US2187772A - Tone arm - Google Patents

Description

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Patented Jan. 23, 1940 signments,

'roNE ARM Roy Daily, Racine, Wis., assignor, by mesne asto Webster Electric Company,

Racine, Wis., a corporation of Delaware Original application September 24, 1936, Serial No. 102,303, now Patent No. 2,145,389, dated January 31, 1939. Divided and this application February 27, 1937, Serial No. 128,073

9 Claims.

The present invention relates to improved tone arms, and is particularly concerned with tone arms of the type adapted to be used with crystal pick-ups. 'I'his application is a division of my 5 prior application, Ser. No. 102,303, filed September 24, 1936, entitled Pick-Ups, now Patent No. 2,145,389, granted January 31, 1939, which now relates to the pick-up unit per se, and the present application relates to the complete tone arm unit.

One of the objects of the present invention is the provision of an improved tone arm assembly ywhich is sturdy, etlicient, capable of being used for a long time Without necessity for repair, and

capable vof being manufactured at a low cost.

Another object of the invention is the provision of an improved pick-up arm of the sheet metal type, in which the undesirable vibrations have been damped out and eliminated so as to 20 prevent the effects of resonance occurring in the arm.

Another object is the provision of an improved tone arm structure by means of which most of the lparts of the tone arm may oeconstructed of sheet metal and therefore manufactured by stamping operations so that the tone arm unit may be constructed more economically and brought into the reach of a great number of purchasers.

Other objects and advantages of the invention will be apparent from the following description and the accompanying drawings, in which similar characters of reference indicate similar parts throughout the several views.

Referring to the two sheets of drawings,

Fig. 1 is a top plan view of a fragment of a phonograph equipped with a pick-up and tone arm constructed according to the invention;

Fig. 2 is a side elevational View of the tone arm 40 and pick-up; y

Fig. 3 is a side elevational view of the pick-up unit;

Fig. 4 is a side elevational view of parts of the pick-up unit, with one of the covers or clamping 45 members removed, showing the fastening members in section;

Fig. 5 is an elevational view of the inside wall of one of the clamping members, which also forms the pick-up housing;

Fig. 6 is a vertical sectional view through the pick-up unit, taken on the plane ofthe line 6--6 of Fig. 4;

Fig. 71s a horizontal sectional view through the pick-up unit, taken on the plane of the line 1--1 55 of Fig. 4, looking in the direction of the arrows;

Fig. 8 is a vertical sectional view through the pick-up unit, taken on the plane of the line 8--8 of Fig. 2, showing the details of support of the needle; 60 Fig. 9 is a fragmentary sectional view, similar to the right end of Fig. 7, showing the details of connection for a series connection of the crystal elements;

Fig. 10 is a vertical sectional view through the trunnion for the tone arm, taken on the plane of the line III- I0 of Fig. 2, looking in the direction of the arrows;

Fig. l1 is a transverse sectional View through the tone arm, taken on the axis of the sleeve andv conical portion I8, which is extended into a cross piece I9 and riveted therein. The cross piece I9 preferablyhas an integral, upwardly curved stop arm 20, which is adapted to engage the inside of the`tone arm I3 and support the tone arm with its needle elevated when the tone arm is not resting on the record I2.

n The tubular shaft I1 is rotatably supported by means of its frusto-conical portion IB at the top engaging in the frusto-conical flange surrounding the bore I6, and by means of a metal cross piece located below said bore I6 and having an aperture for receiving the tubular member Il, the cross piece being riveted to the cup-shaped member I4. A thrust collar on the lower end of tubular member Il and secured by a set screw thereto,

holds the tubular shaft I1 in its bearings. The cross piece I9 is secured between annular shoulders on the tubular shaft I'I at the upper end thereof, the uppermost annular shoulder being formed by riveting over the end of the tubular shaft I'l. y

The base I4 may be secured to the top of the phonograph by means of ,screws or other convenient fastening means, and it is conveniently provided with a groove 2| in its side wall for pas-,- sage of the electric conductors 22, 23 provided with the pick-up. The base I 4 supports the frusto-conical portion I8-of the shaft II for rotation on a vertical axis, thereby adapting the tone arm to move to different positions radially with respect to the record I2.

