US3160694A - Percussion circuit - Google Patents

Description

Filed Aug. 7, 1961 United States Patent 3,169,694 PERCUSSION CIRCUIT Herbert E. Meinema, Lake Forest, ilL, assignor to Harnmond (l rgan Company, Chicago, Ill., a corporation of Delaware Filed Aug. 7, 1961, Ser. No. 129,368 7 Claims. (Cl. 84-112) This application relates generally to musical instruments and more particularly to an improved percussion circuit for use therewith.

The use of percussion circuits in electrical musical instruments such as organs is universal, and the circuits have taken widely different forms. It has been suggested to provide a variable impedance in the form of electronic amplifier gain control to provide percussion in circuits such as that shown in United States Patent No. 2,828,659, issued April 1, 1958, to John M. Hanert. These devices, however, are inherently distortion producing devices; and therefore proper care in circuit design must be utilized in order to achieve a commercially acceptable percussion circuit, the cornmercial counterpart of the patented cir cuit being designed with a minimum of cost to provide an unusually desirable musical impression with respect to the percussion feature.

It has also been suggested to control the desired percussive envelope by means of photoelectric devices in which a photocell is cont-rolled by a source of light to produce a voltage which is a function of the light intensity for varying the gain of an amplifier. A typical example of this approach is shown in United States Patent No. 2,513,109, issued June 27, 1950, to Alexander Roth; however, so far as is known, none of these photosensitive voltage producing devices has been completely satisfactory for commercial use in percussion circuits.

Accordingly, it is a primary object of the present invention to provide in an electrical musical instrument an improved commercially practicable percussion circuit characterized by an inherently non-distortion producing device which is reliable, stable, and eiiicient in operation, and which is very rugged and easily controllable. This object is achieved in the preferred embodiment by the incorporation in the musical tone channel of a photoresistive device, preferably a cadmium selenide photorcsistive cell although a lead sulfide or cadmium sulfide photoresistive cell can be used, and by providing variable intensity light source for changing the instantaneous resistance of the photoresistive device in accordance with a pattern producing the desired percussion envelope.

It is another object to provide, in one form of the invention, for the control of the variable intensity light source by the tone signals upon the actuation of a playing key.

It is another object of the present invention to provide, in a percussion circuit of the type called for in the preceding objects, means suppressing the high frequency tone signals which, due to the inherent capacity of the photoresistive device, are passed at appreciable signal levels by the device when its capacitive reactance becomes lower than the resistance as occurs when the light intensity decreases to very low values.

It is another object of the present invention to provide an improved circuit controlling the attack and decay characteristics of the percussion envelope and maintaining a low-intensity minimum current flow through a neon tube light source at all times in order to minimize the inherent time delay of the photoresistive device in increasing its resistance to the proper value when the intensity of the light impinging on the device is reduced to its minimum value.

Other objects and the various features of the invention will be apparent upon a perusal of the following descrip- "ice tion taken in conjunction with the accompanying drawings in which:

FIG. 1 is a diagram, partly diagrammatic and partly schematic, of one form of the invention; and

FIG. 2 is a fragmentary schematic diagram of a second form of the invention.

In FIG. 1, a source of musical tone signals 1% is connected by way of a bus 11 to the input of a transistor amplifier 12. The source of musical signals may be any well known type such as a tone wheel generator in which suitably shaped magnetic wheels are rotated adjacent respective coils to induce signals, corresponding to the tones of the musical scale, in the coils. The signals induced in the coils are synthesized in a well known manner by means of playing key switches 13 and a bus bar system (not shown), the output of which is applied to the bus ll. Since the tone wheel generators are inherently low impedance devices, they are frequently connected to suitable signal amplifying equipment by means of impedance matching transformers. However, in the preferred embodiment of the present application, signals are fed to the transistor amplifier 12 which amplifies the low impedance input without introducing an excessive noise level.

The transistor amplifier 12 has a low value input resistor 16 connected between the emitter and ground. A parallel connected resistor 17 and capacitor 2% are connected between the base of the transistor 12 and ground. Resistor 18 connects the base of transistor 12 to one end of resistor The other end of resistor 22 is connected to the positive 250-volt anode supply terminal. Resistor it? connects the collector of transistor 12 to the junction of resistors 18 and 22. The collector is also coupled to a voltage amplifier 3@ by means of a coupling capacitor 32 and a grid leak resistor 33.

The amplifier 36 includes a triode having its cathode connected to ground by means of a resistor 34 and its plate connected to a positive ZSO-volt potential by means of a load resistor 36. The plate is connected to the grid of a triode amplifier so by a coupling capacitor 42 and a grid leak resistor 44. The cathode of the amplifier is connected to ground by a resistor 46, and the plate is connected to a positive 250-volt potential by a resistor 48.

