US2301871A - Electrical musical instrument - Google Patents

Description

Nov. 1o, w42. J. M; HANER-r 2,301,871

ELECTRICL MUSICAL INSTRUMENT Filed Oct. 14, 1940 2 Sheets-Sheet l mlb .1. M. HANERT 2,301,871

ELECTRICAL MUSICAL INSTRUMENT Filed 001;. 14, 1940 2 Sheets-Sheet 2,

Nov. 1o, 1942.

ff? z/ef? zor Joh/2 MHa/zerz mnu @u wmmmmw llllillllllltl type. The cathode of VI is connected to ground and its control grid is self-biased through a resistor RI in shunt with a condenser CI, and is connected to ground through an inductance LI of an oscillation transformer TI. The screen grid of VI is connected to a +250 v. terminal of the power supply system through a voltage dropping resistor R2, and screen degeneration is reduced by means of condenser C2. The plate of VI is connected through a load resistor R3 in series with a feed-back winding L2 of oscillation transformer TI, and through a signal resistor R4 to a +250 v. terminal on the power supply system.

The phasing of L2 relative to LI is such as to produce self-oscillation. The frequency of oscillation is determined principally by the inductance of LI and the capacity connected between a conductor I and ground.

There are three octaves of keys plus a semitone, the keys being designated C3 to CE inclusive for notes of frequencies from 261.626 to 2093 C. P. S.

As shown in Figure 3, each of the keys, for ex# ample key C3, is adapted sequentially to open a switch I4 and close' a switch I8. The switch I4 comprises an upper rigid contact arm I8 and a lower resilient flexible contact arm 20, both of these arms being suitably mounted in an insulating supporting structure 22. The switch I6 comprises a relatively strong resilient and flexible arm 24 having a contact adapted to engage a bus bar 26 which is connected to ground. The key may have formed thereon or suitably operated thereby an actuator 28 of insulating material which engages the switch arm 20, and upon initial movement of the key opens .the switch I4.

The switch arm 20 has an insulating projection 30 formed thereon which, after the switch arm 20 has been iiexed a sufficient distance, engages the switch arm 24. The switch arm 24 is sufficiently stiff so that the player in depressing the key will feel a distinct stopping eifect to the downward motion of the key, and will find it necessary consciously to exert additional pressure in order to cause the switch arm 24 to iiex downwardly suiliciently to close the switch i6. In this way the musician may readily control by his ilnger pressure whether switch I4 alo'ne should be operated, or whether both the switch I4 should be opened and the switch I5 closed. Y

- Referring to Figure 1, it will be noted that the switches I4 for all of the keys are connected in series, and that the switch arm 2D'of each of these keys is connected to one of a plurality of tuning condensers C8, each of the condensers C8 having one terminal thereof connected to the common conductor III.

It will be noted that the switch I4 for the key C3 has its switch arm I8 connected to the conductor I0 through a resistor lR5 which is provided to introduce suillcient resistive impedance in shunt with the tuning circuit of the oscillator to cause the latter to cease oscillation when all switches I4 are closed. The condenser C8 associated with the key C6, the highest key of the keyboard, is permanently connected between the conductor I0 and ground. It will thus be seen that the operation of any of the playing keys will result in the connection of all of the condensers C8 to the right (Fig. l) of the key being of oscillation, of the master oscillator. All of the condensers C8 to the left of the key depressed will of course be disconnected from the circuit, and it will thus be seen that if two or more keys are simultaneously depressed, the highest of the depressed keys will determine the frequency of the master oscillator.

Vibrato Apparatus A tap 32 on the oscillation transformer TI is provided as part of means to vary inductance of the winding LI periodically at a vibrato frequency. The means for accomplishing this comprising a vibratory reed 34 which is connected to ground at its fixed end and at its free end carries an iron core 36, the mass of which relative to the stiffness of the reed 34 is such as to cause the latter to have a natural frequency of vibration of approximately 7 C. P. S. The core 38 is preferably made of powdered iron molded in shape by the use of a suitable insulating connected between the conductor I0 and ground,

binder, and moves into and out of the field of a coil L3, one terminal of which is grounded and the other terminal of which is connected to a tap 38 of an inductance L4.

