Patent GB-452803-A (GB)
Title: Improvements in or relating to the recording of sound or like oscillations on a carrier
IPC: G11B7/00
Filed: 1935-03-21
Abstract: 452,803. Recording sound and the like. NAAMLOOZE VENNOOTSCHAP PHILIPS' GLOEILAMPENFABRIEKEN, Emmasingel, Eindhoven, Holland. March 21, 1935, No. 8875. Convention date, March 26, 1934. [Class 40 (ii)] [See also Group XL] Relates to methods and apparatus for recording sound or like oscillations on a carrier, particularly for producing by mechanical means an optically-reproducible record. According to the invention, part of the energy supplied to the recorder is used for actuating a light-relay or light valve, which biasses one or more direct current circuits in such manner that their currents alter step by-step the position of the recording device relatively to the record carrier. An object of the invention is to vary the load on the chisel (in mechanical recording) in accordance with the amplitudes of the sound. A further object is the production of a record with reduced background noise. In the arrangement shown, the audio-frequency current, amplified at 25, is supplied to a coil 16 which vibrates an armature carrying a chisel 12, for recording the sound on a film 23. Part of the audio-current is rectified and, after smoothing if required, supplied through leads 104 to a mirror galvanometer 76. This reflects a thin flat beam of light from a lamp 78 on to one or other of a set of photo-electric cells 82, the particular cell being illuminated at any instant depending, in accordance with the amplitude of the sound, on the strength of the rectified current. The cathode of each cell is connected to the grid of one of a set of gas-filled discharge tubes 88, which are so inter-connected that only one of the tubes operates at a time. As soon as the grid voltage of the tube becomes, due to illumination of the corresponding photoelectric cell, of such a value that ignition or a given increase of the anode current occurs, the anode voltage of the tube previously in operation is reduced by reaction so that the tube becomes inoperative. For this purpose, the anodes of the tubes are connected through condensers. Each tube, when ignited, allows' the passage of a constant direct current, different for each. These currents are supplied through conductors 106, 8 to the coil 16, and so vary the mean position of the chisel in accordance with the sound volume. A diagram showing in detail the circuits employed in the whole installation is given. The rectification of part of the speech currents may be avoided by the use of an oscillograph coil for producing the movement of the light beam. In this case, the variations in the width of the light beam, dependent on the amplitudes of the speech currents, determine the selective operation of the photo-electric cells. Further modifications are described, in which a stepped screen is interposed between a source of light and one or more photo-electric cells. This arrangement may be used in conjunction with several discharge tubes, each associated with several photo-electric cells, as previously described ; or a single cell controlled by the beam modulated by the stepped screen may be connected in the grid circuit of a triode valve, the output of which controls the mean position of the cutter. Specifications 411,144 and 432,988 are referred to.