US2436946A - Capacity-type phonograph pickup - Google Patents

Description

March 2 1948. B. TATRO CAPACITY-TYPE PHONOGRAPH PICKUP Filed April 10, 1941 2 Sheets-Sheet l We a w [a m wm INVENTOR.

75 E 60145 Q4/ 279 vdfind fwzrcll March 2, 1948. F. a. TATRO CAPACITY-TYPE PHONOGRAPH PICKUP Filed April 10, 1941 2 Sheets-Sheet 2 UELZI'OR. JrazaZ-B lat-1'0 45 T0 our-par Patented Mar. 2, 1948 CAPACITY-TYPE PHONOGRAPH PICKUP Frank B. Tatro, Chicago, 111., assignor, by mesne Ialslsignments, to Virgil A. Hamilton, Chicago,

Application April 10, 1941, Serial No. 387,792

2 Claims. 1

This invention relates to a radio-phonograph and more particularly to the phonographic pickups and the circuits connecting such pick-ups to the radio or electronic amplifying and reprO- ducing circuits.

It is an object of my invention to provide an improved apparatus for reproducing sound from phonograph records or the like.

A further object of the invention is to provide a phonograph record pick-up having a higher signal to noise ratio and an improved frequency response to the higher audio frequencies and provide suitable amplifying circuits controlled by said pick-up.

A further object of the invention is to provide an improved radio-phonograph and an improved phonograph pick-up which may be manufactured at materially less cost, but which at the same time possesses greater fidelity and quality in the reproduction of all frequencies within the audio range.

A more specific object of the invention is to provide in a radio-phonograph or a phonograph, circuits connecting the phonographic pick-up to a local oscillator of a superheterodyne radio receiving or reproducing circuit whereby impedance, i. e., capacity varying phonographic pick-ups may be employed to effect a frequency or amplitude modulation of an intermediate frequency voltage which is then fed to a detector and an audio amplifier.

Other and further objects and advantages of the invention will be apparent from the following description when taken in connection with the accompanyin drawings, wherein:

Figure 1 is a fragmentary view in perspective illustrating a phonographic tone arm carrying a capacity varying pick-up forming part of the present invention;

Figure 2 is an enlarged fragmentary view in section taken substantially along the line 2-2 of Figure 1;

Figure 3 is an enlarged end view of the capacity pick-up of Figures 1 and 2;

Figure 4 is a schematic diagram of a superheterodyne radio receiver circuit and its connection to the capacity pick-up of Figures 1 to 3;

Figure 5 is a schematic diagram illustrating the manner of connection of a variable resistance pick-up to the local oscillator of a superheterodyne receiver;

Figure 6 is a view of a rheostat which may be used in the resistance pick-up schematically illustrated in Figure 5;

Figure 7 is a schematic circuit diagram showing the connection of a variable inductance pickup to a local oscillator which may be used remotely from a reproducing radio receiver or which may be part of the radio receiver;

Figure 8 is a view in vertical section through a variable inductance pick-up which may be used with the circuit of Figure 7;

Figure 9 is a view in vertical section of another form of variable inductance pick-up which may be used with the circuit of Figure '7;

Figure 10 is a schematic drawing of the connection of the windings of the single tapped coil forming the inductive pick-up of Figure 9;

Figure 11 is a view in vertical section of another form of inductive pick-up which may be used with the circuit of Figure 7;

Figure 12 is a schematic drawing of the interconection of the coils of the pick-up shown in Figure 11;

Figure 13 is a schematic diagram illustrating the connection of a variable inductance pick-up to a combined local oscillator-converter of a superheterodyne radio receiver;

Figure 14 is a schematic diagram illustrating the connection of a variable capacity pick-up to a local oscillator for effecting amplitude modulation of the local oscillations; and

Figure 15 is a schematic diagram similar to Figure 14, but showing the connection of a variable resistance pick-up to the local oscillator.

Phonographic pick-ups in commercial use are relatively expensive to manufacture and have a limited frequency response. They generally emphasize the lower audio range and have a tendency to attenuate the frequencies in the band from 2000 to 5000 cycles. This is the ordinary scratch or noise range of records played at the usual speed of 33 /3 or 78 R. P. M. Consequently such pickups have a relatively low signal to noise ratio and it is therefore necessary in reproducing the range of frequencies from 2000 to 5000 cycles to further attenuate the signals within this range in order to eliminate noise frequencies or to amplify and reproduce the noise frequencies along with these lower audio frequencies. This results either in the elimination of the desired audio frequencies within this range, or in the unwanted reproduction of the noise frequencies.

