US3641284A

US3641284A - Magnetic phonograph pickup having plural inducing magnets

Info

Publication number: US3641284A
Application number: US885391A
Authority: US
Inventors: Hugo Westerkamp; Robert Dubois
Original assignee: HUBER AND CO
Current assignee: HUBER AND CO
Priority date: 1968-12-16
Filing date: 1969-12-15
Publication date: 1972-02-08
Anticipated expiration: 1989-02-08
Also published as: DE1960545A1; FR2026290A1; GB1300939A

Abstract

A magnetic phonograph pickup comprises interfitting stylus and sensing assemblies. The stylus is connected to a ferromagnetic element which is magnetically saturated by at least a pair of permanent magnets which are arranged, in a common plane at right angles to the plane of symmetry through the stylus assembly, adjacent this element with similar poles directed toward it. The sensing arrangement comprises coils adjacent the element which sense its movement and produce an output signal. The entire pickup is symmetrical about a central plane of symmetry, and the magnets are inclined to this plane.

Description

United States Patent Westerkamp et al. Feb. 8; 1972 [54] MAGNETIC PHONOGRAPH PICKUP [56] References Cited g gg g INDUCING UNITED STATES PATENTS 3,441,688 41969 Sh ..l79 100.4l K [72] Inventors: l-lugo Westerkamp, Prechtal, Germany; 3 294 405 1211966 iggg 274/37 v Robert Dubois Colombiar Switzerland 3,538,266 ll/l970 Cho l79/l00.41 K [73] Assignee: Huber 8: Co., Hautervie, Switzerland I Primary ExaminerStanley M. Urynowicz, Jr. Filed 1969 Assistant Examiner-Raymond F. Cardillo, Jr. [21] Appl. No.: 885,391

[57] ABSTRACT [30] Foreign Application Priority Data A magnetic phonograph pickup comprises interfitting stylus D e c 16 1968 Switzerland 1871 8/68 and sensing assemblies. The stylus is connected to a ferromag- 1969 Switzerland "16922/69 nefic element which is magnetically saturated by at least a pair of permanent magnets which are arranged, in a common plane 52] US. Cl. ..179/100.41K, 274/37 at right angles the Plane symmetry thmhgh the Stylus 51 lm. Cl .1104: 11/12 Semhly, adjacent this element Whh Similar Poles directed [58] Field of Search ..179/100.41 A, 100.41 s, 100.41z; toward The Sensing arrangement comprises eeils adjacent 274/37 the element which sense its movement and produce an output signal. The entire pickup is symmetrical about a central plane of symmetry, and the magnets are inclined to this plane.

10 Claims, 18 Drawing Figures PAIENIED EB 8 2 SHEET 3 [IF 4 Fig.10

MAGNETIC PHONOGRAPI'I PICKUP HAVING PLURAL INDUCING MAGNETS l. FIELD OF THE INVENTION The present invention relates to a magnetic phonograph pickup and, more particularly, to such a pickup for use with stereophonical phonograph recordings. 7

2. BACKGROUND OF THE INVENTION A magnetic pickup or cartridge generally comprises a stylus which resiliently is carried by the pickup housing and is substantially rigidly connected to an element which is either a permanent magnet itself or in which a flux is induced by a permanent magnet mounted in the pickup. As the stylus or needle vibrates or oscillates because of variations in the record groove corresponding to the recording thereon, coils adjacent the magnetically permeable movable element of the stylus detect the variations in the flux therethrough and produce an output signal corresponding to variations in the flanks or root of the groove.

In the case of a stereophonic recording each flank of a usually right-angle groove carries one channel and the movement of the element in two mutually perpendicular planes is separately sensed byrespective sets of coils.

Such a pickup or cartridge is often bulky and relatively insensitive to minute variations in the groove, while being open to influence from external magnetic sources. Furthermore, the power output of such a pickup is often insufficient for many amplifiers, and must be fed through a costly preamplifier for use. Also, to achieve high power outputs, large cartridges have been necessary, thereby increasing the tracking weight of the pickup arm, increasing wear of the record, reducing sensitivity to minute changes of the track, and increasing wear of the jeweled tip or point of the stylus assembly.

It is, therefore, an object of the present invention to provide an improved magnetic phonograph pickup.

Another object is to provide such a pickup which is highly sensitive, which produces a relatively strong and distortionfree output, and which is relatively insensitive to outside magnetic fields.

