Please explain this circuit to me

[kuiy11]

Circuit operation

I'm late in this conversation, but I was just a little amused with the diode in parallel with the darlington pair. With the rest of the circuit I see now.

 

[audioguru]

I'm late in this conversation, but I was just a little amused with the diode in parallel with the darlington pair. With the rest of the circuit I see now.

There are two darlington pairs in series and they need 4 diodes to bias them, not just two diodes. The diodes are not in parallel with the darlingtons, they are supposed to provide the bases with enough voltage so that the amplifier does not have crossover distortion. The diodes have the same thermal/current response as the transistors so the diodes should be fastened to the transistors' heatsink.