TOUCH-RESPONSIVE TONE ENVELOPE CONTROL CIRCUIT FOR ELECTRONIC MUSICAL INSTRUMENTS
United States Patent 3626074
In a keying system for an electronic musical instrument in which an individual keyer is adapted to be controlled in response to the intensity of depression of a corresponding playing key so that a keyed tone signal has an amplitude in accordance with the key depression intensity, a common DC supply means with a voltage selector is provided to additively control the keyer irresponsive to the key depression intensity. The voltage selector determines which one of said two controls should prevail. The system is simple in construction and operation and inexpensive and easy to manufacture as well as provides a variety of excellent tonal effects.
US Patent References:
Electronic piano having means responsive to the velocity of the action
Markowitz et al. - April 1966 - 3248470
Electronic organ keying device
Boenning - April 1967 - 3313877
CIRCUIT ARRANGEMENT FOR IMITATING THE TOUCH OF MUSICAL INSTRUMENTS WITH PERCUSSION
Disksterhuis - December 1970 - 3544695
Electronic piano having means responsive to the velocity of the action
Markowitz et al. - April 1966 - 3248470
Electronic organ keying device
Boenning - April 1967 - 3313877
CIRCUIT ARRANGEMENT FOR IMITATING THE TOUCH OF MUSICAL INSTRUMENTS WITH PERCUSSION
Disksterhuis - December 1970 - 3544695
Application Number:
05/046682
Publication Date:
12/07/1971
Filing Date:
06/16/1970
View Patent Images:
Export Citation:
Assignee:
Nippon Gakki Seizo Kabushiki Kaisha (Hamamatsu-shi, JA)
Primary Class:
Other Classes:
84/658, 984/319
International Classes:
G10H1/055; G10H1/00
Field of Search:
84/1.01,1.04,1.11,1.12,1.13,1.17,1.19,1.26,1.27
Primary Examiner:
Kozma, Thomas J.
Assistant Examiner:
Weldon U.
Claims:
I claim
1. In an electronic musical instrument having a plurality of keys, a touch-responsive keying system comprising:
2. A touch-responsive keying system according to claim 1, in which each of said charge storage elements is connected to a discharge element when its associated key is not fully depressed.
3. A touch-responsive keying system according to claim 1, in which said predetermined DC voltage is substantially equal to the touch-responsive DC voltage generated and stored by a weak key depression intensity.
4. A touch-responsive keying system according to claim 1, in which said predetermined DC voltage is substantially equal to the touch-responsive DC voltage generated and stored by a strong key depression intensity.
5. A touch-responsive keying system according to claim 1, in which there are provided two voltage supply means, one of which provides a predetermined DC voltage substantially equal to the touch-responsive DC voltage generated and stored by a weak key depression intensity and the other of which provides a predetermined DC voltage substantially equal to the touch-responsive DC voltage generated and stored by a strong key depression intensity, and means for selecting either one of said two predetermined DC voltages for connection to a respectively corresponding control terminal.
6. A touch-sensitive keying system for an electronic musical instrument comprising a plurality of individual key actuated circuits, each having:
7. A touch-sensitive keying system according to claim 6, in which said keyer circuit includes:
8. A touch-responsive keying system according to claim 7, in which said active elements are field effect transistors.
9. A touch-responsive keying system according to claim 6, in which said voltage supply means includes a voltage divider and a voltage selecting switch combined therewith.
10. A touch-responsive keying system according to claim 6 in which said voltage supply means includes a potentiometer to permit continuous preselection of a DC voltage to said control terminal.
1. In an electronic musical instrument having a plurality of keys, a touch-responsive keying system comprising:
2. A touch-responsive keying system according to claim 1, in which each of said charge storage elements is connected to a discharge element when its associated key is not fully depressed.
3. A touch-responsive keying system according to claim 1, in which said predetermined DC voltage is substantially equal to the touch-responsive DC voltage generated and stored by a weak key depression intensity.
4. A touch-responsive keying system according to claim 1, in which said predetermined DC voltage is substantially equal to the touch-responsive DC voltage generated and stored by a strong key depression intensity.
