US2128367A

US2128367A - Electrical musical instrument of the type employing gaseous discharge tubes

Info

Publication number: US2128367A
Application number: US53955A
Authority: US
Inventors: Winston E Kock
Original assignee: BALDWIN CO
Current assignee: BALDWIN Co
Priority date: 1935-12-11
Filing date: 1935-12-11
Publication date: 1938-08-30
Anticipated expiration: 1955-08-30

Description

W. E. KOCK ELECTRICAL MUSICAL INSTRUMENT OF THE TYPE EMPLOYING G'KSEOUS DISCHARGE TUBES Filed Dec. 11, 1935 J NE Q AT 0 u -w R Q Q 9 ma fuwbwhx N T z O M Q m N J 3 O-i hl l l l H .umS mt Patented Aug. 30, 1938 ELECTRICAL MUSICAL INSTRUMENT OF THE TYPE EMPLOYING GASEOUS DIS- CHARGE TUBES Winston E. Kock, Cincinnati, Ohio, assignor to The Baldwin Company, Cincinnati, Ohio Application December 11, 1935, Serial No. 53,955

8 Claims.

This invention relates to an electrical musical instrument of the type employing gaseous discharge tubes.

In instruments previously devised employing the ordinary glow tube oscillators, difllculty has been experienced in obtaining suflicient stability of pitch, due to the fact that changes in the characteristics of the glow lamps aifect the frequency of the electrical oscillations generated.

Several methods overcome this to a certain extent] For example the insertion of an inductance in the condenser circuit in order to obtain an inductive glow discharge oscillator, as described in my United States Patent No. 2,046,463, issued July 7, 1936, from an application Serial No. 701,173, copending with this application, will materially reduce the instability. However, this procedure requires an inductance for each note of the scale, which introduces weight and expense in an organ, where '73 to such oscillators may be required.

Another method is to provide coupling between those oscillators which are at octave separation, since such oscillators have frequencies which are harmonically related, and coupling means would cause them to lock into step with one another.

For the ordinary glow discharge oscillator (the relaxation oscillator) this procedure is of no value because of the fact that in order to obtain sufliciently tight coupling to hold the various octaves in step even to within a semitone or so, a voltage from the other oscillators must be used which would introduce objectionable harmonics and subharmonics into the outputs of the individual generators. Coupling between oscillators of the inductive glow discharge type is more effective in this respect, due to the fact that their control circuits (inductance and capacity) resonate at the frequency of their corresponding oscillators and the undesirable harmonic and subharmonic components are automatically filtered out.

It is an object of this application to describe a novel coupling means which dispenses with inductances for all but one octave, and completely eliminates the undesirable presence of subor super-harmonics in the output of the generators.

In this method, use is made of the control action of the grid electrode of a three-electrode discharge tube. If a three-electrode tube, operating as a relaxation oscillator, has a certain frequency of oscillation with fixed grid bias, the introduction into the grid circuit of a small alternating.

voltage of a frequency 50% or even greater than this original frequency will cause the discharge tube to oscillate at the frequency of this impressed grid voltage. Furthermore, frequencies at octave separation are easily obtained.

In the drawing Fig. 1 is a main oscillator and one an octave below.

Fig. 2 shows part of the circuit of an electrical musical instrument, including the circuit of Fig. 1.

Fig. 3 shows a filter circuit.

In Figure 1 oscillator 02 is oscillating at say 10 400 cycles, so that a 400 cycle voltage appears across R2. With switch S1 open, oscillator 03 is oscillating at say cycles. When switch S is closed and the alternating voltage on R2 is impressed on the grid of 03, the oscillator 03 will lock into step at 200 cycles, so that 02 and 03 will be at octave separation. This procedure can be cascaded to obtain oscillators oscillating at 100 cycles, 50 cycles, etc. so that the entire bank of oscillators are at octave separation.

It is to be noted that a tendency for O3 to shift in pitch is not transferred to 02. For example, a change in the condenser C2 will effect no change in the frequency of 03 until the natural frequency of 03 (i. e. the frequency at which it would oscillate with no A. C. voltage on its grid) exceeds the differential of 5 or 6 semitones in either direction. This presents a marked distinction between the method of three-electrode and two-electrode tubes. In order to couple a plu rality of two-electrode tubes, the voltage from each tube must be impressed on all of the remaining tubes, so that a tendency for any single oscillator to shift in pitch will cause the rest of the coupled tubes to shift in pitch. Of course, this shift will be smaller with coupling than without, nevertheless there will be some shift. With threeelectrode tubes, on the other hand, each oscillator influences only the tube an octave below it, sothat if the top master oscillator is of constant frequency, all of the remaining tubes will exhibit constant frequency. In Fig. 1, for example, 03 cannot affect the pitch of O2, and if the grid of a third oscillator were coupled to 0: it could not afiect the pitch of 0:. nor of O2, and so forth.

