US2212530A - Magnetic pickup - Google Patents

Description

Aug. 27, 1940.

j INVENTOR 3i? l g l /llanzzfm'an Weil BY f ATTORNEYS M. WEIL v2,212,530

MAGNETI C PI CKUP Filed Sept. 4, 1936 scribed as hang-over.

.Patented Aug. 27, 1940 UNITED sTArss 21 Claims.

My present invention relates to magnetic` pickups for phonographic reproduction.

As conducive to a clear understanding of the invention, it is noted that the moving armature mass of magnetic pickups generallyr has a natural frequency of vibration within that audible frequency range required for satisfactory performance, with consequent marked damping out of frequencies above that of resonance. Rapid changes in amplitude of frequency in the normal use of such device due to its considerable inertia result in a distorted performance, commonly de- While damping of the armature movement alleviates these difliculties to some extent, great increase in stylus-point impedance is thereby entailed, with consequent reduction in the eliiciency of the unit and marked increase in the wear and tear Von the sensitive record groove.

Among the objects of the invention are to provide a magnetic pickup unit, the performance of which approximates that of the highly de-` veloped microphone used in recording, so that the output of said pickup is practically indistinguishable from the original performance as recorded.

Another object is to provide an instrument of the above type, which is simple, sturdy and compact in construction7 and in which the inertia of the moving system is so low that its natural frequenc is outside, preferably beyond that of the useful range of audibility, with consequent uniform delicacy of response substantially throughout the effective audible range.

Another object is to provide an instrument of the above type, in which the light moving mass is mounted effectively to control the flux through the magnetic elements without weavingor wobbling and in which the resistance imposed to vibration is so slight that the weight resting on the record, and the wear on the record groove are greatly reduced.

Another object is to provide an instrument of the above type which requires no adjustment in j use for adaptation to various types of renditions ,and which maintains its initial sensitiveness and efficiency for long periods of use.

According to the invention, the vibratory system of the instrument, that is, the vibrating magnetic element and associated moving parts by `which the uX is controlled in synchronism with the vibrations imposed by the record upon the stylus is greatly reduced'in inertia. To this end, the magnetic circuit is so contrived that a fixed magnetic element having only a small fraction of the mass of the usual armature actually oscillate's, and serves as a magnetic flux-relay piece, the relatively greater bulk and mass of the armature proper being anchored against vibration.

In a desirable construction, the magnetic vflux relay piece is positioned in the gap between the field poles and the armature and is carried preferably by a non-magnetic extremely light shaft supported `in the casing and carrying the stylus. The predominating part of the mass of the vibratory assembly is the stylus itself, the rest of the parts being extremely light in mass and moving in low friction bearings, while the stylus itself is preferably of special construction, affording a vminimum of mass at its point and end with the' major portion of its small mass at the central clamped portion thereof. f i

In the accompanying drawing in which are shown one or more of various possible embodiments of the several features of the invention,

Fig. l is a perspective view of the completely assembled unit,

Fig. 2 is a view in-longitudinal cross section thereofktaken on line 2 2 of Fig. 1 and on a larger scale, 4

Fig. 3 is a plan View of the device with the cover removed, parts being shown in section,

Fig. 4 is a transverse sectional view taken on line d-Li of Fig. 2, v Fig. 5 is a transverse cross sectional view taken along the line 5 5 of Fig. 2,

Fig. 6 is a perspective View of the pole pieces and armature in correlated position,

Fig. '7 is a perspective view of the magnetic l ux relay assembly,

Fig. 8 is a perspective view of the stylus shown in the embodiment of Figs. 1 to 7,

Fig. 9 is a fragmentary View in longitudinal section of the forward end of the casing showing an alternative sylus,

Fig. l is a perspective view of the stylus shown in the embodiment of Fig. 9,

Fig. 11 is a fragmentary detail view of a modification, and

Fig. l2 is a similar view 'of another modification. i

Referring now to the drawing, the pickup comprises a casing including a base iii specially molded to accommodate the parts mounted therein and hereinafter described, and equipped with a sheet metalicover il telescoped over the sides thereof and preferably tapering downward at its front as at liand attached by screws i3. The shank M of the casing has terminal sleeves l therein for the terminal members I6 protruding therefrom, from which insulated conductors il lead to the electro-magnetic coil i8 known as the Voice coil.

