Beyerdynamic mc930 SDC repair

[RuudNL]

IMHO V10 and surrounding components could have been omitted and C15 ad C16 could have been connected to the collector and the emitter of V7.
V1 functions as a 'switch' and places the 150 pf capacitor in parallel with the input (or not).
I suppose this method of 'soft switching' avoids loud 'thumps'.
R1 is responsible for the polarisation voltage on the capsule. FET bias is provided by R3, R4 and R5.
V4 / R6 are a current source.

 

[LevinGuitar]

Interesting! So the bias is determined at the gate rather than in the source in this kind of arrangements, like current Rode circuits and so...

Maybe C10 also provides a softer switch for the low cut pad?
Anyway this switches have a quite hard action and in order to engage them, the physical impact of the action is not so soft