GB310284A - Improvements in and relating to apparatus for the electrical reproduction of sound - Google Patents

Abstract

310,284. British Thomson-Houston Co., Ltd., (Assignees of Kendall, J. M.). April 21, 1928, [Convention date]. Gramophone pick-ups; magnetic instruments. -In a sound-reproducer, such as a gramophone pick - up, the vibrating armature is at one end mechanicallv coupled to a resilient member subjected to substantially no compressive and frictional force. The armature is preferably pivoted near its other end between two pole-pieces, and surrounded by a low impedance coil. The armature 18, Fig. 2, is flattened at its upper end and provided with a pivot 19, surrounded by resilient bushings 20 clamped between the lower extensions 16, 17 of the pole pieces 11, 12 of the permanent magnet 10. At its lower end the armature may carry a stylus clamped by screw 21, while the upper flattened portion engages a notch in a resilient block 24 of rubber or the like, resting on ledges 40 at the top of the polepiece extensions 14, 15 and clamped thereto by an adjustable plate 25 and screws 26. The armature moves freely through a small distance compared with the dimensions of the resilient block 24 in the direction of travel. A coil 13, of low impedance, placed between the upper and lower extensions of the pole-pieces, surrounds the armature and is connected through a lowresistance volume control potentiometer, Fig. 3 (not shown) and step-up transformer to the output terminals. The armature has a low moment of inertia. Specifications 260,148 and 300,115 are referred to.