US3617599A - Keying circuit for electronic musical instruments - Google Patents

Abstract

A keying circuit for electronic musical instruments in whichbetween a bank of keyer circuits and a subsequent circuit such as a tone-coloring circuit, a tone-mixing circuit or a tone-signalamplifying circuit- there is provided a circuit including a resistor and a DC-bias-applying means. This arrangement may allow respective differences in DC potential between tone generators and said keyer circuits and between the latter and the subsequent circuit to be zero in direct coupling so that no DC isolation is needed which has hitherto been effected by employing capacitorresistor coupling circuits between circuit stages. This results in acquisition of an inexpensive keying circuit.

Description

United States Patent Inventor Norio Tolnisawa Ilantamatsu, Japan Appl. No. 60,278 Filed Aug. 3, 1970 Patented Nov. 2, 1971 Assignee Nippon Galtlti Seizo Kabusllikl Kaiaha llamalnatau-alti, Sltizuolta-lren, Japan Priorities Aug. 5, 1969 Aug. 5, 1969, Japan, No. 44/742360; Aug. 5, 1969, Japan, No. 44/74361; Aug. 5, 1969, Japan, No. [7062; Nov. 20, 1969, Japan, No. 44/110254 KEYING CIRCUIT FOR ELECTRONIC MUSICAL INSTRUMENTS 6 Claims, 20 Drawing Figs.

US. Cl. 84/l.0l, 84/ 1.14

Int. Cl. G101: 1/00 Field of Search 84/1 .01,

[56] References Cited UNITED STATES PATENTS 2,599,510 6/1952 Campbell et al 84/].01 2,618,753 11/1952 Mierlo 307/115 2,959,693 11/1960 Meyer 84/1.01

Primary Examiner-Milton O. l-lirshfield Assistant Exam iner-Ulysses Weldon Attorney-Cushman, Darby & Cushman ABSTRACT: A keying circuit for electronic musical instruments in which--between a bank of keyer circuits and a subsequent circuit such as a tone-coloring circuit, a tone-mixing circuit or a tone-signal-amplifying circuit-there is provided a circuit including a resistor and a DC-bias-applying means. This arrangement may allow respective differences in DC potential between tone generators and said keyer circuits and between the latter and the subsequent circuit to be zero in direct coupling so that no DC isolation is needed which has hitherto been effected by employing capacitor-resistor coupling circuits between circuit stages. This results in acquisition of an inexpensive keying circuit.

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An object of the present invention is to provide a keying circuit for an electronic musical instrument permitting the omission of a number of parts used in the circuit of this type so that it may be inexpensive.

Another object of the present invention is to provide an arrangement of a keying circuit in which all stages of the circuit are directly coupled without using any capacitor-resistor coupling circuit.

A further object of the present invention is to provide an arrangement of a keying circuit to achieve no difference in potential between stages of the circuit so as to make average DC voltages match the preceding as well as the subsequent stages and also to prevent key click.

A still further object of the present invention is to provide an arrangement capable of compensating for tone outputs in a high audiofrequency range.

Other object, features and advantages of the present invention will become apparent from the following detailed description when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram showing an example of a conventional keying circuit of this type;

FIG. 2 is a circuit diagram showing an embodiment of the present invention;

FIGS. 34 through 3f are views showing modifications of essential portions of FIG. 1;

FIG. 4 is a circuit diagram showing another embodiment of the present invention;

FIG. 5 is a circuit diagram showing a further embodiment of the present invention;

FIGS. 6a through 60 are views showing modifications of essential portions of FIG. 5;

FIG. 7 is a view showing a modification of the embodiment of FIG. 5;

FIG. 8 is a diagram showing an example of a circuit of this t e;

FIG. 9 is a diagram showing an improvement of the circuit shown in FIG. 8 according to the present invention; and

FIGS. 10a and 10b are views showing modifications of essential portions of FIG. 9.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Like references or symbols indicate like parts hereunder.

Prior to describing the embodiments of the present invention, description of an example of the prior art will be made hereunder.

Referring to FIG. I, there is shown a conventional keying circuit, in which there are provided a number of tone generators A (shown. in block) each including a tone-generating oscillator, a frequency divider and (when necessary) an amplifier, which block A in the drawing schematically indicating only an output portion of the circuit. An output terminal A, of each tone generator is connected through a capacitorresistor coupling circuit consisting of a DC blocking capacitor C, and a resistor R, with a mixing resistor R. The resistor R is connected to one of two contacts of a corresponding keying switch S, and the other contact is connected to a common connecting point a as a bank connection point and then connected to an output terminal T of the keying circuit. At the terminal 'I', a subsequent circuit B (shown in a block) is connected through a coupling circuit consisting of a capacitor C anda resistor R and thus either a single tone signal or a synthesized tone signal may be derived in accordance with the key operation associated with the key switches S. That is, by the provision of the capacitor C,., a DC voltage from the preceding stage such as the tone generator is blocked and by using the resistor R the DC potential at the common connecting point of the key switches is rendered zero. Such a coupling is known as a CR coupling which has been practiced in coupling between amplifiers. Therefore, if this coupling is used, there are needed the CR coupling circuit as many as the number of the tone generators plus the subsequent circuits. This is disadvantageous in that the number of parts and the assembling cost become much greater, so that the circuit of this type has been very much expensive.

