US3908096A

US3908096A - Electromagnetic pickup cartridge with tension wire and induction magnet alined axially with armature

Info

Publication number: US3908096A
Application number: US428765A
Authority: US
Inventors: Yonezo Furuya
Original assignee: Micro Labo Co Ltd
Current assignee: Micro Labo Co Ltd
Priority date: 1972-12-28
Filing date: 1973-12-27
Publication date: 1975-09-23
Anticipated expiration: 1992-09-23
Also published as: DE2364767A1

Abstract

A pickup cartridge comprises essentially a cartridge body provided with an inducing magnet and a stylus assembly which is detachably installed in the cartridge body. This stylus assembly comprises: a vibrating structure comprising a stylus, a cantilever arm, and an armature; a tubular guard member surrounding this vibrating structure; a damper for holding the vibrating structure in a manner permitting its oscillatory vibration within this guard member; a tension wire for pulling the vibrating structure in the direction opposite to that in which it is pulled as a result of the frictional force between the stylus and the record disc; and a magnetic member for anchoring one end of the wire and, at the same time, when the stylus assembly is installed in the cartridge body, intimately contacting the inducing magnet thereby to direct and pass the magnetic flux thereof toward the armature.

Description

United StatesPatent n91 Furuya 1 ELECTROMAGNETIC PICKUP CARTRIDGE WITH TENSION WIRE AND INDUCTION MAGNET ALINED AXIALLY WITI-I ARMATURE [75] inventor: Yonezo Furuya, Tokyo, Japan [73] Assignee: Micro Labo Co., Ltd., Tokyo, Japan [22] Filed: Dec. 27, 1973 [2 1] Appl. No.: 428,765

[30] Foreign Application Priority Data Dec. 28, 1972 Japan 47-1839 Oct. 16, 1973 Japan 48-120053 [52] U.S. Cl. l79/I00.4l Z; 179/100.4l K [51] Int. Cl. I-I04R 11/08 [58] Field of Search. 274/37, 38; 179/1004] K, 179/100.41 M, 100.41 D, 100.41 Z

[ Sept. 23, 1975 3,731,009 5/1973 Watanabe et a1. 179/1004! K Primary Examiner-Bernard Konick Assistant Examiner-Stewart Levy Attorney, Agent, or Firm-Waters, Schwartz 8:. Nissen ABSTRACT A pickup cartridge comprises essentially a cartridge body provided with an inducing magnet and a stylus assembly which is detachably installed in the cartridge body. This stylus assembly comprises: a vibrating structure comprising a stylus, a cantilever arm, and an armature; a tubular guard member surrounding this vibrating structure; a damper for holding the vibrating structure in a manner permitting its oscillatory vibration within this guard member; a tension wire for pulling the vibrating structure in the direction opposite to that in which it is pulled as a result of the frictional force between the stylus and the record disc; and a magnetic member for anchoring one end of the wire and, at the same time, when the stylus assembly is installed in the cartridge body, intimately contacting the inducing magnet thereby to direct and pass the magnetic flux thereof toward the armature.

11 Claims, 9 Drawing Figures US Patent Sept. 23,1975 Sheet 2 of3 3,908,096

ELECTROMAGNETIC PICKUP CARTRIDGE WITH TENSION WIRE AND INDUCTION MAGNET ALINED AXIALLY WITH ARMATURE BACKGROUND OF THE INVENTION The present invention relates generally to a phonograph pickup cartridge and more particularly to an electromagnetic transducing type pickup cartridge wherein a tension wire and an inducing magnet are dis posed in alinement in the axial direction with an armature.

A moving-magnet type stereo cartridge, which has heretofore been used most generally asan electromagnetic type pickup cartridge, has a construction wherein a magnet is provided at one end of a cantilever having a stylus tip on its other end, and this magnet is held between two pairs of pole pieces by a damper rubber member. A pickup cartridge of this type operates on the principle that vibrations due to the groove of a record disc are mechanically transmitted to the magnet, which thereby vibrates and causes a magnetic flux variation in the pole pieces, whereby output signal voltages are led out from coils.