Upon the base is mounted the horseshoe magnet l closely fitting against the sides of the base and contacting at the forward end of its legs, the magnetic pole pieces 2li and 2i which are attached to the base by means of screws 22 countersunk in the underiace of the base BG. The magnet is :retained in place by means of a leaf spring 23 preferably of copper alloy reacting at its ends against shoulders il molded in the base, with a central bowed part reacting against the extremity of the horseshoe magnet, and pressing it forward against the pole pieces. Preferably the spring is longitudinally slit at on a level with the upper face of the magnet-and the strap 26 determined thereby is pressed forward to overlap the magnet and retain it against the base lil.

The pole pieces are preferably U-shaped as shown'with their upper legs or ledges 2l aligned, but spaced from each other as shown, and their lower legs or ledges t similarly aligned and spaced. The space determined between ledges of the facing pole pieces accommodates the v coil I8.

A xed armature piece 2d extends downward centrally-of the coil, as shown, is symmetrically spaced from the upper ledges 2l of the pole pieces and its lower end is slightly above the lower ledges 28 of the pole pieces. Said ixed armature is mounted by screws 3Q to ar plate 3l of non-magnetic material, which, in turn, is attached by means of screw 32 to the upper ledge of the pole piece Z0. While the specic construction and arrangement shown is preferred, it is manifest that the coil could be disposed to encircle any part of the magnetic circuit other than the armature, if desired.

The magnetic flux relay comprises an extremely light piece of magnetic material, including a shank 33 with an upstanding iiattened wing 34E the latter disposed centrally between the lower ledges 28 of the pole pieces, preferably to protrude slightly above ledges 28 and slightly below the lower extremity of the fixed armature 29 so as to determine small predetermined air gaps with respect to said three pieces, as best shown in Fig. 4. This relay piece is mounted by frictionally fitting its shank 33 into a shaft or tube 35 Vof extremely light material, preferably of the alloy known as Duralurninf which extends longitudinally of the base piece and is mounted in bearings 36 and 3l at opposite ends thereof. Preferably, rubber bushings- 3d encircle the ends of the tube, which are mounted upon the base, by bearing cap pieces 39 attached to the base by screws lili.

In order to maintain the wing piece normally in, properly centered position, the sleeve 3&5 is provided with an upstanding pin or stud il iixed therein, with a flattened upper extremity 132 extending into a corresponding notch it on a stop piece 44 i'l'xed by screws i5 upon a corresponding ledge d6 molded in the base lil.

The stylus il extends transversely through corresponding apertures lil in the base l@ and aper- 'tures in sleeve 35 and bearing ill and is clamped at its median portion against the wall of the tube apertures by means of a set screw 5@ extending through the forward end of the base lll and threaded into the forward end of the tube 35.

While the stylus may be of conventional `construction, it is preferred to employ the structure said V shown in Fig. 8 in which the main shank of the stylus is of conventional diameter, but the pointed end 5i thereof is not the ordinary conical point but is concave longitudinally as shown, for reduction of mass and for effecting a particularly sharp point. Moreover, the upper part 52 of the stylus is of greatly reduced diameter for further reduction in mass. By this construction, those parts of the stylus, namely, the parts near the lower and upper ends, which perform the major movement in operation, are of greatly reduced mass, while the major part of the mass is that intermediate portion in the region clamped by the set screw lli? which performs relatively slight movement, whereby the inertia of the stylus is effectively reduced. Preferably the stylus is insertedthrough an aperture 53 in the cover l l and its position is thus accurately determined as shown in Fig. 2, by bringing the upper end of the stylus flush with the outer wall of the cover ll.

The entire assembly of Duralumin tube and magnetic flux relay as shown in Fig. 7 is of almost negligible weight, as little as 11A-2 grains, the preponderating inertia ci thevibratory parts in the device residing in the stylus 565 in a preferred construction.

In use ci the device on the conventional laterally cut disk record, it will be seen that the vibrations of the stylus point lll effect corresponding rocking of the tube 35 in its bearings 3&5 and 3l against the resiliency of rubber bushings 38 which act to damp the vibration, and the wing piece of the magnetic relay in partaking of this movement 'causes corresponding variations in the air gaps and controls the variations and alternations of magnet-ic between the pole pieces 2u and il in manner readily understood by those skilled in the art. As is clear to those skilled in the art the construction may readily be embodied for use with hill and dale records.