The present invention, therefore, has been worked out to obviate such drawbacks of the prior art as mentioned above.

Description of the present invention will be made on several embodiments of the present invention by referring to the drawings.

Referring now to FIG. 2, there is shown a keying circuit arrangement of an embodiment of the present invention as compared with the circuit of FIG. I, in which reference A and A, indicate respectively tone generators and their output terminals which are the same as those in FIG. 1. Each of the output terminals is directly connected to a mixing resistor R and therefrom connected to a contact of the corresponding one of a number of key switches S. The other contact is connected to a common connecting point a and then connected to an output terminal T of the keying circuit through a voltagedropping resistor R,. At the point a and the terminal T, biasing power sources E, and E, are connected through resistors R, and R, respectively.

By appropriately selecting the polarity and the amount of value of voltages of the sources E, and E, and so selecting the resistances of the resistors R. R, and R, the DC potential at the point a is set at the same DC potential as that of the output terminal A, of the tone generator, while the DC potential at the output terminal T is rendered to be at the same level as the input DC potential of the subsequent circuit 8 which may be one of a tone-coloring circuit, a mixing circuit, and an amplifier as known. Thus, a difference in DC potential between the point a and the terminal T is burdened with a voltage drop across the resistor R so that the tone generators and the subsequent circuit may be used in a direct coupling therebetween, that is, without using any coupling capacitor.

In operation, since the respective outputs of the tone generator circuits A are only different in frequency from one another, all of the circuits A may be substantially of the same construction, and hence, the DC potentials at the output terminals A, may also be almost the same. Accordingly, if the DC potential at the other contact of the key switches is the same as those of the output terminals A, no potential difference occurs across the two contacts of the each key switch. For this reason, the construction, of FIG. 2 does not cause any key click due to the abovementioned DC potential difference upon playing the key-operated electronic musical instrument.

Furthermore, the DC potential at the output terminal T is set to be the same as that located at the input terminal of the subsequent circuit 8, and therefore, direct coupling does not adversely affect each terminal, so that the key switches and the subsequent circuit may perform their normal operations.

Of course, the means by which the DC potential at the common connecting point a of the key switches S is rendered to be the same levels as those at the output terminals A, of the tone generator circuits, and by which the DC potential at the output terminal T is rendered to be the same as that on the subsequent circuit B side may be replaced, for example, by circuits shown in FIGS. 3a through 3f, in which, one of the biasing power sources is connected to a zero potential source. In other words, this means that said power source is grounded and that one power source is used in common to two biasing means, or in other words, for example, resistors are connected to form a bleeder resistor. Further, even when the subsequent circuit B is formed with an active element and even when the DC potential at the input side of circuit B is at zero, the

present circuit still can operate as desired by arranging the biasing power source E so that it has an opposite polarity to that of the source E Referring to FIG. 4, there is shown another keying circuit arrangement embodying the present invention, in which a capacitor C for passing AC components is connected in parallel with the resistor R in addition to the circuit of FIG. 1. This capacitor serves to improve the transmission characteristics of high-frequency signals, that is to say, it can compensate for the drop of the levels in the tone signals due to the influence from the subsequent circuit.

Referring now to FIG. 5, there is shown a modified circuit of FIG. 2, in which the resistor R is provided with an intermediate tap to which one end of the resistor R is connected, the other end thereof being grounded.

The tap may be used so that resistance portions of the resister R divided thereby at the point R serve as bleeder resistors for determining the respective DC potentials at the common connecting point a and the output terminal T. This results is a reduction of the number of the bleeder resistors used in the present circuit and greatly facilitates the settings of the above-mentioned DC potentials. FIGS. 60 to 6e show various modification of biasing register network which operate in the same manner as those described in connection with FIGS. 3a to 3f in regard to the circuit of FIG. 5.

FIG. 7 shows another arrangement which incorporates a capacitor C for easily passing AC components of tone signals, in addition to the arrangement shown in FIG. 5. The capacitor may serve in the same manner as that described in connection with FIG. 4.

FIG. 9 shows a circuit of another embodiment of the present invention, which has been worked out as an improvement of the arrangement of FIG. 8 which has been invented by the same inventor. More specifically, the keying circuit of FIG. 8 has one thing which may be disadvantageous in that it would be difficult to make a matching of the DC voltages between the output terminals A of the tone generator circuits and an input terminal a of an amplifier B since in the selection of the transistor 0, and in the designing of bleeder resistors Ra and Rb for biasing the base of the transistor Q other significant requirements for the amplifiers such as obtaining a desired amplification, selecting its input and output impedances so as to minimize the distortion thereof and enhancing the working efficiency must simultaneously be satisfied.

