Krell KSA 50 pcb - Page 836

alibear · 8th December 2011, 07:18 AM

Hi all, thanks for the swift replies.
ANDREW T. I am using jan Du ponts PCB's and circuit shown in post 63,there is no relay shown and I am not using one, I don't know if original KSA50 had any protection.

MOOLY, A WAYNE, PINKMOUSE. the power supply for each channel is 2x 18volt secondaries 2 bridge rectifiers 2 47000uf 2 1ohm 2 47000uF in CRC for each rail. I wanted to run with approx 24v rails instead of the 37v to give me a KSA25.I do not require lots of output power and certainly did not want to dissapate too much heat.
Because of the lower voltage Jan;s circuit was modified thus:
R108 and R109 were reduced from 1.6K to 1.3K
R110 and R 111 were reduced from 9.1K to 4.7K
ZD101 and ZD102 were reduced from 27v to 13v zeners.
These mods were to retain the correct current through the LTP
The other thing was that the current limiting circuit for the output was ommitted.
C102 and C103 are 1000uF as per drawing.
No other alterations were carried out on the PCB.
As I said, when the amp was playing it sounded sweet from both channels.
Both channels set up easily and were stable.
I can,t help but think I have done something daft but don't know what.
Thanks
Alan

john65b · 19th February 2012, 01:33 PM

Hey all,

Off-Topic, but has anyone considered "X'ing" a KSA-50 Clone?

I have been thinking of this lately and I have the component parts / PCB / tranny / heatsinks for such an animal...but I believe its a little more involved than what I think I need to do -

What I think I need to do: (go easy on me please):
Balanced input and neg signal / ground to one KSA-50, and the pos signal / ground to the other amp (looks to be a simple bridged config). Speaker outs not referenced to ground.

Thought I would throw this out to see if anyone would further consider this? Bad Idea?

Roosevelt Jopie · 27th February 2012, 08:43 AM

I have a question about the use of the 2SA968/2SC2238 pair for Q5 (or Q105) and Q7 (or Q106). Also replaced by MPSA42/92 and MJE15033/32 in later KSA50 clone designs.

Both transistors are biased at appx. 0.5mA. This wil achieve very low loading of the differential input stage. But with this low collector current the transition frequency (Ft) drops to about 10 MHz, while the current gain linearity is not at its best. The actual dissipation is only 25mW, these transistors are rated for 20 Watts.

I could imagine that its high internal capacitance could act as a lag compensation or the 3.3k resistor value simply is not correct. So what is the secret behind the use of the 2SA968/2SC2238 here?

alibear · 19th March 2012, 07:39 PM

Hi all, sorry for the long delay in getting back. Problem was very simple ( like me ) I had somehow omitted to ground the input ground on the PCB's, did this and amplifiers set up and worked fine.
I think I have become obsessed with this amplifier, it was passivly cooled and I felt that the other components within the chassis were running too warm, transformers, filter caps etc. So i have decided to now re-build using fan cooling with a completely different layout.Progress will be quite slow as not much spare time, but if anyone is interested I will post some pics during the build.
Off to the doctors now to see if there are any pills for Krell paranoya.
Alan.

Mooly · 19th March 2012, 07:47 PM

Thanks for the update. Pleased it's all sorted.

VT67 · 19th March 2012, 07:49 PM

Of course we want pictures!

Regards

19th February 2012, 01:33 PM	#8352
john65b diyAudio Member Join Date: Jan 2005 Location: Chicago	Hey all, Off-Topic, but has anyone considered "X'ing" a KSA-50 Clone? I have been thinking of this lately and I have the component parts / PCB / tranny / heatsinks for such an animal...but I believe its a little more involved than what I think I need to do - What I think I need to do: (go easy on me please): Balanced input and neg signal / ground to one KSA-50, and the pos signal / ground to the other amp (looks to be a simple bridged config). Speaker outs not referenced to ground. Thought I would throw this out to see if anyone would further consider this? Bad Idea? __________________ "I speak Spanish to God, Italian to Women, French to Men, and German to my Horse" - Charles V

19th March 2012, 07:47 PM	#8355
Mooly diyAudio Member Join Date: Sep 2007	Thanks for the update. Pleased it's all sorted. __________________ ------------------------------------------------------- *A simulation free zone.* *Design it, build it, test it.*

19th March 2012, 07:49 PM	#8356
VT67 diyAudio Member Join Date: Jun 2004 Location: Belgium	Of course we want pictures! Regards __________________ VBITNGC Krell KSA-50 Krell KSA-100MkII

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8th December 2011, 07:18 AM	#8351
alibear diyAudio Member Join Date: Feb 2009 Location: Somerset	Hi all, thanks for the swift replies. ANDREW T. I am using jan Du ponts PCB's and circuit shown in post 63,there is no relay shown and I am not using one, I don't know if original KSA50 had any protection. MOOLY, A WAYNE, PINKMOUSE. the power supply for each channel is 2x 18volt secondaries 2 bridge rectifiers 2 47000uf 2 1ohm 2 47000uF in CRC for each rail. I wanted to run with approx 24v rails instead of the 37v to give me a KSA25.I do not require lots of output power and certainly did not want to dissapate too much heat. Because of the lower voltage Jan;s circuit was modified thus: R108 and R109 were reduced from 1.6K to 1.3K R110 and R 111 were reduced from 9.1K to 4.7K ZD101 and ZD102 were reduced from 27v to 13v zeners. These mods were to retain the correct current through the LTP The other thing was that the current limiting circuit for the output was ommitted. C102 and C103 are 1000uF as per drawing. No other alterations were carried out on the PCB. As I said, when the amp was playing it sounded sweet from both channels. Both channels set up easily and were stable. I can,t help but think I have done something daft but don't know what. Thanks Alan

27th February 2012, 08:43 AM	#8353
Roosevelt Jopie diyAudio Member Join Date: Jan 2012	I have a question about the use of the 2SA968/2SC2238 pair for Q5 (or Q105) and Q7 (or Q106). Also replaced by MPSA42/92 and MJE15033/32 in later KSA50 clone designs. Both transistors are biased at appx. 0.5mA. This wil achieve very low loading of the differential input stage. But with this low collector current the transition frequency (Ft) drops to about 10 MHz, while the current gain linearity is not at its best. The actual dissipation is only 25mW, these transistors are rated for 20 Watts. I could imagine that its high internal capacitance could act as a lag compensation or the 3.3k resistor value simply is not correct. So what is the secret behind the use of the 2SA968/2SC2238 here?

19th March 2012, 07:39 PM	#8354
alibear diyAudio Member Join Date: Feb 2009 Location: Somerset	Hi all, sorry for the long delay in getting back. Problem was very simple ( like me ) I had somehow omitted to ground the input ground on the PCB's, did this and amplifiers set up and worked fine. I think I have become obsessed with this amplifier, it was passivly cooled and I felt that the other components within the chassis were running too warm, transformers, filter caps etc. So i have decided to now re-build using fan cooling with a completely different layout.Progress will be quite slow as not much spare time, but if anyone is interested I will post some pics during the build. Off to the doctors now to see if there are any pills for Krell paranoya. Alan.

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