F for true balanced differential.

lemme see

F1 - bal in, bal out, truly dif. mode, can work as se/bal converter

F2 - pure SE

F3 - pure SE

F4 - pure SE

F5 - pure SE

F6 - pure SE

F7 - pure SE

F8 - pure SE

Aleph J - bal in, SE out, input differential, of course SE in is working

J2 - bal in, SE out, input differential, of course SE in is working

M2 - pure SE

SIT-1 - purest SE

SIT-2 - pure SE

SIT-3 - pure SE

well, damn, why I'm typing all that, it's plain visible at FIRST WATT PRODUCTS

silly ZM