US 2497661 A
Description (OCR text may contain errors)
Feb. 14, 1950 R. B. DOME 2,497,661
ELECTRONIC MUSICAL INSTRUMENT Filed June 10, 1948 2 zfl g Inventor;
Robert B. Dome, I b9% 0% His Attor'nes.
Patented Feb. 14, 1950 UNITED STATES PATENT OFFICE ELECTRONIC MUSICAL INSTRUMENT Application June 10, 1948, Serial No. 32,082
3 Claims. 1
My invention relates to musical instruments of the piano type which employ electronic means for producing their musical tones.
The object of my invention is to provide a new and improved device for producing musical notes with the use of a piano-type keyboard.
Another object of my invention is to provide a new and improved musical instrument that utilizes a simplified keyboard whereby true harmonic octaves of music are produced with only one octave of keys.
The conventional piano covers a frequency range of seven and one-third octaves. It is equipped with 88 keys each of which produces one musical note. The size of the keyboard and the large number of parts preclude low cost manufacture. Being very heavy and cumbersome, it cannot be easily moved about and since it is completely mechanical in its operation, it requires periodic adjustment and repair. Another object of my invention, therefore, is to provide a piano-type of musical instrument that is light in weight, does not necessitate frequent adjustment and may be manufactured at low cost. This instrument may be sold as a toy or used to play serious musical numbers in the hands of accomplished musicians.
The objects of my invention are accomplished by a piano-type keyboard which is shortened to one octave and which will sound one note at a time. The musical notes are produced electronically by means of oscillations from a vacuum tube oscillator. This oscillator may be a single tube or a two-tube oscillator of the types known to the art. into a power amplifier connected to a loud speaker or the audio frequency oscillations may be used to modulate a very low power radio frequency transmitter. In the latter case, the signal may be picked up by a radio receiver in the same or nearby room and reproduced through its amplifier. This latter construction would also permit the user to employ the radio receiver volume and tone controls to obtain various effects which may be desired. The keyboard has the usual seven white keys and five black keys representing the one-twelfth intervals of the octave arranged to play in conventional tempered scales. The keyboard would normally be played With the right hand and octave sel ction would be performed by the left hand. The instrument is designed to include the normal voice range of frequencies from basso to soprano, thereby comprising three octaves: (1) 130 to 261 cycles per second; (2) 261 to 522 cycles per second; and (3) 522 to 1,044
The output of the oscillator may be fed cycles per second. With this arrangement, it is possible to play the voice part or dominant treble part of almost any musical composition.
The features of my invention which I believe to be new and desire to protect are pointed out with particularity in the appended claims. The invention itself, together with further objects and advantages thereof, may best be understood by reference to the following description, taken in connection with the accompanying drawing, in which Figure 1 is a schematic wiring diagram of the invention in its preferred form; and, Figure 2 is a Vertical sectional view of a keyboard of the piano type as used in the invention.
Figure 1 shows in schematic a keyboard i having seven white keys and five black keys, the white keys being drawn longer than the black keys. The keys are numbered 2' through it with ascending pitch or fr quency. Octave selector keys l4, l5 and it, also numbered with ascending frequency, are connected in parallel with the keys 2 through it on the keyboard 5, and are provided with contacts by which the respective circuits to variable inductances l7, l8 and i9 are closed. Each of the variable inductances I'i, l8 and H) has one terminal connected to a bus to which is also connected one terminal of each of the variable capacitors 2t, 22, and 23. The other terminals of the variable capacitors 25, 22 and 23 are connected to the opposite terminals of variable inductances l7, l8, and i9 respectively.
In Figure 2, which shows the keyboard i in cross-section, the key 2, pivoted at 24, has a thin metal contact plate 25 securely fastened to its underside and which is electrically connected to a bus 26 (Fig. l) by a conductor 2?. A contact 28 is attached to the underside of the metal plate 25 which, when the key 2 is depressed approximately half way, closes the circuit to a contact 29 attached to a stiff horizontal metal spring 38 which is electrically connected to one side of a variable capacitor 3! (Fig. l.) by a conductor 32. Fastened to the base of the keyboard 2 is a contact 33 which is electrically connected to a bus 34 (Fig. 1) by a conductor 35 and which makes electrical connection with a contact 36 fastened to the underside of the metal sprin so when the key 2 is fully depressed. A metal spring 3": is compressed between the keyboard i and the key 2 in order to return the key 2 to its normal position after being depressed.
Referring again to Figure the bus '38 is connected to the control electrode 38 of a first triode 39 included in the vacuum tube it. Tube 40 also includes a triode M which, by virtue of the criss-cross connection to triode 39, functions as a feedback amplifier to sustain self-oscillations. A grid leak resistor 42 is connected between control electrode 38 of triode 39 and ground to insure the return of bias potential to control electrode 38 in the event that one of the octave selector keys l4, IE, or I6, is not depressed prior to the depressing of a key on the keyboard 5. A fixed resistor 43 is connected between the positive direct current supply 4 8 and the cathode 45 of triode 39 to provide cut-ofi bias for the triode 39 when no key is depressed on the keyboard l.
The coupling impedance across which audio frequency voltage, produced by the combined action of triodes 39 and 41 in envelope it, is impressed comprises a blocking capacitor 45 in series with a fixed resistor 41 between the anode d8 of triode M and the positive direct current supply M. A vacuum tube oscillator it, provided for radiating a weak radio frequency signal to a nearby radio receiver, is plate modulated by audio frequency voltage coupled to its anode 59 from the anode 48 of triode 4! through blocking capacitor 45 in series with a plate tickler coil 55.
