US3001431A - Musical instrument system - Google Patents

Description

Sept. 26, v1961 C, w. ANDERSE'N 3,001,431

MUSICAL INSTRUMENT SYSTEM Filed Sept. 22. 1954 4 Sheets-Sheet 1 33a, GEM AMF? 50a, 54

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4 MUSICAL INSTRUMENT SYSTEM Filed Sept. 22, 1954 4 Sheets-Sheet 3 N INVENToR.

Clar/(021525 ffzaenjew Mw/Wd s Sept. 26, 1961 c. w. ANDERsEN 3,001,431

MUSICAL INSTRUMENT SYSTEM Filed Sept. 22, 1954 4 Sheets-Sheet' 4 INVENTOR.

United States Patent() This invention is concerned generally with the electronic production of music, and more particularly with a system for selectively rendering musical tones generated f audible from any one ormore of a group of instruments;

Heretofore, teaching the art. ofk piano playing has generally required individual supervision of each. student. Space limitations have militated. against a. large number of pianos being playedin oneroom, andthe sound. coming from other pianos is likely to distract astudent.. As a result, it has been common practice forA studentsv to have a minimum of individual lessons with long hou-rs of un.- supervised practice. Generally,v such practice: hasl been in small student practice rooms which are scarcely large enough to-hold an upright piano and the student.. The small rooms have precluded proper resonance. and have renderedv it extremely diicult for a student tof ascertain whether or not he is playing the proper tones., During unsupervised practice, it is impossible for anyone. to` as;- certainy whether or not the student is fingering properly.

Heretofore, I have solved the space requirements for pianos by inventing an electronic piano occupying no more space than a small desk. The pianois portable, and may be supported on a desk, table, or detachablev legs. The electronic piano which I have invented utilizes. Vi.- bratoryI reeds as variable capacitors to develop electrical oscillations corresponding to piano tones. These oscillations are amplied electronically and: are transduced either by means of a loudspeaker or by means of earphones. A student may utilize earphones to listen tok his own playing without anyone else in the room being consciou's of such playing; Y Itis an object of this invention to provide a system of piano instruction utilizing such electronic pianos, or other electronic musical instruments, whereby eachlstudentfmay listen to his own playing, and whereby a teacher canobserve the fingering or other manipulation of each student and can listen selectively to any given student.

More particularly, it is an object of this inventionto provide a piano teaching or playing system in accordance with the lforegoing object wherein the teacher can move about the room and connect earphones to any: of the pianos or other instruments for listeningv thereto;

More specically, it is an objectv of this inventionr to provide a piano teaching or playing'system wherein a large number of electronic pianos or the like can be played inthe same room without audible sound,v the-play ers or students individually listening to themselvesby means of earphones, and wherein there is provided a central station wherein the teacher or monitor can. selectively connect one or more of the pianos to a loudspeaker or earphones for listeningto such piano or pianos without moving from the central station.

Furthermore, it is an object of this invention to provide a piano or other instrument teaching or playing system wherein a plurality of pianos or the like is played in a single room without audible tones emanating from the pianos, each student orV player listeningto his own pianoV with. earphones, and wherein a teacher or monitor can move about the room individually to observe the fingering or manipulation, and wherein the teacher or monitor can connect any givenpiano: to` ai central station for. audible reproduction. of?Y the: tones of thatfjpiano by means of a loudspeaker or the like.

Patented Sept. 2.6 1961- It Ifurther isL au4 object of this invention vtoy providea system: for teachingthepianoor the like wherein? student pianos' individually or in. groupsfmay be compared with a recording made by one offthe recognizedl master pianists of the. day with such; control available tot ther teacher from a central station or from any one of a number of pianoslocated in the same room. 4

Another object ofi-this: invention is to` produce afsystem inaccordance with. all ofthe foregoing objects which does not require. complicatedwiring and which` is. simple and economical to set. up.. Y

A further object of this invention is to produce a. sys.- tem. in. accordancezwith. thepreceding objects wherein all tones will be reproduced. at; the. central or, master station ata predetermined adjustable intensity regardless of the volumelevelset ateach instrument.

The invention hereinafter. will. be-'explained in detail with. regard to electronic pianos, all played in the same room. However, it. will be understood' that electronic organs,` electric guitarsor any other instruments which produce or can be, adapted to produce electrical oscillations rather than audible tones are equally subject to the principles of the invention. It further will be apparent that many of the objects of the invention could be at'- tained'A with the students or players in one or several rooms andv with the teacher in aroom isolated from any or allof. the pianos or other instruments.

