US3761647A - Cartridge for detecting vibrations representing stereophonic sound - Google Patents

Abstract

A stereophonic pickup cartridge for reproducing two channel sound from record discs which are cut according to 45*-45* system, comprises one or more armatures of high magnetic permeability material and mounted on a cantilever which transmits vibrations of a stylus tip, a permanent magnet secured to a cartridge body adjacent the armature so as to provide magnetic excitation thereto, and an electromagnetic current generating arrangement responsive to a change in magnetic flux passing through the armature from the permanent magnet which is caused by vibration of the armature. The electromagnetic arrangement includes two pairs of pole pieces located on opposite sides of and with an inclination of 45* with respect to an imaginary vertical plane passing through the axis of the cantilever so that the pole pieces of each pair extend in directions perpendicular to the respective modulation walls of a sound groove, the pairs of pole pieces forming independent gaps for each channel, and the armatures being positioned to be separately operable within the independent gaps. The pickup cartridge provides good channel separation, reduced equivalent mass of the vibrating system and improved frequency response as well as improved sound groove tracking.

Description

United States Patent [191 Nemoto et al.

[ 1 CARTRIDGE FOR DETECTING VIBRATIONS REPRESENTING STEREOPHONIC SOUND [75] Inventors: Mitsuo Nemoto; Kimiyasu Honma,

both of Tokyo, Japan [73] Assignee: Kabushiki Kaisha Audio-Technica,

Tokyo, Japan [22] Filed: Aug. 13, 1969 [21] Appl. No.: 849,767

[30] Foreign Application Priority Data Aug. 14, 1968 Japan 43/57408 Feb. 3, 1969 Japan 44/7290 [52] US. Cl. 179/100.41 K, 274/37 [51] Int. Cl H04r 11/12 [58] Field of Search 179/l00.41, 100.41 ST, l79/100.41S,100.41 MM, 100.41Vl, 100.41 PE; 274/37 156] References Cited UNITED STATES PATENTS 1,663,884 3/1928 Harrison 179/100.4l 2,864,897 12/1958 Kaar 179/1004] 3,056,861 10/1962 Grover 179/l00.41 3,184,555 5/1965 Marshall... l79/100.4l 3,230,317 l/l966 Freise l79/100.4l 3,294,405 12/1966 Pritchard.. 179/10041 X 3,299,219 1/1967 Madsen l79/100.41 3,444,335 5/1969 Walton l79/l00.4l 3,526,728 9/1970 lga 179/10041 FOREIGN PATENTS OR APPLlCATlONS 718,099 9/1965 Canada 179/1004] [451 Sept. 25, 1973 1,000,035 8/1965 Great Britain 179/100.41

Primary ExaminerRaymond F. Cardillo, Jr. Att0rney.lecies and Greenside ABSTRACT A stereophonic pickup cartridge for reproducing two channel sound from record discs which are cut according to 45-45 system, comprises one or more armatures of high magnetic permeability material and mounted on a cantilever which transmits vibrations of a stylus tip, a permanent magnet secured to a cartridge body adjacent the armature so as to provide magnetic excitation thereto, and an electromagnetic current generating arrangement responsive to a change in magnetic flux passing through the armature from the permanent magnet which is caused by vibration of the armature. The electromagnetic arrangement includes two pairs of pole pieces located on opposite sides of and with an inclination of 45 with respect to an imaginary vertical plane passing through the axis of the cantilever so that the pole pieces of each pair extend in directions perpendicular to the respective modulation walls of a sound groove, the pairs of pole pieces forming independent gaps for each channel, and the armatures being positioned to be separately operable within the independent gaps. The pickup cartridge provides good channel separation, reduced equivalent mass of the vibrating system and improved frequency response as well as improved sound groove tracking.

11 Claims, 14 Drawing Figures PATENTEI] SEP25 ms SHEET 1 UF 4 FIG.

FIG. 2

INVENTOR Mitsuo Nemoto and Kimiyasu 'Honma- PATENTED$EP25I975 3.761.647

SHEET 2 OF 4 Mitsuo Nemoto and Kimiyasu Honma I NVENT OR PATENTED 3.761 .647

SHEET 3 OF 4 INVENTOR Mitsuo Nemoto d Kimiyasu Honma PATENTEDSEPZS'QH 3.761.647

SHLEI l NF /1 FIG. l4 4| INVENT OR Mitsuo Nemdto a d Kimiyasu Honma CARTRIDGE FOR DETECTING VIBRATIONS REPRESENTING STEREOPIIONIC SOUND SUMMARY OF THE INVENTION The invention relates to a stereophonic pickup carteidge of the electromagnetic type for simultaneously reproducing two sound channels from a single groove record disc, and more particularly to such a cartridge of the induced magnet type in which an armature of high permeability magnetic material is adapted to oscillate with the stylus tip and a permanent magnet is disposed adjacent the armature to magnetize the latter, the vibration of said armature causing a change in magnetic flux derived from the permanent magnet.

