US3018336A - Phonograph transducer - Google Patents

Description

J. F. GRADO PHONOGRAPH TRANSDUCER Jan. 23, 1962 2 Sheets-Sheet 1 Filed March 6, 1957 INVENTOR. A 7. M aw 27. fizz Jan. 23, 1962 J. F. GRADO 3,018,336

PHONOGRAPH TRANSDUCER Filed March 6, 1957 2 Sheets-Sheet 2 United States Patent 3,018,336 PHONOGRAPH TRANSDUCER Joseph F. Grado, 641 46th St., Brooklyn 20, NIY. Filed Mar. 6, 1957, Ser. No. 644,370 16 Claims. (Cl. 179100.41)

My invention pertains to an electro dynamic phonograph pickup device for reproducing a signal modulated on a recorded disc.

One of the objects of my invention is to further the art of such reproduction by designing a pickup which eliminates or minimizes the deficiencies present in current transducers.

Another of the objects of my invention is to produce a movable coil on a shaft which has a positive centered axis, and the coil rotates in a definite plane.

A further object is to provide mechanical adjusting means for maximum quality control and optimum performance characteristics.

A still further object of my invention is to provide a movable coil which is connected to a replaceable stylus.

With the foregoing and other objects in view as will appear from a reading of the following specification and claims, the invention resides in the novel arrangement and combination of parts and in the details of construction and process of manufacture hereinafter described and claimed, it being understood that changes in the precise embodiment of the invention may be made within the scope of what is claimed without departing from the spirit of the invention. It will be further understood that the invention is susceptible of embodiment in many and various forms, some of which are illustrated in the accompanying drawing, and that the structural details or particular steps of the method herein set forth may be varied to suit particular purposes and still remain within the inventive concept.

FIG. 1 illustrates my electromagnetic pickup.

FIG. 2 is another view of my pickup taken at right angles to that of FIG. 1.

FIG. 3 is a view of a modified form of my invention in which a cylindrical armature is used.

FIG. 4 is a view taken at right angles to FIG. 3.

FiG. 5 illustrates another modified form of armature in which the armature is in the form of a rectangular solid.

FIG. 6 is a view of FIG. 5 taken at right angles thereto.

The purposes of my invention are accomplished by a structure which includes adjustments to compensate for tolerances made necessary due to manufacturing procedures, and adjustments that also control the quality of performance.

Referring in detail to the various figures, and particularly to FIGS. 1 and 2, my pickup consists of a winding 1 of wire carried by a main pivot 2 which rotates on a coned point 3 at its upper end. This coned point works in conjunction with a cone bearing 4 which is threaded and adjustable in height position.

On the opposite end of the main pivot is a taper 5 with a cylindrical extension 13. The tapered portion is set into a rubber bushing 6 and the rubber bushing is in turn mounted in a tapered hole 7, in a channel-shaped or U-shaped bridge support 12. The channel support contains a tapered hole 7 on one end and a threaded fihififii Patented Jan. 23, 1352 hole for the threaded cone bearing 4- on the opposite end. The main pivot 2 oscillates, suspended between the cone bearing 4 and the rubber bushing 6.

The main pivot 2 is mounted vertically between two magnetic poles 14. On the main pivot 2 is mounted a wire wound bobbing 16 of plastic, brass, aluminum or other conventional non-conducting material which is centrally located between the two magnetic poles. The wire 1 is wound on the bobbin 10 in such a manner that the movement of the coil 16 in the magnet field will generate a voltage.

On the cylindrical extension 13 of the main pivot 2 is attached a stylus arm 9 which extends beyond the axis of the main pivot 2. This stylus arm contains a stylus 8 of diamond, sapphire, or metal. In operation, the stylus 8 makes contact with the modulated record groove, and thereby transmits mechanical energy to the coil 16 in an oscillatory manner, and the coil 10, oscillating within the magnetic field, causes voltage to be generated.

The adjustable support shown in FIGS. 1 and 2, can be used with various types of shafts or armatures.

FIGS. 3 and 4 show one variation in which cylindrical armature 16 has a slot on either end to accommodate turns of wire 17 wound in a longitudinal manner, i.e., around the circumference. On the upper end of the armature is secured a conical pivot 15 and on the lower end is fitted a tapered pivot 18. Wire leads 19 are connected to the coil. Armature 16 works the same as the bobbin and shaft illustrated in FIGS. 1 and 2.

