US2984711A

US2984711A - Gramophone pick-ups

Info

Publication number: US2984711A
Application number: US762584A
Authority: US
Inventors: Bayliff Raymond William
Original assignee: Individual
Current assignee: Individual
Priority date: 1957-10-08
Filing date: 1958-09-22
Publication date: 1961-05-16
Anticipated expiration: 1978-05-16
Also published as: NL103122C; FR1212894A; CH363499A; BE571819A; NL231921A; GB856829A; DE1113584B

Description

May 16, 1961 R. w. BAYLIFF GRAMOPHONE PICK-UPS 2 SheetsSheet 1 iled Sept. 22, 1958 Fig.1

man

y 1961 R. w. BAYLIFF GRAMOPHONE PICK-UPS 2 Sheets-Sheet 2 Filed se p. 22, 1958 United States Patent GRAMOPHONE PICK-UPS Raymond William Baylilf, Wings, 15 Ormond Ave.,

Hampton, England Filed Sept. 22, 1958, Ser. No. 762,584

'Claimspriority, application Great Britain Oct. 8, 1957 Claims. (Cl. 179100.41)

The present invention relates to gramophone pick-ups for use with sound records for stereophonic reproduction in which signals from two suitably spaced microphones are recorded as modulations in the same sound groove, the two modulations producing vibrations of the pick-up stylus about two mutually perpendicular axes. In one system, using whatwill be called a symmetrically modulated sound groove, theseaxes are displaced by 45 on either side of the vertical. In another system one axis is vertical, corresponding to hill and dale recording, and the other horizontal, corresponding to lateral recording.

With such a sound record it is required to be able to generate separate signals from each modulation, such signals being amplified and" applied to suitably spaced loudspeakers respectively.

A pick-up for such a purpose is required to operate in such a manner that interaction between the signal generating systems for the two modulations is of a satisfactorily low order over the acoustic frequency range, and also that in neither set of signals shall the non-linear distortion be significantly greater than is acceptable in a normal monaural system.

The present invention has for its object to provide a pick-up whereby these requirements can be met.

According to thepresent invention a gramophone pickup for stereophonic reproduction comprises a ferromagnetic armature adapted to carry a stylus and mounted with freedom of movement in two modes, namely one corresponding to lateral and the other to vertical movernents of the stylus, two separate magnetic cores each provided with a winding and each having pole tips adjacent the armature, and one or more magnets arranged to pass a polarising flux through the cores and armature, the arrangement being such that lateral movements of the stylus produce flux changes substantially only in one of the said windings and vertical movements of the stylus produce flux changes substantially only in the other of the said windings.

In a preferred form of the invention the armature is elongated, and is mounted for rocking movement about an axis perpendicular to its longitudinal axis between four pole tips. of one core, the rocking movement producing flux changes in a coil surrounding the armature and constituting one of the said windings, and the other core having two pole tips disposed above the armature in such a position that movements of the armature in the direction of its longitudinal axis produce flux changes in one or more coils surrounding the said other core and constituting the other of the said windings.

The invention will be described, by way of example, with reference to the accompanying drawing, in which:

Fig. 1 is a view in part sectional elevational of one embodiment of the invention,

Fig. 2 is an underside plan view of the embodiment of Fig. 1,

Fig. 3 is a view in front elevation of a part of a modification of the embodiment of Figs. 1 and 2.

Fig. 4 is a view in side elevation of the part in Fig. 3,

Fig. 5 is an underside plan view of another part of the modification of Figs. 3 and 4,

Fig. 6 is a circuit diagram showing one form of coil connections that may be used, and

Fig. 7 is a diagram showing the preferred way in which the connections of Fig. 6 are made.

The embodiment illustrated in Figs. 1 and 2 is a modification of the pick-up described in the specification of my application Serial No. 583,074 which is adapted for reproducing from lateral modulation only.

