US3383453A - Percussion circuit for electronic organs - Google Patents

Description

May 14, 1968 P. H. SHARP PERCUSSION CIRCUIT FOR ELECTRONIC ORGANS Filed June 2s, 1965 14 l 5k-: 21 T101 7c3 /L/ Fira. 3.

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United States Patent O 3,383,453 PERCUSSION CIRCUIT FOR ELECTRONIC ORGANS Paul H. Sharp, Electro Music, P.O. Box 2267D, Altadena, Calif. 91105 Continuation-impart of application Ser. No. 214,331, Aug. 2, 1962. This application June 28, 1965, Ser. No. 467,219

Claims. (Cl. 841.26)

This application is a continuation-in-part of my prior application Ser. No. 214,331, filed Aug. 2, 1962, entitled Percussion Circuit Utilizing a Single-Pole Key Switch, now Patent No. 3,244,790, issued Apr. 5, 1966.

Percussive effects can be crudely produced on a conventional electronic organ by depressing a key and immediately releasing it. Immediate release is required because, in the conventional organ circuit, the tone continues as long as the key is depressed. In contrast, a piano key can be held down or released without altering the tone. Thus percussive tones are produced by imparting a burst of energy to a vibrating body, rather than a continuous supply of energy. After the energy pulse is initially applied to a percussive tone generator, it decays at a rate determined by the damping characteristics of the generator.

Some electronic organs utilize circuits that require, for the production of percussive effects, continued depression of a key. This, too, is an unnatural operation as compared, for example, to the piano. Other electronic organs superimpose a percussion envelope on the entire organ output. This severely restricts versatility.

One of the primary objects of this invention is to provide improved circuitry for producing percussive eiTects in which the organ key, after depression, can be released or not without affecting the tone produced. Thus the action truly simulates that of a piano or equivalent percussive instrument.

In still other known organ circuits for producing percussive effects, a key-operated switch has both a backcontacting and a front-contacting position. In such organizations, movement of the switch rst disconnects a capacitor from a source, and then connects it to a tone generator. These circuits have proved impractical since' they require major revisions in the conventional singlepole switch assemblies used in electronic organs. Further, they require undue maintenance to ensure proper engagement of a switch arm with a back contact and a front contact. Such adjustments are ordinarily not required.

Accordingly, an important object of this invention is to provide means for producing percussive effects by the natural key manipulation described with the aid of a simple single-pole switch. This means that existing switch assemblies can be utilized.

Another object of this invention is to lprovide simple circuits by the aid of which two transient periods for operation of a tone generator may be determined, corresponding to initial closure of a single-pole key switch, and Iopening thereof.

This invention possesses many other advantages, and has other objects which may be made more clearly apparent from a consideration of several embodiments of the invention. For this purpose, there are shown a few forms in the drawings accompanying and forming part of the present specication. These forms will now be described in detail, illustrating the general principles of the invention; but it is to be understood that this detailed description is not to be taken in a limiting sense, since the scope of the invention is best defined by the appended claims.

Referring to the drawings:

FIGURE 1 is a diagram of one form of the present invention;

ICS

FIG. 2 is a circuit diagram equivalent to that of FIG. 1; and

FIG. 3 is a circuit diagram of a modified form of the present invention in which one of the transient circuits incorporates a normally charged rather than a normally discharged condenser.

In FIG. 1, a typical piano gate circuit incorporating the present invention is illustrated. Within the rectangle is a typical transistor amplifier that operates upon a signal of constant amplitude provided by a tone generator (not shown) for a particular note. This signal, corresponding, say, to Fil, is applied to an input terminal T1. Through a transistor Q1, this signal is translated to an output terminal T2. The amplitude of the signal at the output depends upon the conductivity of the transistor Q1. This, in turn, is determined by two factors, the cut-off bias imposed upon the base of the transistor, and a superimposed signal.

Cut-otl bias is provided by a suitable adjustable voltage source through a resistor R6 that connects with the transistor base. The superimposed signal is provided by a transient circuit formed by elements outside the rectangle. The superimposed signal appears at the terminal`T3 and is applied through a resistor R3 to the transistor base. In the present example, the voltage at the terminal T3 is normally about zero. Upon closure of a switch S, the voltage at the terminal T3 instantly rises, and then decays, and the amplitude of the output signal is correspondingly determined to simulate a percussive tone.

