Running the KSA-100 in Class A/AB?

[Jan Dupont]

As a great fan of amps using symmetrical circuits, I wonder if there was some one out there who have tried to convert the KSA-100 into Class A/AB mode? Considering the huge idle current (rather expensive these days) and the amount of heat (no use in heating up the living room in the summertime) this amplifier produces, a Class A/AB version might be in place.

I’ve haven’t seen the schematic of the Mk.II using variable biasing, however I’m more into the pure and simple design of the original KSA-100 and the fact that there are no caps in the signal path and no FET’s (sorry… do not like FET’s).

Anybody who has suggestions on how to convert this amp or having schematics of similar amps running in Class A/AB??

By the way….. For you having the QUAD 33 or 44 preamps
I have made a modified one to operate from DC to 300 kHz with an amazing listening result.

 

[Tube_Dude]

The hot amp...

Anybody who has suggestions on how to convert this amp or having schematics of similar amps running in Class A/AB??

Why not only to reduce the bias current??...say to100 mA for device!!!

regards

 

[Elso Kwak]

As a great fan of amps using symmetrical circuits, I wonder if there was some one out there who have tried to convert the KSA-100 into Class A/AB mode? Considering the huge idle current (rather expensive these days) and the amount of heat (no use in heating up the living room in the summertime) this amplifier produces, a Class A/AB version might be in place.

I’ve haven’t seen the schematic of the Mk.II using variable biasing, however I’m more into the pure and simple design of the original KSA-100 and the fact that there are no caps in the signal path and no FET’s (sorry… do not like FET’s).

Anybody who has suggestions on how to convert this amp or having schematics of similar amps running in Class A/AB??

By the way….. For you having the QUAD 33 or 44 preamps
I have made a modified one to operate from DC to 300 kHz with an amazing listening result.

Hi Jan,
The Gas Son of Ampzilla has a very similar schematic and is class AB.
http://home.kimo.com.tw/skychutw/ampzilla/index.html
Do you hace accress to thre Krell schematic with FET's ?
That would be most appreciated!

 

[KaLok]

Hi Jan,

You have KSA100II schematic? Could you email a copy for my reference?
And I have Quad Pre 34&44, How to modifiy it?Pls give me advice

Regards

 

[Jan Dupont]

Hey and thanks for joining this thread.

Tupe_Dude: I have thought of that, but I can´t seem to
figure out the correct resistor values..
Do you have any suggestions??

Elso Kwak: I have the schematiscs of the GAS amps (very nice
by the way). Perhaps I should take another look
at those
Sorry... have no schematics of Krell with FET's

Kalok: Sorry I do not have the schematic of the MKII
Regarding the QUAD modification, I will soon make
a list of modifications and email it to you.

 

[Tube_Dude]

A colder KSA100...

Tupe_Dude: I have thought of that, but I can´t seem to
figure out the correct resistor values..
Do you have any suggestions??

You can adjust the 5k pot that adjust the bias current ...if the variation is not enough for your desired value of bias...change the 4,7 K resistor for a small value or put a resistor in series with pot...

See the Bias detail in post #36 of the thread:



http://www.diyaudio.com/forums/show...erpage=15&highlight=Krell KSA100&pagenumber=3

 

[Jan Dupont]

Tube_Dude:
Thanks Jorge… It’s not because I think I am stupid, however I have had some bad results earlier by only adjusting the bias and not replace the resistors in the bias circuit, so therefore I was interested if somebody has tried this on the KSA-100 before me……..

By the way… Changing the input transistors to newer types makes a hell of a difference..

 

[fmak]

As a great fan of amps using symmetrical circuits, I wonder if there was some one out there who have tried to convert the KSA-100 into Class A/AB mode?
---------------------------------------
Seems to me you may be loosing out on sonics by doing so. Every amp I have sounds better in Class A than Class AB. Why not install a switched bias facility and you can cpmpare.

I cannot understand why manufacturers should bias their amps below 1 or 2 W dissipation. Cool sounding amps perk up if you raise the bias to 5 times that without fear of overheating.

 

[KaLok]

Jan,
Thanks a lot! I will wait your list for modify Quad preamp.
Regards

 

[Jan Dupont]

fmak:
Thanks, but I am not so worried about loosing out the sonics, because it is my opinion that the most important key to a good sound is in the circuit design followed by the selection of components and then the bias….
Each design has it own “sound” or “soul”, and when you have found the right design and components for you, then you can mingle with the bias to see if this make any differences.
Other key factors is to keep the bias 100% stable under all conditions and avoid caps when possible

Comments anyone ?????

Please note that I will be on Ester Holiday from the 16th to the 21nd , and will not be able to respond in the meantime, but please keep the comments coming.