Krell KMA 100

[2SA991]

Hello
I get a pair KMA 100. 1 amp works the other not.Sombody steals some parts
from the board.The board is different to the KSA 100 MK II boards.
No FET,s in the second stage .I have to change the driver transistors.Are they the same than in the KSA.

Regards
Piet

 

[Ketje]

The two are very different.In the KSA100 the final transistors are with the collectors on the power supply, the others have the emitters at the power.
Therefore the drivers get the full powervoltage + to - in the KSA100.The other circuits only half of that.
You could try the BD937(NPN) and BD938(PNP).
Mona

 

[2SA991]

Hello
I think you are wrong .In the ksa100 the voltage for the input stage is regulated
by the two 37v zehner diodes.the drivers with the same voltage like the output
transistors. On the kma 100 board you did not find the diodes and the voltage
comes from the extern regulation board. The drivers have the same rail lik ,the output transistors .The driver emitter resistors in the KSA rates 75 Ohm in my kma 43 ohm.

Regards

 

[Ketje]

Possible, the schematics i have are bad copy's of what is supposed to be Krell.
If the construction is with collectors on the supply's the driver sees the sum of both pos and neg supply voltage.That 's to much for transistors i suggested.
BD941(npn) and BD942(pnp) are fot a (much) higher voltage.
Mona