US2403664A - Solo electrical musical instrument - Google Patents

Description

- N. LANGE R SOLO ELECTRICAL MUSICAL INSTRUMENT July 9, 1946.

Filed Oct. 24, 1942 3 Sheets-Sheet l in NM \M WS W n hm,

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' N/CHOLFIS LHNGER HTTORNEY July 9, 1946.

N. LANGER 2,403,664 SOLO ELECTRICAL MUSICAL INSTRUMENT Filed Oct. 24, 1942 3 Sheets-Sheet 2 INVENTOR. IV/CHQL H5 Lfl/VGER H TTORNE' Y y 1946. N. LANGER 2,403,664

SOLO ELECTRICAL MUSICAL INSTRUMENT 'Eiled Oct. 24, 1942 s sneets-sheet 3 L E a o IN VEN TOR.

L E I 3 N/CHOLHS L HNG E R Patented July 9, 1946 UNITED STATES PATENT OFFICE V i 3.40am

soLo ELECTRICAL MUSICAL ms'rammn'r I Nicholas Langer, NevhYork, N. Y., asaignor to Central Commercial Company, Chic go. 111-, a corporation of 111111011 a' Application October 24, 1942, Serial No. 463,291

9 Claims. (oasis-s28) an electrical musical instrument of the mono-' phonic, or melody, type.

It is an object o! the present invention to provide an electrical musical instrument of the described type having a novel and improved character and presenting substantial advantages over conventional electrical musical instruments.

It is another object of the present invention to provide an electrical musical instrument of the melody type, capable of producing a single musical sound at a time within a relatively wide range of pitch and tonal quality.

It is a further object of the present invention to provide an improved electrical musical instrument oi the solo, or melody, type in which a single oscillator tube of the gaseous discharge type is adapted to-produce musical oscillations go over a musically useful range of several octaves and having a large variety of tone colors or timbres, without recurring to the heretofore employed complex procedure of employing a plurality of octavely related cascaded oscillators.

Still another object of the invention is to provide a monophonic electrical musical instrument employing a single glow-discharge tube oscillater operatively associated with a keyboard or playing manual of relatively restricted range and so adapted to control the pitch of the oscillations produced within a considerably greater musical range.

Still another object of the present invention is to provide an electrical musical instrument originally producing electrical oscillations of very. complex waveform which may be readily converted into musically useful and valuable oscillations of a great variety of tone colors, simulating the tone colors of most of the orchestral instruments and in addition to this also capable of producing many additional tone colors or an altogether novel character not now found in conventional musical instruments, or in the stops of conventional organs.

Moreoventhe invention provides means and ins'trumentalities for producing additional tonal The invention also provides novel tone color modifying circuits and devices capable of being.

pose of phase shifting, distortion and the like effects now, commonly used ior such purpose.

It is also within the contemplation of the invention to'provide an electrical musical instrument including a glow-discharge oscillator of special type which is tree from the detrimental v eflects of leakage and atmospheric variables and is capable to maintain its correct tuning for a relatively long time.

The invention also contemplates an electrical musical instrument of the melody type, which is extremely simple in constructlon'and generally includes only a single oscillator tube, provides excellent musical effects of a practically unlimited variety, and whichv may be readily manufactured and sold on a practical and commercial scale at a low cost.

Other and further objects and advantages of the present invention will become apparent from thefollowing description taken'in conjunction with the accompanying drawings, in which Fig. 1 illustrates in a somewhat fragmentary manner the circuit diagram of an electrical musical instrument embodying the principles of the present invention.

Fig. 2 depicts the circuit of a preferred form of tone filter system employed in connection with the electrical musical instrument illustrated in Fi 1: and

86 Fig. 3 shows the circuit diagram of a universal tone filter system which in combination with an oscillation generator producing oscillations 0! complex wave form is capable of producing a practically endless variety of different tone colors.

40 The invention will be best understood from effects, particularly tremolo effects and percussion type eflects resembling those of plucked strings by inertialess or electronic means in the absence of mechanical interrupter-s. and similar conventional devices.

description 01'. a preferred embodiment thereof reference being had to Fig. 1 0! the drawings. In order to facilitate understanding of the invention such elements which are of a more or less conventional character and are well known to those skilled in the art, such as the source of current, or power pack, the amplifier and volume control, have been either omitted, or have been only diagrammatically shown.

8.0 Generally speaking, 'the electrical musical instrument of the invention comprises a main oscillator section.- a range control section, a

tremolo-banjo section and a tone control or output section.

Main oscillator section The main oscillator section essentially comprises an oscillator tube or the gaseous discharge type which is operatively associated with a source of direct current voltage and with a plurality of tuning elements, such as condensers and resistors determined value to produce electrical oscillations the frequency of which may be varied in steps within a wide range.