The cross piece I9 is preferably providedA in its I ends with the stamped, frusto-conical sockets 24, each of which is adapted to receive the conical end of -a screw bolt 25 held in place by a lock nut 26. The cross piece I9 comprises a resilient bronze leaf which is sprung suiiiciently to place a.

slight spring pressure on the conical bearings, the faces of which are kept constantly engaged bythe tof leaf. This eliminates entirely any tendency toward chattering in the bearing when vibration is applied to the tone arm, and wear is automatically compensated for by the tendency of the cross piece IS to take up any wear. The tubular mem.- ber |1 is rotatably supported at its lower end by the cross piece |00 (Fig. 2) and retained in its bearings by the collar IUI.

Screw bolts 25 are threaded into the side walls 21, 28 of the tone arm |3 and are so adjusted that they engage in the frusto-oonical sockets 24 of the cross piece i9, thus rotatably supporting the tone arm I3 on the cross piece I9. This permits the tone arm to be lifted from the record so as to remove the needle from the record, and at the b'eginning or end of the playing/oi' a piece. It also permits the tone arm to follow the irregularities in the record so that the needle may rise or fall as required when the record rotates.

rlihe tone arm i3 preferably comprises a stamped sheet metal member which is inherently resilient, which may be provided with the side Walls 21, 28 and an end wall 29, the opposite end being open at 30 until closed by the insertion of the pickup unit. The tone arm i3 is pivotally supported on the cross piece i5 by the screws 25 at a point which is closer to the end 29 than the end 30.

The end' portion 29 of the tone arm is suitably enlarged to provide space for a frequency adjust-u ing unit 3|. This unit 3| comprises an electrical filter unit having one or more resistance coils in connection with a condenser intended to be used to adjust the frequency response of the pick-up to any desired degree.

'Ihe tone arm is preferably used with an additional amount of resistance required to make the shunt resistance load between pick-up and tube grid circuit not less than 500,000 ohms.

The sidewalls 21, 28 and end walls 29 arajoined by a top wall 32, and thereby form an armI of substantially Ug-shaped cross-section, except for certain ornamental coniigurations made for the purpose of improving its appearance.

The side walls 21, 28 are provided with apertures 32, which are aligned with each other and which are adapted to receive the threaded sleeves 33 and the screw bolts 34 which pass through these walls, through a metal stirrup 35, and through the pick-up unit 36, to seoure,the pickup unit to the tone arm. The metal stirrup 35 comprises a sheet metal member having two legs 31, 38, which embrace the sides of the pi'ckup unit 36,'and a wider yoke 39, which' substan-4 tially covers the end of the pick-up unit. and which is provided with an aperture for passing the n eedle securing screw 40.

The pickup unit 36, with its enclosing sheet metal stirrup 35, is a substantial iit between the `si'd' eflanges 21 and 28 of the channelled tone arm, wherein it is secured by threaded members as described.

The pick-up unit 36 preferably has its housing made of two identical halves 4|, 42 of molded insulating material, such as Bakelite or other phenolic condensation compound, or die cast metals. The half housing members are provided with the iiat or plane side Walls 43, top 44, and back 45, which are substantially rectangular in shape, but it is provided at the needle end with a downward extension 46 adapted to house the needle chuck 41 and the screw 40.

While the halves of the housing are identical in shape, they diier in the factthat the half portion 4| preferably has embedded in'its end 48 a pair of longitudinally projecting connector strips 49. These connector strips comprise strips of metal embedded in the Bakelite and have at their outer ends threaded bores for receiving the screw bolts 50, which clamp the conductors 22, 23 to the connector strips,49.

' The connector strips 48 project into an element chamber 5|, wherev they :have extensions that are soldered to leads 52 suitably connected to the foil whichis associated with the crystal elements. When the crystal elements are connected in parallel, as exemplified in Fig. 7, one lead 52 may be brought out from the central foil 53, or from any number of alternate, centrally located foils, andthe other lead 54 may be connected to the two outer ioils 55, or to the alternate series of foils, if a larger number of crystal elements and foils are used. When the elements are to be connected in series, one -ad 52 is connected to the outermost of the foi s 55, and the other lead 54 ls connected to the outermost of the foils 56 associated with the crystal elements.

