JPS6342594Y2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a graphic equalizer circuit, which can substantially eliminate variations in circuit gain without using a gain adjustment circuit, etc., and outputs an input signal with arbitrary frequency characteristics. The purpose of the present invention is to provide a graphic equalizer circuit that performs the following functions.

FIGS. 1A and 1B show circuit diagrams of examples of conventional graphic equalizer circuits. In FIG. 1A, for example, an audio signal entering input terminal 1 is input to operational amplifier 2.
The signal is supplied to the non-inverting input terminal of , and is non-invertingly amplified with a desired gain for each of the n (n is plural) divided frequency bands, as described later, and then passed through the resistor R ₁ and the amplifier 3, respectively. It is output from the output terminal 5. Here, the output terminal of operational amplifier 2 is a resistor
connected to its inverting input terminal via R ₂ ,
Further, the connection point between the resistor R ₁ and the input terminal of the amplifier 3 is connected to the inverting input terminal of the operational amplifier 2 through n variable resistors VR ₁ to _{VR o} , respectively, in parallel.
The variable resistors VR ₁ to _{VR o} each have a midpoint tap c at the midpoint position between fixed terminals a and b (hereinafter abbreviated as terminals a and b), and a sliding resistor between fixed terminals a and b. It has a slider d.

Each slider d of the variable resistors VR ₁ to _{VR o} is grounded via a resonant circuit 4 ₁ to 4 _o configured to resonate at mutually different resonance frequencies, while each center tap c is connected to the ground, respectively. Commonly grounded. The sliders d of the variable resistors VR ₁ to _{VR o} are configured so that they can be slid independently of each other, and the input audio signal is transmitted depending on the contact position of the slider d. It is well known that level enhancement, level attenuation, or flat frequency characteristics are imparted to the resonance frequency of the resonant circuit and its neighboring frequency band. For example, when the slider d is in contact with the center tap c, it exhibits a flat frequency characteristic, and when it is slid in the direction of the terminal a, the amount of negative feedback decreases accordingly, so the level is gradually increased. showing the characteristics,
Furthermore, when it is slid from the center tap c toward the terminal b, it exhibits a characteristic in which the level is gradually attenuated.

Furthermore, the conventional graphic equalizer circuit shown in FIG. 1B differs from the conventional circuit shown in _FIG .
The only difference is that terminal a of VR _o is connected to the inverting input terminal of operational amplifier 2, and terminal b is connected to the non-inverting input terminal, and the frequency characteristics given are different from the conventional circuit shown in FIG. It can be done by the same method.

In the conventional graphic equalizer circuit shown in FIG. 1A or B above, the variable resistors VR ₁ to
The resistance value between each terminal a and c of VR _o (hereinafter referred to as R _ac
) and the resistance value between terminals b and c (hereinafter referred to as
R _bc ) are supposed to be manufactured to have the same value, but in reality, due to manufacturing accuracy issues, if many variable resistors are manufactured at once, the resistance value R _ac , R _bc tends to be larger than the other. In this way, the resistance values R _ac and R _bc
If these are unequal, the gain will vary in the above conventional circuit.

That is, in the conventional circuit shown in FIG. 1A,
The gain G when the slider d is at the center tap c is as follows: G=R ₂ +R _ac /n/R _ac /n×R _bc /n/R ₁ +R _bc /n(1
), and if R _ac = R _bc and R ₁ = R ₂ , then G = 1, so a flat frequency characteristic can be obtained.
However, in the case of R _ac >R _bc , if R _ac =K·R _bc (K is a constant and K>1), the gain G becomes as shown in the following equation.

G=R ₂ +K・R _bc /n/K・R _bc /n×R _bc /n/R ₁ +R
_bc /n Here, if R ₁ = R ₂ , the above formula becomes G = R ₁ +K・R _bc /n/K・(R ₁ +R _bc /n) = 1+R ₁ (1-K)/K(R ₁ + R _bc /n) (2). Here, since K>1, the second right-hand side of equation (2)
Since the term is negative, the gain G is less than 1, indicating a tendency to attenuate.

On the other hand, in the case of R _ac < R _bc , the above K is 0 < K < 1, so the second term on the right side of equation (2) is positive, and the gain G is larger than 1, so it shows an increasing tendency. .

Therefore, conventionally, in order to correct the variation in gain caused by the above-mentioned inequality in the resistance values R _ac and R _bc ,
A resistor as shown in Fig. 2 is placed at the point A in Fig. 1.
By inserting and connecting a gain adjustment circuit consisting of R ₃ and a variable resistor VR _a , the gain G was apparently kept constant as R _ac /n = R _bc /n (G = 1 in the case of R ₁ = R ₂ ). .

However, the above conventional circuit requires a circuit for gain adjustment, which increases the number of components.
There were disadvantages such as high cost and complicated adjustment.

The present invention eliminates the above-mentioned drawbacks, and one embodiment thereof will be described below with reference to FIG. 3.