Referring now more particularly to Fig. l of the drawings, reference character l0 denotes a source or direct current of suitable voltage which in practice is a power pack converting the alternating current taken from the electric mains into filtered direct current oi substantially stable voltage. In most cases this power pack may be in common with that of the amplifier in view of the iact that the total current consumption or the instrument is relatively low. Between the positive and the negative terminals or this source oi direct current is connected a voltage divider resistance II from which various operating voltages may be taken of! for the diflerent sections of the instrument, this resistance being connected in series through lead wire l2, and switch I 3 to a group II of individual tuning potentiometers comprising a number of small potentiometers l5 connected in parallel, the other end of said group being connected to ground through lead wire i8. Voltage divider resistance H is provided with sliders I! and It to take off voltages of desired value, as it will appear more fully hereinafter;

and its total resistance is so adjusted thatthe voltage drop across each of the tuning potentiometers I5 is about 4 to 6 volts. Condensers i9, 20, 2| and 22 are connected across the various taps of voltage divider resistan ii and ground in order to reduce the alternating current resistance of the system to a relatively low value.

Between the two taps l1 and i8 of voltagedivider II is connected main pitch control potentiometer 23 which serves to adjust the operating l0 2911, one contact 0! which is connected through a balancing resistance 40 to the sliding contact of one of the potentiometers i! of group H and then through common lead it of such group to ground. Thus, it will be noted that upon closing of any one of key switches 35 to 39, etc., a predetermined number of the serially connected resistances 30 to Mn will be connected across condenser 29 through one of balancing resistances l0 and through one of potentiometers 1!. Selection of the proper value for resistances iii to 3411. permits approximate tuning of the respective note, while displacement of the slider on the corresponding potentiometer [5 will permit to individually adjust the operating voltage effective upon depression of said key and thereby to accurately adjust the pitch for that note. In

- this connection it may be pointed out at this time voltage of the oscillator tube and thereby controls the general pitch of the instrument. With the movable arm of thispotentiometer are connected in series tremolo coupling resistor 24, pitch balancing resistor 25 and output resistor 26, together with glow-discharge tube 21, range control switch 20, tuning condenser 29, the latter being connected to the negative terminal or the source or current l0. While any glow-discharge tube oi good make and 0! stable characteristics may be used, I iound that a glow-discharge tube oi type VR75/30 provides excellent results.

To the common terminal of tube 21 and condenser 28 is connected 0. chain of fixed resistors which comprises serially connected resistances 00, ii, 32, l3, l4 11. These resistances correspond in number to the number or notes of different pitch which may be produced in a single range of instrument. Thus, for example, for an instrument having a range or three octaves from C to C, 31 resistances are used and their resistance is so determined that upon connecting a selected serially connected plurality thereof across tuning condenser 28, the oscillator will be approximately tuned to notes or successively decreasing pitch in correspondence with successive notes or the tempered scale. Between the common terminal or any two adjoining resistances there is connected a switching key SI, II, 21, I,

that the value of resistances 31 to 3411, balancing resistances l0 and individual tuning potentiometers iii are of a diflerent order. For example. when main tuning resistor 30 is or about 1,500,000 ohms, resistance 3| to 3411. may be of progressively increasing values from about 70,000 to about 500,000 ohms, balancing resistors 40 may have a resistance oi about 25,000 ohms each and inclvidual tuning potentiometers 15 may have a resistance of 5,000 ohms each. The object of such coordination of resistance values will appear as the description proceeds.

Range control section Generally speaking, it is not advisable to provide a single range greater than about 3 octaves for various practical reasons. First or all, the extension of a single range obviously determines the number of switches and thereby the length of the playing manual. In addition, as the total resistance of the resistance chain II to 3011 increases with increasing range, if the range is unnecessarily extended, the relation between the value of resistances in the circuit and the permissible leakage becomes unfavorable and aflfects the permanency or stability of tuning. A range oi 3 octaves is in most cases sufficient for playing any melody with the accompaniment of another instrument, such as a piano. In order to permit operation within various ranges of tone irequencies, such as soprano, alto, tenor or i, t. ranges, it is preferred to shift the range oi the oscillator as a whole by one or more octaves. in the circuit of Fig. 1 two such ranges are shown. it being understood that, of course, three or more diiiferent ranges may be incorporated into the instrument, if desired.

