JPS5921428Y2 - Modulation signal generation circuit for delay vibrato - Google Patents

Description

[Detailed description of the invention] The present invention provides a delay vibrato circuit that adds a vibrato effect to a musical sound signal output to a subsequent circuit in response to a key depression operation of an electronic musical instrument after a certain period of time after a key depression operation. The present invention relates to a modulation signal generation circuit for frequency modulating musical tone signals.

This modulation signal generation circuit usually connects the collector and base of the transistor (or the drain in the case of a field effect transistor).
A positive feedback circuit consisting of a multi-stage C-R phase shift circuit is connected between the gates), and a switch element is inserted and connected in series with the positive feedback circuit, and the switch element By closing the circuit, a modulation signal for delay vibrato was output.

However, in the above modulation signal generation circuit, when the switch element is opened for a short time from the oscillation state, oscillation temporarily stops, and then oscillation starts, the voltage between the terminals of each capacitor constituting the phase shift circuit becomes transient. oscillation starts smoothly, but if the switch element is open for a long time, or even if the switch element is opened for a short time, it may be opened repeatedly within a certain period of time. In this case, the voltage between the terminals of each of the capacitors will settle down to a constant voltage, and oscillation will not start smoothly even if the switch element is closed.

That is, in the conventional modulation signal generating circuit described above, large variations occur from the time when the switch element is closed to the time when oscillation starts, which is a major drawback in performance.

In view of the above-mentioned drawbacks of the conventional art, the present invention seeks to provide a modulation signal generation circuit for delay vibrato in which oscillation starts smoothly when the switch element is closed.

An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, 1 is an NPN type transistor,
Its collector is connected to a power supply (G) through a resistor 2, and its emitter is grounded through a parallel circuit of a resistor 3 and a capacitor 4.

Further, the collector of the transistor 1 is connected to the base via capacitors 5 to 7, a field effect transistor 8 operating as a switching element, and a resistor 9 in series.

10.11 is a resistor connected between both terminals of the capacitor 6 and the power supply (G)■, and 12 is a resistor connected between the common connection point of the field effect transistor 8 and the capacitor 5 and the power supply (1)■. be.

Reference numerals 13 and 14 denote bias resistors connected between the common connection point of the capacitor 7 and the resistor 9, the power supply (g), and the ground, respectively.

The capacitors 5 to 7 and the resistors 9 to 12 constitute a positive feedback circuit, and this positive feedback circuit and the transistor 1 constitute a phase shift oscillation circuit.

Reference numeral 15 denotes an NPN type transistor, the collector of which is connected to the power supply (1), the base of which is connected to the collector of the transistor 1, and the emitter of which is grounded via a resistor 16 and connected to a modulation signal output terminal 17. There is.

18 is a PNP type transistor, its emitter is connected to the power supply (→■) via a capacitor 19, and its base is connected to a resistor 2.
0 to the power supply (+)V, and the collector is grounded.

Reference numeral 21 denotes an input terminal for a trigger signal generated in synchronization with a key press operation, and is connected to the base of the transistor 18.

Further, the emitter of the L transistor 18 is connected to the power supply (+)V through a resistor 22 and then through a parallel circuit of a variable resistor 23 and a potentiometer 24.

A movable terminal of this potentiometer 24 is connected to the gate of the field effect transistor 8.

This transistor 18. Capacitor 19. Resistance 22. The variable resistor 23 and potentiometer 24 constitute a delay signal generation circuit.

25 is always the oscillation frequency of the phase-shifted oscillation circuit (usually about 7
(b) An excitation signal generating circuit which supplies a signal at a higher frequency (for example 220 Hz) and a lower voltage level, and is connected to the common connection point between the capacitor 6 and the field effect transistor 8.

This excitation signal generation circuit 25 is actually derived from the sound source (220H2) of A3, which is one of the sound sources of the electronic musical instrument, via an attenuation resistor.

Next, the operation of the above configuration will be explained with reference to FIG.

When the key is not pressed, the trigger signal input terminal 21
There is no signal present at , and the field effect transistor 8 is in a conductive state.

Therefore, a vibrato modulation signal of approximately 7 Hz is output from the collector of transistor 1.