This conventional pickup cartridge of moving magnet type, however, has been accompanied by problems such as large stylus vibration mass and low effective efficiency. If, in order to overcome this problem, the damper rubber is made soft to increase the compliance, the support of the magnet center will become unstable. If the field strength of the'magnet is increased, operational defects such as waveform distortion caused by magnetic inertia and unbalance of the left and right output voltages will occur.

Another known pickup cartridge is an inducedmagnet type pickup cartridge ofa construction wherein a high-strength magnet is provided in the cartridge housing, and an armature comprising a ferromagnetic material and fixed to the rear end of a cantilever is disposed in the vicinity of the magnet. In the operation of this pickup cartridge, the armature magnetized by the magnet vibrates mechanically in accordance with the record disc groove thereby to cause coils to produce electrical output signals. However, when a stylus traces the groove of a record disc, however, the frictional force between the stylus and the disc caused a pulling force toward the rear with respect to the relative advance direction of the stylus relative to the record disc is imparted to the stylus.

Consequently, while a pickup cartridge of this type has the advantage of very small vibration mass of the stylus assembly, it is accompanied by the problem of the damper for holding the vibrating system being forced rearward and deforming, whereby the vibratory support point of the vibrating system becomes indefinite, which gives rise to a change of simple vibrations to complicated vibrations, and the modulated vibrations of the sound groove are reproduced in a distorted state.

On one hand, there is a recent, world-wide spreading of a fourchannel record known as a compatible discrete four-channel (CD-4) record. On a discrete fourchannel record of this type, a direct wave of from 20 Hz to KHz and an angle modulated wave of from KHz to 45 KHz are recorded in superimposed state. Accordingly, a pickup cartridge for affording excellent reproduction of this discrete four-channel record thus recorded must fulfill the following conditions.

l. The frequency characteristic deviation must be within i 1 dB in the frequency range of from 20 Hz to 15 KHz and within 5 dB in the range of from 20 KHz to 45 KHZ.

2. The mechanical impedance of the vibrating system must be as small as possible.

3. The output voltage must be 2.5 mV/Scm. or higher.

4. The output impedance of the catridge must be small.

5. The crosstalk of the left and. right channels at 30 KHZ is preferably greater than 20 dB and greater than 15 dB at the worst.

6. The phase characteristic deviation in the frequency band of from 20 KHz to 45 KHz must be within 5 asec.

In order to satisfy the above conditions (I) and (2) in the case of the above described conventional moving-magnet pickup, the vibrating system must be miniaturized as much as possible, and, therefore, the mass of the magnet must be made as small. This measure, however, will lower the sensitivity, whereby the above condition (3),cannot be fulfilled, and the S/N ratio of the demodulated signal will drop. If, in order to overcome this problem, with winding turns of the coils are increased, the above condition (4) cannot be met. For this reason, a moving-magnet type pickup cannot be advantageously used for producing good reproduction of discrete four-channel records.

If, in the case of the above described conventional induced-magnet type pickup, the damper rubber is made soft for fulfilling the above condition (2), deleterious effects will be produced with respectto the above conditions (5) and (6). For this reason, an inducedmagnet type pickup is unsuitable for reproducing discrete four-channel records of the above mentioned The applicant has previously proposed a variable-flux type pickup which may be considered to be one kind of modification of an induced-magnet type pickup, and in which the above described difficulties accompanying the conventional moving'magnet type pickup and induced-magnet type pickup have been overcome. This proposed pickup has been granted U.S. Pat. No. 3,538,266, entitled Magnetic pickup having a magnet alined in axial direction with an armature.

This proposed pickup has a construction wherein a magnet is disposed in a position slightly separated from the rear end of an armature and functions to magnetize the armature or to form a magnetic field with respect to the armature and, at the same time, to impart a rearward attractive force to the armature thereby to cancel or nullify the force with which the armature is pulled forward as a result of frictional force between the stylus and the record disc sound groove.

This proposed pickup fulfills the above conditions (1) through (6) for the most part and, in comparison with the above described conventional pickups, is particularly suitable for use with discrete four-channel records. However, the following problem still remains in the case of this pickup.