The grid of the amplifier 5% is connected to a photoresistive device 54 and thence to an output circuit includinga power amplifier 5t and a speaker 51 which are illus trated diagrammatically. An attenuating resistance 53 is connected across the output of the photoresistive device 54 and ground. The value of the resistor 53 is twice that of the minimum resistance of the device 54. A capacitor 56 couples the output of the photoresistive device 54 to the plate of the amplifier 46) to provide an out of phase current which cancels the current flowing through the capacitive reactance of the device 54.

' Capacitor 52, is connected to the resistor 58 which is part of the voltage divider network comprising resistors 58 and 59. Diode 70 connects the junction of resistors 58 and 59 to ground. The diode polarity is such that when the junction of resistors 58 and 59 is negative with respect to ground, it is in the conductive state. A glow lamp 60 which by light intensity controls the resistance of device 54 is energized by a control circuit which includes triode 64, resistors 58, 59, 72, 74, 76 and 78, capacitors 63, 66 and diodes 7t), '71. Resistor 72 connects the junction of resistors 58, 59 and diode 70 to capacitor 66. Capacitor63 connects the junction of resistor 72 and capacitor 66'to ground. Capacitor 66 conmeets the junction of resistor 72 and capacitor 63 to the grid of triode 64. The resistor 74 connects the junction of capacitor 66 and grid of triode 64 to a negative voltage source The potential of the negative voltage source is sufficient to cut off the plate current of triode 64 when the circuit is in the quiescent state, i.e.

when no playing key is pressed. Diode 71 is shunted across resistor 74 with the polarity such that it is conductive when the junction of capacitor 66, grid of triode 64 and resistor 74 is negative with respect to the negative voltage source. Resistor 78 connects the plate of triode 64 to ground. The value of this resistor 78 is a function of the desired ratio of peak light intensity to minimum light intensity of the glow lamp. Glow lamp 60 is connected to the junction of the anode of triode 64 and resistor 78. Resistor 76 connects glow lamp 60 to the anode supply voltage.

The operation of the circuit of FIG. 1 will now be discussed. It will be assumed by way of example that the circuit of FIG. 1 is connected in an organ in a manner similar to that shown in United States Patent No. 2,953,055, issued September 20, 1960, to John M. Hanert, and that the output of a desired tone wheel generator is coupled to the bus 11 upon depression of one of the playing keys. The tone signal is amplified by the circuits 12 and 30 and applied to the photoresistive device 54 by capacitor 42. The tone signal is further amplified by triode 40 and applied to the voltage divider comprising resistors 58 and 59 by means of capacitor 52. The anode current of triode 64 is normally cut off by the negative grid potential and the light emitted by glow lamp 60 is at its minimum value which is determined by the current flowing through resistor 76, the glow lamp and resistor 78.

Initially the amplitude of the tone signal applied to amplifier 50 is low due to the large voltage drop across device 54 compared to that across load resistance 53.

When a playing key is depressed, the positive half cycles of the tone signal which are developed across the diode 70 and resistor 59 rapidly charge capacitor 63 by means of resistor 72. This charge, which at the junction of resistor 72 and capacitor 63 is positive With respect to ground, is applied to the grid of triode 64 by means of capacitor 66. The initial charging potential reduces the negative bias on the grid of triode 64 causing anode current to flow through the glow lamp 60. The resulting light intensity falling on photoresistive device 54- causes its internal resistance to rapidly decrease to a value lower than that of resistor 53 with the result that most of the signal applied to the device 54 appears as an output signal across resistor 53 which is applied to the input of power amplifier 50. After the initial charge potential causes rapid conduction by the triode 64, a voltage will begin to develop across capacitor 66 at a rate determined by the value of capacitance of 66 and resistor 74. This voltage will finally assume a value such that the negative potential on the grid of tube 64 will be its original negative potential of 3 volts. At this time there will be no current flowing through resistor 74 so the voltage across it will be zero. The time necessary for the potential on the grid to become seven-tenths of its final value is known as the time constant of the circuit, which is essentially the time constant of the decay of the percussion envelope.

