Moving-coil type pickup cartridge

In a moving-coil type pickup cartridge, a vibrating system including an armature wound with a coil is disposed at an open end area of a magnet with a damper being interposed between the armature and the magnet, and the armature is placed directly under the influence of magnetic flux produced between the one and other ends of the magnet for generating a voltage without using any yoke.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a moving -coil type (MC-type) pickup 
cartridge, and particularly to a pickup cartridge which generates voltage 
by using the leakage flux of a magnet without using any yoke. 
2. Description of the Prior Art 
In prior art MC type pickup cartridges, such a construction as shown in 
FIG. 1 is generally known. In this example, a vibrating system provided 
with a cantilever is oscillated within a parallel magnetic field. 
In FIG. 1, a magnet 1 is prepared and, for example, two yokes 2 and 2a are 
attached to the both ends of the magnet 1 to form a substantially "U" 
shape, while a pole piece 3 is fixed to the yoke 2a at its lower end. A 
vibrating system 7 including a cantilever 6 with a stylus 4 fixed at its 
tip and an armature 5 provided thereabout at its rear is inserted into a 
bore 9 formed through the yoke 2 so that the armature 5 is fixed to one 
end of the pole piece 3 through a damper 8. Thus, the vibrating system 
including the armature 5 is forced to vibrate within the parallel magnetic 
field produced by the yoke 2 and pole piece 3 to induce an output voltage 
corresponding to the stylus vibration in the coil wound on the armature 5. 
FIG. 2 shows another example of the prior art pickup cartridge, in which a 
cylindrical magnet 10 is provided in place of the magnet 1 and pole piece 
3 of FIG. 1 and the vibrating system 7 is fixedly inserted through the 
damper 8 into a bore 12, which is formed in the magnet 10 at its one end. 
A front pole piece 11 is disposed in front of the coil-wound armature 5, 
and the cantilever 6 is inserted through a bore 13 provided in the front 
pole piece 11, which is in turn fixed to a cartridge body or the like, 
though not shown. With the pickup cartridge as mentioned above, the 
armature 5 is held between the yoke 2 and the pole piece 3 as shown in 
FIG. 1 or between the front pole piece 11 and the magnet 10 as shown in 
FIG. 2 so that its voltage generation efficiency is good. However, since 
the cantilever 6 penetrates through the bore 9 or 13 provided in the yoke 
2 or the front pole piece 11, it is necessary for the cantilever 6 to have 
an excessive length. For this reason, there is strong possibility that the 
cantilever 6 will bent. To prevent such bending, the cantilever must be 
made thick, and hence the equivalent mass of the vibrating system is 
increased. 
Further, when the cantilever 6 is inserted through the bore 9 or 13 of the 
yoke 2 or the front pole piece 11, the vibrating system 7 including the 
cantilever 6 is first fixed to the pole piece 3 or the magnet 10 through 
the damper 8 and then the yoke 2 or the front pole piece 11 is disposed. 
Therefore, when disposing the yoke or front pole piece, it is difficult to 
insert the cantilever into the bore of the yoke 2 or the front pole piece 
11 through the influence of the magnet 1 or 10 so that the cantilever may 
be damaged during its fabrication. In addition, a signal having a large 
amplitude from the record disc affects the cantilever bringing it into 
contact with the inner wall of the bore to damage the cantilever. Further, 
since the armature 5 is interposed between yokes or between yoke and 
magnet to cause vibration within parallel magnetic field for voltage 
generation, the yoke or the like becomes necessary making the construction 
more complicated. 
SUMMARY OF THE INVENTION 
Accordingly, the present invention is concerned with a pickup cartridge 
free from the aforesaid drawbacks inherent in the prior art pickup 
cartridge. 
It is a primary object of this invention to provide an effective MC type 
pickup cartridge in which a vibrating system is disposed within the open 
magnetic field of a magnet without using any yoke. 
It is another object of this invention to provide an MC type pickup 
cartridge in which a magnet is made large and also one surface of the 
magnet opposite to a record disc is cut out in order to enhance the 
voltage generating efficiency of a yokeless type pickup cartridge without 
increasing the equivalent mass of a vibrating system. 