Range shifting is accomplished by means oi range shifting switches l3 and 28 which are preterably combined into a single unit or the doublepole, double throw type, so that these two switching operations are simultaneoushr performed. 0! these switches, 28 switches tube 21 over into series connection with condenser II from condenser 29. The relationship between the capities of 28 and 41 substantially determines the frequency difference between the two ranses. Thus, for example, if condenser 44 has a capacity twice as great as that of 28, the pitch of the instrument will be lowered by an octave, ii condenser ll has a capacity four times as great as that of 2a, the pitch or the instrument will be lowered by two octaves. While the range-chansing effect of the capacity in the oscillator circuit is more or less equal for all 01 the frequencies corresponding to actuation oi the verious key switches, certain slight differences frequently occur due to the diflerent impedance of the other portions of the circuit at widely different Irequency ranges. Therefore, to obtain and to maintain musically perfect and correct pitch for the several ranges, it is desirable to also provide a second group 42 of individual tuning potentiometers 43 for the second range. It will be readily observed that in the first or "high range popression of any one of switching keys will connect a controlling potential to the oscillator tube determined by the setting of the corresponding potentiometer of group 42, This potential is delivered to the tube through the resistance chain 30 to 3m and through a balancing resistance 44 which corresponds in function and in value to the balancing resistors 40 connected between the keying switches and the sliding contacts of potentiometer group H.

The objectof the provision of the balancing resistors 40 and H, one set for each group of tuning potentiometers, is to substantially eliminate the effect of the setting of the unenergized group of potentiometers upon the energized group oi po-.

tentiometers. As it will readily appear from Fig. 1, each switching key is at all times connected to the sliding contact of two potentiometers, one in each group, through a balancing resistance. Assuming that, for example, group H ofthe potentiometers is energized, a predetermined potential,

generally different from ground potential is applied to the switching key in accordance with the setting of the respective potentiometer. At the same time, however, a portion of this potentiometer is shunted by a secondary current path comprising the two balancing resistors l0 and 44 in series, lower bus bar 45 of group it and lower bus 50,000 ohms, while the portion of the potentiometer across which such resistance is connected is generally considerably less than.5,000 ohms so that the setting of the energized potentiometer l5 will be the governing factor whereas the setting of the other potentiometer in the second group will be of practically no effect. This arrangement is of considerable importance and value because otherwise it would be necessary to provide a complicated and bulky multiple switch arrangement capable of switching over as manyas 37 key contacts from one group of potentiometers to the other. It is also worth noting that the total resistance of the current path between the lower terminal of any one switching key to ground through the respective balancing resistor and tuning potentiometer is quite low with respect to the resistance of the resistance chain 30 to 3412. at that point. Generally speaking, the former resistance is only slightly in excess of about 25,000 ohms whereas the resistance chain 6 may have a resistance or 1.5 million ohms up to 10 million ohms, and more, according to the keying switch actuated. This p p rtion of the resistances is of considerable importance in assuring that upon actuation of several switching keys at the same time always the higher note will sound, as it will be explained more fully when the operation of the instrument will be described.

Tremolo and bomb sections The main oscillator section and the range shifting section in proper-cooperation are capable of producing a single sustained note of complex wave form over a range of several octaves, such as, for example, three octaves, this range being shiftable by 1 or 2 octaves up or down by actuating the range-shifting means described in the foregoing. It has been found desirable to incorporate means for producing a tremolo, that is: to cause slight periodic changes in the pitch of the oscillations produced, such periodic changes having a relatively slow rate such as about 6 or 7 times a second. Such' periodic changes in pitch provide a musically valuable result similar to the well-known vibrato efiect of the string instruments and of the singing voice.

In accordance with the principles of the present invention, the tremolo efiect is obtained by means of an auxiliary glow-discharge tube oscillator tuned to a very low frequency, such as 6 or '1 oscillations per second. This tremolo oscillator is so coupled with the main oscillator circuit that every time when the tremolo oscillator draws current from the common source, the available operating voltage for the main oscillator is somewhat decreased. Decreasing operating voltage causes decreasing frequency of the main oscillator.

In Fig. 1, reference character 4! denotes the tremolo tube, which preferably is a glow-discharge tube having two cold electrodes. One terminal of this tube is connected to' the common point of pitch-balancing resistor 25 and output resistor 26, the other terminal of the tube being connected through a fixed resistance 48 of about 1,500,000 ohms and an adjustable resistance 49 of about 2,000,000 ohms to ground Two condensers 50 and SI of about 0.15 and 0.1 microfarad capacity, respectively, have one of their terminals connected to the common terminal of tube 41 and resistance 48, their other terminals being respectively connected to two arms 52, '53

of a three-pole three-position switch 55. The third arm, 54,0f switch 55 is connected across pitch-balancing resistor 25 and is capable of shorting the same in the third position 01' the switch through lead wires 56 and 51. It will be noted that in the first position of the switch. as illustrated in Fig. 1, arm 52 of the switch will connect condenser!!! across tube 41 while the other two arms of the switch are inoperative. In this position slow oscillations will be produced by tube El and the tube will be lighted and extinguished about 6 or 7 times per second. Every time the tube is lighted, in addition tc the current flowing to themain oscillator, additional current will be drawn through resistors 24 and 2B, and the voltage'drop across these resistors will slight ly decrease the frequency of the main oscillator at the same rate as the tremolo oscillator is oscll= lating. The speed of the tremolo is determined by the value or elements 50, it and t9, and may be approximately adjusted by proper selection of 50 and accurately adjusted by the adjustment oi resistance 6..

