JPS58234Y2 - Electronic musical instrument key switch circuit - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a key switch device for an electronic musical instrument that reduces noise signals.

Since electronic musical instruments use a large number of key switches that correspond to keys, the level of noise signals leaking to subsequent stages through the stray capacitance that exists between the contacts of open key switches has become high.

Therefore, in key switch circuits in which musical tone signals are directly opened and closed by a key switch, this leakage noise signal has traditionally been a problem, especially when a pair of fixed terminals arranged on a board as a key switch When a movable terminal is used to electrically bridge the contacts, the stray capacitance between the contacts is large, and the noise signal level is also high, which poses a practical problem.

In view of the above-mentioned conventional drawbacks, the purpose of the present invention is to connect a series circuit of a resistor and a key switch to each sound source in order to derive each musical tone signal, and to connect a common connection point between the resistor and the key switch to a constant potential. The present invention is intended to provide a key switch circuit for an electronic musical instrument in which the above-mentioned noise signal is reduced by connecting capacitors between the two points.

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

First, in FIGS. 1 to 4 showing the first embodiment of the present invention, in FIGS. 1 to 3, 1 is a shelf board of an electronic musical instrument;
is a frame placed on the shelf board 1, and its protruding piece 2
The key 3 is swingably supported at point a.

4 is an actuator provided at the central lower end of the key 3;
is a spring stretched between the rear end of the key 3 and the frame 2; 6 is a board fixed to the frame 2 by holding members 7 and 8; 9 is a dome-shaped flexible plate placed on the board 6; It is a flexible member, and a movable terminal 10 made of a conductive flexible material is attached to the ceiling of the member.

11 is a protrusion formed integrally with the flexible member 9 in order to engage with the through hole 12 of the board 6 and fix the flexible member 9 to the board 6; 13 and 14 are printed wirings on the board 6; a pair of fixed terminals, 15.16 are lead wires led out from each of the fixed terminals 13.14, 17 is one electrode plate of a capacitor formed by making a part of the lead wire 15 into a large area, 18 is a The other electrode plate of the capacitor is disposed on the electrode plate 17 opposite to each other with a dielectric sheet interposed therebetween, and the electrode plate 1
8 is grounded via a printed lead wire 19.

Next, in FIG. 4, 20 is a sound source that outputs a plurality of square wave musical tone signals that are chromatically spaced from each other, and their output terminals are LOOK, ! Q resistance 21. They are commonly connected after passing through the pair of fixed terminals 13 and 14 and the movable terminal 10, and are further connected to a capacitor 22, a tone circuit 23, and an amplifier 24.
, is connected to a speaker 26 via a volume 25 controlled by an expression pedal.

27 is a 100 pF capacitor connected between the common connection point of the resistor 21 and the fixed terminal 13 and the ground, and is constituted by both the electrode plates 17 and 18.

28.29 is the input side of the capacitor 22 and the positive power supply (+)
4 and 7 are resistances β connected between (2) and ground, respectively.

The operation of the above configuration will now be described.

First, if we press the key 3 against the spring 5,
The actuator 4 compresses the flexible member 9, so that the movable terminal 10 electrically bridges the pair of fixed terminals 13,14.

Therefore, a musical tone signal corresponding to the key 3 is supplied from the sound source 20 to the speaker 26 via the timbre circuit 23 and the like, and is emitted.

By the way, when the key 3 is not pressed down, the key switch composed of the movable terminal 10 and the pair of fixed terminals 13 and 14 has a capacity of Equation 1) F, and the musical tone signal from the sound source 20 is as follows. On the output side of the resistor 21, harmonic components are removed by the presence of the capacitor 27, and a waveform with gentle rises and falls is transmitted to the key switch.

As mentioned above, this key switch has a capacitance of several pF, but since the impedance of the capacitor is inversely proportional to the frequency of the transmitted signal, the capacitor 27 is The impedance becomes larger and therefore the leakage noise signal becomes smaller.

Note that when the movable terminal 10 electrically bridges the pair of fixed terminals 13.14, that is, when the key switch is closed, the resistance value of the resistor 28.29 is greater than the impedance of the capacitor 27. Since it is small, the rise and fall of the waveform of the musical tone signal is outputted to the subsequent stage without becoming gradual.

Next, a second embodiment of the present invention will be described with reference to FIG.

This embodiment differs from the previous embodiment only in that the connection positions of a key switch constituted by a movable terminal 10 and a pair of fixed terminals 13 and 14 and a resistor 21 are interchanged.

In this embodiment as well, when the key switch is open, the stray capacitance of several pF existing in the key switch acts as a large impedance to the low frequency components of the musical tone signal, and acts as a large impedance to the high frequency components of the musical tone signal. act as small impedances, so mainly high frequency components are transmitted as leakage noise signals, but since most of this component is grounded by the capacitor 27, the noise signal output to the subsequent stage becomes extremely small.

Furthermore, in this embodiment, the noise signal leaking through the key switch is outputted via the resistor 21, so that it is further reduced.

As detailed above, in this embodiment, the noise signal leaking through the key switch in the open state and transmitted to the subsequent stage becomes very small, and in particular, the noise signal that leaks through the open key switch and is transmitted to the subsequent stage is extremely small.
．． 14 and the fixed terminals 13 and 14 are electrically bridged by the movable terminal 10 placed opposite to the fixed terminals 13 and 14. Conventionally, a large leakage noise signal was generated, but this problem was solved until there was no problem in practical use. Can be removed.

Furthermore, since the capacitor 27 is formed by printed wiring as shown in FIG. 3, manufacturing is extremely easy.

As mentioned above, in the key switch circuit of the electronic musical instrument according to the present invention, the leakage noise signal caused by the stray capacitance existing in the key switch can be greatly reduced, and this has a great effect.

[Brief explanation of the drawing]

FIG. 1 is a side view of the keyboard section of an electronic musical instrument for explaining the first embodiment of the present invention, FIG. 2 is an enlarged sectional view of the key switch section, FIG. 3 is a partial plan view of the board, and FIG. The figure is a block circuit diagram, and FIG. 5 is a block circuit diagram for explaining a second embodiment of the present invention. In the figure, 6 is a substrate, 9 is a flexible member, 10 is a movable terminal, 1
3.14 is a pair of fixed terminals, 20 is a sound source, 21 is a resistor,
27 is a capacitor.

Claims (1)

[Scope of utility model registration request] 1. A sound source that outputs a plurality of musical tone signals at chromatic intervals, a series circuit of a key switch and a resistor derived from the sound source corresponding to each musical tone signal, and a resistor and a key switch of each series circuit. A key switch circuit for an electronic musical instrument, comprising a common connection point with a switch and a capacitor connected between a constant potential point. 2. The key switch is composed of a pair of fixed terminals arranged oppositely on the board, and a movable terminal made of a conductive flexible material to electrically bridge the fixed terminals. A key switch circuit for an electronic musical instrument according to claim 1, characterized in that it is a utility model.