Applicant has found that this undesirable characteristic of attenuation of the lower audio frequencies is characteristic of all pick-ups which generate voltages from the mechanical vibrations of a needle traversing a record groove.

Applicant has also found that it is impossible to reproduce these generated audio-frequency voltages with fidelity by means of direct amplification. of the audio-frequency voltages. In seeking to overcome these difficulties of present phonographic pick-ups and reproducing circuits, applicant has found that by means of the invention, if an impedance varying or voltage varying pick-up, as distinguished from a voltage generating pick-up, is used to convert the undulations of the sound record into electrical variations and such variations are used to effect the frequency or amplitude modulations of a locally generated oscillation such as produced in -'a super-heterodyne receiver, the fidelity of response to all audiofrequeneies is greatly improved and audio or acoustical frequencies within the scratch or noise range of frequencies may be reproduced with clarity, and further that all this may be accomplished by means of devices and circuits which may be manufactured at a cost less than the cost of the present type of pick-ups and reproducing circuits.

' As shown in Figure 1, the tone arm 2 which may be of conventional construction and mounted in the usual manner, carries at its "outer free end a capacity pick=up 4 which may comprise a block 6 of suitable insulating material secured to the tone arm in any desired manner as, for example, by means of the bracket 8 fixed to the tone arm and screws or bolts' H1 passing through the block 6 and received in the bracket 8. The tone arm 2 is hollow as is conventional, and the pick-up 4 is housed within the arm and the necessary leads pass through the hollow arm from the free end to the opposite'end and pass fr'ointhe arm adjacent to or through the pin or pivot on which the arm is mounted. The capacity pick-up 4 comprises in addition to the block 6 a plurality "of thin'metal plates 12 separated by layers 14 of dielectric material which may comprise strips of relatively soft rubber or may comprise coatings or strips of any suitable dielectric material. The plates I2 are made of such material and of such thickness or mounted in such manner that they may be readi1ymoved"orfiexed toward and from each other by means of a needle as 16 secured to -the outer plate 12, the needle traversing the sound grooves of the record "the record 18 shown in Figure '1. I

The needle 16 ma be soldered to the outer plate 12, or it may be received in a suitable light needle holder mounted on this plate. The clamping screw 28 passes through enlarged central openings in the plates i2 and is receivedin a nut '22 mounted in the block 6. One or more strips or washers '25 of insulating material such as soft rubber insulate the head of the screw 20 from the outer plate 12. The strips [4 which may be of a plastic cushioning material or sponge rubber cushion the plates and minimize resonant frequencies that the assembly may have so that'the assembly will not resonate mechanically at a frequency within the audio range. The number "of platesythe dimensions of plates, the thickness and kind of insulating or dielectric material used between the plates, and the pressure applied to the plates with the clamping screw all determine the sensitivity and frequency of response of the pick-up 4.

I The pick-up device being sensitive to side-toside, or lateral, movements and relatively insensitive to up and down movements, capacity variations are produced only by the lateral undulations of the record grooves, or side-to-side move- .inents of the'stylus.

O'ne lead 26' (Figure 4) "from the pick-up '4 may e be grounded while the other and shielded lead 28 extends to the contact point 31) of a switch 32 by which it may be connected to the superheterodyne radio receiver 34 of a combined radiophonograph. The switch 32 connects the phonograph lead 28 to the circuits of the local oscillator or mixer tube 36. The tube 36 comprises a plate 38, a screen grid '40, an oscillator anode 42, an oscillator grid 44, and a control grid '56. The out-put or plate circuit of the tube 36 is coupled "to the in-put of an intermediate frequency ampli- 'fier tube "48 by means of the doubly tuned transformer coupling 50 tuned to the intermediate frequency. The primary 52 of this transformer is tuned by the condenser 54 and the secondary 56 is tuned by the condenser 58. The plate 38 is connected to the positive direct current supply terminal 60 through the primary 52 and the wire '62. The screen grid 40 is connected to this terminal through the resistance 64 and the oscillator anode 4? is connected to this same terminal through the resistor -66. V

The cathode 58 is connected to ground through the 'seli biasing resistor 10 and the by-pass condenser 12, The screen grid is maintained at ground potential with respect to radio frequency Voltages through the condenser 14. The filament (6 for the cathode maybe energized from the "ordinary low Voltage filament circuit of the radio receiver "supp-1y circuit. The oscillator an* ode 42 is coupl'edto the "grid "44 whenthe ganged switches '32 and ltare inthe position shown in Figure "4 through the wire '83, the blocking condenser 82, the wiper 84 of the switch 78, the switch-contact 86,'the wire 88, the feed-back couplingtransformerfl, the wire 94, the wiper 96 of the switch 32, the wire 98, the grid condenser 1'00 and the wire I 02. The grid condenser we is shunted by the resistor I04 and the tuning condenser 106 as is conventional.

