Balanced input phonograph preamplifier circuit

摘要

A balanced input phonograph preamplifier circuit according to the present invention incorporates a matched differential pair of transistors having a gain control system therefor and having a load matched to standard phonograph cartridge output characteristics by means of a 47,000 ohm resistor and a capacitor that is designed for the particular cartridge involved. A differential voltage amplifier is defined by the matched differential pair of transistors functioning in conjunction with a differential amplifier which is in the form of an operational amplifier functioning in the differential mode. The output signal of the differential voltage amplifier system is processed by a deemphasis network incorporating a voltage amplifier and a current amplifier that are bridged by a feedback loop that is designed specific to the equalization curve of the Record Industry Association of America. Each channel of a stereo phonographic system will incorporate a differential voltage amplifier circuit and a deemphasis network that may be substantially identical.