Monophonic Electronic Musical Instrument With A Variable Frequency Oscillator Employing Positive Feed Back

Abstract

A monophonic musical instrument having a variable frequency oscillator including an amplifier, a plurality of frequency determining networks whose input sides are connected to the output side of the amplifier, a tapped resistor having a plurality of taps several of which are respectively connected to the output sides of the frequency determining networks, and a plurality of switching elements each connected between each of the taps and the input side of the amplifier thus constituting a positive feed-back loop; a plurality of key switches; a latching selector having output lines respectively connected to the switching elements and associated key switches so that the closure of the key switch makes the corresponding one of the output lines to deliver a gating signal to render the corresponding switching element conductive; and circuit means for providing rising and sustaining characteristics to the output signal of the oscillator.

Description

BACKGROUND OF THE INVENTION

This invention relates to a monophonic electronic musical instrument in which a frequency variation within wide range as well as required sustaining characteristics and accompanying rising characteristics of notes can be obtained.

In general, monophonic electronic musical instruments require usually 32 times the width of (five octaves) a normal range of frequency variation. But in a CR oscillator utilized in a conventional monophonic electronic musical instrument the frequency variation is usually achieved by varying a capacitor C or a resistance R, with the result that a range of a frequency variation in one variable element is limited to at most 10 times of width of a normal range of frequency variation.

For this reason, a conventional monophonic electronic musical instrument has generally a very narrow frequency range. Accordingly, in order to widen the range described above, it was proposed to switch over a plurality of variable elements to make them variable, but this resulted in a complex and expensive structure of the monophonic electronic musical instrument. Therefore, a continuous variation of the frequency over that wide range was impossible using an ordinary means. While in case a multivibrator is utilized to widen the frequency range the bias-control of the oscillation frequency becomes unstable and is subject to the influence of the fluctuation of the bias caused by the variation of a voltage and temperature.

A conventional monophonic musical instrument has another big drawback in that there cannot be obtained a sustained effect of the tone. It is because the key switch has a function of starting, and ending of the oscillation, as well as a function of frequency determination; therefore the tone signal is generated only while the key switch is kept closed, and consequently no tone signal is available after opening the key switch.

SUMMARY OF THE INVENTION

Therefore, an essential object of the invention is to provide a monophonic electronic musical instrument capable of providing wide frequency range characteristics as well as sustaining characteristics to an output signal thereof.

It is another object of the invention to provide a monophonic electronic musical instrument having a circuit for providing predetermined sustaining and rising characteristics to an output signal upon closing of the key switch.

It is a further object of the invention to provide a monophonic electronic musical instrument the characteristics of which are not affected by variations of voltage and temperature.

The foregoing objects and other objects as well as the characteristic features of the 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.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a circuit block diagram showing an example of a monophonic electronic musical instrument according to the invention; and

FIG. 2 is a detailed circuit diagram showing the circuit of FIG. 1 more concretely.

DETAILED DESCRIPTION OF THE INVENTION

This invention relates to an improved monophonic electronic musical instrument.

Referring now FIG. 1, the instrument circuit comprises a plurality of frequency determining networks 1A, 1B, 1C and 1D composed of capacitors and resistors, a resistor 2 with a plurality of taps T.sub.l -T.sub.n , a voltage amplifier 3, field-effect transistors FET.sub.l - FET.sub.n as switching elements, and a latching selector 4 adapted for selectively gating one of the transistors at a time. In the latching selector 4 there are provided a plurality of key switches S.sub.1 S.sub.n in a preference-connection and a memory circuit M, said key switches being so arranged that only one of the key switches is connected between a DC source E and memory circuit M even when more than two key switches are closed.

In addition, the circuit of FIG. 1 comprises further switches SW.sub.l - SW.sub.n which cooperate with each of the key switches S.sub.l - S.sub.n , an envelope shaping circuit 5, frequency-dividing circuits FF.sub.1 - FF.sub.3 , switching circuits G.sub.1 - G.sub.4 , a filter circuit 6, and tone switches TS.sub.1 - TS.sub.4 . A variable frequency oscillator VO is composed of the voltage amplifier 3, a group of frequency determining networks 1A - 1D, the resistor 2 with a plurality of taps and field-effect transistors FET.sub.l - FET.sub.n all connected in a positive feedback loop. When one of the field-effect transistors FET.sub.l - FET.sub.n is rendered conductive by the memory circuit M as described hereinafter, the variable frequency oscillator VO oscillates. Now, assuming that a field-effect transistor FET.sub.2 is in the state of conduction, the variable frequency oscillator VO oscillates at an intermediate frequency which is determined by each of values of respective resistors between a tap T.sub.2 and the networks 1A and 1B and is between tuned frequencies of two frequency determining networks 1A and 1B which are at the nearest of the tap T.sub.2 . When another field-effect transistor is in the state of conduction, the variable frequency oscillates in same manner described above but at a different frequency.

