PURPOSE: To prevent interference between the signal negative feedback and the DC negative feedback circuit which are perfectly isolated, by respectively setting the frequency characteristics independently.

CONSTITUTION: The differential pair npn transistors TrQ1, Q2 amplify positive half wave input with the collector resistor RL1 of TrQ1 and the junction FETQ6 constituting the common emitter current source. Similarly, the differential pair pnp TrQ3, Q4 amplify the negative half wave input. Further, drive is made by using driving TrQ7, Q8, output is made from the outputs TrQ9, Q10, the bases of TrQ2, Q4 are used as the negative feedback terminal of signal, and the signal negative feedback circuit 2 is connected. On the other hand, the gate of FETQ6 is used as the negative side terminal from DC to ultra-low region, DC feedback circuit 3 is connected. By completely isolating the both negative feedback circuits 2 and 3, the respective frequency characteristics are independently set to prevent mutual interference.