Two recording techniques are known to record two separate channels in a single groove of a stereographic record disc. In one technique, one channel is recorded laterally and the other vertically. In the other technique, a channel is recorded on each of the two sides of the groove at an angle of 45 with respect to the horizontal disc surface. In the former or lateral vertical system, the degree of harmonic distortion is so different as between the two channels as to cause a difference in tone quality. Moreover, owing to the pinch effect, the second harmonic of the signal from the lateral channel is mixed with the vertical channel. For these reasons, there is a general tendency to use the other socalled 4545 system.

Stereophonic pickup cartridges for reproducing two sound channels from a record disc cut according to the 45-45 system, are usually of the electromagnetic type. In particular, a pickup cartridge of the moving magnet type as disclosed typically in US. Pat. No. 3,077,522 is in wide use, which comprises a tubular or post-shaped permanent magnet secured lengthwise to the end of a cantilever remote from the stylus tip, the magnet and the cantilever being supported within a sleeve by means of bearings of elastic material. The sleeve is placed in a common gap formed by four pole pieces each arranged at an angle of 40 with respect to the vertical. It is also known to replace the permanent magnet of such a cartridge with an armature of high permeability material having a permanent magnet disposed adjacent the armature to magnetize the armature, thereby forming a cartridge of the induced magnet type.

However, both types of cartridges are designed to provide channel separation from a change in magnetic flux in the common gap, which change results from the vibration of the permanent magnet or of the armature within the gap. This presents an inherent difficulty to providing an improved channel separation. In addition, because the stylus assembly must be supported by using elastic bearings between the permanent magnet or armature and its surrounding sleeve, there exists the drawback of producing cross modulation which is most deleterious to the tone quality. Furthermore, while the removal of the stylus assembly upon wear of the stylus is simple, the compression applied to the sleeve when it is being inserted into the gap across pole pieces, makes it likely that the pre-adjusted orientation of the permanent magnet or armature which is supported by elastic bearings, will be disturbed when the assembly is replaced.

Therefore, it is an object of the invention to provide an improved stereophonic pickup cartridge which is capable of completely avoiding the above disadvantages of the prior art cartridges.

It is another object of the invention to provide an electromagnetic pickup of the induced magnet type having a vibrating system of reduced equivalent mass in which the armature is formed of high permeability material whose mass is substantially reduced as compared with a permanent magnet, and in which a permanent magnet for magnetizing the armature is disposed separately from the vibrating system.

In accordance with the invention, there is provided a stereophonic pickup cartridge having an improved channel separation which substantially remains unchanged with frequency and reproduction level, thereby permitting an improved stereophonic sensation and depth.

According to the invention, a stereophonic cartridge can be provided with a stylus assembly which can be readily inserted into the cartridge body, maintained in proper orientation over a prolonged period and readily removed for replacement upon wear of the stylus tip.

Further according to the invention, the electromagnetic cartridge can be designed to support the vibration system by a cantilever holder including a suspension wire, without recourse to the use of elastic bearings surrounding the system, and to apply a damping action to the vibration system with a damper formed of elastic material and disposed separately from the suspension wire.

Additional advantages of the invention are the increase of high-region resonance frequency and reduction of mechanical impedance as well as improved tracking properties for the stylus.

The invention will be described in further detail with reference to the drawings.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a perspective view of the stereophonic pickup cartridge transducer according to one embodiment of the invention,

FIG. 2 shows the embodiment of FIG. 1 in simplified elevation,

FIG. 3 is an elevation of a similar embodiment as shown in FIG. 2 except that the permanent magnet is disposed rearwardly of the armature and a guide element is placed between the permanent magnet and the armature,

FIG. 4 shows, in elevation, a further modification of the transducer shown in FIG. 2 in which the permanent magnet is located inside the electromagnetic current generating means and is provided with a pole piece formed as an extension directed towards the armature disposed between the pair of pole pieces of the electromagnetic means,

FIG. 5 shows, in elevation, a still further modification of the transducer of FIG. 2 in which one additional permanent magnet is placed between the pole pieces of the electromagnetic means,

FIG. 6 is a perspective view of a stylus assembly which employs an armature in'the form of a disc,

FIG. 7 is a perspective view of a stylus assembly using a square plate armature,

FIG. 8 is a perspective view of a stylus assembly of the form generally similar to that of FIG. I, but in which an auxiliary armature is fitted on the rear end of the cantilever,

FIG. 9 is an elevation of another stereophonic pickup cartridge transducer of the invention incorporating an improved stylus assembly,

FIG. 10 is a bottom view of the stereophonic pickup cartridge according to a further embodiment of the invention,

FIG. 11 is a section along the lines 11l1 in FIG. 10,

FIG. 12 is a perspective view of the stylus assembly shown in FIGS. 10 and 11,

FIG. 13 is a section, on an enlarged scale, on the line 13l3 in FIG. 12, and

FIG. 14 is a view similar to FIG. 13 but of a modified stylus sub-assembly.

DETAILED DESCRIPTION OF EMBODIMENTS include an angle of inclination of 45 with respect to the vertical plane. Coils 5 and 6 are connected in series as are coils 7 and 8. The two groups of coils are adapted to respond separately to a change in magnetic flux through the respective independent gaps to produce an electric current.

