US2689275A - Electrodynamic pickup - Google Patents

Description

Sept. 14, 1954 H. c. HANSEN ELECTRODYNAMIC PICKUP 2 Sheets-Sheet l Filed May 4, 1950 I IN VEN TOR.-

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Patented Sept. 14, 1954 ELECTRODYNAMIC PICKUP Hans Christian Hansen, Copenhagen, Denmark Application May 4, 1950, Serial No. 159,998

Claims priority, application Denmark May 4, 1949 This invention relates to phonograph pick-ups for reproducing phonograph records having a laterally out groove and more particularly to phonograph pick-ups of the socalled moving coil type.

It is a main object of the invention to provide a pick-up structure of the character here referred to in which distortions resulting from various sources which are likely to cause distortions in pick-ups of this type can be reduced to a minimum.

It is another object of the invention to provide a pick-up of the type referred to which has a moving coil system of extremely low weight and with small directive force so as to enable reproduction of a phonograph record with a high fidelity characteristic.

In the design of pick-ups of the kind here referred to there are various problems inasfar as a pick-up of this type should be a mass produced item. A pick-up of this type comprises a pair of 'pole pieces arranged in opposed spaced relationship and having therebetween an armature mounted for rotational oscillation between opposed surfaces of the pole pieces.

This leaves various possibilities for designing the suspension of the armature, fastening of the pole pieces, centering the armature in the space between the pole pieces, arranging the outlet wires from the armature coil etc.

If either pick-up unit is made to order so that it does not play any roll in what the price is it will of course be possible to design the relative arrangement of the parts here mentioned as precision work and having the assembly made by specially skilled workers.

It is, however, a further object of the invention to provide a pick-up structure of the type referred to in which the various parts comprising substantially the parts here mentioned can be made in mass production according to normal mass production methods and in which the parts further are designed for easy assembly without the necessity of employing specifically skilled labour.

A further purpose is to designa unitary pole piece structure for a pickup of the type here referred to in which the armature can easily be brought in position and centered adequately between opposed surfaces of the pole pieces.

Another purpose of the invention is to design an armature structure for a pick-up of the type here referred to in which the outlet wires from the armature coil can be arranged so as to urge practically no resistance against the rotational oscillation of the armature and further be located 17 Claims. (Cl. 179--100.41)

so as to allow easy access to connection with exterior wires.

Still another object of the invention is to provide a structure in which the armature can be held in bearings without the us of any intermediate members.

With these and other objects in mind the inven-- tion will now be further explained with reference to the accompanying drawing in which Fig. 1 is a perspective view of a pick-up according to the invention seen from the front end,

Fig. 2 is a similar perspective view partly in section seen from the rear end with the permanent magnets withdrawn to show a construction of the different parts,

Fig. 3 is a fragmentary sectional perspective view taken on line 33 of Fig. 1,

Fig. 4 is a perspective view of the armature with the stylos holder arm in enlarged scale; and

Fig. 5 is a sectional view, taken on line E-5 of Fig. 1.

In the drawing the same parts in the different figures are designed by the same reference numerals.

l0 and H! are pole pieces of a magnetic material forming between them an air gap Id. The adjacent edges of the pole pieces are as indicated in dotted lines in Fig. 1 wedge shaped at l6 leaving relatively narrow opposite edge portions of the two pole pieces enabling a strong magnetic field to be concentrated in the air gap. Looking apart from the wedge shaped opposite edge portions the two pole pieces are formed like fiat members having parallel exterior surfaces of which the front surfaces in Fig. l are designated by it and 50 and one rear surface in Figs. 2 and 5 is designated by 52.

The two pole pieces are sealed or moulded in a body generally designed by [8 which encloses the air gap between two pole pieces. As clearly shown in the drawing this body has a bottom portion 20 surrounding the lower edges of the pole pieces l0 and i2 and a top portion 22 surrounding the top edges of the pole pieces iii and [2. The top and bottom portions 29 and 22 respectively are connected by vertical portions of which one at 24 extends on the front side as shown in Fig. 1, while the other at 26 extends at the rear side as shown in Fig. 2.

As most clearly shown in the section in Fig. 3 and Fig. 5 an elongated hollow space is defined in the body l8 between the edge portions of the pole pieces :0 and I2. This hollow space is along the substantial part of its length cylindrical and adapted to receive the armature more detailed shown in Fig. 4. At the ends the hollow space 28 has portions 30 and 32 of increased diameter adapted to receive resilient bearings 34 and 36 formed like rings or washers of rubber or a similar resilient material, see Fig. 4.

