US2393184A - Tone control - Google Patents

Description

Jan. 15,1946.

E. B; P sSow TONE CONTROL Filed Oct. 14, 1944 INVEINTOR EDWARD B. PAYSSOW BNM HIS ATTORNEY Patent'ed Jan. 15, 1946 'rorm ooN'raoL Edward B. Passow, Park mm, m, assignor to Zenith Radio Corporation,

linois a corporation of Il- Application October 14, 1944, Serial No. 558,723

QCLaims.

This invention relates to tone control arrangemcntsof the type particularly useful in hearing aid or other portable hearing apparatus.

In hearing aid or other small portable hearing apparatus it is advantageous to have incorporated in such apparatus a single control element readily movable by the wearer to one of a plurality of operating positions corresponding to the particular character of tone desired from such apparatus. This advantage in a tone control arrangement should be obtained by using as few electrical and mechanical elements as possible; otherwise, the cost of the component parts is expensive, the apparatus is needlesly heavy and bulky and it may not be so readily carried or concealed on the person of the user.

It is, therefore, an object of the present invention to provide an improved tone. control arrangement which is inexpensive to'manufacture, readily operable by the user and which does not add materially to the weight or bulkiness of the apparatus with which it co-acts to produce difl'erent characters of tone. f

A further object of the present invention is to provide an improved inexpensive switch construction having a minimum number of parts and al-' tliming; mass production in a relatively short Still another object of the present invention is to provide a simple improved tone control arrangement especially useful in small portable hearing apparatus.

The features of the present invention which are believed to be novel are setforthwith particularlty in the appended claims. The present invention itself, both as to'its organization and manner of operation, together with further objects and advantages thereof may best be understood by reierence to the following description taken in connection with the accompanying drawing in which: I

In Fig. 1 there is illustratedan improved hearing aid circuit, incorporating a high gain amplifler including electron discharge device I and a second amplifier including electron discharge device 2. The two amplifiers successively amplify signals from microphone 3 and impress such amplified signals on sound reproducing device 4 in linearly amplified form. A switch 5, described in detail hereinafter, for effecting tone control is interconnected with device I.

Sound waves impinging on microphone 3 are transformed into electrical variations in the main control electrode circuit of discharge device i. The microphone 3 is preferably of the piezo-electric typeas illustrated. The device I greatly amplifies electrical variations producedby microphone 3 and the amplified electrical variations are further amplified by electron discharge device 2 before being applied to the sound reprogo ducing device 4.

Fig. 1 shows an improved hearing aid circuit incorporating an improved tone control arrangement in accordance with the present invention;

l'flgs. 2 through 4 show certain elements of the switch shown in Fig. 5 in different operating positions thereof; M

Fig. 5 shows a sectional view taken substantially on line ll1of Fig. 1; I

Fig. 6 shows, in enlarged form, the other side of the switch construction shown'in Pig. 1;

Figs. 7 and a show respectively plan and eleva tional views of a portion of a portable case having incorporated therein a tone control in accord'ance with the present invention. 1

Microphone 3, which produces electrical variations in response to sound waves impinging thereon, is connected between the main control grid i and the grounded filamentary cathode I of discharge device I; and a grid leak resistance 8 is connected in ,parallel circuit relationship with microphone I to bypass continuous current flowing around microphone 3 between control grid I and the cathode I. Substantially no grid current flows through resistance I, because the grid 0 is at a negative potential with respect to the cathode 1, such negative bias potential being provided by connecting grid 8 through resistance 8 to the grounded negative terminal of voltage source 9 across which are connected the opposite terminals of the filamentary cathode I. It is to be understood, of course, that other conven' tional means may be used to establish a suitable continuous operating potential between grid 8 and cathode I and such means may be a battery or a voltage drop produced by space current flowing through discharge device I. Resistance l0,

-. much smaller than resistance I, is also connected in parallel to microphone I through switch 5 for a different purpose than resistance I as is described hereinafter.