However, an even more important distinction is the absence of the coupling voltage in the outputs of the various generators. For example, in Fig. 1, although 02 oscillates at 400 cycles and O; at 200, the voltage output of 03 contains no' trace of the additional 400 cycle coupling voltage. The is due to the unique characteristic of a three-electrode glow tube, the failure of the grid to aifect the plate current once the discharge has been initiated. In Fig. 1, because 03 has a 400 cycle voltage on its grid, the grid will go slightly positive twice in every cycle of the discharge current (200 cycles). on one of these twooccasions, it will trigger the discharge, whereas, on the other, it will have no influence on the plate current. Thus each oscillator will generate a rich tone of the correct fundamental frequency and all will be dependent on the top master oscillator.

Fig. 2 shows an arrangement of three tubes, using as a top master oscillator 01, the grid coupled inductive glow discharge oscillator as described in my previous application, Serial 16,449, series of 1935, which, as was pointed out, possesses extreme stability. The lower generators, O2 and 0:, are simple relaxation oscillators and hence require no inductanoes. With 01 oscillating, a voltage of frequency 2093 (corresponding to high C) is developed on resistor R1, and by means of the connection RC, this voltage is impressed on the grid of oscillator 02. This causes oscillator 0: to pull into step at 1046.5 cycles (corresponding to the next octave below )and a voltage of that frequency is developed across R2. This is then impressed on the grid of O: causing it to oscillate at 523.3 cycles and a voltage of that frequency is developed on B1. The circuit diagram shows only three oscillators, but as many as desired could be used. For a complete organ there would be 6 or '7 octaves, therefore each master oscillator would control 5 or 6 other tubes, and since there are 12 notes in an octave, 12 master oscillators would be required and 60 to 72 relaxation oscillators.

As indicated in Figure 2, the leads L1, La and L: can be connected through decoupling resistors R5 to switches S, which in turn are connected through resistors Re to transformers T1 and T2. In the apparatus labeled T. C. various tone colors and timbres can be imparted to the notes, which may then be amplified in A and transferred into sound by the loudspeaker L. S. The tone color device T. C. #1 is used to accentuate the high harmonics to give string and reed quality to the notes, and the device T. C. #2 is used to filter out the high harmonics to give a pure, flute-toned quality. Without the resistances Re and with only T. C. #2 in operation, the high frequency note on Ll would be attenuated more than the low frequency note on L: because the filter device T. C. #2 suppresses the high frequencies. In the same way, without Rs and with only T. C. #1 in operation, the high frequency note on L1 would have a much greater intensity than the low note on LJ. By proper selection of Re and the primary impedances of Ti and T2, the notes all over the scale can be equalized in intensity, whether flute quality or rich quality is played. By making R5 large in comparison with R1, R2. R: and the primary impedances T1 and T2, the playing of several notes simultaneously will not affect the pitch or intensity of any single note.

Switch 81 permits the application of a pitch or frequency vibrato to the issuing notes. The generator G supplies an alternating voltage of 4 to 6 cycles per second and thus periodically varies the grid bias of the master oscillator. A sufllcient voltage swing can change the pitch of the master oscillator enough to produce a pleasing vibrato, and since the master oscillator has complete control over the frequencies of the remaining oscillators, a vibrato is produced on all notes.

1 1g. 3 shows a type of filter which is very eflective in producing a flute quality tone from an oscillation which is rich in harmonics. This filter would correspond to T. C.'#2 in Fig. 2. The oscillations are fed in at I and taken out at 0. 'I'hecondensers C form low impedance paths to the high frequency notes and the signal at 0 is very free from harmonics. Such an arrangement would discriminate against those tones of high fundamental frequency, but as explained before, an arrangement as shown in Fig. 2, where the resistors Rs cut down the intensities of the low notes before they reach T. C. #2, produces final signals of approximately equal intensity throughout the scale. Although such a filter system is not novel, it is believed that this method has not heretofore been applied to electrical musical instruments. Most filters in such instruments comprise inductances, which cause them to discriminate against certain bands of frequencies.

The important improvements which I have herein set forth may thus be summarized:

First, a new method of controlling the frequency of several three-electrode glow tube oscillators in cascade, thereby preventing any fluctuations in succeeding tubes from affecting the pre ceding tube or tubes, and thereby yielding no undesirable subor super-harmonics in the outputs of the individual generators.

Second, the use of a grid coupled inductive glow discharge oscillator in an electrical musical instrument as the topmost or master oscillator, in conjunction with which the above mentioned control system produces a very rigid bank of 0scillators.