The crystal elements 51, 58 comprise flat plates of suitable crystals, such as Rochelle salts, and in the present case the strips are preferably trapezoidal in form, as shown in Fig, 4. The crystal elements 51, 58 are separated by the metal foil 53, which serves to collect any electric charge generatedJrom all parts of the surface of the crystals, and on each of the outer surfaces of the crystal elements 51, 58 there are the foil coverings 55 and 56, The foils and crystal elements are cemented together by suitable cement, such as, for example, melted Rochelle salts, thereby forming a unit which may be installed in the pick-up as such.

The housing halves 4|, 42 are provided with the substantially rectangular depressions 5|, forming the chamber 5| when the two halves are placed together as shown in Figs. 6 or 8. Each of the halves has projecting into the chamber a plurality of lugs 59, 60, 6| and adapted to serve as clamping jaws for engaging the sides of the crystal unit to clamp it in position in the pick-up. These lugs 594| may consist of small blocks of rubber cemented to the interior walls of the chamber 5| and thick enough so that the resilient rubber blocks 59-6l are suitably compressed to clamp the crystal unit in place when the halves 4|, 42 are secured together as shown in Fig. 6.

Any number of such resilient rubber blocks may be used, two ofthembeing preferably located atthe extreme right ends of the broadest part of the crystal/element so as to secure that end of the element against rotation.

The additional rubber block 6| disposed near lthe middle of the element also serves to clamp it, but, being made of rubber, does not prevent transmission of torque from one end of the element to the other. The left ends of the housing parts 4|, 42 are each formed with half of the sockets `necessary to house the armature 41.

The needle chuck 41 comprises a metal member which may be made of die cast metal having a pair of cylindrical trunnions 62, 63, which are aligned with eachother and are carried by a body having a downwardly and outwardly extending needle supporting portion 631,'. The needle supporting portion 63' may be substantially rectangular or round in section, and is provided at its lower end with an axially extending bore 64 adapted to receive the needle 65.

AThe trunnion 62 may have a threaded bore 86 communicating with the needle bore 64 and threaded to receive the securing screw 40 which engages the needle and clamps it inthe bore 63.- Each of the trunnions 62, 63 is provided with-a resilient rubber bearing sleeve 68 which is held on the trunnion by its own tension, being a closed rubber band tensioned about the cylindrical surface. 'Ihe rubber bearing members 68 are adapted to be received in the hemi-cylindrical grooves 68 which are formed in the housing halves 4i, 42, and which provide bores for receiving the rubber sleeves 68 when the housing halves are secured together.

The sockets 10 in each half 4I, 42 surrounding the amature body 41 provide a'clearance around this body so that it may rotate on the trunnions 62, 63, and each side of the armature is preferably engaged above and below the trunnions by resilient rubber blocks 1l to 14. These rubber blocks may be slidably received in the threaded bores 15 yand engaged by the threaded members 16 so that they can be driven into resilient engagement with the armature 41 to regulate the resilient pressure under which this member moves. y

The housing maybe sealed against moisture by an additional resilient rubber band or ring 16 which surrounds the body `41 in the bore 11 and eectsa water-tightl and hermetic seal at this point. One of themos't important purposes of the rubber sleeve 16 is to automatically center the needle chuck 63 in the cavity in such manner that it cannot strike. the housing during normal operation. The rubber sleeve 68 seals the housing at the trunnion 62, and suitable cement or a gasket may be applied, if desired, between the opposing surfaces 18, 19 of the halves 4| 42 of the housing.

The trunnion 63 has a flat attaching flange projecting axially therefrom and provided with a threaded bore 8| for. receiving a screw bolt 82. A clamping plate 83 has a bore 84 -for receiving the screw bolt 82, and its plate is driven into clamping relation with the crystal element by means of screw bolt 82. Rubber sheets 85, 86 are interposed between the ange 8|! and the crystal element and between the flange 83 and the crystal element, insulating the foil from the needle and providing a. resilientgripping action for the clamping members 80, 83. The left and smaller end of the crystal element is, therefore, secured to rotate with'the trunnions 62, 63 of the needle chuck. e

The adjusting clamp, comprising the shoulder 80, screw 82, clamp 88, and rubber sections 84 and 85, comprise a means for varying the voltage output of the pick-up without disturbing the frequency response. The motion of the needle point and needle chuck up to the clamp is constant, depending upon the frequency being reproduced. The torque developed by the clamp as a result of this motion also depends upon the frequencies being reproduced, but when applied through rubber to .the crystal elements the torque applied to the crystall element may be varied over a large degree by varying the pressure applied to the clamp-and rubber by the screw 82. The greater the pressure applied, the greater the voltage output will be, due to the added stress induced in the crystal element, and one of the most important features of the invention is the arrangement whereby the voltage out- .put may be adjusted without disturbing the frequency response.

