US3546399A - Induced magnetic moving iron stereophonic phonograph pickup with replaceable stylus assembly - Google Patents

Description

O United States Patent [u13,546,399

[72] Inventors Walter O. Stanton 3,077,521 2/1963 Aherns et al 179/ 100.41 Laurel Hollow; 3,294,405 12/1966 Pritchard 274/37 John P. Kuehn, Huntington, New York 3,441,688 4/1969 Shaper 179/ 100.41 PP 794921 Primary Examiner-Bernard Konick [22] Filed Jan. 29, 1969 A sslstan! Examiner-Raymond F. Cardillo Jr. Continuation-impart of Ser. No. 725,457, Anome Kane Dalsimer Kane S d K April 30, 1968, abandoned y [45] Patented Dec. 8, 1970 [73] Assignee Pickering 8: Company, Inc.

Plainview, Long Island, New York a h York ABSTRACT: A magnetic stereophonic phonograph pickup is disclosed wherein the stereophonic output is produced by an [54] INDUCED MAGNETIC MOVING IRON elongated tubular armature of permeable material pivotally STEREOPKONC PHONOGRAPH PICKUP WITH mounted at one end for movement of its opposite end within a REPLACEABLE STYLUS ASSEMBLY quadrangular cluster of four pole pieces, said four pole pieces 9 chims, 6 Drawing F18, forming the terminal portions of two closed path magnetic circuits each completed through a core with a voltage generating 1 n "179/ 101,41 coil mounted thereon, magnetomotive force being provided 274/37 by a stationary permanent magnet magnetically coupled with cl the pivotally mounted end of the moving armature to [50] Field ol'Search ....l79/ 100 41, minimize motion between the permanent magnet d arma Cyclopedw); ture in the region of the magnetic coupling and to maintain the Q/26i274/37 armature tube in substantially magnetically saturated condi' tion, and wherein a shorted turn device is electromagnetically [56] References Cited coupled with each magnetic circuit to improve high frequency UNITED STATES PATENTS response and in the preferred embodiment additionally pro- 3,062,925 11/1962 Pritchard i. 179/ 100.41 vide crosstalk compensation.

PATENTEU DEC-81970 sum 2 OF. 9

INVENTORS W/IL TEA 0- Sin/via WA/ R Kl/f/Ml BY 7 21. -DM, A M ,W

ATTORNEYS PATENTED DEC-8 I970 SHEET 3 OF 9 ATTORNEYS PAtimtum-aam I 35463 SHEUEOFQ ATTORNEYS PATENTED BEE-8 19m SHEET 7 OF 9 PATENTED DEE-8 mm SHEET 8 OF 9 PATENIEnusc-emm 3546399 SHEET 9 BF 9 INVENTOR S BY 5 bm #1 I $144; .w

ATTORNEYS INDUCED MAGNETIC MOVING IRON STEREOPHONIC PHONOGRAPH PICKUP WITH REPLACEABLE STYLUS ASSEMBLY RELATED APPLICATIONS This application is a continuation-in-part of our prior copending applicationfor United States Letters Patent entitled MOVING IRON STEREOPHONIC PHONOGRAPH PICKUP which was filed Apr. 30, 1968, and which bears U.S. Pat. Ser. No. 725,457 now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a new and' improved magnetic stereophonic phonograph pickup of the moving iron type and in particular to a stereophonic phonograph pickup wherein the moving armature is composed of a material of high permeability and magnetomotive force is provided by a stationary permanent magnet.'

2. Description of Prior Art Stereophonic phonograph pickups of the moving iron type in which the source of flux is a stationary permanent magnet, magnetically coupled with the moving armature, provide an advantage over stereophonic pickups of the moving permanent magnet type in that the mass of the moving'armature may be significantly reduced, thereby providing increased compliance of the armature in response to undulations of the stylus in the record groove. In the past, however, stereophonic pickups of the moving iron type have been deficient in the separation of the two channels of the output and the sensitivity and linearity of response because of changes of flux induced in one channel of the stereo output by motion of the arr'natui-e in response to undulations of the stylus in the record groove corresponding to the other stereo channel, and because of variations in the magnetization of the moving armature.

SUMMARY OF THE INVENTION It is an object of the present invention to overcome the difficulties and disadvantages heretofore encountered and to provide an improved stereophonic phonograph pickup of the moving iron type having a minimum number of parts which may be readily assembled together to thereby reduce the bulk and mass of the pickup and facilitate manufacture and assembly.