When the key is released, the voltage across resistor 59 and capacitor 63 will very rapidly drop to zero. The charge potential across capacitor 66 will then appear across the grid of triode 64 and ground. Assuming that diode 71 were not used, this potential will be 6 volts negative on the grid, driving the tube further into the anode current cutofi region. If the playing key were suddenly depressed again, the voltage on the grid would only drop to 3 volts negative and the tube anode current would still be cut off with the result that no percussive signal would be produced. The charge on capacitor 66 would drain off through resistors 59, 72 and 74 at the same rate as the initial charge when the key is released. The value of resistance 74 is many times that of resistors 59 and 72 and it is thus the controlling resistance value of the charge-discharge rates.

However, it is necessary to have the discharge rate of capacitor 66 greatly increased when a key is released so that a percussive tone will immediately be produced it the key is quickly depressed again. This is accomplished in the circuit by connecting a diode across resistor 74 With the polarity such that the grid of tube 64 can never be more negative than the negative bias supply voltage. Capacitor 66 is then forced to discharge through resistors 59 and 72 and diode 71, the resistors being of very low Value compared to resistor 74 greatly reducing the discharge time of capacitor 66. Thus two percussion tones can be produced in rapid succession.

Photoresistive devices possess some capacitance and when they are operated in the near dark region where their resistance is of the order of many megohms, the capacitive reactance at higher audio frequencies is lower than the resistance. This is detrimental to the operation of such devices in percussion circuitry as the higher frequencies are not attenuated sufliciently to become inaudible. This photocell capacitive reactance is nullified in the applicants circuit by feeding an out of phase current through a capacitor to the output terminal of the photoresistive device 54. If the current due to the capacitive reactance of device 54 is equal to the out of phase current supplied through the auxiliary capacitor, cancellation of the reactive signal occurs and the output signal appearing across resistor 53 is purely a function of the ratio of photoresistive device resistance to shunt load resistance. In this circuit the out of phase current is obtained from the anode of triode 40 and is fed through the auxiliary capacitor 56 to the junction of photoresistive device 54 and load resistance 53. The value of capacitance of capacitor 56 is a function of the gain of triode 40 and the effective capacitance of photoresistive device 54 and can be readily calculated by anyone skilled in the art.

There is an additional important reason why this photoresistive device capacitive reactance should be minimized. In the circuit shown, if the reactive current is not canceled and the original tone signal is keyed during the part of the cycle which produces transients, the higher order harmonics so produced will appear directly across the output resistor 53 before the percussive tone which is slightly delayed time wise. This results in a noticeable click which is objectionable.

Typical values for certain of the components are as follows:

Resistor 16 10 ohms. Resistor l7 220 ohms. Resistor 18 4700 ohms. Resistor 19 15,000 ohms. Resistor 22 100,000 ohms. Resistor 33 1 megohm. Resistor 34 3300 ohms. Resistor 36 270,000 ohms. Resistor 44 1 megohm. Resistor 46 1200 ohms. Resistor 48 47,000 ohms. Resistor 58 39,000 ohms. Resistor 59 12,000 ohms. Resistor 72 22,000 ohms. Resistor '74 4.7 megohms. Resistor 53 100,000 ohms. Resistors 76 and 78 values depend on type of glow lamp 60 and photoresistive device 54.

reactive signal.

FIG. 2 shows a second embodiment in which a key operated switch rather than the tone signals controls the operation of the neon tube control circuit. Components corresponding to those shown in FIG. 1 are assigned similar numbers.

Thus the tone signals are selected on operation of the playing keys and forwarded through a tube such as 30 to a photocell such as 54 and to a power amplifier 50, as explained for FIG. 1, and a second switch 90 is provided for each playing key. Actuation of a key operated switch 90 connects a positive three-volt potential to the junction of resistor 59 and a capacitor 66 whenever a playing key is operated to select a particular tone. This positive pulse is transmitted through capacitor 66 to the grid of triode 64 causing anode current to how through the glow lamp 60. The remainder of the percussion sequence is the same as previously described with respect to FIG. 1. That is, the tone signal is applied to a tube such as 30 and the output extended through a photocell such as 54 as disclosed in FIG. 1. In the case of FIG. 2, however, the resistor 58 together with capacitor 52 and diode 76 is omitted, but the glow lamp 60 operates to control the photocell as previously described.

While I have shown and described the preferred embodiments of my invention, it will be apparent that nu merous variations nad modifications thereof may be made without departing from the underlying principles of the invention. I therefore desire, by the following claims, to include within the scope of the invention all such variations and modifications by which substantially the results of my invention may be obtained through the use of substantially the same or equivalent means.

