GB1381888A - Pickup cartridge - Google Patents

Abstract

1381888 Moving magnet gramophone pickups MATSUSHITA ELECTRIC INDUSTRIAL CO Ltd 19 Jan 1972 [23 Feb 1971] 2572/72 Heading H4J A pickup (Fig. 2a) has a flat plate permanent magnet armature 7 magnetized in the same polarity (N) on both major surfaces and in the opposite polarity (S) at the central plane between the two major surfaces. The armature 7 is supported at its centre of gravity 14 and is movable together with a cantilever stylus arm 26 in all angular directions about its centre of gravity. A U-shaped yoke of high permeability magnetic material has a pair of polepieces 16, 17 adjacent and astride the armature 7. A coil 18 is wound on it. As the stylus 25 tracks a record the armature 7 moves closer to one or other of the polepieces 16, 17 (Figs. 3a to 3c, not shown), thereby inducing an E.M.F. in the coil 18. A support 11 having a portion 10 of reduced diameter is coaxial with the cantilever stylus arm 26. The portion 10 is of phosphor bronze wire or plastics material and is embraced by a butyl rubber damping sleeve (not shown). The armature 7 is made of two magnetized plates of barium ferrite or platinum cobalt bonded together. It is provided with a central hole for receiving cantilever stylus arm 26. The armature 7 may be of circular or semicircular form or of cruciform or V-shape. Only part of the armature 7 (e.g. a semicircle) may be magnetized. As shown in Fig. 2a a monaural pickup has the yoke 15 vertical. Another monaural pickup (Fig. 7b) has two yokes 15a, 15b arranged one on each side of the armature 7, their coils 18a, 18b being connected in series. Each arm of each yoke 15a, 15b may carry a coil. A first stereophonic pickup (Fig. 2b) is generally similar to the pickup of Fig. 2a but has two yokes 15L, 15R at 45 degrees to the vertical. An alternative stereophonic pickup (Figs. 8a, 8b, not shown) has two yokes below the armature 7 as well as the two yokes above it. Appropriate coils are connected in series and there may be two coils on each yoke, one on each limb, i.e. 8 coils altogether. Another stereophonic pickup (Fig. 6) has yokes 15L and 15R including polepieces 16L, 17L, 17R. The yoke-coil unit is in a shield case 19 of "permalloy" fixed on a housing 20. The vibration system is removably fitted in a holder 22. A butyl rubber damper 23 interposed between the armature 7 and the support 11 controls the vibration system which is attached from under the yokes 15R and 15L at an appropriate tracking angle. The shape of the damper 23 is such that the armature 7 is not displaced towards the polepieces 16L, 16R, 17L 17R because of the static bias force due to the stylus pressure.