5. A touch-responsive keying system according to claim 1, in which there are provided two voltage supply means, one of which provides a predetermined DC voltage substantially equal to the touch-responsive DC voltage generated and stored by a weak key depression intensity and the other of which provides a predetermined DC voltage substantially equal to the touch-responsive DC voltage generated and stored by a strong key depression intensity, and means for selecting either one of said two predetermined DC voltages for connection to a respectively corresponding control terminal.
6. A touch-sensitive keying system for an electronic musical instrument comprising a plurality of individual key actuated circuits, each having:
7. A touch-sensitive keying system according to claim 6, in which said keyer circuit includes:
8. A touch-responsive keying system according to claim 7, in which said active elements are field effect transistors.
9. A touch-responsive keying system according to claim 6, in which said voltage supply means includes a voltage divider and a voltage selecting switch combined therewith.
10. A touch-responsive keying system according to claim 6 in which said voltage supply means includes a potentiometer to permit continuous preselection of a DC voltage to said control terminal.
Description:
The present invention relates to a touch-responsive tone envelope control circuit for electronic musical instruments, and more particularly, to a specific tone envelope control circuit which can improve the tone envelope effects in a key-operated electronic musical instrument such as an electronic organ to provide excellent effects of music being played.
It, therefore, is the principal object of the present invention to provide a tone envelope control circuit which is simple in construction, and easy and inexpensive to manufacture and which permits the electronic musical instrument incorporating the circuit to provide a variety of excellent tonal effects by making use of the effect that the tone envelope is subjected to the intensity of a playing key depression, called a "touch-responsive control effect."
According to the present invention, there is provided a combination of a plurality of keyer circuits and a circuit connected through a manual changeover switch and allowing the keyer circuits to provide a loud tone signal having a predetermined large amplitude regardless of the intensity of key depression while providing a soft tone signal having a predetermined small amplitude when the intensity of the key depression is very low, so that the player can easily provide various kinds of keying effects at will.
Other objects, features and advantages of the present invention will be apparent from the following detailed description taken in conjunction with the accompanying drawings in which,
FIG. 1 is a circuit diagram showing an embodiment of the present invention,
FIGS. 2 and 3 are partial circuit diagrams showing modifications of the essential portion of the embodiment of FIG. 1.
The same characters or references are hereafter used to indicate the same parts.
Reference is made in detail to a preferred embodiment of the present invention with reference to the accompanying drawings.
L designates a coil grounded at one end thereof and adapted to vary the interlinking fluxes in association with depression of an operating key arranged on a keyboard of an electronic musical instrument (e.g. the key carries a magnet thereunder), the other end of which is grounded through a series circuit of a rectifying element D and a capacitor C. A junction d between the element D and the capacitor C is connected to a movable contact SA o of a changeover switch SA of one-pole two-position type, which is actuated in association with the operation of the key K. The connection point d is also connected respectively through resistors R 1 and R 2 to the gates of field effect transistors Q 1 and Q 2 (hereunder referred to as FET's) between whose sources series connected resistors R 3 and R 4 are connected. The connection point r a of the resistors connects with the juncture r a1 of bleeder resistance elements R 5 and R 6 connected in series between a DC voltage +Vcc of a power source and ground. The juncture r a1 is also grounded via a capacitor C o .
The sources of the FET's Q 1 and Q 2 are adapted to receive through terminals t 1 and t 2 individual tone signals each having a predetermined frequency of different footage, produced by conventional tone generators of the electronic musical instrument (not shown), respectively. At the drains of the FET's Q 1 and Q 2 , load resistors R 7 and R 8 connected to the power voltage +Vcc at their one ends are connected at the other ends, respectively. At the connection points of the drains of the FET's Q 1 and Q 2 and the load resistors are provided respectively output terminals T 1 and T 2 which are adapted to develop the tone signals each having a required envelope (amplitude) and a different footage number applied to the input terminals t 1 and t 2 from the respective drains thereof by varying the gate potentials at the FET's Q 1 and Q 2 in association with the operation of the key. As a whole, the above-mentioned arrangements are shown as a key depressing speed detecting circuit S 1 and a keyer circuit S by two two-dot chain blocks in FIG. 1.