A pair of switches 40 and 4I is connected together for simultaneous manual operation, the arrangement being such that the switches are alternately closed in such manner that both switches are never closed at the same time. When the switch 40 is closed and the switch 4| is open. as the switches are illustrated in full lines in Fig. 1, one terminal of the coil L3 is connected directly to the ungrounded terminal of the coil L4, and the coil L4 is thus completely disconnected from the circuit so as to have no effect upon the operation. I'he degree of frequency shift is then dependent upon the change of inductance oi' LI as the iron core 36 vibrates in its field. Because the core 36 is preferably made of a powdered iron in which the particles are suitably insulated from one another and bound together, the core losses for the inductanoe L3 are reduced toan extremely low value. The amount of vibrato of course will also depend upon the position of the tap 32 on the inductance LI.

When the switch 40 is open and the switch 4I closed, as indicated in dotted lines in Fig. 1, the ungrounded terminal of L3 is connected to the tap 38 on L4. The tapped inductance L4 then functions as an autotransformer to reduce the effectiveness of the variable inductance L3 in producing variations in the tuning inductance LI. Thus, the degree of vibrato is reduced. However, the average inductance (likewise the frequency of the master oscillator) looking out of the tap 32 of the winding LI, is the same whether the switches 40, 4I are in their full line vibrato "on" position, or whether these switches are in their dotted line vibrato "oil'" position. 1 'I'his is because of the added shunt inductance L4. In eii'ect, the shunt inductance of L4, which of course is not variable, compensates for the loss in effectiveness of the variable inductance L3 when the vibrato switches 48, 4I are turned off. The position of the-tap 38, together with the inductance of L4, determines the degree of residual vibrato present when the switches 40, 4I are in "olf" position. It is of course desirable to have at least a small .amount of vibrato present in the tones when rendering substantially all musical selections.

The vibrato reed may be driven by any suitable mond, Serial No. 362,018, led October 21, 1940, now Patent No. 2,251,052, granted July 29, 1941.

The switches 40, 4I are actuated by the armature of a relay winding 39, one terminal of which is connected. to a suitable voltage source such as a terminal +20 v. of the power supply system, and the other terminal of which is connected. through a normally closed switch 43 to a conductor 42, the latter being connected to the contact switch arms 24 of all of the switches I6. It will thus be seen that whenever a key is depressed to a suicient extent' to close its switch IB, the relay 40 will be energized to cause the switch 40 to close and the switch 4I to open, thus rendering the vibrato apparatus fully eiective to produce a wide vibrato effect in the frequency of' oscillation of the master oscillator.

Upon such occasions when the player does not desire the wide vibrato effect throughout the rendition of a complete selection, or a substantial portion thereof, the vibrato second touch may be rendered ineffective by manually opening the switch 43 Conversely, if the player desires the `vibrato continuously, without necessitating full depression of the playing keys, a switch 45 may be manually closed to complete an energizing circuit for relay winding 39, thus maintaining the switches 40, 4I in vibrato "on position until the switch 45 is opened.

Master oscillator'wave shape distorter The master oscillator produces a signal whose quality is not particularly desirable musically, and means are therefore provided to change the wave shape of this output signal to a form in Y which there is high harmonic development. This means comprises a tube V2 which may be a triode oi the 6J5G type, the grid of which is connected through a. condenser CII), a feedback winding L5, and a protective resistor R6, to the output of the master oscillator tube VI, bias being provided through a grid return resistor RI connected to asuitable source of negative grid bias of the power supply system,

The plate of tube V2 is connected through a charging resistor R8 to a +250 v. terminal of the power supply system, and is also connected to kground through a timing condenser CII and the primary Winding L6 of thetransformer T2, the

winding L6 being shunted by a load resistor R9.

The cathode of the tube V2 is connected to ground. The tube V2 together with its associated circuits constitutes a relaxation oscillator whichv is normally prevented from oscillating by the high negative bias impressed on the grid of the tube V2 through the resistor R'I. However, upon positive pulses of the signal transmitted through the condenser CIO, the bias is reduced suficiently to permit discharge of the condenser CII through the tube. This discharge through from the master oscillator transmitted through the condenser CIU is again effective to trip the tube V2. 4

When no signal is being supplied to the grid of the tube V2 through the condenser CID, i. e.,

when the master oscillator is not in operation, the bias on the tube V2 is never reduced sufficiently to permit plate current ilow. This prevents selfoscillation from occurring when the master oscil lator is not in operation.

Furthermore, it will be noted that' while the tube V2 is tripped by the signal from the master oscillator, it continues a complete cycle of rew laxation after being tripped irrespective of whether or not the master oscillator stops oscillating. Thus, transients due to the stopping of oscillations of the master oscillator do not ap-1 pear to any appreciable extent in the output of the tube V2.

