US3246071A - Electronic organ - Google Patents

Description

R. H. PETERSON 3,246,071

ELECTRONIC ORGAN 3 Sheets-Sheet 1 flll April 12, 1966 Filed March 29, 1962 Inl/C1153* fllrardflpersorf April y12, 1966 R. H. PETERSON ELEGTRONI C ORGAN 3 Sheets-Sheet 2 Filed March 29, 1962 April .12, 1966 ELECTRONIC ORGAN Filed March 29, 1962 moc -J -rvgb I 3 Sheets-Sheet 3 OSC.

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150 LV-J .D.c. pou/5a Aun /F/EQ 'DAC-g, 6,4m/ ccm/T204 amJ 761 7a IPH/my' j] fLcfZaY-d A( Persorz T1 ME United States Patent O 3,246,071 ELECTRONIC ORGAN Richard H. Peterson, 10108 Harnew Road E., Oaklawn, Ill. Filed Mar. 29, 1962, Ser. No. 183,487 1 Claim. (Cl. 84-1.17)

My invention relates to electronic musical instruments of the organ type, and is a continuation-in-part of my copending application Serial Number 735,854, now Patent 3,038,365, issued June 12, 1962.

It includes among its objects and advantages a signal source capable of extremely prolonged decay without undesirable transitory sound effects. It also includes playercontrolled percussion effects variable over a wide range. It also includes the peculiar transitory percussion effect commonly produced by piano strings or by chime bars equipped with felt dampers. Further objects and advantages will become apparent as the description proceeds.

FIGURE 1 is a schematic wiring diagram of a signal source and accessories according to the invention.

FIGURE 2 is a perspective view of a complete organ with the front panel removed;

FIGURE 3 is a similar view of the rear side only of the same organ;

FIGURE 4 is a diagram indicating various decay charactenstics;

FIGURE 5 is a diagram of a multiple stop switch; and

FIGURE 6 is a diagram of an alternative signal source.

In the embodiment selected to illustrate the invention, the organ itself may comprise a conventional console having a solo manual 10, an accompaniment manual 12, and a pedal board 14, assembled in a conventional geometrical relationship. There is also an expression control pedal 16 and a tremolo rotor 18. Behind the pedal board 14, I have indicated twelve different tone generator chasses 20. The chassis illustrated is according to my co-pending application, S.N. 598,582, filed July 18, 1956, now Patent Number 2,924,784. Due to the exceptionally small volume occupied, it is possible to house seventy-two signal sources assembled in twelve groups of six each within the shallow space occupying about thirty-two percent of the rear side of the casing and about twenty-five percent of the depth of the casing, behind the pedal board 14.

This extreme reduction in the volume occupied makes it possible to include within the confines of a conventional spinet body, not only the entire generator equipment, and electronic accessories, but an entire loud speaker 78 and an enclosure 80 for it for securing the correct acoustics, and a tremolo rotor 18 for delivering the sound. In FIGURE 3, there is also indicated the location of the power amplifier 19, and the percussion unit 28.

Referring now to FIGURE 1, it is convenient to discuss the wiring shown in four sub-divisons, comprising the amplifier unit 22, the signal source 24, the manual control 26, and the unit 28. This unit provides unique and desirable percussion and reverberation effects. It is hereinafter identified, for brevity only, as the percussion unit. There is also a power source 30 provided with a plurality of voltage taps 32. In this specific embodiment, the source 30 may receive 60cycle alternating current through supply cables 34 and deliver predetermined selected D.C. potential, as selected from time to time by the player, to the various terminals and busses of the entire organ. The voltages employed in practice at present vary in steps of three volts each from plus 3 volts to minus 27 volts. As Ithe details of transforming 120 volts 60 cycle A.C. into D.C. at various voltages are well known in the art and may be conventional, this description is not encumbered therewith.