It is a further object of this invention to provide an MC type pickup 
cartridge in which an open end surface of a magnet is curved in order to 
concentrate magnetic flux on the armature. 
It is a further another object of this invention to provide an MC type 
pickup cartridge in which an auxiliary magnetic pole with one surface 
thereof curved is used for easy shaping of an open end surface of a 
magnet. 
It is an additional object of this invention to provide an MC type pickup 
cartridge in which an open end surface of a magnet is slanted so that a 
large magnet can be used to raise the voltage generating efficiency and a 
cantilever can make its axial direction substantially coincident with that 
of the magnet when a pressure is applied to a stylus. 
It is yet another object of this invention to provide an MC type pickup 
cartridge in which coil winding on an armature of a vibrating system is 
made quite easy. 
It is also an object of this invention to provide an MC type pickup 
cartridge in which a plurality of dampers can be quite easily used by 
eliminating a yoke or a front pole piece so that damping factor may be 
freely controlled. 
It is a further additional object of this invention to provide an MC type 
pickup cartridge in which a visco-elastic member is disposed on one 
portion of a cantilever to change the vibrating mode of the cantilever. 
The above and other objects and features of this invention will become 
manifest from a consideration of the following description taken in 
connection with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A description will hereinafter be given on an example of this invention 
with reference to the drawings. 
In FIG. 3A, a substantially cylindrical magnet 10 is magnetized at its one 
end with N-pole and at its other end with S-pole, and a bore 12 is 
provided penetrating through the center portion of the magnet 10. A 
suspension holder 15 for holding therethrough a suspension wire 14 is 
fixedly inserted into the bore 12 of the magnet 10, and the suspension 
wire 14 is stretched through the suspension holder 15 between one end of a 
cantilever 6 and the other end of the suspension holder 15. The cantilever 
6 is provided with a stylus 4 at its one end and an armature 5 at its 
other end. The armature 5 is shaped suitably in cross or square and two 
coils 16 are wound thereon so as to intersect each other at right angles 
as shown in FIG. 3B or 3C. A vibrating system 7 including the stylus 4, 
armature 5 and cantilever 6 is attached through a damper 8 to the 
N-surface of the magnet 10. 
With the above-mentioned construction, magnetic flux from the magnet 10 is 
distributed from the N-pole toward S-pole as shown in FIG. 4. As a result, 
when the armature 5 of the vibrating system 7 is oscillated within the 
magnetic flux .phi. directed from the N-pole of the magnet 10 to the 
S-pole, an electromotive force is inevitably induced in the coils 16 wound 
on the armature 5. It is of course that if a magnet having small permeance 
factor and large magnetomotive force, such as ferrite magnet or rare earth 
magnet, is used as the above magnet 10, magnetic flux near the magnetic 
pole N can be greatly enhanced. 
When the above non-magnetic armature 5 is replaced by a magnetic armature 
5', the magnetic flux generated from the N-pole of the magnet 10 is 
concentrated into the magnetic armature 5' as shown in FIG. 5B. As the 
vibrating system is changed in position, the magnetic flux passing through 
the armature 5' is changed in volume and direction as shown in FIGS. 5A 
and 5C so that an output of higher efficiency can be obtained from the 
coils 16. 
FIG. 6 shows one example of an MC type pickup cartridge formed by using the 
aforesaid voltage generating theory. In FIG. 6, a casing 17 is made of 
synthetic resin or the like and output terminals 18 penetrate through the 
casing 17 from its front end portion 17a to its rear end portion 17b. A 
projection 17c is provided at the lower end portion of the casing 17, and 
a bore 17d is formed through the projection 17c as shown in FIG. 7. The 
magnet 10 is inserted into the concave portion provided in the projection 
17c so that the bore 12 of the center of the magnet 10 may be aligned with 
the bore 17d formed in the projection 17c of the casing 17. Thus, the 
suspension holder 15 is inserted through the bores 12 and 17d and fixed to 
the projection 17c by a set screw 19. Then, the cantilever 6 having the 
stylus 4 at its tip and the coil-wound armature 5 at its near end is 
pushed to the open end of the magnet 10 through a main damper 8 and the 
suspension wire 14 so that the cantilever 6 is fixed to the casing 17 
through the suspension holder 15 which is fixed with the suspension wire 
14. Further, in the front of the armature 5 a second damper 20 is fixed to 
the cantilever 6 or the armature 5. In FIG. 7, 21 indicates a cover and 22 
a terminal sheet. At the front end portion 17a of the casing 17 a front 
body 17e for rotatably pivoting a needle protecting cover 23 is fixed by 
means of coupling or the like. 