Electron discharge device I is of the pentagrid type in commercial use and may, for example, be

. of the type commonly knownas the 1R5; The

185, but within the scope of the present inven-- tiolr any discharge device which performs equivalent functions is suitable. Large gainis realized when device I is connected in the manner hereinafter described and such large gain is substantially independent of signals applied between the main control grid 6 and cathode of discharge device I.

In general, device I is connected so as to be effectively two amplifiers in cascade with regeneration between the two amplifiers. In addition to the main control grid 6, discharge device It has what is termed a second control grid H, a suppressor grid l2 connected to the cathode l, a main anode l3, and a pair of screen electrodes I4 and i5 on opposite sides of the second control grid I Operating continuous potentials for device 1 are supplied from a voltage source It whose negative terminal is grounded and whose positive ter minal is connected to the main anode I: of discharge device i through a series circuit including adjustable voltage dropping resistance l7 and output coupling resistance ii. The electrodes it and 15 are cozmected together and are maintained positive with respect to the cathode by connection. to the positive terminal of voltage source l6 through the series circuit including voltage dropping resistance I! and coupling re sistance is. The continuous operating potential of the second control grid 1 i is stabilized connecting it to ground and the cathode I through resistance 20, which also serves as a coupling re sistance for audio frequency current as descrii: ii hereinafter.

When alternating current signals are impressed between the main control grid 8 and cathode 1 substantially all of the, alternating output voltage appears across output coupling resistance l8, a bypass capacitance II of low reactance being connected between the grounded cathode of discharge device I and the lower terminal of resistance is removed from the main anode l3. Potential variations'on electrodes H and i due to an alternating voltage applied between main control grid 8 and cathode I are impressed on the second control grid H through a coupling capacitance 22 connected between grids H and I! and grid ll.

Therefore, alternating voltages applied directly to control grid 6 and indirectly to control grid ll cause alternating output signals to appear across resistance 18, which output signals are then up plied to the grid circuit of another linearly am pliiying discharge device 2. Coupling capacitance 23 and input resistance 24 are connected in series and the series circuit formed thereby is connected in parallel circuit relationship to the series circuit formed by output coupling resistance l8 and low reactanoe bypass capacitance 2|. Capacitance 23 is of relatively low reactance and serves essentially as a means for blocking the flow or continuous current from source Is to resistance 24. The alternating voltage developed across resistance u through condenser 13 is applied between the first or control grid 28 and cathode 28 of discharge device 2 so as to control the space current therein, which current norrr iii fact that voltage sour is preferably of the n. J having its supncssor grid 00 connects to the cathode it; and with the voltage source ii connected between its screen grid ll and cathode 23 through a voltage dropping resistance a. The

screen grid II is maintained at constant potential in the presence of signals 01 irequency corresponding to audio frequency by means 01' low reactance bypass capacitance at which is connected between the screen grid II and cathode 28.

Alternating voltages developed across input resistance 24 are amplified linearly by discharge device 2, and appear across the secondary winding 34 of transformer 29 which is connected to impress those amplified voltages on the sound reproducing device 4 which is connected across the terminals of secondary winding 34.

The filamentary cathodes of discharge device I and 2 are preferably heated by current flowin therethrough, as shown in Fig. l, in such case the cathodes and 26' are connected in parallel circuit relationship to voltage source 9.

The circuit thus far described is especially useful as a hearing aid circuit and, because of the high gain obtained by the use of discharge device i, only two discharge devices requiring small space current are necessary for good performance, even though a tone control arrangement in accordance with the present invention is provided. Because of the high gain obtained from the use of discharge device I, a highly efficient and useful hearing aid circuit is provided which requires a small current drain from voltage source W 51. This is particularly true when, as in this instance, resistances H, I! and is are relatively large.

The volume of signals reproduced by speaker I may be controlled by adjusting volume control resistance H. An adjustment oi resistance ll causes no substantial non-linearity between the intensity of input signals applied to grid 5 and the intensity of signals developed across resist: ance (8 over a large range of input signals.

