Stylus suspension

A stylus suspension for a phonograph pick-up cartridge. A first improvement includes an asymmetrically mounted ring and washer clamping the suspension block in a manner that dampens vertical compliance of the suspension. A further improvement includes a suspension block specifically adapted to accommodate the ring, thus more particularly defining the pivot point. In this instance the ring may be mounted symmetrically or as in the first improvement. A still further improvement includes an armature of reduced mass that, surprisingly, does not result in lessened performance.

FIELD OF THE INVENTION 
The present invention relates generally to phonograph pick-up cartridges, 
and, more particularly, it relates to the suspension of the stylus 
assembly therein and, in one aspect, the stylus assembly itself. 
A stylus assembly in modern, electromagnetic pick-up cartidges generally 
comprises a cantilever tube flattened at one end to accommodate a diamond 
stylus, and an armature tube of a magnetic material, to which the 
cantilever is attached. The armature may be a permanent magnet, or it may 
be a magnetizable alloy charged by a separate magnet. The armature is 
supported in a rubber suspension block which establishes a pivot point for 
the assembly. A wire connected to the armature near the pivot point may 
provide a restoring force. The stylus moves in the recording groove and 
the free end of the armature describes a mirror-image of that motion 
between the pole pieces of the two magnetic circuits creating a signal for 
each channel of the recording. 
There are several criteria for a successful stylus suspension system: 
transverse motion must be perfectly symmetrical, the pivot point must be 
fixed and not "wander", frictional and elastic moments must be controlled, 
torsional and axial movement, along with resonances, must be suppressed, 
and vertical movement should be damped. Additionally, of course, are 
considerations of achieving uniform quality without excessive cost. 
In the above-noted co-pending application there is described a suspension 
block having inwardly tapering sidewalls and a square, central aperture. 
The armature includes a section having a corresponding square outside 
configuration of smaller overall dimensions than the remainder of the 
armature, so that the stylus assembly may be literally snapped into place, 
vertical alignment is assured, and torsional movement is effectively 
suppressed. 
The present invention provides further improvements in such a stylus 
suspension. 
OBJECTS OF THE INVENTION 
A general object of the present invention is to provide an improved stylus 
assembly and suspension. 
Another object of the present invention is to provide a stylus assembly of 
reduced mass. 
A still further object of the present invention is to provide a stylus 
suspension with a more fixed pivot point. 
Yet another object of the present invention is to provide a stylus 
suspension that may be adjusted to compensate for minute variations in the 
suspension block. 
Various other objects and advantages of the invention will become clear 
from the following description of embodiments thereof, and the novel 
features will be particularly pointed out in connection with the appended 
claims.

