US2376456A - Signal translating apparatus - Google Patents

Description

y 1945. c. M. SINNETT 2,376,456

S IGNAL TRANSLATING APPARATUS Filed Oct. 9, 1941 2 Sheets-Sheet 1 y 1945- C. M. SINNETT SIGNAL TRANSLATI'NG APPARATUS Filed Oct. 9, 1941 2 Sheets-Sheet 2 10; 3nventor PatentedMay 22,1945 2,376,456

UNITED STATES PATENT OFFICE SIGNAL TRANSLATING ArPARA'rUs Chester M. Sinnett, Westmont, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application October 9, 1941, Serial No. 414,305

16 Claims. (01. ire-100.41) This invention relates to signal translating apin the tuning circuit of a 40-50 megacycle oscilparatus, and more particularly to a signal translator, and when its capacity is varied, frequency lating device of the capacity type adapted for use shift occurs in the oscillator circuit and frequency especially in connection with phonograph records, modulation results. This may be passed throug the primary object of my invention being to prothe regular FM channel 0 a radio receiver, for vide a capacity type pickup as aforesaid the example.

capacity of which is varied in accordance with The movable electrode preferably consists of a the record groove modulation to provide frerelatively thin, narrow, fle b Strip of metal quency modulation in an oscillator circuit wheretending across the stationa y ele trode a d in the pickup constitutes a tuning element. anchored at its ends. Suitable 'means are pro- More particularly, it is an object of my present vided for tensioning the electrode whereby to coninvention to provide an improved capacity picktrol its natural period. The need e is P ra up as aforesaid the operating parts of which have secured to the movable electrode substantially a low mechanical impedance and the needle presway w n its ends, a m nt of t sure of which is very low on the record whereby l5 electrode is confined substantially to a region to provide long record and needle life, thereof in the vicinity of the needle. This avoids Another object of my present invention i t vibration reflections from other parts of the movprovide an improved pickup as above set forth able electrode back toward the needle, thereby which has great sensitivity and is operable over u stantially mina n di t rtion and xtenda much wider range than pickups of this type s the range v which h P up i p te heretofore known. with great efliciency. If desired, the fixed elec- A further object of my present invention is to ode may be arranged for adjustment relative to provide an improved capacity pickup whi h will the movable electrode so as to control the normal afford a large gain in signal to noise ratio. ir can h r w n a d th s t e s n i i y of Still another object of my invention is to prothe d The Pi up device s e t em y light vide an improved capacity type pickup wherein n Weight, having a needle p essure o approxithe natural period of the vibrating electrode can t y 20 rams, or about two-thirds of an ounce, be easily controlled. as compared with about three-and-a-half or four A further object of my present invention i to ounces characteristic of the prior art pickups. provide an improved pickup as aforesaid which Also, since the movable electrode is light and flex- Will not cause the record with which it is coible, t has a w e han cal impedance. This, operating during reproduction to radiate exombined With the light weight of the needle traneous sounds and which will not itself produce on the record, affords long life to both records such sounds. and needle.

still a further object f my invention is to pro- The novel features that I consider charactervide an improved pick-up as set forth above istic of my invention are set forth with particuwhich will operate with a minimum of distortion. arity in the app d c aimshe invention it- -It is also an object of my present invention to self, however, both as to its organization and provide an improved pickup device of the charmethod of operation, together with additional Obacter et forth which i Very simple, yet sturdy, 40 jects and advantages thereof, will best be underin construction, hich i e o mic l i o t, stood from the following description of several which is highly efficient in use, and which will em o iments thereof, when read in connection have a long life. with the accompanying drawings, in which In accordance with this invention, Iprovide a u e 1 is a Side elevation of one form of suitable supporting member which carries a pair p up constructed in accordance with my Dr of electrodes in capacitive relation to each other, t t on, the pi kup bein shown mounted one of the electrodes being stationary and the on a suitablesupporting arm shown partly in other being mounted for movement relative to section,

the stationary electrode. The movable electrode Figure 2 is an inverted plan view of this form carries a needle adapted to cooperate with the of my invention, a

groove of the record. Due to the, wave shape Figure 3 is a side elevation of a second form form in the record groove, the capacity between of my invention shown with its arm mounted the electrodes is caused to vary in' accordance in operative position,

with the movements imparted to the needle by Figure 4 is an enlarged, top plan view of the the record groove. The pickup may be connected pickup device of Figure 3,

