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Title:
ELECTRONIC MUSICAL INSTRUMENT CIRCUIT
United States Patent 3813474
Abstract:
A key actuated electronic musical instrument of the type suitable for use with piano or organ keyboards, or the like, has a single relaxation oscillator circuit for producing melody tones from selected keys of a keyboard, and three relaxation oscillator circuits for producing chord tones from other selected keys of the keyboard. A delta pitch circuit which produces a sawtooth-like output signal is coupled to one of the inputs of the single oscillator to provide a rapidly changing sound going from a flat tone to a natural tone. The signals for producing melody sounds are delivered through a selective filter circuit which will selectively simulate the sounds of, for example, a saxophone, brass, horn, or a string instrument. The sound signal from the filter circuit is then delivered to an audio amplifier and loud-speaker system. The three oscillator signals for producing chord sounds are mixed together in a transistor buffer stage and then delivered to the audio amplifier through a gate circuit formed by a light-emitting diode and a light-dependent resistor. The gate circuit is responsive to an automatic rhythm generator so that chord sounds may have a selected rhythm. Also connected to the audio amplifier is the automatic rhythm sound generator which can play one of several rhythms utilizing desired percussion sounds. An adjustable vibrato circuit is connected to the melody oscillator to produce a pulsating sound that can be varied in frequency.


Application Number:
05/283832
Publication Date:
05/28/1974
Filing Date:
08/25/1972
Assignee:
The Wurlitzer Company (Chicago, IL)
Primary Class:
Other Classes:
84/706, 84/713, 84/DIG.22, 984/311, 984/324, 984/347, 984/380
International Classes:
G10H1/043; G10H1/06; G10H1/36; G10H5/04; (IPC1-7): G10H1/02
Field of Search:
84/1
View Patent Images:
Other References:

J Venn, "A Simple Electronic Chord Organ," Electronic Engineering, July, 1961, pp. 421-425..
Primary Examiner:
Wilkinson, Richard B.
Assistant Examiner:
Witkowski, Stanley J.
Attorney, Agent or Firm:
Olson, Trexler, Wolters, Bushnell & Fosse Ltd.
Claims:
The invention is claimed as follows

1. An electronic musical instrument comprising: a first sound generator means having a single oscillator and a first output for producing melody tones, a first group of resistor means connected to said single oscillator, a plurality of switches connected to said first group of resistor means to switch said resistor means into and out of circuit therewith for producing said melody tones at said first output, a second sound generator means having a plurality of oscillators and a second output for producing chord tones, a second group of resistor means forming a plurality of sub-groups of resistor means, a plurality of switches connected to each of said sub-groups, each sub-group of resistor means including discrete resistor elements being connected to a selected one of said plurality of oscillators and each discrete resistor element of each sub-group selectively switched into and out of circuit with its oscillator for energizing the oscillator at different frequencies to produce predetermined chord tones at said second output, audio amplifier means connected to said first and second outputs for simultaneously receiving said melody and said chord tones, and loud-speaker means connected to said audio amplifier means to provide melody and chord sounds therefrom.

2. The electronic musical instrument of claim 1 further including a source of alternating current voltage, and circuit means including a switch connected between said source of alternating current voltage and said single oscillator of said first sound generator means for selectively inserting into said single oscillator a supplemental fix frequency sound.

3. The electronic musical instrument of claim 1 wherein said plurality of oscillators of said second sound generator means is three oscillators, and said second group of resistor means includes three sub-groups of resistor means, one sub-group connected with each respective oscillator.

4. The electronic musical instrument of claim 1 wherein each of said oscillators includes a programmable unijunction transistor operated in a relaxation oscillator circuit mode.

5. The electronic musical instrument of claim 1 wherein said first group of resistor means is formed of a plurality of discrete resistors and connected in series and forming a circuit point between each resistor, said discrete resistors of said first group being switched into and out of circuit with said single oscillator at the circuit points between the resistors of said first group, whereby the total resistance value connected with said single oscillator is the sum of the values of the discrete resistors between said single oscillator and a selected one of said circuit points.

