Patent GB-310762-A (GB)
Title: Improvements in or relating to gramophone and the like reproducing devices and circuits therefor
IPC: H04R19/06
Filed: 1927-12-31
Abstract: 310,762. Gill, E. W. B. Dec. 31, 1927. Condenser telephones and other electrostatic instruments; gramophone pick-ups.-An electrostatic gramophone pick-up comprises a pair of conductive plates separated by a thin dielectric spacing and vibration damping material constituted by rubber or similar resilient material and a stylus carrier or equivalent device 'operatively connected to one of the plates whereby it is flexed or pivotally moved by the acoustic frequency movements of the stylus. The stylus carrier is preferably so arranged relatively to the moving plate that the weight of the reproducer is carried substantially wholly directly through the stylus. The pick-up is connected in series in a closed circuit with a source of potential and a high resistance, the ends of the resistance being connected to the grid and cathode respectively of an amplifying thermionic valve. The device shown in Figs. 1 and 2 comprises a rigid brass plate 1 fixed to a massive fitting 3 adapted to be attached to a gramophone tone arm and a thin metal plate 2 to which the stylus carrier 7 is attached. The plates are separated by pieces 4, 5 of rubber &c., the pieces 5 being considerably thicker than the piece 4 which is of rounded section so as to provide for a pivot-like action of the plate 2. Pieces 8, 9 of damping rubber &c. are provided on, the underside of plate 2, the device being held together at the end at which the rubber 8 is situate by means of clamping members 10, 11 which are held to the plate 1 by screws 12, 13 and carry clamping screws 14, 15 for exerting an adjustable pressure on rubber 8 through a brass sheet 10. A rubber band (not shown) holds the device together at the other end. Fig. 3 shows a modified construction in which the movable plat 2. stiffened by a perpendicularly arranged plate 20. is mounted on the stylus carirer 7 whidh is pivotally mounted by means of a shaft 17 carried by plates 18 attached to an ebonite &c. plate 19 The fixed plate 1 is rigidly attached at one end to the plate 19 by bolts 21, its' other end being adjustable towards or away from the plate 2 by a screw 22. The plates are separated by a layer 23 of thin rubber &c. The degree of damping can be adjusted by means of a tensioned rubber &c. cord 24 extending between a notch 25 in plate 20 and a hook 26 on a screw 27. The fitting 3 is carried by a plate 28 secured to plate 19 with an interposed sheet 30 of rubber &c. Fig. 5 shows a further modification in which the fitting 3 is formed with a flat part circular plate 1 and carries a thin aluminium strip 2 separated therefrom by a thin strip of rubber 23. On the outer side of the strip 2 are a second strip of rubber 32, an ebonite plate 35 and an ebonite clamping piece 36, the whole being secured to the plate 1 by screws 37. The lower end 2<a> of the strip 2 is secured in a slot 7a in the upper end of the stylus carrier 7. In a modification of this construction, the plate 1 is formed with a circular groove on the face towards the strip 2 and a rubber ring, preferably of rectangular section, is located in the groove and replaces the rubber strip 23. A thin layer of oiled silk is held in position between the plate 1 and strip 2. The third Provisional Specification states that th strip 23 shown in Fig. 3 may be of oiled silk.