The tone of signals reproduced on sound reproducing device 4 may be controlled by connecting resistance [0 and, capacitance in the hearing aid circuit thus far described. In general, resistance I0 which may be connected in parallel circuit relationship to piezoelectric microphone 3 serves to reduce the intensity of low frequency signal components, and capacitance I! which may be connected between the electrode II and cathode 1 of discharge device I serves to reduce the intensity of high frequency signal components. For this purpose, switch 5 serves to connect the lead ID of resistance III to ground and alsoserves to connect the lead 31 o! condenser 35 to ground. Different types of tone may be produced corresponding to the four positions of the tone control switch member 88 shown in Figs. 1-4. That is, switch member or metallic short circuiting bar 38 having an inwardly disposed body portion 89 and an outwardly extending projecting body 0 is of such shape that in its clockwise movement, bar 8| assumes positions whereby: (1) as in Fig. l the capacitance ll alone is connected in the hearing aid circuit and high frequencies only are suppressed, and (2) as in Fig. 2 when pro U a. time is connected in the hearing aid circuit only 1 lead ll grounded causes noattenuation in ordinary sense of the word, but its function is to.

the

present a dlil'erent degree of mismatch as a function of frequency to the crystal microphone I whose equivalent circuit may be represented by a section including the cathode I, main control grid 6 and electrode it, which electrode operates as the anode of a conventional triode. The second amplifying stage operates as a pentode and includes control electrode ll, screen electrode i4, suppressor electrode l2 and anode II.

The overall gain of discharge device I is preferably'adjusted by adjusting the amount of regeneration in discharge device I. It is desirable to make the amount of regeneration such that linear operation of the stage including device I is assured consistent with as high gain as possible. For purposes of analysis, the two stages may be considered to be equivalent to two separate discharge devices, a triode and a pentode, connected in cascade, wherein the regeneration may be viewed as a negative resistance of the dynatron type connected across the anode load of the triode.

The regeneration which comes into being is believed to be due to negative transconductance from second control grid H to the screen electrodes I4 and I8.

This negative transconductance efiect is produced in accordance with the following constructions: the total cathode space current of device 1 is substantially independent of the voltage applied to the second control grid H, which controls the distribution of current between electrode It on one side and electrode it and anode II on the other side. Since the two electrodes II and it are connected together, substantially equal and opposite effects are produced on the electrode II and on electrode l4 and anode i3 by a change of the voltage on the second control grid ii. That is, if electrode ii is made more negative, more space current tends to ilow to 4 electrode I I and less to electrode I4 and anode I 3. But the decrease in current to elect'rode H, which shares its current with anode I3, is less than the increase in current to electrode I5. Therefore, the total current to electrodes l4 and It increases with a more negative potential on electrode .II and current to anode l3 decreases.

. Accordingly, the transconductance between sec- 0nd control grid H and anode I3 is positive, and

the transconductance between second. control grid ii and connected electrodes l4 and I5 is negative. When, as in the illustrated circuit, the

. current flowing to connected electrodes II and II stream in discharge device I regeneratively by voltage on electrode ii. That is, in Fig. 1, it 1 appears as though a negative resistance etlect,

which causes regeneration for signals of audio frequencies, occurs between connected electrodes I4 and i 5, second control grid II and the cathode I, considered as a group, since coupling condenser 22 is of low reactance for signals of audio frequency.

In the particular amplifier circuit shown in Fig. 1, when properly adjusted, the increase in triode gain in discharge device I due to regeneration is about 70%. It is possible, however. to increas the regenerationto such an extent that a gain of about 2000 is obtained in the triode section alone. This condition is not satisfactorily stable.

In general, any means that causes a change in transconductance between the control electrode II and anode I 3 maybe used to control negative transconductance between control grid H and connected electrodes 14 and I5 so that o the amount of regeneration in discharge device sistance l8. When anode resistance l8 is'de-I creased below a critical resistance, the transconductance between the control grid i I and anode l3 is increased so that device l breaks into oscillation, due to the corresponding increase in negative transconductance between control grid H and connected grids l4 and i5. The signal voltage developed across resistance i8 is, of course, equal to the signal current flowing therethrough, multiplied by the ohmic magnitude of resistance l8. By making resistance l8 high in magnitude the transconductance of the device is lowered but the voltage developed across resistance tends to remain constant.