DESCRIPTION OF EMBODIMENTS 
The present invention is based, in one aspect, on the discovery that 
damping and stiffness of the stylus assembly are improved by clamping the 
suspension block with a ring asymmetrically. More particularly, the 
clamping ring will be generally in a plane normal to the center-line axis 
of the stylus assembly, but is tilted about 5.degree. from that plane to 
more tightly clamp the suspension block on the side parallel to the stylus 
tip. 
In another aspect the invention is based on the use of a suspension block 
having an annular shoulder to accommodate the above-noted clamping ring. 
This more precisely defines the pivot point of the stylus assembly. In 
this embodiment, the ring may be asymmetrically mounted, with the 
above-noted improvement in damping properties, but this is not essential. 
In still another aspect, the invention is based on the discovery that the 
free end of the armature, e.g. the end moving between the pole pieces, can 
be tapered or reamed, with a consequent reduction in mass, without 
impairing the response of the cartridge. 
Understanding of the invention will be facilitated by referring to FIG. 1. 
A housing 10, generally a molded plastic, includes an aperture 12 
including an inwardly extending shoulder 14 in which the stylus suspension 
is mounted. The stylus assembly includes a cantilever 16, generally an 
aluminum tube, with the diamond stylus 17 at the distal end thereof, and 
an armature 18, also tubular, made of a suitable magnetic alloy, generally 
a nickel alloy. The suspension block 20 secures the stylus assembly within 
aperture 12. As shown, suspension block 20 has inwardly tapered sidewalls 
22 terminating in an axial, square opening 24 into which a corresponding 
square portion of the armature is snap-fit. This arrangement, which is 
disclosed in the above-noted co-pending application, is preferred but, as 
will become apparent, is not an essential part of the present invention. 
It is also preferred that a washer 26 be seated against shoulder 14, and 
that suspension block 20 be seated against it but, again, this is not 
essential. Washer 26 inhibits longitudinal motion of block 20 and provides 
a seating therefor. 
What is essential to the FIG. 1 embodiment is the use of clamping ring 28, 
which asymmetrically clamps block 20 against washer 26 and, more 
importantly, around armature 18. Thus, while ring 28 lies generally in a 
plane 30 normal to the centerline axis of the stylus assembly, it is in 
fact tilted about 5.degree. (see plane 32) to more tightly clamp block 20 
on the same side of the stylus assembly as stylus 17 (e.g. above the 
centerline axis in FIG. 1). 
It has been determined that this dampens vertical motion of the stylus a 
small but significant amount, and increases the "stiffness" in a similar 
fashion. Damping of vertical motion is important in operation, because all 
signal motions generated by the record groove are 45.degree. from 
vertical. The clamp ring 28 is mounted on a mandrel in proper 
juxtaposition with the housing 10, which is held in a suitable jig. By 
pressing ring 28 against block 20 with a predetermined force, the 
suspension properties of the completed system are found to be remarkably 
uniform, even though there might be minute defects (air bubbles, 
dimensional inaccuracies, etc.) in block 20. Or, if a given unit is found 
to be out of specification with respect to compliance, the ring 28 can be 
adjusted. It is noted that the plastic of housing 10 is sufficiently 
compliant to accept ring 28 at the prescribed angle. 
Further improvements in the suspension system are illustrated in FIG. 2. In 
this embodiment, a modified suspension block 34 is provided with an 
annular shoulder 35 specifically adapted to receive clamping ring 28. A 
second washer 36 is provided between ring 28 and block 34, and its size 
and fit are important to the invention. More particularly, as can be seen 
in FIG. 2, washer 36 has a smaller inner diameter than ring 28, and pivot 
block 34 bulges slightly around the inner edge of washer 36; the latter 
thus pre-tensions the block and provides a dynamic spring effect with the 
block being the resistive element. With this combination, it is thus 
possible to control damping and compliance independently to a substantial 
degree. This combination also provides a more sharply defined pivot point 
for the armature, the tensioning of block 34 acting to suppress axial 
movement. It will be appreciated that washer 36 and ring 28 could be a 
single piece, and the improvements brought about by the washer obtain 
whether or not the ring is asymmetrically mounted. 
FIG. 2 illustrates an armature 18 of reduced mass due to the interior 
surface 38 being tapered so as to have a thinner cross-section at the free 
end 40. Alternatively, the inner surface may be merely bored or reamed 
out, as shown in phantom at 42. 
It was initially thought that, by reducing the mass of armature 18 at its 
"working" end 40, e.g. the end that moves between the pole pieces, the 
cartidge output would be significantly reduced. In practice, this turned 
out not to be the case; while not wishing to be bound to a particular 
theory, it is believed that the thinner cross-section at end surface 40 
merely concentrates the magnetic flux lines over a smaller area without 
diminishing the total magnetic flux that, through the coils, generates the 
output signals. Of coure, as those skilled in the art appreciate, any 
reduction in the mass of the "moving system", i.e., the stylus assembly, 
will have beneficial consequences. 
A still further improvement in operation is brought about by fabricating 
ring 28 of permanent magnet material that is oriented (poled) so as to 
interface with the magnetic flux field created by the main charging 
magnet, 44 in FIG. 2. It is believed that this arrangement distorts the 
flux field of magnet 44 in a way that concentrates more flux in the free 
end 40 of armature 18. At the same time, the opposing field of magnet-ring 
28 balances any magnetic moments that the distorted flux might create. The 
flux concentration at the free end of armature 18 produces a small but 
significant increase in output. 
Various changes in the details, steps, materials and arrangements of parts, 
which have been herein described and illustrated in order to explain the 
nature of the invention may be made by those skilled in the art within the 
principle and scope of the invention as defined in the appended claims.