Phonograph tone arm with counterweight and method of use

An improved tone arm with counterweight assembly for use in a phonograph record player, the tone arm comprising at the rearward end a first counterweight sleeve element and a second counterweight, the first sleeve element having markings thereon to indicate the stylus force and adapted to be slidable on the arm and then to be secured in place, and the second counterweight adapted to be slidable over the sleeve element and in cooperation with the markings to be positioned, to provide the desired weight of stylus force to the stylus on the tone arm.

BACKGROUND OF THE INVENTION 
Phonograph tone arms used in record players are generally of an elongated 
form and contain, at the one forward end, a pickup cartridge which 
includes a downwardly extending stylus thereon, the tip of which engages 
the grooves of the record for playing purposes. Intermediate of the 
forward and rearward ends of the tone arm, pivoting means are provided. 
Typically, a counterweight is employed on the rearward end of the tone 
arm, to provide for some adjustment of the pressure on the tip of the 
stylus by the weight and position of the counterweight. 
The amount of stylus pressure typically measured in grams or a fraction of 
a gram or the stylus force is quite important. Excessive stylus force 
causes excessive record wear and may damage the record groove and affect 
playing performance, while insufficient force also affects record-playing 
performance and may permit the stylus tip to contact and damage the side 
walls of the record groove. In addition, since different pickup cartridges 
are used on tone arms with different weights, it is desirable to provide 
for a different or adjustable stylus force for optimum tracking. Thus, it 
is important to provide a stylus-force adjustment mechanism to be used in 
tone arm systems, and such mechanism should allow for the variation in 
weight of the pickup cartridges. 
In practice, a number of adjustable counterweight systems have been 
proposed for use on phonograph tone arms. One system employs a sliding 
counterweight on the rearward end of the tone arm, which reads against 
stylus-force markings screened onto the exterior surface of the tone arm, 
whereby positioning of the slidable weight over the markings provides for 
desired stylus force. 
Tone arms with counterweights are set forth, for example, in U.S. Pat. No. 
3,093,379 which employs a weight which is adjusted by a threaded, 
precalibrated screw to the desired position. U.S. Pat. No. 3,167,317 
discloses the use of a frictionally slidable counterweight and a 
threadably adjustable counterweight. U.S. Pat. No. 3,384,380 shows a 
counterweight secured to a screw for movement within a sleeve. U.S. Pat. 
No. 3,502,339 shows an adjustable counterweight with an adjustment of the 
weight by rotation of a screw. U.S. Pat. No. 3,417,999 provides a 
sleeve-like counterweight adjustable by a wheel on a sleeve. U.S. Pat. No. 
3,416,807 shows a counterweight sleeve adjustable by pinion- or 
sleeve-engaging rack teeth on the tone arm. U.S. Pat. No. 3,378,267 
discloses a spring-loaded sleeve counterweight on a tone arm. 
SUMMARY OF THE INVENTION 
This invention concerns a tone arm having a counterweight assembly, a 
record player containing the improved tone arm, and the method of 
manufacture and use of the tone arm. In particular, the invention relates 
to an improved tone arm with a counterweight assembly, which permits 
simple, rapid and accurate adjustment of the stylus force. 
The invention provides for a simple method of accomodating different 
weights of pickup cartridges on tone arms and for adjusting the stylus 
force to the optimum tracking force. It has been discovered that a unique 
and improved counterweight system comprises a movable counterweight sleeve 
element with a calibration scale on the sleeve element, in combination 
with a second counterweight disposed on and positioned for movement over 
the first sleeve element. The counterweight system provides for movement 
of both counterweights, to obtain a zero balance of the tone arm, and, 
thereafter, by movement of only the second outer counterweight toward the 
pivot point of the tone arm, the precise amount of stylus force on the 
stylus tip can be produced. The second counterweight is moved to a desired 
position, with the stylus force indicated by the position of the record 
counterweight on the precalibrated markings or scales on the first sleeve 
element. 
The counterweight assembly has means to secure the first counterweight in 
position on the tone arm, when the zero balance or other designated 
position of the first counterweight is reached. The first counterweight 
may be marked, such as slid over the tone arm by hand, and then secured in 
position to the tone arm by a simple mechanical means, such as a set screw 
in the sleeve element, which, on tightening one end, is secured against 
the tone arm. In one embodiment, the first counterweight is threadably 
moved with the second counterweight to a desired position, such as the 
zero-balance position. 
The second counterweight optionally is isolated against further movement, 
once in the desired stylus-force position, by means to isolate the second 
counterweight from any vibrations or resonance from the tone arm. 
Isolation is accomplished by the use of resilient material, such as the 
use of rubber, plastic or elastomeric material, between the second 
counterweight and the first counterweight. Typically, isolation occurs 
through the use of peripheral rings of rubber surrounding the first 
counterweight, such as O-rings disposed in the second counterweight. 
In addition, it is desirable to provide for low-friction slidable movement 
of the second counterweight over the first counterweight for ease of 
movement and adjustment of the second counterweight. The employment of 
low-friction material, or a coating or surface covering over the exterior 
surface of the first counterweight, such as the use of low-friction 
plastics, is desirable. The low-friction material should extend over that 
portion of the surface over which the second counterweight is slid while 
being adjusted. The low-friction material may comprise a Mylar belt 
material peripherally surrounding the first counterweight, or nylon, a 
fluorocarbin resin or other material. 
In practice, the low-friction material and the material used to isolate the 
second counterweight should be so selected to provide, in contacting 
combination, easy movement and adjustment of the second counterweight, and 
yet enough frictional force to provide that the second counterweight will 
not be moved easily, once in the desired position. It has been found that 
the combination of a rubber isolation material and a plastic polyester 
material provides such operation, although other materials and 
combinations may be employed. 
In operation of the tone arm and counterweight assembly, a zero balance is 
achieved by setting the second counterweight on the zero or other marking 
on the first counterweight, and then moving both the first and second 
counterweights, such as by use of a screw drive, until zero balance of the 
tone arm is accomplished. After the tone arm is balanced for the zero 
position, the second counterweight is then moved toward the pivot point, 
such as by sliding the second counterweight mounted on its O-ring isolator 
over the low-friction surface to the properly marked position on the first 
counterweight, which will produce the desired force on the stylus tip. 
The tone arm and counterweight assembly of the invention will be shown and 
described for the purpose of illustration only in connection with a 
particular embodiment; however, it is recognized that various changes and 
modifications can be made by those persons skilled in the art, all without 
departing from the spirit and scope of the invention.

