Patent GB-1181069-A (GB)
Title: Magnetic Stereophonic Phonograph Pickup
Inventor: STANTON WALTER OLIVER
IPC: H04R11/12
Filed: 1966-12-20
Abstract: 1,181,069. Stereophonic pick-ups. W. O. STANTON. 20 Dec., 1966, No. 57065/66. Heading H4J. Reduction or elimination of cross-talk in a stereophonic pick-up of moving armature type is effected by a magnetic compensator 42 (Figs. 2, 4) or 82 (Fig. 15) and a phase compensator 44 (Figs. 2, 4) or 83, 84 (Fig. 15). The pick-up has current generating coils designed for connecting into load circuits having predetermined resistance characteristics and presenting a predetermined impedance triangle, and the phase compensator 44 or 83, 84 has resistance and inductance characteristics presenting an impedance triangle geometrically similar to the impedance triangle of the load circuit. The phase compensator comprises a short-circuited coil of electrically conductive, non-magnetic material encircling the magnetic compensator. A plastics casing 15 (Figs. 2, 4) has a hinged block 17 in which are moulded four terminal prongs 20-23. It is divided by a flange 25 into forward and rear compartments 26, 27. The forward compartment 26 receives a subassembly comprising a core 34 and polepieces 35a, 35b of low reluctance material. Mounted on the core 34 are a pair of current generating coils 36a, 36b having leads 37-40 connected to prongs 20-23 respectively. Frictionally fitted on the core 34 between the coils 36a, 36b is a magnetic compensator 42 of low reluctance material. Grooves 43 at the lower end of the magnetic compensator 42 frictionally hold a phase compensator 44 in the form of a loop or closed circuit coil of electrically conducting non-magnetic material, e.g. copper, brass, bronze. An earthing strap 45 extends between the sub-assembly and a shielding casing 16 and an earthing strap 58 connects casing 16 and terminal 22. A removable stylus assembly comprises a tubular casing 46 and a plastics handle 47. Within the assembly a permanent magnet 49 is connected by a tapered aluminium tube 50 to a stylus 48, an elastomeric collar 51 permitting oscillations of the magnet 49 in response to stylus movement. Non-magnetic spring wire 52 retains the magnet 49 in properly centred relationship. The casing 46 has a dimple 54 and is a snug frictional fit in a socket 28 between the polepieces 35a, 35b. The handle 47 shown hooks over the top of the shielding casing 16. Alternatively, it extends laterally across the front casing wall and overlaps both side walls. In use, the magnet is positioned between the polepieces 35a, 35b so that, when one pole of the magnet 49 moves towards one of the polepieces, the opposite end moves towards the magnetic compensator 42 in such a manner as to reduce cross-talk. A double-sided cartridge (Fig. 15) has a plastics casing 60 in two mirror-image halves 60a, 60b (Fig. 16). A magnetic circuit subassembly is disposed in forward compartments 61 and prongs 64-67 extend into rear compartments 62. A socket opening and groove face forwardly and receive one moving system 85 while, on the opposite surface, a socket opening and groove receive the other moving system 85<SP>1</SP>. A shielding casing is in two halves 72a, 72b, each half having an aperture to register with the socket openings. The magnetic subassembly has a single core 75 around which two current generating coils 76a, 76b are mounted. Two polepieces 74a, 74b engage opposite ends of the core 75 and terminate in angularly disposed poles 74a1 74a2, 74b1, 74b2. Poles 74a1, 74b1 form a gap on one side of the cartridge and poles 74a2, 74b2 form a gap on the other side of the cartridge. Between the coils 76a, 76b is a low reluctance magnetic compensator 82. Around opposite ends of the compensator 82 are phase compensators 83, 84, each in the form of a closed loop of electrically conductive non-magnetic material. Leads 77, 78 are connected to prongs 64, 65 and leads 79, 80 are connected to prongs 66, 67. Each moving system 85, 851 comprises a tubular housing 86 of non-magnetic material and a plastics handle 87. A stylus 88 is connected to a permanent magnet 89 by an aluminium tube 90, an elastomeric collar 91 being interposed between the magnet 89 and housing 86. Reference has been directed by the Comptroller to Specification 943,873.