Characteristics and operating features of device i are further set forth in the co-pending application of John G. Prentiss, filed October 4. 1943, Serial Number 504,958, and assigned to the same assignee as the present invention.

Tone control is produced by adjusting the position of the manually operated movable element II which is rotatably mounted on insulating support 42 by means of pin 43. (Fig. 5). Movable element ll has an integrally formed projection ll which extends out from the housing or hearing aid case 45 for convenient manipulation by the finger of an operator and. also has suitable indicia 46 for indicating to the operator the operating position of movable element 4|. Movable element ll may be held in any one of the four positions by means of a resilient finger 41, having one of its ends fastened to support member 42 by means of rivet 48 and its free end arranged to enter-into one of a series of four equally spaced notches 49 on the'periphery of rotatably mounted element 4|.

Rotationalmovement of element 4| is limited substantially to the angular distance corresponding to the overall spacing of the four notches by means of the heads of rivets 50 and I|,re'- spectively engaging the opposite sides of the walls defining aperture 52 in support member 42. Rivets 50 and Si not only serve to limit rotational movement of element 41 but also serve extends beyond the periphery of element H where such bar has a width corresponding substantially to the angular distance through which element 4| may be rotated. Bar 38 comprises an inwardly disposed body portion 39 and a projecting portion 40 which extends outwardly from the axis of element rotation so as to engage contact members 53 and/or 54 respectively, fixedly mounted On insulating support 42 by means of rivets 55 and 58. A third contact member 51 fixed on insulating support 42 by means of rivet 58 extends iurther inwardly than the other two contact members 53 and 54 so as to engage the body portion 59 of bar 38 in all positions of element 4!. Contact members 53, 54 and 51 are preferably equally spaced in that order at the periphery of element 4| with the overall distance from contact member 53 to contact member 51 being of the order of the permissible angular movement of element 4i and with contact member 51 extending further inwardly in a radial direction than the other two contact members 53 and 54 such that contact member 51 continuously engages bar portion 3! and contact members 53 and 54 engage only bar portion 40 when it is in predetermined positions determined by the position of resilient finger 41' in aparticular notch 49. Bar projection 40 has a width substantially equal to the spacing between contact members 53 and 54 and so disposed as to short circuit those members 53 and 54 in one predetermined position of .contact member 4| as shown in Fig. 2 and to engage respectively only one of the two contact members 53 and 54 in other predetermined positions of element 4| (Figs. 1 and 3). In the fourth predetermined position shown in Fig. 4 neither the contact member '53 nor the contact member Si is engaged by bar portion 40.

As shown in Fig. 1, contact member 53 is connected through lead 31 to one terminal or condenser 35, contact member 54 is connected through lead 36 to one terminal of resistance Hi, and contact member 58 is grounded so as to continuously maintain the short circuit bar 3! at ground potential for effecting the tone control previously described by manipulating control element 4|. 7

Control element H is rotatably mounted not only to be easily operated by the ringer oi the operator but also such as to be placed at the corner of a hearing aid case 115 where it is readily accessible to the operator and does not distract from the general appearance of the case. The case 45 is preferably made with rounded corners so as to reduce noises produced by rubbing of the operators garments on the housing. As shown in Fig. '7, even though the tone control element 4! is mounted at a corner of the housing, the element H is so shaped and so moved and positioned in its dirierent operating positions that the benefits of a rounded corner are obtained together with easily accessibie and easily operated tone control.

In Fig. 7, the edge 59 of the hearingaid case 45 serves to obscure certain indicia on control element 4! depending upon its particular position. The arrow engraved on the hearing aid case points to the particular predetermined position oi the tone control element 4! and the position 3 shown in 1 corresponds to the position of element 38 shown in Fig. 2.

While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may :be made without departing from this invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of this invention.