The shape of the record sound groove changes in accordance with recorded signal. Furthermore, the relative speed between the stylus and the part of the record disc contacted by the stylus differs with position of the stylus on the disc in the radial direction. Consequently,

the frictional force between the stylus and the disc furing playing of the record is not always constant.

For this reason, in the above described, previously proposed pickup, the gap between the rear end of the armature and the magnet becomes large when a large force due to friction is imposed on the stylus, and the armature is pulled forward with great force. At this time, the magnet preferably should pull the armature with even greater force to counter the great forward pulling force, but because of the widening gap therebetween, the attractive force of the magnet for pulling the armature rearward becomes less instead, whereby the forward pulling force cannot be fully nullified.

SUMMARY OF THE INVENTION Accordingly, it is a general object of the present invention to improve the above described, previously proposed pickup and to provide a novel and useful pickup cartridge in which the above described problem is solved.

A specific object of the invention is to provide a pickup cartridge of a construction wherein an armature is magnetized from its rear by a magnet and subjected to attractive force thereby and, moreover, is subjected to a rearward tensile force by a wire, whereby the armature iseffectively prevented from being pulled forward as a result of frictional force between the stylus and the record disc. A feature of the invention afforded by this construction is that the center of vibration of the armature is constantly fixed, and, moreover, the distribution of the pressure imposed on the damper rubber holding the armature is uniform, whereby distortion is prevented. Furthermore, the characteristics of the two left and right channels are uniform, and crosstalk can be reduced. 7

Another object of the invention is to provide a pickup of the above described construction in which, moreover, the stylus assembly can be readily exchanged. For this purpose, the rear end of the wire applying a rearward force to the armature is anchored on a magnetic member, which is adapted to be detachable from the magnet, and the magnet is adapted to magnetize the armature via this magnetic member.

A further object of the invention is to provide a pickup cartridge having a mechanism whereby the armature can be held and supported uniformly over its entire circumference on its outer peripheral surface by a damper.

Other objects and further features of the invention will be apparent from the following detailed desctiption when read in conjunction with the accompanying drawmgs.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a side view, partly in longitudinal section, illustrating one embodiment of a pickup cartridge according to the invention and indicating the principle thereof;

FIG. 2 is a side view, in longitudinal section, showing another embodiment with specific structural details of a pickup cartridge of the invention;

FIG. 3 is a bottom view of the cartridge shown in FIG. 2 with the stylus assembly removed from the catridge body thereof;

FIG. 4 is an enlarged side view, in longitudinal section, showing the essential parts of the stylus assembly of the catridge illustrated in FIG. 2;

FIGS. 5 and 6 are sections respectively taken along the lines V-V and VIVI in FIG. 4 as viewed in the arrow directions;

FIG. 7 is an enlarged side view, in longitudinal section, showing the essential parts of another embodiment of a stylus assembly;

FIG. 8 is a section taken along the line VIIIVIII in FIG. 7 as viewed in the arrow direction; and

FIG. 9 is a partial section taken along the line IXIX in FIG. 8 as viewed in the arrow direction.

DETAILED DESCRIPTION An embodiment illustrating the principle of the pickup cartridge of the invention will first be described with reference to FIG. 1.

In this pickup cartridge, a stylus 12 is secured to the foremost end ofa tubular cantilever 11 made of an aluminum alloy and terminating within a tubular armature 13 made ofa ferromagnetic material such as permalloy and fitted onto the rear end part of the cantilever 11. These three parts form a vibrating structure 14, which is swingably held within a sleeve 16 as a guard member of a non-magnetic material by a ring-shaped rubber damper 15 fitted onto the outer surface of the armature 13.

A yoke 17 made of a magnetic material is fitted into a fixed to the rear part of the sleeve 16. The front surface of this yoke 17 is separated slightly from the rear end surface of the armature 13 so as not to obstruct or affect the swinging vibration of the armature. The rear surface of the yoke 17 lies in the same transverse plane as the rear end of the sleeve 16.