6. The electronic musical instrument of claim 5 wherein each of said sub-group of resistor means is formed of a plurality of discrete resistors connected in series and forming a circuit point between each resistor, said discrete resistors of each of said sub-groups being switched into and out of circuit with its associated oscillator of said second sound generator means at the circuit point between the resistors of said sub-group.

Description:
BACKGROUND OF THE INVENTION

This invention relates to electronic musical instruments of the type which can electronically reproduce melody tones, chord tones, and selected rhythm patterns of percussion instruments. More particularly, this invention relates to electronic organs or the like.

Electronic organs per se are old in the art and this invention is directed to an improved electronic circuit for organs wherein great cost savings and circuit simplicity are obtained. Heretofore, electronic organs have been provided with either built-in or add-on rhythm tone generator systems which provide rhythm patterns of, for example, march music, rock-and-roll music, swing music and the like, and each of these rhythm patterns includes a plurality of different percussive instrument sounds. However, prior art rhythm sound generator systems have been relatively expensive and therefore they have been associated only with the more expensive electronic organs. Also, electronic musical instruments such as organs may include vibrato circuits which cause pulsing of audio signals when a key is sustained in a depressed condition. Here again, the circuitry utilized to generate the vibrato effect has been relatively expensive and incorporated only in more expensive electronic organs. In the more expensive electronic organs there may be provided two or more keyboards for generating melody tones and chord tones. Also, a pitch changing circuit may be included which allows the tone of the sound to change from a flat or sharp tone signal to a natural tone signal when the key on the keyboard is depressed. This will cause a tone signal of either a flat or sharp tone initially to be reproduced when the key is initially depressed, and after a short time interval, and while the key is still depressed, the flat or sharp tone signal will automatically change in frequency to a natural tone signal.

All of these features require complicated circuitry and a multitude of oscillators and mixers incorporated in these electronic musical instruments to achieve the desired result.

SUMMARY OF THE INVENTION

Accordingly, it is an object of this invention to provide an electronic musical instrument circuit arrangement which is simple and inexpensive to manufacture while still being efficient and reliable in operation.

Another object of this invention is to provide an inexpensive electronic musical instrument circuit suitable for use in an electronic organ but which has all of the features of the more expensive electronic organ circuits.

Many other objects, features and advantages of this invention will be more fully realized and understood from the following detailed description when taken in conjunction with the accompanying drawings wherein like refrence numerals throughout the various views of the drawings are intended to designate similar elements or components.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1, 2, 3, 4 and 5 taken together illustrate a detailed schematic diagram of an electronic musical instrument circuit which can be used in an electronic organ in accordance with the principles of this invention; and

FIGS. 6, 7 and 8, taken together, is a detailed schematic diagram of the logic circuit utilized in the rhythm sound generator circuit shown in FIG. 3.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT

Referring first to the FIGS. 1 and 5, the electronic musical instrument circuit of this invention includes a first sound generator circuit designated generally by reference numeral 10 and which has an output transistor 11 associated therewith. A second sound generator circuit is designated generally by reference numeral 12, and has a second output transistor 13 associated therewith. The first sound generator circuit 10 has a single oscillator circuit 14 connected to resistor means, here being a plurality of resistors 16 through the leads designated by reference letters A between FIGS. 1 and 5.

The second sound generator circuit 12 has a plurality of oscillator circuits for generating a plurality of tones of corresponding chord signals. Preferably the second sound generator circuit has three such oscillator circuits 17, 18 and 19. The oscillator circuits 17, 18 and 19 are connected to corresponding groups of resistor means 20, 21 and 22, respectively. The plurality of resistors 16 are associated with a corresponding plurality of key switches 23, which are associated with the keys on a piano-like keyboard used in electronic musical instruments such as organs. The keys are actuated to cause the switches 23 to engage a bus bar 24 when melody tones are played. Upon actuation of each different key of the keyboard, different amounts of resistance are placed in circuit with the single oscillator 14 to change the frequency of oscillation thereof. This change in frequency for each incremental change in resistance will produce the desired melody tones. The chord tones are produced by keys associated with the switches 26, 27 and 28 connected to the groups of resistor means 20, 21 and 22, respectively. Actuation of one or more of the keys 26, 27 or 28 will produce oscillation within the respective oscillators 17, 18 and 19 and are mixed together within the output transistor 13.