Figure 5 is a side elevation thereof with certain parts in section,

Figure 6 is a bottom plan view thereof,

Figure 7 is an enlarged, bottom, perspective view thereof with certain parts broken away for the sake of clearness,

Figure 8 is an enlarged sectional view taken on the line VIII-VIII of Figure 6,

Figure 9 is a wiring diagram illustrating one circuit in connection with which my improved pickup may be used advantageously and Figure 10 is a set of curves showing the resonance of the pickup arm of Figure 3 under various conditions.

Referring more particularly to the drawings,

, wherein similar reference characters designate corresponding parts throughout, there is shown, in Fig. 1, a pickup arm I which carries on its free end a supporting block 3 recessed to provide a face 5 and a pair of lugs or projections I and 9 which terminate in a plane beyond the face 5. The block 3 is also formed with a slot H which substantially separates the projection 9 from the body thereof. A screw l3, which is threadedly received in the projection 9 and has its end bearing against the body of the block 3, as clearly shown in Fig. 2, is adjustable to more or less separate the projection 9 from the body of the block for a purpose presently to be set forth.

The block 3 is also cut away centrally to receive a block of the insulating material l5 which has its face flush with the face 5. Secured to one end of the block l5, as by a screw I1, is one end of a plate l9 which may be made of copper, for example, and constitutes the stationary electrode of the capacitor. The movable electrode 2| is constituted by a relatively narrow, thin, flexible strip of nickel-steel alloy or any other suitable material, having a thickness of about 3 mils and a width of about 5 2 inch. The strip 2| extends across the lower part of the stationary electrode l9 and has its ends bent over the lugs or projections I and 9 to which they are secured, whereby the electrode 2| is anchored in place. By adjusting the screw I3, it is obvious that the tension of the electrode 2| may be varied, and therefore its resonance, or natural period of vibration, controlled at will. The projections I and 9 extend sufliciently beyond the stationary electrode iii to provide an air gap 23 between the electrodes i9 and 2|, wherebythe two electrodes constitute a capacitor. If desired, any other suitable dielectric material may be interposed between the electrodes I9 and 2| instead of air, or, when they are spaced from each other by an air gap, they may each be coated with a thin layer of some suitable dielectric material, such as zinc chromate. The normal width of the air gap 23 is of the order of three or four mils. However, a set screw 25, which is threadedly received in the insulating block 15 and the end of which bears against the lower end ofthe plate or stationary electrode i9, may be adjusted to vary the width of the air gap so as to control the sensitivity of the pick-up.

Secured to the lower edge 2|a of the movable electrode 2| at a point substantially midway between its ends is a needle 21 which is adapted to cooperate with the grooves of a phonograph record. The needle 21 has its major portion extending in a plane substantially parallel to that of the electrode 2| and terminates in a record engaging tiplla which may be of sapphire or the like for long wear. portion of the needle is rigid torsionally and is Preferably, the major wire or the like having a diameter of the order of 10 or 12 mils and having a length of about a to $43", its upwardly extending shank 21b being the portion by which it is secured to the electrode 2 I ,-asby solder 29 or the like.

'When the needle tip 21a tracks the groove of a record of the laterally undulating type, the groove will cause the needle to move correspondingly, and since it is rigid in torsion, it will cause the flexible electrode 2| to move toward and away from the stationary electrode IE! to thereby vary the capacity of the capacitor. It' is desirable to confine the movement of the movable electrode 2| to a region substantially in the vicinity of the needle 21, such as the region bounded approximately by the dotted line A and the lower edge 2|a of the electrode 2|, since this will prevent reflections of vibrational movements of the flexible electrode 2| between its opposed, free edges 2m and 2|b. For this purpose, the edge 2|b may be made much stiffer than the lower ed e 2|a by bending a marginal portion thereof adjacent the edge 2") out of its plane to provide a stiffening flange 2 lo in a plane substantially normal to the plane of the electrode 2|. If desired, a block of damping material 3| may be secured to the block 3 and the flange 2|c, as shown in Fig. 1, to clamp the vibration of the upper portion of the movable electrode 2|;