When switch 55 is placed into its third position, arm 52 will be inoperative, arm 53 will connect condenser across resistors 48' and 9 and arm Bl will short-circuit pitch-balancing resistor 2!. Connection of condenser 5| across resistors ll and. 48 will likewise cause oscillations of tremolo tube 01, but the wave form will be greatly diflerent. While the tube with a condenser across the same produces a wave form characterized by slow charge and rapid discharge of the condenser through the tube, connection of the condenser across the resistance will produce almost instantaneous charging of the condenser through the tube and gradual discharge of the condenser through the resistance across the same. The latter arrangement gives a wave form with very abrupt peaks which superimposed upon the main oscillator by means of tremolo or coupling resistor 24 causes such modulation of the main oscillation which closely simulates the sound of a string, plucked or struck in rapid succession.

In the following, this effect, which is very attractive musically, is referred to as "banjo effect. In view of the fact that generally faster oscillations, about 10 to 12 per second are required for this banjo effect, condenser 5! has a lower capacity than condenser 50 to take care of the difference of speed between the tremolo and banjo effects.

Experience has shown that in general the tremolo oscillator has a slight effect upon the general pitch of the main oscillator. More particularly, switching over from tremolo to banjo would slightly raise the general pitch of the main oscillator. To compensate for this undesirable change, is the object of the provision of pitchbalancing resistor 25 which is in series with both the tremolo and the main oscillator tube. Shorting out of this resistor of about 15,000 ohms simultaneously with switching over from tremolo to banjo effect will lower the pitch of the main oscillator by the same amount as it would be raised by the different impedance of the auxiliary oscillator in the banjo connection. In this manner, the pitch will be maintained constant regardless of whether the tremolo or the banjo effeet is used.

In the middle position of switch 55 all three arms thereof are inoperative. This is the neutral position in which the auxiliary oscillator does not produce any oscillations. It is worth noting that tube 41 is continuously lit in this case, its circuit being completed from the positive terminal of the source of current i0 through resistors 24 and 25 and then through resistors 48 and 00 to ground. This is essential in order to avoid any change in the general pitch of the main oscillator in the tremolo-off position.

Output and tone control section The output signal is taken off at a resistance II connected in series with the main oscillator circuit. Any change in the impedance of the output circuit is likely to change the general pitch of the oscillator. Therefore, to substantially elminate such changes, it is desirable to have the coupling between the oscillator proper and the output circuit as loose as possible. This is accomplished by making the value of output resistance 20 relatively small with respect to the internal resistance of the oscillator circuit such as, for example, 10,000 ohms. The signal corresponding to the voltage drop along resistance 26 is introduced into the primary winding 58 of an output transformer ll through a decoupling resistance 6| having a value of about 25,000 ohms. One end of the secondary winding ii of transformer II is connected to ground through shield 82 while the other through a lead 83 shielded by means of shield 82 is introduced into the tone control device generally denoted by reference character 64. A second decoupling resistance B5 of about 25,000 ohms is preferably connected in series with this lead to prevent changes in the output impedance being reflected back into the main oscillator circuit and thereby causing slight pitch variations.

The tone control device has the object of converting the oscillations originally produced by the oscillator and generally having an extremely complex saw-tooth wave shape into other oscillations of diiferent wave form by filtering out some of the harmonics and by reinforcing others. The tone control device essentially comprises a plurality of switches such as for example eight switches of the push button type which can be actuated individually or in any desired combination of two or more switches at a time. By actuating these switches, filter systems I to I may be selectively connected in series with the outgoing signal, passing through some of the oscillations in modified form and grounding other portions of harmonics of the oscillations through a lead wire 88.

While the general principles governing the frequency response of various filter circuits comprising capacitors, inductances and resistors in various combinations are known, the theoretical determination of filter systems to obtain a certain musical result is so involved and uncertain in the final result that experiment has been found the simplest and quickest way to decide the type and the value of the electrical elements for obtaining a wave form simulating a determined musical tone co or.

I have found that excellent results are obtained by means of small transformers employed as inductances in filter circuits with or without combination with other elements such as condensers and resistances. Transformers of the type used in amplifiers as interstage coupling transformers are. especially advantageous because they are readily obtainable on the market with a great variety of winding ratios and taps and also because they are relatively small and inexpensive. A single transformer may be used to selectively provide a plurality of widely different inductances according to whether the primary winding, the secondary winding, or only a portion thereof is used. I have also found that by unipolarly introducing the signal into one of the windings of the transformers and unipolarly withdrawing the signal from the other winding also provides novel and interesting filtering effects. A transformer used in. such a manner corresponds to an electrical filter of unique characteristics in that the signal is transferred from one winding into the other by means of a combination of uniformly distributed capacitive and inductive coupling, which deforms the original wave pattern in a manner unobtainable in any other way. It is also possible to employ one winding of a transformer as an inductance and to short circuit the other winding either directly or through a highly. resistance or small capacity whereby further modifled tone colors are obtained.

