Patent GB-439800-A (GB)
Title: Improvements in pick-up devices for reproducing sound records applicable also to recording apparatus
IPC: H04R11/08
Filed: 1934-03-15
Abstract: 439,800. Sound reproducing and recording devices. SYKES, A. F., The Dell, Sandpit Lane, St. Albans, Hertfordshire. March 15, 1934, Nos. 8195/34, 11832/34, 36595/34, 2884/35, 5551/35, 6593/35, and 6594/35. [Class 40 (iv)] In a pick-up device, applicable also for recording and as a vibration motor, a flexible armature, or armature or coil carrier, is held in an extended grip of rubber or other material constituting a damping channel which progressively damps out transverse vibration along the gripped portion. A stylus may be connected to the free portion of the armature close to the magnet pole. The armature may be centrally operated with both ends gripped in damping channels. The drawings were filed with the Provisional Specifications. As shown in Fig. I (8195/34), the magnetic system comprises a bar magnet 4 with slotted polepieces 5, 6, and is braced by a split-strut 23 and screw 24. The polepiece 6 is pivotally connected at 16 to a bar 15 on the stud 3 freely rotatable in the housing 1. The polepiece 5 is extended to carry the coil 10 and is provided with a bent wire 21 engaging a stop 22 to limit the movement of the pick-up in the housing 1. A thin steel armature 7 carrying the stylus holder 8 is held between rubber strips 12 secured to the polepiece 6 by a copper clamping plate 13, the clamping pressure being adjusted by screws 14. The rubber strips may be replaced by a rubber tube, Fig. IX (8195/34), (not shown). In other modifications, Figs. V-VIII and XXIII (8195/34) (not shown), the device is adapted for use with cylindrical records, with a gramophone tone-arm, with the Edison Diamond Disc phonograph and with a moving coil instrument. Shaping and control circuits are shown in Fig. XIV (8195/34) comprising a resistance 63 across the pick-up, a potentiometer 65 for volume control and a condenser 64 which may be connected when desired at intermediate positions along the resistance. As shown in Fig. III (11832/34), the stylus lever 68 of an Edison Diamond B reproducer with floating weight is connected to a copper cross-head on the armature 7 by a knotted loop of thread 73. In a modification, Fig. IV (11832/34), the armature 7 is set in a rubber tube 47 or a folded sheet gripped in a sheetiron holder 75 formed with tabs 76 for securing to the polepiece. A spring may be used in addition to the floating weight. To prevent noises due to deformities of celluloid recordcylinders a series condenser may be inserted in the pick-up leads in conjunction with the shunt resistance of the volume control so as to reduce the bass response, or a small rubber pad may be inserted between the armature and the bobbin. As shown in Fig. III (36595/34), the pickup is fitted in a casing 78 adapted to take the floating weight 67 and stylus lever 68 of an existing machine, and replaces the soundbox in order to convert from mechanical to electrical reproduction. The magnetic system may be supported in the casing on soft washers at top and bottom. For adjustment of the air-gap, a core in the pole 11 is moved by turning the cap 86. The pole 11 may be saw-cut and the pole 6 laminated. The magnet 4 and laminations 6 may be moulded into the casing, leaving a cavity for the coil 10, or the parts may be moulded together as a block to be slipped into the casing. The rubber tube for damping the armature may be cut to a V-shape and the clamping plate may be held more tightly at the fixed end, in order to vary the damping along the length of the armature. As shown in inverted plan in Fig. II (6593/35), the armature 7 is set in front of the poles 6 of a magnet with two windings 10. The clamping plate 13 is screwed down on to a ledge of the moulding 90 in order to compress the rubber 12 uniformly, and the air-gap may be adjusted by paper washers beneath the rubber. As shown in Fig. 1 (6594/35), the armature is set between magnetic poles. The armature 7 carrying the stylus 8 is held by rubber strips 12 or a flattened rubber tube between the polepieces 6 of magnets 4, and the armature vibrates between the pole tips 11 and within the coil 10. In modifications not shown, the pick-up is mounted with a pad of rubber, cork, or other damping material clamped between the magnet and the top of the casing over the whole length of the magnet ; the magnet is wrapped in a rubber sheet and forced into the housing; the stylus lever is connected to the armature by a chainstitch cord with the loops pulled tight, which reduces resonant vibration between these parts, or this connection may be a silken cord gripped by a crosshead soldered to the armature, and the armature may be stiffened by making this crosshead as a web. Specifications 227,391, 263,502, and 303,579, [all in Class 40 (ii)], are referred to.