JPS6056325B2 - Tone control circuit - Google Patents

Description

[Detailed description of the invention] The present invention relates to improvements in tone control circuits.

The present invention provides that when an element other than the resistor and capacitor that determines the tone control characteristics is connected to the tone control circuit, such as a heavy load, a DC feedback resistor, etc., it causes interference with the resistor and capacitor that determines the tone control circuit's characteristics. To provide a tone control circuit which eliminates the occurrence of undulation in tone control characteristics and asymmetrical boost and cut characteristics. FIG. 1 is a circuit diagram of a tone control circuit previously filed by the applicant.

This tone control circuit applies the input voltage applied to the input terminal IN to the non-inverting input terminal of the operational amplifier 1,
A first circuit with a resistor 2 and a capacitor 4 is connected to the output terminal of the operational amplifier 1.
A first series circuit consisting of a resistor 6, a variable resistor 8 and a resistor 7 is connected between the other ends of the first and second parallel circuits. A second series circuit consisting of a resistor 9, a resistor 11, a capacitor 13, a variable resistor 15, a capacitor 14, a resistor 12, and a resistor 10 is connected in parallel to the first series circuit. The slider of the variable resistor 15 is grounded, the common connection point of the resistors 9 and 11 is connected to the output terminal 0UT, and the common connection point of the resistors 10 and 12 is connected to the inverting input terminal of the operational amplifier 1. . That is, the variable resistor 8 is for low frequency control, the variable resistor 15 is for high frequency control, and the output terminal of the operational amplifier 1 and the output terminal 0U, which are bridged at the upper part of FIG. 1 with the ground terminal as the border.
The output circuit between T and the feedback circuit between the output terminal and the inverting input terminal of the operational amplifier 1 configured in the lower part of FIG. 1 are symmetrical, and the variable resistors 8 and 15 are respectively It is configured across an output circuit and a feedback circuit, and has variable resistors 8,
By changing the position of slider 15, the amount of attenuation can be changed in the output circuit by changing the position of slider 15.
The amount of feedback is varied in the feedback circuit, and tone control characteristics are obtained by adding the amount of attenuation and the amount of feedback. In the above tone control circuit, in particular, the resistance values and capacitances of the paired resistors and capacitors are selected to be equal, for example, the resistance values of resistors 2 and 3 are equal, the capacitances of capacitors 4 and 5 are equal, and so on. , variable resistors 8 and 15
When the resistance values of the resistors are equal and the sliders are set at their respective midpoint positions, the resistance values of the resistors of variable resistors 8 and 15 are divided into two equal parts, and the resistance change rate characteristic with respect to the slider position is When variable resistors 8 and 15 having linear characteristics such as type B are used, the tone control characteristics of the tone control circuit are such that the sliders of variable resistors 8 and 15 are set at their midpoints as shown in Figure 2. In this case, the attenuation amount of the output circuit and the feedback amount of the feedback circuit are equal, and the gain is 0 dB, resulting in completely flat characteristics without waviness.

Furthermore, when the offset position from the center point of the slider of variable resistor 8 or 15 is the same, the same amount of cut and the same amount of boost are obtained, and the tone control characteristics are completely symmetrical with respect to the frequency axis. Provides tone control characteristics. However, if the load 16 and/or the impedance circuit 18 is connected to the output terminal 0UT' between the output terminal and the inverting input terminal of the operational amplifier 1, the load driving ability of the operational amplifier 1 is sufficient, and the resistors 2, 3, 6, 7, 9 to 12, capacitors 4, 5, 13, 14, and variable resistors 8, 15, if the resistance values and capacitances can be set sufficiently low, that is, the output impedance of the above tone control circuit is
If the impedance of the operational amplifier 1 is sufficiently lower than the impedance of the load 16, the load 16 can be regarded as open, and the tone control characteristics of this tone control circuit are as shown in FIG. Alternatively, when the impedance of the resistor, variable resistor, and capacitor constituting the tone control circuit must be set sufficiently high, the output impedance inevitably becomes large and is strongly influenced by the load.