A pickup device such as that described above may be employed to control the frequency of any tuned circuit and finds its particular application in modulating an oscillator in a phonograph reproducing circuit. By way of example, the pickup device, as shown in Fig. 9, is connected with such an oscillator which comprises a suitable oscillator tube 33 provided with an oscillator tuning-inductance 35, the pickup capacitance being shunted across the inductance 35 and connected therewith through a shielded cable which may be constituted, for example, by the grounded pickup arm I within which is a conductor 31 connected to the stationary electrode l9. The capacity of the shielded cable should be relatively low with respect to that of the pickup |92|, arid it may be maintainedconstant by passing the conductor 31 through'a plurality of spacers 39 of damping material such as printers roll, Glyptal, Du Pont Viscaloid, etc., interposed between the conductor 31 and the pickup arm I. The output circuit 4| of the oscillator tube 33 is provided with a tuned circuit 43 which is tuned off resonance with respect to the oscillation steady state-or mid-frequency. The'variation of the,

capacity at the pick-up will cause the oscillation frequency to vary above and below the normal frequency, that is, the mid-frequency, thereby resulting in a frequency modulated signal which is delivered to a suitable output circuit and may be utilized in any suitable mannenas to operate a loudspeaker or the like (not shown). This type of circuit is more particularly disclosed and claimed in my copending application, Serial No. 459,375, filed September 23, 1942, and assigned to Radio Corporation of America.

In Figs. 3 to 8, inclusive, I have shown a modification of my invention wherein the supporting block 3 is constituted by an annular member which is removably carried by a head 45 to which of set screws 41. The head 45 is preferably secured to the pickup arm I by means of a pair of leaf springs 49 of phosphor bronze. or the like, which are secured to and extend from the head 45 in parallel relation. Thesprings 49 straddle the adJacent end of the pickup arm I and their opposite ends are secured to a pair of blocks 50 which are carried by the pickup arm. Preferably, although not necessarily, a pair of strips or blocks of damping material which may be of the same nature as the damping blocks 39 above described, are secured to the springs 49 by a suitable adhesive 53. The arm I is pivotally mounted on a horizontal pivot 55 which is formed on the upper end of the yok 51 having a downwardly extending, vertical pin or post 59 received in a standard 6!. Thus, the arm I and its translating device are capable of movement both in horizontal and vertical directions relative to the record.

The curve X of Fig. 10 shows what the response of the system would be if the head 45 were coupled rigidly to the pickup arm I. When the springs 49 alone are interposed betweenthe pickup head 45 and the arm I, the resonance of the system becomes that represented by the curve Y, from which it will be seen that there is a fairly sharp peak at about 60 cycles. By providing a damping strip 5| on each of the resonance of the system is changed to that shown by the curve Z, from which it will be noted that springs 49, the u there is a smaller peak at about 80 cycles, and

that at the extreme, low frequency end, the response drops way down.

The insulating block I5 is made substantially semi-cylindrical in the form of my invention shown in Figs. 3 to 8 and it is recessed slightly to receive the stationary electrode l 9. The set screw 25 in this modification extends down through the top of the insulating block I 5, as clearly shown in Figs. 5 to 8, for the purpose of enabling adjustment of the air gap 23. The annular block 3 is formed with a groove 63 on its bottom surface, as clearly shown in Figs. 6 and 7, and the movable electrode 2| is secured to the block 3 within the groove 63, as best shown in Fig. 7. The block 3 in this modification is also formed with a radial slot 65 corresponding to the slot ll of the first described modification of my invention, the screw l3 again serving to place the movable electrode 2| under more or less tension by expanding the annular block, or increasing its diameter slightly.