Other andfurther, objects and' advantages of the present invention will be apparent from the following description when taken in connectionk with the accompanying drawings wherein:

FIG. 1 is a' schematic view illustratingy a. piano teaching or playing system set up in accordance with the principles of my invention;

2 is aY schematic wiring diagram4 of the master panelor station; FIG. 3I is a viewisinn'lar to a portion ofy FIG; 2 showing a moditlcation'thereof; liIG. 4 is a schematic wiring diagraml of the electronic piano or other linstrument including the output connections therefrom; f ,FIG. `5 is a view similar' to FIG. 4'showingan1odied connection; FIG. 6 isa somewhat schematic diagram'illustratingthe selector at the master station or panel;

FIG. 7 is a cross sectional view through the-selector; FIG. 8 isa cross sectional ViewV of a control member located: at each pi-'ano or other instrument;

FIG. 1(1"is` a vertical cross sectional view through the piano and taken along the line 10-10 in FIG. 9 FIG. 11 is a fragmentary horizontal view partially in section taken substantially along the line 11--11' in FIG; 1o; l

FIG. 12 isa schematic wiring diagram' of an amplier preferably provided at'the centr-all or master* stationfor maintaining a constant', pre-set volume; and v FIG. 13v shows some details' of a portion of FIG. 12".

Referring first Ito FIG. 1 there will be seen a plurality of pianos illustrated somewhat diagrammatically and identified by the numeral 20, the various pianos being indicated asv number 1, Y2, etc. There are ten pianos' in the illustrative embodiment* of FIG. 2, and there is also provided a recorder 22. This recorder may be. of any suitable type, such as for playing commercially available discrecord's-in order to reproduce the artistry of a master pianisti, or the recorder' may be a tape recorder whereby the progress offa student readily. may be observed. The pianos and' the: recorder are.l connected by means of a cable: and aiplurality= of branch cables Z6 to a. main station'or panel indicated somewhat schematically at 28.

This main sta-tionV or panel 28Yis provided with a loudthe jacks being indicated at 32 and preferably being two in number. Y The main station 28Y also is provided with an indicator 34,v which in the presen-t illustrative invention isgp'rovided with twelve vindicating stations. Aprow of pushbuttons 36 is provided adjacent the indicator 34, and the pushbuttons correspond innumber with the stations of the indicator 34, there being twelve illustrative embodiment. f I I Each of the branchcables 26fas; readily may be seen in FIGl-:Z comprises three insulated wires 38, 40 and 42 carried'within a conductive sheath 44 which may conveniently be ofv the braided variety. The wires 38, 40 and 42 preferably'are limited to three in number inasmuch as;cableshavingconductive sheaths or shielding and three internalwires are readily available in commerce at a reasonable price and are not unduly bulky.

pushbuttons in the 4 Such a record may provide speaker30 and with jacks for accommodating earphones,

The wire 38 of each'sub-cable 26 is connected to a f common connector or' bus line 46, the connection for piano No. 2 being illustrated in FIG. 2, ,and the connections for the other pianos to the bus line merely being indicated.` The wires 40 of each of thegsub-cables 26 are connected individually to fixed contacts 48 associated with the indicator 34, and a rot-ary arm or contact 50 is selectively engageable with any one of the contacts 48. The switch arrn 50 is connected throughV a normally closed relay switch 52 to thevoice coil 54 of loudspeaker 30. The relay switch 52 is openable by means of a relay coil or a solenoid 56, the wire 42 of each sub-cable 26 being connected to this coil, and the other side of the coil being grounded as indicated at 58.` The conductive `sheath or shielding 44 of the individual sub-cables also is connected to ground by a wire as indicated at 60. The operation of the relay 62 comprising lthe switch 52 and coil 56 willbe described shortly. Y Each piano is shown in FIG. 4 schematically as comprising a tone generator or generators 64 connected to the input connections of an amplifier 66. The output connections of this amplifier are connected tothe primary 68 of anv output transformer 70.