FIGS. 5 and 6 show a longitudinal wire coil 21 without any armature or support. The wire is wound and hardened in this form. On the top end of this coil is a conical pivot 20 and on the lower end is a tapered pivot 22. The wire leads are shown at 23. Obviously, an armature in the shape of a rectangular solid could be used if desired. This coil, with or without a core, works somewhat the same as the ones shown in FIGS. 1-4.

By turning the adjustment screw 4 for its full range the compliance (the amount of displacement per unit of applied force) and damping factors can be set from zero to infinity. This wide range of adjustment allows a critical or optimum setting of compliance and damping, thereby allowing excellent manufacturing quality control, resulting in an improved product. The ability to adjust the compliance in accordance with the mass of the tone arm will definitely result in superior bass frequency response. The adjustment feature also makes possible lighter tracking forces which tend to decrease record wear.

In my construction the damping rubber 6 is placed between the stylus 9 and the coil assembly 10 thereby isolating the coil from spurious resonances. In addition, since the coil assembly is in a fixed vertical position, the only element which has any movement during the groove pinch efiect is the stylus. Also in my device I have made the vertical compliance greater than the lateral compliance by reason of the stylus design. This results in a tremendous reduction of record wear and distortion. With the coil in a fixed vertical position, and with the vertical motions absorbed by the stylus, the only motion the coil can make is a lateral oscillation. Hence, the result is a lowering of distortion.

By designing a fixed vertical assembly it now becomes 3 feasible to use a light compliance pickup in record changers. Heretofore this was not possible since all previous light compliance cartridges were very fragile, and were quickly damaged by the rugged action of record changers.

By utilizing low friction pivoting, the total moving mass is kept very small and the inertia low. The object of keeping the mass small is to keep the plastic resonance (resistance of the armature mass to the record plastic material) frequency beyond the range of audibility. The primary purpose of the low inertia of the stylus is to keep the stylus in the modulated groove even during the most intricate of signals.

In order to allow the stylus arm (made of metal or plastic) to be removed and replaced at will, it is simply secured by friction. The end'of the stylus arm is cylindrical in shape with a hole in it. The hole is slightly smaller in diameter than main pivot extension. When it is frictionally forced onto the extension, it holds securely, and yet is replaceable by the consumer.

The arrangement of cone pivot and cone bearing allows movement of the main pivot with a minimum of friction. As stated before, the other end of the main pivot or shaft is tapered in a frusto-conical shape and set into a rubber bushing, the rubber bushing in turn being mounted in a tapered hole. Turning the adjustable cone bearing 4 forces the main shaft or pivot downward into the tapered hole thereby compressing the rubber bushing, and altering the compliance and damping factors. This is possible without changing the axial center of the main pivot.

The stylus arm contains a stylus and extends outward beyond the vertical plane of the main pivot. Here it will make physical contact with the recorded material, :and receive mechanical energy. This mechanical energy is transmitted to the pivot as oscillatory motion, and the coil then oscillates within the magnetic field and :thereby generates electrical energy.

While I prefer that the support 12 be made of aluminum, any nonmagnetic material will be satisfactory as, 'for example, plastic. Likewise, while I prefer the wire of the coils to be silver copper alloy, gold plated, and :the cone pivot be hardened and tempered for maximum performance, these are not essential.

Thus it can be seen that I have made an improvement in a moving coil construction in which the upper pivot moves in a threaded adjustable cone bearing where- 'by adjustments may be made for variable damping and .lateral compliance.

The idea of using in a phonograph pickup a cone pivot, tapered point, and adjustable cone bearing, as far as I know, is new. Also, my invention can be used for a variable reluctance type pickup which does not use a moving coil, but rather a moving iron. Other features and objects have been set out hereinbefore.

What I claim is:

1. Means for generating voltage in a phonograph pickup comprising an oscillatable unit in a magnetic field, said oscillatable unit having a tapered end on its upper portion, an adjustable bearing having a cone surface therein on its lower portion, said tapered end positioned in and movable in said cone surface of the bearing and a bushing at the opposite end of said oscillatable unit for adjusting the compliance and damping of said unit.

2. A phonograph pickup as set forth in claim 1 in which said tapered end of the upper portion of the oscillatable unit is cone shaped, and the bottom portion is tapered, and a support having a resilient bushing supporting the weight of said unit and in addition resisting whatever pressure is exerted by said adjustable bearing.