A signal from the variable frequency oscillator VO is directly introduced successively through switching circuit G.sub.1 and frequency-dividing circuits FF.sub.1 .about. FF.sub.3 to switching circuits G.sub.2 .about. G.sub.4 , whereby the oscillator output signal and the frequency-divided signals are subjected to envelope controls according to an envelope signal from the envelope shaping circuit 5. The envelope controlled signals are supplied to the filter circuit 6 to be given predetermined tone colors, and finally taken out through the tone switches TS.sub.1 .about. TS.sub.4 .

The latching selector 4 for selectively gating the transistors performs electrically a function of a lock-and-release push button switch. When, among the switches S.sub.l - S.sub.n which are selectively connected to a DC source E, for example the switch S.sub.2 is switched on, the DC source E is connected only through the switch S.sub.2 to the memory circuit M even if anyone of the switches S.sub.3-S.sub.n which are located behind the switch S.sub.2 is switched on simultaneously. Thus, the memory circuit M supplies an output gating signal to only the output line TO.sub.2 corresponding to the switch S.sub.2 , thereby rendering the field-effect transistor FET.sub.2 conductive. After the switch S.sub.2 has been switched off, the memory circuit M continues to deliver the gating signal at the output line TO.sub.2 for gating the field-effect transistor FET.sub.2 so long as another one of the switches is not subsequently switched on. Therefore, the variable frequency oscillator VO, as described before, oscillates at the frequency determined by the tap T.sub.2 .

In FIG. 2, there is shown a detailed circuit diagram which illustrates a part of FIG. 1. Hereinafter, mainly the operation of the memory circuit 4 will be described in detail. The memory circuit M is composed of a plurality of flip-flop circuits, and all transistors 10 of each of said flip-flop circuits are switched on to their conductive states in the original state of FIG. 2, i.e., before no switches are actuated after the electric power in the memory circuit is first connected, because both potentials of collectors 13 of transistors 10 and the potentials of collectors 23 of transistors 20 have increased similarly through a load resistor 14 or 24, but the potentials of bases 22 of the transistors 20 have not increased so much as the potentials of bases 12 of the transistors 10 due to the existence of grounded resistor 26. In such a state, when the switch S.sub.2 is closed, the transistor 10 of the flip-flop circuit corresponding to the switch S.sub.2 is turned off, while the transistor 20 corresponding to the switch S.sub.2 is turned on. Now, since the collector potential of the transistor 10 is kept at a positive potential, it renders the field-effect transistor FET.sub.2 conductive. This state is kept unchanged even after the switch S.sub.2 is released back. And next, when another one of the switches, for example, S.sub.n-1 is closed, the transistor 10 of the flip-flop circuit corresponding to the switch S.sub.n-1 is turned off, while the transistor 20 of that corresponding to the switch S.sub.n-1 is turned on. However, in a moment of the turning on of the transistor 20, a current flowing through the coil L immediately increases and a potential of an emitter common line l suddenly increases by action of an inductance of the coil L against the rapid current variation. Consequently, the transistor 20 corresponding to switch S.sub.2 which has been on, is now off. The sudden increase of the potential of the emitter common line 1 does not, of course, affect at this moment the now turned-on transistor 20 of the flip-flop circuit corresponding to the switch S.sub.n-1 , as the transistor 10 thereof is now kept stably off by the closing of the switch S.sub.n-1 . The operation of such a memory circuit M may be more clearly understood from the description in the U.S. Pat. No. 3,488,515 to Hiyoshi.

In FIG. 1 and FIG. 2, switches SW.sub.1 - SW.sub.n cooperating with key switches S.sub.1 - S.sub.n are provided for supplying signals derived from switching on and off the key switches to an envelope shaping circuit 5. When any one of the switches SW.sub.1 - SW.sub.n is switched on or off, the envelope shaping circuit 5 produces an envelope signal having, for example, a rising time 10 miliseconds and sustaining(decaying) time 1 - 2 seconds, thereby to perform an envelope control in each of the switching circuit G.sub.1 - G.sub.4.

Further, although in the embodiment described above there is provided a variable frequency oscillator VO which has four frequency determining networks, it is within the scope of the invention to change the number of the frequency determining networks as well as the field-effect transistor, and the switching circuits can be increased or decreased as necessary.

Claims

I claim:

1. A monophonic musical instrument which comprises:

a variable frequency oscillator including an amplifier, a plurality of frequency determining networks whose input sides are connected to an output side of said amplifier, a resistor having a plurality of taps a corresponding number of which are respectively connected to output sides of said frequency determining networks, a plurality of switching elements each having a control electrode and connected between each of said taps and an input side of said amplifier thus constituting a positive feed-back loop, and an output terminal connected to said output side of said amplifier;

a latching selector including a plurality of key switches, memory means connected to said key switches and a plurality of output lines connected to said memory means, each said output line corresponding to each of said key switches and connected to said individual control electrode of each said switching elements, and upon closure of one of said key switches the corresponding one of said output lines delivering a gating signal to render its corresponding switching element conductive;

and circuit means connected to said output terminal which is connected to the output side of the amplifier for providing rising and sustaining characteristics to an output signal from the oscillator.