Balanced STAX amplifier "Eris 6V6/PP" (FSDD)

During development of cheap Stax amplifier, got a idea about hi-end symmetrical model. 

Sort of cheaper version of WooAudio WES (5000$)

The components selected to best linearity and low distortion.
Endstage can give ~325Vrms, choke max 390Vrms. That's enough to damage ears, and maybe destroy the headphones.
Input full sensitivity is <1Vrms; for 100dB out it should be ~0,2Vrms.
For example to decrease input sensitivity,  different input transformer should be used (LL1922 8:1+1 or  4:1+1)
STAX headphone amplifierDue to lower demands of Stax, and  PP mode; stages run in narrow ranges of working points.
Therefore very small distortion is made, also no feedback used here. (bonus)
Second harmonic is canceled due to  PP mode, the 3rd is about 0.05%, the 4th is ~0,003%.
Inductors with a mid tap, is good way to improve symmetry of PP stages and distortion.
800H is a huge number, about XL = 5megohms @ 1kHz .. (This gives horizontal loadline => very low distortion)
Next upgrade would be amorphous core or even a silver windings model (~2000€/choke)..
Lundahl does not make PP chokes, therefore a 5 mA model used.