A plug 18 made ofa low-density material such as aluminum is fixedly fitted within the rear end part of the cantilever 11 disposed within the armature 13. The front end of a thin wire 20 is fixedly anchored to the central part of the plug 18. This wire 20 passes coaxially through a through-hole 19 bored through the yoke 17 along the front-and-rear centerline thereof, and the rear end of this wire 20 is fixed to the yoke 17 at the rear end of the through-hole 19. The wire 20 is in a tensioned state between the plug 18 and the rear end of the yoke 17.

The anchor point 0 of the wire 20 on the plug 18 is positioned at the center of the damper 15 in the diametric direction and axial direction thereof.

The above described vibrating structure 14, the sleeve 16, the yoke 17, the damper 15, the wire 20, and related parts constitute a stylus assembly, which is removably inserted in a cartridge body (not shown). With this stylus assembly thus installed within the cartridge body, the rear end surface of the yoke 17 is in intimate contact with the front surface of a permanent magnet 23. Furthermore, within the cartridge body, there are provided two pairs of pole pieces 21 and coils 22 wound on coil bobbins, which are disposed with clear ance for insertion of the sleeve 16.

In the operation of the pickup cartridge of the construction summarily outlined above, the stylus 12 is placed in the sound groove of a rotating record disc and thereby relatively traces the sound groove, whereby the vibrating structure 14 vibrates in accordance with the shape of the sound groove. Since the armature 13 is being magnetized by the magnet 23 by way of the yoke 17, the oscillatory vibration of the armature 13 about the above mentioned center 0 as it is held by the damper causes an output signal in accordance with the vibration to be produced from the coil 22.

Then, as the stylus l2 traces the sound groove of the record disc, the vibrating structure 14 is subjected to a tension force in the forward direction, that is, toward the left as viewed in FIG. 1, due to the frictional force between the stylus 12 and the record disc, but a magnetic attractive force due to the magnet 23 through the yoke 17 and a tension force due to the wire are im parted in a superimposed manner to the vibrating structure 14. As a net result, the above mentioned forward tension force due to the frictional force is effectively nullified.

During this operation, the space between the rear end of the armature 13 and the front surface of the yoke 17 is prevented from becoming large by the action of the wire 20. Furthermore, although the front end of the wire 20 is fixed to the vibrating structure 14, its vibration is not affected in any way whatsoever since its center of vibration is at a central position within the armature 13 similarly as in the case where the wire 20 does not exist.

Another embodiment of more specific structure of the pickup cartridge according to the present invention will now be described with reference to FIGS. 2 through 6.

The pickup cartridge illustrated in FIGS. 2 and 3 comprises essentially a cartridge body 31 and a stylus assembly 38 detachably mounted thereon. The housing of the cartridge body 31 has a metal shield case 32 with an openable rear end, which is covered by a terminal block 36 made of an electrically insulative resin and supporting four terminal pins 37 projecting 'parallelly rearward out of the cartridge housing. On the upper surface of the shield case 32, there is fixed flange 35 for mounting the cartridge by means such as screws to a tone arm or pickup arm of a record player.

At the bottom of the shield case 32, a resin block 33 is fixed to the inner surface of the bottom wall of the case and faces an opening 61 formed at the front part of the bottom of the shield case 32. This resin block 33 at its rear part fixedly holds a permanent magnet 49 and is provided with a prismatic hole 34, into which is inserted a sleeve 40 of the stylus assembly 38 described hereinafter. This hole 34 extends rearward to the front face of the magnet 49.

Two pairs of

pole pieces

43 and 44 are molded in the block 33, and their lower ends are disposed in respectively opposed positions on the inner wall surface of the hole 34. Two pairs of

coils

46 and 47 are wound on these

pole pieces

43 and 44 above the block 33, and the upper ends of the

pole pieces

43 and 44 are magnetically connected by a yoke 45. Lead wires 48 led out from the

coils

46 and 47 are respectively connected to the inner ends of the terminal pins 37.