3. SUMMARY OF THE INVENTION The above objects are attained, in accordance with the present invention, by a pickup or cartridge of the abovedescribed type wherein at least two coplanar magnets are mounted adjacent the'element, with similar poles directed at this element. In this manner the element is subjected to a relatively strong field which can be sensed by the coils of the pickup. These magnets are preferably permanent magnets which are each lined up with the element, that is, whose north poles are turned away from the element while their south poles are turned toward this element, or vice versa. The use of two or more magnets arrayed around the element creates a field which is concentrated in the element to a much larger extent than would be possible with a single, large magnet.

According to another feature of the present invention, the entire pickup is symmetrical about a median plane of the stylus and the element, with one magnet to each side of this plane. Another feature of the invention provides for arraying the magnets, each with an inclination at about 30 to the symmetry plane.

A pickup so constructed can produce a large output while having relatively low weight. Since the field is concentrated in the little element to a much higher degree than otherwise possible, this element and the stylus can be of lighter weight than heretofore and yet can produce an output corresponding to the minimum standards of the industry or better. Of course, the smaller the pickup, the more sensitive it is. Furthermore, the concentrated field is so strong that any outside fields will have no effect on it, since these outside fields will be relatively weak.

The above and other objects,features, and advantages will become apparent from the following description, reference being made to the accompanying drawing, in which:

LII

FIG. 1 is a perspective view of the stylus assembly of a first embodiment of the present invention, partly broken away;

FIG. 2 is a perspective view of the sensing arrangement of the first embodiment of the present invention;

FIG. 3 is a schematic diagram of the sensing arrangement of the first embodiment of the present invention shown in FIG. 2;

FIG. 4 is a top view, partly in section, of the needle assembly of the first embodiment of the present invention;

FIG. 5 is an end view, taken in the direction of arrow V of FIG. 4 of the first embodiment of the invention;

FIG. 6 is a cross section through a second embodiment of the present invention corresponding roughly to a section taken through line VI-VI of FIG. 4;

FIG. 7 is a top view, partly in section, of a third embodiment of the present invention;

FIG. 8 is an end view taken in the direction of arrow VIII of FIG. 7 of the third embodiment of the present invention;

FIG. 9 is a longitudinal section through a fourth embodiment of the present invention;

FIG. 10 is an end view of the fourth embodiment shown in FIG. 9;

FIGS. 11 and 12 are details of FIGS. 9 and 10, respectively, in enlarged scale;

FIGS. 13 and 14 are views corresponding to FIGS. 11 and 12, respectively, showing a fifth embodiment of the present invention; and

FIGS. 15, 16, 17, and 18 are views corresponding to FIGS. 9, 10, 11, and 12, respectively, showing a sixth embodiment of the present invention.

THE EMBODIMENTS OF FIGS. 1-5

A pickup comprises a needle or stylus assembly formed by a solid block 2 of synthetic resin in which is embedded a pair of magnets 3 with their north poles turned inwardly and south poles outwardly. The block 2 is notched out at 4 between the two north poles, with the base 5 of the notch 4 being V-shaped and having an apex lying in and defining a plane S of symmetry. Fitted into the back of the block 2 is a brass sleeve 6 of square cross section which is rigidly held in the block and extends along the plane S. The magnets 3 lie symmetrically on opposite sides of the symmetry plane S and have faces exposed at the notch 4.

An annular resilient rubber washer 7 having a square outline but a round center hole is snugly received in the tube 6 just behind the block 2 and in turn receives and resiliently mounts a ferromagnetic element 8 in the form of a short cylindrical sleeve having a diameter equal to about half the width of the tube 6 and a length equal to about a third that of the tube 6 and block 2 together along the plane S of symmetry. A substantially S-shaped aluminum tube 9 is fitted into the end of the element 8 extending into the block 2 and has a flattened end 10 which extends beyond the block 1 and carries a small diamond or sapphire stylus 1 1. A small nonmagnetic wire 12 is soldered to both the tube 8 and sleeve 6 to prevent them from being displaced axially relative to each other and to hold the element 8 parallel to the tube 6 when the head of the tone arm holding the pickup is resting on a record.

