US2964986A - Push button chord derivation and apparatus - Google Patents

Description

Dec. 20, 1960 P. c. l-IQHNSQN 2,964,986

PUSH BUTTON cHoRD DERTvATToN AND APPARATUS Filed May 10, 1956 2 Sheets-Sheet 1 IN V EN TOR.

BY PHIL/P C J'OHA/SN' @gw/9M ATTO I? NEYS,

Dec. 20, 1960 P. c. JOHNSON 2,964,986

PUSH BUTTON cHoRD DERIVATION AND APPARATUS Filed May l0, 1956 2 Sheets-Sheet 2 IN V EN TOR.

/DH/L /P C.' rfohwson,

ATTORNEYS.

United States Patent O PUSH BUTTON CHORD DERIVATION AND APPARATUS Philip C. Johnson, Cincinnati, Ohio, assignor to The Baldwin Piano Company, Cincinnati, Ohio, a corporation of hio Filed May 10, 1956, Ser. No. 583,987

17 Claims. (Cl. 84-1.19)

The invention relates to electrical musical instruments of a type in which a keyboard is provided comprising ranks of push button or plunger means, the operation being such that when a plunger is depressed a chord sounds in the reproducer system of the instrument. This need not necessarily be true of all plungers, since it may be desired to have a plunger arranged to sound a root note of a chord combination in a low register, and sometimes another plunger arranged to sound a low register note which is the third interval above the root. Various arrangements of the plungers are possible, but they are normally organized into groups, the plungers in eac-h group representing the chords pertaining to a given root tone plus, if desired, the root and third as indicated above. Thus, for the key of C in addition to the root and third there may be a major chord consisting at least of C, E and G, a minor chord consisting at least of C, Eb and G, a dominant seventh consisting at least of C, E, G and Bb, a diminished seventh consisting at least of C, Eb, Fit and A, an augmented chord consisting of C, E, and Ab, and perhaps others. Thus the plunger keyboard resembles the left hand keyboard of an accordion and may be used for similar purposes, i.e. accompaniment.

` The instrument will normally have at least one other keyboard of the usual organ type, which may be ernployed to carry the melody.

The invention relates primarily to that type of electronic musical instrument in which the tones are generated in a form richt in harmonics by electrical oscillators, and in which differing voices are obtained primarily by filtering plus such expedients as combining tones of different footage, out-phasing, and the like. Reference to the Kock U.S. Patent No. 2,233,948 may be made for an instrument in which the tones are so generated and treated. The invention of this application will be described in connection with such modes of tone generation and modification; but it will be understood that the utility of the invention is by no means confined thereto.

Hitherto, the provision of an accordion-type keyboard in an electronic musical instrument has entailed a very great complexity both of mechanical operating elements and of circuitry, which it is a fundamental object of this invention to simplify and cheapen.

lt is an object of the invention to provide a switch construction of simple and inexpensive character which will effect the closing of all circuits necessary to the production of a desired chord, and in which the only moving parts for each plunger are the plunger itself and one or at most two contact elements.

It is an object of the invention to simplify the wiring of a gang of switches of the type aforesaid through the use of so called printed circuitry as an integral part of the switch itself.

It is an object of. the invention to provide individual, self-contained gang switch elements adapted for combination into an accordion-type keyboard.

It is an object of the invention to provide a gang switch ice including the plungers for all of the chords based on a given root plus, if desired, the root and third, the gang switch combination having in addition to output terminals only the same number of terminals as the number of tones required in the construction of the several chords.

It is an object of the invention to provide an electronic system employing an accordion-type keyboard, capable 'of producing richer chords with a greater variety of voices than those hitherto obtainable.

These and other objects of the invention which will be set forth hereinafter or will be apparent to one skilled in the art upon reading these specifications, are accomplished by that construction and arrangement of parts and in that system of which certain exemplary embodiments will now be described. Reference is made to the accompanying drawings wherein:

Figure l is a perspective view of a gang switch capable of being joined with other such combinations to make up such a keyboard.

Figure 2 is a transverse sectional view thereof taken along the section line 2-2 of Figure l.

Figures 3 and 4 are respectively plan views of the side elements of the gang switch combination, their relationship to Figure 2 being indicated by the section lines 3 3 and 4 4.

Figure 5 is a perspective view of a movable switch finger.

Figure 6 is an elevational view of another type of switch finger.

Figure 7 is a sectional view of the end of the same switch finger taken along the line 7-7 of Figure 6.