FIG. 3 shows a circuit diagram of a main part of an embodiment of the graphic equalizer circuit according to the present invention. In the figure, the same components as in FIGS. 1A and 1B are designated by the same reference numerals. In Figure 3, the same type of variable resistor
Each terminal a of VR ₁ to _VR i-1 of i-1 variable resistors VR ₁ to _{VR i-1} (where i is a natural number smaller than n, and is 4 or more here) among VR 1 to VR o is connected to the remaining variable resistor. connected to each terminal b of the devices VR _i to VR _o , and
Each terminal b of the variable resistor VR ₁ ~ _{VR i-1} is VR _i ~ VR _o
are connected to each terminal a of the terminal a. That is, in FIG. 3, the variable resistors VR ₁ to VR i-1 within the range shown above the dashed-dotted line and VR _i to VR _i-1 within the range shown above.
VR _o and each other are connected in opposite directions. However, the center tap c of each variable resistor VR ₁ to _{VR o} is commonly grounded, and the slider d is connected to the resonant circuit 4 ₁ to VR o.
4 _o is connected to each other separately as in the conventional circuit. Note that the terminals a and b can be distinguished based on the terminal numbers attached to the variable resistors VR ₁ to VR _o or, for example, marks indicating directions.

This makes the variable resistor VR ₁ ~ _{VR o} the resistance value
Even if R _ac >R _bc or R _ac <R _bc , the influence of variations in gain G due to the inequality of R _ac and R _bc can be reduced or eliminated.
That is, if half of the variable resistors VR ₁ to _{VR o} are connected in opposite directions (in this case, the above i-1 becomes n/2), the resistance value R _A between and ground is as follows. It is equal to the resistance value R _B between ground.

R _A = R _ac /n/2R _bc /n/2 R _B = R _bc /n/2R _ac /n/2 The resistance values R _A and R _B are R _ac /n and R _bc /n in equation (1) Since it corresponds to R _ac /n=R _A = R _B = R _bc /n, it appears that R _ac = R _bc . Therefore, the gain G is constant and variations can be eliminated. Moreover, in this case, no gain adjustment operation is required at all.

In addition, in this embodiment, the variable resistors VR ₁ to
Assuming that a level enhancement characteristic (or level attenuation characteristic) is obtained when the slider d of VR _i-1 is slid in the direction of terminal a or b, the slider d of variable resistors VR _i to _{VR o} It is clear that a level enhancement characteristic (or a level attenuation characteristic) is obtained when the terminal is slid in the direction of terminal b or a.

Incidentally, the best results are obtained when the number of variable resistors _VR1 to _VR0 connected in opposite directions is half the total number, n/2, but this is not limited to this as long as it is possible to prevent gain variation from becoming a problem in practice.

As described above, the graphic equalizer circuit according to the present invention includes an amplifier for amplifying an input signal, a first fixed terminal connected to the input terminal of the amplifier, a second fixed terminal connected to the output terminal of the amplifier, and a second fixed terminal connected to the output terminal of the amplifier. a first variable resistor consisting of a plurality of variable resistors whose midpoint tap terminal is grounded and whose resistance values between the midpoint tap terminal and the first and second fixed terminals are unequal; a second fixed terminal is connected to the input terminal of the amplifier, a first fixed terminal is connected to the output terminal of the amplifier, and a center tap terminal is grounded; A second variable resistor group consisting of a plurality of variable resistors having unequal resistance values between the first and second fixed terminals, and a first and second variable resistor group that are slidable independently of each other. a plurality of resonant circuits each connected to each slider of the variable resistor group and having mutually different resonant frequencies in order to control the level of the input signal for each of the plurality of divided frequency bands; This eliminates the variation in gain of the graphic equalizer circuit that conventionally occurred due to the unequal resistance values between the midpoint tap terminal of the variable resistor and the first and second fixed terminals. , it is possible to eliminate the need for any new parts for gain adjustment, with almost the same number of parts as the conventional circuit, and the manufacturing cost is the same as before, and the gain adjustment operation that was required in the past is completely unnecessary. This has the advantage of being able to completely eliminate the complexity of gain adjustment.

[Brief explanation of the drawing]

FIGS. 1A and 1B are circuit diagrams showing conventional examples, respectively;
FIG. 2 is a circuit diagram showing a main part of an example of a conventional graphic equalizer circuit having a gain adjustment circuit;
FIG. 3 is a circuit diagram showing a main part of an embodiment of the present invention. 1... Input terminal, 2... Operational amplifier, 3... Amplifier, 4 ₁ to 4 _o ... Resonant circuit, 5... Output terminal,
VR ₁ ~ VR _o ...Variable resistor.

Claims (1)

[Claims for Utility Model Registration] 1. An amplifier for amplifying an input signal, a first fixed terminal connected to the input terminal of the amplifier, a second fixed terminal connected to the output terminal of the amplifier, and a center point tap. a first variable resistor group consisting of a plurality of variable resistors whose terminals are grounded and whose resistance values between the center tap terminal and the first and second fixed terminals are unequal; , a second fixed terminal is connected to the input terminal of the amplifier, a first fixed terminal is connected to the output terminal of the amplifier, and the center tap terminal is grounded, and the center tap terminal and the first fixed terminal are connected to each other. , a second variable resistor group consisting of a plurality of variable resistors having unequal resistance values between them and the second fixed terminal, and the first and second variable resistors that are slidable independently of each other. A plurality of resonant circuits each connected to each slider of the resistor group and having mutually different resonant frequencies in order to control the level of the input signal for each of the plurality of divided frequency bands. The constructed graphic equalizer circuit. 2. The graphic equalizer circuit according to claim 1, wherein the first and second variable resistor groups each include substantially the same number of variable resistors.