US2545432A

US2545432A - Electronic tremulant

Info

Publication number: US2545432A
Application number: US96545A
Authority: US
Inventors: Francis M Schmidt
Original assignee: Wurlitzer Co
Current assignee: Wurlitzer Co
Priority date: 1949-06-01
Filing date: 1949-06-01
Publication date: 1951-03-13
Anticipated expiration: 1968-03-13

Description

March 13, 1951 F. M. SCHMIDT ELECTRONIC TREMULANT Filed June 1. 1949 l/mrf f INVENTOR. firzczaflimdf BY W Patented Mar. 13, 1951 UNITED STATES PATENT OFFICE ELECTRONIC TREMULAN T Francis M. Schmidt, North Tonawanda, N. Y., assignor to The Rudolph Wurlitzer Company, North Tonawanda, N. Y., a corporation of Ohio Application June 1, 1949, Serial No. 96,545

. 11 Claims.

This invention relates to musical instruments and more particularly to an electronic tremulant for use in an electronic musical instrument.

- It is often desirable in musical instruments, particularly electronic organs, to have a tremulant efiect producing a fluctuating intensity or pitch for desirable musical tones.

Prior tremulants in electronic musical instruments have generally fallen into one of two classes, either mechanical or electrical. The mechanical systems have generally employed a slowly rotating fan mounted adjacent to and directly in front of the output translator or speaker. Typical electronic tremulants have utilized a low frequency oscillator to modulate a sound amplifier stage or to modulate the tone generator. Mechanical systems are generally unsatisfactory in that they require too frequent attention, are difficult to control and are inclined to be noisy. Prior electronic tremulants have often been unsatisfactory in that they presented an undesirable time lag in starting and ending, required control of high voltages, or caused undesirable interactions in the electronic circuits.

An object of this invention is to present an electronic tremulant which does not require the direct control of high voltages.

. A further object of this invention is an electronic tremulant which is substantially instantaneous in starting and ending operations.

. Another object of this invention is to produce an electronic tremulant, the operation of which is not affected by connection into circuit with the amplifying stages of an electronic musical in-.

strument.

Another object of this invention is to produce an electronic tremulanthaving a controllable degree of tremulancy.

, Other and further objects and advantages of the current invention will be apparent from the following description when taken in conjunction with the accompanying drawings in which:

. Fig. 1 is a perspective view of the console of an electric organ in which the electronic tremulant may be used; 7

Fig. 2 is a schematic wiring diagram of the electronic tremulant; and

Fig. 3 illustrates the relative variation in volume and pitch of the sound amplifier output when the tremulant is used.

' A console I of an electronic organ in which the electronic tremulant which is the subject of this invention may be used is shown in Fig. l.

The console has one or more banks of keys 3 to beactuated by hand and may also have a. pedal keyboard 5 to be actuated by the musician's feet. Foot pedals 'l are also provided for varying the volume and may also be used to control the de-'. gree of tremulancy if desired. A row of stop tablets ii is also provided for selecting tone generators, and one or more of these stops may control the operation of the tremulant. An electronic tremulant is used to shunt the input of one of the amplifier stages. circuit of one stage which may amplify a musical tone produced in any desirable manner, such as the vibrating reed capacitor explained by Hoschke in his Patent 2,015,014, is shown comprising a vacuum tube H having a plate load resistor and a source of positive plate potential shown as a battery l5. An isolating resistor I! is provided to prevent the tremulant from having any effect on the amplifier stage having the tube H. The signal from the previous stage passes through the isolating resistor I! to the next stage including a coupling capacitor l9, grid.

resistor 2l,.vacuum tube 23 and cathode resistor 25. The output circuit of the tube 23 may be conventional and is not shown as the electronic tremulant operates most particularly in conjunction with the input circuit.

The electronic tremulant includes a low frequency oscillator 2'! which may be of any desirable type operating at a sub-audible frequency. 6.4 cycles per second is recommended as producing a pleasing result. The low frequency oscillator is coupled as by direct coupling to a.

limiter 29 which may be of any convenient conventional type which limits the amplitude of the output of the low frequency oscillator so that.

the tremulant effect may be readily controlled by the musician With no random variations. The limiter also provides some degree of shaping to the output wave of the generator and acts as a buifer to prevent unstable operation of the os-' cillator under load. One of the output terminals of the limiter is grounded and the other is coupled to the control grid 33 of a voltage amplifier tube 35 which may be deemed a control tube. Plate potential for the plate 31 of control tube 35 isv supplied through a plate load resistor 39 from a convenient source of positive potential which is grounded at its negative end as at 4!. Potential for the screen grid 43 is supplied through a screen grid resistor 45 from the same source of positive potential. The suppressor grid 41 is directly connected to the cathode 49 which is in turn connected to ground through a pair of series resistors 5| and 53, the latter of which is shunted by a switch 55. The cathode 49 is also The output.

connected through a resistor 51 to the positive source of potential and a capacitor 59 shunts both of the resistors i and 53 to ground. The resistors 5!, 53 and 51 constitute a voltage divider providing cathode bias for the control tube 35. With the switch 55 closed, the control tube 35 is biassed at its normal operating potential, but when the switch 55 is open, the: additional bias developed across the resistor 53 causes the tube 35 to cut off and become inoperative.