The audio output signal from the output transistor 11 is delivered to an audio amplifier circuit 29 of FIG. 4 through a line indicated by reference letter B between FIGS. 4 and 5. On the other hand, the audio signals producing the chord tones are mixed in the output transistor 13 and delivered to the audio amplifier 29 through a rhythm gate circuit 30, therefrom through terminal C to an audio amplifier and buffer transistor 31 and a variable resistance volume control element 32 which acts as a volume control for both chord and percussion rhythm tone signals. The output from the potentiometer 32 is delivered to the audio amplifier circuit 29 through line D between FIGS. 2 and 4. The output of the audio amplifier is connected to a loud-speaker system 33 which will reproduce all of the mixed sound, i.e. the melody tones, the chord tones and the rhythm percussion sounds.

The electronic musical circuit of this invention also includes a logic circuit 36, shown in FIG. 3, for automatically producing rhythm percussion sounds which can be used as accompaniment. The logic circuit 36 has a variable resistance element 37 which functions as a tempo adjustment so that the speed or tempo of the selected rhythm can be adjusted to suit the person using the electronic organ, or the like. The desired rhythm pattern for the percussion sounds can be selected by actuating one of several switches 38, 39 or 40 which are associated with march music, rock-and-roll music and swing music, respectively. A switch 41 will provide a metronome signal which may be used to aid beginners in learning to maintain a tempo. A plurality of output leads having designations bass drum, snare drum, cymbal and brush receive the percussive sounds in accordance with the rhythm pattern selected, and these percussive sounds are applied to correspondingly marked terminals of FIG. 2 to be gated therefrom to an audio amplifier. The cymbal, brush and snare drum terminals are connected to a gate logic circuit designated generally by reference numeral 42 which also has associated therewith a noise generator circuit 43. The cymbal and brush signals are applied through the gate circuit and therefrom over a line 44 to the input of the amplifier transistor 31 and therefrom to the volume potentiometer 32. However, the snare drum signals are applied to a filter circuit 46 which also receives signals from the noise generator 43 to selectively pass a desired band of intermixed noise signals to more accurately reproduce the sound of a snare drum. The output of the filter circuit 46 is also connected to the line 44 and therethrough to the base electrode of transistor 31. The bass drum circuit 47 does not receive noise signals and is directly connected to the base of the transistor 31. The snare drum terminal is also connected through a line 48 to terminals E between FIGS. 2 and 3 for connection to a two hundred hertz output signal terminal on the logic circuit 36.

Also associated with the electronic musical instrument circuit of this invention is a variable frequency vibrator oscillator circuit 50, FIG. 1, which produces a triangular wave shape at the output thereof and which triangular wave shape is transformed substantially into a sine wave by a wave shaping circuit 51. A power supply 51, FIG. 3, has an output lead 53 connected to the secondary winding of an input transformer 54 and therefrom through a switch 56 via terminals F and G to the input of the single oscillator of the first sound generator circuit. This will apply a 60 cycle signal to the oscillator for modulating the frequency thereof at a continuous 60 cycle rate. This type of musical effect is selectively switched in and out of the circuit by means of the switch 56.

For a better understanding of the details of each of the discrete circuit arrangements of the overall electronic musical instrument system, reference is again made to FIG. 5. Since the first sound generator means includes a single oscillator which is substantially similar to the plurality of oscillators 17, 18 and 19 of the second sound generator means, only a detailed description of the single oscillator 14 will be given.

The oscillator 14 includes a programmable unijunction transistor 60 connected in shunt current relation with a capacitor 61 which, in turn, is connected in series current relation with a current feed resistor 62 which applies charging current thereto. The current feed resistor 61 is connected through terminals A back to the plurality of resistors 16, FIG. 1, and receives an operating voltage from the bus bar 24 when any one of the key switches 23 is actuated. When power is applied across resistor 62 and capacitor 61 the programmable unijunction transistor 60 operates as a relaxation oscillator whose frequency is determined by, among other things, the voltage developed across a resistor 63. This voltage is applied to resistor 63 from a terminal 64 which, in turn, is connected to a voltage divider network comprising resistors 66, 67 and potentiometer 68. The junction between resistor 67 and potentiometer 68 is connected to resistor 63 through a diode 69. Adjustment of potentiometer 68 will select the firing potential of the programmable unijunction transistor 60 so that the initial frequency of the relaxation oscillator can be adjusted. Frequency changes for different notes are then accomplished by inserting different resistance values into the circuit by actuating the desired key switches 23.