The magnet 10 is provided at its lower side with a cut surface 10a as shown 
in FIG. 7 by the following reason. In other words, while in FIG. 1 the 
armature is disposed within the parallel magnetic field for voltage 
generation, according to the construction as shown in FIG. 4 the magnetic 
flux is almost not focused, or the armature is placed in a so-called open 
magnetic field, so that its voltage generating efficiency is lowered by 10 
to 20 dB. To resolve the above problem, it is considered to increase the 
number of turns of the coil on the armature. In this case, however, the 
mass of the vibrating system is accordingly increased so that its 
performance is inevitably lowered. Therefore, when a strong and large 
magnet such as a rare-earth samarium.multidot.cobalt magnet is used as the 
magnet 10 to enhance the surface magnetic flux and to increase the voltage 
generating output, as shown in FIG. 9 one end 24 of the magnet 10 comes to 
contact with a record disk surface 23' so that the stylus 4 may not 
correctly trace a sound groove to make its practical use improper. 
Meanwhile, it is considered to elongate the cantilever to prevent the 
above drawback, but this procedure makes vibration unfavorable. In order 
to eliminate the above disadvantage, one portion of the magnet 10 opposite 
to the record disc surface 23' is cut out to form the cut surface 10a as 
shown in FIGS. 7 and 8 so that the outside diameter and length of the 
magnet 10 can be increased thereby to set the permeance factor to a 
desired value and to raise the flux density of the surface opposite to the 
armature 5. Accordingly, a simple construction can be effectively utilized 
and also a magnet of large configuration can be used so that the 
generating output to be obtained may exceed that of the prior art 
construction of FIGS. 1 and 2. As a result, the number of turns of the 
armature coil can be made equal to or smaller than the prior art and hence 
improvement on the tracing performance can be achieved by lowering the 
weight of the vibrating system. This is the reason why the cut surface 10a 
is provided on the magnet 10. 
FIGS. 10 to 12 show other embodiments for producing high output by focusing 
open magnetic flux from one end of the magnet into wound coil. 
In FIG. 10A, one end surface of the magnet 10 is curved in a concave shape 
so that magnetic flux .phi. emitted from the concave surface 10b is 
focused into the center portion 5a of the armature 5. Of course, the 
carvature of the concave surface 10b will affect the distance F from the 
end surface of the magnet 10 to the center portion 5a of the armature 5 
focused with flux, but by properly selecting these values the magnetic 
flux .phi. can be focused to the center portion 5a of the armature 5. In 
this case, as shown in FIG. 10B the generating coils 16 may be wound near 
the center of the armature 5. 
In the example of FIG. 11A, the end surface of the magnet 10 is convexly 
curved so that magnetic flux emitted from the convex surface 10c of the 
magnet 10 is concentrated to the exterior periphery 5b of the armature 5. 
Similarly in this case, the distance F from the end surface of the magnet 
10 to the flux-concentrated exterior periphery 5b of the armature 5 is 
varied according to the curvature of convex surface 10c. However, if these 
values are properly selected, the magnetic flux can be concentrated to the 
external periphery 5b of the armature 5. In this case, as shown in FIG. 
11B the armature 5 may be formed, for example, in a cross shape and wound 
with the coils 16 near its external periphery 5b. 
In the above embodiments, the end surface of the magnet is formed in a 
concave or convex shape. However, it is also possible that the above 
shapes of the end surface of the magnet are properly combined to form 
another curved surface having two or more flux concentrating points. 
