Electromechanical record disk dynamic range expander

An electromechanical record disk dynamic range expander for use in a stereophonic system. The invention includes a pivotally mounted stylus-bearing shank. Received within the shank are iron inserts which are maintained opposite electromagnetic coils and extended pole pieces. A permanent magnet communicates with the iron inserts by means of a steel fulcrum, and communicates with the extended pole pieces by means of a steel canister receiving the assembly as a whole. The coils are maintained between respective pairs of extended pole pieces and iron inserts, and are wound in such a manner that the number of coil windings increases with distance from the coil centerline. A magnetic gap exists between the extended pole pieces and associated iron inserts, with the respective coils being received within such magnetic gap. Movement of the stylus in a record groove causes the magnetic gap of the associated channel to move, cutting the coil windings and inducing a signal corresponding to the stored tonal image. The coil winding technique results in amplified increases in coil signal strength for linearly increasing mechanical movement of the stylus, achieving dynamic range expansion.

BACKGROUND OF THE INVENTION 
The instant invention resides in the art of stereo sound apparatus, and 
more particularly in that of stereo generators and dynamic range 
expanders. 
In recent years, there has been a great increase in the popularity of 
stereo sound systems for retrieving the tonal image stored upon the 
modulation sidewalls of a record groove. With the increase in popularity 
has come a number of attempts to sophisticate and refine such stereo 
systems to improve channel separation, noise suppression, frequency 
response, and the like. Indeed, in U.S. Pat. No. 3,040,136, to J. F. 
Grado, a number of advances were made in the art. In applicant's own 
copending patent application Ser. No. 949,742, for "STEREO CARTRIDGE," 
filed Oct. 10, 1978, still further improvements in the art have been set 
forth. The structure of the instant invention yet further advances the art 
beyond the point to which it has been taken by the teachings of Grado and 
those of applicant's referenced application. 
In the prior art, other stereo systems have customarily emitted a low level 
sound known as "record hiss," particularly when the volume of the stereo 
amplifier has been increased to enhance loud sounds. Record hiss is a low 
level sound, but with the increase in amplifier volume, the hiss is 
accentuated and becomes audible to the discerning listener. Yet further, 
low level harmonics of the tonal image recovered by the stereo system from 
the record have often been lost in present systems utilizing an armature 
for saturating electromagnetic coils with magnetic flux. Such armatures 
have had a tendency to magnetize with time and to thus maintain a residual 
magnetization in the range actuated by low level harmonics. With an 
existing threshold of residual magnetization upon the armature, the coils 
have been incapable of responding to or recognizing low level harmonics 
from the tonal image. 
In the prior art, other problems have existed with the general mechanical 
structure of the stereo pick-up cartridge and generator. Indeed, there are 
no known systems, apart from applicant's own, which utilize a shank 
assembly and associated moving generating elements which may be readily 
removed from a cartridge assembly and be easily replaced without the need 
for special tooling and the like. Heretofore, such removal has generally 
resulted in the costly discarding of the stereo pick-up itself and the 
subsequent total replacement of the same. 
Additionally, known systems have generally been ineffective in optimizing 
full frequency bandwidth channel separation, but have allowed cross-talk 
between channels without reliably correlating the mechanical modulation of 
the sidewall of a record groove with the associated output channel of the 
stereo system. 
Additionally, known systems have required sophisticated and expensive 
add-on equipment to achieve dynamic range expansion or enhancement. All 
known dynamic range expanders have been totally electronic in nature and 
there are no known electromechanical assemblies and particularly no such 
assemblies which may be found directly within a cartridge or pick-up other 
than that taught by applicant's copending patent application. 
The vast majority of stereo cartridge generators known to applicant utilize 
elastomers as fulcrums for the moving iron or moving magnet signal 
inducers of the stereo pick-up. Such elastomers inherently result in 
audible distortion since such elastomers subject the fulcrum to random 
mispositioning. Hence, response of the signal inducer attached thereto is 
not a true electrical reproduction of the tonal modulations stored within 
the stereo record grooves. 
OBJECTS OF THE INVENTION 
In light of the foregoing, it is an object of the instant invention to 
provide an electromechanical record disk dynamic range expander which is 
capable of squelching record hiss by including the characteristics of a 
dynamic range expander within the pick-up itself, alleviating the 
necessity of increasing amplifier volume or adding additional electronic 
components to the stereo system. 
Another object of the invention is to provide an electromechanical record 
disk dynamic range expander which is capable of mechanically responding to 
low level harmonics of the tonal content stored within the record grooves 
and producing the electrical complement of the same by providing a pick-up 
which utilizes no armatures but includes stationary coils. 