The flanges 80-88 may be made trapezoidal in shape, increasing in size toward theright end,

as shown in Fig. 4, to clamp across the full width of that end of the crystal element. The v two halves 4I, 42 of the housing are preferably secured together by tubular rivets 80, which are adapted to pass the lsecuring screws 33, 34 which extend through the side walls 21, 28 ofthe tone arm and through the pick-up to secure it in place.

The present pick-up is adapted to be used with records ofthe type having a groove which causes the needle 65 to move laterally in response to the contour of the groove to reproduce sound. When the needle 65 vibrates in a lateral direction about the axis of the trunnions 62, 63, the needle chuck has a rotative movement which tends to twist the crystal element, since the opposite end of the crystal element is held in fixed position. f The torque produced in the crystal element produces a condition of strain which generates an electromotive force, the amount of the electromotive force depending upon the amount of torque, which depends upon theramplitude of vibration of the needle at any time. The present pick-up is, therefore, adapted to produce an electromotive force which, when amplified, reproduces sound recorded upon the record, and it may be used with any suitable amplifying circuit, such as that of a radio receiver.

Referring to Fig. 11, this is a cross-section, taken through a damping block 90, which is shown in dotted lines in Fig. l. The channeled arm I3 is preferably provided with a lead block i. 90, which is a substantial lit between the flanges of the channel. This block has an aperture 9| for passing the screw sleeve 92 and screw bolt 93, the heads of these members engaging the outside of the flanges of the tone arm and drawing them into close engagement with the lead block 90.

The block may have a groove at the top for holding conductors in proper place. The purpose of this lead block or plug is to damp out the -resonancewhich occurs in the` arm, and it is found that the most satisfactory material is lead, due to its very inert nature.

Materials other than lead have not proved satisfactory for the reason that they do not have a satisfactory damping action. The free edges of the channeled tone arm are tightly clamped in engagement with the lead plug by means of making the aperture 9| an over-sized hole.

The pick-up is adapted to be used for a long period of time Vwithout deterioration because of its improved structure and because of the crystal being sealed against access to moisture, not only by the coverings of foil, but by the sealing of the housing with the rubber bearings and gaskets.

It is found that a pick-up operating upon the' torque principle reproduces sounds faithfully and eiiiciently and that the present pick-up may be constructed at a low cost which places it within the means of a large number of purchasers.

While I have illustrated a preferred embodiment of my invention, many modifications may be made Without departing from the spirit of the invention, andaI do not wish to be limited to the precise details of construction set forth, butv de sire to avail myself of all changes within the scope of the appended claims.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent of the United States, is:

l. In a tone arm, the combination of a pick-up element with a resilient sheet metal tone arm for supporting said pick-up element, said tone arrn having a natural period of resonance and a block of inert material clamped to said tone arm for damping outthe vibrations in said tone arm due to its natural period of resonance.

2. In a tone arm, the combination of a pick-up element with a resilient sheet metal tone arm for supporting said pick-up element, said tone arm having a natural period of resonance and a block of inert material clamped to said tone arm for damping out the vibrationsin said tone arm due to its natural period of resonance, said tone arm having oppositely disposed flanges, and said block comprising a lead member fitting between said flanges, which are clamped in close engagement with said block.

3. In a tone arm, the combination oi a supporting stool having a resilient cross piece carried thereby, said cross piece having oppositely disposed conical depressions therein, a tone arm comprising a resilient sheet metal member having oppositely disposed flanges adjacent the opposite edges of said cross piece, and a pair of screw members carried by said tone arm, each screw'. member having aconical end .engaging in said conical depressions, said screw members being adjusted to place a predetermined tension in their associated parts to prevent rattling and automatically compensate for wear.

