Electronic apparatus comprising an audio amplifier providing shunt voltage regulation

Electronic apparatus comprising:

• A. a source of bias voltage having two output terminals, one common, said source having appreciable internal resistance and requiring voltage regulation,
• B. a push-pull audio output stage comprising:
• a first and a second output transistor of a first conductivity type, each connected in a base input configuration with the collector of said first output transistor being connected to the non-common terminal of said source, the emitter of said first output transistor being coupled to the collector of said second transistor, and the emitter of said second output transistor being returned to said common terminal, said output transistors having sufficient current capacity for shunt regulation of said source, the audio output of said output transistors being taken at their interconnection,
• C. a driver stage for said push-pull output stage, comprising:
• 1. a third transistor of said first conductivity type for driving both output transistors, connected in base input, emitter-follower configuration, the emitter of said third transistor being d.c. coupled to the base of said second output transistor,
• 2. a phase inverting intermediate driver for coupling the output from the emitter of said third transistor to the base of said first output transistor and comprising a fourth transistor,
• a. said fourth transistor being of said first conductivity type and having its base d.c. coupled to the emitter of said third transistor through a first resistance and the emitter common to parallel the input junctions of said fourth and second transitors to stabilize their current ratio, and
• D. output voltage regulating means coupled between said source output terminals comprising:
• 1. a voltage reference for sensing a deviation in bias voltage from a desired value,
• 2. means for producing an error current in response to said deviation, and
• 3. means for applying said error current to said first resistance to cause a change in base-emitter voltage in said second output transistor in response to said bias voltage, said change in base-emitter voltage altering said current ratio and changing the idling current of said second output transistor;
• and by virtue of said interconnection to the emitter of said first output transistor causing a corresponding change in idling current in said first output transistor, said idling current changes in said output transistors being in a sense to provide shunt regulation of said bias voltage.