US2483196A - Phono-pickup - Google Patents

Description

J. F. GORDON PHONO PICKUP Sept. 27, 1949.

Filed April 11, 1947 P WE P I 1 ii JAMES- F. GORDON Patented Sept. 27, 1949 srArrs UNITE.

Q TEN PHQlgO-PICKUP h I James l f.--GordonTowsonfiMdg-assignw to Ben- I v Application April This invention is directed to phonogr p k ups. More speciflca lly it is directed to magnetic phonograph pickups of the"type"employing"the modulated flux gap or variable reluctancep'rim c p .1 at. .L'v .ei, v

There are many ways Wherebythe intelligence activ br:generating element in the pickup'is often a 'pi'eZoelectric'-"rystal 'whichf'generates a small" electric purrent when 'itsfmechanical di mensions are,alteredrorfoftenj small coil ofwire situ'atetil'in ama'gnet'icr-fieldi "The-piezoelectric type-is 'usually referrjec'i to simply as a' crystal pickupj'aiid"hasfoundwide application.- "Thef'piezdelectrivcrystal" used'insuchcrystal pickups isunfortunatelyfsubject to "considerable variatiori of as uyham e" Zcharacteristics under varying conditions 'oftemperatureand' humidity; Thisfact, amongotherg has accelerated 'the dcvelo'piiientof other types'o'f pickups. The magneticHp'ckupj as described above:-'=is closely ana-lag'ous=to*-the conventional dynamoelectric generator of the type employing a permanent magnet to'supply its field' excitation, and a phonograph stylus tocsupply the relative motion between the armature, in :thiscasera 'coil -of wire, and the magnetic lines of forcen As can be understood from the foregoing analogy, the constructiori of such a magnetictpickup is usu'ally'. difiicult and expensive. if be'stvzres'ults 'are to'xbe obtained H It is an' bjectoflthis invention to provide a phonograph pickupwwhi chiaziszrnot afie'ctedshy changes of ambient temperature.

It is a further object of this invention to provide 'aphonograph pickup which is not lfec' ted by-'therelative-humidity 'of'its environment;

It is a further object of this invention to provide a magnetic phonograph pickup of simple construction.

It is a further object of this invention to provide a magnetic phonograph pickup having good vertical compliance.

These objects are attained by the use of fixed pickup coils associated with a magnetic circuit the reluctance of which is varied by a phonograph stylus.

The above and further objects and novel features will more fully appear from the following detailed description when the same is read in connection with the accompanying drawings. It is to be expressly understood, however, that the drawings are for purposes of illustration only,

chief methods in" use at 'this nte'dstyluswhich cooperates dix'Aviation-Corporation, TowsonrMds-acorn rpdratibnzof Delaware I 11, 1947, Serial No. 740,840 (Cl. 179-100.)

t! and are not intended as a definition of the limits of the invention, reference for this purpose being had to the appended claims.

In the drawings, wherein like reference charref ke partsthroughoutthe "several inent df the instant end viewsiof 'the Fig i r aheehanicar operation "-"Referrin'g o to F1 horseshoe m agnetf ffl haying strip 1| and lz se cur'e'd t'o the arms there The-"strips l hand 12 swam ed-t6 'provide a arrow g-apfl 3 between them, and a stylus l4 astically -aifixedto'the strip's 'li I a-nd l 2 'by a' hioldd rubber piece =1 5. The stylu' M is bo rided t'd the pie'ce l5 which is -in tiirn on'dd t the stiips- -Tl afid l2."- A pair of are 11 eany wound on the I IniFi'g. 21 therelati' juxt A osition" of the ends of the strips ll and l2--at tli g'ap il ii may be seen in greater detail. It will be noticed -thatthe strips ll and l' :aremot: coplanait butiithat one of the --case strip 12 is" -slightly higher than theiedg'e of th'e strip I l--when the stylus I4 is in a verticalip'dsitiona This is the: rest position that the .lassemblyv maintains when no lateral force is applieditoithestyluszl4.

f; Analyzing'lthe magneticcircuit now,where:

ear hen? ,t ea Lof the strips I I 8 or I dF=dls (3) Which tells us that the change in magnetic flux surrounded by the coils l6 and IT is a linear function .of the changes of dimension of the gap I3. It will be seen from Figs. 3 and 4 that 13 will be minimum when the stylus is deflected to the left, as in Fig. 3, and will reach a maximum when p it is deflected to the right as in Fig. 4.

