Abstract: A power amplifier is constituted by a complementary pair of one N channel and one P channel unsaturated junction type FET's constructing a single ended pushpull circuit, the N channel FET having a drain connected to the positive terminal of a first dc power source of a predetermined voltage and a source connected via a load to a ground potential, and the P channel FET having a drain connected to the negative terminal of the first dc power source and a source connected via the load to the ground potential.

Abstract: A power amplifier stage for an audio amplifier is constituted by a complementary pair of one N channel and one P channel unsaturated function FETs forming a single ended pushpull circuit. The stage is energized by a first d.c. power source. The gate potentials of the FETs are controlled by a series of control type constant voltage source comprising a pair of complementary series connected control transistors energized by a second d.c. power source which varies at the same rate as the first d.c. power source. A comparison circuit including a second pair of complementary transistors is connected to a d.c. reference voltage which varies to a smaller level than the first and second d.c. power sources in order to provide a constant quiescent current flowing in the drain circuits of the FETs even if the first and second d.c. voltage levels fluctuate.