GB329784A - Improvements in sound reproducing instruments and the like - Google Patents

Abstract

329,784. Yearsley, R. A. April 18, 1929. Gramophone pick-ups; magnetic instruments. -The armature of an acoustic apparatus, such as a gramophone pick-up, is formed with or carried by parts that directly rock on an end plate of the coil bobbin or other relatively hard surface carried thereby, the parts being pressed towards the surface on which they rock by a pad or pads of resilient material. The invention is shown applied to a gramophone pick-up comprising a U-shaped magnet 1, pole pieces 2 and an armature 3 surrounded by a coil 4. The pole pieces are formed with flanges 9 adapted to embrace the coil bobbin, the upper and lower end plates 8<a>, 8 of which act as distance pieces between the pole pieces being preferably recessed as shown at 10. The pole pieces are connected together by upper and lower non-magnetic cross pieces 11, 12, the cross pieces, bobbin and pole pieces constituting a rigid unit which is fixed to the magnet limbs by bolts or screws passing through slots 13 in the pole pieces. The armature 3 is formed integral with a socket-like extension in which the needle 5 is clamped by a screw 6 and is provided with lateral projections 7 of triangular cross section to form knife edges that engage and pivot in a groove 8<b> in the lower end plate 8 of the bobbin. The lower cross piece 12 is formed with a central hole through which the armature extends and with lateral extensions 12a that are recessed to receive pads 14 of indiarubber sheet on which the lateral projections 7 rest. The upper cross piece 11 is formed with an upwardly pressed portion 15 which houses two short lengths of vulcanized indiarubber tubing 16 engaging one on each side of the upper end of the armature. The holes in the cross pieces for the securing bolts or screwls may be clearance holes so that the armature can be accurately positioned between the pole pieces by adjustment of the cross pieces. The unit is enclosed in a felt &c. envelope prior to enclosure in a stamped metal or moulded case. According to modifications the screw 6 may be passed through a tapped hole in one of the projections 7 which may be more or less circular in cross section instead of triangular. Further, the rocking parts may be formed separate from the armature in which case, the stylus or needle may itself constitute the armature. Such a construction is show in Fig. 9 in which the needle 3 is clamped in a separate member 7 adapted to rock on the upper end plate 8<a> of the coil bobbin and pressed towards this plate by an indiarubber pad 14a which may be extended downwardly to form side buffers 16<a>. The hole in the lower cross piece 12 through which the armature extends may be provided with an indiarubber bush which may be formed integrally with the pads 14.