The shape of the decay characteristics is adjusted by the bias `adjust circuit and by components R5, R4, D3. The remaining components determine the basic decay characteristic. R3 has a value many times greater than the input resistance of the amplifier; hence, the mechanics for the production of the basic decay characteristic can be examined by the aid of an equivalent circuit (FIG. 2) in which the amplifier is replaced by a zero impedance. Thus R3 is now connected directly across the terminal T3 and the lead L1. In this equivalent circuit, the components that merely adjust the shape of the decay characteristics likewise are omitted.

In FIG. 2, R3, enclosed in a circle, thus represents a tone generator that produces a signal the intensity of which is directly proportional to applied Voltage or current. It will be understood that R3 represents the equivalent input impedance of an oscillator or keyer for a continuously operating generator or the like. That impedance may incorporate reactive elements.

A small battery B (which may be a suitable DJG. power supply common to all circuits) serves as a source of voltage for application to the generator R3. When the key switch S is closed, a series circuit is established through series connected capacitors C1 and C2. The generat-or R3 parallels the operating capacitor C2; the other capacitor serves a controlling function. The series circuit Ican be `traced from one side of the battery B, switch S, controlling capacitor C1, a reverse blocking diode D2, capacitor C2, and lead L1 to Ithe other side of the battery B or source. As soon as the switch closes, the source voltage divides between the two capacitors, and about 99% of the voltage appears across C2 because the capacity of C1 is about 100 times that of C2. Accordingly, immediately upon switch closure, a high signal level is produced.

At this instant of switch closure, the controlling capacitor C1 has very little charge; but `a charging circuit is provided through R2 so long as the switch S is kept closed. At the same time, .the generator R3 forms a discharging circuit for the operating capaci-tor C2. The controlling capacitor C1, however, has another very slowcharging circuit through R3 and D2. Whether this supplemental charging circuit is effective depends upon whether 3 D2 is forward biased or reverse biased. This, in turn, depends upon the time constants of the circuit.

The voltage at the `terminal T3 on the cath-ode side of D2 tends .to fall from the initial seven volts substantially 'in accordance with the time constant CZ*R3. The voltage at the anode terminal T4 -tends t-o fall from the initial .seven volts substantially in accordance with the time constant (l1-R2.

In the present example, the time constant C2-R3 is a good `deal shorter than for Cl-RZ. Accordingly, the diode D2 remains 'forward biased, and the supplemental charging circuit for the controlling condenser is effective. The charging current for C1 through R3 adds to the discharging current of C2. Both currents, of course, decay. But since both are operative, the rate of decay is less than if the supplemental charging circuit were not effective.

If the switch S is held down, ultimately C1 charges fully, and C2 discharges fully, and the signal intensity is zero. However, if the switch S is opened while the signal produces an audible sound, then the decay rate changes. C1 now discharges very rapidly through -resistor R1 and diode D1. Consequently, the current previously liowing through resistor R3 for charging capacit-or C1 has ceased. Signal intensity now reduces at a faster rate. The signal intensity continues to reduce acc-Ording to the time constant C2-R3. Release of the lswitch S produces a damping function much as the release of a piano key does.

By changing the values of the circuit elements, the time constant of the charging resistor R2 and the controlling capacitor C1 can be made less than that of the generator R3 and operating capacitor C2. Ilf so, then the decay rate becomes independent of the continued depression of the key S. Thus immediately upon switch closure, the full voltage appears across the operating capacitor C2. At the next instant of time, the diode D1 becomes reverse biased, and no supplemental charging circuit for the controlling capacitor C1 is elective. The decay of voltage across the generator R3 depends solely upon the capacity of the capacitor C2 and the value of the irnpedance of R3. Operation then simulates instruments having no key released dampers.

The circuit can take a number of forms. For example, a normally closed key switch can be substituted with slight changes in the circuit arrangement. The polarities can also be reversed. Furthermore, the control capacitor can be normally charged rather than normally uncharged. In FIG. 3, there is illustrated a percussion circuit in which the polarities are reversed and the control capacitor C1 normally charged;

When the switch is open, the control capacitor C1 is in series with a small ohmic value resistor R1', a battery B', and a reverse blocking diode D1. The terminal T4', on one side of the capacitor C1', is clamped to the voltage of the negative terminal at lead L1'. The other side of the control capacitor is at the voltage of the positive terminal of the battery. Hence, the capacitor is normally fully charged. As soon as the switch S' is closed, the operating capacitor C2 is connected directly across the control capacitor C1'. The circuit can be traced through` switch S', lead L1', capacitor C2', diode D2', capacitor C1', back to the switch. Thev diode D2' is of such polarity as to allow the charge to be immediately redistributed between the capacitors. The voltages across the capacitors must now be the same. But since the operating capacitor C2' has a much smaller capacity, there is very little voltage drop. As soon as the switch is closed, the source B1 is isolated from all circuit elements except Rl'. l

As in the previous form, the signal amplitude starts at a high level. The decay rate may depend upon the switch S' in accordance with the time constants of the circuit.