FIG. 12 shows a practical construction of this invention, in which elements 
corresponding to those of FIGS. 10 and 11 are shown by the same reference 
numerals with description thereof being omitted. In FIG. 12, the 
cantilever 6 having the stylus 4 at its tip is inserted into the center 
portion 5a of the armature 5 and the coils 16 are wound on the armature 5 
concentrically near its center portion 5a. A clamp 25 is fitted to the 
inside of the cantilever 6 at its side opposite to the stylus side, while 
another clamp 26 is fitted to the end of the suspension holder 15 inserted 
through the bore 12 of the magnet 10. Thus, the suspension wire 14 is 
stretched through the suspension holder 15 between the clamps 25 and 26, 
and a nut 27 or the like is provided to adjust the compressible rate of 
the damper 8 which is held between the armature 5 and the concave surface 
10b of the magnet 10. With the above arrangement, the 
samarium.multidot.cobalt magnet or the like can be simply provided only by 
forming therein the curved surface 10b and the bore 12 before 
magnetization and also magnetic flux from the magnet 10 can be 
concentrated to a given point. 
In the above embodiments of FIGS. 10 to 12, there is a problem of cutting 
or processing the open end surface 10b or 10c of the magnet 10. On the 
contrary, in the examples shown in FIGS. 13 to 15, the opposite end 
surfaces of the magnet 10 are formed as parallel, while an auxiliary 
magnetic pole 28 with one end surface being made concave or convex is 
disposed between the magnet 10 and the damper 8. The other end surface of 
the auxiliary magnetic pole 28 is brought into contact with one end 
surface of the magnet 10. Then, magnetic flux, .phi. emitted from the 
concave surface 10b of the auxiliary magnetic pole 28 is concentrated to 
the center portion 5a of the armature 5. The other construction is similar 
to those of FIGS. 10 to 12 so that the description thereof will be 
cancelled. In the constructions of FIGS. 13 to 15, the magnet 10 is not 
necessary to have a curved end surface, but it is necessary only to 
provide an easily finished auxiliary magnetic pole 10b or 10c and to bring 
it into contact with the magnet end surface. Further, in case of using a 
samarium.multidot.cobalt magnet or the like, the bore 12 can be relatively 
simply formed therethrough before being magnetized. 
Furthermore, in order to remove the drawback encountered when a large 
magnet is used as mentioned in FIG. 9, upon being applied with stylus 
pressure, the cantilever can be arranged so that its axial center 
coincides with that of the magnet, while when applied with no stylus 
pressure, the cantilever is biased in a direction of a record disc in 
accordance with the inclination provided at the magnet end surface. 
In other words, as shown in FIG. 16, one end surface of the magnet 10 
opposite to the damper 8 is slantwise cut to form a cut surface 10a, and a 
cut angle .theta. between the cut surface 10a and the damper 8 is so 
selected that when applied with no stylus pressure, the cantilever is 
properly biased, but when applied with stylus pressure, the cantilever 
makes its axial center coincident with the axial direction of the magnet 
10. In this case, it is also possible that opposite end surfaces of the 
magnet 10 are cut out with the same angle .theta. as shown by dotted line 
or only one surface thereof opposite to the coil-wound armature 5 through 
the damper 8 is made slantwise. 
FIG. 17 shows one embodiment of this invention as mentioned in FIG. 16. In 
this embodiment, a vibrating system including the cantilever 6 and the 
armature 5 is biased toward the record disc by the inclined angle of the 
magnet 10, and the axial direction of the suspension holder 15 is adjusted 
by a set screw 19 which is provided in a supporter 29 disposed at the rear 
of the magnet 10. It is of course possible that without using the 
supporter or the like the set screw 19 is provided in a direction 
perpendicular to the axial direction of the magnet 10 to carry out lateral 
adjustment of the suspension holder 15. In the above embodiment of FIG. 
17, a magnet of large size can be used and one portion of the magnet is 
not brought into contact with the record disc surface only by slantly 
cutting the magnet end surface. In addition, when the stylus pressure is 
applied to the cantilever, the cantilever axis is aligned with the magnet 
axis so that magnetic flux can be uniformly applied to the armature and 
also the stylus pressure is stabilized. As a result, a pickup cartridge 
having a large output can be obtained. 
FIG. 18 shows another embodiment of this invention wherein the magnet 10 
can be made larger. The magnet 10 is disposed above a supporting plate 30 
(it can also be disposed at a position shown by dotted line) and the 
armature 5 of the vibrating system 7 is placed in the path of the magnetic 
flux directed from the pole N to the pole S. 