Preferably, the movable electrode 2| of Figs. 3 to 8 is formed of a very narrow, thin, strip of medium-hard phosphor bronze or any other suitable material, being. in fact, even narrower and thinner than the corresponding strip of Figs. 1 and 2, and again having its free, opposed edges 2 la and 2 lb extending across the stationary electrode I9. In this modification of my invention, the strip 2| may have a thickness of about 1 /2 mils and a width of about 1 6 inch.. The purpose of making the electrode 2| so narrow is to make overlapping portions of the two electrodes as small as possible consistent with the desired results. The needle 21 of this form of my invention extends entirely across the strip 2| and terminates, as above, in the needle tip 21a beyond the lower edge am of the movable electrode. The other end of the needle 21 extends beyond the upper edge Nb of the movable electrode and terminates in a relatively long shank 2111 which is secured to an anchoring block 61 held in place on the annular supporting block 3, as by a screw 5 69, best shown in Fig. 8. This arrangement, like the flange 2|c of Figs. 1 and 2, confines the upper position illustrated by the dotted lines of Fig. 8,

pivoting substantially about the adjacent, lower edge of the block 61 as a center. In such movement, it is obvious that the lower edge of the electrode 2| must move a greater distance than a the upper edge 2") thereof. Furthermore, since the strip 2| is anchored at its ends, only substantially the mid-portion thereof in the region where the needle 21 is secured thereto (that is, the region bounded substantially by the edges 2 la and 2H) and the dotted linesA-A) will vibrate to any appreciable extent and sufficient to cause an appreciable change in capacity of the capacitor unit. The operation of this form of my invention is precisely like that of the first described form, but has a response up to between 25,000 and 30,000 cycles, whereas the modification of Figs. 1 and 2 has a response of only up to about 10,000 to 12,000 cycles.

Although I have shown and described but two embodiments of my invention it will be apparent to those skilled in the art that many other modifications thereof, as well as changes in those described, are possible without departing from the spirit of the invention. Therefore, I do not wish to be limited except insofar as is made necessary by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. A phonograph record signal translating device comprising a pair of cooperating electrodes spaced from each other by a dielectric and constituting a capacitor, a needle carried by one of said electrodes and having a free end adapted to cooperate with a record, said needle being unconfined for free movement between its said free end and its point of attachment to said one electrode, said last named electrode-being mounted for movement relative to the other of said electrodes in response to movements imparted to said needle by the record whereby to vary the capacitance of saidcapacitor, means confining the movement of said movable electrode substantially to a region thereof in the vicinity of said needle, and means for placing said movable electrode under more or less' tension whereby to vary the natural period thereof.

2. A phonograph record signal translating device comprising a pair of cooperating electrodes space from each other by a dielectric and constituting a capacitor, one of said electrodes comprising a thin, flexible member mounted for movement relative to the other of said electrodes, a needle carried by said first named electrodeand having a free end adapted to cooperate with a record to vibrate said'first named electrode in accordance with movements imparted. thereto by the record and thereby to correspondingly vary the capacitance of said capacitor, said needle being unconfined for free movement between its said free end and its point of attachment to said movable electrode, means for confining the vibratory movement of said first named electrode substantially to a region thereof in the vicinity of said needle, and means for placing said movable electrode under more or less tension whereby to vary the natural period thereof.

3. A phonograph record signal translating device -comprising a pair of cooperating electrodes spaced from each other by a dielectric and constituting a capacitor, one of said electrodes comprising a thin, flexible member mounted for movement relative to the other of said electrodes, a needle carried by said first named electrode adapted to cooperate with a record to vibrate said first named electrode in accordance with movements imparted thereto by the record and thereby to correspondingly vary the capacitance of said capacitor, and means comprising a portion of said first named electrode for confining the vibratory movement thereof substantially to a region in the vicinity of said needle.

4. A phonograph record signal translating device comprising a relatively fixed and a relatively movable electrode, said electrodes being spaced from each other by a dielectric and constituting a capacitor, said movable electrode comprising a thin, flexible member including a pair of opposed edges, a needle carried by said movable electrode adjacent one of said edges, said needle being adapted to cooperate witha record to vibrate said first named electrode in accordance with movements imparted thereto by the record and thereby to correspondingly vary the capacitance of said capacitor, and means for stiffening the other of said edges whereby to render said movable electrode more freely movable adjacent its needle carrying edge than along said other edge.

