JPS581792B2 - Denshigatsukino Kaihei Cairo - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an opening/closing circuit for an electronic musical instrument, and more particularly to a circuit that changes the waveform of a generated musical tone depending on the strength of a key touch.

Generally, the opening/closing circuit of an electronic musical instrument opens and closes a sound source signal produced by a sound source circuit in response to key presses, and at this time an envelope is added to the sound source signal.

Conventional opening/closing circuits use a discharge waveform via a capacitor and a resistor as this envelope. Using an appropriate method (for example, using a switch contact time difference, etc.), a voltage corresponding to the pressing speed of the key is obtained, and this is applied to the capacitor. Charge it to
An envelope waveform is added to the musical tone signal using the discharge of the capacitor.

In this circuit, the amplitude of the musical tone signal only changes according to the envelope, and although the volume corresponding to the amplitude changes depending on the pressing speed of the key, the waveform, that is, the tone does not change.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide an opening/closing circuit for an electronic musical instrument that changes the waveform of a musical tone signal depending on the strength of a key touch.

For this purpose, a key touch detection means detects a key touch during a key press operation and outputs a voltage having a value corresponding to the touch, and a first capacitor is charged by the voltage output from the key touch detection means. a second capacitor that is charged with the voltage output from the key touch detection means and stores and retains the voltage at least while the key is pressed; and a terminal of the first capacitor that is provided in parallel with the first capacitor; a third capacitor that is charged by a voltage; a gate that is provided in parallel with the third capacitor and repeatedly turns on and off in accordance with a musical tone signal to intermittently discharge the third capacitor; and the first capacitor. and the third capacitor, and controls the current charging the third capacitor according to the terminal voltage of the second capacitor to change the charging time constant of the third capacitor. A control circuit is provided, and musical tone signals having different waveforms are obtained from the terminal voltage of the third capacitor depending on the touch of the key.

Hereinafter, the present invention will be described in detail based on one embodiment of the accompanying drawings.

FIG. 1 shows an embodiment of an opening/closing circuit for an electronic musical instrument according to the present invention.

The switches SW1 and SW2 correspond to a key (not shown) and work in conjunction with each other, and when the key is not pressed, the switch SW1 is connected to the contact a side,
The capacitor C1 is charged to the voltage Va by the battery A.

When the key is pressed, the switch SW1 switches from contact a to contact b.

Capacitor C1 starts discharging via resistor R1 when switch SW1 separates contact a, so before switch SW1 switches to contact b, the voltage of capacitor C1 changes from voltage Va to contact time difference (from contact d to contact b). The voltage is discharged only during the time required to switch to the key press, that is, the voltage has a value corresponding to the key pressing speed.

Since this voltage is applied to the transistor Tri through the contact b and the diode D1, the transistor Tri
is turned on, and the power supply B instantaneously charges the capacitors C2 and C3 to a voltage corresponding to the key pressing speed.

When the key is released immediately, the switch SW1 is connected to the contact a side, and the capacitor C1 is instantly charged, while the switch SW2 is closed and the capacitor C3 is instantly discharged via the diode D3 and the low resistance R3. This is to prepare for the next key press operation, but if the key is kept pressed, the charge charged in the capacitor C3 is held by the diode D2, and is applied to the gate of the field effect transistor FET via the resistor R3, and is transferred to the gate of the field effect transistor FET. The base potential of the transistor Tr2 is determined by the voltage drop.

This controls the current flowing through the transistor Tr2.

On the other hand, the electric charge charged in the capacitor C2 is transferred to a path via a resistor R6, a transistor Tr2, a resistor R5, and a resistor R7.
The capacitor C4 is discharged through a path through which the capacitor C4 is charged.

A transistor Tr3 is provided in parallel with the capacitor C4, and an input terminal I is connected to the base of the transistor Tr3.
A square wave musical tone signal of a predetermined frequency selected by pressing a key from N is added.

This square wave musical tone signal is a negative pulse, and the transistor T
Since the emitter of r3 is at O level, when the level of the input square wave musical tone signal is low, the transistor Tr3
is turned on, the charge in the capacitor C4 is discharged, and the voltage at the output terminal OUT, which is the collector voltage of the transistor Tr3, is set to 0 level. When it is high, the transistor Tr3 is turned off, and the capacitor C4 is connected to the path including the transistor Tr2 and the resistance It is charged via a path via R7.

In this way, the square wave musical tone signal applied to the input terminal IN turns the transistor Tr3 on and off, causing the capacitor C4 to turn on and off.
By repeating charging and discharging, the charge in the capacitor C2 is discharged, and a signal with an envelope added according to the discharge characteristics of the capacitor C2 is obtained from the output terminal OUT.

Note that here, since the resistor R7 has a higher resistance than the resistors R5 and R6, the charging path of the capacitor C4 is mainly a circuit via the resistor R6, the transistor Tr2, and the resistor R5.

Since the current flowing into the capacitor C4 of the transistor Tr2 is controlled by the voltage of the capacitor C3 charged with a voltage corresponding to the key pressing speed as described above, the charging current of the capacitor C4 is set according to the key pressing speed. This causes a change in the fall time of the square waveform of the output signal.

In FIG. 2, a is the input square wave musical tone signal in the same embodiment, and b
, c is a graph showing an example of an output signal.

If the key is pressed with a weak touch, capacitor C3
The charging voltage sets the gate of the field effect transistor FET to a high voltage.

As a result, the current flowing through the transistor Tr2 is controlled to have a dog shape, so that the output waveform becomes close to a square wave as shown in b.

Furthermore, if the key is pressed with a strong touch, the charge in the capacitor C3 increases, the gate voltage of the field effect transistor FET is set low, and the current flowing through the transistor Tr2 is controlled to be small, so the output waveform is The waveform becomes distorted as shown in C.

Note that by changing the channel of the field effect transistor FET, it is possible to obtain a waveform that is distorted by a weak key touch and a waveform close to a square wave by a strong key touch.

Since the present invention has the above structure, it is possible to obtain a musical tone signal having a rectangular waveform with different fall times as an output signal depending on the strength of the touch of the key, and the tone color can be changed according to the strength of the touch of the key.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the opening/closing circuit of an electronic musical instrument according to the present invention, and FIG. 2 is a graph showing an example of an input signal and an output signal in the same embodiment as a function of time. C1-C4...Capacitor, R1-R7...
...Resistor, Tr1, Tr2, Tr3...Transistor, A, B...Power supply, D1, D2...
...Diode, FET...Field effect transistor.

Claims (1)

[Claims] 1. A key touch detection means that detects a key touch during a key press operation and outputs a voltage corresponding to the touch, a first capacitor that is charged by the voltage output from the key touch detection means, and a first capacitor that is charged by the voltage output from the key touch detection means; a second capacitor that is charged by the voltage output from the touch detection means and stores and retains the voltage at least while the key is pressed; and a second capacitor that is provided in parallel with the first capacitor and is charged by the terminal voltage of the first capacitor a third capacitor; a gate provided in parallel with the third capacitor and repeatedly turning on and off in accordance with a musical tone signal to intermittently discharge the third capacitor;
Provided between the first capacitor and the third capacitor, the current for charging the third capacitor is variably controlled according to the terminal voltage of the second capacitor, when charging the third capacitor. An opening/closing circuit for an electronic musical instrument, comprising a control circuit that changes a constant, and obtains musical tone signals having different waveforms from the terminal voltage of the third capacitor according to the touch of the key.