Title:
TOUCH-RESPONSIVE KEYING CIRCUIT FOR ELECTRONIC MUSICAL INSTRUMENTS
United States Patent 3784718


Abstract:
In an electronic musical instrument, tone keyer circuits are respectively controlled by touch-responsive keying circuits. The touch-responsive keying circuit comprises: a key switch having a break contact, a make contact and a movable contact; a first charge-discharge circuit having a charging capacitor and a discharging resistor both connected between the movable contact and the ground; an electrical source +B connected to the break contact; a switching transistor with its base connected to the make contact; and a second charge-discharge circuit being provided between the emitter of the transistor and the ground with a second capacitor and with a series circuit of a second resistor and an normally closed switch which is ganged with the key switch, the capacitor being connected to the keyer circuit. While the movable contact of the key switch travels from the break contact to the make contact, the first charge-discharge circuit is discharged with a predetermined time constant. The switching transistor is brought conductive to the extent responsive to a charged voltage remaining in the first charge-discharge circuit at the time the movable contact touches the make contact. The second charge-discharge circuit is charged through the transistor to establish a keying voltage.



Inventors:
UCHIYAMA Y
Application Number:
05/273608
Publication Date:
01/08/1974
Filing Date:
07/20/1972
Assignee:
NIPPON GAKKI SEIZO KK,JA
Primary Class:
Other Classes:
84/720, 84/DIG.23, 984/322
International Classes:
G10H1/00; G10H1/02; G10H1/34; H03B11/00; G10H; (IPC1-7): G10H1/02
Field of Search:
84/1
View Patent Images:



Primary Examiner:
Wilkinson, Richard B.
Assistant Examiner:
Witkowski, Stanley J.
Attorney, Agent or Firm:
John, Holman Et Al C.
Claims:
I claim

1. A touch-responsive keying circuit comprising: a circuit ground; a power source; a key switch having a break contact connected to said power source, a make contact and a movable contact; a first charge-discharge circuit having a charging capacitor and a discharging resistor both connected between said movable contact and said ground; a transistor having a base connected to said make contact, a collector connected to said power source, and an emitter; and a second charge-discharge circuit including a second capacitor connected between said emitter and said ground, a second resistor and a second switch connected in series between said emitter and said ground, said second switch being of a normally closed type and gang-operated with said key switch.

2. A touch-responsive keying circuit as claimed in claim 1, in which said first charge-discharge circuit is provided with means for applying across said charging capacitor a divided voltage of said power source, whereby when the first charge-discharge circuit is discharged, the resultant voltage of the first charge and discharge circuit is maintained not lower than said divided voltage.

3. A touch-responsive keying circuit as claimed in claim 1 which further comprises a change-over switch having a first stationary contact connected to said charge-discharge circuit, a second stationary switching contact connected to the break contact of said key switch, and a movable contact connected to said power source.

4. A touch-responsive keying circuit as claimed in claim 3 in which a movable contact of said change-over switch is connected to a separately provided adjustable power source.

5. A touch-responsive keying circuit as claimed in claim 3, in which a plurality of touch-responsive keying circuits are provided, and one common change-over switch is provided for these touch-responsive keying circuits.

Description:
BACKGROUND OF THE INVENTION

The present invention relates generally to electronic musical instruments and more particularly to a touch-responsive keying circuit to be used in electronic musical instruments.

Conventional touch-responsive keying circuits for electronic musical instruments have been of a type as shown in FIG. 1 which comprises a key switch 1 having stationary contacts b and m and a movable contact c. The movable contact c is connected to a first charge-discharge circuit 2 consisting of a charging capacitor C1 and a discharging resistor R1, and the break stationary contact b is connected to a D. C. source 3. The make stationary contact m is connected through a reverse-current-blocking diode 4 to a second charge-discharge circuit 5 consisting of a charging capacitor C2 and a discharging resistor R2. An output W for keying a keyer circuit 6 is obtained across the second charge-discharge circuit 5.

In this conventional touch-responsive keying circuit 7, as long as a key (not shown) is not depressed, the contact c is maintained connected to the contact b, and therefore the capacitor C1 is charged through these contacts by the D.C. source 3. Under this condition, if the contact c is separated from the contact b at an instant t1 and is brought into contact with the contact m at a subsequent instant t2 by depressing a key, as shown in FIG. 2, the capacitor C1 will be discharged through the resistor R1 during the period of this travelling time (from t1 to t2).

