Patent GB-1487548-A (GB)
Title: Pick-up devices for gramophone records
IPC: H04R1/18
Filed: 1973-11-23
Abstract: 1487548 Gramophone pick-up A R RANGABE 22 Nov 1974 [23 Nov 1973] 54415/73 Heading H4J A gramophone pick-up stylus assembly 4 (Fig. 2) comprises a rigid stylus arm 10, a stylus tip 38 mounted adjacent a forward end of the stylus arm 10, a substantial part of the length of the stylus arm 10 extending from the rear end thereof being straight and the stylus tip 28 being located in the vicinity of the axis of the straight part of the arm 10. A resilient wire 8 substantially shorter in length than the stylus arm 10 is fixedly attached at its forward end to the stylus arm 10 so as freely to support the stylus arm and has at least a major portion in alignment with the stylus arm. In operation the arm 10, the resilient wire 8 and the compliance of the stylus tip 28 and record surface form a vibratory system of which the lowest natural frequency is greater than 20 kHz. A stereophonic pick-up comprises a body (2) Figs. 1, 4 (not shown) carrying the stylus assembly 4. The stylus assembly 4 includes a transverse nickel strip 6 (Fig. 5) to which the wire 8 is attached. The rear portion of the arm 10 acts as the movable electrode of an electrostatic transducer, the transducer comprising a pair of stationary capacitor plates 12 each inclined, in use, at 45 degrees to a vertical plane passing through the axis of the assembly 4. The capacitor plates 12 are in a V-sectioned groove 14 in an insulating block 16 secured to the underside of the body (2). The arm 10 forms with each plate a respective variable capacitor. A non-conductive film 20 (e.g. polyethylene terephthalate) is interposed between the plates 12 and the arm 10 and covers the undersurface and the sides of the block 16. A beryllium copper alloy screen 22 (Fig. 4, not shown) screens the plates 12 and is secured to the underside of the pick-up body (2) Figs. 1, 4 (not shown) by conductive epoxy adhesive. The body (2) is conductive and is of drawn aluminium alloy or of A.B.S. moulding plated on its outer surface. The wire 8 may be encased in damping compound carried by an extension of the film 20. In use the arm 10 is at an angle of 20 degrees to the record. The wire 8 is of high tensile steel wire or high grade tungsten wire. The stylus arm 10 is formed from beryllium wire, high modulus carbon fibre composite or of aluminium tube. The wire 8 is inserted into an axial hole in the arm 10 which is then swaged, or alternatively it is soldered or welded to the underside of the arm 10, the front end of the wire being offset so that the major portion of the wire 8 is aligned with the axis of the arm 10. The wire 8 is inserted into a slot in the lower surface of the strip 6 and the strip 6 is then swaged to anchor the wire 8. The capacitor plates 12 may be inclined by less than 90 degrees in order to cancel out cross talk. Dimensions of the stylus arm 10 and the wire 8 are given. Alternative pick-up (not particularly described) may use a photoelectric or other non- contact type transducer or piezoelectric polyvinylidene chloride film. Attachment of the stylus to the arm (Fig. 6, not shown) forms the subject of co-pending Specification 1,487,549.