In the transducer according to this embodiment, a pair of armatures 9, 10 of high permeability material are positioned in the above mentioned independent gaps, respectively, in proper orientation. Thus in order to provide proper operation of the armatures in response to the vibration of a stylus tip 11, these armatures are arranged at the rear end of a cantilever arm 12 extending rearwardly from the stylus, in a manner such that they extend perpendicularly with respect to the axis of the cantilever arm 12 and extend at right angles to each other in corresponce with the independent air gaps. Each armature is secured, not directly to the cantilever arm 12, but to an armature securing member 13 carried by the cantilever arm 12. In order for the armatures 9,10 to be properly positioned in the respective independent gap, the vibration system including the armatures is carried by a holder 14. As will bedescribed in detail later, the holder 14 is a so-called cantilever holder and constitutes a cantilever unit together with the arm 12. A support or fulcrum wire (not shown in FIG. 1) secured to and extending axially rearwardly from the rear end of the cantilever arm 12 is connected to the holder 14 through the intermediary of a damper 15 of elastomeric material placed between the holder 14 and the armature securing member 13 so as to compress the damper 15 through a suitable tension in the wire, thereby holding the vibration system. For assembly purposes, the vibration system assembly including the cantilever arm 12 and the holder 14 is suitably positioned with respect to the electromagnetic means so as to align thearmatures within their associated gaps, and then the holder 14 is set in position. The damper 15 is formed from elastorneric material, for example, synthetic rubber such as butyl rubber it allows for the oscillatory motion of the armatures 9, 10 in any direction and serves to return them to their neutral position. Similarly, the above mentioned support or fulcrum wire allows for such oscillatory motion of the armatures 9, 10

and eliminates the risk that the armatures are displaced by a force transmitted from the stylus tip 11 and acting in the running direction of sound grooves.

The transducer shown further includes a rod-shaped permanent magnet 16 which is placed adjacent the independent gaps in a vertical plane including the cantilever arm 12, for the purpose of magnetizing the armatures 9 and 10. The permanent magnet 16 is magnetized in its axial direction and forms separate magnetic circuits for the right-and left-hand channel, through armatures 9, 10 and pole pieces 1, 2 and 3, 4. Thus when armatures 9, 10 are subjected to vibration transmitted from the stylus tip 11, there is caused a change in magnetic flux in the gaps in which the armatures are placed, thereby inducing a voltage across coils 5, 6 and coils 7, 8 of the electromagnetic means which forms these gaps. In a double channel disc recorded according to the 45 45 system, each channel is cut at an angle of 45 with respect to the horizontal disc surface so that both channels are formed at right angles to each other. When the stylus tip is placed into a groove of the disc, one channel causes a movement of the stylus tip in a direction normal to that channel surface, so that one of the armatures, for example armature 9, will oscillate about the fulcrum of the vibration system in a plane including the cantilever and said one armature to thereby induce current in coils 5, 6, while the other armature, or armature 10, will be only subjected to rotary motion about its axis so that no change in magnetic flux is caused in the gap in which said other armature is placed, with the consequence that no current is induced in coils 7, 8. The other channel similarly causes a movement of the stylus tip 11 in a direction normal to its channel surface, and the result of this is that only armature 10 will oscillate about the fulcrum of the vibration system in a plane including the cantilever arm 12 and annature 10, thereby inducing current in coils 7,8. No current is induced in coils 5, 6. In actual operation, the movement of the stylus tip 11 is influenced by both channels and the motion of the armatures 9, 10 will be complex. However, because the coils of each pair are only responsive to one channel component which causes a change of magnetic flux in the gap formed by their associated pole pieces, two separate signals are produced by the two pairs of coils.

In, FIG. 2, which shows only one half of the transducer, namely the armature 9, the pole pieces 1, 2 and the coils 5, 6 corresponding to one of the channels, it will be understood that the armature 9 extends in the direction in which the stylus tip 11 is moved by said one channel, so that the armature 9 will oscillate across pole pieces 1 and 2 or in the plane of the sheet of drawmg.

FIG. 3 shows another form of the transducer in which permanent magnet 16 is placed rearwardly of the armature 9, as viewed from the stylus tip 11, and there is provided a guide or pole piece 17 for passing flux from the permanent magnet tothe armature. The guide piece 17 is disposed within a hollow holder 14 and extends to the abutment of holder 14 and damper 15, thereby providing an effective, low reluctance path for the flux.

The permanent magnet 16 and the guide piece 17 are arranged in direct contact. As will be readily appreciated, it is preferable to mount the stylus assembly including the cantilever holder 14 detachably on the body including the electromagnetic means. At this end,

the parts can be arranged so that as the holder is mounted, it fits with the permanent magnet 16 as by forming a groove in the end of the holder and the guide piece 17 is brought into contact with the permanent magnet 16.

FIG. 4 shows a further modification of the transducer which is similar to FIG. 3 in that a guide or pole piece 17 is provided to pass the flux from the permanent magnet 16 to the armature 9. In this embodiment, the permanent magnet 16 is located between the coils 5 and 6, and the guide piece 17 extends towards the armature 9 placed below the magnet. This feature allows a greater amount of flux to be supplied to the armature 9, thereby enabling reproduction of sound with an improved S/N ratio to be obtained.

