US1782781A - Reproducing device - Google Patents

Description

Nov. 2s, 1936.

J. S. HIGHl REPRODUC ING DEVI CE Filed June 24. 1927 5. l 'fam 17 INVENToR ATTORNEY Patented Nov. 25, 1930 i Unire STATES JURJEN s. nien, or WILKINSBURG, PENNSYLVANIA, iissrcfNonY To wnsrrNeHoUsE PATENT OFFICE ELECTRIC SL MANUFACTURING: COMPANY, A CORPORATION OF PENNSYLVANIA FEPBODUCING DEVICE `Application led June 24, 1927. Y Serial 1\To.h2l,049.`

wideirange of sound-frequencies. A

Another object of my invention is to pro-` vide a pick-up device that shall be free from moving circuit-connectors and, consequently, subject to only slight deterioriation through USS.

` `Another object `of my invention is toV provide a picleup device that may be easily adjusted to preferentiailyres ond to high or low frequencies.

vide, in a pick-up device, adjustable damp.- ing means that shall also serveto `center cer* tain of the elements of the device with reference to other elements thereof.

Another object of my invention is to provide, in a pick-up device, a needle-holding lever of an improved type. At the present time there is a very decided tendency toward the electrification of phonograph reproducing devices. ln other words,

instead of having the phonograph .reproducer convertthe sinuosities or the record directly into air vibrations, `they are first translated into electric-potential, or current,

fluctuations which, in turn,are utilized to control a therrnionic amplifying system similarto those now well known in connection with radio receiving apparatus. A complete y system of the type referred to is shown in the 40 patent to Jones, No. 1,531,252, to which reference may advantageously be made 1n order i to gain a clear understanding of the functionsof a device constructed according to my invention. y .l

` The pick-up devices heretofore used have been of `four generaltypes, electromagnetic, microphonic, electrostatic, and electrodynamic. The electrodynamic typeis exempliied in the Jones `Patent,- No. 1,531,222,7the mi# mi crophonic type ina patent to Moore, No.

Another obyect of my invention is to pro-V 1,83,067, the electrostatic type apatent to Groenebaum, No; 1,544,001, and the electromagnetic in a patent to Egerton, 1,284,623.

My invention is concerned primarily with a A modification of the electrodynainic typeand isin the nature of aradical improvement on pick-up devices of that type, as known to the prior art.

According to my invention, I construct anV electrodynamic pick-up in a manner ana-lo.-

gous to the manner in which a step-up transformer is made, utilizing for the primary coil a sinOle turn or a luralit of turns which are short circuited, and soactuate the said` primary coil in a magnetic field that eddyycurrents are induced therein. `The eddy-cur@` rents so produced inductively affect a second! ary coil associated with the magnetic circuit which generates the eld referred to, and the output ofthe secondary coil is utilized tocon trol aV therIni-onic amplifienin the manner referred to previously.

Among the novel features of my invention,

are those particularly set forth in the apf` pended claims.` The invention, in its ge neric aspect, however, as `well as further objects and advantages thereof, will best be understood by reference to the following description of certain specific embodiments talren in connection with the accompanying drawings,` in which: p

Figure l is a view, partly in section and partly in elevation, of a `preferred embodiment of my invention, taken along a line corresponding to the line 1-1 of Fig.`2.

Fig.` 2 is a front view of the device,lthe coverplate being removed. l

Fig. 3 is a view, partly in elevation `and partly in section, -of a `preferred form of selfad iusting hearing, taken along a linelcoi responding to the line III-#III of Fig. 4.

Fig. 4 is anend elevational view of the de vice shown in Fig. 3.y

Fig. 5 is aview, partly in elevationand adjusting bearing.` .4 i i Fig. 6 is a sectionaliview, taken along a line corresponding tothe line VI'HVI ofjFig. 5, as viewed from the left.` Y f l Referring specifically to FigsE 1 and 27h partlv in section,iofamodified form of selfpreferred embodiment of my invention comprises a circular base plate 1 of magnetic material whicl shrunk onto one end ot a permanent magnet E2. The base portion is provided with screw threads 3 by means of which a shell element 4 is ai'iif'zed thereto. The shell clement 4 is provided with an inwardly projecting circular rim 5, the inner edge of which approaches o within a short distance of the pole piece 2. The upper edge ot the shell element 4 is provided with screw threads 6 by means ot which a second rim 7 is affixed thereto. The inner edge of the rim 7 also approaches to within a short distance of the central pole piece, the space between the rims 5 and 7, and the pole piece 2, constitutes an air gap in the inao'netic circuit.

The annular space between the elements 5 and 7 accommodates a secondary coil 8, Jfrom which connecting;` leads 10 and 11 extend to the exterior of the shell portion through an opening 12.