Another object of the invention is to provide a stereophonic pickup of the moving iron type having a novel flux path configuration and shielding means providing two separate magnetic circuits which effectively minimize crosstalk.

A further object of the invention is to provide a stereophonic pickup in which the moving iron armature is maintained in a substantially uniformly and consistently magnetically saturated condition to provide increased sensitivity, linearity of response, and channel separation.

Yet another object of the invention is to provide a stereophonic pickup of the moving iron type having flat frequency response and uniform phase characteristics between the channels of the stereo output.

In order to accomplish these results the invention contemplates the provisionof a supporting structure having flux path means of permeable material supported thereon for providing two closed path magnetic circuits each including a core means, having a voltage generating coil mounted thereon, terminating in a pole piece, and a flux path leg terminating in another pole piece in opposing spaced relation with the respective core pole piece, and wherein the pole pieces from the two magnetic circuits form a quadrangular cluster about a common space.

Another aspect of the invention contemplates the provision of an improved moving system including a record engaging stylus, a tubular armature of permeable material, stylus connecting means, pivotally mounting the armature at the end adjacent the stylus, for movement of the opposite end of the armature within the common space formed by the quadrangular cluster of pole pieces in response to undulations of the stylus in the record groove.

Yet another aspect of the invention contemplates the provision of an improved flux source including a permanent magnet mounted in the supporting structure outside the pole pieces and magnetically coupled at one of its poles to the pivotally mounted end of the armature,'to minimize the relative motion between the permanent magnet and armature in the region of magnetic coupling, and thereby maintain the armature tube in substantially uniformly and consistently magnetically saturated condition, improving sensitivity and linearity of response and separation of the stereo channels.

Another aspect of the invention contemplates the provision of a shorted turn device electromagnetically coupled with each magnetic circuit to add to losses normally encountered in the permeable material of each magnetic circuit in an amount controlled by empirical selection of the dimension of the shorted turn device for best flat frequency response of the pickup cartridge and for uniform phase characteristics between the channels of the stereo output and wherein a preferred embodiment the shorted turn device additionally provides crosstalk compensation.

The invention also contemplates the provision of an improved supporting structure including a first molded plastic body and a second molded plastic body shaped to accommodate the various elements of the pickup and contoured to frictionally and tensionally engage each other to form a unitary supporting structure for ease in manufacturing and assembly.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a magnetic stereophonic pickup embodying the invention;

FIG. 2 is an exploded view showing the several parts making up the cartridge body of the pickup illustrated in FIG. 1;

FIG. 3 is a side elevation view of the first molded plastic body with appropriate pickup parts assembled thereon, and the second molded plastic body with the permanent magnet assembled thereon before joining to form the unitary supporting structure for the pickup cartridge;

FIG. 4a is a side elevation view of the first and second molded plastic bodies illustrated in FIG. 3 after joining to form the assembled supporting structure for the pickup cartridge;

FIG. 4b is a similar view of the supporting structure illustrated in FIG. 4a with additional parts assembled thereon after joining; I

FIG. 4c is an end elevation view of the supporting structure illustrated in FIG. 4a showing the mounting of the external group strap;

FIG. 5 is an enlarged longitudinal sectional view in the direction of the arrows on line 5-5 of FIG. 1;

FIG. 6 is a transverse sectional view in the direction of the arrows on the line 6-6 of FIG. 5;

FIG. 7 is a transverse sectional view of the pickup in the direction of the arrows on the line 7-7 of FIG. 5;

FIG. 8 is a longitudinal sectional view in the direction of the arrows on the line 8-8 of FIG. 5;

FIG. 9 is a detailed sectional view in the direction of the arrows on the line 9-9 of FIG. 5 illustrating joinder of the first molded plastic body and the second molded plastic body;

FIG. 10 is an exploded perspective view of the pickup illustrated in FIG. 1 showing the cartridge body and replaceable moving system assembly in separated relation;

tion;

FIG. 13 is an exploded perspective view of portions of another modified structure which is a preferred embodiment;

and

FIG. 14 is a segmentary sectional view of the embodiment shown in FIG. 13.

THE DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiment of the invention illustrated generally in FIG. 1 includes a removable and replaceable moving system designated generally by the number which responds mechanically to the undulations of a record groove and a cartridge body designated generally by the number 21 which includes a transducer system which responds electrically and magnetically to the motion of the moving system to produce a stereophonic output of two channels through the left channel terminal pins 22 and 23 and the right channel terminal pins 24 and 25. A bracket 26 secured to the cartridge body provides a means for securing the pickup to a phonograph player tone arm.