Figure 8 is an elevational View of a modified form of plunger having two abutments, together with a modified form of switch finger.

Figure 9 is a plan view of a side member appropriate for use with the plunger of Figure 8.

Figure 10 is a circuit diagram of the electrical system of an instrument insofar as it pertains to the accordiontype keyboard.

Figures 11 and 12 are respectively plan views of modified side members which may be employed in a gang switch of the general type of Figures 1 to 4 inclusive.

Referring rst to Figure 10, which gives a circuit diagram for the C chord series, electronic oscillators are represented by the notes C1 to Bbz. It will be noted that for each tone two oscillators have been provided. Thus C2 is an octave above C1. The outputs of the generators are combined through isolating resistors 10 and 11 as shown. The combination for the several tones in each chord of the outputs of octavely related generators makes for an enhanced richness of tone.

The index numbers 12 to 16 inclusive indicate gang switches operated by plungers as hereinafter described. It will be noted that elements 12, 13 and 16 comprise each the equivalent of three ganged single-pole, singlethrow switches. The elements 14 and 15 comprise each four ganged single-pole, single-throw switches. The numeral 17 indicates a switch for obtaining the root tone alone while the numeral 18 indicates a plunger for obtaining the third alone. These plungers each operate one single-pole, single-throw switch. The seven plungers illus- 1 trated thus operate a total of nineteen switches.

One side of each of the switches operated by elements 12 to 16 inclusive is connected to a common outlet lead 19. The C note combination (C1, C2) is connected to the other side of one of the switches in each combination, e.g. 12a to 16a. The E note combination (El, E2) is connected to the switches 12b, 14b and 16b. The Eb combination (Ebl, Ebz) is, however, connected to the switch 13b and to the switch 15b. The G combination (G1, G2) is connected to the switches 12e, 13C and 14eA But the switch 15e is connected to the Ft combination 3 (Fitl, Fitz). The switch 14d is connected to the Bb cornbination (Bbl, Bbz) while the switch 15d is connected to the A combination (A1, A2), and the switch 16e is connected to the Ab combination (Abl, Abg).

One side of each of the switches 17a and 18a is connected to a common output conductor 20. The other side of switch 17a is connected directly to the C1 output as shown at 21. The output lead 20 will thus receive very little of the output of the C2 generator since it is isolated therefrom by resistors 10 and 11 in series. Similarly the switch 13a is connected directly to the output of the El generator by lead 22.

The common output lead 19 lfrom the plunger devices '12 to 16 is connected to a preamplifier 23 through an assembly of voicing filter arrangements or tone color filters 24 to 27, of which there may be as many as desired. These are selectable through switches 28 to 31, normally operated by stop tabs on the instrument. The chordal outputs of the several plungers may thus be transmitted to the preamplifier in any voice for which the instrument provides. If combinations of voices are desired, isolating resistors, one of which is shown at 32 may be included in the leads of the several tone color filters so that their effect will be additive. The tone color filters, as is well known, are networks inclusive of various combinations of capacity, resistance and inductance.

The output lead 2G from the plungers 17 and 18 is connected to a frequency divider 33 which is employed to lower the C1 and El tones by an octave, thereby eliminating the necessity for additional generators. The output of the frequency divider passes to the preamplifier through additional tone color filters 34 to 37. These may be conveniently coupled to the filters 24 to 27, as shown, so that their outputs will be handled concurrently by the voicing switches 28 to 31, although other arrangements may be made. There is a provision for means for setting the general amplitude level of the accompaniment tones and chords. This has been represented as a multi-contact switch 38, the points of which are connected to resistors 39 to 42 of different values and serving tobypass portions of the output to ground. The level setting device 38 may be operated in any way desired as by a hand lever or by means operated by a knee lever or a foot pedal.

While the circuits for a single switch assembly have been shown in Figure l() for the tones and chords appropriate to the key of C, it will be understood that the instrument will contain similar circuit arrangements for all of the other keys of the tempered musical scale. Thus there will be twelve such assemblies. The output leads 19 and 20 from all of the assemblies may be connected together so that the divider 33, the tone color ciri cuits 24 to 27 and 34 to 37, and the chord level device will serve all of the assemblies in common.