The sensitivity of the device may be greatly increased by providing means therein for the suppression of undesired eddy-currents in the material composing the magnetic circuit, namely, the central permanent magnet and the emcircling` rims 5 and 7. I have successfully accomplished the suppression of such eddy-currents by making` a plurality of radial Saw-cuts in all of these elements, er, if desirable, the pole piece may be provided with cuts and the elements 5 and 7 maj,Y be laminate( rlie rim 7 has a central projectinga flange 13 which is exteriorly threaded and carries a compression device 14 thereon.

A cup-shaped element 15 of non-magnetic material, such aluminum or the like, extends into the gap between the central pole piece 2 and the annular elements 5 and 7 and is maintained centered therein by a washer 16 of resilient material, such as felt, which has a central protuberance 17 to iit into, and be carried by, a depression in the end of the central pole piece 2.

circular washer 18 of resilient material is interposed between the bottom of the cup 15 and the pressure device 14, the pressure thereon being` regulated by screwing the said device either in or out on the flange 13. threaded edges of the pressure device are preferably provided with saw-cuts (not shown) in order that it may maintain whatever adjustment is given it.

The cup-shaped member 15 has a deprcssion in the bottom thereof, through an opening in which extends a connecting device 19 which is held in position by a loci: nut Q0.

To otherwise free end of the connectingde- `-ice 18 attached to the upper end ot a needle-carrying element Q1. r1`he element 2l is provided with trunnions 22 having reduced end portions. fis shown in Fig. 5, the reduced end portions of the trunnions 22 lit into openings 23 and 24 provided in the branches 25 and 2G of a resilient U-shapcd bearing device 27 which is aiiixed to the rim 7 by means of a plurality of bolts or screws 28. The branches 25 and 26 are so arranged as to exert a slight amount of pressure axially upon the trunnions 22 in order to thereby compensate for wear caused by the oscillation of the needle-carrying` element 21 therebetween.

The needh-i-carrying` member 21 is provided with a needle-holding set screw 30 which so projects into it that aline drawn through the axis of the set screw would cut the axis of the supporting trunnions 22. By reason of this speciiic location of the set screw 30, pressure exerted thereon during the process of inserting:r or removing a needle will not be transmitted to the cup-shaped member 15 to any great extent.

The needlecarrying member 21 is pre erably extremely rigid throughout that portion thereof which accommodates the needle and is provided with a semi-rigid, or relatively flexible portion, adjacent the point where it is ainxed to the connecting device carried by the protul'erance in the bottom oi the cupshaped element 15.

Referring to Figs. 3 and 4, the resilient adjusting bearing` may be so modified that the openings in the branches 25 and Q6 thereoiI are interiorly threaded and carry a plurality of hollow screw-threaded elements 31 and having ends counter-sunk to accommodate the reduced ends of a trunnion When a modification, such as is illustrated in Fia'. 3, is employed, the device is so initially adj usted by turning in or out the screw-threaded bearin devices that a slight pressure is exerted axially upon the trunnions. As the trunnions and the bearing devices wear during use, this initial pressure is relieved without, however, permitting the device to work loose and rattle.

1n the assembly of the device illustrated in Fig. 1, the shell element 4 is first mounted on the base 1 and screwed down as far as possible. The coil 8 is next placed upon the rim 5 of the shell and the second rim 7 is screwed in place, thus holding the coil firmly in position. The felt washer 16 is next mounted on the central pole piece 2 and the cup-shaped member 15 slipped over it and centered in the air gaia. rl`he resilient washer 18 is next placed around the protuberance ot' the cupshaped member 15, and the pressure device 14 is placed on the iange 13 and turned d wn suiilciently to exert a slight amount of pressure on the cup-shaped member through the uf'asher 18.

The resilient bearing 27 may then be mounted on the rim 7 by means of the screws 28 and, by expandiirT slightly the branches 25 and Q6 thereof, the trunnions 22 of the `mear/e1 needle-carrying member 21 may be positioned i inthe bearing openings 23 and 24e. f i The connecting device 19 may then be `sol-- i dered directly to the reduced extension of the needle-carrying member 21, and the device is then ready to be adjusted andtested.

In Fig. 1 ofthe dravvings,.a cup-shaped cover` 34 `is shown as being press-litted upon the end of therdevice,.this cover being made 'removable `for the purpose of changing:thev `pressure exerted upon the damping'means.

, `The operation of my` improved pick-up,

i `device may probably bestbev-explained by may reach a considerable magnitude.

The currents thus generatedV flow circumferentially of the cup-shaped element and, in so flowing, induce potentials in the secondary coil which is linked vvitli the linx of these currents. The potentials thus induced in the secondary coil, and the frequency of the currents caused to flovv thereby ivillcorrespond to the amplitude and frequency ofthe sound record Which is being utilized to actuate the needle-carrying element.

