Improvements in electrical systems for reproducing recorded signals

摘要

894,528. Automatic speed control systems. AMPEX CORPORATION. June 22, 1960 [Aug. 11, 1959], No. 21909/60. Class 38 (4). In a magnetic recording and reproducing system, a signal indicating the speed of a rotating head assembly is derived from a photoelectric cell and applied to limiter 53, through phase-splitter 54, to a phase-sensing circuit 56. The signal from a control track on a magnetic tape is applied to limiter 57, thence to a second limiter 58, through phase-splitter 59, to the phase-sensing circuit 56 which provides an output signal to reactance tube 61. This tube controls the frequency of oscillation of a Wien bridge oscillator 63 whose output is passed through amplifier 64 and is applied to a capstan motor drive amplifier 37. The oscillator functions at a predetermined basic frequency which is slightly modified by a correction signal from the phase comparator. In this manner, the capstan is rotated during play-back in the same relationship to the rotating head assembly as it did during the recording process. The signal from the control track is also applied to voltage doubler circuit 66, thence to amplifier 67, and to relay-coil 68. In the absence of a control signal, the contact 69 is moved to earth the input to the reactance tube so that the oscillator operates at its basic frequency. This prevents hunting of the capstan motor and loss of tracking during reproduction. When the sliders of potentiometers 99, 100, are in the positions shown, the frequency of the oscillator is controlled by the reactance tube. Displacement of the sliders allows the speed of the capstan motor to be controlled manually for synchronizing the machine with other machines. The potentiometers each have a dwell position to which they are returned after the synchronizing operation.