GB651432A - Improvements in or relating to electromagnetic pick-ups - Google Patents

Abstract

651,432. Gramophone pick-ups. ELECTRIC & MUSICAL INDUSTRIES, Ltd. April 8, 1948, No. 9828. [Class 40 (iv)] In a moving armature pick-up the armature is supported by a shaft which is mounted for oscillatory movement about its axis and which carries at one end a stylus arm resilient in directions substantially parallel to the axis of the shaft but having substantial stiffness in directions at right-angles thereto. The pick-up comprises a rectangular bar magnet 1 (Fig. 1), with a pair of L-shaped polepieces 2, 3 denning an air gap in which the armature 5 is mounted. The armature 5 (Fig. 4), is a lateral extension projecting from the shaft 8 which is supported in a vertical position by being clamped between a pair of metal plates 9, 10 (Figs. 1, 3), secured to the polepieces by screws 11, the pick-up coil 12 being clamped between the plate 9 and the polepieces. The plate 10 has a groove to accommodate the shaft 8 which is of circular cross-section and the end portions of the shaft are covered by short lengths of rubber or like tubing 14 (Fig. 4), to enable oscillation of the shaft to take place under the control of a stylus arm 15 fixed to its lower end. This arm which is substantially co-planar with the armature consists of a length of leaf-spring and is resilient in directions substantially parallel to the axis of the shaft but has substantial stiffness in directions at right-angles thereto. The sleeves 14 provide restoring forces for the shaft but if desired an additional spring may be provided for this purpose. The base plate 6 (Figs. 1, 3), may be made of non-magnetic material and the coverplate 7 of magnetic material in order to shield the magnetic system from a turn-table. To prevent damage to the stylus should the pickup be dropped on to a record the stylus arm projects through an aperture 18 in a spring arm 19 (Figs. 1, 3), secured to the cover-plate 7.