In the detecting circuit S 1 , one stationary contact SA 1 (normally closed) of the circuit changeover switch SA is grounded via a resistor R o , and the other stationary contact SA 2 (normally open) is connected through a unidirectional conducting element D o such as a diode to a movable contact SB o of one-pole three-position type changeover switch SB, which may be manually operated and is used in common to the whole keying circuit in the electronic musical instruments. One stationary contact SB 1 of the switch SB is grounded, while other stationary contacts SB 2 and SB 3 respectively are connected to r b and r c which are connection points between series-connected bleeder resistors R 9 , R 10 and R 11 connected between the power voltage +Vcc and ground. The movable contact SB o is connected to a common line l o , to which the indicated D o and all the other D o 's in other detecting circuits (not shown) are connected.
The keyer circuit S is so constructed that the gate-to-source potential of each FET's Q 1 and Q 2 is set through the resistors R 5 and R 6 at such a required value that when each of the gate potentials is at an earth potential, i.e., 0 volts, each of the FET's is caused to be nonconducting so that the drain-source impedance is rendered extremely high. The movable contact SA o of the changeover switch SA provided in the detecting circuit S 1 is arranged to contact the stationary contact SA 2 only when the key is depressed. The number of the detecting circuits S 1 and the keyer circuits S which are installed in the console of the electronic musical instrument corresponds in number to the playing keys, for example, 61. Now, it is to be noted that the changeover switch SB may be of one-pole two-position type in case either of SB 2 contact and SB 3 contact is not required in design.
Now, description will be made on the operation of the above-mentioned circuit arrangement.
At first, under a condition that the movable contact SB o of the circuit changeover switch SB is contacted by the contact SB 1 , when any one key K provided in the electronic musical instrument is depressed, a magnetic member attached to the key moves close to or away from a fixed coil L, thereby resulting in a damped pulse voltage approximately proportional to the intensity or speed of depression of a playing key due to a variation in interlinking fluxes established round the coil. The induced alternative voltage is rectified through the element D and as a result, a positive DC voltage developed at the element D is stored in the capacitor C. As soon as the charge stored on the capacitor C is applied respectively through the resistors R 1 and R 2 to the gates of the FET's Q 1 and Q 2 , the respective drain-source impedances are caused to be reduced in response to the gate input levels of the FET's, so that the individual tone signals applied to the sources of the FET's may be derived at the output terminals T 1 and T 2 provided at the drain side thereof. At this time, since the movable contact SA o is actuated in interlocked relation with the operation of the key K, namely, since the contact SA o is made in contact with the stationary contact SA 2 only during depression of the key as shown by a dotted line in FIG. 1, the positive charge stored on the capacitor C is blocked by a reversely connected diode D o to flow in the common line l o , thus, no discharge is caused, and hence, the charge is applied through resistors R 1 and R 2 to the gates of the FET's Q 1 and Q 2 , resulting in reduction of the source-drain impedance of each of the FET's in response to the intensity of key depression as mentioned above. As a result, the tone input signals separately applied to the respective sources of the FET's may be derived at the output terminals T 1 and T 2 which are on the drain side of the FET's separately. The envelope (amplitude) of the output tone signal varies in response to the intensity or speed of the key depression. That is, upon quick depression of key, the charge stored on the capacitor C provides a high potential, causing an output tone signal of a high level, while with slow depression of key, the output tone signal may be obtained at a low level. Thus, the present arrangement permits a tone envelope control which provides a so-called touch-responsive effect in an electronic musical instrument and which provides said effect resembling that of a piano.
In the case described above, if the playing key K is kept depressed, no further alternating voltage is induced in the coil L. However, since the input gate impedance of each of the FET's Q 1 and Q 2 is very high (for example, 10 9 ohms) the charge stored on the capacitor C immediately after depression of the key has no discharging path, and accordingly, it does not discharge for a long period of time, so that the FET's Q 1 and Q 2 are held in their conducting states during the depression of the key, at each of terminals T 1 and T 2 , continuously providing the output tone signal having a level responsive to the intensity of the key depression.
Upon release of the key being depressed, the key is made restored by its self-return action and simultaneously, the movable contact SA o of the changeover switch SA is also returned to be in contact with the contact SA 1 at the position as shown by a solid line in FIG. 1, so that the charge stored on the capacitor C discharges in a short period of time through the resistor R o having a relatively low resistance. Accordingly, the gate potential of each of the FET's Q 1 and Q 2 becomes the earth potential, i.e., 0 volts to render the FET's Q 1 and Q 2 to be in their nonconducting states, so that no output signal is developed at both terminals T 1 and T 2 .