FIG. 5 shows a still another transducer which is similar to the embodiment shown in FIG. 2 in that permanent magnet 16 is placed forwardly of the armature 9, as viewed from the stylus tip 11, but differs from FIG. 2 by the provision of an additional permanent magnet 18 disposed between the pole pieces 1 and 2. The purpose of the permanent magnet 18 is to attract flux from the permanent magnet 16 so as to achieve a more effective passage of the flux through the armature 9, rather than directly acting to magnetize the armature 9. An improved S/N ratio can be assured by this means as in the embodiment of FIG. 4.

FIGS. 6 to 8 show slightly different forms of the stylus assembly from that previously described. In FIGS. 6 and 7, the stylus assembly comprises a single armature 19 in the form of a disc (FIG. 6) and of a square plate (FIG. 7). Such stylus assemblies can be incorporated into any of the transducers illustrated in FIGS. 1 to 5. Because of its shape, such disc or square plate armature 19 can be directly mounted on the cantilever arm 12 without the need for providing the armature securing member 13 shown in FIG. 1. However, as before, the armature 19 is supported, together with the cantilever arm 12, by the cantilever holder 14 via an interposed damper 15 of an elastomeric material. The stylus assembly of FIG. 8 is similar to that shown in FIG. 1 but is provided, in addition to armatures 9 and 10, with a tubular auxiliary armature which is fitted around the cantilever arm 12 forwardly of the armature securing member 13. The auxiliary armature 20 is formed of similar high permeability material as used for the armatures 9 and 10 and is adapted to move with the oscillation of the stylus tip 11. When this stylus assembly is used in a transducer as shown in FIGS. 1, 2 and 5 in which the permanent magnet 16 is disposed forwardly of the gaps, the auxiliary armature 20 will aid in the change of magnetic flux across pole pieces 1, 2 and across pole pieces 3, 4 by the armatures 9 and 10. This serves to provide more positive separation of channel components of the vibration. In addition, the auxiliary armature 20 will assist in better guiding the flux from the permanent magnet 16 to the armatures 9, 10. Still further, the auxiliary armature 20 provides a strengthening effect for the thin cantilever arm 12 to prevent flexure of the same which may otherwise occur as a result of the vibration thereof, thereby removing secondary resonance.

The transducer shown in FIG. 9, which is depicted in similar fashion as FIG. 2, has a vibration system and an electromagnetic means which are both different from those described above. The vibration system of this transducer does not have the cantilever holder previously mentioned, but terminates in an armature securing member 13 mounted at the rear end of the cantilever arm 12 and carrying armatures (only armature 9 being shown). Forwardly of the member 13 there is provided on the cantilever arm 12 a support member 21 of an elastomeric material which acts as a damper, and the support member 21 is securedly received in a tubular holder 22 which is in turn secured to the cartridge body, thereby positioning the whole vibration system. In the electromagnetic means, pole pieces 2 and 4 associated with the armatures 9 and 10 extend at an angle of 45 with respect to the vertical planes, but pole pieces 1 and 3 do not extend parallel to their mating pole pieces 2 and 4, but instead extend vertically. Furthermore, pole pieces 1 and 3 are bent at their lower end to extend towards the rear ends of the cantilever arm 12. The pole pieces 2 and 4 are bent as shown, and the magnetic circuit for one half of the electromagnetic means is completed through pole pieces 1, armature 9, pole pieces 2 and permanent magnet 16 which is placed in contact with or close to a yoke 23. If desired, pole pieces 1 and 3 can be unified into a single piece. The resulting structure still forms independent gaps for the two channels.

FIGS. 10 to 13 show a still further embodiment of the stereophonic pickup cartridge according to the invention which corresponds to the transducer of FIG. 5, but in which the stylus assembly is replaced by that of FIG. 8. Except for a stylus assembly 30, all of parts and components are assembled and properly secured in position in a casing 31 of high permeability material, which also serves as a shield. The casing 31 has a pair of flanges 32 for use in mounting the cartridge on a tone arm. Two pairs of terminals 33 project from the rear end of the casing 31 for connection with an amplifier which amplifies reproduced signals. In the bottom wall of the casing 31 there is formed a window 34, and in communication with the window 34 is a receptacle 58 (not shown in FIG. 10 but shown in FIG. 11) into which a part of the stylus assembly 30 is inserted for attachment, the stylus assembly 30) covering a substantial part of the bottom of the casing 31. FIG. 10 shows part of the stylus assembly 30, that is, a knob 35 moulded from synthetic resin, cantilever arm 36, stylus tip 37, auxiliary armature 38, armature securing member 39, a pair of armatures 40, 41 secured to the member 39 and only partly shown, and damper 42. The pair of armatures 40, 41 are secured to the member 39 at the rear end of the cantilever arm 36 so as to extend in a plane perpendicular to the cantilever arm 36 and at an angle of indication of 45 with respect to the vertical plane including the axis of the cantilever arm 36 as previously described. These armatures are positioned in independent gaps formed by two pairs of pole pieces, only one pole piece of each pair being shown in FIG. 10 at 43 and 45 as seen within the window 34 of the casing 31. Obviously opposite pole pieces are provided to define the gaps. In FIGS. 10 and 11, it will be seen carrying the terminals 33. Thus the board 48 is mounted in place after the transducer has been assembled within the casing 31.