, The secondary coil 72 of the outputtransformerffm is connected by means of wires 7 4, 76 and l78 to Vthe `voice coil Y80 of a,loudspeaker-82'.locatedr at each piano.V The `voice coil also is connectedby means of a wire. 84 rola ,switch Contact 86 in an ,Vearphone -jack 88, one" of the contacts 90'of the jack normally engaging thecontactr86, The contact 90 is connected by means of a vwire 9,2 to a v3,001,431 A a i 4 l I n .1 y Y local instructions for thestudent, or it may provide -an orchestral background for the student, or it may provide a. time or metronome signal, or it may suit any of a further variety of purposes. As is shown in FIG. 4 a phonograph 101 is connected through a preamplifier 103 to the amplifier 66. The phonograph may compiise any suitable sort of record player known in the art, and may rest on top of the piano as hereinafter will be disclosed.

It will be appreciated by those skilled in the art that if the cables or sub-cables 26 are unduly long, there will betransmission losses which will adversely affect the tonal output from the speaker 30 or from the phone jacks 32. Accordingly, if the pianos aretobe located'at asubstantialdistance from themain Istation or'panel 28, itis preferable to use transmission lines to eliminate or minimize losses. Connections for a transmission line are shown in FIGS. 3 and Sas modifications of FIGS. 2 and 4 respectively. Most of the parts remain the' same and description thereofis unnecessary inasmuch as the similar parts are identiiiedV by similar numerals with theV addition of the Vsuflixta The modification resides, in FIG. 5, in adding Ia pair of wires 104 connected to the output of the amplifier 66af inparallelY with the primary 68a ofthe out. putftransformer. 70a. These wires 104 could be connected .to the wires 74 and 94 in the same manner as the cable -wires 38 and 40 (FIG. 4) but are illustratedas connected in parallel with the transformer 70a.VV Aline e A matchingtransformer 106 connects the wires104 tothe wires 38a and 40a -as may be seen in FIG. 5.

The structure in FIG. 3 is substantially the same as that in FIG. 2, the only change comprising the insertion of a line matching transformer 108 between the voice coil .54a of the loudspeaker 30a and the bus 46a and switch 52a. With this modification the pianos may be located at a substantial distancefrom the main station Y or 'panel 28 without any substantial transmission losses.

' The windows 112 preferably are providedwith trans wire 94 at the oppositeend of the output 7'2, from thewire74. 1 A e When a plug is inserted into the jack l88, Ythe contact 90 is moved away from the contact 86 into engagement with a contact '96, this latter.. contact beingconnected` through aresistor 98 of low valueand a wire .100 to the v wire 78. Accordingly,-when an earphone plug is inserted in the jack 88 the resistor 98 is connected in parallel with the high impedance of the earphones. so `as to Ypresent a load to the output of the amplifier which is substantially the same as that presented by the voice coil 80 ofthe loudspeaker A82. As a specific example, the resistor' 98 may be a 7.5 ohm resistorrated at lwatts.

A second earphoneljack 102 connected directly to the wires l74 land 94, thereby. being in parallel vwith the e loudspeaker -voice coil 80. Thus, the output of the piano can be listened to by one person on earphones, and by others via the loudspeaker. This often is advantageous when the student wishes to hear his own playing without being distracted by external sounds. l e e The phone jacks` 32 at the central station and shown in FIG. l preferably are `interconnected with ,the voice coil 54 in the, same manner as` the jacks 8 8 andr102 are interconnected with thevoice coil 80. They have been omitted from FIG. 2 for clarity of illustration.

dicator 34 formed thereon. The indicator 34 preferably v comprises a circular` area having windows 112 equally arcuately spaced thereabout and corresponding ,to the indicia previously mentioned with regard to the indicator.

parent or translucent plastic Vor glass of keye catching color such as red so that when a light is positioned'behind one of the Windows, it will be easy to observe from across the room which window is illuminated. e

` A shaft 114 is journaled in the` faceplate 110 concentric with the windows 112, and also is journaled in a bear ing 115 spaced therefrom and supported by any suitable support 116. A disc 118 is fixed on the shaft 114 immediately adjacent and behind the face plate 110. This disc 1181s provided with a single aperture 120 selectively alignable with the Windows 112 -upon rotation of; the

v 128 and are energized preferably at a low voltage from the secondary of a power transformer 132 having the primary `connected to the usual 110 volt alternating currn rent supply. A knob 134 is preferably provided on the protruding front end of the shaft 1714 for turning the shaft whereby to move the light bulb 124 from one window 112 to the next. v Y

