GB1245031A - Stereophonic gramophone pickup - Google Patents

Abstract

1,245,031. Stereophonic pick-ups. PICKERING & CO. Inc. 24 April, 1969 [30 April, 1968; 29 Jan., 1969], No. 21078/69. Heading H4J. A stereophonic pick-up (Fig. 5) comprises a supporting structure carrying a quadrangular cluster of four polepieces 33, 34, 46, 47 (Figs. 2, 7) which define a common space. A tubular armature 93 of high permeability material is pivotally mounted at one end outside the common space for movement of the opposite end within the common space. A permanent magnet 66 is mounted on the supporting structure and is magnetically coupled at one of its poles to the pivotally mounted armature 93. Its other end is remote from the magnetic circuitry. Relative motion between the permanent magnet 66 and armature 93 in the region of magnetic coupling is small and the armature 93 is maintained in a substantially uniform and constant state of magnetic saturation. The armature 93 is preferably mounted and damped by a flexible collar 94 of natural or synthetic rubber. Two magnetic circuits are provided, one for each channel. The right-hand channel circuit comprises polepiece 46, leg 44, coupling member 53, core member 31, coil 38 and polepiece 33. The left hand channel circuit comprises polepiece 47, leg 45, coupling member 53, core member 32, coil 40 and polepiece 34. A " shorted turn " non-magnetic member 35 for reducing cross-talk and providing a relatively flat frequency response electromagnetically couples the core members 31, 32 beneath the coils 38, 40 and may have two holes as shown or a single large hole (Fig. 13, not shown). An earthing strap 61 connects the magnetic circuits to a shielding casing 85. The quadrangular cluster of polepieces need not be in rightangled configuration (Fig. 12, not shown). The permanent magnet 66 may be cemented in position or its channel housing (Fig. 11, not shown) may be provided with a window (200) in the base of the channel and a wall (201) at the front of the channel. The magnet is inserted between the wall (201) and the base and held by projections (202, 203). A removable stylus assembly comprises a tubular casing 88 of non-magnetic material having a handle 90 which provides positive location relative to the shielding casing 85. A springy metal tie wire 95 between the easing 88 and armature 93 allows pivoting of the armature 95. The pick-up supporting structure is in two moulded interfitting parts, the first part accommodating the magnetic circuit arrangements apart from the permanent magnet which is accommodated in the second part (Fig. 3, not shown).