US3645541A

US3645541A - Pickup arms

Info

Publication number: US3645541A
Application number: US807547A
Authority: US
Inventors: Alastair John Roberts Steyning
Original assignee: Individual
Current assignee: Individual
Priority date: 1968-03-19
Filing date: 1969-03-17
Publication date: 1972-02-29
Anticipated expiration: 1989-02-28
Also published as: GB1273981A

Abstract

This invention relates to an improved phonograph pickup arm assembly affording a wide range of adjustments. In particular, the arm includes means for adjusting playing weight in which variation of playing weight is accompanied by automatic adjustment of a force correcting the side thrust of skating force at the stylus. The correcting force is produced by inclination of the pivotal axis of the arm by an angular amount about which produces an appropriate horizontally resolved part of the vertical force of the stylus. The pickup arm can be unplugged towards its inward end.

Description

United States Patent Rohertson-Ailtman Web. 29, 11972 [54] HICKUP ARMS 3,088,742 5/1963 Alexandrovich.... .....274/23 [72] Inventor: Masmir John kobensonflikman 3,219,351 11/1965 Sharper et al ..274/23 Stokes Steymng Sussex England Primary ExaminerLeonard Forman [22] Filed: Mar. 17, 1969 Assistant Examiner-Charles E. Phillips [2]] Appl NOJ 807,5W7 Attorney Laurence E. Laubscher [57] ABSTRACT [30] Foreign Application Priority Data This invention relates to an improved phonograph pickup arm Mar. 19, 1968 Great Britain ..13,318/68 bl ff ding a id range f adjustments. In particular, the arm includes means for adjusting playing weight in which [52] U.S. Cl. ..274/23 R va i ti n of playing weight is accompanied by automatic ad- [511 p 3/10 justment of a force correcting the side thrust of skating force Fleld of Search at the stylus. The correcting force is produced inclinaion of the pivotal axis of the arm by an angular amount about [56} References Cited which produces an appropriate horizontally resolved part of UNITED STATES PATENTS the vertical force of the stylus. The pickup arm can be un l 792 830 2/1931 Goudy 274/23 plugged towards its inward end. 3,051,494 8/1962 Walton ..274/23 18 Ciaims, 6 Drawing Figures Patented Feb. 29, 1972 3 Sheets-Sheet 1 V U) AlaS fkfl R Cr S n-H KM INVENTOR BY W zem ATTORNEY Patented Feb. 29, 1972 I 3,645,541

3 Sheets-Sheet 2 INVENTOR ATTORNEY PICKUP ARMS This invention relates to support arms for gramophone pickups and has for its object to provide an improved construction of arm in which adjustments of the playing conditions can be readily effected.

\ Apickup arm for use with high-quality pickup cartridges must have certain facilities of adjustment, and this is especially so where an arm is intended for use with different heads or cartridges, of different weights and playing weights. For example, it is essential that the counterbalancing of the arm should be adjustable, to allow for different weights of head or cartridge and it is also desirable that there should be a separate means adjusting the playing weight of the cartridge, preferably by means which allows the playing weight to be indicated, and set or reset as desired.

Pickup arms used for pickups for gramophone reproduction are almost exclusively of the pivoted type, where the arm can pivot about a vertical axis to allow the pickup stylus to traverse across the radius of the gramophone record. With this type of arm, it is not possible for the longitudinal axis of the pickup cartridge to be tangential to the record groove at all radii as the pickup traverses the record. To minimize the tracking error due to this fact it is the practice to make the stylus overhang, that is, to make the distance from the pickup stylus to the arm pivot slightly greater than the distance from the record center to the arm pivot. The axis of the cartridge is then disposed at a suitable angle to the line forming the stylus and the vertical pivot axis.

This arrangement can be shown to cause a side thrust on the pickup stylus, in a direction towards the center of the record. Such a side thrust is generally undesirable as it means the stylus is working in a nonsymmetrical, biased condition with respect to the groove; it is particularly undesirable when single roove stereophonic records are being played. The inclined side wall of the record groove gives the side thrust a resolved part which tends to lift the stylus from the groove, and this requires an increase of playing weight of the stylus, which is also undesirable.

