Pick=up and control device for sound record plates - has four pole sync. motor for driving and has control unit using photocoupler responsive to tone arm angle

摘要

The control system relates to a sound record disc with a spiral groove track (10) driven by an endless belt (14) from the spindle of an electric motor (12). A tone arm (16) rests on the upper face of the disc, and moves through an angle (alpha) during the progress of the recording or playback. The tone arm works in conjunction with an angular position sensor (36) which supplies a function signal, f(alpha) to a transistor chopper circuit (20) incorporating a thyristor (26), and a transformer (28), the primary of which is fed by 200 V a.C. mains through a rectifier (22) and a filter (24). The output frequency is determined by the thyristor circuit which is determined by the thyristor circuit which is connected to the motor. In one embodiment, the frequency is controlled by a crystal oscillator.