In the remaining gures of this application there are shown various forms of simplified constructions in which the various switches of the circuit diagram Figure l0 are organized. Referring to Figure 2 each switch assembly comprises plungers, one for each root tone and chord desired in the assembly. Each plunger is a unitary structure of insulating substance. Any insulating substance may be employed, including wood; but the various plastics, well known in `the art, are convenient and inexpensive to use, enabling the plungers to be made by molding operations. Each plunger comprises an elongated upper neck portion 43. Below this neck portion there is an abutment or operating portion 44 preferably of conical shape, terminating in an upper shoulder larger in diameter than the `neck portion. There is also a lower neck portion .45 which carries an integral annular abutment 46.

In the switch assembly there is an upper Arail element 47 perforated at suitable intervals to receive the upper neck portions of the several plungers in sliding relationship. There is a lower rail portion 48 also perforated to receive the lower neck portions of :the plungers. -The rail portions are held apart by side plates 49 and 50 of insulating substance fastened to the rails in any suitable way as by screws 51 provided with lock washers 52. Side plates 49 and 50 are conveniently made of solid or laminated resinous products. The arrangement is such, as will be evident from the drawings, that the several plungers will be supported vertically for vertical reciprocation. The opening in the lower rail member 48 may if desired be bushed with felt 53 to silence the operation of the plunger. A light coil spring `54 surrounds the lower neck 45 of the plunger and engages between the lower rail 48 and the abutment 46 on the plunger. This spring urges the plunger upwardly. A felt washer 5S overlies the shoulder of the conical operating element 44 and insures that the plunger will be stopped in yan upward position without a clicking noise. A strip of felt 56 may be caused to underlie the perforations of the lower rail member 48 and hence the lower end of the plungers so as to avoid clicks when the plungers are driven downwardly by the pressure of the fingers. The felt strip 56 is held in place by a resinous strip 57 held to the lower rail by screws 53.

The number of plungers provided in any given assembly may vary; but there will be a plunger for each chord of the series plus a plunger for each individual root tone to be produced as such. In the example of Figure l, plungers 12 to 16 are provided respectively for the major, minor, dominant seventh, diminished seventh and augmented chords of the series, while the plunger 17 is provided for the low register root tone. If additional chords were to be provided there Would be additional plungers; and if an additional low register tone, e.g. the third, were to be provided there would be an additional plunger corresponding to 18 of Figure l0.

In the embodiment of Figures l to 4 each chord plunger operates two switch fingers, one on each side. The tone plunger or plungers each operate one switch finger.

The side plates 49 and 50 each contain printed circuitry `and switch fingers coacting with the printed circuitry. Referring to Figure 3, the side plate 49 carries on its inner surface a printed circuit bus 59. The printed circuitry including this bus may be formed on the surface of the side plate in any of the ways known in the art. Thus it may be imposed on the side plate by printing, stencilling and spraying, by silk screen methods, by covering the surface of the side plate with a deposit layer or foil of metallic substance, printing the circuit thereon with a resist and etching away unwanted portions of the deposit. It is only necessary that the printed circuit elements be formed `of a material having adequate electrical conductivity and substantial physical strength and resistance to abrasion. A series `of spring switch ngers 60 to 64 is attached to the bus 59. Each spring finger (as shown also in Figure 5) comprises a base 65 and a contact head 66, the two being connected by an elongated relatively narrow neck portion 67 which is humped as at 68. The base portion 65 is provided with perforations 69. The -base portion of each spring finger will be attached to side plate 49 in electrical contact with the bus 59. This attachment is conveniently effected by means of rivets 70 extending through the side plate. The mounting of each spring finger by means of two rivets or grommets prevents sidewise displacement. As will be evident from Figure 2, the configuration of the spring finger is such that normally its contact head 66 lies away from the side plate 49. The hump 68 engages or lies near the plunger, however, so that when `the plunger is depressed the conical operating element 44 will engage the hump and cause the contact head 66 to move against the side plate. The spring contact fingers may be made of any suitable resilient light metal, for example, spring brass, beryllium copper, or Phosphor bronze. To prevent corrosion and to improve the effecting of a more perect electrical contact, the spring fingers, or at least their contact heads, may be electroplated with some highly conductive and relative oxidation resistant metal such as silver, gold or others of the rare metals.

The bus 59 is provided with a contact lug 71 attached to the side plate in contact with the bus by means of a rivet or grommet 72.