Turning more particularly to the cartridge body and transducer system mounted therein, the invention provides for the production of a pickup cartridge of simplified design having a minimum number of parts which can readily be assembled together. As illustrated in FIG. 2, the cartridge body includes a supporting structure formed in two separate interlocking parts for fully automatic molding from a plastic such as high-impact polystyrene.

The first molded body 27 is contoured with holes 28 and 30 through which the right and left channel core means 31 and 32, terminating in right and left channel pole pieces 33 and 34 respectively, are inserted from below. Coil strap 35 is placed over the core means 31 and 32 so that it rests upon the first molded body with the core means projecting through the two holes formed in the coil strap. Voltage generating coil bobbins 36 and 37 upon which are wound voltage generating coils 38 and 40 may then be placed over core means 31 and 32 respectively. Vertical grooves 42 and 43 in the first molded body 27 receive and retain the right and left channel flux path legs 44 and 45 which are inserted from below andterminate in right and left channel flux path legpole pieces 46 and47 respectively. The pole pieces are thus arranged in a quadrangular cluster wherein the cluster has opposing or facing angles of equal magnitude.

Vertical passageways 48 and 50 receive and retain the legs 51 and 52 of core coupling strap 53 respectively adjacent and in engagement with flux path legs 44 and 45 while the other legs 55 and 56 of strap 53 are retained in the bobbin openings 57 and 58 adjacent and in engagement with the right and left channel core means 31 and 32 respectively. Resilient metal strap 61 is used to ground the internal metal parts to the shell.

A longitudinal recess 62 through the base of the first molded body frictionally and releaseably retains the moving system. Terminal pins 22, 23, 24 and 25 illustrated in FIG. 1 may be inserted through terminal pin holes 22a, 23a, 24a and 25a formed in terminal block 63 of the first molded body assembly and cemented in place. To provide proper orientation for plug-in of the pickup into a tone arm the terminal pins are placed in a nonsquare configuration as shown in FIG. 4c. The first molded body assembly with appropriate parts in place before joining the first and second molded plastic bodies is illustrated in FIG. 3.

The second molded body assembly 64 includes a vertically elongated magnet retaining block section with a rectangular indentation 65 in which is housed the permanent magnet 66. A circular longitudinal aperture 67 in the base of the magnet retaining block provides a channel through which the moving system may be inserted. v

Laterally extending legs 68 and 70 of the second molded body have internal projections 68a and 70a formed thereon to provide interlocking relation with projections 68b and 701) formed on the rear molded body to retain the molded parts in assembled relationship as shown in FIG. 9. Grooves 7i and 72 formed between the laterally extending legs 68 and 70 provide support from below for the right and left channel flux compen sating pole pieces 46 and 47 respectively when the two molded body parts are assembled. Projections 73 and 74 formed in the molded body 64 provide support from below for the right and left channel core means 31 and 32 and pole pieces 33 and 34 respectively when the parts are assembled as shown in FIG. 7. As illustrated in FIG. 3, complementary contacting slanted surfaces 75a and 75b, and 76a and 76b are provided in the first and second molded plastic bodies respectively which provide a wedging action and pressure between the two portions to firmly maintain the pole pieces in position when the first and second molded plastic bodies are snapped together.

Permanent magnet 66 includes a semicircular indentation 77 and is cemented in place before magnetization in the rectangular groove 65 so that indentation 77 is alined with the opening 67 in the magnet retaining block of the second molded body 64. The second molded body assembly with magnet in place is illustrated in FIG. 3.

After the permanent magnet, the four terminal pins, the cores and compensators have been mounted in the molded body portions 27 and 64, the molded body portions may then be assembled together with the internal projections 68a and 70a on the extending legs 68 and 70 respectively of the second molded body 64 in interlocking relation with the projections 68b and 701; formed on the first molded body 27 as illustrated in FIG. 9, to form the unitary magnetized, body illustrated in FIG. 4a.

Thus, the embodiment of the invention provides for a pickup cartridge which can be readily assembled together. In making the cartridge body, the first and second molded bodies may be formed by fully automatic molding since no parts are inserted during the molding process. Terminal pins 22, 23, 24 and 25 may then be pressed into the appropriate holes in the rear molded body and cemented in place. Permanent magnet 66 is assembled in the recess 65 of the second molded body before it is magnetizied, then subsequently magnetized to eliminate the necessity of directly contacting the magnet after magnetization. The right and left channel core means 31 and 32 and right and left channel flux path legs 44 and 45 may then be inserted from below in the first molded body 27. The second molded body 64 is then snapped into place with the first molded body to thereby retain the right and left channel core means and flux path legs in place.

