Patent GB-924547-A (GB)
Title: Sound-record transducing devices for stereophonic and like recording systems
IPC: H04R17/06
Filed: 1959-05-26
Abstract: 924,547. Stereophonic pick-ups. SONOTONE CORPORATION. May 26, 1959 [June 9, 1958], No. 17867/59. Class 40 (4). Parallel linkages pivotally engaged with a single stylus are used to drive two transducers in response to two recordings in a single groove. The linkages may be made of aluminium or titanium alloys, phosphor bronze, steel, nylon, polyethylene, polystyrene, or cellulose-acetate butyrate. As shown in Fig. 7, a single sheet of material is shaped to form four links with substantial rigidity separated by narrow waist portions, the flexibility of which provides virtual pivots. A yoke 45 engages the arm of a stylus 12 to deflect piezo-electric bimorphs 21 set with their major surfaces at right angles to each other and mounted at their far ends to project perpendicularly towards the linkage which they each engage with a pivot pin 28 in an upper link or a pin 28-C in a lower link, or with two pins 28-D which embrace the narrow flexible portions between links. The pins may drive twistor bimorphs through a crank arm, see Figs. 10 and 12, not shown. Similar pin connections may be made between the linkage and the moving armatures of two magnetic circuits, the flux gaps of which are set at right angles to one another and the armatures of which are mounted on radius arms; see Fig. 8, not shown. The linkage may be made from metal tubing flattened to form the flexible pivot points at 36-2 and 36-3, Fig. 5, and to form mounting flanges 36-6 for a single fixed pivot. This construction makes necessary the use of a shoe 36-4 to engage the arm of stylus 12 and may equally well be formed from flat metal strip twisted to form flexible elbows, see Fig. 6, not shown. In all constructions stops may be provided to limit the deflection of the linkage. Detailed description of a pick-up cartridge using two crystal bimorphs is given and is here to be seen in Figs. 13, 20 and 21. The pick-up is built round a body member with a central portion 20-1 having two parallel through bores, a head portion 57 and forwardly projecting side flanges 58, and rearwardly projecting side flanges 61-2. A piezo-electric bimorph 21 is mounted in each through bore by means of an elastomer body 23 at one end and projects through the bore to connect with a linkage 40 by means of a pin 28. The linkage, of the kind shown in Fig. 7, is riveted to the head portion 57 and engages the stylus arm 13, which is of the turnover kind. Between the rear side walls 61-2 are sandwiched four terminal strips 62, together with spacing members, connected to give three terminal output. The terminal strips are tucked between the bimorphs and the elastomer bodies to make contact with the bimorph electrodes. A rubber pad 65-9 and a cover-plate 65 are clamped down on top of the terminal strip assembly by a sheet metal clamp 66-3, the side walls 66-1 of which are held by a rivet 66-2 passing through the assembly and the side walls 61-2. Also secured by this rivet are the side flanges of a spring clip which releasably and rotatably secures the reduced portion 14-3 of the stylus arm shaft 14 which, by crank arm 14-2, may be rotated to change from one stylus to another. As best seen in Fig. 13, the front edge of the clamp 66-3 is formed with two spring arms 66-7 carrying a transverse metal plate 66-6 by means of which the cartridge is flexibly mounted to a pick-up arm. The front of the cartridge is enclosed by a metal plate 88 which clips into rebates round the inner edges of the side walls 58. The piezo-electric crystal bimorphs and most of the linkage 40 are embedded in a semisolid silicone oil 75-4, Fig. 20.