The contact heads of most of the spring fingers are arranged to make contact with two circuit elements. In this way, since each chord plunger operates two of the spring tingers, it is possible to cause the closing of as many as four circuits through the operation of any one plunger. For example, in IFigure 3 the contact head of spring finger 60 is arranged to contact a printed circuit area 73 having a terminal lug 74 (Ab) and another printed circuit area 76 having a terminal 77 (E). The head of spring iinger 61 engages a contact area 78 having a terminal lug 79 (Fit), and also a contact area 80 having a terminal lug 81 (A). The head of spring finger 62 engages a contact area 82 which is connected to the circuit of terminal 77 (E) and a contact area 83 having a terminal 84 (G). The head of spring finger 63 need only engage a contact area 85 connected to the G terminal 84. The head of spring iinger 64 engages a contact area 86, also connected to the G terminal 84 and a contact area 87 connected to the E terminal 77. The disposition of the printed circuitry will be clear from Figure 3.

On the side plate 50 (Figure 4) there is a printed circuit area or output member 88 having a terminal lug 89 to which the base of spring finger 90 is attached. Since this is a spring nger for a single tone, the root tone, the head of this spring finger need only contact a single contact area 91 having a terminal 92 (C1, lead 21, Figure 10).

The spring vfinger 93 contacts by means of its head a contact area 94 having a terminal 95 (C). The spring finger 96 can contact by means of its head a contact area 97 also connected to the terminal lug 95 (C) and a contact area 98 having a terminal lug 99 (Eb). The spring finger 100 can make contact with a contact area 101 having a terminal lug 102 (Bb), and also with an area in connection with terminal lug 95 (C). The spring finger 103 contacts a contact area 104 again connected to the terminal lug 95 (C) and a contact area 105 again connected to the terminal lug 99 (Eb). The spring finger 106 need only contact the contact area 107 which is again connected to the terminal lug 95 (C). The spring fingers 93, 96, 100, 103 and 106 have their bases connected to a bus 108 having a terminal lug 109. The nature of the printed circuitry on the side plate 50 will be clear from Figure 4.

The contact areas with which the heads of the spring fingers make contact may, if desired, be the heads of rivets or grommets 1'10 (Figure 2) to save wear on the printed circuitry itself; but such precaution is not usually necessary. That is to say the contact heads of the spring fingers may be caused to contact the appropriate contact areas of the printed circuitry itself. In this event, as shown in Figures 6 and 7, the several heads of the contact fingers may be made with slight spaced depressions 111 and :112 to increase the perfection of the contact. The humped shape of the contact fingers assures a slightly sliding contact when the fingers are actuated.

It will be understood that an accordion-type keyboard may be made up of twelve of the units illustrated in Figure 1 in side by side relationship, and fastened together in any suitable way. Normally they will be fastened together by means of end supports attached to the various upper rail members by bolts passing through perforations 113 and 114 therein. A single covering plate of suitable material (not illustrated) may be used to cover the whole assembly. In some instances this cover plate may be used as the means vfor fastening the several units together. In an electrical musical instrument the combined assembly may be let into a recess in the console with only the cover plate in an exposed position. In another instrument the cover plate may form part of a housing containing the combined assemblies.

Wiring becomes relatively simple. The contact lugs 71 and 109 are bus lugs corresponding to the common lead 19 in Figure 10, and all of them will be connected together and to the 4tone color system 24 to 27. The lugs 89 of the several exemplary units correspond to the common lead 20 of Figure 10 and will `all be connected together .and to the frequency divider unit 33. For the rest, it merely remains to connect the several lugs to the appropriate oscillation sources. Since the same oscillation source will be used ifor tones making up chords in a plurality of the assembly units, there will be cross connections; but these are readily effected.

It is possible to provide a structure in which for each unit assembly only one printed circuit bearing side plate member is necessary. This involves the provision of spring contact `lingers so arranged as to be brought into contact with the side plate each at two separated points; and it involves the provision of a plunger element capable of actuating such a spring linger. Reference is made to Figures 8 and 9. In Figure 8 there is shown a plunger having an upper neck 115 and a lower neck 116 with an annular integral abutment 117. This plunger differs primarily from the plunger of Figure 2 in that it has an upper conical actuating element 118 and a lower conical actuating element 119. It is used in conjunction with a spring finger element having a base 120, spaced contacting heads 121 and 122 and intermediate humps 123 and 124 so placed as to be actuated respectively by the conical members 118 and 119. By reason of the length of the spring finger and to prevent lateral movement, its end may be turned over as at 125 to provide a portion which will operate in a perforation in the side plate.