The magnitude of the side thrust depends upon a number of factors, but for any particular arm, the side thrust will be a fixed proportion of the frictional force or drag imposed on the stylus in the direction along the record groove at the point of contact. The value of this proportion is fixed by the dimensions of the pickup arm, in particular the distance from the vertical pivot of the arm to the stylus tip, and the overhang. The value of the proportion will also depend to some extent on the radius of the groove of the record which is being reproduced, but it is convenient to take, as reference, a radius of about 4 inches, which is the center radius of the playing area of a conventional 12 inch record. For practical purposes, therefore, with a given arm installation the ratio of the side thrust to the frictional force can be regarded as sensibly constant.

The frictional force at the stylus will be equal to the product of the playing weight of the pickup, that is, the downward force at the stylus, and the coefficient of friction which exists between the stylus tip and the record. This in turn depends on certain factors: the material of the record, and the finish and tip radius of the stylus. With modern longplaying vinyl records, and with a suitable stylus tip radius the coefficient of friction for a given cartridge and stylus is reasonably constant.

In practice, with different pickup installations, it is found that they side thrust lies in a range of about 0.15 to 0.30 times the playing weight. For a given pickup, the side thrust tends to be a fixed proportion of the stylus playing weight, so that if the playing weight is changed, there will be a corresponding change in the side thrust.

In the past, means have been suggested for imposing on the pickup a force which is substantially equal and opposed to the side thrust. For example, a widely used expedient is a small weight suspended by a thread attached to the arm. Magnetic bias, and bias by means of small weighted arms have also been suggested but with all these forms of adjustment it has been necessary to make a separate adjustment of the side thrust counterbalancing force each time that an adjustment is made of the playing weight.

One feature of a pickup an accordance with the present invention is that means are provided whereby the playing weight of the pickup can be adjusted; means are also provided whereby a force is applied to balance the side thrust and, in addition, it is arranged that any adjustment of the playing weight by the means afforded for changing playing weight also changes the side thrust correcting force.

In a pickup arm of a type which is intended for use with different cartridges arrangements are often made for unplugging the head, including the cartridge, and replacing it with another head and cartridge. The back of the head, for this purpose may include the necessary mechanical coupling means, in conjunction with electrical plug and socket means for establishing the necessary electrical connections to the cartridge.

While this facility of head change is: a requirement, it adds to the weight of the head, which is undesirable. In accordance with another feature of the invention, in a pickup arm construction the head is made separable, but the separable portion includes a substantial part of thepickup arm. By this means the separable mechanical and electrical couplings are disposed closer to the horizontal arm pivot axis, where the resultant increase of moment of inertia will be less.

Other features and advantages of the invention will appear from the following description of an embodiment thereof,

given by way of example, in conjunction with the accompanying drawings, in which FIG. 1 is a plan view of a gramophone pickup and arm;

FIG. 2 is a side elevational view of the pickup and arm of FIG. ll;

FIG. 3 is a side elevational view, partly in section, on the line 3-3 of FIG. 11;

FIG. 4 is a sectional view taken on the line 4-4 of FIG. 3;

FIG. 5 is a sectional view taken on the line 5-5 of FIG. 1, and

FIG. 6 is a fragmentary elevational view looking in the direction of arrows 5-5 of FIG. l.

The pickup arm shown comprises a main base plate 10, in which is carried a sliding bush ll, forming a bearing for a main support pillar 12. The base plate is adapted to be carried by a support plate 13 so as to be readily detachable therefrom, and for this purpose the base plate has securing and locating pegs 114, which are adapted to engage in sockets K5 in the support plate. The pegs are split, so that they will each engage a socket l5 accurately and with sufficient frictional grip to hold the base plate in position on the support plate in use. The support plate is intended to be fastened to a motor board 16, for example by screws 17.

