GB416574A - Improvements in and relating to electromagnetic vibratory devices for use in the electrical reproduction of sound - Google Patents

Abstract

416,574. Gramophone pick - ups. ELECTRIC & MUSICAL INDUSTRIES, Ltd., Blyth Road, Hayes, Middlesex, and WHITE, J., 26, Connaught Gardens, Palmers Green, London. Feb. 13, 1933, No. 4433. [Class 40 (iv).] An electromagnetic vibratory device, more particularly a gramophone pick-up, comprises an acoustic current coil associated with a magnetic circuit, an auxiliary coil arranged close to the acoustic current coil but so as to link with substantially none of the varying flux set up in the neighbourhood of the acoustic current coil when, in operation, acoustic frequency current flows therein, and a pair of terminals, the auxiliary coil being of such a nature, and the two coils being so connected together and to said terminals that, when said device is disposed in a fluctuating external magnetic field, such as that due to a talking machine motor, substantially no potential difference due to said field is set up between said terminals. The Figure shows a pivoted armature gramophone pick-up having an auxiliary coil 10 mounted on a base plate 9 below the yoke of the permanent magnet 1. The coil 10 has the same physical dimensions as the acoustic current coil 7 with which it is connected in series with respect to two leads 11 which are connected to the output terminals of the pick-up. The coils may, however be connected in parallel with respect to the output terminals. The coil 10 may be slightly tilted with respect to the base 9 so that both coils 7, 10 may lie more nearly in the same mean horizontal plane and the coil 10 may also be provided with a magnetic core in order to balance its inductance with that of coil 7. According to a modified construction, the coil 10 is mounted between the poles of the magnet 1 so as to lie upon the polepieces and to be coaxial with coil 7. In this case, the inductance of coil 10 may be made greater than that of coil 7.