Coil strap 35 is placed over the core means to rest on the molded body and the right and left channel voltage generating coil bobbins 36 and 37 and coils 38 and 40 which are wound thereon, are then slid onto the core means 31 and 32 respectively. The bobbins 36 and 37 may be formed of a plastic material such as medium-impact polystyrene. The lead wires from the voltage generating coils may then be led through the protective cavity 78 formed in the first molded body 27 and connected to the terminal pins. Lead wires 80 and 81 from the right channel voltage generating coils are connected to the right channel output terminal pin 24 and ground lead terminal pin 25 respectively while leads 82 and 83 from the left channel voltage generating coil areconnected to the left channel output terminal pin 22 and ground lead terminal pin 23 respectively as illustrated in FIG. 8. The core coupling strap 53 may then be inserted from above.

A shielding casing 85 of a material of high permeability such as soft iron or an alloy such as Hy Mu 80 is then slid over the cartridge body assembly to rest upon the shelf 84 and against the lip 86 formed on the first molded body 27 so that the shielding casing comes into electrical contact with ground strap 61 as illustrated in FIG. 5. Epoxy cement placed in cavity 89 in the first molded body retains the shielding casing and cartridge body together. Raised portion 89 of the case 85 provides a mechanical interlock. The shielding casing for the pickup cartridge body extends over a major portion of the top, bottom, two sides and stylus end of the pickup and includes a circular hole 87 at the base of the end wall which is alined with the hole 67 in the front molded body and indentation 77 in the stationary permanent magnet 66 when the shielding casing encloses the cartridge body. Secured to the shielding casing 85 is the bracket 26 made of stainless steel which is used to mount the pickup cartridge within a phonograph player tone arm. An external ground strap '79 is secured to ground lead pin 23 as shown in FIG. 40 and folded around terminal pin base 63 in the first molded body 27 through a suitable groove formed therein to contact the shielding casing on its inner surface, as illustrated in FIG. 5.

The transducer system housed within the assembled cartridge body includes a quadrangular array of four pole pieces arranged about a common space, the opposing pole pieces 34 and 47 and 33 and 46 respectively forming the terminal portions of two closed path magnetic circuits. As illustrated in FIGS. 6 and 7, the'closed path magnetic circuit associated with the right channel is completed through right channel pole piece 33, core means 3!, strap 55, flux path leg 44 and flux path leg pole piece 46. The closed path magnetic circuitassociated with the left channel'is completed through left channel pole piece 34, core means 32, crossover strap 56, flux path leg 45 and flux path leg polepiece 47.

Referring to FlG. 2, the leg 55 of strap 53 is magnetically coupled with right channel core means '31 within the bobbin hole 57 of bobbin 36, and the leg 51 magnetically coupled with right channel flux path leg 44 within the adjacent passageway 48 and groove 42 of the first molded body 27 thus providing a continuous closed path magnetic circuit between the right channel pole piece 33 and the right channel flux path leg pole piece 46 for alternating magnetic flux effects associated with the right channel of the stereo output and produced by movement of the armature. The leg 56 of strap 53 is magnetically coupled with the left channel core means 32 within hole 58 of bobbin 37 and the leg 52 is magnetically coupled with the left channel flux path leg 45 within adjacent groove 43 and passageway 50 of the first molded body 27 thus providing a continuous closed path magnetic circuit between the left channel pole piece 34 and flux path leg pole piece 47.

The core means, flux pathlegs, coupling strap, and pole pieces are made of a material of high permeability such as soft iron or an ironnickel alloy such as Hy Mu 80 metal to provide closed path magnetic circuits of high permeability. V

A coil strap 35 which comprises a rectangular strap of copper material is placed immediately beneath the coil bobbins and the coil bobbins rest thereon. Two holes are provided through the rectangular copper strap through which the right and left channel core means extend. The coil strap adds to the losses of the electromagnetic system at high frequencies and flattens the frequency response at high frequencies. Varying the dimensions of the coil strap varies the eddy current losses, and the optimum dimensions are determined by empirical investigation.

Stationary permanent magnet 66 in the front molded body provides the magnetomotive force or flux for the transducer system and is made of a ferromagnetic material of high coercive strength such as Alnico .V metal, cast or sintered.