4. In a tone arm for electric pick-ups, the combination of a pick-up with a channelled tone arm, said pick-up being carried by one end of said tone arm inside the channel thereof, and means for pivotally and rotatably supporting said tone arm adjacent the other end thereof, and a damping block of lead carried by said tone arm within the channel thereof and engaging the walls of said channel, said damping block being secured to said walls for the purpose of damping out objectionable resonant frequencies in said tone arm..

5. In a tone arm, the combination of a supporting stool having a resilient cross piece carried thereby, said cross piece having oppositely disposed conical depressions therein, a tone arm comprising a resilient sheet metal member having oppositely disposed flanges adjacent the opposite edges of said cross piece, and a pair of screw members carried by said tone arm, each screw member having a, conical end engaging in said conical depressions, said screw members being adjusted to place a predetermined tension in their associated parts to prevent rattling and automatically compensate for wear, said cross piece having a forwardly and upwardly extending arm adapted to engage a part of said tone arm to effect a support of said tone arm with the needle out of engagement of parts located below the level of a record.

6. In a tone arm, the combination of a supporting stool having a resilient cross piece carried thereby, -said cross piece having oppositely disposed conical depressions therein, a tone arm comprising a resilient sheet metal member having oppositely disposed flanges adjacent the opposite edges oi' said cross piece, and a pair o i' screw members carried by said tone arm, each screw member having a conical end engaging in said conical depressions, said screw members being adjusted to place a predetermined tension in their associated parts to prevent rattling and automatically compensate for wear, said cross piece A having a forwardly and upwardly extending arm adapted to engage a part of said tone arm to eil'ect a support of said tone arm with the needle out of engagement of parts located below the e level of a record, said cross piece being carried by a tubular metal member having oppositely disposed shoulders engaging the sides of said cross piece, and being rotatably mounted in said stool.

7. In a tone arm, the combination of a supporting stool having a resilient cross piece carried thereby, said cross piece having oppositely disposed conical depressions therein, a tone arm comprising a resilient sheet metal member having oppositely disposed flanges adjacent the opposite edges of said cross piece, and a pair of screw members carried by said tone arm, each screw member having a conical end engaging in said conical depressions, said screw members being adjusted to place a predetermined tension in their associated parts to prevent rattling and automatically compensate for wear, said cross piece having a forwardly and upwardly extending arm adapted to engage a part of said tone arm to effect a sup- Dort of said tone arm with the needle out of engagement of parts located below the level of a record, said cross piece being carried by a tubular metal member having oppositely-disposed shoulders engaging the sides of said cross piece, and /being rotatably mounted in said stool, said stool comprising an inverted sheet metal cup having an annular shoulder intermediate its open end and closed end, and having a bearing formed in its closed end, said annular shoulder supporting a cross piece provided with an auxiliary bearing.

8. In a tone arm, the combination of a supporting stool having a resilient cross piece carried thereby, said cross piece having oppositely disposed conical depressions therein, a tone arm comprising a resilient sheet metal member having oppositely disposed flanges adjacent the opposite edges of said cross piece, anda pair of screw members carried by said tone arm, each screw member having a conical end engaging in said conical depressions, said screw members being adjusted to place a predetermined tension in their associated parts to prevent rattling and automatically compensate for wear, said cross piece having a forwardly and upwardly extending arm adapted to engage a part of said tone arm to effect a support of said tone arm with the needle out of engagement of parts located below the level of a record, said cross piece being carried by a tubular metal member having oppositely disposed shoulders engaging the sides of said cross piece, and being rotatably mounted in saidstool, said stool comprising an inverted sheet metal cup having an annular shoulder intermediate its open end and closed end, and having a bearing formed in its closed end, said annular shoulder supporting a cross piece provided with an auxiliary bearing, said bearing in said closed end having a frustoconical bore at its upper end and said tubular member having a complementary frusto-conical formation whereby wear between the parts may be taken up.

9. In a tone arm, the combination of a pickup element with a resilient sheet metal tone arm having a pair of parallel side flanges joined by a top flange, the said parallel flanges having undesirable natural resonance characteristics, and a. block of' lead interposed between the said parallel walls oi said tone arm, said walls being clamped against said block, whereby the lead is adapted to absorb and damp out the said undesirable resonance characteristics which are due to the natural period of resonance of said tone Bl'm.

ROY DALLY.

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