The pickup also comprises a sensing arrangement 13 having a pair of substantially U-shaped magnetic bands 14 and 15 forming a pair of

poles

16 and 17 and each wrapped by a

coil

18 or 19. This unit 13 (see FIGS. 2 and 3) is held in an openended housing 20 forming a magnetic return path while permitting insertion of the needle assembly (and arrangement 13 in its open end). These

poles

16 and 17 lie in mutually perpendicular planes flanking the symmetry plane S. Similar to the tube 6 of square cross section, the poles l6 and 17 define a square whose diagonal lies on the plane S of symmetry. These

poles

16 and 17, in the assembled pickup, lie just adjacent the brass tube 8.

As the stylus 11 rides in a groove of a stereophonic recording, it is displaced with components of displacement in two separate mutually perpendicular planes by the variations cut into each flank of the groove. Each flank of this groove corresponds to one stereophonic channel and lies generally at 45 to the symmetry plane S. Thus, the element 8 moves in two planes along with the stylus, the resilient washer 7 allowing a slight conical movement of this element 8. Since both north poles of the magnets 3 are directed at the element 3 and the strength of these magnets is sufficient to saturate the element 3, the magnetic field in it also gyrates and generates a varying output voltage in the

coils

18 and 19. The magnetic effect of the two magnets 3 in the element 8 is much greater than that which would be produced by a single magnet, even if it were larger than either of the magnets 3, so that the field is stronger and easier to sense. It follows that the element 8 and other parts of the pickup 1 can be much smaller than customary, yet deliver a more than adequate output, in such a manner that a lighter, more sensitive pickup is produced.

The usual desirable voltage output for a magnetic pickup having a stylus velocity of 1 cm./sec. and a load of around 47,000 ohms is between about 0.5 and 1.0 millivolts. The entire weight of the stylus assembly can be greatly reduced according to the present invention while still producing this above-described output. Of course, the lighter the stylus is, the more sensitive the pickup is. At the same time, the relatively intense magnetic field passing through the element 8 and housing 20 is less sensitive to outside magnetic fields.

THE EMBODIMENT OF FIG. 6

A needle holder la has a synthetic-resin base 2a which is identical to that of FIGS. l-S in every way except that it mounts a third magnet 3a which lies in the plane of symmetry S. The two magnets 3 lie in a common plane perpendicular to the plane of symmetry, as in FIGS. 15. In such an arrange ment the strength of this third magnet is so chosen that the element 8 is just saturated. Three very small magnets here have the effect of a very large one, all with their north poles lying very near the element 8.

THE EMBODIMENT OF FIGS. 7 AND 8 A needle holder lb has a synthetic-resin black 2b in which are mounted two long magnets 3b of square cross section. These magnets 3b are arranged with their axes A at an angle of around 30 to the plane of symmetry of the pickup. The stylus 11 is mounted in an aluminum tube 9b which has an end 24 press fitted into a ferromagnetic element 8b formed by two parallel ferromagnetic strips 25. The magnets 3b include an angle of 60 with one another.

In this embodiment the elongated magnets 3b both have their south poles turned toward the element 8b and their north poles extending to the edge of the block 2b. Such a construction very exactly focuses the lines of force of the magnets 3b on the element 817 while the outer ends are well arranged for the path of the magnetic field. In all other respects, this embodiment is identical to that of FIGS. l-S.

THE EMBODIMENT OF FIGS. 9-12 A pickup cartridge has a removable needle assembly 1c formed by a block 2c in which are mounted two magnets 30 extending perpendicularly to the symmetry plane S with their south poles turned toward the element 8 which, with the stylus l l and tube 6 is essentially identical to that of FIG. 1.

The pickup further comprises a housing 26 formed by a pair of

plastic members

27 and 28 which are held together by pins 29. Holes 30 are provided in the wide underportion 28 of the housing 26 to allow the entire assembly to be mounted in a tone arm by a pair of screws.

The sensing means includes four parallel magnetic core pieces 31 defining four poles 32 and each provided with a coil 33. Diagonally opposite coil 33 are connected in series and thence to connecting pins 35 fixed on a synthetic-resin element 34. These sensing coils 33 function essentially the same as the coils of FIGS. 1-5.

The needle assembly 1c has a brass tube or sleeve 36 which is only slightly longer than the element 8 of FIGS. 15,

although in all other respects this assembly 1c is virtually identical with that of FIGS. 1-5. The magnets 3c each have a beveled corner adjacent the element 8 but their upper surfaces lie parallel to a line L through the center of this element- 8. As in FIGS. 1-5, 7, and 8 the magnets lie in a plane perpendicular to the symmetry plane S, that is, with their north and south poles in line behind each other and orthogonal to this plane.

