Tone arm return systems for record player with eccentric spindle hole

Abstract

A first generator 1 produces a continuously increasing signal corresponding to the tone arm pick-up stylus position, and a second generator 2 produces a synchronizing signal comprising a pulse for each turntable rotation. The synchronizing pulses alternately trigger a pair of parallel sample and hold circuits 4a, 4b supplied with the position signal, whose differential output S is compared with a reference signal T. When the former exceeds the latter the tone arm is returned. Any cyclical variations in the position signal due to the eccentricity of the record spindle hole are self-cancelling during the differential comparison because their magnitudes are substantially the same when sampled during the same relative periods of the turntable rotation cycle. The high pitch of the lead-out groove at the end of the record play produces a large differential output signal, to thereby trigger the tone arm return. In a second embodiment a variable amplitude pulse generator is employed whose turntable revolution synchronized output pulses each have an amplitude corresponding to the instantaneous tone arm position. Such pulses thus serve the dual functions of providing synchronized gating signals and indicating the rotational position of the tone arm.