US2545469A - Vibrato system - Google Patents

Description

J. F. JORDAN VIBRATO SYSTEM March 20, 19,51

Filed Oct. 29, 1947 Patented Mar. 20, 1951 VIBRATO SYSTEM John F. Jordan, Terrace Park, Ohio, assignor to The Baldwin Company, Cincinnati, Ohio, a

corporation of Ohio Application October 29, 1947, Serial No. '782,897

(Cl. Sli- 1.25)

12 Claims. l

` This invention relates to electrical musical instruments, and in particular to a frequency tremolo or vibrato system for such instruments. By acivibrato, as distinguished from an amplitude tremolo, is meant an effect produced by periodically varying ata sub-audio rate, the frequencies of the electrical oscillations produced by the generating circuits of the instrument.

-In electrical musical instruments in which oscillations for notes of the same nomenclature are produced in cascade systems each having a master oscillator of high audio frequency and a plurality of controlled generators for harmonically related lower frequencies, it has been proposed to provide an oscillator operating at a sub-audio frequency appropriate for vibrato purposes, and s o tocouple this sub-audio oscillator with the master oscillators of the several cascade systems as to cause their oscillations to fluctuateV at the sub-audio rate to either side of normal frequency. Similar frequency fluctuations occur in the outputs of the controlled generators.

In the electrical organ it is not suicient simply to provide for the presence or absence of a fixed vibrato in the output of the instrument. Musical expression requires at different times different degrees of audible vibrato. This can be obtained by varying the voltage applied to the master oscillators by the vibrato oscillator so as to change the extent oi the fluctuations of the oscillations of the master oscillator to either Side oi the frequency norm.

'-It has been ascertained, however, that Ia much superior eiect can be obtained if the rate of vibrato uctuations can be varied concurrently with the extent of the frequency variations. The principal object of my invention is the provision of means and a method of accomplishing this.

' It is an object of -my invention to providea system for varying concurrently and commensurately the rate and the extent of vibrato in the tones produced by electrical musical instruments. Another object of my invention is to provide a simple, inexpensive and trouble-free electrical circuit for accomplishing the above object.

These and other objects oi the invention which will be set forth hereinafter or will be apparent to one skilled in the art from the following teachings, I attain by that circuit arrangement and in that mode of operation of which I shall now describe an exemplary embodiment. Reference is made to the accompanying drawings, wherein:

Figure 1 shows a circuit diagram of my invention as applied to a cascaded group of oscillation generators together with control means for supplying fixed amounts of vibrato. Figure 2 shows a continuously variable vibrato control which may be used in place of the control shown in Figure 1 A VThe lower portion A of Figure 1 is the circuit dlagramof one of a series oi generator groups or cascades, each group producing all the octavely-'related electrical oscillations corresponding to one note of the musical scale. Such a generator group and its mode of operation is fully described and vclaimed as to certain features in United States Patent application, Serial No. 714,601, led Dec. i945, and entitled Interlocked Gerierator Circuits, in the name of Edward M. Jones. My invention is not limited to the employment of this particular cascade system, since others will serve.

It will be suflicient for the purposes or this description to point out that in the exemplary cascade system the left hand set of triade elements of the thermionic tube l is used in conjunction with the master oscillator circuit designated generally at 4, which determines by means oi an interlocking system the frequencies of the rem-aining ve oscillation-generating circuits which employ, respectively, the right-hand set of triode.

elements of tube I and both sets of triode elements in the tubes 2 and 3. The six octavely related electrical oscillations generated in any of the above mentioned generator groups are available at points 5 through Iii for subsequent keying, modification and translation into sound in an instrument such as that described in de-tail in U. S. Patent application Serial No. '756,126 led June 21, 1947, and entitled An Electric Organ, in the name of John F. Jordan.V

The upper portion B of Fig. 1 comprises a double-pole vibrato control switch Il, 5I and a vibrato oscillator circuit employing the thermionic tube l2, the transformer I3 and various capacitors and resistors which will hereinafter be described. A source of plate potential for all the ther-mionic tube circuits may be connected at the point i4! to lead I'I. The output potential from the vibrator oscillator circuit may be supplied to the master oscillator circuit 4 at point l5 through the connecting lead i6. The voltage so supplied has the effect of varying at a vibrato rate the bias on the master oscillator grid circuit. The coil TI of the transformer I3 provides a path to ground for the grid currents oi the master oscillator triode, the iirst section of tube l, and of the corresponding tube of the other cascade generator groups (not shown) in the complete instrument.