The switch arm 50 previously mentioned is insulatedly supported on the shaft 114 by means-such as a slip ring 136. The contacts 48 are arcuately spaced concentrically about the shaft 114 for selective engagement by the switch arm 50. The'contacts 48 als previously indicated VIn manyv instances it will be found desirable foreach i' 7 student er piamsttoiliaen m a pecera-wane he spraying.1

with respect to FIG.- 2 and as also shown in FIG. 6 are individually connected by means of the wires 40 to the various pianos. A brush 138 slidingly engages'the slip doen/tai ri1`1g`136` and is 'connected via therelay switch 52 to' the loudspeaker 30. The switch arm 50,v is radially aligned with the light bulb 124, and accordingly the lightbulb' indicates the contact v48 that is engaged-by the arrnfS. Theknob 134 may be usedvto rotate the shaft 114 for connecting any of the pianos 2t) to` the loudspeaker orto earphones connected to the jacks 32. `Howeveryit is desirable that the teacher or monitor be able towalkabout to observe the individual students or pianists and to connect any desired piano t'o fthe Iloudspeaker 30 without the necessity of walking over `to the main or master station 28. Remote' control is effected by means of a pushbutton 140V FIG.' 8.) located at each piano. Each pushbutton includes a depressible element 142, preferably of insulatingV material, and bridged at the bottom by a conductive member 144'. A spring 146 bears upwardly beneaththe conductive member to hold the depressible element 142 in raised position, and simultaneously to hold the conductivemember out of contact with a pair of contacts 148. The contacts 148 are respectively connected to the wirel42 of the sub-cable associated with the piano in whichA the pushbutton is located and to a wire 150 connectedlto the sheath or shield 44 of that cable.

A' ratchet wheel 152 is fixed on the shaft 114, and a solenoid 154 is positioned adjacent the edge of this ratchet wheel. The solenoid as may be seen in FIG. 6 is providedrwith a coil 156, and this coil is connected by means of wires 158 to bus line 160 (FIG. 2) which are connected to the wires l52 of the sub-cables 26 and to the grounded wires' 60 vof the sheath or shield. The solenoid 154 is provided with a non-magnetic plunger 162. (FIG. l

6) and a magnetic slug 164 is threaded onto the outer end of this plunger, a jam nut 166 also being provided to lock the slug in place. Each time the solenoid coil 156 is; energized the slug 164`is drawn up against the solenoid 154, thus to m'ove the plunger 162 and to determine the exten-tof throw of the plunger. A- pawl 168 is pivoted on theopposite end of the plunger -162 from the slug 164 and urged by a spring 170 into engagement with the teeth 172 ofthe ratchet wheel 152.

A source of electromotive force is arranged for con-v nection into each wire 42 and is conveniently il-lustrated at 174 (FIG. 2) as a battery. However, it will be-under- `stood that this conveniently could be a rectied voltage `taken from the ampliiier of each piano, andithus would be located at the piano end of the wire 42 rather than at the master station end as illustrated in FIG. 2. AIn any event, eachtime one of the pushbutton elements 142 Vis de-V pressed, the battery 174 or other source of electromotive force is connected to energize the solenoid coil 156, thereby attracting the slug 164 against the end of the solenoid and acting through the plunger` 162 and pawl 168 to ro'- tate the ratchet wheel 152 a predetermined distance. Such rotation eiects movement of the rotary switch arm V50 from one of the contacts 48 to the next. A second depression of the element' 142 will advance thearm 50 'another step, and so on. Thus, the teacher or monitor may push any of the pushbutton elements 142 while observing the indicator 34 until the correct piano' is connected to the speaker 30.

It would be ,undesirable to hearthe clicks associated 'with' such switching and to hear a portion of each piano being played until the desired piano was connected in circuit.` Accordingly, the aforementioned relay coil 56 (FIG. 2) is connected in parallel with the solenoid 156 across the'bus lines 161i. Therelay `62 is o-f the quick operating, slow release type readily available in commerce. More speciiically, the switch 52 opens substantially instantaneously upon depression of the depressible element of Vone of the pushbuttons 140, and the switch does not re'close until a predetermined time thereafter, two seconds being a suitable illustrative time lag. flf the selector must be moved through several steps, each suc- 'needing impulse caused by depression of one of the pushbutton depressible elements will serve to delay the time the switch 52 i's held open.A l Accordingly, no clicks or spurious piano tones are audible, andthe desired' piano may be heard over the loudspeaker 30 a predetermined time after the last depression of the pushbutton depress. ible element.