The output of the single oscillator 14 is delivered to the output transistor 11 through a coupling capacitor 70. The output transistor 11 operates as an emitter follower circuit having a signal developing resistor 71 connected between the emitter and ground potential and a coupling capacitor 72 for feeding the signal from the oscillator 14 into a selected one of a multiple filter network 73.

The multiple filter network 73 includes a plurality of discrete filter paths between the output transistor 11 and an amplifier transistor 74. For example, the filter network may include a path 76 which has a filter configuration to simulate a saxophone sound, a filter path 77 has a filter configuration to simulate a brass sound, a filter path 78 has a filter configuration to simulate a horn sound, and a filter path 79 has a filter configuration to simulate a string sound. The desired filter path or corresponding sound simulation is achieved by actuation of corresponding switches 80, 81, 82 and 83 connected in series circuit relation with the associated filter paths 76, 77, 78, 79, respectively. The modified signal from oscillator 14, i.e. the signal now having a sound configuration corresponding to one of the sounds of the filter paths, is amplified by transistor 74 and delivered through a coupling capacitor 86 and a potentiometer 87 and series resistor 88 through terminals B, FIGS. 4 and 5, to the input capacitor 89 of the audio amplifier circuit 29.

In the illustrated embodiment of this invention the audio amplifier 29 has the active electronic components thereof formed on an integrated circuit element designated generally by reference numeral 90 and can be of any suitable configuration. For example, the audio amplifier circuit 90 may be a five watt amplifier having capabilities of producing an audio output without the use of audio coupling transformers. The audio amplifier circuit 90 can take the form of the transformerless audio amplifier as illustrated in the GE Transistor Manual (1964) page 263, which is an 8-watt amplifier, but which may have the output thereof reduced to 5 watts. The input terminal 91 of the integrated circuit element 90 is provided with a filter circuit comprising capacitor 92 and resistor 93 which eliminates extraneous high frequency noise pulses from the desired musical instrument tone signals. Power is applied to the integrated circuit 90 through a power receiving terminal 94 which applies operating bias to the input terminal 91 through a resistor 96 and which applies operating potential to a terminal 97 through a pair of series connected resistors 98 and 99. A feedback capacitor 100 may be provided to effect regenerative or degenerative feedback as desired, depending on what point in the circuit it is connected. Additional high frequency filtering may be provided at an output line 101 by means of a series resistor and capacitor circuit 102. A relatively large value capacitor 103 is in series relation with an output jack terminal 104 which, in turn, is connected in series with the speaker system 33. The large value capacitor 103 is effective as a DC blocking element while passing substantially all audio signals of the entire frequency spectrum being reproduced. The jack switch unit 104 can be used to operate a headphone unit, in which instance the loud-speaker system 33 is completely disconnected from the circuit. Also connected in circuit with the input capacitor 89 of the audio amplifier 29 are a pair of jack plugs 106 and 107 which may correspond to a tape recorder output and a tape recorder input, respectively. Therefore, the melody tones generated by manipulation of the key switches 23 and delivered to the audio amplifier 29 by the filter network 73 can be recorded on a tape recorder. Also, prerecorded tapes can be fed into the audio amplifier 29 to accompany the person playing the electronic musical instrument of this invention.