The pillar 12 supports a pillar head assembly 20 from the rear end of which is supported a cross shaft bearing sleeve 21. In this sleeve a hollow shaft 22 is mounted in miniature ball bearings 23. To one end of the shaft is secured a cap 24-, by

means of a screw 25, while the other end of the shaft carries a yoke 26, held by a hollow screw 27 and washer 28. Means are provided carefully to seal the bearings 23 against the ingress of dust or other foreign material. It will be observed from FIG. 5 that the axis of shaft 22 is at an angle a to the horizontal.

The outer ends of the arm of yoke 26 support the pickup arm assembly indicated generally at 30. This includes a bearing section 31 which is mounted in the arms of the yoke 26 by bearings arranged to provide a pivotal movement which is substantially at right angles to the axis of shaft 22. At its section 31, the pickup arm is hexagonal, as shown in FIGS. 1 and 5, and is pivotally mounted by precision ball bearings 32, fitting in the arms of the yoke, and pillar screws 33, threaded into the hexagonalrsection 31 of the arm. Caps 34 and sealing rings 35 are provided to prevent ingress of any dust or the like to the bearings 32.

Rearwardly of the section 31, the arm has an extension 36 (FIG. 3) on which is arranged a cou'nterbalancing assembly.

munn nlun which permits the arm to be balanced about the axis of shaft 22, and also about the axis defined by bearings 32. A sleeve 37 is supported from the rearward end 36 of the arm by means of three spaced grommets 38 and a rubber plug 39; this provides a decoupling of mass between the sleeve and the arm. A cap 40 is internally threaded and screwed on the rearward part of the sleeve 37. A milled ring 41, which houses removable annular weights 42, is held frictionally on the outside of cap 40 by means of a shaped nylon ring 43. When the milled ring 41 is rotated, the cap will be adjusted axially, to pennit variation of the counterbalancing. Rings 42 can be used or removed as necessary to counterbalance the arm.

A further ring 45 is captive on the forward end of cap 40; ring 45 will be moved axially along section 31 of the arm when the milled ring 41 is rotated to adjust the counterbalancing but is held against rotation by means of a key way and grub screw arrangement, between the ring 45 and the sleeve 37. The outer part of ring 45 carries a second milled ring 46 to which is fastened an adjusting weight 48 (FIG. 4) of semicircular shape, so that by rotating the milled ring, with respect to the inner ring portion 45, lateral balance of the arm can be adjusted.

To the forward end of section 31 of the arm is attached a cranked coupling section 49. Section 49 has a tubular portion 50 which receives the rear end of a separable section 51 of the pickup arm. The tubular portion 50 carries one portion 52 of an electrical coupling, the other part 53 of which is carried by section 51 of the arm. The rear end of section 51 is a snug and vibration free fit in section 50 of the coupling section. The forward end of section 51 carries the pickup head 54. By applying gentle endwise pressure to the arm section 51, it can be separated electrically and mechanically from the coupling member 50, thus permitting alternative pickup heads, each of which will be fitted with its section 51 of pickup arm, as desired. By arranging the coupling 52, 53 at the inward end of the pickup arm, the mass at the head of the arm is reduced, requiring a lesser counterweight and permitting a correspondingly lighter arm construction. The coupling 52, 53 will normally be located as near the vertical pivot axis as is convenient, it is desirable that the coupling should be at least within the inner half of the length from the stylus to the vertical axis. There will be an improvement if only a short length of section 51 is attached to the head.

Means may be provided for permitting slight angular adjustment for the coupling member on section 31 of the arm so that the stylus may be disposed vertically with respect to the record. Electrical connections to the socket member 52 pass first through an opening 55 in the coupling member 50 and through section 31 of the arm, then through an opening 56 (FIG. in the wall of section 31 and thence through the center of sleeve 22, before emerging through the center of pillar 12.

Means are provided for varying the playing weight of the pickup. Cap 24, fastened to shaft 22, is fashioned to provide a sliding fit for a rod 60 (FIG. 1), which bears two weights 61 and 62 at its respective ends. The rod carries gradations 63, with an index mark on cap 24. In use, the rod 60 is moved to its initial or zero playing weight marking, and the arm is then counterbalanced by adjustment of the main counterweight by means of milled ring 41. The lateral arm balance can then be adjusted by ring 46. In this condition, the arm will be precisely balanced and there will be no downward force exerted at the stylus 64. To impose the desired playing weight at the stylus 64, the rod 60, with its weights, can now be moved forwardly, that is, to the left as viewed in FIG. 2; conveniently, each gradation 63 will correspond to a given increase of playing weight, such as 0.25 or 0.50 gram.