At times it may be desirable lto connect two or more pianos simultaneously to the speaker 30 for the playing of a duet, or a quartet, or the like. Similarly, it might be desired to connect the recorder 22 and one of the pianos simultaneously to the speaker 30 for the student or other player to compare his playing with that of a piano artist, or to play a duet with the piano artist. It is to be under;

stood that the student also could play the piano accom@k paniment to a recorded solo on some other instrument s uch jas a violin or a clarinet in this manner. Also, it might be desirable to-have several of the student pianos played with the recorder. Such eventualities are provided for bymeans of the pushbuttons 36 and the switch con= tacts associated therewith. The various contacts 48 are individually connected to contacts beneath the pushbuttons 36 as may be seen in FIG. 6. Twelve pushbuttons are provided in the illustrative example, one for each of the ten pianos and for the recorder, and one which is not connected. A common bus line 176 is connected to the opposite contact associated with each pushbutton 36. The pushbuttons 36 are of .the type which may individually or simultaneously be depressed, and which will remain in depressed, closed position until 4the non-'connected pushbutton, i.e., the top one in FIG. 6, is depressed, thereby' releasing all of the remaining pushbuttons for movement to raised or non-connected position. Such pushbutton 'arrangements are well known in the art and are available in commerce. Specic illustration thereof accordingly has been omitted. It thus will be apparent that any number of the pianos and the recorder can be connected simultaneously to the speaker 30 by means of the pushbuttons 36.

A relay 17S is associated with the uppermost or non-` connected pushbutton 36 as may be vrseen in FIG. 2 and comprises arelay coil or solenoid 188 connected' tothe bus lines 160, and also a magnetic slug 182 aflixed Vto the depressible element of the pushbutton and attractable toward the solenoid or relay coil 180. Thus, eachtirne an impulse is imparted lto the bus lines by depression of the depressible element of one of the pushbuttons '140 the depressible element of the-uppermost or non-connected pushbutton 36is depressed. Accordingly, if' the teacher or monitor has a certain playing combination set up at the master station, Vhe may eliminate this combination remotely from any of the pianos simply by pushing the depressible element 142 of the pushbutton 140 at any of the pianos.

" A suitable electronic piano 20 for use in the sy's# ally rectangular outline and relatively low in height; The

case may rest on a desk, table or the like or maybe provided with detachable metal legs 186 of the wrought iron or simulated wrought iron variety, or any 'othersuit able or desirable type. The case is provided with a hngedly connected, downwardly inclined lid 188 which opens to expose the keyboard 190 comprising conventional piano keys. The lid 188 tilts back into position for cooperation with a tray V192 to form a music rack. The phone jacks 88 and 102 previously described are preferably located above and below the shelf respectively at the right end thereof. 'Ihe speaker 82 is mounted within the case adjacent the opposite end thereof and opens upwardly through a grille 194.,

Ihe tone generators 64 comprise a series of vibratory reeds 196 capacitively related to a conductive pickup-element 198, preferably having a slotted edge confronting the reeds with the reeds vibrating in the slots. 196,f and pickup element 19S` are respectively connected to the input of the amplifier 66, and impart oscillations The reeds l Ycorresponding to piano tones to the amplifier when the reeds are vibrated.' The reeds are vibrated by hammers v 200 of piano actionsa202 which may be of conventional or special manufacture, each piano action corresponding Y means of a push-pull control such as a Bowden cabler210 v tothepiano.

It Will be observed that a handle 212'is provided at the front of the piano case for carrying the same, and that slots V2114 are provided at opposite ends of the case to facilitate handling thereof `and also to control back loading of the loudspeaker 82.

` The pushbutton 140 associated with each piano may be located at any` convenient location thereon, such as on the top and near the rear as illustrated in FIGS. 9 and 10. The phonograph or record player 101 also may rest on top ofthe piano with the preamplifier in the record,` playerV housing (not shown) and suitably connected to the ampliiier 66 byfa cable 204 of any suitable design and preferably having a plug for detachable association with a jack lin the piano case.