.The electrical circuits incorporated into the tone color section will b best understood from Fig. 2 of the drawings. Reference character II generally denotes a filter system which is capable of producing three distinctly diil'erent tone colors according to whether push button I, 2 or 5 is actuated. The filter system comprises a small transformer 80 of the type used as interstage coupling in amplifiers having a secondary winding 95 with a greater number of turns than the primary winding 86. One end of winding 85 is connected to the upper terminal of a condenser 81 of about 0.003 mf., of which the lower terminal is grounded, and to one contact of both switches I and' 68. The other end of said winding] of transformer 82 is connected to contact 89 of doublethrow single-pole switch 89. The center .point 90 of this switch is connected to the upper terminal of another condenser 9I of about 0.003

mf., likewise groundedat the other terminal, and is also connected to one contact of both switches 89 and 61. The second stationary contact 92 of switch 89 is connected to the center tap of winding 85 of transformer 84 and also to one contact of switch I9 coordinated to push button unit of which the other switch I5, has one of its contacts connected to one end of the other winding of the transformer.

This single filter combination is capable of producing three difierent tone colors. Thus, upon actuating push button I, switch 61 and switch 99 are closed and switch 99 connects contacts 88 and 90. In this case the full winding 85 is connected between input bus bar 93 and output bus bar 90 and two condensers 81 and 9I are connected to ground at either end of such inductance. The result will be a tone color corresponding to flute in the high-pitch. range of the instrument and to French horn in the low-pitch range of the instrument. Upon actuation of push button 2, both switches 89 and III are closed and only one half of the inductance will be connected between bus bars 93 and 94, the same condensers being connected between the ends thereof and ground. This produces a tone color corresponding to that of a soprano saxophone in the high-pitch range and to a bass clarinet in the low range. Upon actuation of push button '5, switches I5 and I0 are simultaneously closed and the signal will be introduced at the center tap of winding 85 of transformer-8| and is withdrawn through lead 98 connected to one end of winding 90 of the transformer. It will be noted that one end of winding 85 is floating, while the other end thereof is grounded through condenser 81, and that the other end of winding 88 is likewise floating. This filter of rather unusual construction produces a muted trumpet quality in the high range and an effect closely similar to vox humana in. the low range. I

Depression of push button 3 simultaneously 'closes switches II. and I2, and connects a resist- 0.003 mf. This filter produces an excellent string quality corresponding to the tone color of a violin in the high range and to that of a cello in the low range.

Depression of push button- 4 simultaneously closes both switches I8 and I iand thus connects,

lower number or turns. At the input end of winding 98 it is grounded through an inductance III of relatively high. value and also of a relatively highdirectcurrentresistancesuchaaiorcxample, a small telephone coil of about 2000 ohms resistance, with its usual iron core. At its output end, winding 98 is grounded through a capacity I02 of about 0.004 mf. This stop provides an excellent oboe in the high range and a bassoon in the low range.

Push button 5 has been already discussed in the foregoing. Push button 6 upon actuation will simultaneously close switches 11 and I8 and thereby connects one winding of a small transformer I03 between the input and output signal bus bars 99 and 94. This transformer is of very small dimensions, such as are sometimes used in hearing aids and has a primary to secondary ratio of about 1 to 10, and a direct current resistance of about 45 ohms and 450 ohms, respectively. At the input end of the secondary or high resistance winding I04 there is a condenser I05 of about 0.003 mi. and an inductance I06 connected to ground. The inductance is a conventional telephone coil having a direct current resistance of about 4000 ohms. The other winding of the trans- I former 'I 03 is either left floating or may be shorted by means of'a high resistance I08 of the order of about 50,000 ohms. This shorting lead of predetermined resistance introduces distortion intothe filter system, the amount of which can be and a secondary winding III is connected-in such a'manner that the input bus bar 93 is connected unipolarly to one end of the primary and the output bus bar 94 is likewise unipolarly connected to the secondary winding at one end thereof. The transformer is of the same type as the one used in filter 6. As it has been already explained in the foregoing, a filter of this type has rather peculiar electrical characteristics in that it corresponds to a uniformly distributed inductance and a uniformly distributed capacity combined in a single electrical element. The resulting tone color is a trumpet in the high range and a tenor saxophone in the low range.

Stop button 8 simultaneously closes switches resistance. The resulting tone color is corresponding to an organ stop commonly called flageolet, both in the high and low ranges.