As a'result of the imposition of a playing weight at the stylus, a side thrust will be created in the manner described above, of a magnitude which for a given installation is a fixed proportion of the playing weight. Conveniently, additional means may be provided whereby the side thrust produced can be offset by giving to the pickup arm a further bias tending to move it in the outward direction; the bias is adjustable and must be adjusted for each change of playing weight.

However, with the pickup arm described, the axis of the shaft 22 is at an angle to the horizontal and the axis of the pivot defined by bearings 32 will be correspondingly inclined to be vertical. As a result, the imposition of force at the stylus in the downward direction will be accompanied by a lateral force, proportional to the downward force, and related to that downward force by the tangent of the angle that the axis of shaft 22 makes with the horizontal or, what is the same, the angle [3 between the axis of bearings 32 and the vertical. By suitable choice of this angle and B being equal) the desired proportion can be obtained between the horizontal and vertical forces imposed at the stylus by the playing weight. Further the desired relationship between the downward force and the lateral force will be maintained for different settings of the playing weight adjustment afforded by slide rod 60. Any change of playing weight effected by means of the rod 60 will cause. a corresponding and appropriate change of the side thrust compensation.

As mentioned above, the relationship between the vertical force and the side thrust depends on certain factors in any given installation but may vary somewhat from one pickup installation to another. It is therefore desirable that the angle of the shaft 22 to the horizontal should be adjustable. To this end, the sleeve 21 is mounted on the pillar head assembly by means of a pillar screw 66, thus permitting the sleeve 21 to rotate about the axis of the screw. Located in a recess in the sleeve 21 is a plunger 67, loaded by a compression spring 68, and the plunger 67 bears against the overhanging portion 69 of the pillar head assembly. A grub screw 69a threaded into the overhanging portion 69 bears against part of the sleeve 21, so that by rotation of the grub screw 69a the angle of inclination of the shaft 22 can be varied, against the compression of spring 68.

It is desirable that the playing weight adjustment system, including shaft 22 and yoke 26, should be independently balanced, that is to say, if the pickup arm were released from the yoke bearings at 32 the parts including the shaft 22 and weights 61 and 62 should be at the position of zero playing weight adjustment and the parts balanced about the axis of shaft 22. A facility of adjustment that is desirable in a pickup arm in general, and essential in a versatile pickup arm, is a ready means of adjusting the extent of overhang by varying the position of the vertical pivot axis of the arm with respect to the center of the record turntable. With this object the bush 11 is mounted in a slot in the base plate 10, and these two relatively movable parts are connected by a threaded rod 70 and engaging a nut 71 on the bush, with a milled screw 72 on the rod; by rotation of the milled screw the position of the bush inn the slot can be varied and the overhang adjusted. Graduations 75 can be provided to enable a given setting to be noted and reestablished.

Another desirable facility of adjustment is variation of the vertical height of the pickup arm such as 51 above the motor board 16. In the pickup described, the pillar 12 is made vertically movable in bush l1, and the relative position of the two parts can be adjusted by a threaded rod 78, screw threaded into the bush, and rotatable in the pillar head assembly 20, by means of a milled knob 76.

It is also convenient to arrange for a lowering device for the arm. For this, an arm rest 77 can be fastened to a vertically movable part of the pillar head assembly 20, this arm being vertically movable, controlled by a dash pot, not shown, by suitable operating lever, which may extend from the assembly 20.