3. A phonograph pickup as set forth in claim 2 in which said support is provided with a threaded aperture in its upper surface and a tapered lower surface, said adjustable bearing being threaded and movable in said threaded aperture for changing the compliance of said 4 oscillatable unit whereby to exert more or less pressure on the said rubber bushing which is resilient and is housed in said support and thereby increase or decrease the damping of the oscillatable unit from 0 to infinity.

4. A phonograph pickup as set forth in claim 3 in which the oscillatable unit comprises a metal shaft, and a coil of wire carried by said shaft.

5. A phonograph pickup as set forth in claim 4 in which a bobbin of non-conducting material is mounted on said metal shaft which in turn carries said coil.

6. A phonograph pickup as set forth in claim 4 in which said metal shaft is in the form of a cylinder and has grooves cut into both the upper and lower edge, said coil being positioned in said grooves.

7. A phonograph pickup as set forth in claim 4 in which said oscillatable unit comprises a core in the shape of a rectangular solid and said coil of wire wrapped around said solid.

8. A phonograph pickup as set forth in claim 4 in which said coil of wire has an air core.

9. Means for generating voltage in a phonograph pickup comprising a vertically arranged oscillatable unit in a magnetic field, said oscillatable unit having a pivot, and a bearing cooperating therewith, and movable means associated with said bearing for adjustment of oscillatory compliance from 0 to infinity said movable means being 'a threaded screw and said screw being formed with a cone-shaped surface to provide a bearing.

10. A phonograph pickup as set forth in claim 9, in which a rubber bushing is provided at the lower end of the oscillatable unit whereby when said bearing is adjusted pressure will be applied to or released from said rubber bushing for adjustment of axial compliance.

11. A phonograph pickup as set forth in claim 9 in which said vertically arranged oscillatable unit comprises a metal shaft, a cylindrical bobbin of non-conducting material mounted centrally on said metal shaft, and wire wound circularly on said bobbin.

12. A device as set forth in claim 11, comprising a U-shaped support, said bearing being screw threaded into one side of said support and being movable toward and away from the opposite side of said support, a soft, compressible bushing in the opposite side of said support and surrounding one end of said shaft whereby when the adjustable bearing is moved toward one end of said shaft, the opposite end of said shaft will be forced more firmly against the bushing and thereby decrease the compliance of the pickup.

13. A device as set forth in claim 1, comprising a U-shaped support, said bearing 'being a screw threaded into one side of said support and being movable toward and away from the opposite side of said support, a soft, compressible bushing in the opposite side of said support and surrounding one end of said shaft whereby when the adjustable bearing is moved toward one end of said shaft, the opposite end of said shaft will be forced more firmly against the bushing and thereby decrease the compliance of the pickup.

14. A device as set forth in claim 13 having a stylus arm which extends beyond the axis of the oscillatable unit, said stylus arm being bent near said stylus to provide a hinge-like effect and thereby make the vertical compliance greater than the lateral compliance, and said bushing isolating the oscillatable unit from spurious resonances.

15. A device as set forth in claim 1 having a stylus arm which extends beyond the axis of the oscillatable unit, said bushing isolating the oscillatable unit from spurious resonances.

16. A phonograph transducer whose operating structure consists of a main shaft mounted vertically within a magnetic field formed by 2 magnetic poles, a wire wound bobbin mounted on said main shaft and positioned between said magnetic poles, said bob-bin being made of non-conducting material, said wire being wound on the bobbin so that oscillatory movement of the main shaft will cause the bobbin to move within the magnet field and thereby generate a voltage, a main support, a cone bearing mounted in said main support, said cone bearing being threaded and adjustable, and a pointed cone on one end of the main shaft which moves in conjunction with said cone bearing, and a resilient bushing operatively associated with the other end of said main shaft whereby when said cone bearing is turned inwardly pressure will be exerted through said shaft upon said resilient bushing and increase the compliance or torque necessary to move said wire wound bobbin.

References Cited in the file of this patent UNITED STATES PATENTS Jones Mar. 24, 1925 Dyer Jan. 19, 1926 Robinson Jan. 28, 1930 Copelin Feb. 2, 1932 De Sart Jan. 23, 1945 Rieber July 19, 1949 Arentzen Apr. 8, 1952

Images