This also applies to the impedance circuit 18. Therefore, the tone control characteristic in this case is the third
As shown in the figure, the flat characteristic attenuates over all frequencies,
Moreover, there was a drawback that undulation occurred in the low frequency range, and the symmetry of the boost and cut characteristics with respect to the frequency axis was lost. Further, in this case, the problem can be solved by connecting a buffer amplifier or the like with a sufficiently large input impedance as a load, but the problem is that the entire circuit becomes complicated and expensive.

Therefore, the present invention eliminates the above-mentioned drawbacks, and will be described below with reference to Examples.

FIG. 4 is a circuit diagram of a tone control circuit according to an embodiment of the present invention.

In the tone control circuit of this embodiment, a load 16 is connected to the output terminal 0UT of the tone control circuit shown by the solid line in FIG.
An impedance circuit 17 having an impedance equal to the impedance of is connected.

Therefore, the output circuit including the load 16 in the tone control circuit of this embodiment shown in FIG. 4 maintains complete symmetry with the feedback circuit including the impedance circuit 17. By selecting the same resistance value and the same capacitance for each of the resistor and capacitor pairs, it is possible to maintain the completely flat tone control characteristic shown in Figure 2, which is symmetrical about the frequency axis. can.

That is, even in the case of a heavy load, it is not necessary to cascadely connect buffer amplifiers with large input impedances, and it is possible to obtain beautiful symmetrical tone control characteristics simply by connecting the impedance circuit 17.

Next, other embodiments of the present invention will be described.

FIG. 5 is a circuit diagram of a tone control circuit according to another embodiment of the present invention. The tone control circuit of this embodiment includes an impedance circuit 18 between the output terminal of the operational amplifier 1 and the inverting input terminal, and an output terminal 0UT between the output terminal of the operational amplifier 1 and the output terminal An impedance circuit 18 and an impedance circuit 19 having the same impedance are connected between them.

Therefore, in the tone control circuit of this embodiment shown in FIG. 5, the feedback circuit including the impedance circuit 18 and the output circuit including the impedance circuit 19 maintain complete symmetry, and the resistance of the tone control circuit,
By selecting the same resistance value and the same capacitance for each pair of variable resistor and capacitor, the completely flat tone control characteristic shown in Fig. 2 and symmetrical about the frequency axis can be maintained. Can be done.

That is, even when an impedance such as a DC feedback resistor is connected to the operational amplifier 1, a perfectly symmetrical tone control characteristic can be obtained. Furthermore, when the impedance circuit 18 includes a DC feedback resistor, forcibly increasing the resistance value of the DC feedback resistor deteriorates the drift characteristics, which is a problem, but according to this embodiment, an appropriate DC feedback resistor is selected. It is possible to improve the drift characteristics. Next, modified embodiments of the present invention will be described.

FIG. 6 is a circuit diagram of a tone control circuit according to a modified embodiment of the present invention. The circuit of this modified embodiment is the same as that of the tone control circuit shown in FIG. Connect capacitors 20 and 21 separately between both ends of the resistor and its slider, short-circuit resistors 9 and 10 and capacitors 11 and 14, and replace resistors 11 and 12 with resistors 22 and 23, respectively. and a capacitor 24 is connected between the slider of the variable resistor 15 and the ground terminal, the load 16 is connected to the output terminal 0UT, and an impedance circuit having the same impedance as the impedance of the load 16 is connected to the inverting input terminal of the operational amplifier 1. is configured by connecting an impedance circuit 18 between the output terminal of the operational amplifier 1 and the inverting input terminal, and connecting an impedance circuit 19 having an impedance equal to that of the impedance circuit 18 between the output terminal of the operational amplifier 1 and the output terminal 0UT. do. In this modified embodiment as well, the capacitor 24 is shared, and the output circuit and the feedback circuit are completely symmetrical, and the resistor, variable resistor, and capacitor of the tone control circuit are connected to each other with the same resistance value and the same resistance value. By selecting the capacitance, it is possible to maintain the tone control characteristic shown in FIG. 2, which is completely flat and line-symmetrical with respect to the frequency axis.

That is, the impedance of the load 16 and the impedance of the impedance circuit 18 do not affect the tone control characteristics.

Next, other modified embodiments of the present invention will be described. FIG. 7 is a circuit diagram of a tone control circuit according to another modified embodiment of the present invention.