The sensitiveness of the device is a consequence of the fact that it is not a relatively heavy armature which is to move in response to the vibrations of the stylus, but the control of magnetic flux is effected by the extremely light moving element 3ft which is notan armature properly speaking, but may be properly designated a magnetic iiux relay piece the movement of which determines the course of of magnitude greater than that which traverses the relay piece itself. The natural frequency of the vibratory system is beyond the eiective range of audible frequencies. The course of the magnetic flux is substantially connned as is obvious to the magnet, its pole pieces, the stationary armature, the relay piece and the air gaps therebetween, and in nowise reaches the stylus 5t, since the intervening tube 35 is desirably of non-magnetic material as set forth.

In the embodiment of Figs. 9 and 10 is shown a modification of stylus 5153 which illustratively is iiattened near its upper end as at 55 to aord a stop resting against the upper portion of the forward bearing 3l of the tube 35' so that it is positively positioned with respect to the tube, as distinguished from the mode of positioning previously described and resorted to in the embodiment of Fig. 2.

It is, of course, understood that the width of the notch i3 is such as to permit the magnetic relay wing 3Q to move laterally in the gap between the pole pieces without ever touching either of said pole pieces and the resilience of the rubber bushings 38 serves properly to return the wing piece Sil to the correctly centered Aposition shown inFig. 4, so `that no bias occurs toward one or the other pole in the absence of impulse applied through the stylus. If damping in addition to that afforded by'resilient bushings 38 is required, this can conveniently be aorded by rubber stops (notl shown) interposed in the space between stud extremity 42 and the walls of `notch d3 in stop piece 44. l

It is important in the initial assembly of the device that the magnetic relay wing piece 34 be correctly centered between the two pole pieces and that it be correctly spaced from the lower end of the armature piece 29. For ythis purpose, resort may be had to a `two-prong fork (not shown) of width snugly to fit between the pole pieces and which has a space between its tines `snugly to straddle the thickness of the wing piece 34., The distance of the magnetic flux relay wing piece 34 from the armature 29 is determined by applying the armature after the pole pieces and flux relay wing have been positioned as' ldescribed. The armature piece is iirst caused to engage the upper edge of the wing piece 312i which result may be readily accomplished by loosening fastening screws'll and moving the armature up or down slightly along its elongated screw slots `Sil' until such adjustment has occurred.

Thereupon `a shim 5t of suitable thickness, desirably in the order of @03 in thickness, is interposed between the mounting plate y3l and the pole piece 2li whereupon the screws Jill are tightened and the desired distance between the `armature' piece and the relay piece viz'. that of the shim thickness is thus readily and accurately determined.

The embodiment of Fig. l1 shows a reiinement in the correlation between the armature 29' and the iiux relay wing 34'.' In this case the armature is shown with a concave lower end Gli so that in the vibratory movement of the iiux relay piece the width of the air gap with respect to the armature will vary, decreasing in a direct ratio with the amplitude of the vibration. By this expedient the reluctance of the magnetic circuit automatically decreases with the lower frequencies which correspond to the wider amplim tude of vibration so that the low pitched notes are correspondinglyA accentuated, thereby to `compensate for the reduction inthe amplitude of :low pitched notes on the record frequently made necessary by the close spacing of the spiral convolutions.

Fig. 12 shows another alternative embodiment in which the armature 292' is provided with a fork end presenting parallel lugs `lil and @7i ben tween which the flux relay 342 extends. As will be seen in this case also the air gap between the armature and the flux relay willalso decrease in a direct'ratio of the amplitude of vibration to perform an effect corresponding to that accomplished by the embodimentof Fig. 11.

It will thus be seen that there is herein described apparatus in which the several features of this invention are embodied, and which appa ratus in its action attains the various objects of the invention and is well suited to meet the requirements of practical use.