The source 24 indicated in FIGURE l employs a tran- 3,246,071 Patented Apr. 12, 1966 sistor 35 of the PNP type usually employed for audio-frequency work. It has a base connection at 36, an emitter connection at 38, and a collector connection at 40. The connections 36 and 38 are part of an exciting loop running from the base 36 through a base resistor 42, a base capacitor 44, a minor upper fraction 46 of the winding 48, and an emitter resistor 50 back to the emitter 38. The winding 48 is physically associated with a ferro-magnetic core 52 of ceramic material, as described in my copending aplication, S.N. 598,582, filed Iuly 18, 1956, now Patent Number 2,924,784. The oscillating loop, proper, or tank circuit, is completed by the capacitor 53 connected across the ends ofthe winding 48, and the entire loop is grounded at 54. It will be noted that the exciting circuit sub-divides the winding 48 into an upper minor fraction 46 and a lower major fraction 56.

To energize the exciting circuit, potential is delivered from terminal 58 through resistor 60 to point 62 and from there through a resistor 64 of low impedance to the collector 40. The same potential from the point 62 is also connected through a resistor 66 of 33,000 ohms to the base 36.

The point 62 is also connected through a capacitor 68 to ground. It will be apparent that the resistor 60 and the capacitor 68 are an RC time-delay circuit tending to control the time-potential curve for the point 62 when the potential is first delivered to the terminal 58. During the building up of the oscillation, a minor influence on the potential of the point 62 is exerted by the oscillator itself. The base capacitor 44 is also charging through the following circuit: (l) portion 46 of the inductor winding 48; (2) resistor 50; (3) a split circuit of which one branch is the transistor from emitter to base, and the other branch is the transistor from emitter to collector and resistors 64 and 66; (4) base resistor 42. However, the charging of capacitor 44 is relatively slow and its effect in lowering the potential at point 62 relatively slight, so that the potential of the point 62 rises at a rate determined almost entirely by capacitor 68 and resistor 60. Because of this relationship, there will be one time-potential curve for the collector 40 and a different timepotential curve for the base 36.

When the energy supply to terminal 58 is interrupted, as by opening the key switch, resistor 60 is left unconnected at its lower end and no longer performs any function. But the charge on capacitor 68 has to find its way to ground at 54 entirely through resistor 64, the transistor, collector to emitter, resistor 50, and the lower major segment 56 of the winding 48. The impedance of this path is much greater than that of resistor 60, and, accordingly, the decay of working potential in the exciting circuit will be relatively slow, and the decay of the oscillation will be much longer than the attack period. Except for abnormally staccato music, this relationship between attack and decay is esthetically preferable.

At the same time that capacitor 68 is discharging, as above outlined, capacitor 44 is discharging through a different network having certain portions in common with the discharge path of Capacitor 68. Capacitor 44 discharge through the same path through which it charged during attack, but its time-discharge curve will not be the same as its time-charge curve because the competing potential drop in those portions of its circuit that must also discharge capacitor 68 will be different during attack and during decay. Therefore, during decay, the time-potential curve for the collector and the time-potential `curve for the base will be materially different, and neither of them will be the counterpart of the same potentials during attack.

From the point 70 of the oscillator, signal is delivered through resistor 72 to an assembly bus 74 connected to aaaaori iii receive signal from all the oscillators. The amplifier unit 22 includes an amplifier proper 76 receiving a signal from the bus 74. It may also receive signal from a plurality of additional busses 77, which may be those described in detail in Patent 2,649,006. The amplifier includes player-controlled expression means for varying the gain ratio, which may be according to Patent 2,712,- G40, operating under the control of the expression control pedal 16. The amplilier delivers the composite signal from the bus bar 74, after amplification, to a loudspeaker 7S. The loud-speaker 73 opens downwardly through an opening in the bottom of the speaker enclosure 30, and the resultant sound issues from the tremolo rotor 18 through sound outlets at S2 and 84 in the organ casing. If the rotor 18 is stationary, a Vconstant tone will be delivered. If the rotor is rotated by means of the motor $4, the Doppler etect described in U.S. Reissue Patent 23,323 will change the constant sound emanating from the loud-speaker to give it a slightly variable frequency, and a slight variation in intensity, with the ultimate eiiect of a most pleasant and natural vibrato.

