GB857643A - Improvements in push-pull power amplifier - Google Patents

Abstract

857,643. Transistor amplifier circuits. GENERAL ELECTRIC CO. Aug. 18, 1959 [Aug. 20, 1958], No. 28177/59. Class 40(6). A transistor amplifier comprises a first transsistor having its collector coupled to one supply terminal and its emitter coupled to the output terminal and to the collector of a second transistor having its emitter connected to the other supply terminal, the input signal being applied to the base of the first transistor while the base of the second transistor receives a signal from the collector of the first by way of a third transistor such that the first and second transistors supply an output signal in aiding relation to the load. In Fig. 2 the input signal is applied to the base of a transistor 62, the collector of which feeds a pair of emitter follower transistors 116 and 216 having the output emitter coupled through a capacitor 46<SP>1</SP> to a loudspeaker load 70. A signal derived from a small resistor 22<SP>1</SP> in the collector circuit of transistors 116 and 216 is applied through a common base transistor 20<SP>1</SP> circuit of complementary type to a pair of emitter follower transistors 118, 218, the output of which is coupled to the load in push-pull fashion with respect to transistors 116 and 216. The circuit through transistor 20<SP>1</SP> provides negative feedback for signal frequencies and also serves to stabilize the D. C. operating conditions. In addition, the base circuit of transistor 20<SP>1</SP> feeds any hum which exists in the supply source into the circuit in anti-phase to that flowing directly into the output stage. Negative feedback is provided from the loudspeaker to the input transistor through a network 84, 82. Resistances may be connected between the emitters of transistors 116, 118 and ground if necessary.