The operating capacitor` C2' has a discharge circuit through the generator yR3'. The control capacitor has a discharge circuit through a resistor R2. The diode D1' is now reverse biased. The control capacitor C1' has a supplemental discharge circuit through the generator R5' and the diode D2. This circuit may or may not be eiective, depending upon circuit Values. Thus the diode D2' may or may not be reverse biased.

IIf the circuit values are such that the diode D2' is reverse biased, then the signal decay characteristic depends upon C2' alone, whether the switch S' is held down or not. If, however, the circuit values are such as to forward bias the diode D2', then the signal decay characteristic depends 'both upon the current produced by the control capacitor and the operating capacitor so long as the key switch S' is held closed. Thus the discharge circuits for C1 are then interrupted, and the charging circuit therefor again becomes operative. At the same time, the operating capacitor C2' continues to discharge, but the sign-al level drops abruptly as the key switch S is opened. This simulates the key released d-amper action of a piano.

By virtue of the fact that the control capacitorkhas a much greater capacity than the operating capacitor, it is unnecessary to provide special anti-pump up circuitry to -avoid voltage building upon rapid opening and closing of the key switch.

The inventor claims:

1. In an electrical musical instrument: an electrically operated generating device that produces a signal correspondingto a musical tone with an intensity related directly to the intensity of electrical energization: an operating capacitor; an operating circuit for said generating device including said operating capacitor; a single pole key switch cooperable with a source of direct current; a control capacitor; circuit means providing charging and discharging circuits for said control capacitor, and operable respectively in accordance with the position of said key switch; and unidirectionally conductive means interconnecting the operating circuit and said control capacitor upon operation of said key switch; said circuit means having characteristics determining the continued electiveness of said unidirectionally conductive means following key switch operation.

2. In an electrical musical instrument: an electrically operated generating device that produces a signal corresponding to a musical tone with an intensity related directly to the intensity of electrical energization: an operating capacitor paralleling said generating device whereby charge applied to the operating capacitor energizes said generating device; a control capacitor; a normally open single pole switch cooperable with a source of direct lcurrent for connecting the capacitors in series across said source; a diode between the capacitors, and polarized to permit the charging of said capacitors by said source; a resistor forming a first charging circuit for said control capacitor independent of said diode; said generating device also providing a supplemental charging circuit for said control capacitor dependent upon said diode; said tirst charging circuit being designed to reverse bias said diode immediately after switch closure whereby the decay characteristic of said generating device is independent of key switch opening.

3. The combination as set forth in claim 2 together with means for quickly discharging said control capacitor upon opening of said key switch.

4. In an electrical musical instrument: an electrically operated generating device that produces a signal corresponding to a musical tone with an intensity related directly to the intensity of electrical energization: an operating capacitor paralleling said generating device whereby charge applied to the operating capacitor energizes said generating device; a control capacitor; a normally open single pole switch cooperable with a source of direct current for connecting the capacitors in series across said source; a diode between the capacitors, and polarized to permit the charging of said capacitors by said source; a resistor forming a rst charging circuit for said control capacitor independent of said diode; said generating device also providing a supplemental charging circuit for said control capacitor dependent upon said diode; said first charging circuit being designed to forward bias said diode immediately following key switch closure whereby said supplemental charging circuit remains effective while said key switch is closed.

5. The combination as set forth in claim 4 together with means for quickly discharging said control capacitor upon opening of said key switch.

6. In an electrical musical instrument: an electrically operated generating device that produces a signal corresponding to a musical tone with an intensity related directly to the intensity of electrical energization: an operating capacitor paralleling said generating device whereby charge applied to the operating capacitor energizes said generating device; a normally charged control capacitor; a normally open single pole switch for connecting the control capacitor across the operating capacitor; a diode between the capacitors, and polarized to permit the exchange of charge between said capacitors upon closure of said switch; a resistor forming a first discharging circuit for said control capacitor independent of said diode; said generating device also providing a supplemental discharging circuit for said control capacitor dependent upon said diode; said first discharging circuit being designed to reverse bias said diode immediately after switch closure whereby the decay characteristic of said generating device is independent of key switch opening.

7. The combination as set forth in claim 6 together with means for quickly charging said control capacitor upon opening of said key switch.

