Patent GB-864306-A (GB)
Title: Improvements in or relating to phonograph pickups
IPC: H04R17/06
Filed: 1957-08-21
Abstract: 864,306. Gramophone transducers. TECHNICAL CERAMICS Ltd. Aug. 21, 1957 [Aug. 21, 1956 (3)], No. 26365/57. Class 40 (4). The active element of a gramophone transducer is coupled to a stylus by means of a link which carries a vane oscillated by the element or stylus in a direction perpendicular to its plane, the vane being surrounded by a quantity of a viscous silicone medium. As illustrated, the invention is applied to a pick-up having a casing formed by a metal block 43 shaped to provide cavities for a barium titanate transducer 30 and a terminal block 49. A coverplate 44 closes the cavities on one side and is secured to block 43 by means of hollow rivets 46 which also secure mounting flanges 47 and a stirrup 70 which provides a bearing enabling the double headed stylus 21 to be moved from one spring-loaded operative angular position to another and, if necessary, to be detached from the pick-up. The barium titanate transducer 30 comprises two plates of titanate united to an intervening resilient metal strip, so as to be permanently polarized, and having electrodes on their outer faces. At one end the plates are clamped between elastomer blocks and at the other end are secured between the sidewalls of a tapering U-sectioned arm 34 which has a downturned bifurcated end 36 engaging a stylus arm 23. One of the sidewalls of arm 34 is extended to form a vane 38 and the end 36 projects through a slot in a flexible spring sheet sprung between opposed notches 453, 454, to close the mouth of the cavity containing the transducer. The dimensions of the vane are chosen to give a resonance which, in the absence of the vane, would be a resonance peak of the titanate transducer but which, by virtue of the vane, is smoothed out. Alternatively, or additionally, if more than one vane is employed, the resonance frequency of the vane may be higher than the highest response frequency of the transducer without such a vane and in consequence extends the range of response to higher frequencies. Surrounding the vane and the lower part of the titanate plates is a mass of silicone fluid (such as dimethyl silicone oil mixed with less than 2% of ethyl or phenyl silicone oil) stiffened by repeatedly rolling it through a three-stage paint mill several times to disperse a powder through it (the powder being preferably a silica soot produced by combustion of the gas phase of silicon tetrachloride and being added to the extent of 2 to 7 parts by weight of silicone fluid). To prevent the powder passing into solution, the particles are preferably coated with polyalkalene glycel. Alumina or zirconia powders may also be used to consolidate the silicone fluid. Terminal blades 481 are clamped against the titanate electrodes by the elastomer blocks and are part of larger blades 48 separated by an insulator clamped into the casing. The stirrup 70 is stamped from a single sheet of metal and provides two open journal bearings 82 for a shaft 67 and a retaining spring arm 76 which bears on an eccentric portion of the shaft 67 which at one end has a crank arm 69 whereby the shaft may be rotated 180 degrees as defined by the shaft eccentric, the spring arm 76 and stops 85 on each side of the stirrup. At its other end the shaft carries a coaxial cylinder 65 in which an elastomer bush provides a universal bearing for stylus arm 23. In a construction using only one stylus point, the elastomer bush may be mounted in a clip detachably secured to the casing (see Fig. 13, not shown).