The foregoing tone effects may be either in-.

dividually employed by actuating a single push button, or stop, or two or even more stop push buttons may be simultaneously closed. In the latter case further interesting and pleasing tone colors are obtained rather than a direct additive effect of the individual stops. The following table should give some idea as to the principal tone colors obtainable by the judicious application of the foregoing stops. Whenever a number follows the name of a tone color or instrument, this indicates that while the resulting quality istslmilar to the instrument in question it is slightly diflerent from another quality of the same name obtainable by means of another combination of stops. This can take care of in asoacss 11 dividual difference of judgment or preference frequently found among different musicians.

Stop High range Low range 1 Flute French horn.

Soprano saxophone... Bass clarinet. Violin. (Jello. Oboe Sax horn. 7...- Tenor saxophone.

t Flsgeolet.

Do. Do. Muted cello.

Do. Viols.

Bassoon 2.

Bassoon 3.

ello

4.-- Bassoon 4. Viola d'amour Do.

S rin- Do. a Mutedstring. Do.

8 Do. ii and 7 Woo wind Do.

6 and 8 Shepherd's pipe Do.

an ILA 0000i" NB Htt- Htm E 5.5. 5555 E5555 l After the output of the instrument has been appropriately'modifled by means of the tone color filters, the output taken off at output bus bar it is introduced into a volume control p0- tentiometer ill of any appropriate taper and from this it is introduced into an amplifier Ill of suitable output and finally into a sound producing means III. In view of the fact that the amplifier may be of any suitable type and does not form part of the present invention, it has been merely diagrammatically indicated.

Resistancel i'l connected directly across main oscillator tube 21 has a very high value, generally in excess of 500 megohms, and may be up to 2000 megohms. This resistance has been found extremely effective in eliminating the variable elect of leakage on the permanency of tuning. As it has been set forth in the foregoing. certain portions of the circuit are very sensitive to leakage in view of the fact that some of the current-carrying portions of the circuit themselves have a very high resistance, such as the resistance chain It to lln which'might have a value of up to 10 to megohms. A certain amount of leakage through the wiring and particulariy through the keyboard contacts is practically unavoidable. particularly in humid weather. This is substantially compensated for by voluntarily introducing a leakage path of constant value which is much lower than the accidental and variable leakage in the circuit. Experience has demonstrated that this simple expedient practically completely eliminates all difliculties heretofore experienced in the, constancy of tuning under unfavorable atmospheric conditions.

Operation instrument of very constant tuning, such as a reed organ, for standard. or by means of the same method as is now generally employed by trained piano or organ tuners. First of all, the

general or standard pitch of the instrument is adjusted by means of main tuning potentiometer 23. Thereafter, range switches l3 and 2B are placed in the high range position and the tuning of the individual notes is correctly and accurately adjusted by means of the individual tuning potentiometers of group i4 and then the same procedure is repeated for the low range by placing range control switches i3 and 28 into the low range position and by adjusting the individual tuning potentiometers of group 42. If at any time there is some discrepancy between the exact octave relationship of the high and low ranges, this can be readily corrected by adjustment of range control condensers 29 or H, which are preferably of the mica compression type to facilitate ready and continuous adiustment. It has been found that the instrument is very stable in tuning and as a rule does not require retuning for long intervals of time.

Attention is directed here to the advantages provided by means of the main tuning potentlometer 23 which permits continuously adjusting the general pitch of the instrument within the range of a few notes, simultaneously for both ranges and without affecting the relative pitch of the various individual notes which will retain theircorrect intervals determined by the equal temperament. Thus, by means of this single control element, the instrument can be readily and instantaneously tuned to any standard pitch such as the international or the concert pitch or to any other instrument of constant tuning, such as a piano or organ, whatever its general pitch is. Moreover, the same feature of my instrument makes it a transposing instrument so that a melody written in a difficult key or tonality, such as C# major, may be instantaneously transposed into another very simple key. Thus, for example, by shifting the general pitch half a note higher, the operator may play a melody in C major and it will sound in C# major. This is a very great advantage not only for the operator having but limited musical knowledge or skill but also for the highly trained musician.

In playing the instrument little experience is required due to the fact that the playing manual controlling switching keys I! to 351: is closely similar to a conventional piano keyboard with which most people are familiar. In view of the fact that only one note is produced at a time, the simple technic of depressing a single key at a time is easily mastered. In case at any time accidentally. or intentionally more than one key is depressed at the same time, the highest key will be the controlling one, while the others have practically no effect on the resulting note. This will be readily understood from the circuit shown in Fig. 1. Provided that switching key 3! is depressed, in the high range, resistances l0 and II will be connected across condenser 20 through a balancing resistance 40 and an individual tuning potentiometer II. If now also switching key 30 will be simultaneously depressed, this will cause additional connection of resistances 3! and it but these, having a value of several hundred thousand ohms will be practically short circuited by the low resistance path through a balancing resistor ll, two potentiometers II and another balancing resistor III. This path is hardly in excess of 50,000 ohms.