Furthermore the bottom portion 28 of the body l8 has a plate like extension 38 and the top por tion 22 of the body 18 has a similar plate like extension 48, the-two extensions 38 and 40 being arranged in substantially parallel planes in spaced relationship. Furthermore the rear central portion 26 of the body I8 is provided with a rib like member 42 extending between the plates- 38 and 48 to support these and give the structure mechanical rigidness. A vertical bore 44 having at least along part of its length screw'threads 46 is arranged through the rib 42 in order to enable the mounting of the structure in an outer casing preferably formed in the end of a pick-up arm (not shown).

As shown in Fig; lthebody. l8 is'of such a shape as to leave a part of the front surfaces 48 and B of the pole'pieces unernbedded and exposed and as seen iniFig. 2;the1rear surface '52 of the pole piece l2 isalsoleftj unembedded and exposed. It will be understood that the rear surface ofthe other pole piece I in a similar manner alsois left exposed asshown in Fig. 5 where this rect'vposition between theopposedsurfaces of the pole pieces. In the production the two pole pieces are inserted in the form together with a core; memberof a; size 1 corresponding to the elongated hollow space 28, said core member havingqend-portions corresponding; to the two end portions 38 and 32 with increased diameter. The arrangementgis so that the twopole pieces withtheir narrow opposite edges engage the core member; The two pole pieces are kept in position in the form by parts thereof abutting the front and rear surfaces adapted ,to be exposed. The remaining interior hollow space of the form corresponds to the form of the body l8 with extensions 38 and 48, rib 42, etc. Upon filling the formwith a suitable non-magnetic material such as a thermoplastic substance and allowing it to be hardened the form is separated in its necessary; different partswhereafter the moulded structure in which now the twopole pieces are embedded is removed. from the form. Finally the core member is removed, to which purpose it might consist of two parts which for instance are screwed together, thus completing the operation and finishing the structure with the air gap between the two polepiece edges ready for the mounting of the armature.

Referring now to-Fig. 4 the armature generally referred to as 54 is in form of a substantially rod like member 56 having at eachend head portions 58 and .60 of increasing diameter. The lower headportion .58 has an extension 62 of slightly reduced. diameter leaving. at the end of the head 56 ashoulder 64. In each of the head portions transverse slots 86 and 68 are provided respectivelymjlhe slot 68 in the end portion having the extension 62 is cut so deep that the bottom thereof is under the surface of the shoulder 64. The slots 66 and 88 also extend along the opposite surfaces of the cylindrical parts of the two head portions 58 and 68. In the slots a coil 10 is arranged. It will be appreciated that by means of the slots the outer surface of the coil is totally within a cylindrical surface surrounding the two end portions.

The extension 62 at the end of the head serves the purpose of attaching to the end of the armature' the stylus holder arm 12. To this purpose this arm has a substantially circular portion 14 in which are provided two half-moon formed apertures corresponding to the cross section of the two portions of the extension 62 on each side of the slot. 66 to allow passage thereof through the part 14. The arm 12 is put in position so as to engage the shoulder 84, whereafter the end edges of the extension 62 are deformed by riveting or in any other;convenient manner: The." arm I2 further. has'an inclinedportion 1.8 and. 1.;

at the end thereof a portion 88. having-a small hole82for the mounting of the stylus 84, which for instance may be a fine sapphire needle secured-in the --hole 82 by some; thermo-plastic;

material or in any other convenient manner; The two-portions I4 and 88' are so arranged that a they are substantially.parallel, the inclined por 1 tion 18 serving to keep, the :top of the stylus 5+" at a substantially lower level than the end .of the armature.

The armature is mounted in the hollow'space.

28, forming, the air gap between the two polepieces, by means of the two resilient ring meme; bers '34 and 36 the holes of which correspond substantially to the exterior, diameter of the head portions 58 and ,68 and the outer diameters.

of whichcorrespond substantially, to the interior. diameter of the-two portions and 32 at: the 1 end of the air gap. i

It will be appreciatedthat this mounting is extremely: simple and that no adjustment .is. required afterithe mounting because the embedding 1 of the pole pieces andthe body-l8v automatically 1 i will secure the right position of-the armature in in the sound groove of the record. Neither will the wires prevent the rotational Oscillating move.- ment of the armature.

As shown in Fig. 1 there are provided in the top surface of the extension 40 grooves 88 and r 98 extending from the rear edge to the top ofthe portion 32with increased diameter. In each .of

the two grooves electrical connecting members 92 and 91 are arranged for instance secured by small rivets orscrews and having in opposite die rections extending soldering flaps 84 and96 and :c?