The frequency of the oscillations produced by the vacuum tube oscillator 49 may be adjusted to the desired value by means of the variable capacitor 52 which resonates with the fixed inductance 53 in the tuned grid circuit of the radio frequency oscillator 49.
The multiple contacts on the keys 2 through it perform the double function of switching on and off the audio-oscillator and changing the capacitance in the grid circuit of triode tli in order to change the frequency of the audio-oscillations. A half-way depression of a key completes the tuned-grid circuit of the triode 39, while a full depression of a key lowers the bias on the triode St to the extent that oscillation begins. A softening of the impact of the sound is accomplished by incorporating a short time delay in the build-up of the oscillations. This is done by inserting a capacitor 55 between the cathode 15 of the triode 39 and ground. In order for the bias to be lowered enough to permit oscillation of the triode St, capacitor 55 is partially discharged by a resistor 56. An appreciable time delay is realized by the capacitor 55 being of a relatively large value of capacitance. The variable capacitors 2 i, 22, and 23 serve the vital purpose of cancelling the stray capacitance and variable distributed capacitance in the three inductances iii, l8, and #9, respectively. Only in this way may the octaves be true octaves and the capacitors be preset to produce the scalar steps in frequency.
The circuit may be adjusted as follows: The three inductances ll, l8, and i9 are Varied until a ratio of 16:4:1 exists between their individual values of inductance. The three capacitors 2!, 22, and 23 are adjusted until the three inductances El, l8, and i9 together with their self and added capacitances produce oscillations in the output of the vacuum tube 40 of three harmonic frequencies such as 300, 600, and i200 cycles per second. Key 2 and the octave selector key M are then depressed and variable capacitor 3! is adjusted until the circuit oscillates at a frequency of 130 cycles per second, which is the lowest note to be produced. Next, key 3 and octave selector key M are depressed and the variable capacitor -3, corresponding to key 3, is adjusted until the output frequency of the triode 3S) is of such a value as to produce a tone corresponding to the next higher note in the tempered musical scale. This same process is repeated for each successive key up to and including key I3, the tone of which corresponds to the musical note immediately preceding the note which begins the next octave. Assuming that the variable inductance I8 and the variable capacitor 22 have been adjusted to the proper values, a frequency of 261 cycles per second is produced when key 2 and the octave selector key 15 are depressed. With octave selector key 55 depressed, the scale within the octave of 261 cycles per second to 522 cycles per second may then be played by depressing the keys 2 to IS in succession. Like- Wise, assuming that variable inductance l9 and variable capacitor 23 have been adjusted to the proper value, a frequency of 522 cycles per second is produced when key .2 and octave selector key It are depressed, and the scale within the octave of 522 cycles per second and 1,044 cycles per second may be played by depressing the keys 2 to I3 in succession with the octave selector key It depressed. Thus, the normal voice range of frequencies from cycles per second to 1,044 cycles per second may be produced with the instrument.
While a singular embodiment of the present invention has been herein described, it will be understood that many modifications may be made by those skilled in the art without actually departing from the invention. I, therefore, aim in the appended claims to cover all such equivalent variations which come within the true spirit and scope of my invention.
What I claim as new and desire to secure by Letters Patent of the United States is:
l. A musical instrument comprising a first set of keys corresponding in number to the notes of a single octave, each of said keys having a pair of contacts, a plurality of octave selecting keys, an audio oscillator comprising a pair of input terminals, a plurality of inductances connected respectively between one of said terminals and respective of said octave selecting keys, respective capacitances connected between said one terminal and one of the contacts of said first keys, the other contacts of said first keys being connected to the other of said terminals, the inductance connected with a selected octave key and the capacitance connected to a selected one of said first keys resonating at an audio frequency cor responding to the note corresponding to the selected first key in an octave corresponding to the selected octave key.
2. A musical instrument comprising a first set of keys corresponding in number to the notes of a single octave, a plurality of octave selecting keys, an audio oscillator comprising an electron discharge device having a pair of input terminals and a pair of output terminals, feedback means connected between said output terminals and said input terminals, respective inductances connected between one of said input terminals and respective of said octave selecting keys, respective capacitances connected between respective of said first keys and said one terminal, a common connection between each of said keys, said octave keys being depressible to connect the inductance associated therewith to said common connection, each of said first keys being depressible to connect the capacitance associated therewith to said common connection and to connect said common connection to the other of said terminals, the inductance connected with the selected octave key and the capacitance connected with a selected one of said first keys resonating at an audio frequency corresponding to 5 the note corresponding to the selected first key in an octave corresponding to the selected octave key.
3. An electronic musical instrument comprising a plurality of keys corresponding respectively to desired ones of a plurality of octaves to be reproduced, a set of keys corresponding in number to the notes of a single octave, an audio oscillator comprising a pair of input terminals, a lurality of reactances of given sign selectively connectable to said input terminals by means of respective ones of said octave keys, and a plurality of reactances of opposite sign selectively connectable to said input terminals by means of respective ones of said set of keys whereby opera- 15 tion of one of said sets of keys causes said oscillator to produce a note in an octave selected by operation of one of said octave keys.
ROBERT B. DOME.
REFERENCES CITED The following references are of record in the file of this patent:
UNITED STATES PATENTS Number Name Date 2,233,258 Hammond et a1 Feb. 24, 1941 2,274,199 Hammond Feb. 24, 1942 2,276,390 Hanert Mar. 17, 1942