Krell KSA 100 schematic, resistor value question

[millwood]

the emitter resistor for the VAS stage (121ohm) is pretty big, considering that JC2 has a 20ohm or so resistor there.

[Tube_Dude]

Originally posted by millwood
the emitter resistor for the VAS stage (121ohm) is pretty big, considering that JC2 has a 20ohm or so resistor there.

And the current in the VAS is 8,3 ma...

[Tube_Dude]

The unbiased electolitc capacitor in the emmiters of the LTP...is a strange feature...

Any comments??

[millwood]

Originally posted by Tube_Dude
The unbiased electolitc capacitor in the emmiters of the LTP...is a strange feature...

Any comments??

I think it is to reduce degeneration for a/c signals without causing excessive d/c offset. with the cap, the two 200r resistors are essentially tied together, thus no more emitter degeneration.

for a/c signal, the cap is open, thus each leg has a 200r resistor.

[millwood]

Originally posted by Tube_Dude



And the current in the VAS is 8,3 ma...

if this circuitry behaves like our simulation, the vas is likely running in the 1ma range.

maybe someone will have a service manual for the amp.

[UrSv]

Originally posted by K-amps
Based on the schematic. looks like 3 pairs of outputs. If it runs 100watts class-A into 8 ohms, i'd say the bias is as follows:

Total bias 2.5 amp per rail.
Bias per device 0.84 (x3 devices for each cycle of push pull) .
voltage across each emmitter resistor = 416.6mv.

This amp will dissipate 235 watts per channel at idle.

All this is based on the 100 watt class-A spec and the values on the schematic.

Chocoholic and Millwood, did I make you proud?

K-Amps

With regards to the 3 pairs of outputs I think it could easily be 4 pairs as the schematic clearly says x4 for the output transistors.

[Tube_Dude]

Originally posted by millwood



if this circuitry behaves like our simulation, the vas is likely running in the 1ma range.

maybe someone will have a service manual for the amp.

Not needed the service manual...if the simulation gives you 1mA...your simulation is flawed...

The current un the VAS is +-8,3 mA...

PS : How a 1 mA current can drive a follower that is not even a triple follower but only a double!???

[MikeW]

Has anyone built this amp?
How many output devices? Now I see the X4
How much bias? 2.5 amps per rail
How does it sound?
Is it worth doing a board for it?

Can it be scaled down so to +/- 40 volt rails?

Is anyone interested in boards if they are made?

[Tube_Dude]

Originally posted by millwood



I think it is to reduce degeneration for a/c signals without causing excessive d/c offset. with the cap, the two 200r resistors are essentially tied together, thus no more emitter degeneration.

Yes!

for a/c signal, the cap is open, thus each leg has a 200r resistor.

No..i think that what you mean is....for DC !!!

[millwood]

Originally posted by Tube_Dude


Not needed the service manual...if the simulation gives you 1mA...your simulation is flawed...

The current un the VAS is +-8,3 mA...

I thought it was settled on that other thread that for such a topology, you cannot calculate VAS and LTP current. Assuming that the current in the LTP legs is evenly split is falwed.

hopefully, the time and effort there were not wasted.