The pickup arms construction described is very advantageous in use. It can be adjusted for counterbalance, lateral balance, playing weight, vertical height, and overhang, and thus lends itself to use with a wide variety of pickup heads and cartridges. Change of playing weight is automatically accompanied by the appropriate side thrust correction once the adjusting screw 70 has been adjusted. The pickup head can be rapidly changed by the withdrawal of the arm 51, and the arrangement of the electrical and mechanical couplings towards the rear part of the arm reduces the head weight. The entire pickup assembly complete with the base plate can be rapidly removed from the mounting plate, by virtue of the pegs M, a facility which is valuable with professional use f the pickup assembly. It is also an advantage that the pickup arm is cranked as appears more clearly from H6. 3, especially in conjunction with the feature that the arm is pivoted by the offset arrangement, as appears from FIG. 1. This permits of a low-compact construction.

What is claimed is: 1. A pickup arm assembly for reproducing sound from a disk type phonograph record supported by a rotatably driven generally horizontal turntable, comprising a. a pillar head assembly adapted for arrangement ad jacent said turntable; b. pickup arm means for supporting at one end a pickup cartridge (54) having a stylus (64)); 0. means connecting said pickup arm means with said pillar head assembly for vertical and horizontal pivotal movement, said connecting means including 1. intermediate support means (22, 26) pivotally connected with said pillar head assembly for movement about a first generally horizontal pivot axis, and

2. means (32, 33) connecting said pickup arm means with said intermediate support means for movement about a second pivot axis that is inclined to the vertical by an acute angle (B):

d. counterbalance means (41, 416) balancing said pickup arm means to a counterbalanced condition relative to said generally horizontal pivot axis; and

e. biasing means (60, 61, 62) for rotating said intermediate support member about its axis to impose on the stylus a selected downwardly directed playing force that is automatically accompanied by a corresponding horizontally directed antiskating side thrust component which is a function of said acute angle (,8).

2. Apparatus as defined in claim 1, wherein the first pivot axis is inclined to the horizontal by an acute angle (or) equal to said acute angle ([3).

3. Apparatus as defined in claim 1, and further including third pivot means (66) connecting said intermediate support means with said pillar head assembly for pivotal adjustment about a horizontal adjustment axis normal to the vertical plane containing said first pivot axis, and adjustment means (690) for pivoting said intermediate support means about said horizontal adjustment axis to vary the angle of inclination of said first pivot axis.

4. Apparatus as defined in claim 11, wherein said biasing means includes weight means (61, 62) radially adjustable relative to said intermediate support means.

5. Apparatus as defined in claim 1, and further including a base plate (10); and shaft means (E2) connecting said pillar head assembly to said base plate for vertical movement relative to said base plate.

6. Apparatus as defined in claim 5, and further including means ('78) or adjusting the height of said pillar head assembly and said shaft means relative to said base plate.

7. Apparatus as defined in claim 5, and further including means including a sliding bush (11) for horizontally adjusting said shaft means and said pillar head assembly relative to said base plate.

8. Apparatus as defined in claim l, and further including means for adjusting the lateral balance of said pickup arm means, comprising an eccentrically weighted member (48) connected for coaxial rotation relative to said pickup arm means.

9. Apparatus as defined in claim 8, wherein said counterbalance means is threadably connected with said pickup arm means for axial adjustment relative thereto.

10. Apparatus as defined in claim 9, wherein said counterbalance means includes separable sections (42).

11. Apparatus as defined in claim 9, wherein said lateral balance weight means (48) is connected for axial displacement of said pickup arm means simultaneously with said counterbalance means.

12. Apparatus as defined in claim 11, .and further including means preventing rotational movement of said lateral balance weight means relative to said pickup arm means upon rotation of said counterbalance means.

13. Apparatus as defined in claim ll wherein said pickup arm means includes pickup head means 54 for supporting a stylus, said pickup head means including detachable electrical and mechanical coupling (52, 53) for the removal of said pickup head means from said arm means.

M. Apparatus as defined in claim 13, wherein said couplings are arranged within the length of the arm, so that upon removal of the pickup head means, at least a part of the length of said arm means is removed therewith.

115. Apparatus as defined in claim M, wherein said couplings are arranged in the inner half of the length of said arm means between the stylus and the arm pivot means.

16. Apparatus as defined in claim l, wherein said pickup arm means is cranked, the portion of the arm means near the pillar head assembly being lower in use than the stylus-supporting end portion of said arm means.

