Patent GB-389272-A (GB)
Title: Improvements in and relating to electrical pick-ups for gramophones
IPC: H04R9/12
Filed: 1932-03-09
Abstract: 389,272. Gramophone pick-ups. SYMONDS E. E., 1, Cottemore Terrace, Waltonon-Thames. March 9, 1932, No. 6991. [Class 40 (iv).] A gramophone pick-up comprises a magnet body attached to a swinging supporting arm, a moving coil mounted on a resilient diaphragm, a needlecarrying arm pivoted to the magnet body and having an abutment adapted to bear against and to transmit vibration to the diaphragm, the pivotal means for the needlecarrying arm embodying resilient buffers permitting of twisting or lateral movement of the arm against resilient resistance and the other or needle - carrying end of the arm being supported in a resilient cradle or bridge permitting movement of this end in a lateral sense against resilient resistance. The pick-up shown comprises a pot magnet 1 which carries an angle bracket 6, the plate 8 of which is flush with the lower face of the magnet whilst the plate 7 is perforated to fit over threaded studs 5 on the magnet, the studs carrying rubber sleeves 11 and being secured to a plate 9 on a socket 4 by nuts 10. Beneath the magnet body is mounted a non-magnetic metal plate 12 with central aperture 13, a relatively thick insulating plate 14 having a central aperture 15 of larger diameter than aperture 13, the assembly for supporting the moving coil 20 in the air gap and a lowermost plate 16 with central aperture 17, all these parts being secured together by screws 18. The coil assembly comprises the former 19 mounted on a disc 21 of bristol board, mica, &c. which is fastened by adhesive to a thin rubber diaphragm 22 which in turn is fixed by adhesive to an insulating plate 23 having a central aperture 24 somewhat larger than disc 21. A small metal disc 25 is fastened to the underside of diaphragm 22 and hollow rubber buffer ring 26 is located in the aperture 15 in plate 14 so that, when the parts are assembled, the ring is under slight compression between the upper side of disc 21 and the underside of plate 12. The stylus is held in a holder 27 comprising a flattened head 41 formed with a cylindrical member 39 which projects through a second flattened head 37 into contact with the disc 25 on diaphragm 22. The head 37 is adjustably secured by screw 36a in the bore 35 in one end of a lever 34, the other end 29 of which is pivoted between rubber washers 32 on a spindle 30 carried by lugs 31 on the plate 8. Each head 37, 41 is provided with two longitudinal bores 43 as shown in Fig. 4 and lengths of indiarubber 44 are passed through these bores and have their ends held in adjustable nipples 45, 46 mounted in lugs 42 depending from plate 16. Screws 42a are threaded through the lugs 42 and are provided at their inner ends with rubber buffers 42b or house spring-backed balls adapted to press against the sides of heads 37, 41. The central magnet pole 2 is also centrally drilled and provided with a compressed spring bearing on the diaphragm 22. The hollow arm 48 for supporting the pick-up is pivoted at 49 to one end of an elbowed bracket 50, the other end of which is attached to a sleeve 51 rotatable on a hollow pillar supported by the base 52. The weight of the pick-up is balanced in a resilient mariner by providing the arm 48 with a bracket 53 and the sleeve 51 with an extension 54, a screw 55 surrounded by a spring 57 being adapted to pass freely through member 53 and screw into the extension 54. The leads from the coil 20 are brought out through registering openings 61 in.the members 8, 12, 14, through the aperture 62 in the plate 9, along the interior of arm 48, and through opening 60 therein and down through the hollow pillar on base 52.