Patent GB-1013481-A (GB)
Title: Phonograph recording and playback apparatus
IPC: G11B3/00
Filed: 1963-07-01
Abstract: 1,013,481. Phonograph recording and playback circuits. RADIO CORPORATION OF AMERICA. July 1, 1963 [July 24, 1962], No. 26071/63. Headings H4J and H4R. In the recording or playback of phonograph records, tracing distortion is reduced by apparatus which produces distortion which complements the tracing distortion. The apparatus comprises a delay means coupled to an input circuit for receiving the signals to be recorded or played back, means for controlling the amount of delay exhibited by said delay means as a function of the rate of change of signal applied to the input circuit, and means coupling the delay means to an output circuit. The delay means comprises a delay line including series connected inductors 35-40 (Fig. 5) and tap points 90-96 which receive input signals from terminals 32. Gating transistors 53-59 each have their base electrodes connected to a different tap point 90-96. A source of operating potential and an impedance 62 are connected in series between the emitter and collector electrodes. Forward bias is provided between the base and emitter electrodes of transistor 56 and progressively less forward bias is provided between the base and emitter electrodes of transistors 55, 54, 53 and 57, 58, 59, i.e. in each direction from transistor 56. The minimum forward bias at any given point is greater than the maximum signal voltage. In recording a sine wave (Fig. 3) as a hill-and-dale cut the maximum negative voltage has zero rate of change of voltage and the signal is passed by transistor 56. As the signal begins to go positive, the record cutter cuts deeper into the record and the signal is successively passed by transistors 55, 54, 53 and this causes the signal at the output terminals to be successively advanced. As the signal approaches its positive peak the signal is passed successively by transistors 54, 55 to provide successively less advance and at the positive peak (deepest portion of groove) transistor 56 is operative. As the signal then goes negative it is passed successively by transistors 57, 58, 59 and back through transistors 58, 57, 56 to provide an increasing and then decreasing amount of delay. The amount of delay required is a function of record groove velocity relative to the stylus, which is greater near the record periphery than the centre. Signals to be recorded from a source 100 (Fig. 7) are fed through complementary distorter 102 (Fig. 5) coupled to a record cutter head 104 of a lathe 106. Lathe 106 is mechanically coupled to distorter 102 to increase the delay characteristic of distorter 102 as the cutter head 104 moves towards the record centre. The delay characteristic is altered by adjusting the values of shunt capacitors 41-46 by means of ganged switches 47-52. Alternatively the shunt capacitors may be continuously variable. Terminating resistor 83 is also ganged to switches 47-52 and is continuously variable. Alternatively a plurality of terminating resistors may be selectively switched. Displacement error of the stylus due to the varying vertical distance between the point of contact of the stylus with the groove and the centre of curvature of the stylus is compensated for by appropriate choice of D.C. bias voltage at the taps 90-96. In recording 45-45 stereophonic records two " complementary distorters " are used, one in each channel (Fig. 4, not shown). Gramophone playback apparatus has a complementary distorter 114 (Fig. 8) analogous to that of Fig. 5, for playing back records which have not been recorded with a complementary distorter. Distorter 114 is by-passed by switch 120 when records recorded with complementary distortion apparatus are played back.