I claim:

1. In combination, a support, a movable element rotatably mounted on said support, means for limiting the rotatable movement of said element with respect to said support to a relatively small arc 01' a circle, said element having spaced notches therein along a length thereof corresponding to said are, three spaced insulated contact members mounted on said support and arranged along said arc of said circle, a metallic short circuiting bar carried on the periphery of said rotatable element and arranged to make contact with said contact members in diii'erent predetermined positions of said element, said her having a width corresponding to the length of said arc, resilient means mounted on said support and :biased into said notches for maintaining said movable element in any one of a plurality oi predetermined positions wherein said bar is positioned differently relative to said contact members, said bar having an inwardly disposed body portion and a projecting portion, said projecting portion extending outwardly from the axis of rotation of said element and having a width at least as great as the distance between two adjacent ones of said contact members, the other one of said contact members extending radially inwardly a distance sufficient to engage said body portion in all positions of said element, said notches having such spacing that in one position of said element said projecting portion engages only one of said two adjacent contact members, in a second predetermined position :both of said adjacent contact members are engaged by said projecting portion and in a third predetermined position only the other one of said adjacent contact members is engaged by said projecting portion.

2. In combination, a support, a movable element rotatably mounted on said support, said support having an aperture, said element having spaced notches therein along a length thereof, three spaced insulated contact members mounted on said support and arranged near the periphery of said element, a metallic short circuiting bar, means for fastening said bar on the periphcry of said rotatable element whereby said bar makes contact with said contact members in dii- Ierent predetermined positions of said element, said fastening means having a head thereon arranged to engage the walls defining said aperture of said support whereby the rotatable movement of said element with respect to said support is limited to a relatively small arc of a circle, said bar having a width corresponding to the length of said arc, resilient means mounted on said sup port and [biased into said notches for maintaining said movable element in any one of a plurality of predetermined positions wherein said bar is positioned relative to said members, said bar having an inwardly disposed bodyportion and a projecting portion, said projecting portion extending outwardly from the axis oi rotation of said element and having a width at least as great as the distance between two adjacent ones of said contact members, the other one of said contact members extending radially inwardly a distance sulficient to engage said body portion in all positions of said element, said notches having such spacing that in one position of said element said proiecting portion engages only one of said two adjacent contact members, in a' second predetermined position both of said adJacent contact members are engaged by said projecting portion and in a third predetermined position only the other one oi said adjacent contact members is engaged by said projecting portion.

3. In combination, an electron discharge, device having a first and second electrode, separate means including a control grid for providing in said device an electron discharge stream modulated in intensity at frequencies within a predetermined band of frequencies, said first electrode being so arranged with respect to said stream as to develop an alternating potential in response to the intensity modulation of said stream, said second electrode being arranged to aflect said electron stream in response to potentials ims pressed on said second electrode after said stream aflects said first electrode, means forimpressing substantially all of said alternating potential developed by said stream on said first electrode upon said second electrode, whereby potentials impressed on said second electrode after being developed on said first electrode increase the efl'ect on said first electrode of intensity modulation of the electron stream beyond the effect which would exist without the impression of such alternating potential upon said second electrode, an electroacoustical transducer connected to said control grid, a first frequency selective impedance element for transferring selectively certain electrode, means for impressing substantially all of said alternating potential developed by said stream on said first electrode upon said second electrode, whereby potentials impressed on such '.second electrode after being developed on said frequency components of signals from-the transducer to said control grid, a second impedance element for altering the degree to which signals of diflerent frequencies are amplified in said discharge device, and means for operatively connecting said first and second mentioned imquencies, means for impressing a positive average potential on said first electrode whereby said I stream develops an alternating potential on said first electrode in response to the intensity modulation of said stream, said second electrode being arranged to afiect said electron stream in response to potential impressed on said second electrode after said stream afiects said first electrode, means for impressing substantially all of said alternating potential developed by said stream on said first electrode'uponsaid second electrode, whereby potentials impressed on said second electrode after being developed on said first electrode increase the efl'ect on said first electrode of intensity modulation of the electron stream beyond the eflect which would exist without the impression of such alternating potential upon said second electrode, an impedance element discharge stream modulated in intensity at irequencies within a predetermined band of frequencies, means for impressing an average positive potential on said first electrode whereby first electrode increase the efiect on said first electrode of intensity modulation of the electron stream beyond the effect which-would exist without the impression of such alternating potential upon said second electrode, an impedance element for altering the degree to which signals of diflerent frequencies are amplified in said discharge device, and means for selectively connecting said impedance element to said first electrode.

