It's like a big opamp... jfet input ltp, followed by a bjt ltp for high gain, followed by a quite basic double emitter output stage.
I'm a bit puzzled because the gain stage is very good: good fast transistors, nice design, extra regulation. But the output stage is crude: it uses old, slow transistors and simply a zener for the output stage biasing. The slow output transistors probably don't help to compensate the whole thing. At the power required by headphones, they could have used the same small signal bjt and bd139-bd140 (or the like) for the output. In cfp fashion, it would have helped both linearity and thermal stability (see the ckIII).
Gain is 6 btw.