It will be apparent from the foregoing that each student or other player on one of the pianos 20l can play and listen with earphones plugged into the jack 88 to hear his ofwn playing Without any other playing being audible. A teacher orrmonitor can walk around the room, observing the lingering and other manipulation Yof each player, and can carry earphonesto plug'into each jack` 102 to listen to the playing of each piano one by one, `If the teacher wishes to hear the playing on the central station loudspeaker,` all he needs to do is to push the depressible member 142 ofthe pushbutton 140 onfvvhi'ch ever pianohe is near and to watch the lights of the indicator V34' for alignment with the proper position number. ,'Ifhe earphone plug of any given piano can be'pulled out momentarily for-the student to listen toV his own playingcompared with that of a piano artist from the recorder 22Vif it is so desired, or he may slip one of lthe earphones aside so'that he may listen to his otwn playing with a single earphone while listening to the recorder with the other ear. Y The teacher or monitor may utilize earphones at the central station if he so desires by means of the jacks 32, and may utilize ythe knob 1.34 to move the selector He may utilizenthe` pushbuttons 36 to set up Vany given combination of the pianos for playing d uets, quartettes, and the like.- l p It will beappreciatedthat various pupils or musicians will play theiry instruments at different volume levels. If

the teacher or monitor were to walk around the room and connectk any given piano to the master or central station,

,l the-intensity of some of the instruments Would be too great, while the tones of some of the other instruments Vwould scarcely be audible. Accordingly, provision preferably ismade for maintaining the volume level emanating from the Vloudspeaker' 30 at any predetermined level adjustablyfpre-set'by the teacher or monitor. v This is Y accomplished by the circuit shown in FIGS. l2 and 13. Instead of connecting the wires 38 and 40 directly through the swi'tch contacts 48, 50 and the relay switch 62 to the speaker'voice coil 54, the connectionsare made'to anA amplifierstage 216. The ampliiier stage 216 is connected inA eXact-lythesame way as the speaker ,coil 54 previously was illustrated, and vthe wiring otherwise rethe same; The ampliier stage 2k6 is connectedl by-means of wires 2418 and 220` to a variable Ygain stage 222 `designed to have-a constant out-put at 224 across a current potential, proportional to the output of the amplivolume control potentiometer 226. VThe sliding Vtap 228 l) or the like at the main station 28. Theisliding tap is connected by means of a wire 230 to ther inputof l amplifier .outputfstage 232, and a wire 233fconnects the lower en d of the potentiometer resistor'226 to the am'- pliiier output stage.V The ampliiier output stage preferably is provided With a matching transformer 234 fordconnection to the voice coil of the loudspeakerY at the main*- station. ,It will be understood that the ampliiier output stage preferably includes a pair of push-pull power output tubes.

A signal is tapped oif the Wires 218 and 220 by means of Wires 236 and 238 respectively, these wires being con.

nected to an input of an auxiliary vampliierV 2540. The amplifier stagek 240 is connected by means of wires 242 to a rectifier 244, which may be of any suitable type `such as a diode, and maycomprise the diode plates of a dual purpose tube including Yalso an amplifier section in the variable gain stage 222. The rectifier output is a direct lier :stage 216, and this of` course` is proportional to the Vvolume of the instrument connected `to the main station;

The output of the rectifier is used to control the gain of the variable gain stagey 222 so that the intensity of the output thereof appearing at 224 is substantially constant regardless of the intensity ofy Ilthe output of the amplifier stage l216, iand hence of the input of the'` lampliiier stage 222. Thus the volume of the tones reproduced by the loudspeaker at the main station is substantiallyentirely independentof the volume of the instrumentconnected to the main station, land the volume of these output tones can be pre-set at any desired level by the instructor or monitor by turning the knob 231 to adjust thepof tentiometer tap 228.

'Themanner in which the the variable gain stage 222 is shown in FIG. 13, the audio input to the controlling stage as applied to the Wires 218 `and 220, being connected directly by means of a capacitor 246 and a` lseries resistor 248 to the plate of a loading or shunt triode tube 25,0 included Yin the variable gain stage 222.k The ou-tput of the rectifier 244 biases the control andthe Vplate also-is connected through a` coupling capacitor 256 to the potentiometer resistor 226. It will be apparent from van inspection of the circuit shown in FIG. 13 that the output intensity of the variable gain stage 222 as applied through the capacitor 256 Iis substantially constant due to the biasing action of the rectilier 244.

Although the invention has been described with reference to electronic pianos, it will be apparent that other instruments could -be used With suitable provision for an electrical output and for audio isolation. Indeed, several different instruments could be used to provide a band or orchestra, quantette, trio,'duet or the like, and the teacher, monitor, or conductor could `listen to each student or instrumentalist individually, or could combine the tones of the instruments by means of the pushbutton switches to obtain the full effect of the orchestra orother group.