Still another object of the invention is to provide an electromechanical 
record disk dynamic range expander which includes a generator which may be 
removed for service or replacement without the necessity of specialized 
tools or knowledge. 
Yet an additional object of the invention is to provide an 
electromechanical record disk dynamic range expander which provides 
superior channel separation over systems presently known in the art. 
A further object of the invention is to provide an electromechanical record 
disk dynamic range expander wherein the fulcrum for stylus motion is a 
machined fulcrum, not susceptible to cocking, misalignment, and 
non-homogeneous characteristics of presently used elastomer fulcrums. 
Still a further object of the invention is to provide an electromechanical 
record disk dynamic range expander which is simplistic in construction, 
reliable in operation, readily producible from state-of-the-art apparatus, 
conducive to implementation with presently existing stereo systems, and 
one which may be manufactured on a cost-effective basis. 
SUMMARY OF THE INVENTION 
The foregoing and other objects of the invention which will become apparent 
as the detailed description proceeds are achieved by an electromechanical 
record disk dynamic range expander, comprising: a shank having a stylus 
depending from a first end thereof; first magnetic flux conducting 
elements received within said shank at a second end therof; pivot means 
operatively connected to said second end of said shank for allowing said 
shank to pivot about a point; a magnet; second magnetic flux conducting 
elements operatively connected to said magnet and positioned opposite said 
first magnetic flux conducting elements; and a plurality of coils 
interposed between pairs of said first and second magnetic flux conducting 
elements.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
Referring now to the drawing and more particularly FIG. 1, it can be seen 
that a stereo generator assembly in accordance with the teachings of the 
invention is designated generally by the numeral 10. The assembly includes 
an elliptically oval shank 12, preferably of ferrous oxide-impregnated 
styrene, which is of a circular cross-section at the ends thereof. An 
aluminum tubular section 14, circular in cross-section, is affixed to the 
smaller end of the shank 12. Connected to and depending from the tubular 
section 14 is a suitable stylus or needle 16. The elliptically oval shank 
12 and tubular member 14, and the benefits thereof, are more fully 
discussed in the aforementioned copending patent application Ser. No. 
949,742. However, as shown in FIG. 4, the shank 12 is not truly elliptical 
as in the copending patent application, but is shaped in cross-section 
like a dog bone. Two outer substantially circular sections 12a, 12b are 
interconnected by a narrower midsection 12c. Such a design reduces the 
mass of the shank 12, while directing the plastic resonance frequencies of 
the record groove to a horizontal plane. With the shank 12 secured in the 
horizontal plane between the record groove and the pivot point 40, to be 
discussed later, the plastic resonances are damped by the shank itself in 
the manner discussed in the referenced copending patent application. 
Further, and as apparent from FIG. 1, the shank 12 tapers from a large 
circular cross-section at one end to a smaller circular cross-section at 
the other, being of the elliptical nature in between as shown in FIG. 4. 
For purposes of better understanding the structure of FIG. 1, it should be 
noted that the axis of the stylus 16 and the longitudinal axis of the 
shank assembly 12, 14 define a plane which forms a 45.degree. angle with 
the sheet of FIG. 1. An appreciation of such relationship is important for 
a complete and proper understanding of the moving magnetic gap technique 
to be discussed hereinafter. The shank 12 has, at an end opposite the end 
of circular cross-section, a cubical block portion 18 adapted for 
receiving iron inserts 20. The inserts 20 may be molded into the plastic 
cubical portion 18 and are preferably shaped like an acorn, substantially 
spherical in nature while coming to a rounded point 22. The end of the 
cubical portion 18 is characterized by a conical recess 24, having an apex 
26. As will be discussed hereinafter, there are four iron inserts 20 in 
the preferred embodiment of the invention with the same being aligned such 
that the rounded points 22 of each of the four inserts 20 define a plane 
containing the apex 26. The importance of such arrangement will become 
apparent hereinafter. 
A cylindrical housing 28 is provided for receiving and maintaining the 
mechanically movable elements of the assembly 10. The housing 28 is 
substantially open at a rear end thereof, while being partially closed by 
means of an annular ring or flange 30 at the front end thereof. 
Preferably, the housing 20 is made of plastic, and the flange 30 may be 
molded as part and parcel of the housing proper. This flange 30 provides a 
surface for abuttment with the pivot pressure and compliance elastomer 32, 
which is of an annular nature and received by the circumferential groove 
34 provided about the shank 12. Further maintaining the elastomer 32 in 
position is a compliance pressure rib or disk 36 which may be molded as 
part and parcel of the shank 12 or otherwise positionally affixed thereto. 