Now, considering the case where the playing key K is quite slowly depressed, voltage induced in the coil L is too small, and as a result, there will occur the case where the gate of each of the FET's Q 1 and Q 2 cannot be at a positive voltage sufficient to be conductive between the source and the drain. Further, there is a possibility of producing no output even though the key is depressed depending upon the intensity of key depression, and hence, the player is required to be skillful in playing the instrument in order to produce desired soft tones without fail, resulting in nervous strain.
On the contrary, when the electronic musical instrument is played at a loud tone level the key K is always required to be quickly and strongly depressed, and a long play under such a condition results in the fatigue of the player. In the present invention, various attempts have been made to obviate these conventional defects. The bleeder resistors R 9 , R 10 and R 11 are arranged to divide the power voltage +Vcc at a predetermined ratio, and a positive voltage V 1 appearing at the connection point r b is set at substantially the same as the charged voltage across the capacitor C when the intensity of key depression is weak. That is, in case any one key is too slowly depressed under the state in which the movable contact SB o is in contact with the stationary contact SB 2 , the induced voltage in the coil L will be too small and the voltage V 1 will prevail to be applied to the capacitor C for charging it via the unidirectional conducting element D o and the movable contact SA o being in contact with the contact SA 2 by key depression. The voltage V 1 is also applied respectively through the resistors R 1 and R 2 to the respective gates of the FET's Q 1 and Q 2 . As a result, the source-drain impedance of each FET is lowered to some limited extent, so that input tone signals of different footage number which are separately applied to the respective sources thereof can surely be derived separately at the terminals T 1 and T 2 on the drain side thereof as output tone signals with low levels. That is, since the voltage V 1 at the connection point r b is set substantially the same as the storage voltage of the capacitor C upon weak key depression, even an extremely slow key depression permits soft tone to be produced with the help of the voltage V 1 . Therefore, the above arrangement facilitates the soft tone producing play as well as a long playing, and the nerve strain of the player is greatly reduced. In this case, release of the depressed key allows both the key and the changeover switch SA to return to their initial state, and allows the charge stored on the charged capacitor C to be discharged in a short period of time via the resistor R o , so that each FET is turned to its nonconducting state to shut off any output signals.
The bleeder resistors R 9 , R 10 and R 11 serve to divide the power voltage +Vcc at a predetermined ratio to provide a positive voltage V 2 at the connection point r c . The voltage V 2 is determined to be substantially the same as the charged voltage across the capacitor C upon key depression with a high intensity. Therefore, in case key depression is effected under the condition in which the movable contact SB o of the changeover switch SB is in contact with the stationary contact SB 3 , the voltage V 2 is always greater than the induced voltage in the coil L and is applied-- via the unidirectional conducting element D o and the movable contact SA o which, by key depression, is brought into contact with the contact SA 2 --to the capacitor C for charging it, and is also applied respectively via resistors R 1 and R 2 to the gates of the FET's Q 1 and Q 2 , so that the source-drain impedances thereof are extremely reduced to allow the output terminals T 1 and T 2 separately to derive desired output tone signals irrespective of the intensity of key depression.
This can be explained as follows. That is, since the voltage V 2 at the point r c is substantially the same as the charged voltage across the capacitor C when the intensity of key depression is high, loud tone-producing play on the electronic musical instruments can be performed independently of the intensity of key depression. For example, even if the player slowly depresses the key K, such loud tone-producing play becomes possible. The operational manner in the circuit upon release of the depressed key is the same as described above. This will be convenient, when the player wants to play the entire music loudly.
Further, as the manual changeover switch SB, a one-pole two-position type switch may be employed. Another embodiment using a switch of this type is shown in FIG. 2, in which a series circuit of a bleeder resistor R 9 , a potentiometer R 12 and a resistor R 11 is connected between the power voltage +Vcc and ground, the stationary contact SB 2 is connected to a movable contact r 12 of the potentiometer R 12 whereby the whole tone envelopes in soft or loud tone generating play by key depressing operation can be varied by changing the dividing voltage ratio by adjustment of the slidable contact r 12 . Further, if there is provided an arrangement that the common line l o is connected directly to a slidable contact r 13 of a potentiometer R 13 as shown in FIG. 3, the above-mentioned actions such as variations in tone levels or envelopes, etc. can be performed without using the changeover switch SB.