88 and- IM respectively. The wire ends 86 from the coil 10 are then soldered to the flaps 94 and 98. The electric leads (not shown) from the.

pick-up to the amplifier will then be, arranged in the grooves 88 and 98 and with their ends soldered to the flaps and I00.

To protect the extending end of the stylus q, holder arm 12 the body l8 may as shown at its l front end have an extension I82 with a bottom. 3 1' groove 104.

The magnetic field in the air gap is producedby 1.1:.

means of ermanent magnets. The magnet system may as indicated in Fig. 2 consist of three block like magnets I06, I08 and H0, of which the two magnets I06 and H18 form the legs, while the magnet I H) forms the rear yoke.

Preferably the magnets are mounted only after the mounting of the whole structure including the armature and the stylus holder. The magnets are then brought in position by pushing them from the rear end see Fig. 2 to abut with the free ends of the two legs against the exposed rear surfaces of the pole pieces.

It will be appreciated that by in this manner leaving the pole pieces unenergized during the mounting any risk of fine magnetic particles being attracted into the air gap until this has been air tight closed by the rubber rings 34 and 36 will be avoided.

Preferably the permanent magnets I06 and I08 are even not energized before they are brought in position. Such energizing is enabled by means of the unexposed front surfaces of the pole pieces allowing one set of poles of anenergizing magnet to be brought in connection with the final structure. The other set of poles of the energizing magnet may then be applied to the two ends of the yoke opposite the rear ends of the legs resulting in a final magnetization with north and south poles as indicated in Fig. 2.

Having now particularly described and ascertained the nature of my said invention and in what manner same is to 'be performed, I declare that what I claim is:

1. In a phonograph pick-up of the moving coil type for reproducing sounds from laterally-cut records, in combination, at least two magnetizable poles including portions having edges arranged in spaced relationship forming between said edges an air gap, magnetic means for energizing said poles to generate a magnetic field traversing said air gap, a body of non-magnetic material adjacent edge portions of said poles embedding the same for holding them in mutual spaced position and defining an elongated chamber open at both longitudinal ends, an armature member angularly oscillatable about its axis in said chamber, resilient bearings for said armature member positioned near said longitudinal ends of said chamber, means movable in accordance with the recorded variations of the sounds and connected to said armature member for oscillating the latter in accordance with said movements, and a coil disposed on said armature and operable to cut the magnetic lines of force in said field for generating and transmitting electric impulses.

2. In a phonograph pick-up of the electrodynamic type for translating sounds from laterallycut records to an electric reproducer, in combination, a body of non-magnetic material surrounding a longitudinal chamber open at both ends, opposite poles molded in said body and having edge portions protruding to the interior surface of said chamber and being flush therewith to seal with said body said chamber along said surface, said poles being magnetizable to generate a magnetic field traversing the gap between said pole edges within said chamber, magnetic means positioned to magnetize said poles, an elongated armature disposed in said chamber and being angularly oscillatable about its axis and including extensions at the opposite ends, means positioned at said open ends of said chamber and in contact with said extensions forjournalling said armature and completing therewith the tight sealing of said chamber, stylus means movable in accordance with the recorded variations of the sounds and operable to oscillate said armature, and a coil disposed on said armature and oscillatable therewith and energizable by said magnetic field to generate electric impulses in accordance with the oscillations.

3. In a phonograph pick-up of the moving coil type in combination: a body of non-magnetic material defining an elongated channel, at least two pole-pieces embedded at least partially in said body and arranged substantially at opposite sides of said elongated channel, magnetic means positioned for energizing said pole pieces to generate therebetween in said elongated channel a magnetic field, at least two supporting members arranged adjacent either end of said elongated channel, an elongated rotatable armature carried by said supporting members in said channel between said pole pieces, a coil suspended on said armature in said channel and operable to cut the magnetic lines of force when said armature is rotated, and means for imparting a rotational oscillation to said armature about its longitudinal axis.

4. In a phonograph pick-up of the moving coil type, in combination, a body of non-magnetic material, a pair of pole pieces firmly secured in said body and arranged in opposite relationship, magnetic means positioned for energizing said pole pieces to generate therebetween a magnetic field, an elongated armature arranged for rotational oscillation in said magnetic field between said pole pieces, bearings supporting said armature at either end thereof, and positioning surfaces defined by said body of non-magnetic material for supporting said bearings in a position centering said armature substantially in a middle position between said pole pieces.

5. In a pick-up, for use in connection with laterally-cut grooved phonograph records, in combination, a body of non-magnetizable material, poles embedded in said body spaced from each other across a sealed space and being magnetizable to generate a magnetic field traversing said space, magnetic means positioned for magnetizing said poles, a longitudinal armature mounted for rotational oscillation in said space, means connected to said armature and to said body and operable to suspend rotationally said armature in said space, coil means wound on said armature within said space and being oscillatable with said armature to cut the lines of force of said magnetic field and to transmit electric impulses generated thereby, and movable record groove follower means connected to said armature and operable to impart rotational oscillation to the armature in response to groove variations.