A side plate element bearing a printed circuit is illustrated at 126 in Figure 9. The printed circuitry comprises a root bus 127, and a chord bus 128. For simplicity, the terminal lugs have been omitted from Figure 9 and the spring fingers have not been shown thereon. The positions of the spring fingers are, however, indicated by dashed lines and appropriate root or chord legends. The root spring finger simply contacts a C1 contact area 129. The C combination is used in all of the chords. As a consequence, C contact areas 130 are provided at all positions. At the position for the major chord there will be an E contact area 131 and a G contact area 132. It will be understood that when the appropriate major chord plunger is actuated, the contact head 121 thereof will contact one of the areas 130 while the other contact head 122 thereof will simultaneously contact areas 131 and 132. Each of the spring fingers excepting the spring finger for the root tone will simultaneously contact one or more contact areas in an upper series and one or more contact areas in a lower series as will be evident from Figure 9, which also illustrates the disposition of the printed circuitry. It will be understood that each plunger in the assembly operates only one spring finger. There need be no plate on the opposite side of the assembly, or a plain plate, devoid of printed circuitry and spring fingers, may be used.

lIn Figures 11 and l2 are shown the side plates for a type of switch construction related to the structure of Figures l1 to 4 but differing therefrom primarily in that the terminal means for the buses and root tones are located and available at the ends of the plates, while the terminals for the tones making up the several chords are organized and available at the bottoms of the plates. This simplifies the wiring.

The plate 133 of suitable insulating substance carries a chord bus 134, to which various contact nfingers may be attached as hereinabove described. This bus has terminal means 135. Printed circuitry is provided having contact areas for the contact heads of the spring fingers and terminal means 136, 137, 138 and 139, respectively for the F ii', A, G, and E tones. These terminal means extend below the bottom of the plate as shown.

The plate 140 (Fig. 12) carries a chord bus 141 to which contact fingers are attachedas hereinabove described. The bus has a terminal member 142.. Since the bus 141 is also a chord bus, the terminal 142 (which in the completed structure will lie adjacent the terminal 135) will be connected to the terminal 135, to similar terminals or the other gang switch assemblies, and to a lead corresponding to the lead 19 of Figure 10.

The plate 14) also has a root tone bus 143 to which, in this instance, spring fingers are attached for the root and third tones. For simplicity, the spring contact fingers have been omitted from Figures ll and 12. The root bus 143 has terminal means 144 at the end of the plate. Printed circuitry is also provided, the general nature of which will be clear from the above description. The printed circuitry provides contact means for the contacting heads of the spring tingers and also leads to the terminal members. At the end of the plate terminals 14S and 146 are preferably located for the third and root tone connections. Terminal members 147, 148, 149, and 15d extend beyond the bottom of the plate 140 for connection respectively to leads for tones going to make up the desired chords, in this instance, Bb, C, Eb, and Ab. The root tone bus terminal members 144 of the several gang switch assemblies will be connected together in the assembled device and connected to a lead corresponding to the lead of Figure 10.

Connections to the various terminal members at the bottoms of the plates 133 and 149 in the assembled device may be effected by point-to-point wiring or by connecting the terminal members to appropriate points on a distributor which can involve printed circuitry on an insulative support, if desired.

lt/lodilications may be made in the invention without departing from the spirit thereof. The invention having been described in certain exemplary embodiments, what is claimed as new and desired to be secured by Letters Patent is:

1. A plunger switch construction for the purpose described comprising upper and lower rails, at least one insulative plate connecting corresponding side edges of said rails and maintaining said rails in spaced relationship, a plurality of plungers mounted for axial reciprocation with respect to said rails, said plungers having necks extending through perforations in said upper rail providing means for plunger actuation, resilient return means for said several plungers, spring contact iingers for actuation to contacting and non-contacting positions by said plungers respectively, each of said spring contact fingers having a base attached to said plate and a contact head, and electric circuit elements comprising bus means interconnecting the bases of a plurality of said contact fingers, and contact means coacting with the contact heads of said spring ngers, the contact heads of a plurality of said spring lingers being -located to contact a plurality of said contact elements, and means interconnecting certain of the contact elements for a plurality of said spring tingers.

2. The structure claimed in claim 1 wherein the recited electric circuit elements comprise printed circuitry on said plate.

3. The structure claimed in claim l wherein certain at least of the said spring iingers each have two contact heads.

4. The structure claimed in claim 1 wherein there is a plate at either side of the said rails, each plate having spring contact iingers `and electrical circuit elements as recited, certain at least of the said plungers operating two spring contact fingers.

