Patent GB-1314506-A (GB)
Title: Pickup device
IPC: H04R19/10
Filed: 1971-08-17
Abstract: 1314506 Capacitor pickups TOKYO SHIBAURA ELECTRIC CO Ltd 17 Aug 1971 [17 Aug 1970 4 Nov 1970] 38505/71 Heading H4J A capacitor type gramophone pick-up (Fig. 2) has a cantilever stylus arm 8 and secured at the end of the arm 8 remote from the stylus 9 is a movable capacitor electrode 39 (Fig. 9) which confronts a fixed capacitor electrode 32 secured to a removable holder 27. An active circuit 19 (including, e.g., F.E.T.s and I.C.s) is incorporated. A stereophonic pick-up has two separate fixed electrodes 32 secured to the holder 27 at an angle of 90 degrees to each other. Preferably each fixed electrode 32 has an electret on its face confronting the movable electrode 39. A stereophonic cartridge 1 has a main body 2 (see also Fig. 3, not shown) in which a transducer device 4 is detachably mounted by a screw 3. The cantilever stylus arm 8 passes through a rubber damper 7. The stylus tip 9 is protected against undue pressure by two protectors 10, one at each side of the main body 2. The main body 2 comprises an inner conductive casing 12 and an outer plastics casing 11. A terminal board 13 having plugs 6 fits into a guide slot 11a provided in the casing 11. The plugs 6 derive output signals and connect in a power source. The upper part and front of the casing 11 have an L-shaped metal screen 14. A support 15 has upper and lower projections 16, 17 and a screw socket 18 is rigidly secured to it. A printed circuit board 19 engages the screw socket 18 and upper projection 16. The board 19 carries active elements (F.E.T. or I.C.) 20 and passive elements (resistors, capacitors) 21. The active elements 20 have input terminals 23 in openings in the board 19. Two L-shaped openings 24 are provided in the support 15 and a springy connector 26 fits into each opening 24 and connects the input terminal 23 of an active element 20 to one of the fixed electrodes 32 through a pin 33 &c. The holder 27 has a hole 28 engaged by the projection 17 and an aperture 29 registers with the screw 3. In the bottom of the holder 27 is a shaped concave hole 31 to the interior wall of which the fixed electrodes 32 are stuck. A stylus support 34 of conductive material and generally box-shaped (Fig. 5, not shown) closes the hole 31. Into the rear part of the arm 8 is inserted a conductive cylinder 36 (Fig. 6). A wire 37 axial of the arm 8 joins this conductive cylinder 36 to a cylindrical conductive holder 38 which in turn is secured by conductive bonding material to the stylus support 34. The wire 37 prevents outward movement of the stylus arm 8 and reduces tracing distortion and at the same time provides electrical connection between the movable electrodes 39 and the stylus support 34. Electrical connection is continued through the screw 3 and screw socket 18 to the printed circuit board 19 and plugs 6. The movable electrodes 37 may be formed by slotting the rear of the stylus arm 8 and bending the slit portion into V-shape (Figs. 7, 8, not shown). The stylus arm 8 is of metal. Alternatively it may be synthetic resin, the electrodes 39 then being formed by evaporation or by sticking conductive plates to its rear end. The spacing between the electrodes 32, 39 is narrow near to the stylus arm 8 and widens at a distance remote from it. The extensions of the electrode surfaces pass through the centre of vibration of the stylus arm 8. The printed circuit converts the high impedance of the capacitor transducer to a low impedance, thereby enabling reproduction with good signal to noise ratio. The electrodes 32, 39 are in a sealed air space so that moisture and dust do not interfere with their action. The support 15 and body 27 may be formed of P.T.F.E., polyphenyloxide, polycarbonate, polyethylene or polystyrene. The printed circuit board 19 is treated with a surface agent to prevent attack by moisture.