6. In a moving coil phonograph pick-up for reproducing sounds from laterally out records in combination, at least two poles including portions having edges arranged in spaced relationship forming between said edges an air gap, means for energizing said poles to generate a magnetic field traversing said air gap, at body of thermoplastic non-magnetizable material adjacent edge portions of said poles embedding the same for holding them in position and defining an elongated chamber open at both longitudinal ends, an armature member angularly oscillatable about its axis in said chamber, resilient bearings for said armature member positioned near said longitudinal ends of said chamber, means movable in accordance with the recorded variations of the sounds and connected to said armature member for oscillating'lthe 'latterl'in accordance avith said movementrsandra acoil .disposed on saidrarmature and 1 operablezto cut the magneticalines of force in said fieldzfor generating and-transmitting electric imi '7. In a phonograph'rpickmpof; the moving coil type for reproducing sounds from: laterally out recordsin: combinations-at least two poles including.=portions having-edges.;arranged in spaced:

relationshipfformingl between said edges an air gapgmeans for energizing. said poles to generate a magnetic-field. traversing said air gap, a body of nonmagnetizablematerial-adjacent edge portions ofssaid poles embedding. the same for holding ithcmssin position and-"defining an elongated chamberextendinglongitudinally along' said air gapsan annular'seating provided at either longitudinal-endiofisaid chamber-,'an armature member angular-1y: oscillatablefiaabout its axis in said chamberyralongitudinal; extensionon either end of saidarmatureioppositeeither of said annular GIldrPOI'tJOIlSnOf said chamber, a resilient annular imembenwsurrounding; eitherof said armature1extensions;.nsaid annular. member defining an aperture receiving and .holding I said armature 1 extension and "said annular member further seated in said annular seating at the endoi saidchamber; means movable in accordance with: therrecorded variations of the sounds and connected to'said armature member for oscillating the latterinxaccordance with said movement, andacoil disposed on said armature andaoperable-rto cut the magnetic lines of force in said field. for generating and transmitting electric impulses.

8. Ina phonograph pick-up of the moving coil type-for reproducing-sounds-from laterally cut records in combination; atleasttwo magnetizable poles including portions having edges arranged in spacedsrelationship forming between said edges an air gap, ajbody of non-magnetic material adjacentedge portionsof said poles embedding the same-for holding them in position and leaving the remaining: portions. of said poles unexposed, said:bod :de fining an elongated chamber, magneticmeans for energizingsaid poles to generate a magnetic fieldtraversing said air gap,an armaturemember angularly .oscillatable about its axis in said =chamber resilientbearings for said armature member: positioned near the ends of said chamberameans movable inaccordance with the recorded variations'of the sounds and connected to said armature member for oscillating the latter in accordance: with said zmovement, and a coil disposed on saidarmature: andzopera'bleto cut the magnetic'l-inesof force'in saidfield for generating andwtransmitting electric impulses:

9. In a phonographipick-up ofthe moving coil type in combination: a body of non-magnetic materiai defining an; elongated channelyat least two poleepieces embeddedwat' leastpartially in said bodyand arranged-substantiallylat opposite sides of said-elongated channel; 'magnetic'means posie tionedafor energizing saidrpole pieces to generate therebetween in said. elongated channel. a magnetic field, :at leasttwo supporting members arrangeda adjacent" either end :of said elongated 10. In a,zphonograph; pick-up of the electro-- 1.; dynamic type in combination, abody of none-Image: j neticmaterial, a pair of pole pieces firmly secured in said body and arranged in opposite-relationship, magnetic means positioned for energizing said pole pieces to generate therebetween a mag netic field, an elongated armature arranged-for rotational oscillation in said magnetic field betweensaid pole piecesgbearings supporting said armature ateither zenda-thereof, and positioning 1 surfaces defined by saidsbody of non-magnetic-:U. material for supportingsaid bearings in apositiont centering said armature substantially in a. middle position between said pole pieces.