Variable percussion The prolonged decay characteristic of chimes, harps, glockenspieis, and instruments of the same general class, is frequently desired only on the solomanual.

Referring `to FGURE 1, terminal S receives potential from any one lor more of three key switches, a solo key switch S6, an accompaniment key switch 83, and a pedal key switch 90. Each of these switches is connected to the point 5S through a rectifier diode 92. Thus, when more than one of the key switches 86, 88, and 90 are closed, the switch delivering the greatest potential will control the lpotential of terminal 58, so long as that switch remains closed. If the switch of greater potential is opened while a switch of lesser potential is still closed, the amplitude `of oscillation will decay back to a lesser intensity, but the oscillator will continue to deliver signal without interruption.

Solo key switch 86 is connected through the on-andon stop switch 94 with the percussion unit 23, as by means of a player-controlled stop element 97 (see FIGURE 2).

Capacitor 98 functions to prolong the decay of the tone, as follows: The charging of capacitor 98 draws current through two circuits. One circuit includes resistor d and 106. The other is through the oscillator as follows: Resistor 60, a divided portion from energizing terminal 62 to the emitter 38, resistor 50 and section S6 of winding 43 to ground at 54;. The divided portion between 62 and 3S has one path through resistor 66 and the transistor, base to emitter; and a parallel path through resistor 64 and the transistor, collector to emitter. The impedance of resistor 106 is many times that of the oscillator network, so that nearly all the charging current for the capacitor 9S comes through the oscillator circuit and is therefore eliective to prolong the oscillation of the oscillator after the playing key is moved to open position. This continued oscillation is of decreasing amplitude and the tone diminishes accordingly. This diminution oi tone is commonly referred `to as the decay of the tone.

To enable the player to select a variety of decay rates at will, it would be possible to provide several sets of resistances 106, with a multiple gang switch for each of the sets of resistors, as disclosed in my co-pending application, S.N, 566,446, led February 20, 1956, now Patent Number 2,924,137. According to the present invention, a single additional set of resistors 108 provides a plurality of different decay rates and at the same `time secures an additional desirable esthetic effect.

Associated with the capacitor 98 is another -charging circuit effectively in parallel with the oscillator charging circuit. rl`his snubbing circuit is for the purpose of controlling the rate of decay by providing a means for charging capacitor 9S more quickly than would be possible if all the charging current had to come through the oscillator circuit (plus a minor fraction coming through resistor 106). It is desirable to have the snubbing circuit effective in varying degrees at the will of the operator to control the length of the decay period throughout a range extending from a small fraction of a second up to about three seconds or more.

The snubbing circuit for each oscillator includes a one thousand ohm resistor 108 and a diode 110. These are connected in series with each other and between the snubbing bus 112 and the side of capacitor 98 remote from the keying voltage. The snubbing bus 112 may be connected by the operator to .any selected potential available in the power source 30 by means of a selector switch 93.

The selector 93 determines the selected potential for bus 11,2, and the grounded resistor 106 completes the circuit back to the power pack 30. It will be understood that there are as many percussion units 28, as there are notes for which percussion eiiects are desired, and that the bus bar H2 is connected to a multiplicity of percussion units.

The keying voltage at S6 may be varied between minus 3 and minus 9 volts and when the key switch is closed, the potential of the conductor 91 will be the keying voltage. When the key switch 86 is moved to open position, this voltage will decrease gradually to zero volts. During most of the time l`of this decrease, the tone will decrease accordingly, and, shortly before the voltage becornes zero, the oscillator will discontinue oscillation and sound will cease. Assuming a keying voltage of minus 9, if the snubbing bus 112 is also at minus 9 volts, the voltage across diode 110 can never be of polarity to cause the diode to conduct. Under these conditions, the capacitor 98 must charge entirely through the oscillator circuit and through resistor 106, and this will result in a maximum period of attenuation.