5. A phonograph record signal translating device comprising a relatively fixed and a relatively movable electrode, said electrodes [being spaced from each other by a dielectric and con stituting a capacitor, said movable electrode comprising athin, flexible member including a pair of opposed edges, a needle carried by said movable electrode adjacent one of said edges, said needle being adapted to cooperate with a record to vibrate said first named electrode in accordance with movements imparted thereto by the record and thereby to correspondingly vary the capacitance of said capacitor, and means formed integrally with said movable electrode along the other of its said edges for stiffening said other edge whereby to render said movable electrode more freely movable adjacent its needle carrying edge than along said other edge.

6. A phonograph record signal translating device comprising a relatively fixed and a relatively movable electrode, said electrodes being spaced material out of its plane along a marginal portion adjacent said other edge.

8. A phonograph record signal translating device comprising a pair of cooperating electrodes spaced from each other by a dielectric and constituting a capacitor, one of said electrodes comprising a thin, flexible member mounted for movement relative to the other of said electrodes and including a pair of opposed, free edges, a needle carried by said first named electrode adapted to cooperate with a record to vibrate said first named electrode in accordance with movements imparted thereto by the record and thereby to correspondingly vary the capacitance of said capacitor, andmeans for s0 confining the movement of said movable electrode in response to said needle that one of its said edges will move to a greater extent than the other of its said edges.

9. A phonograph record signal translating device comprising a pair of cooperating electrodes spaced from each other by .a dielectric and constituting a capacitor, one of 'said electrodes comprising a thin, narrow, flexible strip mounted for.

movement relative to the other of said electrodes and including a pair of opposed, free edges, a needle carried by said movable electrode adapted I to cooperate with a record to vibrate said movable from each other by a dielectric and constitut n a capacitor, said movable electrode comprising a thin, flexible member including a pair of opposed edges, a needle carried by said movable electrode adjacent one of said edges, said needle being adapted to cooperate with a record to vibrate sa d first named electrode in accordance with movements imparted thereto by the recordand thereby to correspondingly vary the capacitance of said capacitor, and a flange on said movable electrode along the other of its said edges for stiffening said other edge whereby to render said electrode more freely movable adjacent its needle carrying edge than along said flanged edge.

'7. The invention set forth in cla m 6 characterized in that said movable electrode is formed of flat, sheet material, and characterized further in that said flange is formed by bending said electrode in accordance with movements imparted thereto by the record and thereby to correspondingly vary the capacitance of said capacitor, said needle extending across said movable electrode beyond said free edges thereof and terminating in a shank beyond one of said edges, and means anchoring said shank whereby said last named edge is confined against movement to a greater extent than the other of said edges in response to movement of said needle.

10. In a phonograph record signal translating device, the combination of a supporting member, a pair of cooperating electrodes carried by said member and having an air gap therebetween whereby to constitute a capacitor, one of said electrodes comprising a stationary plate and the other of said electrodes comprising a flexible strip movably mounted on said supporting member for movement toward and away from said stationary electrode and having a pair of opp0sed, free edges, a needle carried by said movable electrode for cooperation with a record to vibrate said movable electrode relative to said stationary electrode in accordance with movements imparted thereto by the record and thereby to correspondingly vary the capacitance of said capacitor, and

said needle is secured to said strip substantially mid-way between its ends.

12. The invention set forth in claim 10 characterizedby the addition ofmeans on said supporting member for placing said strip under more or less tension whereby to vary the natural period thereof.

13. The invention set forth in claim 10 characterized by the addition of means on said supporting member for adjusting the position of said plate electrode whereby to gap between said electrodes.

vary the normal air 14. The invention set forth in-claim 10 characterized in that each of said electrodes is coated with a dielectric material.

15. The invention set forth in claim 10 characterized in that said confining means is constituted by a flange formed on said strip along a marginal portion adjacent one of its edges.

16. The invention set forth in claim 10 characterized in that said needle extends across said strip beyond its said opposed edges, said needle terminating in a shank beyond one of said edges, and characterized further in that said confining means is constituted by an anchoring member on said supporting member to which said needle shank is secured.

CHESTER M. SINNETT.

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