Tone envelope control circuits A tertiary winding L1 of the transformer T2 has its terminals connected to the grid of control tubes V3 and V4 respectively, and has a center tap 44 connected through a bias controlling cirn cuit by which the attack and volume may be controlled. The plate of tubes V3 and V4 are connected to a +250 v terminal oi the power the tube causes current to flow through the primary winding L6A of transformer T2. This pulse of current through the primary winding LB 1nconstant of Rl! relative to CII and this results in producing current flow in the primary winding L5 which of course reflected in the winding L5, in a direction to decrease the bias on the grid of the tube V2. This operation continues'until the bias is suiliciently small so that the signal supply system through resistors RI I and RI2 re spectively. The Suppressors of tubes V3 and V4 are connected tc ground and the screens are con nected to a +100 v. terminal of the power sup ply system. The amplitude of the output signal from the tubes V3 and V4 is determined by their grid bias, these tubes preferably being remote cutoff pentodes, such as the GK'TG type,

The bias upon the tubes V3 and V4 is controlled through a circuit comprising a volume control mesh consisting of a variable volume con trolling resistor RI3 which is connected across a 50 Volt source of potential indicated by a bai;m tery 46, a protective resistor RM being connected in series with the battery 46. A decoupling resistor RIS is connected between the resistor Ri and the center tap 44 and the resistors RI3 land RI-5 are shunted by a condenser CIZ. The iresistor RIS and condenser CIZ serve to prevent the potential at the terminal d4 from changing rapidly with changes in the resistance R13. using this condenser CI2 and resistor RI 5 in conjunction With the variable resistor RI3, the latter Amay be made in a simple and economical form comprising a plurality of fixed resistors which may be successively connected in parallel,

The resistors RIS and RH are connected by a conductor M with a terminal 48 which is con nected to ground through a condenser CI3. The terminal 48 is connected 'through a normally closed switch 5I) and a damper resistor RIG to a terminal 52 of the power supply system which is at cutoff potential for the tubes V3 and V4. The terminal 48 is connected through a decay resistor RI'I to a switch arm 54 which is adapted to make contact selectively -with any one of three terminals, -50 v., +15 v., and 3 v. of the power supply system.

A switch arm 56 is adapted to make contact either with a contact 51 or a contact 58, thev switch arm being connected to ground through a condenser CI4. An attack resistor RI8 conn nects the Contact 58 with the terminal 48, while an anti-spark resistance RIS connects the con tact 51 with a switch arm 60 which may be operated selectively to make contact'with any one of three terminals -50 v., 3 v., or +50 v..

-is connected to the plate of a tube V5, the winding 62 being shunted by a condenser CI5 of such size as to provide Aa direct current reservoir of electrical energy to prevent chattering of the relay contacts. When this relay is energized the switch arms 50 and 56 are moved from their full line positions to their dotted line positions (Fig..l).

The grid of the tube V5 is connected to a fourth winding L8 of the transformer T2, the other end of the winding being connected to a terminal 64 of the power supply system providing cut-oi bias for the tube V5 when no signal is present on its grid. The tube V5 may be a triode of the 6J5G type. Thus, the tube V5 is non-conducting unless a signal is being provided by the output of the tube V2. When such signal is provided a D. C. voltage builds up across the condenser C5 causing relay 62 to be energized,

thereby rst toopen switch 50 and break the contact between switch arm 561- and contact 51 and thereafter make a contact between switch arm 56 and contact 58.

Output circuit The output of the two control tubes V3 and V4 is transmitted through blocking condensers CI1 and CI8. The output transmitted through the condensers C|1 and CI8 may be modified by suitable tone controlling resonant circuits bearing the legends Deep tone, Full tone, First voice, Second voice, and Brilliant tone, the signal, as thus modified by the tone controls, being amplified by the power amplifier tubes V1 and V8 which may be ofany suitable type such as 6F6G pentodes. The output of the tubes V1 and V8 is coupled to the voice coil of a speaker 65 through an output transformer T3.

Modification shown in Fig. 2

In Fig. 2 I have illustrated a modified form of my invention in which a number of parts have ben eliminated and which may therefore be more economically manufactured. The form of the invention shown in Fig. 2 is capable of producing many interesting musical results, but is not as versatile in the possible variations in tone envelopes as the previously described apparatus. Since most of the parts of the circuit shown in Fig. 2 are identical to those shown in Fig. 1 and above described, the reference characters used in connection with the description of Fig. 1 have been applied to the corresponding parts shown in Fig. 2' and will not again be enumerated.