'I'hesameapplies when any number of keys is depressed at the same time, always the highest note will sound and at no time will be non-harmonic notes foreign to the scale produced. This circumstance is of great importance as in normal connected in all conceivable ways.

- 13 i playing, particularlyi'in legato passages, the si-- multaneous depression of two keys at least transiently canbe hardly avoided. This problem was quite serious inthe art and to avoid the production of non-harmonic. notes upon transient depression of two keys at the same time some inventors were forcemtof include complex switching devices into the instrument which upon depression of more than one key at a time completely de-energize the system and prevent production of any sound at all. 1: Of course, this procedure does not provide anyisolution of the problem because when a legatdgpassage is played, there will be a short intervalibetween passing from one note to the next in i which nothing will be heard and thereby it is inade impossible to obtain a good legato eifectywhich is one of the principal attractions of a sustained-note melody instrument. The present invention provides a com-' plete solution for this problem.

The sustained note of the instrument may be modulated or embellished by means of a tremolo effect by placing efiect switch 55 into its upper position, or may be caused to imitate a plucked string by utilizing a banJo eil'ect by placing said switch into its lowermost position. In the center or neutral position of theeflect switch the produced note is unmodulated. The various tone colors may be readily and selectively obtained by actuating one or more-of stop buttons l to individually or in combinations, as it has been set forth more fully in the foregoing.

In some cases, it has been found desirable to provide filtering means, capable of producing any desired tone color by means of suitable adjustment thereof. A device of this type may be used in addition to the fixed filters described in the foregoing so that when a tone color or timbre is desired which is not included among the fixed stops, such timbre may be readily obtained by means of a few simple adjustments. A universal tone filter which has been found to provide excellent results is diagrammatically illustrated in Fig. 3.

As it will be readily observed in Fig. 3, my novel universal tone filter comprises six, or more, tap switches 8 to I23. Each of these tap switches has six contact points I to l. Threeof the switches H0, H0 and I20 are connected in series and form the horizontal portion of the resultant filter, and the rest of the switches l2l, I22, and I23 are connected across the elements of the horizontal portion and the common ground lead I. Each tap switch is capable of connecting various electrical elements, such as inductances, capacities and resistances of appropriate. value into the filter circuit. For example, the respective values of inductances may be 0.5 to 2- henries oi the capacitors 0.001 to 0.006 mi. and of the resistances 10,000 to 50,000 ohms. In addition, one ofthe taps of each horizontal switch may have a tap connected to a shorting lead I25, while the first tap of the vertical switches may be open. As those skilled in the art will readily understand, a device of this type is capable of providing filter combinationsof an almost infinite number, more than one hundred thousand for the described number of taps, in which filters inductances, resistances and capacities may be In general, each combination produces a diflerent tone color when connected into the output circuit of the instrument of the invention. The universal tone control device of the invention is not only useful as an addition to any electrical musical instrw- 14 meat, but is mentally determining the filter system necessary to obtain a I certain definite tone color. Thousands of combinations can be tested within a few hours, and Jae soon as a tone quality of attractive timbre is found, the particular filter may be readily built up in the, form or a fixed stop, if desired.

01' course, the number of taps on each switch =may be increased; over six in order to accommodate ni re electrical elements such asinductances, capacitors and resistances of different size. Any tone fcolor once/obtained may be reconstructed in a ifew seconds, if record is made of the tap nun ibers to. which the respective switches have to lbe set, each setting being characterized by six figures. Thus] to rexample, the figure 222,533 characterizes a filter in which three inductances are connected in the horizontal or series portion of the filter, and a condenser is connected after each inductance to ground. Obviously, the usefulness of my novel universal tone filter device is not restricte' to my electrical musical instrument but can bei 'isea with good results in any electrical musical 1 trument in which the oscillators initially produce oscillations of relatively complex wave i'orni.

Altholrgh the present invention has "been described in connection with certain preferred embodiments thereof, variations and modifications may be resorted to by those skilled in the art without departing from the principles oi the present invention. I consider all oi' these variations and modifications to be within the 'true' spirit and scope of the present invention, as discomprising in combination a space discharge device, a tuned mesh for saidspace discharge de-- vice, and including variable resistances connected in parallel, switching means for connecting selected resistances of said mesh into oscillationproducing relation with said space discharge device, a conductive path connecting said transducer in the outputof said device, range-shifting means for said device, and correction means in'- dividual for each range to eliminate the eflect of variables incidental to the change of range.

2-. An electrical musical instrument employing an electro-acoustlc transducer, said instrument comprising in combination a space discharge device,a series of tuning elements for said device. manually operable elements for connecting-selected portions or said series in oscillation-producing relation with said space discharge device thereby to selectively produce frequencies approximately corresponding to notes of the tempered scale, a conductive path connecting the aforementioned transducer in the output of saiddevice, range-control means for rendering said series operative in a plurality or ranges, and individual tuning means for each of said ranges to accurately adjust the resulting frequencies.

