GB1367651A - Stereophonic phonograph pickups - Google Patents

Abstract

1367651 Stereophonic pickups W O STANTON 3 Sept 1971 [7 Dec 1970] 41299/71 Heading H4J A stereophonic pickup of the variable reluctance type comprises a circular array of three polepieces 40, 42, 68 (Fig. 3) which define a common space surrounding one end 108 (Fig. 4) of an armature 96 pivotally mounted at its other end 106. A cartridge body consists of two interfitting parts 16, 20 (Fig. 3) and two intermediate parts 18, 19 which serve as bobbins. Such parts are all formed of polystyrene and are moulded with interlocking portions, e.g. tongues and grooves 72 and 70, 76, 74. A magnetic circuit element 22 comprises a base 24, two core legs 26, 28, one for each channel, and a third leg 30 common to both channels. Polepiece members 36 and 38 abut the legs 26 and 28 respectively, within apertures 58 and 60 in the bobbins 18 and 19. The polepieces 40 and 42 are extensions of the polepiece members 36 and 38 and the polepiece 68 is an extension of the leg 30. The element 22 and polepiece members 36 and 38 are of high permeability material. Coils 46, 48 are wound on the bobbins 18, 19 and their outputs are connected to terminal pins 50a, 50b, 50c and 50d. Pins 50b and 50c are joined by a capacitor 52 to reduce cross talk. The pins 50a and 50d are earthed and connected to a shielding casing 11 of high permeability material. A single turn strap 53 of copper is provided about polepiece members 36, 38 and acts as an inductance coupling the magnetic circuits of the two channels to reduce cross talk and as an earth connection from the polepiece members 36, 38 to the casing 11. The pins 50a, 50b, 50c and 50d pass through holes in the body part 16. The moving armature 96 is a high permeability tube within a non-metallic tubular casing 98 of non- magnetic material. A stylus 100 is connected to armature 96 by a support tube 102. A rubber collar 104 on the end 106 of the armature 96 provides a pivot so hat this end of the armature 96, when the stylus vibrates, is substantially stationary relative to a permanent magnet 44 feeding the magnetic circuits and located in a groove 90 in the front of body part 20. The other end 108 of the armature 96 is vibrated by the stylus 100 in the common space between the polepieces 40, 42, 68 and thereby varies the magnetic flux through the magnetic circuits and the E.M.F. induced in the coils 46, 48.