On one hand, the stylus assembly 38 comprises, essentially, a resin knob 39, the prismatic sleeve 40 made of brass fixed to the knob, and a vibrating structure 62 held within the sleeve 40. For mounting the stylus assembly 38 into the cartridge body 31, the knob 39 is grasped, and the sleeve 40 is inserted into the hole 34. At this time, the knob 39 is positioned at the front face and side face of the shield case.

The stylus assembly 38 in a state where its knob 39 has been removed is shown in enlarged longitudinal section in FIG. 4, the sections of which taken along lines V-V and VI-VI are shown in FIGS. 5 and 6. The vibrating'structure 62 comprises a stylus 41, a tubular cantilever 42 fixedly supporting at its forward end the stylus 41, and a tubular armature 50 fixedly fitted onto the rear part of the cantilever 42. The armature 50 is made of a ferromagnetic material such as, for example, permalloy or pure iron, and its dimensions are, for example, an outer diameter of 0.7 mm., an inner diameter of 0.5 mm., and a length of 3 mm. The rear part of the cantilever 42 (the right end as illustrated) terminates in the vicinity of the midway part of the interior of the armature 50.

A plug 60 with the front end of a wire 53 passed therethrough and anchored thereto is fixedly fitted into the rear end of the tubular cantilever 42. The wire 53 passes substantially coaxially through the armature 50 and, at the initial stage of assembly, is made somewhat on the longer side so as to extend somewhat past the rear end of the armature 50. This wire is made of, for example, phosphor bronze and has a diameter of 0.08

Around the outer surface of the tubular armature 50 and at a specific position forward (to the left as viewed in FIG. 4) of the position corresponding to the rear end of the plug 60, there is fixed a flange-like retaining I member 59. This engagement member 59 may be. formed before hand integrally with the armature 50.

A disc-shaped rubber damper 51 of a specific thickness is fitted on the outer surface of the armature 50 on the rear side (right hand side in FIG. 4) of the engagement member 59.

On one hand, a hollow cylindrical spacer 56 having an outer diameter equal to that of a circle inscribed within the prismatic sleeve 40 is inserted through the rear end of the sleeve 40 and disposed concentrically therewithin. A retaining member 57 having an outer square shape conforming to the inner wall surface of the sleeve 40 in cross section. has a central hole 58 of a diameter slightly greater than the outer diameter of the armature 50. This retaining member 57 is inserted from the front of the sleeve 40.

A yoke 52 fabricated from a plate of magnetic material and having a square shape conforming to the inner wall surface of the sleeve 40 is fitted into the rear end of the sleeve 40 and has a central through-hole 55 of small diameter. The yoke 52 has a flat rear surface for intimate contact with the front face of a magnet 49 when the stylus assembly 38 is secured in installed position to the cartridge body 31. Furthermore, the rear surface of the yoke 52 at its center is provided with a recessed part 54 for the purpose of catching the rear end of the wire 53 in a manner as described hereinafter whereby this wire end will not project rearward beyond the rear surface of the yoke.

In the assembling of the stylus assembly shown in FIG. 4 from the above described wire 53, retaining member 59, vibrating structure 62 provided .with the damper 51, spacer 56, sleeve 40 provided with the retaining member 57 inserted thereinto, and yoke 52, the rear part of the vibrating structure 62 is inserted into the sleeve 40 from the front part thereof, and the rear half of the armature 50 is passed through the hole 58 in the retaining member 57. The damper 51 is thereupon placed in a state wherein it is clamped by the retaining

members

59 and 57.

Next, the rear end of the wire 53, which is anchored at its front end to the plug 60 and, passing through the interior of the armature 50, extends through the rear end thereof and through the rear end of the sleeve 40 as described hereinabove, is passed through the hole.55 in the yoke 52. The yoke 52 is then fitted into and fixed to the rear end of the sleeve 40. The rear surface of the yoke 52 is then lying in the same plane as the rear end of the sleeve 40 or is projecting slightly rearward (to the right in FIG. 4) from the rear end of the sleeve 40.