However, ii the voltage on the snubbing bus is changed to Zero, or to a small plus value, the diode will remain conductive until the capacitor 98 is completely charged, and the ordinary decay period will be accelerated in a ratio of about ten to one.

if the voltage of the snubbing bus 112 is made minus six, or minus three, or any negative value less than the keyinor voltage of minus nine, the diode 110 will remain conductive until the potential of conductor 91 has reached the potential of snubbing bus 112, and the remainder of the decay will take place at the slower rate required by charging through the oscillator and through resistor 106. This results in a total time of decay intermediate between the minimum and the maximum. But this intermediate total decay time will comprise a first portion during which the decay is relatively rapid, and a later portion during which the decay is relatively slow. The two-stage decay characteristic just described is remarkably similar to that of chime bars, or the like, with felt dampers, and to that of a piano when played without the sustain pedal.

Because the pedal tones are played with the foot, there is likely to be a time interval between the time that one pedal key is released and the next one depressed. This frequently causes an undesirable lack of continuity in the music. Because the most advantageous decay period for the pedal notes is usually different from that desired for the solo notes, I provide a separate pedal sustaining capacitor 99 connected inseries with resistor 105 and gang switches 95, between ground and the terminal of key switch 9d remote from the power source. Like capactor 68, capacitor 99 is connected in parallel with the oscillator, whereas capacitor 98 is connected in series. The equivalent snubbing circuit comprises an additional, separate snubbing bus 113 connected through resistor 109 and diode 111 to the conductor 103. lt will be obvious that by keeping the snubbing bus 113 at various selected potentials, effects completely analogous with those secured by the snubbing bus 112 are available to the player.

Each of the three time- delay capacitors 68, 98, and 99 can obviously be connected either in series with the oscillator or in parallel with it. The only difference is in the polarity of the capacitor and a capacitor connected in series will be charged when the oscillator is not oscillating and discharged while the oscillator functions, while a capacitor connected in parallel will remain continuously discharged when the oscillator is not oscillating, and be charged when the note is played. l provide also a stop switch 97 for disconnecting capacitor 99 completely, in the same way that stop switch 94 disconnects capacitor 98.

Referring now to FIGURE 4, the diagram indicates graphically one set of time-volume characteristics that may be at the disposal of the player. It will be obvious that the pedal notes associated with snubbing bus 113 will have a generally similar but specifically different step of time-volume decay characteristic. Time is shown as a horizontal dimension and amplitude as a vertical, and the horizontal line at 114 indicates the intensity 0f the sustained note obtained on the solo manual with a playing voltage of minus nine. The smooth curve 116 indicates the effect when the bus oar 112 is also at minus nine. This produces the esthetic effect of a carillon, or the like.

With the bus bar at minus six volts, a curve results having a relatively steep portion ending at 118 and a less inclined portion from 118 to extinction. This may be made to produce a surprisingly accurate illusion of the effect of an organ played in a very large auditorium, where the auditorium itself creates a reverberation equivalent to the decay indicated. Because the diode 110 changes from conductive to non-conductive over a small voltage range, rather than at a precise voltage, the curve at 118 does not come to a sharp point.

With the bus bar at minus three, the curve is steep down to a lower intensity at point 120, and less than inclined down to extinction. This effect may be made to coincide with that of a piano played without the sustain pedal in a room of ordinary size.

With the bus bar at a voltage of zero, the result is curve 122, which is almost, but not absolutely, identical with that secured when the gang switch 94 is open, and the percussion unit is not functioning. Accordingly, it is quite practicable to construct such an instrument with gang switch 94 entirely omitted, and the percussion unit always electricaliy connected, with the so-called normal decay characteristic available `by setting the bus bar at zero.