The control grid 46 is connected by the wire H18 'toth'e radio'frequency coils and band switch of 'the radio "frequency amplifying part of the radio receiver, the band switch which is conventional and not shown, being ganged to the switches 32 'a'n'd'l8 so that with the switches 32 and I8 inthe position shown in Figure 4 and'the R. F. band switch in a corresponding setting, the local oscillator or 'm'ixer tube 36 will be set to oscillate at the proper frequency to produce in the output circuit of the tube 36 the desired in- "termeuiate frequency signals. With the switches 32 and '84 in position bbfinectfii'g the Wipers 95 and 84 to the short wave contacts H0 and H2, the oscillator anode is coupled to the g'rid'through "the short wave feed-back coupling transformer IN, the secondary of this short wave coupling transformer being connected "to the switch point H0 by the wire H6 and the primary connected to the switch fpoi'nt ll'2 by the wire 'I I3. With the wi er 96 in position to engage the contact 30, the phonograph lead 28 is connected by the wiper 96 to the grid lead '98 and to the contact point I20 which is connected by the wire 1'22 and the wire M to the secondary "of the broadcast frequency transformer '92. The wiper '84 of the switch 18 "at this time through the contact 124 and the wires T26 and 88 connects the primary of this broadcast frequency transformer '92 "to the oscillator anode wire through'the blocking condenser 82. The mechanical variatlonst'rans- "mitted by the needle i 6 from the lateral undulations of the record grooves produce capacity variations across the output terminals of the capacity pick-up and in the circuit oi'the 'B. 0; osculater coil across the secondary of the transformer 92 and thetuning condenser I06.

The capacity of the pick-up 4 and/or the lead' 28 together with distributed circuit capacity and condenser I06 tune the broadcast oscillator-coil;

to a frequency within the band width of the in termediate frequency and variations in the ca:

pacity of the pick-up due to the lateral undula-g tions of the record groove effect a. frequency mod ulation in the output circuit of the tube 36. The; doubly tuned resonant coupling circuits of the intermediate frequency amplifier stage or tube. 48 are used to demodulate this frequency modu-;-

The phonograph signals are therefore further amplified by the I. F. stage 48 and are later detected in a diode-detector fed from the doubly tuned transformer coupling I28 and amplified in a subsequent audio amplifier fed from the diode detector. It will be evident that the capacity pick-up 4 effects the frequency of the locally generated oscillations, for this capacity is part of the oscillator tank circuit.

Another method of varying the effective impedance and the resultant frequency of a local oscillator circuit is by means of a variable resistor pick-up as illustrated in Figure 6 by connecting such pick-up and a series condenser in parallel with-the oscillator tank circuit capacity as shown in Figure 5. As shown in Figure 6, any suitable conventional small rheostat may have on its resistance adjusting shaft I30 the record traversing needle I6 so that side-to-side or lateral motion of the needle I6 caused by lateral undulations, in the record groove effect angular adjustments of the shaft I30 and consequently variations in the resistance of the rheostat I32. One terminal of such resistance pick-up I34 is connected to ground while the other terminal is connected to a condenser I36 which may be mounted form part of the pick-up I34.

A wire I38 connects the other side of the condenser I36 tothe ungrounded side of the tuningcondenser I40 of the oscillator tank circuit, which tank circuit includes the secondary of the transformer I 42, the primary of this trans former being grounded at one side and connected by the wire I44 in which is interposed the blocking condenser I46 to the plate of the local oscil-. lator tube I48. The mechanical vibrations of the needle caused by the lateral undulations of the record groove cause variations in the resistance of the rheostat I32. This produces a frequency modulated signal which may be amplified and detected as previously described.

Another method of varying the effective impedance in the local oscillator circuit is by means of a variable inductance pick-up as shown in Figures 8, 9, and 11 connected in a circuit as shown in Figures 7 or 13.