Referring to the drawings, anarmature 10 is a mild steel tube 2.5 mm. long, 0.4 mm. outside diameter and 0.0375 mm. wall thickness. The upper end of this armature is rigidly attached to one end of a cantilever supporting plate 11 constituted by a mild steel strip 0.0375 mm. thick having its plane at right angles to the length ofthe armature. The other end of the plate 11 is firmly clamped by means such asare shown in the earlier specification hereinbefore mentioned (but not shown in the present drawings) to the body 13 of the pick-up. The plate 11 is provided with a longitudinal stiffening ridge 14 extending along the centre line of the plate. This ridge has a smaller depth than in the earlier specification in order to increase suitably the vertical compliance C The compliances C and masses M are herein referred to the tip of a sapphire stylus 16 mounted in the lower end of the armature. The subscripts x, y and 2: refer to the three mutually perpendicular directions shown in the drawing.

A thin steel wire of, for example, No. 48 S.W.G; which is not shown in the drawing, is fixed at one end to the armature 10 close to the stylus 16 and has its other end fixed to the body 13 as described in the earlier specification, this Wire being placed under tension and being straight and perpendicular to the lateral plane of vibra tion of the armature in the direction y.

A pancake-shaped coil 17 is mounted to surround the armature with its axis along the longitudinal axis of the armature. A suitable permanent magnet 33 is provided, fixed rigidly to the pick-up body 13, and soft iron pole pieces 18 of this magnet have pole tips 18' and 18" extending above and below the coil 17 towards the armature. The upper pole tips 18' have their upper surfaces chamfered as shown. The arrangement is such that when the armature is in its rest position the magnetic flux between the pole pieces is in the y direction, no flux traversing the armature longitudinally.

The pole pieces 18 with their pole tips constitute one of the two cores referred to, lateral movements of the stylus 16 (in the y direction) varying the flux distribution in this core and correspondingly varying the flux flowing longitudinally through the armature 10 and hence through the coil 17.

The other core 28 is constituted by 1.25 mm. diameter Radiometal rod, shaped as shown, and having pole tips separated by an air gap 31 of about 1 mm. These pole tips have their lower extremities approximately 1.0 mm. above the upper end of the armature 10 and the front end of the support plate 11. The core 28 is in two like parts each surrounded by a coil 29, these coils being connected in series. An air gap 30 is provided in the upper part of the core 28 in order to increase the incremental permeability in the presence of a strong magnetic polarising field. The air gap 30 also contributes to rendering the

system

28, 29, 3'1 symmetrical about the three major axes, and so achieves a reasonable immunity from the effects of external interfering magnetic fields. For the same purpose the two coils 29 have equal numbers of turns and like dimensions.

The coil 17 has one end connected to a contact 34 and its other end connected to a contact 35 to which one end of the series-connected coils 29 are connected, so that the contact 35 is a common contact. The other end of the coils 2 9 is connected to a further contact 36. These

contacts

34, 35 and 36 serve as output terminals for the pick-up.

In operation, when the two modulations of the sound groove are vertical and lateral, the lateral modulation is reproduced in the same manner as with the pick-up of the earlier specification, signals corresponding to this modulation being generatedlbetween the

contacts

34 and 35.

So far as the reproduction of the vertical modulation is concerned, it will .be noted that the front end of the support plate 11 and the upper end of the armature 10* will become magnetised by induction from the magnetic field existing between the upper .pole tips 18. These magnetised parts may, therefore, be considered to behave as a small magnet with its poles separated in the y direction. As this srnall magnet is displaced in the z direction, that is in a direction parallel to the longitudinal axis of the armature 10, by the action of the vertical modulation of the sound groove, it causes a varying magnetic flux to traverse the core members 28 and coils 29. The E.M.F.-s thereby induced in the coils 29 appear between the

contacts

35 and 36.

One advantage of the pick-up described is that the provision of the facility for reproduction of the vertical modulation does not involve the provision of any extra vibratory parts beyond what are required for reproducing the lateral modulation, and additional mass loading is thus avoided.

In order to achieve a high degree of separation between the signals generated in the two

systems

10, 17, 18.and 10, 28, 29, provision is preferably made for two mechanical adjustments although this is not essential. One of these, shown in Figs. 3 and 4, may be incorporated in the mounting arrangements for the core members 28 to permit these members to be moved laterally (i.e. in the direction y) by a small amount and firmly clamped in a position in which a negligible output is obtained from the coils 28 which the stylus 16 is driven by a sound groove which is modulated only laterally. Thus the core members 28 are cemented to a mounting block 38, for instance of nonmagnetic plastic which is fixed to the body 13 by means of screws 39 which pass through slots 40* in the block 38.