Each of the keys C3 to C6 inclusive is adapted upon depression to close a switch 10, and upon further depression against a mechanical resistance to close the vibrato control I6 as described with reference to Figs. 1 and 3. The conductor Il! forming the tuning connection to the master oscillator is connected by a condenser CI9 to a series of tuning condensers C20.

A resistor R20 is shunted around each of the condensers C20 and the resistors R20 are thus connected in series. The resistors R20 constitute part of a D. C. voltage divider system to be yexplained hereinafter, but are of impedances sufiiciently high so as not seriously to degenerate the Q" of the master oscillator tuning system. The condenser CI8 is a tuning condenser and determines the resonant frequency of the tuning circuit for the master oscillator when the key C3 is depressed. Because of the series connection .of the condensers CI8 and C20, the lowest of several simultaneously depressed keys will determine the resonant frequency of the tuning circuit of the master oscillator, since all of the switches 10 make contact with a grounded conductor 1I. It will be noted that when none of the keys is depressed, the master oscillator would have a tendency to oscillate at a radio frequency due to the distributed capacity in the inductance LI and in the conductors connected therewith, and to prevent this, a condenser C2I of very low value is connected between the plate of the tube VI and ground. This condenser forms an eiectlve by-pass for high frequency and prevents effective energization of the feed-back inductance L2.

The resistors R20, as previously indicated, form part of a voltage divider system which includes a resistor R2I connected to aterminal 12 at approximately the mid-point of the series of resistors R20, the other end of the resistor R2I being connected to a terminal 14, and the latter is connected to a terminal -101 v. of the power supply system through a resistor R22. The resistor R2I may have a value of '7 megohms, while the resistor R22 has a value of 1.42 megohms, the resistors R20 being of value small relative to lthe values of the resistors R2I and R22 so that the potential on terminal 14 will be substantially the same irrespective of which of the keys is depressed.

The terminal 14 is connected to the terminal 48 through a decoupling resistor R23 and the terminal 48 is connected to ground through a condenser C22. A second condenser C23 is adapted to be connected in shunt with the condensers C22 upon closure of a switch 16. When the switch 16 is open, due to the condenser C22, the potential at the point 48 is prevented, to a limited extent, from suddenly changing at the same rate as does the potential at the point 14. When the switch 16 is closed, due to the additional capacity of C23, the potential on the terminal 48 will rise at a very slow rate relative to the potential change on the terminal 14, thus to provide a musically desirable slow tonal attack. The tubes V3 and V4 in Fig. 2 are operated with their plates connected to ground through the resistors RI I and RIZ, and with their screens connected to a terminal -50 v. of the power supply system and their cathodes connected to a terminal -83 v. of the power supply system. It is' thus seen that the plate voltage on these tubes is only 83 volts positive and that their screen voltage is only 33 volts positive with respect to the cathode. Also, the volume control battery 48 is of lower voltage indicated as -17 v. With these voltages, the amplification of tubes V3 and V4, as shown in Fig. 2, is considerably less than that shown in Fig. l. In order to compensate for this reduction in amplification, an additional pair of push-pull ampliiier triodes V8 and VIII (preferably of the 6J5G type) are inserted between the output circuits of tubes V3 and V4, and the input of the power amplifier tubes V1 and V8. By operating tubes V3 and V4 at low potentials, the voltages attained by the tuning condensers C20 are made correspondingly smaller than if the tubes V3 and V4 were operated under their normal rated voltages, thereby decreasing f I as ftheflatter areoperated.

Thus, when the tuning switches I0 are open,

Y whichl is the normal case when the instrument is -not producing a sound, the potential at'the terminal 14, as well as at terminal 4.8,'is 101 v.

"The actual bias applied to the control grids of tubes V3 and V4 may be 17 volts more' negative, namely, -118 volts, depending of course uponthe adjustedfposition of the expression or swell lcontrol variable resistance RI3. However, under these conditions, the tubes V3 and V4 will be cut off irrespective of the position of adjustment of the swell control.