As shown in Figure 8, the variable inductance pick-up I50 may comprise a pair of spaced diaphragms I52 and I54 appropriately mounted in mounting plates I56 and I58. The diaphragms I52 and I 54 fioatingly support a shaft I60, the shaft extending beyond one of the diaphragms as the diaphragm I52, and. having mounted on,

be connected to a local oscillator in a phono-.

or secured to its extending end the record tra=. versing needle IS. The shaft I60 carries a core piece or slug I62 and is positioned within the and-fro movement of the core piece or slug I62 effects corresponding variations in the inductance of the secondary winding. The pick-up I50 may graph. remote from the radio receiver and the output of this phonograph fed over power lines to a local broadcast receiver, or the local oscillater to which it is connected may be used as the oscillator section of a converter tube formoscillator circuit embodying the oscillator tube:

ing part of a superheterodyne receiver. such circuit with which the pick-up may be used is schematically illustrated in Figure 7, wherein it is shown as coupled to a local, electron-coupled I10. Thevtube I10 may have its plate I12 and its screen grid I14 connected to the positive direct current terminal I16 in the usual manner as by the resistors I18 and I and the shunting condenser I82. The control grid I84 of the oscillator tube I10 may be connected to the usual grid condenser I86 which is shunted by the tuning condenser I88 and the grid resistor I90, the common connection of the tuning condenser I88 and the grid resistor I90 being grounded. The.

wire I92 of a two-wire shielded cable I94 con-. meets the terminal A-2 of the secondary I68 of the inductive pick-up I56 to the common con-' nection of the grid condenser I86 and the tun-T ingcondenser I88.

mon terminal A3 of the primary and secondary windings I66 and I68 to the cathode I98 of the local oscillating tube I10. The other terminal AI of the pick-up is connected to the shield of the two-Wire shielded cable I94, which is grounded as at 200. The out-put of the tube I10 may.

be fed through the coupling or blocking condenser 202 and may be fed over a power line into a local broadcast receiver or this electron-coupled oscillator circuit may be used as the oscillator sectionof a converter tube forming part of the usual superheterodyne radio receiver and tuned to the intermediate frequency of the receiver Where the signal is further amplified and detected by the usual detector in such receiver.

In the form shown in Figure 9, the inductive pick-up 204 may comprise a single coil winding 206 having the parts 208 and 2I0 thereof (Figure 10) interconnected as shown in Figure 10, and to the terminals AI, A2, and A3 as shown. The coil 206 may be mounted in any convenient manner as by means of the winding form or cylinder 2I2 upon the mounting support 2I4 to which there is secured at one side of the coil a diaphragm 2I6, the diaphragm being fastened along one edge'and free along its opposite edge.

- The diaphragm 2"; has secured at its free edge in any suitable manner the needle I6. The diaphragm also carries a core piece or slug 2I8 positioned to move into and out of the winding form or cylinder 2I2 in order to vary the inductance of the coil 206. Thus as the needle vibrates due to the lateral undulations in the record groove being traversed, the inductance of the coil 206 is proportionately varied. In. the form shownin Figure 11, the inductive pickup comprises a primary coil 222 and a sec One The second wire I86 of thetwo-Wire shielded cable I94 connects the com-.

advantages, the form herein described being a preferred embodiment for the purpose of illustrating the invention.

The invention is hereby claimed as follows:

1. A sound record pick-up comprising a supporting bracket of insulating material, a condenser including a stack of flexible, metal plates with dielectric material therebetween, alternate plates having wings at opposite ends, said bracket and wings being slidably interlocked to yieldably mount said plates on said bracket and a record traversing stylus secured to one of said plates to effect approaching and recessive yielding movements of the plates.

2. A sound record pick-up comprising a supporting plate of insulating material, a condenser including a stack of flexible, metal plates with dielectric material therebetween, alternate metal plates having wings at opposite ends, said insulating plate having spaced openings therein, said wings being slidably interlocked in said openings to yieldably mount said metal plates on said insulating plate, a record traversing stylus secured to one of said metal plates to effect approaching and recessive yielding movements of said plates,

an adjustable clamping member passing through 10 said metal plates, secured to said insulating plate and bearing upon the outer one of said metal plates for adjustment to determine the normal capacity and also the sensitivity of the pick-up.

FRANK B. TA'IRO.

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

UNITED STATES PATENTS Number Name Date 1,544,001 Groenbaum June 30, 1925 1,557,664 Davenport Oct, 10, 1925 1,689,564 Thorington Oct. 30, 1928 1,702,438 High Feb. 19, 1929 1,732,393 Andrewes Oct. 22, 1929 1,754,293 Weinberger Apr. 15, 1930 1,988,609 Reeves Jan. 22, 1935 2,047,653 Stone July 14, 1936 2,097,874 Farnham Nov. 2, 1937 2,304,633 Farnsworth Dec. 8, 1942 FOREIGN PATENTS Number Country Date 373,973 Great Britain Dec. 31, 1932

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