Is this schematic wrong?

[red]

I was planing to use MJE 350/340 instead of the BD's.They are indeed a bit hot...
(I like the way it sounds but has a little to much treble for my taste.I will probably build a preamplifier too.)

 

[Diode]

Hey Red,

I don't understand the 22K ohm resistor from base to ground on the drivers. I'd also hook it to a scope and look for oscillation. A 100pF cap from the base to its rail will help with oscillation, so I'm told. I don't know if it affects the sound though.

Good luck,

Chris

 

[Rambi]

I don't understand the 22K ohm resistor from base to ground on the drivers.

The way I understand it (but I'm sure someone will correct me if I'm wrong 😉 ):

The 22 kOhm resistors are connected to the collectors of the VASes (BD140/139).
Amplification by the VAS stage is determined by the impedances on the emitter (390 Ohm resistors) and the collector (the output stage basically).
The load the output stage puts on the VAS is determined by the load on the amplifier and is therefore 'unpredictable' (not well defined anyway, remember also that speaker impedance varies with frequency)

By adding the 22kOhm resistors the influence of the amplifier load on the impedance 'seen' by the VAS is minimized; making the operation of the VAS (and therefore of the whole amplifier) more predictable and easier to stabilize (stability less dependant on the load of the speaker).

Hope this helps,

Remco