Patent GB-1283404-A (GB)
Title: Stereophonic pickup cartridge
IPC: H04R11/12
Filed: 1969-08-13
Abstract: 1283404 Stereophonic pick-ups AUDIOTECHNICA KK [trading as AUDIO-TECHNICA CORP] 13 Aug 1969 [14 Aug 1968 3 Feb 1969] 40538/69 Heading H4J A stereophonic pick-up cartridge of the moving armature induced magnet type has two armatures 9, 10, (Fig. 1), carried at the end of a stylus arm 12 remote from a stylus 11 to vibrate therewith, and a permanent magnet 16 for magnetization of the armatures 9, 10. Polepieces 1, 2, 3, 4 have their ends arranged, in use, at an angle of 45 degrees to the horizontal and are threaded through coils 5, 6, 7, 8. Movement of armature 9 along its longitudinal direction provides a series additive energization of coils 5, 6 and movement of armature 10 along its longitudinal direction provides a series additive energization of coils 7, 8. The stylus arm 12 is carried by a holder 14, an elastomeric bearing 15 of butyl rubber being interposed between the holder 14 and the stylus arm 12. A flexible support line (not shown), e.g. of wire, is connected to one end of the stylus arm 12 and extends rearwardly to urge stylus arm 12 against the bearing 15. In one alternative arrangement the permanent magnet 16 is placed rearwardly of the armatures (Fig. 3, not shown) a piece of magnetic material (17) in the holder 14 passing magnetic flux from the magnet (16) to the armatures 9, 10. Alternatively, a magnet (16), Fig. 4 (not shown), is located between each pair of polepieces, a piece of magnetic material (17) extending form the magnets (16) towards the respective armature. Another embodiment has a permanent magnet (18), Fig. 5, not shown), between each pair of polepieces, as well as the magnet 16 as in Fig. 1. Where a magnet 16 is mounted forwardly of the air gaps there may be an auxiliary tubular armature (20), Fig. 6 (not shown), around the stylus arm 12. A pick-up cartridge (Fig. 8) comprises a shielding casing 37 having two upper mounting flanges 32. A removable stylus assembly comprises a base 30 (Fig. 9) having two side walls 63, 64. The polepieces, apart from the air gap portions, are embedded in a resin moulding 52 which has a front end 53, and a rear end 54 shaped to engage a groove 55 in a terminal board 48. A plug 59 on the stylus assembly engages in a receptacle 58 in the moulding 52 and an elastomer lock ring 60 engages a groove 61 in the plug 59. A permanent magnet 47 is embedded in the moulded front end 53. Another magnet, such as magnet 14 is embedded between each pair of polepieces. The stylus arm 36 carries an auxiliary armature 38. Into the rear end of stylus arm 36 is force fitted a pipe 66 (Fig. 10) to which a wire 67 is bonded. This extends rearwardly and is fixed to another pipe 68, the clearance between pipes 66 and 68 defining the centre of vibration. Adjustment of the tension of the wire 67 and of the damping provided by elastomeric bearing 42 is effected after loosening a screw 72. An alternative stylus sub-assembly, Fig. 11 (not shown), has an armature securing member (39) integrally moulded with an intermediate reduced portion (67) and a rear mounting member (69). The armatures 41 and stylus arm 36 are embedded in the securing member (39). Member (39) may be formed with a projection (73) of which extends into the stylus arm (36).