As the key depression speed detecting circuit S 1 , magneto-sensitive elements or pressure-sensitive elements may be used in place of the induction coil used here. Furthermore, the FET's used in the keyer circuit may be substituted by other switching elements such as transistors, diodes or vacuum tubes etc.
It, therefore, is the principal object of the present invention to provide a tone envelope control circuit which is simple in construction, and easy and inexpensive to manufacture and which permits the electronic musical instrument incorporating the circuit to provide a variety of excellent tonal effects by making use of the effect that the tone envelope is subjected to the intensity of a playing key depression, called a "touch-responsive control effect."
According to the present invention, there is provided a combination of a plurality of keyer circuits and a circuit connected through a manual changeover switch and allowing the keyer circuits to provide a loud tone signal having a predetermined large amplitude regardless of the intensity of key depression while providing a soft tone signal having a predetermined small amplitude when the intensity of the key depression is very low, so that the player can easily provide various kinds of keying effects at will.
Other objects, features and advantages of the present invention will be apparent from the following detailed description taken in conjunction with the accompanying drawings in which,
FIG. 1 is a circuit diagram showing an embodiment of the present invention,
FIGS. 2 and 3 are partial circuit diagrams showing modifications of the essential portion of the embodiment of FIG. 1.
The same characters or references are hereafter used to indicate the same parts.
Reference is made in detail to a preferred embodiment of the present invention with reference to the accompanying drawings.
L designates a coil grounded at one end thereof and adapted to vary the interlinking fluxes in association with depression of an operating key arranged on a keyboard of an electronic musical instrument (e.g. the key carries a magnet thereunder), the other end of which is grounded through a series circuit of a rectifying element D and a capacitor C. A junction d between the element D and the capacitor C is connected to a movable contact SA o of a changeover switch SA of one-pole two-position type, which is actuated in association with the operation of the key K. The connection point d is also connected respectively through resistors R 1 and R 2 to the gates of field effect transistors Q 1 and Q 2 (hereunder referred to as FET's) between whose sources series connected resistors R 3 and R 4 are connected. The connection point r a of the resistors connects with the juncture r a1 of bleeder resistance elements R 5 and R 6 connected in series between a DC voltage +Vcc of a power source and ground. The juncture r a1 is also grounded via a capacitor C o .
The sources of the FET's Q 1 and Q 2 are adapted to receive through terminals t 1 and t 2 individual tone signals each having a predetermined frequency of different footage, produced by conventional tone generators of the electronic musical instrument (not shown), respectively. At the drains of the FET's Q 1 and Q 2 , load resistors R 7 and R 8 connected to the power voltage +Vcc at their one ends are connected at the other ends, respectively. At the connection points of the drains of the FET's Q 1 and Q 2 and the load resistors are provided respectively output terminals T 1 and T 2 which are adapted to develop the tone signals each having a required envelope (amplitude) and a different footage number applied to the input terminals t 1 and t 2 from the respective drains thereof by varying the gate potentials at the FET's Q 1 and Q 2 in association with the operation of the key. As a whole, the above-mentioned arrangements are shown as a key depressing speed detecting circuit S 1 and a keyer circuit S by two two-dot chain blocks in FIG. 1.
In the detecting circuit S 1 , one stationary contact SA 1 (normally closed) of the circuit changeover switch SA is grounded via a resistor R o , and the other stationary contact SA 2 (normally open) is connected through a unidirectional conducting element D o such as a diode to a movable contact SB o of one-pole three-position type changeover switch SB, which may be manually operated and is used in common to the whole keying circuit in the electronic musical instruments. One stationary contact SB 1 of the switch SB is grounded, while other stationary contacts SB 2 and SB 3 respectively are connected to r b and r c which are connection points between series-connected bleeder resistors R 9 , R 10 and R 11 connected between the power voltage +Vcc and ground. The movable contact SB o is connected to a common line l o , to which the indicated D o and all the other D o 's in other detecting circuits (not shown) are connected.
