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alibear 12th September 2012 04:13 PM

Krell KSA50 Clone Information Please
Hi all,Some time ago I built a low power version of the KSA50 using the builders thread on this forum. When I say low powered I used 25V rails instead of the normal 37V and adjusted the zeners and ascociate resistors around the VAS. This gave me 30W RMS per channel with a heat dissapation of about 140W ( I don't need lots of power and certainly don't want the heat)
I am now re-housing the amplifier in a different case with more room and fan cooling instead of passive cooling.
My questions
1) can I use seperate supplies for the PCB eg.37V whilst retaining the 25v supplies for the output stage?
2) If I can use another supply what VA transformer should I use and will one transformer be OK for both channels ( I still figure on using 2 for the output stage)
3) What problems am I liable to face.
4) will there be a noticable difference in sound quality to what I have had.
Hope I have not been too confusing.
Thanks for your help.

alibear 14th September 2012 07:56 AM

Any KSA boys ( or girls ) out there?

Nico Ras 14th September 2012 08:59 AM

Are you unsatisfied with the 30/140 watt and do you want to change to 50/225 watt. Or is it a question of needing something for idle hands. If it is the latter then rather leave it alone because you almost always end up breaking something that was working perfectly.

alibear 14th September 2012 11:38 AM

Hi Nico, Perhaps I haven't put my question very clearly.
I do not want to alter the output power I would just like to know if it would be better to supply the input / VAS / driver stages with 37 volt rails as per the original KSA50. At the moment they share the same 24 volt rails that supply the output stage.
I am re-building the amplifier into a bigger case and I find there is enough room for the additional components that would be needed to do this.
Thanks for your help

Nico Ras 14th September 2012 06:01 PM

Hi Alan,

in my opinion as well as experience running the front-end of a higher voltage, better still a regulated higher voltage results in far better performing amplifier (both audibly and measurably). I think that anyone who has practically done this would agree.

alibear 14th September 2012 07:32 PM

Thanks Nico, so to put it in a nut shell, leave the output stage running with 24volt rails and every thing else run at 37 volts as per the original design.
Would it be best to have a transformer and regulator for each channel ( input, VAS, driver ) or would a single transformer be OK. Would a shunt or would a series regulator be best? What sort of current would be required?
Hope there arn't too many questions
Many thanks

Nico Ras 14th September 2012 10:05 PM

A single smalish transformer should be fine, you do not draw much current here. I like making a CCS followed by a shunt regulator for each rail for each amp. I am thinking a simple two transistir CCS and a single transistor shunt. Others would just use a cap multiplier with a zener at the base.

AndrewT 15th September 2012 08:42 AM

I think a difference in rail voltage of (37-24) 13V is too much to be worthwhile.
A 5V to 7V difference will probably give all of the "drive" improvements that become available.

Use the 37Vdc and regulate it down to 28Vdc or maybe 30Vdc.

Do not use this regulated supply for the drivers. They can potentially demand a few amps from the supply in "overdrive" operation. You could run the drivers from the 37V supply or just leave them on the 24V supply.

alibear 15th September 2012 05:28 PM

Thanks Nico & Andrew T.
Perhaps I was wrong in thinking that it would be good to run everything at 37 volts except the output stage.
If I supply the input and VAS stages with 30 volt as suggested and run the pre-drivers, drivers and output stage at 24 volts, will I get a noticable improvement in performance over running everything at 24 volts.
Hope these questions arn't too dumb.

Nico Ras 15th September 2012 07:48 PM


In my experience very noticeably different. The reason for me saying so is that the power stage draws current from the power supply and with separate supplies does not modulate the power of the front end. Modulated power rail causes the sound to be smeared. If you would be willing to test what I have experienced and report your findings whether positive or negative in the thread below, would be a very important contribution

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