The dimensions shown in Fig. lare rela- `tively correct, although the device, as a Whole,

is exaggerated in size. The needle-holding element in an actual embodiment is' only a trifle longer than `the usual phonograph needle and, consequently, has a veryl small mass. The devicehas but a very slight inertia and, accordingly, itis sensitive to the most delicate sinuosities of the record;

By reducing the length of the needle-carrying elementtoa minimum and by increasing its intrinsic rigidity, the possibility of the element itself vibrating is substantially eliminated. This specific construction ofthe needlecarrying arm I consider a very important part of the present invention, inasmuch as it largely prevents unpleasant buzzing and scratching noises Which,in devices construct*- ed according to the prior art, rendered the reproduction of music somewhatunpleasant.

I have described the damping means as be` ing composed of felt. `If this material is used, it is preferable to `employ that 'grade lrnovvn as piano hammer felt, of the type employed onpiano hammers at the treble end of the scale. Although serving primarily as body to enable it to continue to, function as centering means over a long" period of time Without detrimental sagging. The damping of the motion is accomplished both by the internalfriction of the particles of the felt and by the oppositionto'the passage of entrained air therethrough.

In lieu offtheufelnlhave found it feasible to employ several layers of silk or analogous material, such material being particularly useful for the Washer 18 Which lies between the cup-shaped element 15 and the pressure device-14." It is also feasibleto employ `a y combination of silk 4fabric and felt in order to obtain the requisite degreeof damping.

By adjusting the pressure of theV pressure `device 14 againsttlie .damping'vvashen more or less `resistance may be interposed `againstV Y the movement of the cupfshaped member `15.`

If the pressure device is so adjusted that the damping means `is compressechthe pick-up 'will respond mainly to high` frequencies,

` Whereas,` if the damping means is but loose lysheld, the` loiv frequencies `vvill be accentu- Y ated. t i i t i The most marked advantage of a device built according tomy invention lies inthe 4elimination ofinoving conductors. In velectrodynamic pick-up devices, such as that shown in the patentto Jones #referred ito above, it is necessary that the moving coil -be supplied with flexible conductors in order Ythat the currents .representing `the sound be ing reproducedmaybe led therefrom to an amplifying device` i Such flexible conductors are a constant source of trouble,winasinuch as they are continually subjectedto bending forces and, consequently, very often break in service.` k' Ihe cup-shaped single-turn primary of mydevice requires no external connections, and such `connections are not re-` quired if the cup-shaped element is replaced by a non-magnetic form carrying a plurality i of turns which are short-circuited. The sin. gle-turn i conductor is perhaps preferable since, in that form," the resistance is much less than When a plurality of turns are used, and, consequently, a larger eddy-current will tend to ovv in it. y

Although I liaveshovvn and described only a single specific embodiment of my invention, I am thoroughly aware of the fact that many modifications may be "apparent,A to those skilled in the art. My invention, therefore, is not to be limited except insofar as is neces- IGS i sitated by the prior art and by the spirit of i the appended claims. y.

I claim as my invention; y 1. In a piclcup device, the combination between a closed-circuit primary coil mount i ed for motion in a magnetic field, a secondary coil in operative relation thereto, means coiny prising an actuable needle holder for mov- Ving saidpriinary coil'in saideld, and ada damping material, the-felthas suflicientV` `justable damping means independent of said y needle holder for controlling said movement.

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plurality lof circular gaps therebetween, a secondary coil encircling said central element intermediate said annular elements, a closed circuit primary coil of non-magnetic material inovably mounted in said gap and stylusreceiving means connected with said primary cnil.

3. In a piclnp device, a magnetic circuit comprising' a central core, a shell encircling said core, a plurality of annular elements eX- tending inwardly from said shell to provide a plurality of air-gaps, a primary element movably supported in said gaps, a secondary winding positioned in the annular space defined by the said inwardly extending annular elements and the central core, whereby a secondary magnetic circuit having;r relatively low reluctance is established for flux arising from currents induced in said primary element and stylus-receiving,` means connected with said primary element.

ln a pickup device, a magnetic circuit having a gap therein, a closed-circuit primary element mounted for oscillatory motion in said gap, a secondary coil disposed in inductive relation to said primary element ad jacent to said gap, a stylus-holding` element aiiixed to said primary element for imparting motion thereto, and adjustable damping' means for controlling the motion of said primary element, whereby, when said primary element is caused to move in said gap, electrioal potentials are set up in said secondary coil by reason of currents induced in said primary element, and the frequency-response of said device may be controlled.

In testimony whereof, I have hereunto subscribed my naine this 16th day of June, 1927.

JURJEN s. HIGH.

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