The loudspeakers at all of theV instrumentscould be @used toecreate -a similar, but more dispersed ei'ect. Y

The specific structure herein shown and described is for v illustrative purposes only, and various modifications thereof occurring to those skilled in the tart Will be instrument having means providing electrical oscillations corresponding to `the tonesr of that instrument, means at each instrument operatively connected to the oscillation providing means for individually Vlistening to the tones Vof rectiiier 244 is connected' to that instrument, a station located remotely of said instruments, means at said station for transducing said electrical oscillations into audible instrument tones, connecting switch means at said station for selecting which of the oscillations is to be tranduced at said station, means at said station for operating said selecting means, means remote relative to said station and respectively at said instruments and respectively operatively connectedto said selecting means for operating the selecting means,.and means connecting said electrical oscillation. providing means to said selecting means.

2. A musical instrument system comprising a plurality of individually operable musical instruments, each such instrument having means providing electrical oscillations corresponding to the tones of that instrument and further including volume control means for determining the amplitude of said electrical oscill-ations for volume control purposes, means Iat each instrument operatively connected to said oscillation providing means for individually listening to the tones of that instrument, said tones varying in volume in accordance with the intensity of the oscillations as determined by said volume control means, a station located remotely of said instruments, means at said station for transducing electrical oscillations into audible instrument tones, means respectively operatively connecting said oscillation providing means to said station and means at said station connected to said last mentioned connecting means for selectively coupling the electrical oscillations from any of the musical instruments to said transducing means, said selectively coupling means including means for adjustably predetermining the amplitude of the oscillations applied to the transducing means regardless of the amplitude of the oscillations as determined by'said volume control means.

3. A musical instrument system comprising a plurality of individually operable musical instruments, each such instrument having means providing electrical oscillations corresponding to the tones of that instrument, means at each instrument operatively connected to said oscillation providing means for individually listening to the tones of that instrument, a -station located remotely of said instruments, means at said station for transducing said electrical oscillations into audible `musical tones, means at said station for selectively individually connecting said instruments to said transducing means for transducing the electrical oscillations thereof into audible musical tones, separate means at said station `for selectively connecting a group of said instruments to said transducing means for simultaneously transducing the electrical oscillations of said group of instruments into audible musical tones, and

separate means for operating said individual connecting means and said group connecting means, the means for operating the individual connecting means comprising mean-s at said station -and a plurality of means respectively located at said instruments.

4. A musical instrument system as set forth in claim 3 and further including means interconnecting said individual connecting means and said group connecting means whereby operation of said individual connecting means eiects disconnection of said lgroup connecting means.

5. A musical instrument system as set forth in claim 1 and further including indicating means operable in conjunction with said selecting means kfor indicating the position of said selecting means, said selecting means including a light source movable with said selecting means.

6. A musica-l instrument system as set .forth in claim 1 and further including a constant volume device at said station providing a substantially constant output amplitude'of electrical oscillations substantially independent of the amplitude of input oscillations thereto, the output oscillations of said instruments lbeing selectively connected by said selecting means to said transducing means for producing a substantially constant volume of musical tones substantially irrespective of the volume control setting of" said instruments. Y

7. A musical instrument system as set forth in claim 1 and further including an intermittent operating device for intermittently moving said selecting means from one position to another whereby selectively to connect any one of said instruments to said transducing means.

8. A musical instrument system as set -forth in claim 7 wherein the operating device comprises a stepping switch.

References Cited in the iile of this patent UNITED STATES PATENTS 1,296,617 Britten Mar. 11, 1919 1,632,012Y Toomey June 14, 1927 1,685,835 Bascom et al. Oct. 2, 1928 1,924,713 Eremeeff Aug. 29, 1933 2,110,358 -Dreisback Mar. 8, 1938 2,162,369 Campbell a June 13, 1939 2,225,196 iMiessner Dec. 17, v1940 2,258,807 Pitkin Oct. 14, 1941 2,427,078 `Tucker et a1. Sept. 9, 1947 2,492,320 Riggen Dec. 27, 1949 2,496,629` Lamberty et al. Feb. 7, 1950 2,530,251 Luberoff Nov. 14, 1950 2,606,976 Campbell Aug. 12, 1952 2,695,338 Doriot et al. Nov. 23, 1954

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