17. Apparatus as defined in claim il, including a base plate attached to said pillar head assembly;

a fixed base support member (13); and locating and retaining means (1d, 15) for locating and retaining said base plate relative to said base support member.

18. Apparatus as defined in claim 17, wherein said locating and retaining means includes pegs and cooperating sockets on the respective parts.

Claims

1. A pickup arm assembly for reproducing sound from a disk type phonograph record supported by a rotatably driven generally horizontal turntable, comprising a. a pillar head assembly (20) adapted for arrangement adjacent said turntable; b. pickup arm means (30) for supporting at one end a pickup cartridge (54) having a stylus (64); c. means connecting said pickup arm means with said pillar head assembly for vertical and horizontal pivotal movement, said connecting means including 1. intermediate support means (22, 26) pivotally connected with said pillar head assembly for movement about a first generally horizontal pivot axis, and 2. means (32, 33) connecting said pickup arm means with said intermediate support means for movement about a second pivot axis that is inclined to the vertical by an acute angle ( Beta ): d. counterbalance means (41, 46) balancing said pickup arm means to a counterbalanced condition relative to said generally horizontal pivot axis; and e. biasing means (60, 61, 62) for rotating said intermediate support member about its axis to impose on the stylus a selected downwardly directed playing force that is automatically accompanied by a corresponding horizontally directed antiskating side thrust component which is a function of saId acute angle ( Beta ).

2. means (32, 33) connecting said pickup arm means with said intermediate support means for movement about a second pivot axis that is inclined to the vertical by an acute angle ( Beta ): d. counterbalance means (41, 46) balancing said pickup arm means to a counterbalanced condition relative to said generally horizontal pivot axis; and e. biasing means (60, 61, 62) for rotating said intermediate support member about its axis to impose on the stylus a selected downwardly directed playing force that is automatically accompanied by a corresponding horizontally directed antiskating side thrust component which is a function of saId acute angle ( Beta ).

2. Apparatus as defined in claim 1, wherein the first pivot axis is inclined to the horizontal by an acute angle ( Alpha ) equal to said acute angle ( Beta ).

3. Apparatus as defined in claim 1, and further including third pivot means (66) connecting said intermediate support means with said pillar head assembly for pivotal adjustment about a horizontal adjustment axis normal to the vertical plane containing said first pivot axis, and adjustment means (69a) for pivoting said intermediate support means about said horizontal adjustment axis to vary the angle of inclination of said first pivot axis.

4. Apparatus as defined in claim 1, wherein said biasing means includes weight means (61, 62) radially adjustable relative to said intermediate support means.

5. Apparatus as defined in claim 1, and further including a base plate (10); and shaft means (12) connecting said pillar head assembly to said base plate for vertical movement relative to said base plate.

6. Apparatus as defined in claim 5, and further including means (78) or adjusting the height of said pillar head assembly and said shaft means relative to said base plate.

8. Apparatus as defined in claim 1, and further including means for adjusting the lateral balance of said pickup arm means, comprising an eccentrically weighted member (48) connected for coaxial rotation relative to said pickup arm means.

12. Apparatus as defined in claim 11, and further including means preventing rotational movement of said lateral balance weight means relative to said pickup arm means upon rotation of said counterbalance means.

13. Apparatus as defined in claim 1 wherein said pickup arm means includes pickup head means 54 for supporting a stylus, said pickup head means including detachable electrical and mechanical coupling (52, 53) for the removal of said pickup head means from said arm means.

14. Apparatus as defined in claim 13, wherein said couplings are arranged within the length of the arm, so that upon removal of the pickup head means, at least a part of the length of said arm means is removed therewith.

15. Apparatus as defined in claim 14, wherein said couplings are arranged in the inner half of the length of said arm means between the stylus and the arm pivot means.

16. Apparatus as defined in claim 1, wherein said pickup arm means is cranked, the portion of the arm means near the pillar head assembly being lower in use than the stylus-supporting end portion of said arm means.

17. Apparatus as defined in claim 1, including a base plate (10) attached to said pillar head assembly; a fixed base support member (13); and locating and retaining means (14, 15) for locating and retaining said base plate relative to said base support member.