The moving system for the illustrated embodiment of the invention comprises a tubular casing 88 of nonmagnetic material such as aluminum or copper, having a plastic or resin'handle 90 mounted at the outer end thereof as shown in FIGS. 1, 5 and 10. A record engaging stylus 91, which may be made of a diamond or other jewellike material, is suitably supported by a tapered stylus tube 92 disposed inside the tubular casing 88 and projecting outwardly from the forward end thereof so that the stylus can engage the groove of the record and oscillate in response to the modulations ofthe two walls of the groove.

The tapered stylus tube 92 is formed of a light, nonmagnetic material such as aluminum and is connected at its opposite end to the moving iron armature 93. A suitable spacer and damping device such as the collar 94 made of rubber, synthetic rubber or other flexible material having elasticity of a relatively low order is disposed around the moving iron armature at the end adjacent the stylus so that the entire moving assembly including the stylus, the tapered stylus tube and moving iron armature can oscillate in response to modulations of the walls of the record groove.

Moving iron armature 93 consists of a tube of magnetic material of high permeability such as soft iron, for instance, Arrnco iron tubing. The spacer and damping device 94 serves to provide a pivot or fulcrum at the end of the moving iron armature adjacent the stylus for movement of the opposite end of the armature in response to undulations of the stylus in the record groove. Because the magnetomotive force is provided by a stationary permanent magnet and the armature serves as a flux path only, the armature may be formed of a light tube of highly permeable material, decreasing mass and providing increased compliance of the moving system in response to undulations of the stylus thereby improving the tracking characteristics of the pickup. This positioning of the pivot point further improves sensitivity by placing the pivot point near the centroid of the moving system.

The moving iron armature, tapered stylus tube and stylus are maintained in properly centered relationship between the pole pieces and within the tubular casing by means of the tie wire 95 made of a spring metal which is nonmagnetic, such as copper, bronze, brass, beryllium copper or the like. The tie wire extends between the tubular casing 88 and the moving iron armature 93 in a longitudinal direction so as to permit universally pivoting motion by the moving iron armature. Thus, thetie wire may be connected to the lower portion of housing .88 at the opposite end from stylus 9.1 and extend to the end of moving iron armature 93 adjacent its pivotal mounting as illustrated in FIG. 5. Positioning the tie wire beneath the permanent magnet results in improved tracking and low distortion characteristics, and also in a lowered effective cartridge reproduction angle with respect to the record surface.

The moving system assembly is adapted to be inserted into the cartridge body through the aperture 87, formed in the shielding casing 85, indentation 77 in permanent magnet 66, circular hole 67 in the molded body 64, and recess 62 in the rear molded body 27 so that it is frictionally and removably retained within the cartridge body as shown in FIG. 10, and so that the pivotally mountedend of the moving iron armature 93 is alined with indentation 77 in the permanent magnet 66 and the free end of the moving iron armature 93 is alined within the common space formed by the quadrangular cluster of pole pieces 33, 34, 46 and 47 as shown in FIG. 5.

The plastic handle portion is formed to engage surfaces of the shielding casing of the cartridge body and to thereby orient and position the moving system with respect to the stationary permanent magnet andthe quadrangular cluster of pole pieces and to properly orient the stylus with respect to the record surface. As shown in FIG. 1, the inner surface of the plastic handle engages the outer surface of the shielding casing when the moving system is fully installed and laterally extending portions are provided which overlap the sidewalls of the casing so that the interengagement between the inner wall of the plastic handle and the outer wall of the shielding casing and the hooked overlapping portions of the handle and the shielding casing serves to properly orient and position the moving system assembly. The plastic handle 90 may be made of a plastic such as ABS plastic resin.

The lower surface of plastic handle 90 is provided with an appropriate recess 96 communicating with the interior of the v tubular casing, and the moving system and stylus project out wardly therethrough with the lower surface of the stylus projecting beneath the lower surface of the two sides of the recess whereby the stylus may engage a groove of a record. However, due to the resilient mounting of a moving system when the stylus is subjected to impact, as when the tone arm is dropped on a record, the moving system will move up into the recess 96 protecting the record from damage so that the main impact is between the lower portion of the plastic handle and the record. The forward wall of the plastic handle 99 is also provided with a longitudinal recess 97 extending from the top of the handle to the recess 96.The stylus of the moving system is positioned beneath the recess 97 so that it can be sighte'd" from the top of the pickup cartridge and properly alined with a record groove. u

When the entire replaceable moving system assembly has been inserted into the pickup cartridge, the pivotally mounted end of the moving iron armature 93 is positioned within the indentation 77 of the permanent magnet so that the armature 93 is magnetically coupled with the stationary permanent magnet 66. By this positioning, motion between theannature 93 and permanent magnet 66 is minimized in the region of magnetic coupling thereby maintaining the moving iron armature 93 in a substantially uniformly and consistently saturated condition. A further benefit of this positioning of the pivotal mounting is that distance between the center of rotation of the moving system and the stylus is reduced providing increased movement of the free end of the armature.