The operation oi' my vibrato system is as follows:

1. No vibrato With the ganged switch arms I I, I I in the upper position and contacting switch points a and a respectively, the plate circuit of the tube l2 is open, the vibrato circuit is thus inoperative, and constant frequency oscillations are available at points 5 through I@ of the cascaded oscillation-producing circuits of each cascade generator group of the instrument.

3 2. Medium vibrato With the switch arms il, li in the central position, and contacting switch points b and b', the plate circuit of the tube i2 is closed and current flows from the plate supply source connected at ifi through the lead il, the dropping resistor Rl, the plate coil TZ of the transformer i3, the switch arm l l', the Xed contact b', the dropping resistor R2, the dropping resistor R3, to the junction i3, from which a portion of the current from the plate supply is bypassed by way of the switch arm ii, the fixed contact b, the by-pass resistor Rd to ground; the other portion of the current from the plate supply flows through the lead I9 to the plate of the tube l2. In a manner well known in the art, an oscillatory current is generated in the closed circuit comprising the grid coil Tl of the transformer it and the condenser Cl. The oscillating potential thus produced at 20 is applied through the lead it to point i of the master oscillator circuit li.

The result is a vibrato variation in the fre-- quency of the oscillations generated in all master oscillators at a rate dependent upon the oscillatory rate of the circuit ClTE and of an extent dependent upon the potential at the point Since the cascaded oscillation-generating circuits in each generator group are locked to the master oscillator, vibrato variations will be present in the signals at points through it; as well as at which is the signal take-off point in a master oscillator circuit.

The condenser C2 is a grid-blocking condenser. The resistor R is for the self-biasing of the grid of the tube i2. pressing of parasitic oscillations in the grid circuit of the tube l2.

rlhe values of the various circuit elements have been determined experimentally and a typical but non-limiting set is as follows;

The tube i2 may be half of a 6SN7 twin triode.

The transformer 23 may be specified as follows:

Ratio of turns in Ti to 'T2-1.82 to l D. C. resistance of Ti-1750 ohms (max.) D. C. resistance T2-ilo0 ohms (max.)

The purpose of the by-pass resistor Rt is to bring the current through the coil T2 of the transformer il; to a value such that the magnetiaing force cl' the coil is approximately equal and opposite to that of the coil Tl which carries the sum of the grid currents of all the master oscillator tubes.

3. Fall vibrato With the switch arms i l, i t in the lower position and contacting switch points C and C', the resistors RZ and Re are removed from the active part of the circuit as will be evident. The removal of Rd has the en ect of reducing the potential drop in Rl, and because the current which formerly flowed through Ril necessarily flows through Rl and The removal of R2 further reduces the potential drop in the circuit between the points it and iii. Since the plate of the tube i2 is at the same potential as the point i8, the overall effect of this removal of R2 v(and Rai) from the circuit is a rise in the potential at the plate of the tube l2. Therefore the potential across the oscillating circuit ClTi rises resistor Rb is for the Sui,

causing a higher oscillating potential at the point I5, and hence the extent of the vibrato of the signals at 5 through lo is increased. Due partly to the increased potential on the plate of the tube l2 but mostly to the reduced magnitude of the direct current flowing through the winding T2, caused by removal of Rd, the effective inductance of the coil Tl is reduced, and the frequency of the oscillations in the circuit CITI is thereby increased; hence the vibrato rate of the signals at the points 5 through i0 is increased.

Although I may prefer fixed steps of vibrato for economy, a gradual change in the rate and the extent of the vibrato may be accomplished by the modified control means shown in Fig. 2. This control means may be substituted for that shown to the right of the line X-X in Figure l. Identical parts have been given the same index numerals.

Rl and R8 are variable resistors in which the contact arms have also an open position as shown. As the contact arms 2l and 2| are moved from the median (central) position to the full lower position, the Value in the circuit of the resistance Rl is increased and the current through TI, Rl, R3 and R4 is reduced, while the value of R8 in the circuit is decreased and the circuit resistance which corresponds to R2 in Fig. l is reduced. The resultant effects upon the vibrato rate and extent are the same as in Fig. l, except that a gradual, rather than abrupt, transition is made from the medium to full vibrato.

Other modications can be made in my invention without departing from the spirit of it.