In this connection, the discharge quantity in the case of a short travelling period is les than that in the case of a long travelling period. Therefore, the voltage of the capacitor C2, or the output keying voltage W in the case of the short travelling period (curve I) is greater in peak value than that in the case of the long travelling period (curves II and III). Accordingly, it will be apparent that if the key-depressing speed is controlled as desired during the playing of an electronic musical instrument, acoustic volume of the electronic musical instrument can be controlled in response to the key-depressing speed.

However, in such a circuit arrangement as described above, when the movable contact c of the switch is moved into contact with the contact m, the electrical current thereby flowing through the contacts c and m and the diode 4 is relatively large and, therefore, may damage the contacts of the switch 1. The damage to the contacts would be serious if the travelling time of the contacts of the switch 1 were extremely short, as the remaining voltage is high.

Furthermore, it is generally necessary for reasons of performance effect to select the time constants (C1 R1 <C2 R2) of the charge-discharge circuits so that the time period h1 (FIG. 2) from an instant t1 when the contact c of the switch 1 separates from the contact b as a result of a key-depressing operation, to an instant t2 when the contact c comes into contact with the contact m during the same operation, is of the order of from 5-10 ms to 30 ms, and so that the time period h2 from the instant t2 when the contact c comes into contact with the contact m to an instant t 3 when the contact c separates from the contact m upon release of the key is of the order of 1.5s.

Therefore, it is necessary to select capacitors having considerably large value capacitances for these charge-discharge circuits. In addition, if the time period h1 of switching the key switch 1 is made extremely long, all of the charge in the capacitor C1 will be discharged through the resistor R1, as a result of which no output will be produced.

SUMMARY OF THE INVENTION

It is accordingly a primary object of the present invention to provide a touch-responsive keying circuit for an electronic musical instrument, in which capacitors of small capacitances can to used in charge-discharge circuits, whereby the contacts having a key switch are protected against damage by an electrical current, the above-described difficulties accompany the conventional touch-responsive keying circuit being taken into consideration.

Another object of the present invention is to provide a touch-responsive keying circuit for an electronic musical instrument, in which its output can be obtained even when the travelling time of the key switch is made longer by a soft keying operation.

A further object of the present invention is to provide a touch-responsive keying circuit for an electronic musical instrument which can ensure the production of a keying output correctly responsive to a key-depressing speed, with the output level substantially sustained during the key depression.

A still further object of the present invention is to provide a touch responsive keying circuit for an electronic musical instrument in which either a touch-responsive keying voltage of a level dependent on a key-depressing speed or a touch-irresponsive keying voltage of a level independent of the key-depressing speed can be selectively applied to the tone keyer circuit.

A specific object of the present invention is to provide a touch-responsive keying circuit for an electronic musical instrument in which, when a key is depressed very slowly, an output can be obtained even if a first charge and discharge circuit has been discharged, whereby a pianissimo performance effect can be easily and stably rendered as desired.

The foregoing objects and other objects of the present invention will become more apparent from the following detailed description and the appended claims when read in conjunction with the accompanying drawings, in which like parts are designated by like reference numerals and characters.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is an electrical connection diagram showing a conventional touch-responsive keying circuit together with a tone keyer circuit;

FIG. 2 is a chart showing waveforms of the keying voltages for a description of the operation of the circuit shown in FIG. 1;

FIG. 3 is an electrical connection diagram showing one example of a touch-responsive keying circuit according to the present invention together with a tone keyer circuit;

FIGS. 4 and 5 are waveform charts for a description of the operation of the circuit shown in FIG. 3;

FIG. 6 is an equivalent circuit diagram of an essential part of the circuit shown in FIG. 3; and

FIG. 7 is an electrical connection diagram showing another example of the present invention together with a tone keyer circuit.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

With reference now to FIG. 3, the example of the present invention shown therein comprises a touch-responsive keying circuit 11 and a tone keyer circuit 12 whose gating operation is controlled by an output W of the touch-responsive keying circuit 11. The tone keyer circuit 12 itself is a circuit well known in the art and comprises: a transistor 13 for receiving the output W of the touch-responsive keying circuit 11; a transistor 15 for receiving a musical tone signal I which is applied to a musical tone signal input terminal 14; and a transistor 16 for amplifying a gated output produced by the transistors 13 and 15, whereby an output musical tone signal whose envelope is defined by the waveform of the output W from the touch-responsive keying circuit 11 is produced at an output terminal 17 of the keyer circuit 12.

While only one combination of transistors 13, 15 and 16 for one musical tone signal I is illustrated in FIG. 3, this example includes, in practice, other combinations of the same transistors for other musical tone signals in addition to the musical tone signal I. The existence of such other combinations is indicated by the representation 18 in FIG. 3.