When any playing key` is depressed, thereby closing'oneof rthe switches 10, ther potential at tithe point `I4"will yrise from -l01 volts to k--84 volts, causing correspondingincrease rin the potentials of terminals 48 and 49, and thus removing `the cutoff bias on tubes V3 and V4, and rendering them effective to transmit to their output circuit the signal impressed upon their control grids. Thus, the switches 'I0 are effective, not only to complete the circuit to tune the master oscillator to the desired note frequency, but also to causetransmission of the :signal generated by the master oscillator to the output of the instrument. Operation The instrument as above described made either in accordance with the disclosure of Fig. 1 or that of Fig. 2, is operated in the manner of a melody instrument, that is, but one key is operated at a time. Inplaying the instrument, assuming that u a suitable power supply system has been energized, letr us assume the'musician depresses the r`key C3'until the/switch actuator 28 thereof has opened the switch I4, Figs. 1 and 3, orreferring to Fig. 2, has closed the switch 10. Such operation will result in tuning the master oscillator to the frequency of the note' C3 l(261.626 C. P. 5.),

` the exact frequency being determined by adjustment of theinductance LI (and incidentally also inductance L2), as by varying the amount of iron effectively in the core of LI and L2.

In the lcircuit of Fig. l, the master oscillator f being normally rendered nonoscillatory` when the tuning circuit is yshunted by the resistor R5,

' is rendered oscillatoryas soon as the switch C3 V3 and V4 is'not instantaneous in action. Thus,

a. short interval in the nature of 30 milliseconds isl provided, duringwhich time the relay operates and the grid bias changes to a value which renders the tubes V3 and V4 conducting. However, when the key is released, the master oscillator stops oscillating substantially instantaneously. This, however, does not cause instantaneous cessation of operation of the relaxation circuit of the tube V2, since the latter will complete a cycle of relaxation before it ceases operation. Following this cycle the -condenser CII will be charged at a controlled rate through resistor R8 to the potential +250 v. as derived from the power supply system, but this potential vis not suiicient to cause the tube V2 to discharge because ofthe grid .bias thereon.

. pliiied by tubes VI and V8 and supplied to the switches 50 and 56 will result in raising the 'conl trol grid bias on the tubes V3 and V4 at a predetermined rate so as to produce a desired rate cf attack, and permitting this biasing potential to drop at a predetermined rate to produce the desired decay characteristics inthe tone. The signal `from the output of the tube V2 is thus transmitted through the tubes V3 and V4 with a controlled amplitude envelope.

Any transients which may be present incidental to the starting of the'master .oscillator VI and the relaxation oscillator including the tube V2, will not be transmitted to the output of the instrument because of the fact that the circuit and apparatus determining the grid bias on the tubes speaker 66.

Whenever the player desires to have a vibrato .effect in the tones produced, he will exert sufiiof one of the switches I6 will of course not result in energization yof the vibration control relay 39. On theiother hand, if the vplayer desires' to have the vibrato on alltones withoutrequiring the fullv depression of the keys, he may vclose the 'manually' operated switch'45 which will result in maintaining the vibrato relay 40 energized.

As previously described, the player'may adjust ythe switches 54 and 60 to predetermine the characterof the tone intensity envelope. For slow attack the switch 54 is adjusted to its 3 v. contact, while the switch 60 is adjusted' to a -50 v. contact. To attain a percussion tone intensity envelope the switch 54 is adjusted to a :50 v. and the switch 60 is adjusted to a +50 v. To attain a sustained organ-like tone, both switches54 and 60 arev adjusted to their -3 v. contacts. To attain a percussion envelope merging into a sustained tone of constant intensity, the switch 54 is adjusted to its -15 v. contact, while the switch 50 is adjusted to its -3 v. contact.

In the case of a slowfattack tonal envelope, the potential on condenser CI3 is normally maintained at a cutoff potential 52 through the relatively small resistor RIS. Upon depression of a playing key and subsequent operation of relay 62 this cutoff potential is removed through the operation of switch arm 50. The 50 v. potential which is normally on condenser CI4 under these conditions of adjustment is, upon movement of the 'switch arm 56 into engagement with the contact 58, impressed upon junction terminal 48 lthrough a resistor RIB which is of relatively small value; and serves merely to prevent transients. This potential then divides between the condensers CI4 and CI3. By making the condenser CI3 small with respect to condenser CI4, substantially the cutoii potential -50 v. is impressed upon the condenser CIS and thus maintains the control grids of tubes V3 and V4 initially at cutoff. However, at a time dependent upon the time constant of resistor RH and condensers CIS and CIA, the -3 v. potential, as derived from the switch 54, raises the potential on the junction terminal 48, thus removing the cutoff bias on tubes V3 and V4 and causing the signal to be conducted by these tubes at a gradually increasing amplitude.