The electromagnetic means of the transducer is formed as one block as shown in FIG. 1, and the one half is shown in FlG. 11 as comprising pole pieces 45, 46 connected together b a yoke 49 with coils 50, 51 being wound on opposite legs. The coils 50, 51 are connected in series so as to be additive for induced voltages. As will be understood, the ends of the pole pieces 45, 46 are arranged at right angles with respect to the ends of the other pair of pole pieces not shown. in order to facilitate the assembly of the cartridge and to maintain correct positioning of the pole pieces permanently, the pole pieces are embedded in a resin moulding 52, even though it will be understood that free space is left for the gaps defined between the pole pieces. The resin moulding 52 occupies a substantial space within the casing 31, and has a front end portion 53 which extends to the front wall of the casing and a rear end portion 54 which is shaped to be engaged with a groove 55 formed in the terminal board 48. Also the resin moulding 52 has a top end portion 56 which con tacts the inwardly extending end 57 of the terminal board 48, when in place, and thus allows the terminal board 48 to be a sliding fit with the casing wall and portion 56. The resin moulding 52 is formed with a receptacle 58 rearwardly of the pole pieces, for reception of a part of the stylus assembly 58 rearwardly of the pole pieces, for reception of a part of the stylus assembly 30. The magnetic shield provided by the casing 31 encloses the electromagnetic means, but permits a part of the resin moulding 52 to be exposed at its window 34.

The cartridge shown in these Figures is constructed to facilitate the mounting of the stylus assembly 30 on the cartridge body in proper position, thereby ensuring a correct positioning of the armatures within the gaps of the electromagnetic means. To this end, a resin knob 35 is centrally provided with a post-shaped plug 59 which is engageable with the receptacle 58 to hold the entire stylus assembly firmly. To prevent unintended disengagement or loosening of the plug 59 from the receptacle 58, an annular lock ring 60 of an elastomeric material is fitted in a corresponding groove in the receptacle 58 so as to project a slight distance internally from the inner wall of the receptacle. A groove 61 is formed in the periphery of the plug 59 in conformity to the projection end of the ring 60. In this manner, the stylus assembly is detachably mounted on the cartridge body. FIG. 11 best shows that the armatures are properly positioned in the gaps when plug 59 is fitted into position. Further details of the stylus assembly will be described with reference to FIGS. 12 and 13.

The permanent magnet 47 is embedded in the front end portion 53 of the resin moulding 52, but is exposed at its end face opposite to the auxiliary armature 38, through the window 34 in the casing 31. This magnet is axially magnetized and magnetizes the auxiliary armature 38 disposed below it, which in turn passes the flux to the armatures such as shown at 41. Another permanent magnet 74 is disposed between the pole pieces 45 and 46 to force the flux from the permanent magnet 47 to pass through the armature. Because of such nature of the magnet 74, the direction of magnetization thereof should be carefully determined. By experiments, it was found preferrable to magnetize the attraction magnet 74 lengthwise in the similar manner as the permanent magnet 47 when the disposition of both magnets shown in H6. 11 is employed.

FIGS. 12 and 13 show the appearance and the section of the stylus assembly shown in FIGS. 10 and 11. The knob 35 formed from synthetic resin has a bottom wall 62 and a pair of side walls 63, 64, the bottom wall 62 being formed with the plug 59 previously mentioned. The plug 59 is slightly inclined towards the front or the stylus tip 37 and is formed with the groove 61 in the front part of its periphery, for engagement with the lock ring in the receptacle 58 to be detained thereby. A semi-circular raised portion extends from the bottom wall 62 to the front side of the plug 59 and the securing member 39 abuts, through damper 42, against the front end face of the raised portion 65, the parts 42, 39 and 36 being aligned on an extension line from the axis of the semi-circular raised portion 65. The pair of armatures 40, 41 are secured to the armature securing member 39 so as to lie in a plane perpendicular to the axis of the cantilever arm 36 and to have an angle of inclination of 45 with the vertical plane including the axis of the cantilever arm 36. As is apparent, the knob 35 moulded from synthetic resin, covers the bottom of the casing 31 with the bottom wall 62 thereof and externally engages both sides of the casing with the side walls 63 and 64 thereof. Therefore, the spacing between the side walls 63 and 64 depends on the dimension of the casing. it will be seen that the knob 35 is firmly coupled to the cartridge body by means of the plug 59 and side walls 63 and 64.