Considering now the voltage induced in the coils i6 and IT, by the law of induction.

which states that the potential in the coils l6 and IT, or the potential available at the terminals 18 is equal to the time rate of change of deflection of the stylus. This is the same as the equation for the action of a conventional magnetic pickup.

Of course the strips. II and I2 must be quite flexible to allow easy deflection of the stylus 14 by the record groove, and the piece l5 must be sufliciently resilient to prevent the generation of spurious mechanical modes. The piece l5 may serve the dual purpose of a mechanical linkage and mechanical damping,

Although only one embodiment of the presen invention has been illustrated and described in detail, it is to be understood that the invention is not limited thereto. Various changes may be made in the design and arrangement of the parts without departing from the scope and spirit of the invention as the same will now be understood by those skilled in the art. For a definition of the limits of the invention reference will be had primarily to the appended claims.

What is claimed is: 1. In a phonograph pickup: a permanent magnet; a pair of resilient elements of magnetic material, one affixed to each pole of the said magnet, said elements terminating in flat portions lying in close proximity and forming a gap in an otherwise complete magnetic circuit, corresponding major surfaces of said portions defining spaced mutually parallel planes when said portions are in a position of rest, said elements being resilient only in directions normal to said planes; a stylus; and means cooperatively securingsaid'stylus to said portions in a manner suchthat displacement of said stylus in aplane perpendicular to said major surfaces varies the spacing of said planes, said means comprising a body of resilient material formed around said stylus and bearing on the adjacent edges of said portions.

2. In a phonograph pickup: a permanent magnet; a pair of flat resilient elements of magnetic material, one affixed to each pole of said magnet,

said elements terminating in mutual proximity to form a gap in an otherwise complete magnetic circuit, corresponding major surfaces of the terminating portions of said elements defining spaced mutually parallel planes when at rest; a stylus; and means resiliently securing said stylus between said portions with its axis lying in a plane substantially perpendicular to said planes, said means comprising a body of resilient material positioned between and bonded to said portions and having said stylus embedded therein, whereby movement of the point of said stylus laterally with respect to said portions in one direction progressively reduces the size of said gap while movement in the opposite direction progressively increases the size of .saidgap. V a

3. The combination as set forth in claim 2, said elements each having a coil formed around it, said coils being connected in series.

4. In a phonograph pickup: a permanent magnet; a pair of flat resilient elements of magnetic material, one affixed to each pole of said magnet, said elements terminating in mutual proximity to form a gap in an otherwise complete magnetic circuit, corresponding major surfaces of the terminating portions of said elements defining spaced mutually parallel planes when at rest; a stylus; and a resilient member surrounding and being bonded to said stylus; said resilient member spanning the space between said portions and supporting said stylus between said portions with its axis lying in a plane substantially perpendicular to said parallel planes, said resilient member transmitting force to said portions in response to lateral movement to said stylus, whereby movement of the point of said stylus laterally with respect to said portions in one direction progressively reduces the size of said gap while movement in the opposite direction progressively increases the size of said gap.

5. The combination as set forth in claim 4, said elements each having a coil formed around it, said coils being connected in series.

JAMES F. GORDON.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PA'IENTS Number Name Date 1,778,048 Thomas Oct. 14, 1930 1,780,409 Thomas Nov. 4, 1930 1,792,554 Thomas Feb. 17, 1931 2,290,057 Lindenberg July 14, 1942 FOREIGN PATENTS Number Country Date 334,551 Great Britain Sept. 5, 1930

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