Bipolar single power amplifier (Kanzen
This amplifier work like this. First stage FET convert input signal to modulated current.
Final stage multiply this by hFE, and substract DC part. NFB make this amplification
In an another point of view four of N channel J-FETs(2SK117) construct infrastructure
of DC power amplifier.
Notice : "Kanzen" means "perfect"
The reason why Kanzen amp is
1 There exist power devices of which hHF is very flat to collector current.
example:2SA1962 used at Accuphase P1000
This indicates that amplification is
linear as long as the first stage is linear.
But I think NFB is necessary.
2 Heat compensation is not necessary, because idle current is independent
of Vbe. This makes circuit very simple.