The cantilever arm 36 is formed from a nonmagnetic metal, for example aluminum, to a tube form. A pipe of high permeability material which constitutes the auxiliary armature 38 is fitted on and secured to the tubular cantilever arm 36 adjacent the rear end thereof. lnto the rear end of the tubular cantilever arm 36 is forcibly pressed a fixing pipe 66, to which a support or fulcrum wire 67 is firmly bonded. The support of fulcrum wire can be a metal wire, preferably a relatively thin piano wire. The support or fulcrum wire 67 extends a substantial distance rearwardly from the fixing pipe 66, and is surrounded by and unified with another fixing pipe 68 over its length from a point adjacent the rear end of the cantilever arm 36 to the other end of the wire. The securing member 39 for the armatures is mounted on the rear end of the cantilever arm 36, and rearwardly of the member 39 there is disposed the damper 42 of an elastomeric material which is in turn followed by a mounting pipe 69 that is connected with the fixing pipe 68. The clearance left between the two fixing pipes 66 and 68 is important, because it allows the oscillatory motion of the cantilever. lt is also important in establishing and maintaining the fulcrum of vibration at a fixed point. The center of the clearance is at or closely adjacent the fulcrum of vibration, and therefore the armatures 40 and 41 are positioned in a plane passing through this center and perpendicular to the axis of the cantilever arm 36. The armature securing member 39 is moulded, by casting a synthetic resin such as ABS resin, so as to properly position the armatures 40 and 41 therein. Simultaneously, a through hole for subsequently passing the cantilever arm 36 can be formed when casting the member 39. The member 39 and cantilever arm 36 are firmly held together by friction at the wall of said hole.

The stylus sub-assembly including the portion from stylus tip 37 to mounting pipe 69 is carried by the knob 35 by inserting the mounting pipe 69 into a transverse bore extending across the semi-circular raised portion 65 and the plug 59. Thus the knob 35 acts as a cantilever holder. The plug 59 is formed with an axially extending receptacle 70 receiving a nut 71 which is threadably engaged by a clamp screw 72, thereby allowing the mounting pipe 69 of the stylus sub-assembly, which traverses across the plug 59, to be fixed in position by engagement with the clamp screw 72. If desired, by loosening the clamp screw 72, the relative position of the mounting pipe 69 to the plug 59 or the knob 35 can be adjusted. This obviously alters the distance between the rear surface of the armature securing member 39 and the front end surface of the semi-circular raised portion 65, so that the compression applied to the damper 42 and the tension in the support or fulcrum wire 67 can be freely adjusted. It will be appreciated that the stylus assembly of this embodiment is of compact and reasonable design in that it can be mounted on the cartridge body by merely holding it at the side walls 63 and 64 of the knob 35, thus without touching the stylus tip 37 and the armatures 40, 41.

FIG. 14 shows a further improved stylus subassembly in section. The sub-assembly is formed by moulding the armature securing member 39, support or fulcrum wire 67 and mounting member 69 integrally in a synthetic casting resin. The armatures and the cantilever arm 36 are fixed and partly embedded in the portion corresponding to the securing member 39. A use of a suitable metal mould comprising separated parts will permits such moulding without particular difficulty. Once the mould design and manufacturing steps are established, the the mass production with uniform quality is ensured. In order to strengthen the junction between the securing member 39 and the cantilever arm 36, the member 39 may be formed with a projection 73 which extends into the cantilever arm 36. If desired, the cantilever arm 36 need not be partly embedded in the securing member 39, but may be engaged with the projection 73, subsequent to the completion of molding, and secured thereto.

What is claimed is:

1. An electromagnetic stereophonic pickup cartridge for stereophonic reproduction of sound from a record groove having individual sound recordings disposed according to the 45-45 system, comprising electromagnetic generating means having two independently variable magnetic air gaps located at opposite sides of an imaginary first vertical plane and aligned in an imaginary second vertical plane transverse to said first plane;

a cantilever arm having one end portion provided with a stylus, another end portion, and a longitudinal axis coincident with said first plane;

magnetic armature means carried by said other end portion and being located in said second plane;

magnetic means fixedly mounted proximal to said armature means for magnetizing the same; and

mounting means engaging said other end portion of said cantilever arm and mounting the same for movement in more than one plane at substantially equal degrees of restraint about a fulcrum which is located at least proximal to said second plane;

said mounting means comprising an elongated flexible portion and an armature carrying portion, said portions of said mounting means being unitary and composed of synthetic plastic resin material.

2. A multichannel pickup cartridge adapted for simultaneous reproduction of multichannel signals from a record disk having a groove with two modulated walls comprising:

an enclosure having an open window in its bottom;

electromagnetic means including two pairs of pole pieces forming a pair of mutually independent air gaps, respectively, which are located on opposite sides of a first imaginary vertical plane and aligned in a second imaginary vertical plane which intersects with said first vertical plane;

a cantilever arm having its longitudinal axis coincident with said first imaginary vertical plane, said pole pieces of each pair being spaced axially of said arm;

an armature securing member securedly connected to said cantilever arm at the other end thereof;

a pair of armatures secured to said securing member, each said armature being disposed within each of said air gaps at an angle of inclination corresponding to the respective modulated wall of said sound groove of said record disk;

socket means fixed within said enclosure, said socket means including a recess opposite said window;

a knob member of non-magnetic material;

securing means for replaceably securing said knob member in the recess in said socket means, said knob member being channel-shaped in section so as to cooperate with said socket means to substantially cover said window when secured in place, said knob member being formed with a bore which extends through the central portion of said knob member in a direction inclined with respect to the bottom of said enclosure;

a mounting member located in said bore;

further securing means for adjustably securing said mounting member in the bore;

fulcrum means having its one end secured to the other end of said cantilever arm and its other end extending through and secured to said mounting member; and

a damper of an elastic material placed between the other end of said cantilever arm and said knob member;

said fulcrum means extending through said damper and being tensioned so as to maintain said damper in abutting relationship with said knob member and the rear end of said cantilever arm, whereby the knob member carries said cantilever assembly including said cantilever arm and said armatures thereon;

said electromagnetic means being responsive to a change in magnetic flux produced in said air gaps by a motion imparted by the record disk to said stylus tip and thence to said armatures.