8. In an electrical musical instrument: an electrically operated generating device that produces a signal corresponding to a musical tone with an intensity related directly to the intensity of electrical energization: an operating capacitor paralleling said generating device whereby charge applied to the operating capacitor energizes said generating device; a normally charged control capacitor; a normally open single pole switch for connecting the control capacitor across the operating capacitor; a diode between the capacitors, and polarized to permit the exchange of charge between said capacitors upon closure of said switch; a resistor forming a first discharging circuit for said control capacitor independent of said diode; said generating device also providing a supplemental discharging circuit for said control capacitor dependent upon said diode; said first discharging circuit being designed to forward bias said diode immediately following key switch closure whereby said supplemental discharging circuit remains effective while said key switch is closed.

9. The combination as set forth in claim 8 together with means for quickly charging said control capacitor upon opening of said key switch.

10. In an electrical musical instrument: an electrically operated generating device that produces a signal corresponding to a musical tone Iwith an intensity related directly to the intensity of electrical energization: an operating capacitor and a control capacitor; circuit means connecting the capacitors including unidirectionally conductive means and a key switch; means providing a source of direct current voltage and operatively connected to said operating capacitor in accordance with the position of said key switch; and means forming a transient circuit for said control capacitor effective upon operation of said key switch, and having a characteristic to determine the conductivity characteristic of said unidirectionally conductive means and the continued interconnection between said capacitors following key switch operation.

11. The combination as set forth in claim 10. in which said transient circuit determines continued connection between said capacitors following key switch operation whereby said key switch operates as a key released damper.

12. The combination as set forth in claim 10 in which said transient circuit isolates said capacitors following key switch operation whereby said key switch operates as a clapper without a damper.

13. In an electrical musical instrument: an electrically operated generating device that produces a signal corresponding to a musical tone with an intensity related directly to the intensity of electrical energization; an operating capacitor having a discharge path including said generating device; a control capacitor; a single pole normally open switch for transferring charge from the control capacitor to the operating capacitor; means forming a discharge path for one of the capacitors whereby the decay of voltage for the capacitors differs; and a unidirectionally conductive device for isolating the discharge path provided by said generating device in response to a disparity of capacitor voltages whereby the decay of current through the generating device is independent of subsequent switch opening.

14. In an electrical musical instrument: an electrically operated generating device that produces a signal corresponding to a musical tone with an intensity related directly to the intensity of electrical energization; an operating capacitor paralleling said generating device whereby charge applied to the operating capacitor energizes said generating device; a control capacitor; a normally open single pole switch for connecting the control capacitor across the operating capacitor; a resistor forming a supplemental discharge path for the control capacitor; and a diode for isolating said resistor from said supplemental discharge path and for isolating the capacitors upon a disparity in voltage whereby the generating device operates without regard to opening of the switch.

15. rl'he combination as set forth in claim 14 together with means for quickly recharging said control capacitor upon opening of said switch.

No references cited.

ARTHUR GAUSS, Primary Examiner. B. P. DAVIS, Assistant Examiner.

Claims (1)

1. IN AN ELECTRICAL MUSICAL INSTRUMENT: AN ELECTRICALLY OPERATED GENERATING DEVICE THAT PRODUCES A SIGNAL CORRESPONDING TO A MUSICAL TONE WITH AN INTENSITY RELATED DIRECTLY TO THE INTENSITY OF ELECTRICAL ENERGIZATION: AN OPERATING CAPACITOR; AN OPERATING CIRCUIT FOR SAID GENERATING DEVICE INCLUDING SAID OPERATING CAPACITOR; A SINGLE POLE KEY SWITCH COOPERABLE WITH A SOURCE OF DIRECT CURRENT; A CONTROL CAPACITOR; CIRCUIT MEANS PROVIDING CHARGING AND DISCHARGING CIRCUITS FOR SAID CONTROL CAPACITOR, AND OPERABLE RESPECTIVELY IN ACCORDANCE WITH THE POSITION OF SAID KEY SWITCH; AND UNIDIRECTIONALLY CONDUCTIVE MEANS INTERCONNECTING THE OPERATING CIRCUIT AND SAID CONTROL CAPACITOR UPON OPERATION OF SAID KEY SWITCH; SAID CIRCUIT MEANS HAVING CHARACTERISTICS DETERMINING THE CONTINUED EFFECTIVENESS OF SAID UNIDIRECTIONALLY CONDUCTIVE MEANS FOLLOWING KEY SWITCH OPERATION.

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