When the switches 54 and 60 are set for a 10 percussion tone envelope, the condenser Cl4 normally has a +50 v. charge thereon which is impressed (with but slight diminution due to the charging of the condenser CIS), upon the junction terminal 48, thereby rapidly changing the 15 bias on tubes V3 and V4 to a high value. The charge on the condenser CI3 and C|4 is then gradually dissipated through the resistor RH to the -50 v. terminal of the switch 54, until the potential on the grids of the tubes V3 and V4 2g drops to a cutoff value which will correspond to a potential of 40 v. to -50 v. on the terminal 48.

The relay operated switches 5U and 56, as well as the manually operated switches 54 and 60 and their associated circuits, operate in a similar manner to produce the sustained organ-like tone and the percussion followed by a sustained tone level.

In the simplied form of the keying circuit shown in Fig. 2, a wide variety of tonal intensity envelopes is not available to the player, but the attack may be made slower by closing the switch 16 or the tone envelopes. The simplified form of the instrument as shown in Fig. 2 does not require elaborate intensity envelope controls if the instrument is to be used in conjunction with the piano, which of course produces percussion tones.

If the instrument is to be used as a solo instrument, for instance with orchestras, the intensity envelope controls of Fig. 1 are preferably utilized.

In playing the instrument the player may pro- 4o duce many new and interesting musical results, since the notes may be played With or Without the vibrato eifect, merely by applying increased pressure 'to the keys Whenever the vibrato eifect is desired. The various other controls which may be selectively operated by the musician make it possible for hiin to obtain numerous other muslcally desirable eifects, Despite the great versatility of the instrument, it may be economically produced since it is of relatively simple construction.

While I have herein disclosed preferred embodiments o f th venticin, it will be apparent to those skilled in art that numerous variations and modifications may be made without departing from the underlying principles of the invention. In the foregoing description, it will be understood that the values of the circuit elements, the types of tubes employed, and the values of the potentials given are merely exemplary, and may be varied considerably, especially if compensatory changes are made in other components of the apparatus. I therefore desire, by the iollowing claims, to include within the scope of my invention all such variations and modifications of 6,-, the invention by which substantially the results A of the invention may be obtained through the" use of substantially the same or equivalent means.

I claim:

1. In an electrical musical instrument having a frequency generating system and an output circuit including an electroacoustic translating means, the combination of a keyboard having a plurality of depressible keys, means operated by said keys when they are depressed a predetermined distance to cause transmission to said output circuit of signals from said generating system, means to impart a resistive force to the further depression of said keys after they have been depressed said predetermined distance, a relay controllable by any one of said keys when depressed beyond said predetermined distance, and means controlled by said relay `to cause the introduction of a vibrato effect in the signals produced by said generating system.

2. In an electrical musical instrument having an output circuit including electroacoustic translating means and a variable frequency tone signal generating system, means to vary the frequencies-generated by said system to introduce f a vibrato eifect, a plurality of depressible playing keys selectively operable upon, partial depreseWA/'e sion to determine the average frequency of said generating system and to control the transmission of signals from said generating system to the output circuit of the instrument, means common to all and controllable by any one of said playing keys when any one of the latter is completely depressed to render said vibrato means effective, and resilient stops for said keys affording greatly increased resistance to depression of said keys as they approach their completely depressed positions.

3. In an electrical musical instrument, the combination of a variable frequency generator, a plurality of playing keys, a tuning switch operl able by each of said keys, means controlled by said switches to determine the frequency oi' operation of said generator, vibrato means to vary the frequency of operation of said generator at a vibrato rate and through a vibrato range, means associated with said keys to impose a pronounced mechanical resistance to their depression beyond the extent necessary to operate their associated tuning switches, and switch and relay means to render said vibrato means effective upon operation of any of said keys appreciably beyond the extent necessary to operate its associated tuning switch.

4. In an electrical musical instrument, the combination of a normally non-operating oscillator, key controlled means to start said oscil- -lator and tune it to a predetermined musical note frequency corresponding to the operated key, a normally non-operating signal transmission control means connected to receive a signal from said oscillator, and means operated by the signal produced by said oscillator to render said signal transmission control means effective to transmit the signa-l produced by said oscillator, said last named means introducing sufficient delay to prevent the transmission through said signal transmission control means of transients produced incidental to the starting of said oscillator.