6. In combination, an electron discharge device having a cathode, a control electrode and two anode electrodes, means for producing a regenerative efiect on one of said anode electrodes to increase the intensity of signals impressed on said control electrode and appearing on the other of said anode electrodes, means for impressing a signal having frequencies within a redetermined band of frequencies on said control electrode, an

impedance, and means for selectively connecting said impedance between said cathode and one of said electrodes to alter the relative amount of amplification of signals in said discharge device over said band oi frequencies.

7. In combination, an electron discharge device having a cathode, a control electrode and two anodes, means for producing a regenerative eil'ect on one of said anodes 'to increase the intensity of signals impressed on said control electrode and appearing on the other of said anodes, means for impressing a signal having frequencies within a predetermined band ofirequencies on said control electrode, two unlike impedances, and means for selectively connecting one of said impedances between said cathode and said control electrode, the other of said impedances between said cathode and one of said anodes, both of said impedances between said cathode and respectively said control electrode and said one anode simultaneously, and for disconnecting both of said impedances whereby the relative amount of amplification of signals in said discharge device of said band frequencies is correspondingly altered.

8. In combination, a support, a movable element rotatably mounted on said support-means I limiting the rotatable movement of said element with respect to said support to a relatively small arc of a circle, said element having at least one positioning member thereon to hold said element in at least one predetermined adjusted position intermediate the extremities of said are along a length thereof corresponding to said are, three spaced insulated contact :members mounted on said support and arranged along said arc of said circle, a metallic shortcircuiting bar carried on the-periphery oi said rotatable element and arranged to make contact with said contact members in diilerent predetermined positions of said element, said bar having a width corresponding to the length of said are, at. least one cooperating positioning member mounted on said support and cooperating with said first mentioned positioning member to hold said element in said one predetermined adjusted position such that said bar may be positioned diflerently relative to said contact members, said bar having an inwardly disposed body portion and a projectin portion, said projecting portion extending outwardly from the axis of rotation of said element and having a width at least as great as the distance between two adjacent ones of said contact members, the other one or said contact members extending radially inwardly a distance sufllcient to engage said body portion in all adjusted positions of said element, said cooperating positioning members being spaced such that in one position of said element said projecting portion engages only one of said adjacent contact members, in a second predetermined position both of said adjacent contact members are engaged by said projecting portion, and in a third predetermined position only the other one of said adjacent contact members is engaged by said projecting portion.

9. in combination, a support, a movable element rotatably mounted on said support, means limiting the rotatable movement or said element with respect to said support to a relatively small arc of a circle, said element having at least one positioning member thereon to hold said element in at least one predetermined adjusted position intermediate the extremities of said arc, three spaced insulated contact members arranged along said are of said circle, a metallic shortcircuiting bar arranged to make contact with said contact members in dlflerent predetermined positions of said element, movement of said movable element producing relative movement between said three insulated contact members and said shortcircuiting bar, said bar having a width corresponding to the length of said arc, at least one cooperating positioning member mounted on said support and cooperating with said first mentioned positioning member to hold said element in said at least one predetermined adjusted position, and arranged such that said bar may be positioned diiIerently relative to said contact members, said bar having an inwardly disposed body portion and a projecting portion, said projecting portion extending outwardly from the axis of rotation of said element and having a width at least as great as the distance between two adjacent ones of said contact members, the other one of said contact members extending radially inwardly a distance sufllcient to engage said body portion in all positions of said element, said cooperating positioning members being arranged such that in one adjusted position of said element said projecting portion eng ges only one of said two adjacent contact members, in a second predetermined adjusted position both of said adjacent contact members are engaged by said projecting portion, and in a third predetermined adjusted position only the other one of said adjacent contact members is engaged by said projecting portion.

EDWARD B. PASSOW-

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