When the entire replaceable moving system assembly has been inserted in the pickup cartridge, the free end of moving iron armature 93 is positioned within the common space formed by the quadrangular cluster of pole pieces 33, 34, 46 and 47, as illustrated in FIGS. and 7. Stationary permanent magnet 66 is magnetized along a longitudinal axis so that a major portion of the flux generated by the magnet may follow a flux path through the armature and polarize the four pole pieces.

The pole pieces are oriented in a quadrangular cluster so that the two pole pieces associated with each channel of the stereo sound are in respective opposing relationship as indicated in FIG. 7. Thus, motion of stylus 91 in response to the wall of the record groove associated with the right channel of the pickup will produce motion in the free end of armature 93 towards and away from right channel pole piece 33 producing a change in flux in the right channel core means 31 thereby inducing a voltage across the right channel voltage generated coil 38 which varies in response to the modulation of the wall of the record groove corresponding to the right channel output. Motion of the stylus 91 in response to undulations in the wall of the record groove associated with the left channel of the stereooutput will produce movement in the free end of the moving iron armature 93 toward and away from the left channel pole piece 34 producing a change in flux in the left channel core means 32 thereby inducing a voltage across the left channel voltage generating coil 40 which varies in response to the undulations of the wall of the record groove associated with the left channel output.

Motion of the free end of the moving iron armature 93 towards and away from the right channel pole piece 33 is accompanied by an equal and opposite motion away from and towards the flux path leg pole piece 43 thereby producing a corresponding change of flux in the flux path leg 44. Motion of the free end of moving iron armature 93 towards and away from the left channel pole piece 34 is accompanied by an equal and opposite movement away from and towards the left channel flux path leg pole piece 47 thereby producing a corresponding change of flux in the left channel flux path leg 45. By thus effectively limiting flux changes associated with one channel of the stereo output to the closed path magnetic circuit associated with that channel, crosstalk is minimized. In addition, by such flux path means a substantially constant current of flux is maintained through the armature to maintain the armature in a substantially uniform and constant state of magnetic saturation providing improved sensitivity and linearity of response and minimizing crosstalk between the channels. Thus, flux changes induced by the motion of the free end of moving iron armature Q3 in the common space formed by the quadrangular cluster of pole pieces, are substantially limited in their effect to the appropriate closed path magnetic circuit associated with each channel of the stereo output.

In FIG. 11 an alternate form of the second molded body assembly is shown. The alternate form of molded body assembly 164 includes a vertically elongated magnet retaining block section with a rectangular indentation 165 in which is housed the permanent magnet 166. Circular longitudinal aperture 167 is provided in the base of the magnet retaining block to establish a channel through which the moving system may be inserted.

The laterally extending legs 168 and 170 of the body have facing internal projections such as the projections 68a and 70a 64 however, in this embodiment the second molded body 164 has legs 168 and 170 provided with outwardly projecting bumps or interfering portions 268 and 270 respectively which are provided for frictionally engaging the casing in the fully assembled condition of the unit.

The configuration of molded body 164) shown in FIG. 11 otherwise is identical to that of molded body 64 shown in FIG. 2 previously described with the exception of the magnet retaining means.

Whereas in the embodiment utilizing molded body 64 the magnet was cemented in place, in the present embodiment the molded body 16 is provided with a window 200 in the base of channel and a wall 201 opposite the window. Wall 201 is spaced from. the base of the channel to allow the magnet 166 to be inserted between the wall 201 and the base of the channel with projections 202 and 203 respectively formed on wall 201 and the base of the channel, directed toward and engaging the magnet in the fully assemblied condition.

In FIG. 12 a view of the invention similar to a portion of the view in FIG. 7 appears with all parts in FIG. 12 identical to the parts in FIG. 7 and indicated with the same numeral and a prime. In the embodiment of FIG. 12 however the angles between respective adjacent pole pieces are different than the angles shown in FIG. 7, thus illustrating that the quadrangular cluster need not be arranged in right angled configuration.

