Patent GB-783372-A (GB)
Title: Improvements relating to pick-ups for sound reproducers
IPC: H04R11/10
Filed: 1955-08-17
Abstract: 783,372. Gramophone pick-ups. STANTON; W. O. Aug. 17, 1955 [Aug. 17, 1954], No. 23736/55. Class 40 (2). [Also in Group XXXIX] An electromagnetic pick-up of the balanced armature type has a replaceable stylus assemblycomprising a stylus-carrying armature mounted on a torsion wire in a casing which is readily detached by a sliding movement from the other components of the pick-up. A gramophone pick-up having two stylii arranged for use at different times on opposite sides of a record is shown in Figs. 2, 4 and 5 and comprises a common coil 11 and high permeability core 14, permanent magnets 15, and polepieces 17, 18 constituted by integral extensions of high permeability soft or nickel iron bars 16. These components, together with circuit leads 12 and connectors 13, are moulded or cast in a casing which may be formed from insulating plastic material or casing resin such as phenolic resins, ureas, nylon or polystyrene. Each replaceable stylus assembly 30, Figs. 10 and 11, is formed by a similar casting or moulding process which secures the ends 41 of a piano wire or beryllium copper torsion wire 38. This wire may be looped and a tubular soft or nickel iron slotted armature 36 fitted to it as shown in Fig. 13. The armature, in its rest position, is positioned by the wire so that the end remote from the stylus'37 is centrally positioned in a parallel sided recess in a fixed magnetic coupling member 33 formed from the same material. Neoprene or synthetic rubber washers 32 are fitted over the armature on each side of the torsion wire, and plastic damping material acting on the armature is applied by a painting process to a recess 43. Each stylus assembly includes an integral finger grip 32 and is formed with inclined edges for engagement by a sliding movement with recesses 20, 21 in the pick-up. These recesses are formed by brass channel-plates 24 having converging walls 25, 26, and are each provided with a leaf-spring 27 for retaining the stylus assemblies in position with the coupling members 33 in engagement with the core 14. The armatures are then located in an off-set but balanced relationship with the exposed ends of the polepieces 17, 18, which may be protected from corrosion by a plastic or resin coating. The lower recess 21 has an extended portion 22 to facilitate fitting of the stylus assembly. In a modification, Figs. 14 to 17, both stylus assemblies 56 are bevelled and fitted from the same end of the pick-up in recesses provided between the coil 51 and polepieces 55, while the armatures 59 are centrally positioned between their respective polepieces. In each stylus assembly, the torsion wire 61 may be secured to the armature by soldering or brazing and have laterally extending portions 62 embedded or fixed by cement to the casing. A neoprene armature damping pad 63 may also be provided. A further modification having a single replaceable stylus assembly is shown in Figs. 18 to 20. A single permanent magnet 73 and one pair of polepieces 74 centrally offset from the armature 81 are provided. The construction is otherwise similar to that of the first embodiment. The Specification also described a tone arm which includes this pick-up unit as an integral moulding.