5. In an electrical musical instrument, the combination of an oscillator, a playing key, a switch operable by said key, means controlled by said switch to tune said oscillator to a note frequency corresponding to that represented by the key, a device for controlling the output of said oscillator, and means controlled 'by said switch to render said device effective to transmit the output of said oscillator upon depression of a playing key, said last named means including means for introducing a fractional second delay whereby transients incidental to starting said oscillator will not be transmitted to the output of the instrument.

6. In an electrical musical instrument, a master oscillator, a normally inoperative relaxation esoneri device connected to lreceive the output oi said master oscillator and having its frequency of relaxation controlled thereby, key controlled means to tune said master oscillator to a musical note frequency, an amplifier coupled to the out put oi said relaxation device, means normally maintaining said amplifier inoperative, and

,means controlled by the output oi said relaxation device to render said amplieroperative whenever said relaxation device Operates, said lastnamed means including a fractional second delay means whereby said amplier will be rendered gradually effective and its output will be free from undesirable transients produced incidental to starting and tuning said master oscillator.

7. In an electrical musical instrument having a generator of electrical signal impulses, an amplifier ior the output of said generator, key controlled means for rendering said generator opera tive, a circuit connected to said amplifier for controlling the operation thereof, said circuit having a terminal the direct current potential oi' which determines the degree of amplification of saidy amplifier, means normally maintaining a potential on said terminal oi a value to render said ampliner ineective, and means operated by sig nal impulses from said generator to change the potential on said terminal to a value rendering said amplier operative to transmit a signal.

il. The combination set forth in claim 7 in which the means operated by signal impulses from the generator to change theI potential on said terminal includes a condenser connected between said terminal and a point of fixed direct current potential7 said condenser operating to prevent sudden changes in the direct current potential oi said terminal.

9. The combination set forth in claim 7 in which the means operated by said signal impulses from said generator to change the potential on said terminal comprises a rectifier electron discharge device having an output circuit, and an input circuit connected to receive signal impulsesI from said generator, a relay having an energizing Winding connected in the output circuit 'of said electron discharge device, a plurality of switches forming part of said relay and operable to disconnect said terminal from said means normally maintaining la potential thereon which renders said amplifier ineieetive and to connect said terminal to a potential source of adjustable Value capable of rendering said amplifier effective, thereby to produce a Wide variety of tonal en velopes including percussion, organ and slow attack.

l0. The combination set forth in claim 7 in which the means operated by signal impulses from said generator to change the potential on said terminal includes manually adjustable means to predetermine the value to which the potential.

' erative, a terminal connected to said amplifier,

the direct current potential of said terminal deN termining the degree of amplification eiiected by said ampliiler, means normally applying a pon tential to said terminal approaching cutoi value thereby to render said amplifier relatively inef-n fective to transmit thesignal from said generator, and a circuit completed by said switch to cause a change in the potential on said terminal to a value rendering said amplifier effective to transmit said generator signals.

i2., ln an electrical musical instrument having a generator oi electrical signal impulses, an amplifier for the output of said generator, key controlled means for-rendering said generator operative, a terminal connected to said amplifier, the direct current potential of said terminal determining the degree of amplification effected by said amplifier, Vmeans normally applying a cutoff potential to said terminal thereby to ren- 'dersaid amplifier ineiective to transmit the signal from said generator, a vacuum tube relay operated by the signal produced by said generator, and circuits controlled by said relay for changing the potential on said terminal to a value rendering said amplifier effective.

13. lin an electrical musical instrument, the combination of an oscillator having a resonant tuning circuit including an inductance and a plurality of condensers, a plurality of playing lceys, a switch operated by each of said keys to connect selected capacitanees in said oscillator tuning circuit to determine the resonant irequency thereof, an amplifier for the signalsproduced by said oscillator, a terminal the direct current potential of which determines the degree oiamplincation ol said amplifier, and a voltage divider network for determining the direct current potential oi said terminal, said voltage divider network including a circuit completed upon closure oi any one ci said switches and effective to change the direct current potential of saidterminal to a value at which said amplier is efective. l,

le. The combination set forth in claim 13 in which a condenser is connectedv between said teru minal and a point ci? fined direct current potential, said condenser being of sucient/vaiue-to `prevent suddenchangesin the direct current potentialof said terminal. i i

15. The combination set forth inelaimnlB in Vwhich a capacitance is connected `between said tively fixed induetance, a plurality of condensers,

keyV controlled circuits Ator selectively connecting said condensers in said resonant circuit, a variable inductance, means ior'varying said variable inductance at a vibrato periodicity, and means for optionally rendering said variable inductance effective in said resonant circuit, said last named means including a compensating inductance ca- 8`- asoigen for varyingsaid variable inductance at a vibrato periodicity, and means for' optionally rendering said variable inductance effective in said resonant circuit, said last namedmeans including a compensating inductance capable; of rendering the average total inductance of saidresonantcircuit substantially the same whether said variable inductance is rendered effective in said resonant circuit ornot.