As many changes could be made in the above construction, and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

Having thus described my invention, what I claim as new andV desire to secure by Letters Patent is:

1. A magnetic pickup having substantially xed magnetic parts with anassociated voice coil and a vibratory magnetic part, a stylus, a non-magnetic connection between the stylus andthe vibratory magnet part, said connection armature extending into said coil to the vicinity of said pole pieces, a magnetic ilux relay piece intervening between said pole pieces and near said armature, a carrying shaft therefor below said pole pieces and perpendicular to the axis thereof, and a stylus carried by` said shaft and mechanically connected thereby to said flux `relay piece. i

3.` A magnetic pickup comprising a casing having axed magnet therein with a pair of pole pieces with upper and lower ledges, a voice coil housed between said pole pieces, a fixed armature extending between said pole pieces into said coil and terminating above the lower ledges of said pole pieces, and a flux relay extending between said pole ledges contiguous to said fixed armatureand a stylus and a shaft at right angles tothe axis of said coil and mechanically connected to said fluxrelay.

4. A magnetic phonograph reproducer com-` prising a magnet having U-shaped pole pieces with facing legs, a voice coil symmetrically housed therein, a fixed Varmature extending through the air gap between one pair of legs of the pole pieces and terminating at its lower and contiguous the other air gap, a magnetic flux re-` y lay piece extending symmetrically in said latter air `gap and contiguous to the armature end, a stylus and rigidvrneans at right angles to the axis of said coil Vand mechanically connecting the` vstylus to said flux vrelay piece.

5. A` magnetic pickup comprising a base, a pair of pole pieces secured thereto having upper and lower ledges facing each other, a voice coil disposed between said ledges symmetrically of said pole pieces, a fixed armature extending downward axially of said coil between the upper ledges and terminating adjacent the lower ledges, a magnetic iiux relayrpiece disposed in the space between said lowerledges and slightly spaced from the` lower end of said armature, a rigid shaft for said flux relaypiece, at right anglesto the axis of said coil, a bearing mount on said base for said shaft and a stylus clamped to said shaft.`

6. A magnetic pickup comprising a base, a pole piece, voice coil and fixed armature assembly thereon, a magnetic flux relay piece including an upstanding wing, a light shaft rigidly mounting .said wing near one end thereof, bearing means -supporting said shaft upon said base, and a stylus clamped with respect to said shaft near the other end thereof.

7. A magnetic pickup comprising a base and a pole piece, voice coil and iixed armature assembly, a magnetic flux relay including an upstanding wing, a light shaft rigid with said wing and extending forward therefrom, a stylus ixed'with respect to said shaft, an upstanding post on said shaft and stop means laterally of said post to dampen and limit the movement of said wing between the armature poles- 8, A magnetic pickup comprising a base, a unit mounted on said base including a pair of pole pieces, a voice coil mounted therebetween and an armature in xed relation between said pole pieces and extending into said coil, a shaft and bearings therefor mounted on said base, a magnetic flux relay piece attachedto the end of said shaft and having an upstandingV wing extending between the lower parts of said pole pieces to the neighborhood of the lower end of said armature, a stop piece rigid with said base and above said shaft and an upstanding post on said shaft having a fiat upper end extending into a corresponding notch in said stop piece and damping and limiting the movement of said wing between said pole pieces, said shaft having a stylus clamped near the forward part thereof.

9. A magetic pickup comprising a pole'piece, a voice coil and an armature, said'parts mounted in fixed relation to each other and a vibratory assembly including a non-magnetic shaft, a stylus near one end thereof and a magnetic iiux relay piece at the other end thereof with respect to said stylus, said relay piece including a wing extending between said pole pieces and contiguous to said armature, the predominating portion of the mass of said vibratory assembly being said stylus.

10. A magnetic pickup comprising a base, an assembly i-lxed thereon including magnetic pole pieces, a voice coil therebetween and a fixed armature extending into said coil, a coacting magnetic relay assembly comprising a light tube of non-magnetic metal, rubber bushings thereon,

,' bearings therefor afiixed to said base, a stylus extending thereacross and clamped with respect thereto, and a magnetic flux relay piece comprising a shank frictionally fitted into the rear end of said tube and having an upstanding wing extending between said pole pieces to a point adjacent the armature.

l1. The combination set forth in claim 10 in which a pin is xed transversely of said tube and has an upstanding flattened end lodged in a notch in a metallic angle piece afxedyto said base above said bearings.

