Patent GB-1447391-A (GB)
Title: Grooved record playback system
IPC: G11B20/00
Filed: 1973-08-14
Abstract: 1447391 Multichannel pick-ups; multichannel systems F NAGAMURA 14 Aug 1973 [17 Aug 1972 11 Sept 1972 (2) 16 Sept 1972 5 Feb 1973 (2)] 38478/73 Headings H4J and H4R A multichannel pick-up has at least three transducers mounted in spaced angular relationship to one another and responsive to movement of a stylus. The transducers have main detecting axes which are oriented in different directions and which, in the case of an even number of transducers are symmetrically disposed on opposite sides of a plane perpendicular to the surface of the record and tangential to the groove at the point of contact and in the case of an odd number one is disposed in the plane and the remainder are symmetrically disposed on opposite sides of the plane. A pick-up (Fig. 12) has a stylus arm 103<SP>1</SP>, 10311 connected by coupling members 111, 112, 113, 114 to transducers D 1 , D 2 , D 3 , D 4 , which may be piezoelectric or semi-conductor type. In use coupling members 111, 112 are at angles of 22¢ degrees to the plane of the record surface while coupling members 113, 114 are at angles of 22¢ degrees to the normal to the record surface. Two elastomeric damping elements 101, 102 (these may be a single member) are of oblong form so that freedom of movement of stylus arm portion 103<SP>1</SP> is a maximum along the diagonals Lf, Rf of element 101 (Fig. 9) and freedom of movement of stylus arm portion 103<SP>11</SP> is a maximum along the diagonals Lb, Rb of element 102. Transducers D 1 , D 2  detect Lf and Rf motions maximally and transducers D 3 , D 2  detect Lb and Rb motions maximally. The damping elements 101, 102 are such that transducers D 1 , D 4  hardly respond to Lb and Rb motions while transducers D 3 , D 2  hardly respond to Lf and Rf motions. In a moving armature pick-up (Fig. 13) the stylus arm is of magnetic material and co-operates with core structures 115, 116, 117, 118. If desired the damping elements may be at one end of the stylus arm, the stylus being at the other end to form a cantilever structure (not shown). An alternative moving armature pick-up (Fig. 15) has a cantilever stylus arm carrying four projections DRF<SP>1</SP>, DRB<SP>1</SP>, DLB<SP>1</SP>, DLF<SP>1</SP> adjacent ones of which are spaced apart 45 degrees. Each carries a magnetic member 132a ... &c. which co-operates with a pair of spaced core arms D 1 <SP>1</SP>, D 2 <SP>1</SP> ... &c. to define air gaps. Radial motion of a projection varies the reluctance of the associated air gap, thereby generating an E.M.F. in an associated winding (139), Fig. 18 (not shown). Circuitry.-A pick-up having four transducers D 1 , D 2 , D 3 , D 4  (Fig. 7c) has built-in crosstalk reduction circuitry and feeds a quadraphonic amplifier which feeds separate signals to four loud-speakers LF, RF, LB and RB. If desired, adder networks also feed additional loud-speakers CF, CB, CL and CR. When playing a stereophonic record the crosstalk reduction circuitry is replaced by two adder networks which feed a stereophonic amplifier to supply loud-speakers L and R. Crosstalk reduction between the four signals from the transducers is provided by resistors (Fig. 22) which interconnect the four channels, some including inverter amplifiers INV. 1, INV. 2 and by buffer amplifiers BF1, BF2. Phase shift circuits PS3 and PS4 are also used. An alternative crosstalk reduction circuit is also described (Fig. 23, not shown).