The other provision that may be made is shown in Fig. and permits a small lateral adjustment (i.e. in the y direction) of the pole pieces 18, by means of which a setting can be found in which a negligible output is obtained from the coil 17 when the stylus 16 is driven by a sound groove modulated only vertically. Thus each pole piece 18 has an extension 41 in which is formed a slot 42. The pole pieces are clamped to the body 13 by screws 43 passing through the slots 42.

Owing to the increased verticalcompliance of the arma ture mounting in comparison with that in the pick-up described in the earlier specification, there is no need for the special mounting, described in the earlier specification, for preventing damage to the supporting plate 11 and wire if the pick-up should be dropped upon the surface of a record. Instead, it is sufficient to provide as shown in Fig. 1 small blocks 37 of hard rubber or plastic in order to protect the stylus from excessive vertical displacement.

Suitable values of compliance C and mass M (as hereinbeforedefined) in the three directions x, y and z in the pick-up described are as follows:

C 2.0 1 0- cm./dyne.

When the pick-up is for use with records bearing symmetrical modulations, as hereinbefore referred to, which although still at right angles to one another, have their axes rotated through 45 from the vertical, a sum and difference netwonk may be connected between the

contacts

34, 35 and 36 of Fig. 1, and output terminals. If the voltage at 34 with respect to 35 be L' and if the voltage at 36 with respect to 35 be V, the network is so constituted that between one pair of output terminals there is produced a voltage L'+V and between the other pair of output terminals there is produced a voltage L'V. Preferably, however, the coils 29are each wound in duplicate thus providing as shown in Figs. 3 and 4 two

coils

29a, 29b or 2%, 29b on each limb of the core 28. The coils may then be connected as shown in Fig. 6 in such a manner that if V is the voltage developed across each pair of coils 29, and if L is the voltage developed across the coil 17, the voltage between

terminals

34 and 35 is LV and that between the

terminals

36 and 35 is L+V.

The preferred way of interconnecting the .coils 29 in order to achieve symmetry and reduce the effect on the pick-up of interfering external magnetic fields is shown in Fig. 7, the core members 28 being indicated in phantom. The coils are all wound in the same sense.

It will be appreciated that with the arrangement of Fig. 7 a flux change produced by the vertical movement of the stylus traverses the two core members 28 in series from one pole tip, around the system to the other pole tip. Interfering fields (for example hum from transformers) tend to travel through the two core members in parallel, that is in the same direction. Thus the

coils

29a and 29a are connected in series in such a way that signal voltages add whereas hum voltages subtract. The same applies to coils 29b and 29b.

I claim:

1. A gramophone pick-up for stereophonic reproduction comprising an elongated ferromagnetic armature, a stylus at one end of said armature, means supporting said armature with freedom of movement in two modes, namely a mode corresponding to vertical movement of said stylus and a mode corresponding to horizontal move: ment of the stylus, a first winding surrounding said armature, a first magnetic core having four pole tips adjacent said armature, two on each side thereofia second magnetic core having two pole tips adjacent the end of said armature remote from said stylus, magnet means passing polarising flux through said cores and 'said armature, and a second winding surrounding said second core.

2. A gramophone pick-up according to claim 1, where: in said armature supporting means comprise a cantilever supporting plate having its free end fixed to the end of said armature remote from said stylus.

3. A gramophone pick-up according to claim 2, wherein said supporting plate is of magnetic material;

4. A gramophone pick-up according to claim'l, further comprising three output terminals, two of said terminals being connected to the ends of one of saidwindings and the other said terminal being connected through the other said winding to a tap on said one winding.

5. A gramophone pick-up according to claim 1, further comprising three output terminals, two of said terminals being connected to the ends of one of said windings and the other said terminal being connected through the other said winding to the centre point of said one winding.

References Cited in the file of this patent UNITED STATES PATENTS