The control grid 33 is connected to ground through a series of resistors BI, 63, 55 and 61 with the output of the limiter connected between the resistors 6i and 53. Tap switch contacts 69 and H are connected respectively between the

resistors

63 and 65 and 55 and El. A third tap switch contact 73 is not connected and a grounded switch arm '15 may be selectively connected with any one of these three tap switches to provide a means for determining the magnitude of the output of the limiter 29 which is applied to the control grid of the control tube 35. The switch arm may be controlled by one of the foot pedals l or by one or more of the stop tablets 9. The normal input capacitance of the control tube 35 is augmented by a capacitor ll connected between the control grid 33 and the plate 37. The control tube 35 is coupled to the input of the amplifier tube. 23 by means of a capacitor '19 connected between the junction of the resistor SI and capacitor TI and the resistor H and capacitor [9.

As the control grid potential is changed relative to the cathode by the output from the oscillator 21 and the limiter the input capacitance of the control tube varies. The changing of input capacitance in response to varying control grid potential is well known to those in the art and the function of an electronic tube as a voltage controlled capacitance is described in the Patent 2,017,270 to Yolles. During a positive half cycle of output from the limiter the control tube bias decreases, which increases the input capacitance, thus increasing the shunting effect of the electronic tremulant on the. input to the amplifier tube 23. This shunting effect causes the response of the amplifier to be consequently lowered, particularly at the higher frequencies, giving the curve shown at A in Fig. 3. During the negative portion of the cycle the control grid bias increases and the input capacitance decreases, thus decreasing the shunting efiect of the tremulant and giving the curve shown at B in Fig. 3. The relative variation in frequency response is shown by the shaded area in Fig. 3 with the normal response curve of the sound amplifier being at a point midway between the extremes shown.

The low frequency oscillator may be operated at all times when the electronic musical instrument is operating. With the switch open the tube 35 is out oh. and the oscillator has no effect upon the operation of the electronic musical instrument. When the switch 55 is closed, as by means of one of the stop tablets 9, the tube 35 immediately becomes operative and as the oscillator has been running continuously, the shunting effect on the sound amplifier is instantaneous so that there is no time lag between the time the tremulant switch is actuated and the tremulant effect is noticed in the output. Likewise, the tremulant is stopped instantaneously by opening the switch 55 to out off the control tube 35. The limiter prevents reflected impedances from impairing the operation of the low frequency oscillator 21 and the capacitor 59 prevents any clicks from being apparent when the switch 55 is opened or closed. As was noted before, the position of the tap switch arm 15 controls the potential from the limiter applied to the control grid 33 and consequently changes the variation in input capacity of the tube 35 so that the magnitude of the tremulant may be controlled by the musician.

Various changes may be made in the apparatus chosen for illustration without departing from the spirit and scope of the appended claims, and I therefore intend to be limited only by the following claims.

I claim:

1'. An electronic musical instrument including an electronic amplifier stage and an electronic tremulant, said tremulant comprising an electronic tube, an input circuit for said electronic tube and connected substantially in shunt with said electronic amplifier stage, and means for varying the input capacitance of said electronic tube whereby to shunt a variable portion of a musical tone passed by said electronic amplifier stage to produce a tremulant eifect.

2. An electronic tremulant as defined in claim 1 in which the means for varying the input capacitance of the electronic tube includes means for varying its grid potential.

3. An electronic musical instrument including a plurality of electronic amplifier stages and an electronic tremulant, said tremulant comprising a variable impedanc connected between. two amplifier stages and substantially in shunt there with to shunt a portion of a musical tone being amplified to ground, and means for varying said impedance periodically thereby to produce a tremulant effect in said musical tone.

4. An electronic tremulant as defined in claim 3 in which the variable impedance comprises substantially a variable capacitance.

5. An electronic musical instrument including a plurality of electronic amplifier stages, an electronic tube, an input circuit for said tube con.- nected between two amplifier stages and substantially in shunt therewith, and means for varying the input capacitance of said electronic tube whereby to shunt a variable portion of a musical signal to ground to produce a tremulant effect in said musical signal.

6. An electronic tremulant as defined in claim 5 in which the means for varying the input ca.- pacitance of the electronic tube includes means for varying the grid potential of said tube.

7. An electronic musical instrument including an amplifier stage and, an electronic tremulant connected substantially in shunt to vary the response of said amplifier stage, said electronic tremulant comprising an electroni tube having a control grid, a low frequency oscillator, means interconnecting said oscillator and the grid of said electronic. tube whereby to change the input capacitance of said electronic tube, and a network connecting the control grid of said elec'- tronic tube substantially in shunt with said amplifier stage to produce a tremulant effect in the musical tones of said musical instrument.

8. An electronic tremulant as defined in claim '7 in which the low frequency oscillator operates at a sub-audible frequency.

9. An electronic musical instrument comprising an amplifier stage. and an electronic tremulant, said tremulant comprising an electronic tube having a control element, electrical circuit elements connecting said control element of said electronic tube in circuit with said amplifier stage, a low frequency oscillator, and a limiter interconnecting said oscillator and said electronic tube, said oscillator and said limiter supplying oscillations devoid of random variation in amplitude to the control element of said electronic tube with no reaction on said low frequency oscillator to vary the input capacitance of said electronic tube and thereby introduce a tremulant efiect into the circuit in which the electronic tube is connected.

10. An electronic musical instrument including amplifying means and an electronic tremulant, said tremulant comprising an electronic tube having a control grid, means connecting said tube in circuit with said amplifying means to vary the amplifying characteristics thereof, a continually operating low frequency generator, circuit means connecting the output of said low frequency oscillator to the control grid of said electronic tube, means for normally biassing said electronic tube beyond cutofl, and means for bias- REFERENCES CITED The following, references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,301,871 Hanert Nov. 10, 1942 2,322,884 Roetken June 29, 1943