The tone control circuit of this modified embodiment is the same as the tone control circuit shown in FIG.
, the resistors 9, 10, 11 and 12 are short-circuited, the resistor 26 is connected between the slider of the variable resistor 15 and the earth, and the load 16, an impedance circuit 17 having the same impedance as the load 16, and an impedance circuit 18 are connected. , the impedance circuit 18 and the impedance circuit 19 having the same impedance are connected in the same manner as shown in FIG.

This modified embodiment also shares the resistors 25 and 26, so that the output circuit and the feedback circuit are completely symmetrical, and the tone control circuit's resistor, variable resistor, and capacitor are connected to each other with the same resistance value and the same resistance value. By selecting the capacitance, it is possible to maintain the tone control characteristic shown in FIG. 2, which is completely flat and line-symmetrical with respect to the frequency axis.

7, the capacitors 13 and 14 may be short-circuited and another capacitor may be connected between the slider of the variable resistor 15 and the resistor 26.

As explained above, according to the present invention, even when elements other than resistors, variable resistors, and capacitors that determine tone control characteristics, such as loads and DC feedback resistors of operational amplifiers, are connected, there is no interference and lines are lined up neatly on the frequency axis. Symmetrical tone control characteristics can be obtained. Also,
There is no need to cascade buffer amplifiers with high input impedance as loads, and the overall circuit configuration is simple and inexpensive.

Furthermore, selecting an unreasonably high value for the DC feedback resistance of an operational amplifier in order to maintain tone control characteristics deteriorates the drift characteristics of the operational amplifier, but according to the present invention, the tone control characteristics can be maintained without sacrificing. Since the optimum DC feedback resistor can be selected, performance can also be improved.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a tone control circuit that the applicant previously applied for. FIG. 2 is a tone control characteristic diagram of the tone control circuit of FIG. 1. FIG. 3 is a tone control characteristic diagram when a heavy load is connected to the tone control circuit of FIG. 1. FIG. 4 is a circuit diagram of a tone control circuit according to an embodiment of the present invention. FIG. 5 is a circuit diagram of a tone control circuit according to another embodiment of the present invention. FIG. 6 is a circuit diagram of a tone control circuit according to a modified embodiment of the present invention. FIG. 7 is a circuit diagram of a tone control circuit according to another modified embodiment of the present invention. 1
...Operation amplifier, 8 and 15...Variable resistor, 16
...Load, 17, 18 and 19... Impedance circuit.

Claims (1)

[Claims] 1. An output circuit including low-frequency and high-frequency tone control variable resistors whose respective sliders are grounded, and formed between an output terminal and the ground and the output terminal of an amplifier; A feedback circuit is formed symmetrically between the output terminal of the amplifier and the ground and the inverting input terminal of the amplifier, and the slider of the tone control variable resistor for low and high frequencies is at the midpoint position. At some point, the impedances of the paired circuit elements of the output circuit and the feedback circuit are set equal, and the amount of attenuation in the output circuit and the amount of feedback in the feedback circuit are adjusted by adjusting the tone control variable resistor for low and/or high frequencies. In a tone control circuit that obtains tone control characteristics by adding the amount of attenuation and feedback that vary according to the position of the actuator, an impedance circuit with an impedance equal to the impedance of the load connected to the output terminal is connected to the inverting input terminal of the amplifier. A tone control circuit characterized in that it is connected to. 2 Contains low-frequency and high-frequency tone control variable resistors whose respective sliders are grounded, and an output circuit formed between the output terminal and the ground and the output terminal of the amplifier, and an output circuit formed symmetrically with the output circuit. It is equipped with a feedback circuit formed between the output terminal of the amplifier and the ground and the inverting input terminal of the amplifier, and when the slider of the tone control variable resistor for low and high frequencies is at the midpoint position, the output circuit and Set the impedance of each circuit element that pairs with the feedback circuit to be equal, and set the attenuation amount in the output circuit and the feedback amount in the feedback circuit to the position of the slider of the tone control variable resistor for low frequency and/or high frequency. In a tone control circuit that obtains tone control characteristics by adding attenuation amounts and feedback amounts, the output terminal and A tone control circuit characterized in that it is connected between the output end of an amplifier.