In this invention, the equivalent mass of the vibrating system is lessened 
and the weight of the whole cartridge is selected to about 4.7 grams. 
Accordingly, when used in a pickup arm of low mass and high sensibility, 
the pickup cartridge of this invention is not affected by warping, 
eccentricity, etc. of a record disc. If the effective mass is made small 
and compliance is enhanced, the tracing ability of the cartridge is 
improved and the reproduced frequency range is enlarged, but problems 
relating to resonance phenomenon of the vibrating system or the like are 
not resolved and a peak appears in higher frequency range. Therefore, in 
the embodiments shown in FIGS. 6 to 8, the cantilever is constructed in a 
duplex manner and a plurality of dampers are used to damp the middle and 
low frequency range and the high frequency range respectively, thus 
obtaining a frequency characteristic which is linear within a range up to 
60 Hz. In this invention, the yoke 2 and the front pole piece 11 are not 
used in front of the armature 5, so that plural dampers can be effectively 
disposed. The plural-damper construction will be next described with 
reference to FIGS. 19 to 21. 
In the example of FIG. 20, a second damper 20 is fitted to the cantilever 6 
in front of the armature 5. This second damper 20 can properly select its 
external diameter dimension, shape, material quality, etc. in accordance 
with its objects. In the example of FIG. 20, the second damper 20 is of a 
plate-shape such as circular, square or the like. As the second damper 20, 
however, it is also possible to use a concave damper surrounding the 
armature 5 as shown in FIG. 19. FIG. 21 is an enlarged cross-sectional 
view showing the damper portion of FIG. 7, in which the first damper 8 is 
inserted into the recess provided in the open end surface of the magnet 10 
and one end surface of the second damper 20 is cut to form a cut surface 
20a with the remaining parts being equal to those of FIG. 20. 
Being passable through the cantilever 6 from the direction of stylus 4, the 
second damper 20 with the above construction can be easily assembled. 
Different from the first damper 8, the above second damper 20 can be 
disposed on the vibrating system, for example, the cantilever 6 at its 
given position where an optimal effect is obtained, without touching to 
portions other than the vibrating system, so that the damping of high 
frequency range is effected by only the second damper 20 to enhance a 
high-frequency damping effect. In addition, since the second damper 20 is 
not in contact with the portions other than the vibrating system, it has 
no elasticity control effect associated to low-frequency damping, so that 
compliance will not be changed by the second damper 20. The compliance 
viewing from the side of the stylus 4 is determined by the first damper 8 
so that an aimed compliance can be obtained by only selecting hardness of 
the damper 8. 
Further, the mass of the vibrating system affects directly the middle and 
high frequency characteristics so that increase in mass by the second 
damper 20 must be considered. However, the elements practically considered 
as the added mass of a vibrating system are quite small and also these 
elements consist of successive connection of resistor and mass. Therefore, 
in an actual case they will not added, as they are, to the mass of 
vibrating system and damping effect or the like is different dependent on 
the mass of the second damper 20 so that a relatively flat frequency 
characteristic can be obtained. 
According to the above construction, even if a pickup cartridge is made as 
of a high-compliance type, the high-frequency damping is not insufficient 
as in the prior art and hence a flat frequency characteristic is 
obtainable. Also, from a structural point of view, the second damper is 
only added to the prior art construction, so that no particular accuracy 
is required and its assembly is easy with the result that its commercial 
value is increased. 
Further, a cantilever has a spring characteristic with respect to its 
lengthwise direction thereby representing a proper vibrating mode, in 
which stylus and armature positions correspond to node and the middle of 
cantilever corresponds to an antinode. In such a case, the amplitude at 
the stylus side will not be transmitted to the armature position with the 
same amplitude and hence the output level will be lowered. The above 
frequency band is normally in or over the intermediate sound range, so 
that the frequency characteristic is sagged in its middle. In order to 
reduce the above sagging characteristic, it is well known to use a 
material having high stiffness as the cantilever. However, such an 
expensive material can not always be used from an ecconomical point of 
view and hence the tone must have been sacrificed. Accordingly, this 
invention is to improve the sagging characteristic by changing a vibrating 
mode with a mass being added to the intermediate position of a cantilever 
corresponding to the antinode of the vibrating mode. In short, if a 
consideration is taken into only a portion to which a mass is added, a 
mechanical impedance of this portion becomes large to make it difficult 
for the above portion to become an antinode, so that Q of the vibrating 
mode is effectively lowered. Consequently, the sag portion can be made 
small. The construction for the above will be described with reference to 
FIGS. 22 and 23. 