11. A. pole shoe-structure; for use in a phonograph-pickup ofsthe moving coil type having an armature, said pole shoe 'structurexcomprising a bod of non-magnetic material, a pair of pole piecesfirmly: secured insaidubody and arranged, in opposite spaced relationship defining between thexnan elongated space, and means including positioning surfaces formedxon said body and l operable for centering :said armature substan-r tially centrally-of said space;-

' 12. A pole'shoestructura 'for use in a phono-l graph pick-up of the moving coil-type having an armature and magnetic means,*said pole shoe structure comprising a body of non-magnetic ma-' terial, a pairof'pole pieces firmly secured in saida body and arranged in-opposite spaced relationship defining between them an elongated space, means,

including positioning surfaces formed on said:

body and operable for centering said armature substantially centrally of said space; and exposed portions of said pole pieces to be engagedby said magnetic field betweensaid pole pieces substan tially perpendicular to said elongated channel,

an elongated armature extending longitudinally through said elongated channel, means for supporting said elongated armature adjacenteither end of said elongated channel; said supporting means being designed to allow a rotational oscillation of said elongated armature, a phonograph sound" track follower connected with one end of said elongated armature for imparting to' said armature a rotational oscillation inresponse to the variations of a sound track of'a phonograph. record, awinding carried by said armature having its turns extending substantially parallel with theaxis of said armature and outlet wires from"; V

said winding extending beyond the end of said armature'which is remote from said track follower V 7 through said armature supporting means.

14. In a moving coil phonograph pick-up in combinatioma supporting structure defining an elongated channel, a pair of opposed pole pieces. firmly secured to said supporting structure, said pole pieces having "opposite edge portions arranged in substantial mutual spaced relationship I with'respect to said elongated channel means for I producing a magnetic field between said polem 1 piecessubstantially vperpendicular. to said elon-H .17 gated channehan elongated. armature extending: longitudinally through said;:elongated 1 channel; 29;.

means for supporting said elongated armature at either end of said elongated channel and simultaneously centering said armature therein, said supporting means being designed to allow a rotational oscillation of said elongated armature, said armature having ends extending at either end beyond said supporting means, a phonograph sound track follower connected with one of said extending armature ends for imparting to said armature a rotational oscillation in response to the variations of a sound track in phonograph records of the laterally-cut type, a winding carried by said armature having its turns extending substantially parallel with the axis of said armature, and outlet wires from said winding following the other of said extending armature ends which is remote from said track follower.

15. In a moving coil phonograph pick-up, a supporting structure of non-magnetic, electrical insulating material, at least two opposed magnetic pole pieces, means for holding said pole pieces on said supporting structure defining an elongated sealed space between opposed surfaces thereof, an elongated armature extending longitudinally through said elongated space, means supporting said elongated armature adjacent either end of said elongated space, a coil carried by said armature extending longitudinally thereof, said supporting means for said armature being designed for allowing a rotational oscillation of said armature, one end of said armature being provided with a sound track follower member for imparting a rotational oscillation to said armature when said sound track follower is guided in the sound track of the phonograph record of the laterally cut type, said coil on said armature being provided at the opposite end of said armature with outlet wires extending longitudinally through said supporting means adjacent said other end of said armature and outlet terminals secured on said supporting structure, said terminals being electrically connected with said outlet wires.

16. A pole shoe structure for use in a phonograph pick-up of the moving coil type, having a moving coil type armature structure to be mounted in said pole shoe structure in which said pole shoe structure comprises a body of nonmagnetic material defining an elongated channel, a pair of pole pieces embedded at least partially in said body and arranged substantially at opposite sides of said elongated channel and means comprising positioning surfaces defined by said body of non-magnetic material for receiving and centering said moving coil armature structure when mounted in said pole shoe structure.

17. A pole shoe structure comprising a pair of pole shoes for use' in a phonograph pick-up of the moving coil type having magnetic means for energizing said pole shoes and an armature structure of the moving coil type to be attached between said shoes in which said pole shoe structure comprises a body of non-magnetic material defining an elongated channel, a pair of pole pieces embedded partially in said body and arranged in opposite relationship with respect to said elongated channel, said pole pieces having exposed portions adapted to engage said magnetic energizer means and means comprising positioning surfaces defined by said body of nonmagnetic material for receiving and centering said moving coil armature structure when mounted in said pole shoe structure.

References Cited in the file of this patent UNITED STATES PATENTS Number- Name Date 1,767,610 OLeary June 24, 1930 2,148,796 Barbieri Feb. 28, 1939 2,249,161 Mott July 15, 1941 2,351,353 McCarty June 13, 1944 2,400,662 Roberton et al. May 21, 1946 2,416,082 Balmer Feb. 18, 1947 2,496,483 Massa Feb. 7, 1950 2,554,209 Miner May 22, 1951 2,566,604 Eaves Sept. 4, 1951 2,591,996 Arentzen Apr. 8, 1952 FOREIGN PATENTS Number Country Date 599,247 Great Britain Mar. 9, 1948 904,172 France Oct. 29, 1945

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