A suitable tension (for example, of the order of 90 grams) toward the right in FIG. 4 is then applied to the rear end of the wire 53 passed through the hole 55 of the yoke 52, and with the wire in this stressed state, its rear end part is fixed by soldering, with an adhesive, or some other suitable means to the yoke 52 within the recess 54. As a result of the tension in the wire 53, the damper 51 is pressed between the retaining

members

59 and 57. Furthermore, the retaining member 57 is pressed against the front end of the spacer 56, the rear end of which is thereby pressed against the front face of the yoke 52. Accordingly, by fabricating the spacer 56 with high accuracy to the specified length, the retaining member 57 can be positioned with high precision by means of the spacer 56. For this reason, when the stylus assembly assembled in this manner is installed in the cartridge body 31, the armature 50 can always be positioned accurately in a specific position relative to the

pole pieces

43, 44.

The dimensions of the damper 51 are so selected that when it is pressed between the retaining

members

59 and 57, its outer periphery does not contact the inner wall surface of the sleeve 40 or, even if its outer periphery does contact the inner wall surface it is not subjected to any appreciable reaction force due to the inner wall surface. In addition, the rear end of the armature 50 is separated from the front face of the yoke 52 by a slight distance of an order such that the oscillatory movement of the armature 50 is not obstructed.

With the above described state of the various parts, the vibrating structure 62 is being pulled toward the rear (toward the right in the drawing) with a predetermined force by the wire 53 and, moreover, is being held by the damper 51 in a manner permitting free oscillatory vibration thereof. It is to be noted that the center of oscillation of the vibrating structure 62 coincides with the position of the center of the damper 51 in the thickness and diametric directions and with the point of anchoring of the wire 53 to the plug 60.

It is further to be noted that'the center 0 nearly coincides with the center of gravity of the vibrating structure 62. Therefore, the equivalent mass of the vibrating structure 62 viewed from the stylus 41 is extremely small.

The stylus assembly 38 of the above described con struction can be installed in the cartridge body 31 by inserting the sleeve 40 thereof into the hole 34. At this time, the rear face of the yoke 52 is in intimate contact with the front face of the magnet 49, and the armature 50 is magnetized by the magnet 49 by way of the yoke 52. At the same time, the armature 50 is at a specific position relative to the

pole pieces

43 and 44. The operation of this pickup cartridge is the same as that in the aforedescribed first embodiment and, therefore, will not be described again.

For disconnecting the stylus assembly 38 from the cartridge body 31 for replacement or some other purpose, the knob 39 is grasped and pulled forward or toward the left in the drawing. At this time, the yoke 52 separates as it is from the magnet 49, and by extracting the sleeve 40 from the hole 34, and the stylus assembly 38 can be readily disconnected from the cartridge body 31.

Another embodiment of the essential parts of the stylus assembly will now be described in conjunction with FIGS. 7, 8, and 9. In these figures, parts which are the same as these in FIG. 4 are designated by like reference numerals. Detailed description of these parts will not be repeated.

At specific positions on the inner surfaces of the four walls of the prismatic sleeve 40, there are integrally provided flanges 71. The retaining member 57 isengaged at its rear face by the four flanges 71 and is thus positioned. Accordingly, the spacer 56 used in the preceding embodiment is not required in the instant embodiment. In the instant embodiment, a retaining ring 72 of flange shape corresponding to the retaining member 59 in the preceding embodiment is formed integrally with the armature 50.

Further, this invention is not limited to these embodiments but various variations and modifications may be made without departing from the scope and spirit of the invention.