The output of the plurality of chord tone oscillators 17, 18 and 19 are also delivered to the input capacitor 89 of the audio amplifier 29 for audible reproduction thereof within the loud-speaker system 33. However, the chord tone signals are delivered thereto through the rhythm gate circuit 30, amplifier transistor 31 and volume potentiometer 32 via the coupling leads D. The outputs of the chord tone oscillators 17, 18 and 19 are mixed together and amplified within transistor 13 which operates as a class A amplifier biased by means of resistor 108, and a resistor 109 which is connected to a power terminal 110. The amplified and mixed signals are delivered through a coupling capacitor 111, a voltage developing resistor 112 and applied through a variable resistance element 113. The value of the variable resistance element 113 corresponds to the rhythm pulse pattern produced within the logic circuit 36, of FIG. 3, to cause rhythm gating of the chord tones. The variable resistance element 113 preferably is a light-dependent resistor which changes its resistance value between high current passage and low current passage states in accordance with the light intensity impinging thereon. The rhythm gate circuit 30 is responsive to the rhythm pattern of the logic circuit 36 by means of a light-emitting diode 114 which generates light signal pulses in accordance with the pulse pattern of the rhythm circuit. Therefore, the light-dependent resistor 113 will vary between high conductive and low conductive states to vary the amplitude of the chord tone signal from oscillators 17, 18 and 19. The output of the rhythm gate circuit 30 is then delivered through a fixed resistor 116 through leads C, FIGS. 1 and 2, and into the amplifier transistor 31.

The transistor amplifier 31 includes a biasing resistor 117 and a voltage developing resistor 118 connected to a power terminal 119. A feedback resistor 120 is coupled between the collector and base electrode of transistor 31. The output of the transistor is delivered to the volume potentiometer 32 through a series coupling capacitor 121 and a resistor 122. The amplifier transistor 31 also has connected to the base electrode thereof the gating circuit 42 which applies cymbal, brush, snare drum and metronome signals for amplification.

The cymbal sound signals are delivered through a diode 130, capacitor 131 and resistor 132 to a gating diode circuit comprising diodes 133, 134 and 135 connected in series with one another and in series with the collector of a transistor 136. The junctions between diodes 133 and 134 are connected to the cathode of a diode 137 which has its anode connected through a coupling network of resistor 138 and capacitor 139 to the filter circuit 46. Similarly, the brush percussion sounds are delivered through a diode 140, capacitor 141 and resistor 142 to a diode 143 which also is connected to the cathode of diode 137. The cymbal and brush percussion sounds are then mixed together through resistors 501 and 502 and connected to amplifier transistor 31. In each instance, i.e. when cymbal and brush percussion sounds are generated, a noise of suitable frequency and amplitude is mixed therewith by means of the noise generator 43. When the potential at the cathode of diodes 133 or 134 exceeds the reverse bias condition of diodes 134 and 135, the noise generator 43 will produce an output to be mixed therewith.

The noise generator 43 comprises a transistor 150 having the base electrode thereof connected to ground potential and the emitter electrode thereof coupled through a capacitor 151 to a transistor 152. Power is applied to transistors 150, 152 and 136 by means of a voltage terminal 153 and corresponding load dropping resistors connected in series with the respective transistors. The noise generating transistor 150 has the collector electrode thereof free of other electrical component connection so that inherent circuit noise between the base emitter junction of the transistor is generated and amplified through the two transistors 152 and 136.

Also delivered to the filter circuit 46 is the snare drum percussion sound through a diode 156, capacitor 157 and resistor 158. The proper time sequence for the gating of the snare drum percussive sounds is generated within the logic circuit 36 and delivered to the snare drum terminal via the lead marked snare drum, FIG. 3.

Gating pulses from the logic circuit are applied to the bass drum terminal and therefrom through a diode 164, capacitor 165 and resistor 166 to a splitter capacitor network 167 at the input of the bass drum percussion sound amplifier 168. The signal is then applied to the base electrode of transistor 31 through a series coupling capacitor 169 and series resistor 170. Therefore, all of the signals except the melody signal, i.e. the chord tone signals and the percussion sound signals are mixed together within the amplifier transistor 31 and applied to the volume potentiometer 32.

