Input impedance is above 300,000 ohms and output impedance 1 ohm, in d-c amplifier for analog input channel.Q3 and Q4 provide gain and phase inversion for feedback through complementary emitter-follower Q5-Q6 to differential amplifier Q1-Q2.-N. Aron and C.Granger, Analog-To-Digital Converter Uses Transfluxors, Electronics,35:20, p 62-66.