5. The structure claimed in claim 4 wherein the recited electric circuit elements comprise printed circuitry on the said plates.

6. In a structure of the class described, an upper perforated rail, a lower perforated rail, spaced insulative plates interconnecting the edges of said rails and holding them in spaced relationship, and a plurality of plungers mounted for axial reciprocation in the perforations of the rails, each plunger having a neck portion constituting an operator extending through the upper rail and a neck portion guided for movement in a perforation of the lower rail, resilient return means for the several plungers, spring contact fingers each having a base at one end and a contact head at the other, the bases of said spring contact fingers being mounted to said plates, certain at least of said plungers having spring contact ngers lying on each side thereof, means on said plungers for actuating said spring contact fingers to contacting and non-contacting positions .and electric circuit elements in connection ywith said plates, said elements comprising bus means interconnecting the bases of certain at least of said spring contact fingers, contact means coacting with the contact heads of said spring contact fingers, there being two such contact means for each of certain at least yof said spring contact fingers, and means on said plates interconnecting certain at least of said contact means.

7. The structure claimed in claim 6 wherein the recited circuit means involve printed circuitry on said plates.

8. The structure claimed in claim 6 wherein the recited circuit means involve printed circuitry on said plates, and in which terminal means for the printed circuitry extend beyond marginal edge portions of said plates.

9. The structure claimed in claim 6 wherein the recited circuit means involve printed circuitry on said plates, and in which terminal means for the printed circuitry extend beyond marginal edge portions of said plates, there being terminal means for the interconnecting means of said spring nger bases and individual terminal means for the said contact means and groups thereof.

10. The structure claimed in claim 6 wherein the recited circuit means Ainvolve printed circuitry on said plates, and in which terminal means for the printed circuitry extend beyond marginal edge portions of said plates, there being terminal means for the interconnecting means of said spring linger bases and individual terminal means for the said contact means and groups thereof, there being also at least one plunger actuated spring contact member having a separate terminal means and devoid of connection to the other spring contact ingers.

11. A gang switch assembly comprising twelve `of the units claimed in claim 9 fastened together in side-by-side relationship.

12. In an electrical musical instrument having generators producing electrical oscillations in accordance with the tempered musical scale, and having an output system including an amplifier, an assembly of twel-ve of the units of claim 1 in side-by-side relationship, connections between the said generators and the said contact members respectively and connections between the bases of said contact members and said output system, said connections being such that upon the actuation of a plunger in any of said units, a chord will be derived in said output system which is ya chord of a musical key appropriate to the said unit.

13. In an electrical musical instrument having generators producing electrical oscillations in accordance with the tempered musical scale and an output system cornprising an amplifier, a plurality of the units of claim 10 in side-by-side relationship, connections between said generators and said contact members, and connections between the means connecting the bases of said contact fingers and said output system, said connections being such that when a plunger is depressed a chord will be derived in said output system in a key appropriate to the unit containing said plunger, and connections between said generators and the contact members for spring fingers, the bases of which are not connected together such that upon depression of a plunger for such spring iingers, a note will be derived in said output system which is a root tone for the chords of the key appropriate to the unit of which the said plunger is depressed.

14. The structure claimed in claim 13 including a frequency divider in the last mentioned electrical connection.

15. The structure claimed in claim 13 including a frequency divider` in the last mentioned electrical connection, and in which selective voicing lter means are included in the connections between the said units and the output system.

16. The structure claimed in claim l5 wherein a plurality of octavely related generators is connected to each of the said contact members excepting those for the root tones.

17. In an electrical musical instrument, Ia plurality of generators for electrical oscillations in accordance with the tempered musical scale and an output system, a plurality of plunger switches arranged in groups for each of the keys of the musical scale, and connections between said oscillators and said plunger switches and between said plunger switches and said output system such that upon the actuation of a plurality of plunger switches in each group, chords will be derived 1n the output system in the key appropriate to that group, and other connections such that upon the actuation of at least one plunger switch in each group, a root tone in a low register will be derived in said output system, said last mentioned connections including a frequency divider, said rst mentioned connections involving tone derivation leads each connected to at least two octavely related generators, and each set of connections including separate 10 voicing circuits.

References Cited in the le of this patent UNITED STATES PATENTS 2,357,191 Hanert Aug. 29, 1944 2,645,968 Hanert July 21, 1953 2,649,513 Luhn Aug. 18, 1953 2,702,841 Bernstein Feb. 22, 1955 2,740,004 Baldasare Mar. 27, 1956

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