A With the bus bar at plus one volt, the curve 124 results,

and this prcduces a staccato decay characteristic, which will be rendered more striking with the bus bar at plus three or four volts.

In addition, the bus bar 112 may be in multiple, with the range of the instrument subdivided between the different busbars, and an upper octave of oscillators may have one decay characteristic; the next octave a different one, and so on. The following table shows one desirable assortment of values:

Octave 1 2 3 4 5 6 Percussion Long Percussion Mediunn Percussion Short 0 0 0 0 0 0 Chimes -9 -9 -9 -9 -9 -9 Reverberation Short ...-1 plus 3 plus 3 plus 3 plus 3 plus 3 plus 3 Reverberation Medium plus 1 plus 1 plus 1 plus 1 plus l plus 1 Reverberation Long 0 0 0 0 0 0 Piano -9 6 -3 1 0 plus 1 These values relate to the duration of the decay period only, and have nothing to do with tone quality, which is controlled in other ways.

In the piano, as in certain other instruments, the lower notes have a longer decay period than the higher ones. The bottom line of the table indicates how these peculiar and desirable tonal characteristics can be closely duplicated electronically.

Summarizing: With terminal 58 receiving playing potential off, say minus 9 volts, from switch 90, or switch 86; and capacitors 98 and 99 voperatively connected, the capacitor involved will be charged, or discharged, in a few thousandths of -a second. When the key is opened again the current to restore the terminal 58 and its capacitor to cutoff potential is through the oscillator itself, resistor 60 and resistor 104 or 105, all connected in series. But if bus bar 1-12 or 113 is at any potential differing 'from playing potential -in the direction of cutoi the capacitor can also return by current through resistors 108 and 109 and this second circuit acts much faster than the rst one until the potential of the bus 112 or 113 is reached. At this potential diode 110 or 111 .becomes noncouductive, and whatever is needed to restore cutoi potential must be supplied by the rst, slowly acting circuit. Thus the player can set the potential of the bus at any one of a variety of potentials and command a wide repertoire of decay envelopes, a few of which are diagrammed in FIGURE 4.

One set of suitable working values for the components of la transistor oscillator and percussion unit according to the invention is as follows for the note A3 with a frequency of 440 cycles per second.

Table of values Resistor 42 ohms-- 0 to 1000 Resistance of winding 48 do 48 Resistor 50 dow 220 Resistor 66 do 33,000 Resistor 64 do 0 to 1000 Resistor 60 do 330 Capacitor 44 mid 5 Capacitor 53 mfd-- 0.95 Capacitor 68 mf 10 Capacitor 98 mid 200 Capacitor 99 mfd.- 200 Resistors 104 and 105 ohms-.. 22 Resistors 108 and 109 do 1000 Resistor 106 do 10,000 Inductance 48, 52 henries 0.145

Resistors 42 and 64 are at zero in present practice, but values up to 1000 ohms can be used at these points to secure variations in attack and decay characteristics.

The values of capacitor 53 and inductance 46, 52 are approximate only. The core 52 is adjustable lto secure exact tuning.

In the execution of complicated organ music, and in many other types of expert musical performances, the things that the player needs to accomplish almost instantly by a touch of the foot or ringer, include a wide variety of relatively complicated adjustments.

Among the more necessary of such complex adjustments is the adjustment of the relative loudnesses of the notes played on the solo manual and the notes played on the accompaniment manual and the notes played on the pedal clavier, It will be ob-vious that the subject matter already disclosed enables an operator to sound one of the relatively low notes with any one or more of the three sets of key switches. At a given instant, such a note may be connected to receive energizing potential through all three switches 86, 88, and 90, and at such an instant, the volume will be the `relatively high volume due to the relatively high energizing voltage available through the key switch 90. Under such circumstances, if the key switch is opened while the other two switches remain closed, the intensity of the tone will decay back to a lower intensity, which will be the intensity secured by the key switch 86. A fraction of a second later, the key switch 86 may open because the solo air has shifted to another note, whereupon the intensity 4will decay further to that corresponding to the voltage available from the key 88. And finally, if the key 88 is opened, there will be a different decay characteristic in the dying away of the sound to extinction.