The movable contact c of a key switch 21 in the touch-responsive keying circuit 11 is connected through a resistor R7 to a first charge-discharge circuit 22 which comprises a charging capacitor C3 and a discharging resistor R3, and one end of the circuit 22 is connected to ground line E. Furthermore, a break contact b of the key switch 21 is connected to a power source +B (12V), and a make contact m is connected to the base of a switching transistor 23. The collector of the transistor 23 is connected to the power source +B. The emitter of the transistor 23 is connected to a charging capacitor C4 through a charging resistor R4. One terminal of the capacitor C4 is grounded, while the other terminal thereof is also grounded through the resistor R4, a discharging resistor R5 and contacts b and c of a switch 27, which is of a normally closed type and gang-operated with the key switch 21. Thus, a second charge-discharge circuit 28 is formed with the capacitor C4 and the resistors R4 and R5.

The other end of the first charge-discharge circuit 22 is connected through a resistor R6 to the power source +B. The resistor R7 is a limiting resistor which serves to limit an electric current charging the capacitor C3.

In the circuit described above, as long as an associated key is not depressed the contacts c of the key switches 21 and 27 are in contact with their respective break contacts b, and the capacitor C3 is charged through the contacts b and c of the switch 21 and the resistor R7 by the power source +B. In this case, if the resistances of the resistors R3, R6 and R7 are predetermined so that they have the relationships of R6 >> R7 and R3 >> R7, a voltage charged in the capacitor will become substantially equal to the voltage (12V) of the power source +B. At the same time, the capacitor C4 is discharged through the contacts b and c of the switch 27 and the resistors R4 and R5. Therefore, the transistor 23 is in the "off" state and no output W is produced from the circuit 11. Therefore, the keyer circuit 12 is non-conductive and no tone signal output appears at the terminal 17.

Under this condition, when the contacts c of the switches 21 and 27 are separated from their respective break contacts b at an instant t1 by a keying operation, the capacitor C3 begins to discharge through the resistor R3. As a result, a voltage VC3 across the capacitor C3 decreases from about 12V with the elapse of time and with a time constant T1 which is determined by the values of the capacitor C3 and resistor R3, as is indicated in FIG. 4.

Then, under such conditions of the circuit as a decrease in the voltage of the capacitor C3, if the contact c of the switch 21 is brought into contact with the make contact m thereof by a quick keying operation at the instant t2, a relatively high voltage V1 remaining in the capacitor C3 will be applied to the base of the transistor 23 through the contacts c and m of the switch 21, but if the contact c of the switch 21 is brought into contact with the contact m thereof at another instant t3 later than the instant t2 by a slow keying operation, a voltage V2 lower than the voltage V1 will be applied to the transitor 23.

Moreover, if the contact c of the switch 21 is brought into contact with the contact m thereof at another instant t4 much later than instant t3 by a very slow keying operation, the capacitor C3 would have long been being discharged during the time period taken by the considerably slow keying operation. However, since a divided voltage which is determined by the resistor R3 and R6 is applied across the capacitor C3, the voltage of the capacitor C3 will be discharged toward that voltage, and consequently the resultant voltage of the capacitor C3 will never be lower than that divided voltage.

This will be apparent from the following consideration. As is shown in FIG. 6, the charge-discharge circuit 22 has a D.C. power source Ve, the voltage of which is equal to Vc = [R3 /(R3 +R6)] × 12V, that is, a voltage across the resistor R3. The DC power source Ve is connected in series to an equivalent resistance r which is composed of a parallel combination of the resistors R3 and R6, thereby forming a series circuit of r and Ve. This series circuit is equivalent to an arrangement of parallel connection with the capacitor C3.

Accordingly, if the instant t4 is very much later, the capacitor C3 is discharged until the voltage thereacross becomes equal to the voltage Ve, whereupon the capacitor C3 ceases and maintains the voltage Vc.

Thus, when the voltage V1, V2, or Vc is applied to the transistor 23, the transistor 23 becomes "on" or conductive at the instant t2, t3, or t4, respectively to the extent represented by the voltage V1, V2 or Vc. As a result, the capacitor C4 is charged, through the transistor 23, thus made conductive, to a voltage which is lower than the voltage V1, V2 or Vc by a base-emitter drop voltage VBE, and the voltage of the capacitor C4 thus obtained is applied, as an output W of the touch-responsive keying circuit 11, to the keyer circuit 12. In this connection, because the voltage Vc is substantially maintained by the capacitor C4 , the output W of a peak value which corresponds to the voltage Vc is obtained for even a long time period after the instant t1.