3. A multichannel pickup cartridge according to claim 2 wherein said modulated walls are each inclined at an angle of 45 with respect to the vertical and at right angles to each other.

4. A multichannel pickup cartridge according to claim 2 in which said armature securing member, said fulcrum means and said mounting member are all integrally formed by casting resin, the ends of said armatures and said cantilever arm being embedded in the securing member thus formed.

5. A multichannel pickup cartridge according to claim 4 wherein said securing member is provided with a projection on one end thereof and in which said cantilever arm has a bore, said projection engaging said bore.

6. A multichannel pickup cartridge adapted for simultaneous reproduction of multichannel signals from a record disk having a groove with two modulated walls comprising:

an enclosure having an open window in the bottom;

electromagnetic means including two pairs of pole pieces forming a pair of mutually independent air gaps, respectively, which are located on opposite sides of a first imaginary vertical plane and aligned in a second imaginary vertical plane which intersects with said first vertical plane;

a cantilever arm having its longitudinal axis coincident with said first imaginary vertical plane, said pole pieces of each pair being spaced axially of said arm;

a stylus tip adapted to engage said sound groove, said stylus being supported at one end by said cantilever arm;

an armature securing member securedly connected to said cantilever arm at the other end thereof;

a pair of armatures secured to said securing member,

said armatures being of a high magnetic permeability material and disposed within each said air gap at an angle of inclination corresponding to the respective modulated wall of said sound groove of said record disk;

a permanent magnet fixedly disposed within said enclosure adjacent said armatures for magnetization thereof;

socket means fixed within said enclosure, said socket means including a recess opposite to said window;

a knob member of non-magnetic material;

securing means for replaceably securing said knob member in said recess in said socket means, said knob member being channel-shaped in section so as to cooperate with said socket means to substantially cover said window when secured in place, said knob member being formed with a bore which extends through the central portion of said knob member in a direction inclined with respect to the bottom of said enclosure;

a mounting member located in said bore;

further securing means adjustably securing said mounting member in said bore;

a fulcrum having its one end secured to the other end of said cantilever arm and its other end extending through and secured to said mounting member; and

a damper of an elastic material placed between the other end of said cantilever arm and said knob member;

said fulcrum extending through said damper and being tensioned so as to maintain said damper in abutting relationship with said knob member and said rear end of said cantilever arm, whereby said knob member integrally carries said cantilever assembly including said cantilever arm and said armatures thereon;

said electromagnetic means being responsive to a change in magnetic flux produced in said air gaps as derived from the permanent magnet through said armatures, said change being caused by a motion imparted by said record disk to said stylus tip and thence to said armatures.

7. An electromagnetic cartridge as defined in claim 6, said permanent magnet means being located at a side of said armature means and said second plane which is remote from said stylus, and comprising a guide pole portion extending towards said armature means.

8. An electromagnetic cartridge as defined in claim 6, said permanent magnet means being located above said armature means, and comprising a guide pole portion extending towards said armature means.

9. An electromagnetic cartridge as defined in claim 6, said permanent magnet means comprising a first permanent magnet located intermediate said armature means and said stylus, and a second permanent magnet located above said armature means.

10. An electromagnetic cartridge as defined in claim 6, said permanent magnet means being located intermediate said armature means and said stylus; and further comprising an auxiliary armature also located intermediate said armature means and said stylus and being carried by said cantilever arm.

11. An electromagnetic cartridge as defined in claim 6, said air gaps each being elongated, and said armature means including two elongated armatures each located in one of said gaps and having a longitudinal axis which extends substantially at a right angle to the elongation of the respective gap.

Claims (11)

1. An electromagnetic stereophonic pickup cartridge for stereophonic reproduction of sound from a record groove having individual sound recordings disposed according to the 45*-45* system, comprising electromagnetic generating means having two independently variable magnetic air gaps located at opposite sides of an imaginary first vertical plane and aligned in an imaginary second vertical plane transverse to said first plane; a cantilever arm having one end portion provided with a stylus, another end portion, and a longitudinal axis coincident with said first plane; magnetic armature means carried by said other end portion and being located in said second plane; magnetic means fixedly mounted proximal to said armature means for magnetizing the same; and mounting means engaging said other end portion of said cantilever arm and mounting the same for movement in more than one plane at substantially equal degrees of restraint about a fulcrum which is located at least proximal to said second plane; said mounting means comprising an elongated flexible portion and an armature carrying portion, said portions of said mounting means being unitary and composed of synthetic plastic resin material.