DESCRIPTION OF THE EMBODIMENTS 
With reference to FIGS. 1 and 2, there is shown an improved tone arm 30 
comprising a slender hollow tube 12 of aluminum or plastic, a bent 
cartridge housing 32 at the forward end and a counterweight assembly 10 at 
the rearward end. A stylus cartridge 34, with a stylus (not shown) having 
a tip adapted to track in the groove of a record, is attached to the 
cartridge 32. The bend in the cartridge housing 32 permits the stylus to 
track in the groove as near to tangentially as possible; thus, minimizing 
distortion of sound reproduction. The counterweight assembly 10 
counterbalances the stylus cartridge 34, so that an adjustable, steady, 
tracking force may be applied to the record groove. 
The tone arm 30 is designed to pivot in both the horizontal and vertical 
directions about a pivot point 42. This pivotal action is accomplished by 
gimbal rings 36 and 38. A similar two-gimbal ring tone arm is described in 
U.S. Pat. No. 3,949,995 and is hereby incorporated by reference. 
In FIG. 2, the counterweight assembly 10 is shown in detail. The rearward 
end of the tone arm tube 12 is hollow and broken by a longitudinal slot 
40. Retained within the tube 12 is a threaded, worm-drive screw 18. The 
screw 18 is retained within the tube 12 by a retainer 22 made of nylon, 
which projects inwardly from the tube wall, to secure in place the tip of 
the screw 18, and yet permit the worm-drive screw 18 to rotate freely 
within the tube 12. In the preferred embodiment, the head of the screw 18 
may be rotated with any suitably shaped tool. Alternatively, the screw 
head may be formed as a knurled knob for rotation by hand. In one simple 
embodiment, the screw drive means for the sleeve 14 may be omitted, and 
the sleeve slid by hand and then secured in the zero-balance position by a 
threaded set screw threaded through the sleeve, so that one end may engage 
the surface of tube 12 and retain the sleeve in position. 
The first counterweight sleeve element 14, made of aluminum or a plastic, 
surrounds the rearward end of the tube 12, and includes a pin 20 which 
projects inwardly through the longitudinal slot 40 in the tube 12, and 
engages the teeth of the worm-drive screw 18. As shown in FIG. 1, the 
outer top surface of the sleeve element 14, which is visible to the user, 
has marked thereon, such as by printing, a decal, embossing or other 
means, a calibrated number scale 28 in grams and fractions thereof. 
Additionally, as shown in FIG. 2, a portion of the outer surface of the 
sleeve element is coated or otherwise covered by a ring of low-friction 
material 26, such as Mylar or a polyester plastic. 
The low-friction material engages the second counterweight 16, made of cold 
rolled steel or other suitable counterweight high-density material, 
adapted to be mounted slidably on the low-friction material 26. Two inner 
peripheral rings 24 of rubber, or other vitration- and resonance-absorbing 
material, are mounted on the inside of the second counterweight 16, to 
contact actually and to slide the second counterweight 16 over the sleeve 
14 and its low-friction surface 26. 
In operation, the second counterweight 16 is slid to a position on the 
sleeve element 14, where the marking means 28 indicates xero tracking 
force. The sleeve element 14 is then moved toward or backward by rotation 
of the screw 18, until the tone arm 30 is balanced about the pivot point 
42. The second counterweight 16 then may be slid forward on the sleeve 14, 
until an appropriate tracking force is attained, as indicated by the 
marking means 28.