes:

Ps. love the brochure pictures, please add more stuff if possible :tongue:
 
Missing Krell schematics...

I have had a couple of queries on why the schematics have gone missing from my KSA100 Mk II rebuild page at:

http://home.ca.inter.net/~lloyd.maclean/Krell/Krell.htm

I received a message from my ISP that read as follows:

"This morning we were contacted by an agent from Krell Industries, the
manufacturer of high-end audio equipment, with reference to some
documents that you are hosting on your personal web space. The documents
in question are schematics for some of their amplifiers which are
copyrighted material and therefor may be in violation of our Terms of
Service agreement if you did not obtain permission to publish these
documents.

The agent from Krell Industries politely requested that the documents be
taken off the web site. We recommend that you contact Krell Industries
to determine if the content qualifies as fair usage of their copyrighted
material, or if you could obtain permission from them to host the
content and add copyright holder information on the site."

Read into it what you will, this is consistent with their treatment of us whule we were their distributor. By the way, they typically would not provide us with schematics of their products even though we were expected to repair them (often). Those posted were drawn by me from the actual amps...

Regards,
L
:smash:
 
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