The single oscillator circuit 14 of the sound generator means 10 is connected to the variable frequency vibrato oscillator 50 through the lines G between FIGS. 1 and 5. The vibrato oscillator 50 is always oscillating at some frequency. The output of the operational amplifier 172 is of triangular wave shape and is applied to a pair of parallel connected diodes 173 and 174 through a series resistor 176. The diodes 173 and 174 will cause clipping of the triangular wave shape signal from the vibrato oscillator 50. The value of resistor 176 is selected so as to cooperate with the diodes 173 and 174 and produce substantially a sine wave configuration to within 2 per cent of a pure sine wave. This almost pure sine wave configuration is adjustable in frequency from between 1/2 to 60 hertz by means of a potentiometer 177 which has the movable contact arm thereof connected to the output of a second operational amplifier 178. The operational amplifiers 172 and 178 are cross-coupled to operate substantially as a multivibrator oscillator with a square wave signal appearing at the output of the operational amplifier 178. The almost pure sine wave is applied to the input of a third operational amplifier 180 through a potentiometer 181 and a series resistor 182. This vibrato signal is then delivered through a resistor 183 back to the single oscillator circuit 14 through a capacitor 184, FIG. 5. A filter capacitor 186 is connected between the output of the third operational amplifier 180 and ground potential so as to filter extraneous signals therefrom.

The operational amplifier 180 has a second input terminal connected to a delta pitch selector switch 187 through a transistor 188 and a capacitor 189. Upon closing the delta pitch selector switch 187 a pulse signal is applied through capacitor 189 each time one of the key switches 23 is actuated to come into contact with the power bus bar 24. This delta pitch signal is then applied through transistor 188 and operational amplifier 180 to provide a rapidly decaying pulse signal at the output thereof which is delivered through the resistor 183 and to the single oscillator 14 through leads G. Upon actuation of each of the key switches 23, when the delta pitch switch 187 is closed, the tone signal produced at the single oscillator 14 will start out, for example, as a flat tone and then change into a natural tone for the duration of closure of the selected key switch 23.

To provide still another novel sound effect from the single oscillator 14 a fixed frequency 60 cycle signal from the power supply 52 is delivered through a line 53, a switch 56 of FIG. 1, and therefrom into the single oscillator 14 through line G and capacitor 184. When switch 56 is closed, the oscillator 14 will be modulated at a 60 cycle rate. This feature produces sound effects which are often desired by teenage users.

The power transformer 54 of the power supply 52 has a primary winding 190 shunted by an indicating lamp 191 and a series current limiting resistor 192. A power on/off switch 193 is in series with one of the power lines leading from a power plug 194. The transformer 54 has a center tap secondary winding 196 which has the end lead terminals thereof connected to a pair of diodes 197 and 198 which are arranged in a full wave rectifier configuration. The diodes 197 and 198 have their cathodes connected to a relatively large filter capacitor 199 which, in turn, has the other end thereof connected to ground potential. The rectified and filtered voltage developed across capacitor 199 is delivered to a power output terminal 200 for operating various circuit components within the musical instrument circuit of this invention. Also connected to the rectified and filtered DC voltage developed across capacitor 199 is a voltage regulator 201 which has the output thereof connected to the emitter electrode of a transistor 202 which, in turn, is operatively connected to the base electrode of a series regulating transistor 203. The transistor 203 is rendered conductive to a level corresponding to the amount of power needed within the circuit. Additional filtering is obtained by a capacitor 206 which may be in the order of 10 to 25 microfarads. The output voltage at terminal 204 may be in the order of 22 volts more or less. For additional circuit components requiring a lower output regulated voltage a regulating transistor 207 is connected between the output terminal 204 and an output terminal 208. This transistor will develop an output in the order of 11 volts to operate circuit components as necessary.

FIG. 3 also shows the logic circuit 36 and the various external switches and potentiometers associated therewith. For a better understanding of the detailed circuit arrangement of the logic circuit 36, reference is now made to FIGS. 6, 7 and 8 which illustrate the interconnection between the various circuit components.

The logic circuit of FIGS. 6, 7 and 8 includes an oscillator circuit 210, in FIG. 8, which oscillates at an output frequency of about 200 hertz. It will be understood that other frequencies can be used as desired. The oscillator circuit 210 is formed of a pair of inverter circuits 211 and 212 of an integrated circuit chip designated generally by reference numeral 213. The inverter circuit 211 receives power from a terminal 214 through a resistor 216 while the inverter circuit 212 receives power through the resistor 217. A pair of cross-coupling capacitors 218 and 219 are connected between the output of one inverter circuit to the input of the other. The oscillator circuit 210 operates as a conventional multivibrator producing square wave output along the lines K connected between FIGS. 8 and 6. A transistor emitter follower 220 has an emitter resistor 221 associated therewith for developing the snare drum voicing which is coupled to the snare drum filter circuit of FIG. 2.

