Krell KSA 100mkII Clone

[jacco vermeulen]

In case anyone scratches the silkscreen of his boards or damages it in any other way at a later stage :

Both board and silkscreen are usually epoxy resin based. Sometimes the silkscreen has a polyurethane base, basically the only other stuff that has a good holding grip on epoxy resin materials.
Both epoxy resin and polyurethane can be given a preferred color by adding the appropriate pigment.
Scratches and bruises can be touched up with a disposable brush.
After the curing time, the touch-up can be polished to look invisible.

[TomWaits]

It has been said already and I don't want to be redundant but the boards are fantastic! No scratches or scuffs on these ones.

I tip my hat toward you folks who put it together and the DIY forum in general as a wonderful place for all things audio.

Now if only my schedule would allow me to get back to finishing the KSA50 then I could get on to it's big brother. I guess I can start sourcing the parts.

Shawn.

[VT67]

Still no boards overhere

Regards

[K-amps]

Originally posted by MikeBarton


.....This would give about 59v dc according to previous calculations in this thread.

Mike

FWIW... I just finished a mod to a power amp whereby the rails are about 58.5 or 59vdc.

I get 190watts per channel before clipping.... that's a very hi rail for a true KSA-100... unless u are building a KSA-150... then it will be on the money... but then jack all power sections up by 50% as well and have preceeding circuitry able to handle it too...


PS: Has anyone compared a finished KSA-50 to the KSA-100? I know Mark liked the 100.... anyone else do it?

[pollypocket]

Has there been any recommendations regarding heatsinks for this project?
I have read some of the discussions, but I am not sure if there has been a consensus reached. I am most interested in passive heatsinks. Is there a spec on thermal transfer rate that I could use as a guideline when shopping for sinks? I come across some copper heatsinks may prove interesting for the project.

thanks,

Paul

[Mark A. Gulbrandsen]

Something along the lines of what was used for the KMA-160 would work well. That is what I am going to be using on my monoblocks. 4 sinks per amp. They are available through M&M Metals.....

Mark

[AndrewT]

Hi Kamps,

I just finished a mod to a power amp whereby the rails are about 58.5 or 59vdc.

what are the corresponding Vac input and output of the transformer?

Originally posted by pollypocket
Has there been any recommendations regarding heatsinks for this project?
I have read some of the discussions, but I am not sure if there has been a consensus reached. I am most interested in passive heatsinks. Is there a spec on thermal transfer rate that I could use as a guideline when shopping for sinks?

0.05 to 0.08C/W.
Since the output (3pair on each driver pair) conveniently groups into 6pairs or 4triplets you can buy either 4 off 0.2 to 0.32C/W or 6 off 0.3 to 0.48C/W

[pollypocket]

Mark, Andrew:

Thanks for the clarification.

Paul

[AndrewT]

I forgot to mention that each manufacturer rates their sinks at a fixed temperature difference above ambient.
As the working temperature moves towards ambient (deltaT<70Cdeg) the C/W drops off. Most manufacturers quote the deltaT and how to correct Rth s-a for lower/higher values.

The Krell 100 Klone dissipation will be about 270W on +-52Vdc supply rails. Heatsink temperature~=270*(0.05 or 0.08) = 14Cdeg to 22Cdeg+ambient (30degC to 40degC). These deltaT values (14 to 22) are very much below 70Cdeg with the result that a specified 0.05C/W will run much hotter than predicted if the de-rating is ignored.

[K-amps]

Originally posted by AndrewT
Hi Kamps, what are the corresponding Vac input and output of the transformer?

117vac prims and 42-0-42 vac secs. At 120v mains about 43.0.43vac. 1-2kva part... never did find the exact rating. Seller claimed 2kva but size is more like 1kva.... at 4 ohm clipping of 330 watts, rails sag to only about 56.5vdc. caps 40kuF per rail. Panasonics.