3. A solo electrical musical instrument employing an 'electro-acouiltic tranducer, said instrument comprising in combination a glow-div charge tube, a conductive path connecting said transducer in the output of said glow-discharge tube, a tuned mesh for said tube and including variable resistances connected'in parallel, switching means for selectively connecting resistances of said mesh to said tube to approximately tune the same to frequencies corresponding to notes extremely helpful for experiescapee o: the tempered scale with in a range, means for shifting said range, and a set of individual tuning elements for each range for accurately adiusting the frequencies produced.

4. A solo electrical musical instrument employing an electro-acoustic transducer comprising in combination a glow-discharge tube, a conductive path connecting said transducer in the output of said glow-discharge tube, a series of resistances and a plurality of valuable condensers for said tube, switching means for connecting selected portions of said series in oscillation-producing relation with said tube thereby to approximately tune the same to frequencies corresponding to notes of the tempered scale within a range, switching means in selective coaction with said condensers to shift the range of said notes by a fixed amount, a set of individual tuning elements for each range for accurately adjusting the frequencies, and means (or rendering said sets selectively operable concurrently with the shifting of range.

5. A solo electrical musical instrument employing an electro-acoustic transducer, saidinstrument comprising in combination a glow-discharge tube, a conductive path connecting said transducer in the output of said glow-discharge tube, a condenser in series with said tube and a plurality of serially connected resistances, switching means for selectively connecting a selected portion of said plurality across said condenser and in oscillation-producing relation with said tube thereby to cause said tube to produce oscillations of different frequencies within a determined range, switching means for changing the capacity of said condenser and thereby to change said range by at least one octave, a set of individual tuning potentiometers for each range to accurately adjust the rrequencies produced, and means for selectivehv energizing said sets of potentiometers in accordance with the range'which is operative.

8. A solo electrical musical instrument employing an electro-acoustic transducer, said instrument comprising in combination a glow-discharge tube, a conductive path connecting said transducer in the output of said glow-discharge tube having capacitive means connected in series therewith, a series of resistances, switching means for selectively connecting a selected plurality or said series across said capacitive means and in oscillation-producing relation with said tube thereby to cause said tube to produce oscillations approximately corresponding to notes of the tempered scale within a determined range, switching means for changing the effective capacitance value, oi said capacitive means and thereby to shift said range by at least one octave, a set of individual tuning potentiometers for each range to accurately adjust the frequencies produced, means for selectively energizing said sets, of potentiometer: inaccordance with the range which is operative, and balancing means 16' for neutralizing the effect of the setting of the set de-energized potentiometers upon the set of energized potentiometers.

7. A solo electrical musical instrument includ-, ing an electro-acoustic transducer, said instrument comprising in combinationa glow-discharge tube having capacitive means connected in series therewith, a conductive path connecting the transducer in the output of said glow-discharge tube, a series of tuned resistances, noteswitching means for selectively connecting a selected plurality of said series across said capacitive means and in oscillation-producing relation with said tube thereby to cause said tube to produce oscillations approximately corresponding to notes of the tempered scale within a determined range, range-switching means for changing the effective capacitnace value 01' said capacitive means and thereby to shift said range by at least one octave, a set of individual tuning potentiometers for each range to accurately adjust the frequencies produced, means selectively energizing said sets oi potentiometers in accordance with the range which isoperative, and balancing resistances interposed between said potentiometers and said switching means for neutralizing the ctfect of the setting of the tie-energized potentiometers upon the energized potentiometers, said tuned resistances being considerably higher in value than said balancing resistances and said balancing resistances being considerably higher in value than said potentiometer.

8. A solo electrical musical instrument employing an electro-acoustic transducer, said instrument comprising in combination a glow-dis charge tube, a tuned mesh for said tube, said mesh including a plurality of resistances in par allel, note-switching means for said mesh for connecting any selected resistance in oscillationproducing relation with said tube thereby to cause production of oscillations of step-by-step varying frequencies within a range, means for shitting said range in octave steps, a set of potentiometers for each range to accurately adjust said frequencies, means for rendering said sets selectively operative in accordance with the range, means for neutralizing the effect of the inoperative set of potentiometers upon the energized set of potentiometers, and means effective for all ranges for continuously adjusting the general pitch of the instrument.

9. In an electrical musical instrument including an electro-acoustic transducer and a glowdls'charge tube oscillator tunable in steps by .means or a tuned mesh including a set of resistances connected in parallel and keying means for connecting any selected resistance in circuit with said tube, a resistance of the order of about 500 megohms to about 2,000 megohms connected across the electrodes of said tube thereby to neutra lize the eifect of leakage on the constancy of tuning.

NICHOLAS LARGER.

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