I claim:

1. An electromagnetic type pickup cartridge comprising:

a cartridge body having an electromagnetic transducing circuit including pole pieces and coils arranged to function cooperatively within a cartridge housing and a permanent magnet installed in a specific position within said cartridge housing; and

a stylus assembly detachably installed in said cartridge body and comprising a cantilever arm having front and rear ends,

a stylus provided at said front end of said arm,

a tubular armature provided at the rear part of the arm,

a tubular guard member surrounding said armature and having corresponding front and rear ends,

a damper holding within said guard member the armature in a manner permitting free swinging vibration thereof at a position apart from a rear end of the armature with a predetermined distance,

a piece of wire connected at a front end thereof to the armature at a point substantially in the vicinity of a point coinciding with a central point of the damper in the diametric and axial directions thereof, said wire imparting a tensile force to the armature and cantilever arm in the direction from said front end toward said rear end of the armature, and

a magnetic member provided on the rear end part of said guard member with a clearance relative to the armature whereby the vibration of the armature will not be obstructed, rear end of the wire being fixed to said magnetic member, said magnetic member facing the permanent magnet when the stylus assembly is inserted into the car tridge body,

said armature confronting said pole pieces and, at the same time, being magnetized by the permanent magnet via the magnetic member when the stylus assembly is inserted into the cartridge body.

2. An electromagnetic type pickup cartridge as claimed in claim 1 including a plug fitted into and fixed to the rear end part of the cantilever arm, the rear part of said tubular cantilever arm being fitted into and fixed to the tubular armature, said wire being fixed at the front end thereof to the plug, and a fixing point of the wire to the plug coinciding with the central point of the damper.

3. An electromagnetic type pickup cartridge as claimed in claim 1 in which said magnetic member comprises a magnetic plate having at the center thereof a through-hole through which the rear end of the wire is passed through and secured to said magnetic plate on the rear side thereof facing the permanent magnet.

4. An electromagnetic type pickup cartridge as claimed in claim 1 in which the mutually facing surfaces respectively of the permanent magnet and the magnetic member are made planar and are in intimate flush contact when the cartridge is in assembled state wherein the stylus assembly has been installed in the cartridge body.

5. ,An electronagmetic type pickup cartridge as claimed in claim 1 in which said cantilever arm, said stylus, and said armature comprises a vibrating structure, and said central point of the damper substantially coincides with the center of gravity of said vibrating structure.

6. An electromagnetic type pickup cartridge as claimed in claim 1 further comprising retaining means having a first retaining member provided at a specific position on the armature and a second retaining member provided at a specific position in the tubular guard member, said damper being clamped between said first and second retaining members.

7. An electromagnetic type pickup cartridge as claimed in claim 6 in which the securing means further has a spacer interposed between said second retaining member and the magnetic member, and the position of the armature is set by the intimately abutting contact successively between the first retaining member, the damper, the second retaining member, the spacer, and the magnetic member due to the tensile force of the wire.

8. An electromagnetic type pickup cartridge as claimed in claim 6 in which said damper, in the state of being clamped between said first and second retaining members, holds the armature in an oscillatorily vibratable manner and has a sufficiently small outer diameter whereby the outer peripheral surface thereof is spaced apart from the inner wall surface of the tubular guard member.

9. An electromagnetic pickup cartridge as claimed in claim 6 in which said securing means further has a plurality of flange-like members cut out and bent inward from the wall structure of the tubular guard member, and the armature is set in position by the intimately abutting contact successively between the first retaining member, the damper, the second retaining member,

and said flange-like members due to the tensile force of the wire.

10. An electormagnetic pickup cartridge as claimed in claim 6 in which said first retaining member comprises a flange-shaped retaining part provided integrally with and projecting radially outward from the outer peripheral surface of the armature.

11. An electromagnetic type pickup cartridge comprising:

a cartridge body having an electromagnetic transducing circuit including pole pieces and coils arranged to function cooperatively within a cartridge housing and a permanent magnet installed in a specific position within said cartridge housing; and stylus assembly detachably installed in said cartridge body and comprising a cantilever arm having front and rear ends,

a stylus provided at said front end of said arm,

a tubular armature provided at the rear part of the arm,

a tubular guard member surrounding said armature and having corresponding front and rear ends, said cantilever, said stylus, and said armature comprising a vibrating structure,

a damper holding within said guard member the armature in a manner permitting free swinging vibration thereof at a position where a central point of said damper in the diametric and axial directions thereof substantially coincides with the center of the gravity of said vibrating structure,

retaining means comprising a first retaining member provided at a specific position on the armature, and a second retaining member provided at a specific position in the tubular guard member, said damper being clamped between said first and second retaining members,