In the example of FIG. 22, an auxiliary damper 32 is used as an adding 
mass, which is provided with a bore 33 to penerate therethrough a 
cantilever 6. The auxiliary damper 32 is made of a visco-elastic material 
such as butyl rubber or silicon rubber. This auxiliary damper 32 can 
select an arbitrary position on the cantilever in its length direction in 
accordance with the desired characteristic. In this example, 17e 
designates an auxiliary damper supporting base, which is extended from the 
cartridge main body. The example shown in FIG. 23 has the entirely same 
operation, object and effect as those of FIG. 22. However, the auxiliary 
damper 32 is provided with a semi-circular portion 34 at its bottom, which 
is brought into contact with the cantilever 6 to act thereon as the adding 
mass. 
Further, in this invention, an attempt is made to simplify the assembly of 
the vibrating system. In the prior art vibrating system 7 shown in FIG. 3, 
the stylus 4 is fixed to the tip of the cantilever 6 while the armature 5 
is disposed thereon at its rear side, and the suspension wire 14 drawn out 
from the rear of the cantilever 6 is fixed to the suspension holder 15 
thereby providing a sub-assembly member. Finally, the coils 16 are wound 
on the armature 5. In this case, however, the suspension holder 15 is 
caused to disturb the coil winding operation to make it difficult. For 
example, when a cross-type armature is used and a coil is wound on one 
yoke of the armature, a winding operator is required to bend the 
suspention holder 15 toward the other yoke so as not to touch with the 
winding coil so that the winding operation is disturbed. On the contrary, 
when winding a coil on the other yoke which is perpendicular to the one 
yoke, the suspension holder 15 is similarly bent toward the opposite yoke. 
In these cases, the suspension wire 14 happens to be broken and so on so 
that the number of winding process is increased and also proportion 
defective becomes high. 
Thus, as shown in FIG. 24, the aforesaid sub-assembly member is divided 
into a vibrating system section A including the cantilever 6 and the 
armature 5 and a holding section B including the suspension holder 15. At 
first, the winding operation is carried out at a condition of vibrating 
system section A only. After the above winding operation is finished, a 
spacer 25 for defining the position of the holding section B is applied 
with an adhesive agent and then inserted into the cantilever rear portion. 
In the example of FIG. 25, the cantilever 6 is of a double construction 
having an exterior pipe portion 36. The cantilever 6 is not extended to 
the last end but made to have a length to define a position for receiving 
the spacer 25. Accordingly, the operator can do quite easy coupling 
operation between the vibrating system section A and the holding section B 
for a short time with no failure. The last end of the main cantilever 6 
will function as a stopper in this example In the example of FIG. 26, the 
cantilever 6 is of a normal construction but a spacer of special shape is 
used. In other words, the spacer 25 is provided with a flange 35 to define 
the spacer position. 
The above constructions can be separately used in accordance with the 
cantilever shape. According to the above cantilever assembling method, 
upon winding the coil, it is not required to purposely keep the wire away 
from the suspension assembly so as not to be cut by touching thereto at 
every winding operation so that the coil winding efficiency is extremely 
improved. The suspension wire itself is also seldom broken and its 
proportion defective can also be greatly reduced. Further, the suspension 
assembly can be easily coupled to the vibrating system such as cantilever 
and in this case such a tool as required in the prior art is unnecessary. 
Output voltage and crosstalk frequency characteristics according to the 
above pickup cartridge construction are shown in FIG. 27, in which an 
output characteristic 36 is nearly flat up to 40 KHz or more, and a 
crosstalk characteristic 37 is limited to -20 dB or less. Further, as 
shown in FIG. 28 an output voltage characteristic 38 relative to stylus 
pressure can be made substantially flat in a range of about 0.5 g to 2 g 
of the latter. 
It will be apparent that many modifications and variations may be effected 
without departing from the scope of the novel concepts of this invention.