I claim:

1. In an electrical musical instrument having a source of musical tone signals, playing keys for controlling the source to select a desired tone signal, an output system including a speaker and a tone signal channel connecting the source to the output system on operation of any of said keys, a percussion circuit comprising a glow lamp adapted to emit light of one intensity and connected between said source and output system, circuit means effective upon actuation of one of the keys to alter the intensity of the light emitted by the glow lamp at a predetermined rate ad for thereafter automatically enabling said lamp to emit light of said one intensity, and a photoresistive element connected in the channel and controlled by the light emitted by the glow lamp for causing the intensity of the signals applied to the speaker to alter in correspondence with said rate and thereafter return to a condition corresponding to light of said one intensity.

2. The combination claimed in claim 1 together with circuit means energizing the glow lamp at a desired minimum value when the keys are not depressed.

3. In an electric organ having a source of musical tone signals, playing keys for controlling the source to select a desired tone signal, an output system including a speaker and a tone signal chanel connecting the source to the output system on operation of any of said keys, a percussion circuit comprising a glow lamp adapted to emit light of one intensity and connected between said source and output system, circuit means normally energizing the glow lamp at a low current value to provide light of one intensity, an amplifier for energizing the glow lamp, circuit; means effective upon actuation of one of the keys to control the gain of the amplifier and the in- 6 tensity of the light emitted by the glow lamp to change at a predetermined rate in a waveform corresponding to a desired percussion envelope, means for returning the light intensity of said glow lamp to said one intensity after a predetermined time interval, and a photoresistive element connected in the channel and controlled by the light intensity emitted by the glow lamp for causing the intensity of the signals applied to the speaker to correspond to, the desired percussion envelope whereby said signals are first caused to sound loudly and thereafter terminate.

4. In an electric organ of the type having a musical tone generator, key operated means for controlling the output of the generator, an electro-acoustic translating device and circuit means for applying the output of the generator to the translating device on operation of said key means, the combination with the circuit means of a percussion circuit comprising a source of light, a photoresistive device connected in said circuit means and having an electrical resistance characteristic which varies in accordance with the intensity of light applied thereto, an amplifier for energizing the source of light, means normally applying a cutoff bias potential to the amplifier, means including a resistor-capacitor network effective upon the actuation of at least certain of the keys for rapidly applying a high positive bias potential to the amplifier and for gradually returning the bias potential to cutoff to vary the intensity of the source of light in a predetermined desired waveform, the photoresistive device being controlled by the source for varying the amplitude of the tone signals in accordance with the said desired waveform.

5. A percussion circuit for use in an electrical organ wherein any one of a plurality of playing keys is operated for transmitting respective tone signals, the improvement comprising an amplifier circuit to which all of said tone signals are applied, a photoresistive element connected between the output of said amplifier and the input of a second amplifier, a light control means operated responsive to one of said transmitted tone signals for varying the intensity of light intercepted by said element at a predetermined rate and only in response to the operation of one of said playing keys whereby the resistance value of said photoresistive element is caused to vary at a predetermined rate for varying the amplitude of the tone signals applied through said element to said second amplifier.

6. In the arrangement claimed in claim 5 means for supplying a signal out of phase with said tone signals to said photoresistive element.

7. In the arrangement claimed in claim 5 means for controlling the intensity of said light to reach a predetermined value after a predetermined time period irrespective of the continued transmission of said one transmitted tone signal.

Markowitz June 27,1961 De Miranda et al Feb. 2, 1962

Claims (1)

1. 5. A PERCUSSION CIRCUIT FOR USE IN AN ELECTRICAL ORGAN WHEREIN ANY ONE OF A PLURALITY OF PLAYING KEYS IS OPERATED FOR TRANSMITTING RESPECTIVE TONE SIGNALS, THE IMPROVEMENT COMPRISING AN AMPLIFIER CIRCUIT TO WHICH ALL OF SAID TONE SIGNALS ARE APPLIED, A PHOTORESISTIVE ELEMENT CONNECTED BETWEEN THE OUTPUT OF SAID AMPLIFIER AND THE INPUT OF A SECOND AMPLIFIER, A LIGHT CONTROL MEANS OPERATED RESPONSIVE TO ONE OF SAID TRANSMITTED TONE SIGNALS FOR VARYING THE INTENSITY OF LIGHT INTERCEPTED BY SAID ELEMENT AT A PREDETERMINED RATE AND ONLY IN RESPONSE TO THE OPERATION OF ONE OF SAID PLAYING KEYS WHEREBY THE RESISTANCE VALUE OF SAID PHOTORESISTIVE ELEMENT IS CAUSED TO VARY AT A PREDETERMINED RATE FOR VARYING THE AMPLITUDE OF THE TONE SIGNALS APPLIED THROUGH SAID ELEMENT TO SAID SECOND AMPLIFIER.

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