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Ebay KSA50 needs 2 voltages?
Ebay KSA50 needs 2 voltages?
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Old 20th January 2014, 06:25 PM   #41
dihmels is offline dihmels
diyAudio Member
Join Date: Nov 2013
I bought mine without much research and will likely move on to something else in short order. I listen to this daily as it sits in an open mess. I had some old equipment sitting around and that 600va toroidal has Arcam's common two sets of secondary's that with dual rectifier and filter systems puts out +- 40v and +-50v. Almost perfect for this setup. I'll have to look at the NAIM option.
Also, this rookie took some time to sort out that the bias transistor needed removed and mounted to the heat sink to properly regulate bias current. ;P
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Old 19th May 2014, 07:08 PM   #42
simrfid is offline simrfid
diyAudio Member
Join Date: Oct 2011
Location: Geneva
Default Ebay ksa50 PSU design

__________RED ALERT _______

I'm a reel Newbie, so please excuse me if i'm a little lost in it all !

Since I'read this thread, and a part of the enormous original Krell ksa50 project thread, I'm aware that i'm not building the real thing. I would just try to take the best sound possible out of this amp kit.

My problem is that I'm still searching a good option (sound wise) to configure a PSU for this amp kit.

For the information, this amp project is intended to be used in a diy record cutting system. The cutting head is 4.7 ohm, at least 26 dB of voltage gain is needed, and 2X 80W-100W would be enough power. It would have to be as clearest as possible (most linear possible), stable (having the same audio spec for hours), and reliable for years. Etc etc . (I know, I'm a dreamer )

So far, I've two strange toroidal transformer (bought them quite cheap) with four secondary wirings (12V/20A - 12V/20A - 12V/13.5A - 4V/13.5A) that i plan to wire in series, and expect to get 40V/13.5A each.

With my poor knowledge, and the items I already have, I see three PSU design options :

1) feeding +/- 40V to both the output and input stage ? It would keep it simple and cheap, but will not give the differential voltage needed by the amp card . It seem that it has worked for some folks here though.

2) feeding input stage with a boosted/regulated voltage of +/- 55V, using a DC/DC step up converter from ebay like this one ? A little more complex and pricy, with risk of adding "noise to the input stage with the regulated supply", but giving the differential voltage needed . (With this option, I would keep the output stage unregulated at +/- 40V, Pass amp way, as pointed by mullardel34 here). General comments on these DC/DC step up are welcome .

3) Having custom toroidal transformer made specially for this project ? With the transformers I already have, probably a single toroidal transformer with two secondaries at +/-55V/4A could do the trick . It would be not cheap, but would keep voltage unregulated all the way. .

So, have somebody a good advise to give me or a direction to point me to ? Which option seem to be the best one for you experienced diyers ?

And have peoples had good experience sound wise with these kits ? And if yes : how ?

Again, sorry for my very poor knowledge I hope you will understand my questions !

Best regards to all of you diyers !
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