In FIGS. 13 and 14 a preferred embodiment of the invention is shown. FIG. 13 is an exploded view similar'to FIG. 2 and the structure with two exceptions is identical to the structure shown in FIG. 2. In FIG. 13 the shorted turn device has been modified (designated in FIG. 2 by the numeral 35 and in FIG. 13 by the numeral 335) and the structure and means for holding the magnet in position is that of the embodiment illustrated in FIG. 11.

In FIGS. 13 and 14 the first molded body is designated by the numeral 327 and has holes 328 and 330 through which the right and left channel core means 331 and 332 can be inserted from below. Coil strap 335 is placed over the core means 331 and 332 so that it rests on body 327 with the core means 331 and 332 projecting through the hole formed therein.

Voltage generating coil bobbins 336 and 337 upon which are wound voltage generating coils 338 and 340 are placed over core means 331 and 332 respectively. The vertical grooves 342 and 343 receive and retain the right and left channel flux path legs 344 and 345.

The legs 351 and 352 of core coupling strap 353 are retained in passageways 348 and 350 respectively, while the other legs 355 and 356 of the strap are retained in the bobbin openings 357 and 358. The visible terminal pinholes are designated by the numerals 322a, 324a, and 325a and the longitudinal recess for the moving system is designated by the numeral 362. The second molded body assembly 346 includes laterally extending legs 368 and 370, longitudinal aperture 367, window 300 and magnet retaining wall 301. The magnet is designated by the numeral 366 and aperture 367 is formed in the lower end thereof. The grounding strap is shown and indicated by the numeral 361. In FIG. 14 the pole pieces extending from flux path legs 344 and 345 are respectively designated by the numerals 346 and 347 and the shell is indicated by the numeral 385. The tubular casing and the moving iron armature have respectively been given the numerals 388 and 393.

The embodiment shown in FIGS. 13 and 14 utilizes a shorted turn device 335 which differs from coil strap 35 in that a single opening is provided in strap 335 in place of the two openings shown in strap 35. Both straps are formed of a nonmagnetic conductive material, such as copper, which is placed immediately beneath the coil bobbins so that they rest thereon. In each embodiment the coil strap adds to the losses of the electromagnetic system at high frequencies and flattens 9 the frequency response at high frequencies with the optimum dimensions for this purpose being determined by empirical investigation. 7

In addition, however, the coil strap 335 performs the function of minimizing crosstalk in the silent channel. When the pickup is connected to output channels the induced current induces a magnetomotive force in the core of the active channel, which in turnaffects the silent channel. The effect is canceled out or minimized by a counter magnetomotive force induced by the loop 335.

We claim:

1. A magnetic stereophonic phonograph pickup of the replaceable stylus type comprising:

supporting structure comprising a cartridge body;

two magnetic circuits formed of permeable material supported within said body each including core means terminating in a pole piece and fiux path means terminating in another pole piece in opposing spaced relation with said respective first pole piece, the pole pieces from said two magnetic circuits forming a quadrangular cluster about a common space;

voltage generating means including a coil mounted on each of said core means; g

a moving system removablycoupled to said cartridge body including a recordengaging stylus, a tubular armature of permeable material extending into said body from one end thereof when said system is in operative position, stylus connecting means pivotally mounting said armature at one end, said armature one end being outside the common space between the pole pieces for movement of the opposite end of the armature within the common space formed by the quadrangular cluster of pole pieces in response to the undulations of the stylus in a record groove when said system is in operative position; and

a flux source including a stationary permanent magnet mounted on said supporting structure proximal said cartridge one end immediately adjacent said armature one end and magnetically coupled at one of its poles to the pivotally mounted end of the armature, whereby the relative motion between thepe rmanent magnet and armature in the region of magnetic coupling is minimized, and the armature is maintained in a substantially uniform and constant state of magnetic saturation.

2..A stereophonic phonograph pickup as set forth in claim 1 wherein the supporting structure for the pickup includes a first molded plastic body part shaped to accommodate the magnetic circuits and voltage generating coils, a second molded plastic body part shaped to accommodate the permanent magnet, said second molded body part and first molded body part being contoured to frictionally and tensionally engage each other to form a unitary cartridge body for ease in manufacture and assembly, and a shielding casing adapted to extend over the major portions of the front, top, bottom and sides of the unitary cartridge body.

3. A stereophonic phonograph pickup of the magnetic type as set forth in claim 1 in which a socketlike opening extends from said cartridge body front end through the supporting structure between the pole pieces for removably accommodating the moving system and the moving system is provided with a tubular casing removably received in the socketlike opening and provided with a plastic handle at its outer end which engages surfaces of the cartridge body to properly orient the armature with respect to the pole pieces and the stylus with respect to the record surface.