The keyer circuit S is so constructed that the gate-to-source potential of each FET's Q 1 and Q 2 is set through the resistors R 5 and R 6 at such a required value that when each of the gate potentials is at an earth potential, i.e., 0 volts, each of the FET's is caused to be nonconducting so that the drain-source impedance is rendered extremely high. The movable contact SA o of the changeover switch SA provided in the detecting circuit S 1 is arranged to contact the stationary contact SA 2 only when the key is depressed. The number of the detecting circuits S 1 and the keyer circuits S which are installed in the console of the electronic musical instrument corresponds in number to the playing keys, for example, 61. Now, it is to be noted that the changeover switch SB may be of one-pole two-position type in case either of SB 2 contact and SB 3 contact is not required in design.
Now, description will be made on the operation of the above-mentioned circuit arrangement.
At first, under a condition that the movable contact SB o of the circuit changeover switch SB is contacted by the contact SB 1 , when any one key K provided in the electronic musical instrument is depressed, a magnetic member attached to the key moves close to or away from a fixed coil L, thereby resulting in a damped pulse voltage approximately proportional to the intensity or speed of depression of a playing key due to a variation in interlinking fluxes established round the coil. The induced alternative voltage is rectified through the element D and as a result, a positive DC voltage developed at the element D is stored in the capacitor C. As soon as the charge stored on the capacitor C is applied respectively through the resistors R 1 and R 2 to the gates of the FET's Q 1 and Q 2 , the respective drain-source impedances are caused to be reduced in response to the gate input levels of the FET's, so that the individual tone signals applied to the sources of the FET's may be derived at the output terminals T 1 and T 2 provided at the drain side thereof. At this time, since the movable contact SA o is actuated in interlocked relation with the operation of the key K, namely, since the contact SA o is made in contact with the stationary contact SA 2 only during depression of the key as shown by a dotted line in FIG. 1, the positive charge stored on the capacitor C is blocked by a reversely connected diode D o to flow in the common line l o , thus, no discharge is caused, and hence, the charge is applied through resistors R 1 and R 2 to the gates of the FET's Q 1 and Q 2 , resulting in reduction of the source-drain impedance of each of the FET's in response to the intensity of key depression as mentioned above. As a result, the tone input signals separately applied to the respective sources of the FET's may be derived at the output terminals T 1 and T 2 which are on the drain side of the FET's separately. The envelope (amplitude) of the output tone signal varies in response to the intensity or speed of the key depression. That is, upon quick depression of key, the charge stored on the capacitor C provides a high potential, causing an output tone signal of a high level, while with slow depression of key, the output tone signal may be obtained at a low level. Thus, the present arrangement permits a tone envelope control which provides a so-called touch-responsive effect in an electronic musical instrument and which provides said effect resembling that of a piano.
In the case described above, if the playing key K is kept depressed, no further alternating voltage is induced in the coil L. However, since the input gate impedance of each of the FET's Q 1 and Q 2 is very high (for example, 10 9 ohms) the charge stored on the capacitor C immediately after depression of the key has no discharging path, and accordingly, it does not discharge for a long period of time, so that the FET's Q 1 and Q 2 are held in their conducting states during the depression of the key, at each of terminals T 1 and T 2 , continuously providing the output tone signal having a level responsive to the intensity of the key depression.
Upon release of the key being depressed, the key is made restored by its self-return action and simultaneously, the movable contact SA o of the changeover switch SA is also returned to be in contact with the contact SA 1 at the position as shown by a solid line in FIG. 1, so that the charge stored on the capacitor C discharges in a short period of time through the resistor R o having a relatively low resistance. Accordingly, the gate potential of each of the FET's Q 1 and Q 2 becomes the earth potential, i.e., 0 volts to render the FET's Q 1 and Q 2 to be in their nonconducting states, so that no output signal is developed at both terminals T 1 and T 2 .
Now, considering the case where the playing key K is quite slowly depressed, voltage induced in the coil L is too small, and as a result, there will occur the case where the gate of each of the FET's Q 1 and Q 2 cannot be at a positive voltage sufficient to be conductive between the source and the drain. Further, there is a possibility of producing no output even though the key is depressed depending upon the intensity of key depression, and hence, the player is required to be skillful in playing the instrument in order to produce desired soft tones without fail, resulting in nervous strain.