Again, the function and benefit of the elements 32-36 may be appreciated 
by reference to copending patent application Ser. No. 949,742. 
With the housing 28 having an open rear end, the shank 12, having the 
elastomer 32 received in the groove 34, may be passed through the opening 
of the annular ring 30 until the elastomer 32 makes compressive engagement 
between the ring 30 and the rib 36. At this point in time, a steel base 
member 38 may be press-fit into the open end of the housing 28 such that 
the point 40 is received by the apex 26. Such engagement further comprises 
the compliance elastomer 32 between the rib 36 and flange 30. The contact 
established between the point 40 and the apex 26 defines the pivot point 
for movement of the magnetic gap as will be discussed hereinafter. With 
proper machining of the conical recess 24 and the point 40, the defined 
pivot point becomes substantially friction free, with such characteristics 
being further enhanced by a lubricant coating such as that manufactured 
under the trademark "TEFLON." 
The assembly 10 is further defined by a canister 42 manufactured of steel 
or other suitable material capable of conducting magnetic flux. A 
permanent magnet 44 is centrally received by the bottom of the canister 42 
and may be secured thereto solely by the magnetic attraction for the steel 
bottom, or by an appropriate adhesive or the like. The canister 42 is 
partially closed at an opposite end by means of a plastic end cap 46 which 
is of an annular nature, having an opening axially aligned with the magnet 
44. The cap 46 may be cemented or otherwise secured to the rim of the 
canister 42. 
Received within the canister 42 and abutting the cap 46 are extended pole 
pieces 48 comprising mounds of steel or other magnetic flux conducting 
material. The extended pole pieces 48 are complementary to the exposed 
portions of the inserts 20, having rounded points 49 positioned opposite 
associated rounded points 22. Mounted atop the pole pieces 48 are plastic 
coil mount fixtures 50 which, in turn, receive associated coil forms 52. 
It should now be appreciated that there is provided a number of closed 
magnetic paths between the magnet 44, the steel canister 42, pole pieces 
48, coil mounts 50, coil forms 52, iron inserts 20, and the steel base 
member 38. It should further be noted that the cylindrical housing 28 is 
held within the canister 42 by the magnetic attraction between the magnet 
44 and base member 38. The shank assembly and iron inserts are maintained 
within said housing by means of compressive engagement via the elements 
32, 36, 38. The canister 28 may be simply withdrawn from the annular 
opening of the cap 46, overcoming the magnetic attraction between the 
elements 44, 38 for service or replacement of that portion of the 
generator assembly 10. It will also be noted that the rounded points 22 of 
the inserts 20 form a plane which not only contains the point 26, but also 
maintains the central axes of the disk-like elements 46-52. 
With particular reference to FIG. 2, it can be seen that the block end 
portion 18 of the shank assembly receives four iron inserts in 90.degree. 
spaced relationship to each other. Each of the inserts 20 has associated 
therewith corresponding elements 48-52 in the manner described previously. 
The inserts 20 and the coils of the coil forms 52 are connected in pairs, 
one pair associated with each channel or sidewall of the stereo record 
groove. As shown in FIG. 2, those coils diametrically opposite each other 
form such pairs. It will be further understood that the stylus 16, at the 
end of the shank 12, is aligned with the vertical diagonal of the cubical 
block 18. Hence, the axes of the paired elements 20, 48-52 form a 
45.degree. angle with the vertical and with the record surface when the 
stylus 16 is placed thereupon, such that each such pair is uniquely 
aligned with an associated sidewall of the record modulation groove. It 
will also be appreciated that as the stylus 16 is caused to move by a 
sidewall of the record groove, the iron inserts 20, aligned with that 
sidewall, are caused to tilt by the pivoting movement at the apex 26. The 
other pair of inserts 20 merely rotates about the axis common to the pair 
and passing through the apex 26 and the center of the associated 
assemblies 48-52. 
With reference now to FIG. 3, it can be seen that the coil form 52 is a 
spool substantially comprising two cones interconnected by a spindle 54. 
Near the center of the spool, at the spindle 54, there is provided a small 
cross-sectional area which increases in size to the outer area 56. This 
area is adapted for receiving wire 58 wound upon the spool. It will be 
seen that the coil form 52, wrapped with wire 58, provides an increasing 
number of coil turns with increasing distance from the central axis of the 
form itself. Of course, the rate of change of number of turns of wire with 
respect to distance from the central axis may be varied by varying the 
angle of the cones attached to the spindle 54 which define the 
wire-receiving area. The ends of the wire 58a, 58b may be connected to 
appropriate amplifiers of the stereo system in standard fashion, 
diametrically opposed coil assemblies 52 being connected to the same 
amplifier channel. 