In FIG. 9, at the common connecting point a is connected a potential difference compensating or adjusting circuit B including a voltage-dropping resistor R one end of which is connected through a resistor R to a power source +Vc c, and the other end being connected to the subsequent amplifying circuit B at its input terminal A and a resistor grounded and connected to the base or terminal A of the transistor 0,. The emitter of the transistor O is grounded through a resistor R and a capacitor C, connected in parallel to the resistor R The collector of the transistor O is connected through a resistor R to the power source +Vcc and also is connected to a signal output terminal A The potential at the terminal A can be set to provide a required base bias to the transistor 0,, and matched to the potential at the point a by making use of a voltage drop across the resistor R in DC direct coupling.

The same function as described above can be obtained by modified circuits as shown in FIGS. 10a and 1012.

In FIG. 10a the transistor Q is arranged to constitute an emitter follower circuit, whose base is grounded via a series circuit of resistors R and R The connection point r between resistors R and R, is arranged to be connected to the common connecting point a. The base of the transistor Q. is connected through the resistor R to the power source +Vcc.

FIG. 10b shows a modification of FIG. 9 by adding a bypass capacitor C in parallel with the potential difference-adjusting resistor R The effects are the same as those previously described.

In the foregoing arrangements, the circuits as shown in FIGS. 9, 10a and 10b are very much advanta eous in that the can thoroughly prevent key click due to thefiDC potential di ference between circuit connections as well as are capable of desirably determining the bias voltage of an amplifying element such as a transistor in the amplifier by making use of the voltage difference-adjusting circuit.

I claim:

1. A keying circuit for an electronic musical instrument comprising:

a plurality of output terminals of tone generators, each terminal being at a DC potential;

a plurality of keyer circuits, the input of each keyer circuit being coupled, relating to DC to the corresponding one of said output tenninals;

a common connecting terminal to which all of the outputs of the keyer circuits are connected;

a resistor one end of which is connected to said common connecting terminal and the other connected to a subsequent circuit stage; and

DC biasing means substantially disposed at both ends of said resistor, whereby each of said tone generators may be directly coupled to the subsequent circuit stage without using a coupling capacitor.

2. A keying circuit according to claim I, further comprising a capacitor connected in parallel with said resistor.

3. A keying circuit according to claim 1, further comprising an intermediate tap provided in said resistor for permitting the resistor to be adapted as a bleeder resistance to adjust a difference between respective potentials at the common connecting terminal and the input of the subsequent circuit stage.

4. A keying circuit according to claim 3, further comprising a capacitor connected in parallel with said resistor.

5. A keying circuit according to claim 1, in which said subsequent circuit is one of a tone-coloring circuit, a mixing circuit and an amplifier.

6. A keying circuit for an electronic musical instrument comprising a potential difference-adjusting circuit including a resistor and DC biasing means substantially disposed at both ends of said resistor and disposed between a bank of output terminals of keyer circuits and an amplifier circuit for amplifying the outputs of the keyer circuits, whereby a DC potential difference between output terminals of tone generators and an input terminal of the amplifier may be compensated for to achieve a direct DC coupling therebetween.

Claims (6)

1. A keying circuit for an electronic musical instrument comprising: a plurality of output terminals of tone generators, each terminal being at a DC potential; a plurality of keyer circuits, the input of each keyer circuit being coupled, relating to DC to the corresponding one of said output terminals; a common connecting terminal to which all of the outputs of the keyer circuits are connected; a resistor one end of which is connected to said common connecting terminal and the other connected to a subsequent circuit stage; and DC biasing means substantially disposed at both ends of said resistor, whereby each of said tone generators may be directly coupled to the subsequent circuit stage without using a coupling capacitor.

2. A keying circuit according to claim 1, further comprising a capacitor connected in parallel with said resistor.

3. A keying circuit according to claim 1, further comprising an intermediate tap provided in said resistor for permitting the resistor to be adapted as a bleeder resistance to adjust a difference between respective potentials at the common connecting terminal and the input of the subsequent circuit stage.

4. A keying circuit according to claim 3, further comprising a capacitor connected in parallel with said resistor.

5. A keying circuit according to claim 1, in which said subsequent circuit is one of a tone-coloring circuit, a mixing circuit and an amplifier.

6. A keying cIrcuit for an electronic musical instrument comprising a potential difference-adjusting circuit including a resistor and DC biasing means substantially disposed at both ends of said resistor and disposed between a bank of output terminals of keyer circuits and an amplifier circuit for amplifying the outputs of the keyer circuits, whereby a DC potential difference between output terminals of tone generators and an input terminal of the amplifier may be compensated for to achieve a direct DC coupling therebetween.

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