4. A magnetic-stereophonic pickup as set forth in claim 1 wherein there is provided a shorted turndevice of electrically conducting nonmagnetic material electromagnetically coupled with each core means.

5. A magnetic stereophonic pickup as set forth in claim 4, in g which said shorted turn device is a strap formed with a single hole therein through which said core means project.

6. A magnetic stereophonic pickup as set forth in claim 4, in which said shorted turn device is a strap formed with a single 10 hole therein through which said first and second core means project. I

7. A magnetic stereophonic' p onograph pickup of the replaceable stylus type comprising: 5

a supporting structure forming a cartridge body;

first core means terminating in a first channel pole piece;

second core means terminating in a second channel pole piece;

first flux path means terminating in a first channel flux path pole piece in opposing spaced relationship with said respective first channel pole piece and including a magnetic path ofhigh permeability between said first channel pole piece and said first flux path pole piece forming a first magnetic circuit disposed within said cartridge;

second flux path means terminating in a second channel flux path pole piece in opposing spaced relationship with said respective second 'channel'pole piece and including a magnetic path of high permeability between said second channel pole piece and said second flux path pole piece forming a second magnetic circuit disposed within said cartridge;

said first and second channel pole pieces and first and second channel flux path pole pieces forming a quadrangular cluster enclosing a common space within said cartridge;

first channel voltage generating means including a first channel voltage generatingcoil mounted on said first core means;

second channel voltage generating means including a second channel voltage generating coil mounted on said second core means; I

a moving system removably coupled to said cartridge body' including a record engaging stylus, a tubular armature of highly permeable material, stylus connecting means, and mounting means pivotally mounting said armature at one of its ends outside the common space between the pole pieces for movement of the opposite end of the armature within the common space formed by the quadrangular cluster of pole pieces in response to undulations of the stylus in the record groove,'w hen said moving system is in operative position, said moving armature being universally pivotally mounted so that movement of the free end of the armature in a path'towards and away from the first channel pole piece in response to modulations of the first channel sidewall of therecord groove produces an electromotive force across the first channel voltage generat ing coil and so that movement of the free end of the armature towards and away from the second channel pole piece in response to modulations of the second channel sidewall of the record groove produces an electromotive force across the second channel voltage generating coil and so that a flux change produced in one of the channel pole pieces and core means is accompanied by a corresponding change of flux in'the associated flux path pole piece and flux path means to thereby substantially improve sensitivity and linearity of response and channel separation in the output of the two channels;

a flux source including a stationary permanent magnet mounted to said supporting structure proximal one end thereof immediately adjacent and magnetically coupled at one of its poles to. the pivotally mounted end of an armature in operative position to minimize the relative motion between the permanent magnet and armature in the region of magnetic coupling and maintain the armature in substantially uniformly and constantly magnetically saturated condition to thereby provide improved sensitivity and linearity of response and channel separation in the output of the two channels;

a socketlike opening extending from said supporting structure one end through said supporting structure between the pole pieces for removably accommodating the moving system; and

said moving system further includes a tubular casing disposed about said armature adapted to be removably received within said socketlike opening and a handle at its outer end which engages portions of the cartridge body to properly orient the armature with respect to the pole pieces and the stylus with respect to a record surface.

8. A separate and replaceable moving system for a stereophonic phonograph pickup of the moving iron type having a supporting structure forming a cartridge body, first and second channel core means terminating in first and second channel pole pieces about a socketlike opening extending through the supporting structure from one end, first and second channel current generating coils mounted on said core means and a stationary permanent magnet mounted on the supporting structure proximal said one end, said moving system comprising:

a tubular casing for the moving system adapted to be removably received in a socketlike opening extending through the supporting structure from said one end;

a record engaging stylus projecting outwardly from said tubular casing;

an elongated tubular armature of a material of high permeability mounted within said casing and connected with said stylus; and

mounting means pivotally mounting said armature at its end adjacent the stylus for movement of its opposite end in response to undulations of the stylus in a record groove, said mounting means and tubular armature being arranged so that upon assembly of the moving system with a pickup, the pivotally mounted end of the armature is adjacent one pole of the permanent magnet to minimize relative motion therebetween and the opposite end of the armature is positioned between the pole pieces.

9. A separate and replaceable moving system as set forth in claim 8 wherein the mounting means includes a longitudinally extending spring wire connected at one end to the casing at the end of the casing opposite the stylus and connected at its other end to the armature adjacent the pivoted mounting.

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