This land many other sequences of varying intensity result automatically from mere manipulation of the keys by the operator, so long as a predetermined 'relative intensity for each ot the different sets of key switches is appropriate to the requirement of the musical piece. But, when the :operator needs to change from very loud notes on the pedal clavier to notes of normal loudness, or to emphasize a passage played in chords with the key switches 88, While the key switches 86 play a faint obligate, the relative potentials of the different lbanks of key switches need to be shifted substantially in the ilick of an eye-lash.

Referring now to FIGURES 2 and 5, I have indicated balancer switch means at 125 comprising a knurled knob 126. A contact member 128 connected to the key switches 86 of manual 10 and .another contact member 130 connected to the key switches 88 of manual 12 are indicated as rigid with the knolb 126 and rotatable therewith. In the position of FIGURE 5, contact 128 is riding on a sector 1.3-2 carrying a potential of minus 9 received from the potential box through a conductor 133 and contact 130 is receiving the same voltage from sector 134 connected to the same condu-ctor .133. On the right side above the sector 132, I provide a short sector 136 carrying a potential of minus 6 and above that a short sector 140 carrying a potential of minus 3. Similarly, on the left side, the first sector above the sector 134 is sector 138 carrying a potential of minus 6 and above that is sector 142 carrying a potenti-al of minus 3.

It will be obvious that counterclockwise rotation of the knob 126 will move contact 128 across from sector 132 to 136, and in a second step from sector 136 to 140. This will reduce the potential of the switch keys 86 in ytwo successive steps while the contact for switch keys 88 merely slides down along the long sector 134 and continues to receive minus 9 volts. Similarly, clockwise rotation of the same knob 126 will keep the contact 128 in engagement with the long sector 132 while the contact 139 moves up to receive only minus 6 volts from sector 138 and in a second step to receive only minus 3 volts from sector 142.

I thus provide tive different relative intensity ratios between switch keys 86 and 88. In the position of FIGURE 5, keys 86 and 88 deliver the same intensity. Clockwise movement to engage sector 138 will reduce the accompaniment intensity to that resulting from two thirds of the solo manual voltage and further movement to sector 142 will reduce lthe accompaniment to the intensity resulting from one third of the solo manual voltage, making it seem like a mere background echo. iC'ounterclockwise rotation to engage sector 136 will relegate the solo air to a background, and movement to sector 140 will make the solo switches 86 deliver a mere echo compared with the switches 88.

If this change in ratio were the only change in actual volume, the capacity of 4the instrument would be relatively inadequate. But the foot pedal 16 controls the amplifier 76, and superimposes a total control on the actual loudness of everything that is received by the ampliiier, land the expert organist is able to have instant contral of changes from one musical passage to the next throughout the entire range necessary for the performances of complicated music.

Because these adjustments of relative intensity originate in the signal from oscillators themselves, it is possible to make a complete and satisfactory musical instrument with a single set of oscillators, whereas it was previously considered necessary to have separate banks of 'oscillators to secure the same variety in the musical effect.

Finally, the stop switch 97, when closed, merely changes the decay rate of the notes playedgon the pedal clavier, but a touch of the linger enables the player to have four different intensities for the switch keys 9i). Beside the stop tablet (see FIGURE 2) is al duplicate stop tablet 144 labeled soft, another tablet 146 labeled medium, and another tablet 148 labeled loud. With all three tablets horizontal and undisturbed, the clavier notes will be as soft as is ever desired when clavier notes are to be played at all. A tap of the finger to tilt up stop 144 will increase this intensity materially and tablets 146 and 148 provide two more steps of increasing intensity, It should be emphasized also that these bass notes are only adjusted in volume as a matter of intensity ratio between them and the notes emanating from the other two keyboards, while the merged totality is still controlled to have any Iacoustic intensity the player desires by means of the swell pedal 16.