THE EMBODIMENT OF FIGS. 13 AND 14 There is shown here a needle assembly 10 having asynthetic-resin block 2d in which are mounted a pair of small elongated magnets 3d. Each magnet 3d defines an axis A directed at the element 8 and extending at an angle of 30 to the symmetry plane S and at a similar angle to a plane P perpendicular to this plane S and to the element 8. The assembly 1d like all the other embodiments, remains fully symmetrical, with the magnets 3d advantageously directed toward the element 8. In all other respects this embodiment is identical to that of FIGS. 9l2.

THE EMBODIMENT OF FIGS. 1518 A pickup has a housing 37 formed by a top element 27' and a base 38, the latter being essentially identical to the base 28 of FIGS. 9 and 10, as are the coils 31-33 and the connections A needle assembly 1e is provided which is substantially lighter than that of any of the other embodiments, and substantially less expensive to manufacture, as will be seen below. This assembly is identical to that of FIGS. 9-12, except that it has a synthetic-resin base 2e in which are embedded a pair of ferromagnetic cylinders 39 defining axes A".

Mounted in the

blocks

27 and 38 are a pair of cylindrica magnets 3e lying on the axes A which extend at around 30 to the symmetry plane 5 and form a slightly acute angle with the element 8. The cylinders 39 serve as pole pieces to focus the south poles of the magnets 3e on the element 8.

Such a pickup is especially advantageous since the needle assembly, which is held in place by resilient clips, does not include the magnets, but only has a pair of small ferromagnetic cylinders. Thus, this assembly, which is the only part of the pickup prone to wear and often in need of replacement, is simple and inexpensive to manufacture.

What is claimed is:

l. A magnetic phonograph pickup comprising:

a pickup housing;

a stylus resiliently carried by said housing;

a ferromagnetic element operatively connected with said stylus for joint movement therewith;

magnetic means including at least two magnets mounted on said housing adjacent said element and on opposite sides thereof, said magnets having similar magnetic poles turned toward said element, all of the magnets of said magnetic means being disposed adjacent said element and having flux paths passing directly through said element while being the sole magnetized bodies in said housing; and

coil means mounted on said housing adjacent said element for excitation by a magnetic field induced in said element by said magnets.

2. The pickup defined in claim 1 wherein said magnets are coplanar and are arrayed symmetrically with respect to a plane of symmetry passing through said element and said stylus.

3. The pickup defined in claim 2 wherein said magnets lie substantially perpendicular to said plane of symmetry.

4. The pickup defined in claim 2, further comprising a third magnet adjacent said element and having a pole similar to said magnetic poles of the first mentioned magnets turned toward said element, said third magnet lying along said plane.

5. The pickup defined in claim 2 wherein said magnets are inclined to said plane.

6 The pickup defined in claim 5 wherein said magnets are elongated and include angles of about 30 with said plane.

7. The pickup defined in claim 1 wherein said element is a ferromagnetic tube.

8. The pickup defined in claim 7 wherein said housing comprises a nonmagnetic sleeve and a resilient washer therein, said tube being resiliently mounted in said washer.

9. The pickup defined in claim 1, wherein said housing com- I prises a pair of interfitting synthetic-resin blocks, said stylus

Claims

1. A magnetic phonograph pickup comprising: a pickup housing; a stylus resiliently carried by said housing; a ferromagnetic element operatively connected with said stylus for joint movement therewith; magnetic means including at least two magnets mounteD on said housing adjacent said element and on opposite sides thereof, said magnets having similar magnetic poles turned toward said element, all of the magnets of said magnetic means being disposed adjacent said element and having flux paths passing directly through said element while being the sole magnetized bodies in said housing; and coil means mounted on said housing adjacent said element for excitation by a magnetic field induced in said element by said magnets.

6. The pickup defined in claim 5 wherein said magnets are elongated and include angles of about 30* with said plane.

7. The pickup defined in claim 1 wherein said element is a ferromagnetic tube.

9. The pickup defined in claim 1, wherein said housing comprises a pair of interfitting synthetic-resin blocks, said stylus being resiliently carried by one of said blocks, said pickup further comprising at least two elongated metallic bodies extending from said poles of said magnets to immediately adjacent said element.

10. The pickup defined in claim 1 wherein said element comprises a pair of substantially parallel ferromagnetic strips coupled with said stylus.