a piece of wire connected at a front end thereof to the armature at a point substantially coniciding with said gravity center of the vibrating structure, said wire imparting a tensile force to the armature and cantilever arm in the direction from said front end toward said rear end of the armature, and magnetic member provided on the rear part of said guard member with .a clearance relative to the armature whereby the: vibration of the armature will be unobstructed, the rear end of the wire being fixed to said magnetic member, said magnetic member facing the permanent magnet when the stylus assembly is inserted into the cartridge body,

said armature confronting said] pole pieces and, at the same time, being magnetized by the permanent magnet via the magnetic member when the stylus assembly is inserted into the cartridge body.

Claims

1. An electromagnetic type pickup cartridge comprising: a cartridge body having an electromagnetic transducing circuit including pole pieces and coils arranged to function cooperatively within a cartridge housing and a permanent magnet installed in a specific position within said cartridge housing; and a stylus assembly detachably installed in said cartridge body and comprising a cantilever arm having front and rear ends, a stylus provided at said front end of said arm, a tubular armature provided at the rear part of the arm, a tubular guard member surrounding said armature and having corresponding front and rear ends, a damper holding within said guard member the armature in a manner permitting free swinging vibration thereof at a position apart from a rear end of the armature with a predetermined distance, a piece of wire connected at a front end thereof to the armature at a point substantially in the vicinity of a point coinciding with a central point of the damper in the diametric and axial directions thereof, said wire imparting a tensile force to the armature and cantilever arm in the direction from said front end toward said rear end of the armature, and a magnetic member provided on the rear end part of said guard member with a clearance relative to the armature whereby the vibration of the armature will not be obstructed, rear end of the wire being fixed to said magnetic member, said magnetic member facing the permanent magnet when the stylus assembly is inserted into the cartridge body, said armature confronting said pole pieces and, at the same time, being magnetized by the permanent magnet via the magneTic member when the stylus assembly is inserted into the cartridge body.

5. An electronagmetic type pickup cartridge as claimed in claim 1 in which said cantilever arm, said stylus, and said armature comprises a vibrating structure, and said central point of the damper substantially coincides with the center of gravity of said vibrating structure.

9. An electromagnetic pickup cartridge as claimed in claim 6 in which said securing means further has a plurality of flange-like members cut out and bent inward from the wall structure of the tubular guard member, and the armature is set in position by the intimately abutting contact successively between the first retaining member, the damper, the second retaining member, and said flange-like members due to the tensile force of the wire.

11. An electromagnetic type pickup cartridge comprising: a cartridge body having an electromagnetic transducing circuit including pole pieces and coils arranged to function cooperatively within a cartridge housing and a permanent magnet installed in a specific position within said cartridge housing; and a stylus assembly detachably installed in said cartridge body and comprising a cantilever arm having front and rear ends, a stylus provided at said front end of said arm, a tubular armature provided at the rear part of the arm, a tubular guard member surrounding said armature and having corresponding front and rear ends, said cantilever, said stylus, and said armature comprising a vibrating structure, a dAmper holding within said guard member the armature in a manner permitting free swinging vibration thereof at a position where a central point of said damper in the diametric and axial directions thereof substantially coincides with the center of the gravity of said vibrating structure, retaining means comprising a first retaining member provided at a specific position on the armature, and a second retaining member provided at a specific position in the tubular guard member, said damper being clamped between said first and second retaining members, a piece of wire connected at a front end thereof to the armature at a point substantially coniciding with said gravity center of the vibrating structure, said wire imparting a tensile force to the armature and cantilever arm in the direction from said front end toward said rear end of the armature, and a magnetic member provided on the rear part of said guard member with a clearance relative to the armature whereby the vibration of the armature will be unobstructed, the rear end of the wire being fixed to said magnetic member, said magnetic member facing the permanent magnet when the stylus assembly is inserted into the cartridge body, said armature confronting said pole pieces and, at the same time, being magnetized by the permanent magnet via the magnetic member when the stylus assembly is inserted into the cartridge body.