12. In a magnetic pickup, the combination of a base having lateral stops, a U-shaped magnet supported thereon, a pair of pole pieces affixed to said base, a leaf spring reacting at its ends against said stops and exerting pressure on said U-shaped magnet to maintain its ends in contact with said pole pieces, said leaf spring being of width greater than the thickness of said magnet and having a longitudinal slit to determine an upper strap bowed outward above said magnet to retain the same against the bottom of the base.

i3. In a magnetic pickup, a pole piece and armature assembly comprising a U-shaped pole piece, a non-magnetic metal bar affixed to one leg of said pole piece, and a fixed armature affixed to the edge of said vbar and extending transversely of the legs of said U and magnetically spaced therefrom,

14. In a magnetic pickup, va magnetic flux relay assembly comprising a light metal tube, a pair of rubber bushings about the ends thereof, a screw in one end of said tube for clamping a stylus adapted to extend through apertures in said tube and a magnetic member having a shank frictionally fitted in the other end of said tube and having an integral wing upstanding therefrom.

a set screw in one endof said tube for clamping a stylus adapted to extend through apertures in said tube and a magnetic member having a shank frictionally fitted in the other end of said tube and having an integral kwing upstanding therefrom, and a positioning pin axed transversely through said tube and having anupstanding flattened end in the plane of said wing.

16. In a magnetic pickup, a base, a magnet pole piece, coil and fixed armature assembly thereon, a vibratory assmbly co-ordinated therewith and comprising a magnetic flux relay piece including' a wing extending between said pole pieces and contiguous to said armature, a nonmagnetic tube mounting said wing, bearings for said tube mounted on said base, a stylus transversely of said tube, means clamping said stylus between its ends, the ends of said stylus being of diameter and mass greatly reduced with respect to the median clamped portion thereof.

l?. Amagnetic pickup comprising a case having a removable metal cover thereon, a stylus carrying tube longitudinally of said case, a vibratory magnetic member mounted on said tube, pole pieces in said case correlated therewith, a stylus transversely through said tube, an aperture through saidv cover with which the upper end of said stylus is flush when properly positioned and a set screw through the forward end of saidl case for clamping said stylus with re,- spect to said tube.

18. A magnetic pickup comprising a base having a cover, a magnet, an armature and a voice coil thereabout mounted on said base, a magnetic flux relay piece extending between said pole pieces and contiguous to said armature, a hollow shaft mounting said relay piece and having bearings ahixed to said base, a stylus transversely through the forward bearing and Athrough said shaft, said stylus having an enlargement contacting the upper portion of said forward bearing when positioned through a corresponding aperture in said cover and a set screw through the forward end of said base clamping said stylus in position.

19. The method of assembling a magnetic pickup of the. type comprising pole pieces, a fixed armature and a flux relay piece extending between said pole pieces and adjacent said armature, said method comprising the centering of said ux relay piece between the pole pieces by straddling said relay piece with a'fork fitting snugly between said pole pieces, clamping the mount for said flux relay piece in thus centered position, mounting the armature piece in contact with said iiux relay piece, and then interposing a shim of appropriate thickness between-the pole piece' and the armature mount to elevate said armature with respect to said flux relay piece to determine the desired air gap between the stationary armature and the flux relay piece.

20. 'A magnetic pickup including a magnet having pole pieces and having a xed armature, a voice coil encircling part of the magnetic circuit, a magnetic flux relay piece associated with said pole pieces and said armature, a stylus, a shaft 'adjacent to said relay piece and rigid therewith rigidly connected to an end of said shaft for imparting vibration to the relay piece to cause the alternations and variations of magnetic flux through said coil, said armature being concave at the part contiguous to said ux relay piece for reductionof the air gap therebetween in a direct' ratio with the amplitude of vibration of said flux relay piece.

2l. A magnetic pickup including a magnet having pole pieces and having a iixed armature, a voice coil encircling part of the magnetic circuit, a magnetic flux relay piece asso- 1o ciated with said pole pieces and adjacent one end of said armature, a shaft adjacent to and carrying said relay piece, a stylus at anV end of said shaft, said armature having a hollowed out conformation in the region of said flux relay piece to cause the latter to approach one or the other lateral portions of said armature and reduce the air gap in a direct ratio with the amplitude of vibration of said relay piece. Y

MAXIMILIAN WEIL.

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