Patent GB-941254-A (GB)
Title: Improvements in or relating to stereophonic pick-up devices
IPC: H04R17/08
Filed: 1959-11-26
Abstract: 941,254. Stereophonic pick-ups. M. DE VRIES. Nov. 26, 1959 [July 2, 1959], No. 40240/59. Heading H4J. A stereophonic pick-up has a stylus holder 14, Figs. 2, 3, mounted on a removable support 18, Fig. 4, slidable along guide surfaces 20, 21, Fig. 5, of a slot 19 of the pick-up casing 1 to bring an end 33 of the stylus holder 14 within the smaller angle defined by two coupling arms 11, 12 which mechanically couple the stylus holder 14 to two transducers 2, 3. The transducers 2, 3 are crystal elements and one end of each element is fixed to the casing 1 while the other end has a sleeve 5, 6 fitted over it. Arms 11, 12 are integral with each other and with sleeves 5, 6 and are made of material having high internal damping, e.g. P.V.C. Stylus holder 14 is tightly held in an aperture 17 in a resilient bearing 16 carried by support 18. The support 18 may be slid into and out of the slot 19 of the casing 1, being retained in its innermost position by the engagement of projections 27, 28 on the casing 1 in recesses 29, 30 in the support 18. During the inward sliding movement a leaf spring 26 on a wall of the slot 19 is compressed, and the end 33 of the stylus holder 14 is introduced within the junction 13 formed by arms 11, 12, but is held out of contact with them. When the projections 27, 28 and recesses 29, 30 interengage, the holder end 33 is brought into contact with the junction 13 of arms 11, 12 to pre-stress such arms, the pre-stress is increased when the pick-up is placed on a gramophone record. A second embodiment, Fig. 6 (not shown), has two further coupling arms leading from the transducers to a second stylus holder for grooves of a different size. In a third embodiment, Figs. 7, 8, a removable support 41 located within a recess 42 in the casing 43 carries a resilient bearing 46 supporting a stylus holder 44. Two transverse slots 47, 48 in the support 41 provide passages for a U- shaped leaf-spring 49. One end of the leaf spring engages the bearing 46 and its other end has a notch 56 located near the stylus holder 44. As the support 41 is inserted into the recess 42, the central portion 54 of the spring 49 is pressed against a projection 57 forming part of the casing 43 and the notch 56 presses against the stylus holder 44. By this means the end of the stylus holder 44 remote from the stylus is brought within the elbow formed by coupling arms 11, 12 and is only allowed to contact the arms 11, 12 at the end of its inward motion, after the portion 54 has passed the projection 57. When the support 41 is removed from the casing a reverse operation takes place, the stylus holder 44 being tilted out of contact with the arms 11, 12. In an alternative embodiment the stylus holder is free from the coupling arms as long as the pick-up does not bear on a record. a uni-junction transistor 111. The pulses are applied through a condenser 114 to an impedance matching transistor 115, are then amplified by a transistor 116 and applied through a condenser 117 to a point 118 in a potentiometer chain 119, 120, 121 connected across a D.C. power source. The resistance 120 is variable as a function of the spark conditions and may be constituted by a transistor controlled by the voltage at the erosion electrodes. The potentiometer chain is connected to a Schmidt-type trigger circuit 124. The width of the output pulse from circuit 124 is dependent on the setting of resistor 120. The output is applied to the base of a transistor 126, the collector of which controls the current in transistors 127, 128 in diagonally opposed branches of a bridge circuit. It is also applied through a phase inversion transistor 130 to a transistor 131 whose collector voltage controls the current in two further transistors 132, 133 disposed in the other two diagonally opposed legs of the bridge circuit. Thus, dependent on the setting of resistance 120, current is caused to flow through the armature 134, connected across two apices of the bridge, in either direction F or direction F<SP>1</SP>. By suitable matching of the armature inertia and the pulse frequency, it is possible to induce vibrating oscillation in the armature 134. The spark generator (Fig. 5) comprises a pulse generator 60 and three amplifying stages 61, 62 and 63, the latter being an electronic switch valve inserted in a power circuit 66, a branch of which comprises a primary winding 71 of a transformer 74 and reactance windings 72, 73. Condensers 77, 78, 79 are each connected between two windings and earth, the terminal 70 being at a high D.C. potential (e.g. 6,000 v.). To this circuit is connected a discharge circuit comprising a primary winding 80 and a diode 82. In operation, a pulse transmitted to the grid of the valve 63 causes it to become conductive, thus building up current flow in primary winding 71 with a consequent power pulse being produced in the secondary winding 83. The build-up of current is augmented by the discharge of capacitor 58 via diode 65. When the pulse ceases and the valve 63 ceases to conduct, the excess potential in the reactance windings 71-73 establishes the conductivity of the diode 82 and is thus discharged through winding 80 which results, through a secondary winding 86, in a second power impulse to the output terminal.