The output of the oscillator circuit 210 is delivered to a Schmitt trigger circuit designated generally by reference numeral 225 comprising a pair of NAND gates 226 and 227. This signal is applied to the NAND gates through a 0.1 microfarad capacitor 228 and a variable potentiometer 229 which serves as a tempo adjustment to vary the rate which the percussion rhythm sounds are produced. The operation of the oscillator circuit 210 and Schmitt trigger circuit 225 is such that the repetition rate of the Schmitt trigger is determined by the resistance value of the tempo potentiometer 229. The pulse width of the Schmitt trigger is determined by a 3.3 microfarad capacitor 230 and a variable resistance element 231. The pulse width is used to determine the keying on time for all rhythm voices used in the rhythm circuit. When a "Swing" rhythm is used it requires twelve counts or beats per measure, and when a "March" rhythm is used it requires eight counts or beats per measure.

The output of the Schmitt trigger is developed across a transistor 232 and applied therefrom to the input of a multiple flip-flop circuit 233 at the respective input terminals 234 and 235 thereof. The multiple flip-flop circuit comprises a pair of J-K flip-flops of well-known configuration. The output from the Schmitt trigger is also applied to the inputs of a pair of AND gates 236 and 237 which, in turn, have the other inputs thereof coupled to respective different ones of the flip-flops of the multiple flip-flop circuit 233. Therefore, proper gating of signals is obtained between the AND gates 236 and 237. The output of AND gate 236 is delivered to one input of each of the AND gates 240 and 241 and to one of the lines of group H, between FIGS. 6 and 7, to an inverter circuit 242. The output of the inverter 242 is applied to one of the lines of group J and therefrom to a second inverter 244 to provide a brush percussion sound effect. The output of AND gate 237 is applied to an AND gate 246 together with the output of a second multiple flip-flop circuit 247. Flip-flop circuit 247 is also connected to one of the input leads of the AND gate 240.

The AND gates 240, 241 and 246 are interconnected with AND gates 250, 251 and 252 to provide the appropriate pulse pattern corresponding to the desired rhythm, i.e. swing, march etc. The appropriate rhythm pattern is delivered over the H lines between FIGS. 6 and 7 to be applied to the inputs of a plurality of inverter circuits designated by reference numerals 260, 261 and 262 corresponding to a march rhythm pattern, a swing rhythm pattern, or a rock-and-roll rhythm pattern, respectively. These rhythm patterns are then delivered over the J lines back to FIG. 8, as mentioned above through the appropriate inverter circuits 244, 264, 274 and 284 to produce the snare drum cymbal and bass drum sound effects.

In accordance with the principles of this invention the rhythm gate circuit 30 of FIG. 1 is again shown in FIG. 7 but in this instance the light-emitting diode 114 is shown connected in its appropriate operating circuit while the light-dependent resistor is shown only schematically. The light-emitting diode 114 is connected in series current relation with the transistor 267 which is rendered conductive in accordance with the pulse sequence pattern from an inverter complex designated generally by reference numeral 268. The pulse rhythm pattern is applied through a series connected transistor 269 which, in turn, operates the transistor 267. As mentioned above, the gating of the chord tones produced by the chord key switches 26, 27 and 28, FIG. 1, is accomplished substantially in conformity with the rhythm pattern selected.

What has been described is an overall detailed circuit arrangement for an efficient and inexpensive electronic musical instrument which can be used to function as an electronic organ or the like. The electronic circuit illustrated herein has all of the features of more expensive organ circuits which have automatic rhythm accompaniment, vibrato effect on melody tones, a 60 cycle modulation of the melody tones, when switch 56 is closed, and includes a delta pitch circuit selectively to change the tonality of the melody keys when depressed. Accordingly, it will be understood that variations and modifications of this invention may be effected without departing from the spirit and scope of the novel concepts disclosed and claimed herein.