18. In an electrical musical instrument, the combination of an oscillator including a resonant tuning circuit determining. the frequency otoscillation thereof, said'tuningcircuit. comprising a plurality ofv capacitancesvplaying key operated means for selectively connectingsaid capacitances in said tuning circuit, a-relativelyfiixedinductance,e a variable inductance, switchmeans for effectively connecting' said variablev inductance in said tuning'circuit, means i'orxvarying said variable'inductance at a vibrato periodicity, and a compensating inductance associated with said variable inductance torender the average total effective inductance of said variable inductance and. said compensating. inductance substantially the same irrespective of the.- positionY of. saidv ing a resonant tuning circuit determining its frequency of oscillatioman inductance connected' in said circuit, a vibrating reed,- anda magnetic core secured tosaid reedand movable inthe field of said inductance, thereby to vary thefrequency of oscillationof .said oscillator' atna rate deter-Y mined by the frequency of vibration of said reed. 20. The. combination' setforth in claim 19 in which thernagneticrcore consists' ofV finely divided ferrous particles'separated'by an insulatingr binder.

2l. In an electrical musical instrument having an output system', the combination of Ya vnormally non-operating oscillator havingV a1 frequency determining resonant circuit,. a plurality of keys, circuits controlled by said keys to determine the resonantv frequency of said resonant' circuit and to cause said oscillator to oscillate, and means to couple saidoscillator to said output circuit, said means comprising a relaxation apparatus including an` electrondischarge device, an input circuit for said device coupling said device to said oscillator, an output circuit for said device coupling said device to the output system of the instrument, andz-rneans -providing bias to said device suificient to prevent relaxation when said oscillator is not operating, but insufficient to prevent relaxationfof said device when said. oscillator is operating.

22. In an electrical musical instrument,. the combinationl of an amplifier, a signal generator, means for tuning said generator throughoutl a musical .frequency range of at least one octave, a coupling between-said generator'and saidampliiier including a. distorting-relaxation. device to follow the frequency of'saidgenerator, said relaxation device being biased to benon-operating except when a trip'signal is supplied thereto, and' control the frequency of relaxation thereof throughout. the frequency range of said generator.

24. In an electrical musical instrument having an amplifying andelectroacoustlc translating system, saidlsystem includinga terminalthe direct current potential of which determines the intensity of the sound producedby the system, and having key controlled. signal producing means for supplyingjelectrical musicalV signals to saidsystem, the'combination'of a relay, a circuit coupled to saidsignal producing: means and maintaining `said relay energizedonly'during'the time that a signalis beingfsupplied. to said system by sail signal producing means, a circuit between said terminal and a point of'flxed directi current potential normally maintaining said terminal at a potential at which said system is relatively ineffective tovproduce'a sound, a resistance and reactance mesh-associated with said terminal and having one or more junction points, means to adjust the direct current potential upon one or more of. the junction points of said mesh, and means operated by said relay'to render saidimesheffective to' control the potential upon said terminal, whereby said systemv will, during the time that said relay is energized, produce asound having an intensity envelope of form determined by the adjustment of direct current potentials on the junction points of said mesh;

25. In an electrical musical instrument having an amplifying and electroacoustic translating system, said system including a terminal the direct current potential of which determines the intensity of the sound produced by the system, and havingkey controlled signal producing means for supplying electrical musical signals to said system, the'combination of a relay, a circuit coupled to said signal producing means and maintaining said relay energized only during the time that a signal is being supplied to said System by said signal producing means, a. circuit between said terminal and a point of fixed direct current potential normally maintaining said terminal at a potential at which said'system is relatively ineffective to produce asound, aresistance and capacity mesh associated with saldi terminal. and having a pluralityof junction points, meansto adjustv the direct current potential upon various junction points of said mesh, and means operated by said relay vto render said mesh effective to control the potential upon saidv terminal, whereby said system will, during'the time that said relay is energized, produce a sound having an intensity envelopev of form. determined by the adjustment of direct current-potentials on the Junction points of said mesh.

JOHN M. HANERT.

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