In the assemblies shown in FIGS. 1 and 2, the coil forms 52 are positioned 
such that the axis of the spindle 54 of paired coils 52 are in line and 
pass through the central axis of associated iron inserts 20 and the apex 
26. As the stylus 16 tracks in a record groove, the associated iron 
inserts 20 tilt. This tilting or mechanical modulation moves the magnetic 
field across the wires 58 of the coils 52. This moving magnetic field cuts 
the wires and induces a voltage thereinto, such voltage being transmitted 
to associated amplifiers for transmission to a speaker system where the 
output sounds are evidenced. It should be noted in the generator assembly 
10 that there is no moving magnet, nor is there an armature for the coil 
52, with the coil form itself being constructed of plastic or the like. 
However, there is a moving magnetic field created in the gap between the 
extended pole pieces 48 and iron inserts 20. Small movements of the stylus 
16 result in minor tilts of the inserts 20 with only a few coils of wire 
58 being cut by the magnetic field. Greater movements of the stylus 16 
result in greater movement of the magnetic field where even more wires 58 
are cut. Correspondingly, the voltage induced for translation into sound 
is increased. 
Before entering into a detailed description of the operation and benefits 
of the invention, it should be noted that the iron inserts 20 are 
preferably of a size having a major axis of 0.025 inches. Each coil pair 
has 1,000 turns of wire 58, 500 turns per coil, with such wire 58 having a 
diameter of 0.0006 inches. It should therefore be readily appreciated that 
the spool 52 is approximately the size of the head of a pin. 
As the stylus 16 tracks a record groove, the mechanical movement is 
translated to the iron inserts 20 by the pivoting of the cubical block 18 
about the apex 26. While moving along one sidewall of the record groove, 
the associated paired inserts 20 tilt, moving the magnetic gap between the 
inserts 20 and the extended pole pieces 48 to cut the wires 58 of the 
associated coil 52. The magnetic field is more concentrated between the 
rounded points 22 of the inserts 20 and the rounded points 49 of the 
extended pole pieces 48 which are centrally aligned with the pivot point 
of the apex 26, the spindle 54 of the coil 52, and the rounded points 49 
of the extended pole pieces 48. While the one pair of inserts 20 is 
tilting, the other pair of inserts 20 is rotating about its axis passing 
through the apex 26. Such rotation results in no flux motion and, hence, 
no induced voltage at any frequency. Consequently, an output is only 
experienced from the opposite channel. As the iron inserts 20 are caused 
to move progressively more, the moving magnetic field progressively cuts 
more and more turns of wire due to the nature of the coil form 52. In 
other words, the further the inserts 20 swing the magnetic field across 
the center of the spindle 54, the progressively greater the number of 
turns of the coil that are cut by the moving magnetic field and, 
correspondingly, the greater the output signal level from that coil pair 
to the amplifier. Thus, the coils evidence an accelerated progressively 
increasing output response to linearly increasing inputs of the mechanical 
stimulus provided by the modulation of the stylus 16 in the record groove. 
Thus, soft sound levels (lower induced signal voltage) are made softer 
while loud sound levels (higher induced signal voltage) are made louder. 
There is thus provided a mechanical dynamic range enhancer maintained as 
the generator assembly itself, comprising a part of parcel of the coil 
assembly. 
It should also be appreciated that the precise alignment of the center 
lines of the elements 20, 52 with respect to the apex 26 results in a 
superior channel separation. Such arrangement allows one set of iron 
inserts 20 to cause the magnetic field to cut the coil wires 58 during a 
tilt while the other set of inserts 20 rotates, resulting in no magnetic 
flux motion across the coil wires. Further, channel separation is enhanced 
by the mere provision of the coil winding technique shown in FIG. 3. By 
enhancing high level outputs with respect to low level outputs, channel 
separation is optimized in that the listener has a definite appreciation 
for a responding signal changing volume level in the listening depth 
dimension. 
Thus it can be seen that the objects of the invention have been satisfied 
by the structure presented hereinabove. While in accordance with the 
present statutes only the best mode and preferred embodiment of the 
invention has been presented and described in detail, it is to be 
understood that the invention is not limited thereto or thereby. 
Consequently, for an apprecation of the true scope and breadth of the 
invention, reference should be had to the following claims.