The material employed in the core 50 is that disclosed in my copending application, S.N. 598,582, vfiled l'uly 18, 1956, now Patent Number 2,924,784. Many of the-se ceramic magnet materials are well known in the art, and, per se, form no part of my invention. As distinguished from metallic magnet cores, most of them have the peculiar characteristics required for this service, but only over a minor fraction of their normal range of flux densities, which minor fraction occupies approximately the lower third of the uX density range. By keeping the maximum ilux density `of the core 52 down within this abnormally low limit, a desirable constancy of pitch at varying amplitude is obtained.

It has been pointed out that the time-potential curves for the base 36, the emitter 40, and the collector 38 are specifically dilerent from each other during attack, and that during decay a diiferent curve obtains for each of them, the three decay curves being also diiferent from each other. With some of the longer decay periods, the relationship between the three potentials tends to approach an inoperative condition, such that oscillation is interrupted for a very short time, and then resumed. This hiatus sounds like nothing less than an ordinary hiccup, or burp, and would be highly objectionable. Control in thi-s respect is by varying the value of resistor 50. If the value is too low, the burp appears, and if it is too high, the .attack 'becomes sluggish. For this reason, it may be desirable to make the resistor 50 adjustable for ease in manufacture, as by means :of the contact adjustment indicated at 51 in FIGURE l.

In FIGURE 6 I have indicated a modified signal source, in which the oscillator 24-2 is connected for continuous operation `at full amplitude at lall times when the switch is turned on to connect up the primary power source 3i). Terminal 58 and conductor 74 of FIGURE l may be connected as indicated in FIGURE 6 and the combined units 24-2 and 152 will function just as unit 24 does by itself in FIGURE 1. The difference is that because the oscillator 24-2 operates at constant amplitude, it need not be constructed to remain of constant frequency o ver a l0 to l range of activating potentials, and constancy is needed only over a range of about 10% above and below a normal supply voltage, to take care of power source variations.

Others may-readily adapt the invention for use under various conditions of service by employing one or more of the novel features disclosed or equivalents thereof. As at present advised, with respect to the apparent scope of my invention, I desire to claim the following subject matter:

An electronic organ comprising, in combination: a multiplicity of independent oscillatons', each oscillator being adapted to deliver signal of predetermined shape corresponding to a component of an acoustic oscillation to be produced; player-controlled key-switch means for activating key-selected combinations of oscillators; said key-switch means including two banks of keys; connections for activating each oscillator from a key in either bank; player-controlled stop-switch means for delivering a predetermined activating potential to one of said banks, and an independently predetermined potential to the other bank; each oscillator being adapted to oscillate With varying amplitudes upon receipt of varying `activating potentials up to a predetermined maximum; bus bar means for assembling a composite signal from all activated oscillators; a transducer; an operative connection from said [bus bar means to said transducer for delivering the assembled composite signal from said bus bar means t0 said transducer; said operative connection including player-controlled expression means for varying the proportionality Ibetween the assembled signal received by said connection, and the signal delivered by said connection to said transducer; said stop-switch means having one set of contacts arranged to deliver maximum activating potential lesser activating potentials to the other, second bank; and another, set of `contacts arranged to deliver maximum activating potential to said second bank, `and 4any one of a plurality or different, lesser activating potentials to the 5 other, tirst bank.

References Cited by the Examiner UNITED STATES PATENTS 1,561,933 11/1925 Kendall 331--182 10 2,712,040I 6/ 1955 Heytow S30-144 2,924,784 2/1960 Peterson 331-49 3,068,735 12/1962 Anderson Sli-1.17

DAVID I. GALVIN, Primary Examiner.

to one, rst bank, and any one of a plurality of different, 15 BENNETT G- MILLER Examiner-

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