Plessey Handel Und Investments A.g.

Ian W Buckner

John P Wren

An impulse noise detector, for use in impulse noise suppressor circuits which are used for suppressing scratch noises in disc record players, comprises a rectifier operable on an applied signal to provide a rectified signal, a smoothing circuit for smoothing the rectified signal, a pair of delay and invert circuits operable on the smoothed signal for affording a corresponding plurality of time delayed signals, and a combiner for selectively combining the time delayed signals to afford an output which is indicative of the presence, in the applied signal, of impulse noise.

Noise detector employing plural delay circuits

Electrical equipment for controlling an electric motor for the horizontal movement of the pickup member of a disc-record gramophone towards and away from the center of the gramophone turntable comprises position-selector means which, when set to any one of a number of predetermined positions of the pickup member, start the motor and emit a normally constant speed-reference signal controlling the motor speed and, upon receipt of a position-identifying signal from the selected position, cause the motor to be de-energised, thus terminating the motor-driven movement of the pick-up member, individual position-detector means, each so constructed as to perform the dual function of emitting such position-identifying signal and of varying the normally constant reference signal in accordance with the residual distance of the pick-up member from the accurate location of the selected position, thereby varying the motor speed so that the position-detector means work, in conjunction with the motor, as an approach servo.

Electrical control system for the movement of the pickup arm of a

A frequency-comparing device is arranged when in its no-output condition to respond to a pulse from a first one of two inputs by supplying a predetermined one of the two outputs until a pulse of another sequence arrives to terminate this output, whereafter the pulse next arriving will restore the same output if that pulse comes from the first input whereas if that pulse is one of the second input it will initiate the other output. Assuming that the pulse sequence from the first input has a frequency proportional to the speed of a motor unit and the pulse sequence from the second input consists of time pulses produced for example by a reference oscillator and that the output initiated by the arrival of a pulse from the first input is used as a drive-low input for the speed regulation unit of the motor while the other output constitutes a drive-high input for the same unit and that furthermore the pulse frequency derived from the motor speed is arranged to be equal to that derived from the reference oscillator when the motor runs at its desired speed, it will be found that when the motor speed is higher than the desired speed two pulses from the first input will from time to time occur within the interval between two consecutive pulses from the second input.

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Lea, Nr. Malmesbury, United Kingdom

Ian W Buckner