Third, a method whereby the intensities of notes of widely different tone color are equalized throughout the scale.

Although the grid coupled inductive glow discharge oscillator has been described in my previous application, Serial 16,449, series of 1935, its use in an electrical musical instrument as a stable oscillator is herein set forth for the first time.

I claim:

1. In an electrical musical instrument, a plurality of electrical oscillation generators, each of said generators comprising a gaseous glow discharge tube of a type having an anode, a cathode and a grid, and means for applying a voltage generated by one of said oscillation generators to the grid of a second of said oscillation generators, whereby to cause said second oscillation generator to oscillate at a frequency bearing a definite and fixed relationship to the frequency of the first mentioned oscillation generator.

2. In an electrical musical instrument, a plurality of electrical oscillation generators, each comprising a gaseous glow discharge tube having an anode, a cathode and a grid, oscillation circuits for said oscillation generators, and means for impressing a voltage generatedby one of said oscillation generators upon the grid of a second of said oscillation generators whereby to cause the last mentioned generator to oscillate at a frequency which is some harmonic fraction of the frequency of the first mentioned oscillation generator.

3. In an electrical musical instrument at least three oscillation generators arranged in cascade, each of said generators comprising a gaseous glow discharge tube having an anode, a cathode and a grid, said oscillation generators having oscillation circuits, means for impressing 3. voltage generated by the first of said oscillation generators upon the grid of the second of said oscillation generators whereby to cause said second amass? oscillation generator to oscillate at a frequency which is some harmonic fraction of the frequency of said first oscillation generator,- and means for impressing upon the gridiof the third of said oscillation generators a voltage generated by the second of said oscillation generators whereby to cause, said third generator to oscillate at a frequency which is some harmonic fraction of'the frequency of said second oscillation generator.

4. Inan electrical musical instrument, a master oscillator or source of pulsating voltage, and a plurality of electrical oscillation generators, each comprising an oscillation circuit and a gaseous glow discharge tube having an anode, a cathode and a grid, means for impressing the voltage produced by said master oscillator upon the grid of a second of said oscillators to cause the second oscillator to oscillate at a frequency which is half the frequency of the master oscillator, means for impressing a voltage generated by said second oscillator, upon the grid of a third oscillator whereby to cause'said third oscillator to oscillate at a frequency which is half the frequency of said second oscillator and so on throughout the eascaded series.

5. The cascade of oscillation generators as claimed in claim 4, wherein said master oscillation generator comprises a gaseous glow discharge tube having a feed circuit and a control circuit, the frequency of oscillation thereof being determined by both capacity and inductance in said control circuit.

6. The cascade of oscillation generators as claimed in claim 4, in which said master oscillator comprises a gaseous glow discharge tube having an anode, a cathode and a grid, a feed circuit therefor and a control circuit therefor containing an inductance and a capacity by the combined effect of which the frequency of said oscillator is stabilized, and means for energizing said grid with a pulsating frequency derived from said control circuit.

7. In an electrical musical instrument, a plurality of master oscillation generators arranged to oscillate at frequencies related to each other as the notes of the scale, in a high register, and, for

each of said master oscillation generators a cascade of controlled generators, said last mentioned generators comprising each a gaseous glow discharge tube having an anode, a cathode and a grid, and a semi-tuned controlled circuit, means for impressing a voltage generated by a master oscillator on the grid of an oscillator in its cascade, means for impressing a voltage generated by said last mentioned oscillator on a succeeding oscillator and so on throughout each cascade whereby the generators in said cascades are caused to oscillate, each at a frequency which is half the frequency of the generator next highest in the cascade.

8. In an electrical musical instrument, a plurality of master oscillation generators arranged to oscillate at frequencies related to each other as the notes of the scale, in a high register, and, for each of saidmaster oscillation generators a cascade of controlled generators, said last mentioned generators comprising each a gaseous glow discharge tube having an anode, a cathode and a grid, and a semi-tuned controlled circuit, means for impressing a voltage generated by a master oscillator on the grid of an oscillator in its cascade, means for impressing a voltage generated by said last mentioned oscillator on a succeeding oscillator and so on throughout each cascade whereby the generators in said cascades are caused to oscillate, each at a frequency which is half the frequency of the generator next highest in the cascade, and means for deriving from said oscillators portions of the voltage generated therein for amplification and reproduction.

WINSTON E. KOCK.

CERTIFICATE OF CORRECTION. Patent No. 2,128,367. August 50, 1938.

w WINSTON E. xocx.

It is hereby certified that error appears in the above numbered patent requiring correction as follows: In the drawing, Figures 1 and 2 should appear as shown below instead 01 as in the present drawing of the patentand that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 6th day of December, A. D. 1958.

Henry Van Arsdale