On the contrary, when the electronic musical instrument is played at a loud tone level the key K is always required to be quickly and strongly depressed, and a long play under such a condition results in the fatigue of the player. In the present invention, various attempts have been made to obviate these conventional defects. The bleeder resistors R 9 , R 10 and R 11 are arranged to divide the power voltage +Vcc at a predetermined ratio, and a positive voltage V 1 appearing at the connection point r b is set at substantially the same as the charged voltage across the capacitor C when the intensity of key depression is weak. That is, in case any one key is too slowly depressed under the state in which the movable contact SB o is in contact with the stationary contact SB 2 , the induced voltage in the coil L will be too small and the voltage V 1 will prevail to be applied to the capacitor C for charging it via the unidirectional conducting element D o and the movable contact SA o being in contact with the contact SA 2 by key depression. The voltage V 1 is also applied respectively through the resistors R 1 and R 2 to the respective gates of the FET's Q 1 and Q 2 . As a result, the source-drain impedance of each FET is lowered to some limited extent, so that input tone signals of different footage number which are separately applied to the respective sources thereof can surely be derived separately at the terminals T 1 and T 2 on the drain side thereof as output tone signals with low levels. That is, since the voltage V 1 at the connection point r b is set substantially the same as the storage voltage of the capacitor C upon weak key depression, even an extremely slow key depression permits soft tone to be produced with the help of the voltage V 1 . Therefore, the above arrangement facilitates the soft tone producing play as well as a long playing, and the nerve strain of the player is greatly reduced. In this case, release of the depressed key allows both the key and the changeover switch SA to return to their initial state, and allows the charge stored on the charged capacitor C to be discharged in a short period of time via the resistor R o , so that each FET is turned to its nonconducting state to shut off any output signals.
The bleeder resistors R 9 , R 10 and R 11 serve to divide the power voltage +Vcc at a predetermined ratio to provide a positive voltage V 2 at the connection point r c . The voltage V 2 is determined to be substantially the same as the charged voltage across the capacitor C upon key depression with a high intensity. Therefore, in case key depression is effected under the condition in which the movable contact SB o of the changeover switch SB is in contact with the stationary contact SB 3 , the voltage V 2 is always greater than the induced voltage in the coil L and is applied-- via the unidirectional conducting element D o and the movable contact SA o which, by key depression, is brought into contact with the contact SA 2 --to the capacitor C for charging it, and is also applied respectively via resistors R 1 and R 2 to the gates of the FET's Q 1 and Q 2 , so that the source-drain impedances thereof are extremely reduced to allow the output terminals T 1 and T 2 separately to derive desired output tone signals irrespective of the intensity of key depression.
This can be explained as follows. That is, since the voltage V 2 at the point r c is substantially the same as the charged voltage across the capacitor C when the intensity of key depression is high, loud tone-producing play on the electronic musical instruments can be performed independently of the intensity of key depression. For example, even if the player slowly depresses the key K, such loud tone-producing play becomes possible. The operational manner in the circuit upon release of the depressed key is the same as described above. This will be convenient, when the player wants to play the entire music loudly.
Further, as the manual changeover switch SB, a one-pole two-position type switch may be employed. Another embodiment using a switch of this type is shown in FIG. 2, in which a series circuit of a bleeder resistor R 9 , a potentiometer R 12 and a resistor R 11 is connected between the power voltage +Vcc and ground, the stationary contact SB 2 is connected to a movable contact r 12 of the potentiometer R 12 whereby the whole tone envelopes in soft or loud tone generating play by key depressing operation can be varied by changing the dividing voltage ratio by adjustment of the slidable contact r 12 . Further, if there is provided an arrangement that the common line l o is connected directly to a slidable contact r 13 of a potentiometer R 13 as shown in FIG. 3, the above-mentioned actions such as variations in tone levels or envelopes, etc. can be performed without using the changeover switch SB.
As the key depression speed detecting circuit S 1 , magneto-sensitive elements or pressure-sensitive elements may be used in place of the induction coil used here. Furthermore, the FET's used in the keyer circuit may be substituted by other switching elements such as transistors, diodes or vacuum tubes etc.