Low-frequency power amplifier

Claim 1

A power amplifier comprising: an amplification network with several cascaded transistor stages including a first stage and a final stage, said first stage having a noninverting input terminal and an inverting input terminal; an energizing circuit for said network including a supply terminal and a ground terminal connectable across a source of direct current; a first power transistor and a second power transistor in said final stage connected between said supply terminal and said ground terminal, said power transistors being respectively provided with a collector and an emitter jointly connected to an output terminal, said power transistors having input circuits connected to said first stage; a feedback resistor inserted between said output terminal and said inverting input terminal; a first resistance substantially smaller than the magnitude of said feedback resistor connected to said output terminal; a second resistance substantially smaller than said first resistance connected to said ground terminal and forming a junction with said first resistance; a capacitor inserted between said inverting input terminal and said junction for substantially compensating the effect of supply-voltage fluctuations upon the voltage of said output terminal; and a voltage-stabilizing circuit with a pair of twin transistors having interconnected bases and grounded emitters, one of said twin transistors having a collector tied to said inverting input terminal, the other of said twin transistors having a collector connected to said supply terminal via a direct-current path independent of said input circuits including a further resistor of a magnitude substantially exceeding said first resistance.