Having thus described my invention in an exemplary embodiment, what I claim as new and desire to secure by Letters Patent is:

l. In an electrical musical instrument, th combination of a plurality of generators of electric oscillations corresponding to the notes of a musical scale, a sub-audio frequency source in connection with said generators operative to modulate the frequency of said electric oscillations at a sub-audio rate, and control means associated with said sub-audio source whereby the rate and the magnitude of the frequency modulation can be varied commensurately.

2. The combination as set forth in claim 1 in which said control means includes switch means whereby said rate and said magnitude can be varied in definite steps.

3. The combination as set forth in claim 1 wherein said control means includes Variable electric impedance means whereby said rate and said magnitude can be varied gradually.

4. The combination as set forth in claim l in which said generators include an electron discharge tube, and in which said sub-audio frequency source includes a connection to said generators whereb-y the oscillating sub-audio potential generated in said source is effective to vary the bias on the grid of said electron discharge tubo in said generators. Y

The combination as set forth in claim 4, said connection also providing a return path for the grid current passing through said electron discharge means in said generators.

6. The combination as set forth in claim 5, said sub-audio frequency source also including said control means, an electron discharge tube, a transformer, a plate supply circuit, and electrical impedances, said transformer including a first winding for said grid current and a second winding for the current in said plate supply cire.

cuit, said control means and said electric impedances being effective to Vary the value of said plate supply current flowing through said second winding.

7. In combination a. generator for oscillations of audio frequency corresponding to notes of a musical scale, said generator comprising a thermionic tube having coupled grid and plate circuits, and resonant means in said grid circuit for controlling the frequency of oscillation of said generator, a sub-audio oscillator comprising a thermionic tube having coupled grid and plate circuits, and resonant means in said grid circuit for controlling the frequency of oscillation of said oscillator, a connection between said oscillator and said generator for impressing oscillations from said oscillator on the resonant means of said generator, impedance means for Varying the strength of said oscillations, impedance means for Varying the frequency of said oscillations, and a connection between said last mentioned means enforcing concurrent variation thereof.

8. In combination a generator of audio-frequenci.7 oscillations corresponding to noles of a musical scale, an external source of sub-audio frequency oscillations, a connection between said generator and said source, a circuit in connection with said source for varying the frequency of oscillations therefrom, a circuit for varying' the amplitude of said oscillations, and means connection with :both circuits for controlling concurrently the frequency and amplitude of the oscillations from said source.

9. In combination a generator for oscillations of audio frequency corresponding to notes of a musical scale, said generator comprising a thermionic tube having coupled grid and plate circuits, said grid circuit containing resonant frequency-controlling means, a generator for oscillations of sub-audio frequency comprising a thermionic tube having coupled grid and plate circuits, said grid circuit containing resonant frequency-controlling means, a connection between the grid circuits of said generators such that the said resonant means are in series, controllable impedance means in connection with the plate circuit of said sub-audio generator for varying the frequency of the sub-audio oscillations, additional controllable impedance means in the plate circuit of said sub-audio generator for varying the amplitude of the sub-audio oscillations, and an operative connection between said controllable impedance means.

10. The structure claimed in claim 9 in which said audio frequency generator is coupled to a plurality of controlled generators of harmonically related frequencies forming a cascade series, and in which a plurality of said cascade series is similarly7 connected to said sub-audio generator.

11. A process of producing a variable frequency tremolo in an electrical musical instrument having a series of generators of audio frequency for the notes of a musical scale, a generator of subaudio frequency, and a connection between said last mentioned generator and said first mentioned generators effective to transfer oscillations from said sub-audio generator to said first mentioned generators to cause cyclical fluctuations of the frequencies thereof, which process comprises Varying the voltage of the oscillations so transferred to vary the extent of said frequency fluctuations, and concurrently varying the frequency of said sub-audio generator to vary the frequency of said cyclical fluctuations.

12. In combination a generator of audio frequency oscillations corresponding to notes of a musical scale, an external source of sub-audio frequency oscillations coupled to said generator for modulation of the frequency of said audio frequency oscillations, circuit means coupled to said source for varying the frequency and amplitude of the oscillations from said source whereby the rate and magnitude respectively of the frequency of the oscillations from said generator are Varied, and means in said circuit means for effecting concurrent variation of the frequency and amplitude of the oscillations from said source whereby said rate is varied in direct proportion to said magnitude.

JOHN F. JORDAN.

REFERENCES CITED The following references ille of this patent:

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