2. A multichannel pickup cartridge adapted for simultaneous reproduction of multichannel signals from a record disk having a groove with two modulated walls comprising: an enclosure having an open window in its bottom; electromagnetic means including two pairs of pole pieces forming a pair of mutually independent air gaps, respectively, which are located on opposite sides of a first imaginary vertical plane and aligned in a second imaginary vertical plane which intersects with said first vertical plane; a cantilever arm having its longitudinal axis coincident with said first imaginary vertical plane, said pole pieces of each pair being spaced axially of said arm; an armature securing member securedly connected to said cantilever arm at the other end thereof; a pair of armatures secured to said securing member, each said armature being disposed within each of said air gaps at an angle of inclination corresponding to the respective modulated wall of said sound groove of said record disk; socket means fixed within said enclosure, said socket means including a recess opposite said window; a knob member of non-magnetic material; securing means for replaceably securing said knob member in the recess in said socket means, said knob member being channel-shaped in section so as to cooperate with said socket means to substantially cover said window when secured in place, said knob member being formed with a bore which extends through the central portion of said knob member in a direction inclined with respect to the bottom of said enclosure; a mounting member located in said bore; further securing means for adjustably securing said mounting member in the bore; fulcrum means having its one end secured to the other end of said cantilever arm and its other end extending through and secured to said mounting member; and a damper of an elastic material placed between the other end of said cantilever arm and said knob member; said fulcrum means extending through said damper and being tensioned so as to maintain said damper in abutting relationship with said knob member and the rear end of said cantilever arm, whereby the knob member carries said cantilever assembly including said cantilever arm and said armatures thereon; said electRomagnetic means being responsive to a change in magnetic flux produced in said air gaps by a motion imparted by the record disk to said stylus tip and thence to said armatures.

3. A multichannel pickup cartridge according to claim 2 wherein said modulated walls are each inclined at an angle of 45* with respect to the vertical and at right angles to each other.

4. A multichannel pickup cartridge according to claim 2 in which said armature securing member, said fulcrum means and said mounting member are all integrally formed by casting resin, the ends of said armatures and said cantilever arm being embedded in the securing member thus formed.

5. A multichannel pickup cartridge according to claim 4 wherein said securing member is provided with a projection on one end thereof and in which said cantilever arm has a bore, said projection engaging said bore.

6. A multichannel pickup cartridge adapted for simultaneous reproduction of multichannel signals from a record disk having a groove with two modulated walls comprising: an enclosure having an open window in the bottom; electromagnetic means including two pairs of pole pieces forming a pair of mutually independent air gaps, respectively, which are located on opposite sides of a first imaginary vertical plane and aligned in a second imaginary vertical plane which intersects with said first vertical plane; a cantilever arm having its longitudinal axis co-incident with said first imaginary vertical plane, said pole pieces of each pair being spaced axially of said arm; a stylus tip adapted to engage said sound groove, said stylus being supported at one end by said cantilever arm; an armature securing member securedly connected to said cantilever arm at the other end thereof; a pair of armatures secured to said securing member, said armatures being of a high magnetic permeability material and disposed within each said air gap at an angle of inclination corresponding to the respective modulated wall of said sound groove of said record disk; a permanent magnet fixedly disposed within said enclosure adjacent said armatures for magnetization thereof; socket means fixed within said enclosure, said socket means including a recess opposite to said window; a knob member of non-magnetic material; securing means for replaceably securing said knob member in said recess in said socket means, said knob member being channel-shaped in section so as to cooperate with said socket means to substantially cover said window when secured in place, said knob member being formed with a bore which extends through the central portion of said knob member in a direction inclined with respect to the bottom of said enclosure; a mounting member located in said bore; further securing means adjustably securing said mounting member in said bore; a fulcrum having its one end secured to the other end of said cantilever arm and its other end extending through and secured to said mounting member; and a damper of an elastic material placed between the other end of said cantilever arm and said knob member; said fulcrum extending through said damper and being tensioned so as to maintain said damper in abutting relationship with said knob member and said rear end of said cantilever arm, whereby said knob member integrally carries said cantilever assembly including said cantilever arm and said armatures thereon; said electromagnetic means being responsive to a change in magnetic flux produced in said air gaps as derived from the permanent magnet through said armatures, said change being caused by a motion imparted by said record disk to said stylus tip and thence to said armatures.

7. An electromagnetic cartridge as defined in claim 6, said permanent magnet means being located at a side of said armature means and said second plane which is remote from said stylus, and comprising a guide pole portion extending towards said armature means.

8. An electromagnetic cartridge as defined iN claim 6, said permanent magnet means being located above said armature means, and comprising a guide pole portion extending towards said armature means.

9. An electromagnetic cartridge as defined in claim 6, said permanent magnet means comprising a first permanent magnet located intermediate said armature means and said stylus, and a second permanent magnet located above said armature means.

10. An electromagnetic cartridge as defined in claim 6, said permanent magnet means being located intermediate said armature means and said stylus; and further comprising an auxiliary armature also located intermediate said armature means and said stylus and being carried by said cantilever arm.

11. An electromagnetic cartridge as defined in claim 6, said air gaps each being elongated, and said armature means including two elongated armatures each located in one of said gaps and having a longitudinal axis which extends substantially at a right angle to the elongation of the respective gap.

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