Abstract: An audio power amplifier can be operated in either class A, class B or class AB amplifier modes by selectively switching bias values set in a bias setting circuitry provided for a driver stage which drives the main power amplifier stage.

Abstract: A complementary push-pull amplifier comprising a pair of complementary transistors each of which is connected to a voltage source through a relatively large resistance and having the base biased with a voltage formed from the emitter-collector voltage of the transistor. Means for equalizing the amplitudes of second order distortion caused by the respective transistors is provided in a portion of the circuit other than the emitter circuit. The collector current is stabilized by the relatively large resistance connected to the collector and the asymmetry of the pair of transistors can be corrected by the amplitude equalizing means for cancellation of the second order distortion.

Abstract: A power amplifier with an automatic bias control circuit is disclosed. The amplifier includes two complementary Darlington pairs operating in a push-pull mode providing output power. A bias control network including a switching transistor is coupled to the base circuits of the Darlington pairs for controlling the bias current delivered to the pairs. The transistor is switched on and off by a detecting circuit which senses the presence of input signals applied to the amplifier. The bias control network operates to minimize power consumption by the Darlington pairs when no input signal is present and to raise the bias level of the Darlington pairs without distortion in the output signal when an input is applied to the amplifier.

Abstract: An audio- or low-frequency power amplifier comprises a pair of output transistors which are opposite in a conduction type to each other and connected in a complementary push-pull circuit configuration in which an impedance element is connected between the bases of the paired output transistors whose bases are adapted to be applied with an input signal while the output signal of the amplifier is derived from the coupled emitters of the output transistors. The amplifier further includes a current stabilizer transistor having a base-emitter junction across which a fixed bias voltage is applied and a collector, the current from which is supplied to the impedance element thereby to provide a bias voltage for the paired output transistors. A first resistor is connected between the emitter of the current stabilizer transistor and one electrode or pole of a first d.c. power source while a second resistor is connected between the emitter of the current stabilizer transistor and the other pole of the d.c.

Abstract: A Class AB linear power amplifier circuit is connected in a balanced bridge configuration for increasing the fidelity and power output from stereophonic sound systems, such as used primarily in automotive vehicles, the circuitry consisting of a series of NPN transistors and PNP transistors, with bias for the transistors provided by a power source, a series of resistors and thermistors, an optional input overload protection circuit, with the transistors further being matched and balanced so as to effectively double or quadruple output power as would be available from a single ended configuration, so that the amplifier circuitry operates in a Class A mode to eliminate any crossover distortion.