Patent GB-256280-A (GB)
Title: Improvements in electro-magnetic apparatus specially suitable for electrically reproducing sound records
IPC: H04R9/12
Filed: 1925-01-30
Abstract: 256,280. Sykes, A. F. Jan. 30, 1925. Magnetic instruments. - Relates to apparatus for electrically recording or reproducing sound, or for duplicating sound records. According to the invention, the recording &c. device is of the " push-pull " type (i.e. of the kind in which the electro-magnet force changes in direction according to the direction of the control currents in the windings), comprising in combination a field magnet located near to the record or blank, a ferromagnetic armature vibratable between the magnetic poles, and a stylus connected to the armature, the arrangement being such that vibration of the stylus and armature does not involve vibration of the means for supporting the.magnet. Fig. 1 (Prov.) shows a reproducing-device as applied for use with a cylinder record. A permanent magnet 7 is mounted on an arm 65 electrically connected to a block 287 which is pivoted to a feed carriage 125. Between the magnet poles is mounted on torsional or pivotal supports an elongated, armature 291 of soft iron, in slots on which is wound a coil connected by flexible leads to a valve set, through a transformer or directly. The armature has attached thereto a stylus-arm 294. Instead of providing the winding on the armature it may be arranged on the magnet poles. A modification of the above-described apparatus, designed for attachment to the tonearm of a gramophone, or for incorporation with the usual sound-box, is described and shown. Fig. I (Comp.) shows another reproducer for use on a gramophone, in which the armature 1, of square cross-section, is wound with wire in a channel, and is torsionally mounted for vibration between the poles of the magnet 7. Petroleum jelly, rubber, &c. fills a space between the armature and a non-magnetic block 292, for damping. Apparatus with a similarly designed armature, but adapted for hill-and-dale records, is described. In Fig. V is shown an instrument in which an elongated armature 1 is mounted by means of metal leaves 281 on a " neutral " member 347 of the field magnet 7. The armature has teeth or an edging 291 adjacent to the magnet poles. A winding is provided either on the armature or on the neutral member of the magnet. Fig. VI shows a device in which the armature 291 vibrates between four magnet poles carrying windings. A bar 292 has mounted thereon a transverse member 348 containing rubber which engages a peg 350 projecting from the armature. The latter may be torsionally or pivotally mounted at 5. A rectangular armature mounted pivotally at 5 or 5<1> between slotted pole-pieces carrying windings is shown in Fig. IX. This Figure also illustrates a device for mounting the reproducer on a tone-arm, a rubber bush 296 being expanded within a tubular connector 295 by means of an internal screw 354. The coils on the magnet poles may surround the armature. Fig. XI shows an instrument in which the armature is a lamina secured at its ends by screws 358 between magnet poles. The tension of the lamina is adjusted as desired, and the whole structure may be filled in with grease or like damping material. Two forms of instruments are described in which a third magnet pole is provided between two outer poles carrying windings. In one of these constructions the armature is pivoted in the space between the three poles, the gap between the armature and the central limb being filled with grease. In the other construction, Fig. XIII, the armature 7 itself forms the intermediate pole, and is elastically pivoted at 281. A lever 361 enables the armature to be screwed into a split moulded casing, 365, half of which is shown. Damping material is provided at 367. Specifications 126,970, 160,223, 190,759, [Class 40 (ii), Phonographs &c.], 222,174, and 227,391 are referred to.