As long as the key is depressed and the movable contact c of the switch 27 is kept in contact with the make contact m, the output W is kept substantially constant, discharging very slightly through the transistor 23 only.

If, under these conditions where a touch-responsive output W is thus produced by the circuit 11, the contacts c of the switches 21 and 27 are returned into contact with the contacts b thereof, respectively, by releasing the key, application of the charged voltage of the capacitor C3 to the transistor 23 stops. At the same time the capacitor C3 is charged through the resistors R6 and R7 by the power source +B, while the capacitor C4 is discharged through the resistors R4 and R5 and the switch 27. As a result, the output W of the circuit 11 is no longer produced, and the circuit 11 is restored to its original state in which no key is depressed. Consequently, the tone signal is not emitted from the terminal 17.

Thus, one cycle of the operation of the circuit 11 caused by depressing a key is accomplished. In this one cycle of operation, waveforms of the outputs W of the circuit are as shown in FIG. 5. The waveforms W1, W2 and W3 rise with a time constant determined mainly by the capacitance of the capacitor C4 and the resistance value of the resistor R4 at instants t2, t3, and t4, respectively, and, furthermore, undergo decay at an instant t5 with a time constant determined mainly by the capacitance of the capacitor C4 and the resistances of the resistors R4 and R5. The peak values of these waveforms correspond to the time periods required for switching the key switches 21 and 27, that is, the speeds of the key-depressing operations.

Another example of the present invention as illustrated in FIG. 7 has a touch-responsive keying circuit 11 further comprising a change-over switch 25 provided with switching contacts j and k . The contact j is connected to the contact b of a key switch 21, while the contact k is connected to the contact c of the key switch 21 through a resistor 26 and a diode 27 as required. Furthermore, a movable contact l is connected to a power source +B. The diode 27 serves to block a reverse current in the case when a plurality of touch-responsive keying circuits are switched over by using one common change-over switch 25. The other components and their arrangements are the same as those described with reference to FIG. 3.

In the circuit described above, a touch-responsive output of the circuit 11 can be obtained by connecting the movable contact l to the contact j. The other general operations of the circuit are the same as those described with reference to FIG. 3.

When a touch-irresponsive output is to be produced from the circuit 11, the movable contact l is moved into contact with the contact k. Under this condition, when the contacts c of the switches 21 and 27 are brought into contact with their respective contacts m by a keying operation, i.e., by a depressing the key, predetermined voltage is applied to the base of the transistor 23 by the power source +B through the movable contact l, the contact k, the resistor 26, the diode 27 and the contacts c and m of the switch 21.

As a result, the capacitor C4 is charged to a voltage corresponding to the predetermined voltage, and the voltage of the capacitor C4 thus obtained becomes a touch-irresponsive output W of the circuit. In this connection, the predetermined voltage is determined by the resistors 26, R7 and R3, diode 27, and power source +B.

Thus, the keyer circuit 12 produces a musical tone signal having an envelope of a certain level keyed by the constant output W. This operation of the circuit 12 is the same as the ordinary operation of a conventional tone keyer circuit, having no touch-responsive circuit, of an electronic musical instrument.

As is described above, according to the present invention, both the touch-responsive output which causes the keyer circuit to produce a musical tone signal having an envelope of a level determined by the keying speed and the touch-irresponsive output which causes the keyer circuit to produce a musical tone signal having an envelope of a predetermined level regardless of the keying speed can be selectively obtained immediately by merely changing-over the switch 25 without troublesome operations.

In addition, even in the case when the keying operation is conducted quickly or slowly as desired in order to obtain the touch-responsive output, the touch-responsive output can be obtained. For this purpose, since the rising time and decay time of the touch-responsive output are caused to be of a small value of the order of 50ms, the values of the capacitors of the charge-discharge circuits can be made considerably small.

Furthermore, while an example wherein the movable contact l of the change-over switch 25 is connected to a common and fixed power source +B has been described above, it is also possible to connect the movable contact l to a voltage adjustable power source provided separately such as shown by dotted lines in FIG. 7 and then to selectively set the level of the touch-responsive output W or the level of the touch-irresponsive output W by adjusting the voltage of the adjustable power source.

Only one touch-responsive keying circuit 11 is shown in the accompanying drawings, but in practice a plurality of touch-responsive keying circuits are provided. In this case, one changeover switch 25 may be provided in common for those plurality of touch-responsive keying circuits, so that the contacts j and k of the switch 25 are connected to the contact b of the switch 21 and the resistor 26 in each touch-responsive keying circuit.