GB427024A - Improvements in or relating to electro-dynamic phonograph reproducers - Google Patents

Abstract

427,024. Phonographic reproducers. ELECTRICAL RESEARCH PRODUCTS, Inc., 195, Broadway, New York, U.S.A.- (Assignees of Harrison, H. C.; 94, Bayview Avenue, Port Washington, New York, U.S.A.) Oct. 13, 1933, No. 28340. Convention date, Oct. 28, 1932. [Class 40 (iv)] Relates to a phonograph reproducer for use with hill and dale records, and more particularly for use in playing-back an original recording, comprising a frame, a magnet system having an air gap, a stylus and a generating element secured to the stylus and disposed in the gap, and consists in supporting the stylus by two spaced parallel members of low mass and stiffness fixed at one end to the frame and connected directly to the stylus, one of the members being located in the gap and constituting the said generating element of the reproducer. As shown, the reproducer comprises a permanent magnet 11 and polepieces 12, 13, the polepiece 13 having an upwardly extending portion 17 in contact with one of the magnet poles and an L-shaped portion 18 at its other end terminating in a V-shaped pole face (Fig. 3). The polepiece 12, which also has a V-shaped pole face, is supported against the other pole of the magnet by a non-magnetic member 19 which is soldered to the end portion 18 of the polepiece 13. Dust is prevented from entering the gap between the pole faces from below by a rubber washer 21 fitted into a recess 20 in the member 19 and from above by a rubber &c. block 33 secured in place by a screw 34. The stylus 14 is supported by members 15, 16, the former of which is preferably in the form of a single arm of relatively low lateral stiffness as compared with the V-shaped member 16, which constitutes the generating element of the reproducer and has its arms disposed in the gap between the opposed pole faces. The polepieces and stylus supporting means are secured to a brass block 22 by screws 23 insulated from the polepiece 13 by washers 29, 30, 31 whilst the magnet is secured to the block 22 by screws 24. A second brass block 25 is secured to block 22 by insulated screws 26, the two blocks being insulated from each other by a sheet of material 27, whilst both blocks are insulated from the polepiece 13 by a similar sheet 28. The broad end pieces 32 of the member 16 are clamped between the sheet 28 and the blocks 22, 25 respectively, the latter projecting beyond the magnet on either side and contacting with spring clips adapted to support the device on a reproducer arm. The member 16 may be formed from round bronze wire or from thin flat material of relatively greater width than depth. The moving system comprising the members 15, 16 and stylus 14 is proportioned in accordance with the general theory of reproduce design described in Specification 363,449 in which it is shown that the fundamental requirement for good tracking is that the force exerted by the stylus on the record shall never be less than the product of the vibratory velocity of the stylus and the mechanical impedance of the moving system. Preferably, the effective needlepoint mass of the system is of the order of 1À5 grams and the effective needlepoint stiffness is of the order of À35 x 10<-6> dynes per centimetre.