This modulation signal is output from the modulation signal output terminal 17 via the transistor 15 to a vibrato-1 modulation circuit (not shown), but no musical tone is generated since no musical tone signal is supplied to this vibrato modulation circuit.

Now, if the key is pressed, trigger signal input terminal 2
1 is supplied with a negative trigger signal shown in FIG. 2A,
Transistor 18 is made conductive for a certain period of time.

This trigger signal may be generated by providing a switch linked to each key, or may be generated by shaping a musical tone signal outputted via a key switch.

Due to the conduction of this transistor 18, a capacitor 19. is connected to the gate of the field effect transistor 8. A signal having an envelope waveform determined by a resistor 22, a variable resistor 23, and a potentiometer 24 as shown in FIG. 2B is supplied.

Thus, the field effect transistor 8 changes from time t1 to t2.
During this period, the oscillation operation of the phase shift oscillation circuit is stopped, and after time t2, the circuit becomes conductive again.

Due to this conduction of the field effect transistor 8, a high frequency excitation signal from the excitation signal generation circuit 25 is supplied to the base of the transistor 1, and is output from the collector to the positive feedback circuit. Since the voltage across terminals 7 quickly changes from a steady state to an oscillating state, this phase-shifted oscillation circuit smoothly transitions to oscillation operation at an oscillation frequency determined by the system.

Therefore, the signal waveform output from the modulated signal output terminal 17 becomes a waveform that starts oscillating immediately from time t2, as shown in FIG. 2C.

By supplying this modulation signal to the vibrato modulation circuit, the musical tone signal is emitted with a so-called delayed vibrato effect in which vibrato modulation is gradually performed after the elapse of time from time t1 to time t2.

In this embodiment, since the pulse width shown in FIG. 2B is wide and the non-conducting time of the field effect transistor 8 is long,
Capacitors 5 to 7 of the positive feedback circuit are connected to the excitation signal generation circuit 2.
5 is not provided, the voltage between the terminals does not change immediately before time t2 and becomes a steady state. However, even if the pulse width shown in FIG. 2B is narrow,
When the trigger signal arrives continuously in a short period of time, the substantial non-conducting time of the field effect transistor 8 becomes long, and in order to cause the phase shift oscillation circuit to oscillate smoothly after time t2, the excitation signal generation circuit 25 Requires.

As detailed above, in this embodiment, the positive feedback circuit of the phase-shifted oscillation circuit is operated at a frequency higher than the oscillation frequency (experimentally, if it is about 10 times or more, there is no problem with performance) and at a low voltage level. Since the excitation signal is supplied at a level that does not affect the normal oscillation operation of the phase-shifted oscillation circuit, oscillation can be started immediately after the field effect transistor 8 becomes conductive.

Further, since the excitation signal is supplied to the common connection point between the capacitor 6 and the field effect transistor 8, the capacitor 6.
Although there is a small leakage that is output to the transistor 15 via the transistor 5, it is not amplified by the transistor 1 and output to the transistor 15, so the leakage signal becomes small.

As described above, in the present invention, it is possible to provide a modulation signal generation circuit for delay vibra=1 in which the phase shift oscillation circuit reliably oscillates after a predetermined period of time has elapsed, and its practical effects are great.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a waveform diagram of each part thereof. In the figure, 8 is a field effect transistor that operates as a switching element, and 25 is an excitation signal generation circuit.

Claims (1)

[Scope of utility model registration request] 1. collector/base (or drain/base) of a transistor
a phase-shifted oscillation circuit having a positive feedback circuit consisting of a multi-stage C-R phase-shifting circuit connected between the gates); a switch element inserted and connected in series to the positive feedback circuit; a delayed signal generation circuit that generates a signal for making a switch element conductive; and an excitation signal generation circuit that always supplies a signal at a frequency higher than the oscillation frequency of the phase shift oscillation circuit and at a low voltage level to the positive feedback circuit. A modulation signal generation circuit for delay vibrato, characterized by comprising: 2. The excitation signal generation circuit supplies an excitation signal between the collector (or drain) of the transistor and the switch element, as claimed in claim 1 of the patented utility model registration system. Modulation signal generation circuit.