JPS609367B2 - tone control circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a tone control circuit used in an audio amplifier or the like, and particularly to a tone control circuit that can maintain good sound quality when the amount of control is relatively small.

A feedback type tone control circuit as shown in FIG. 1 is known as a general type of slave tone control circuit. This circuit is configured such that an audio input signal is supplied to a buffer amplifier 1 having a flat frequency characteristic, and the output thereof is guided to an amplifier 3 which also has a flat frequency characteristic, and a feedback circuit of the amplifier 3. A frequency characteristic adjustment circuit 2 is provided inside, and variable resistors VR-A and VR for bass adjustment and treble adjustment in this adjustment circuit 2 are provided.
-B changes the frequency characteristics of the feedback circuit as a whole, thereby changing the frequency characteristics as a whole, and shows a change in the gain-frequency characteristics as shown in FIG. Switch 4 is a tone cancel switch for directly extracting the output signal of amplifier 1 when tone control is not required, and may be omitted in some cases.

Further, unlike FIG. 1, as shown in FIG. 3, the amplifier 5 and the frequency characteristic adjustment circuit 6, which have flat frequency characteristics, are used by switching between tone control and non-tone control using switches 7a and 7b. Some have done this. The reason for doing the above is that when performing tone control, the signal passes through a frequency characteristic adjustment circuit with complex frequency characteristics, which deteriorates the sound quality in all aspects such as distortion rate and S/N. This is to ensure that the best sound quality is obtained only when canceling. However, with the conventional circuits mentioned above, good sound quality can be obtained when tone is canceled, but when trying to perform tone control, the circuit must pass through the frequency characteristic adjustment circuit, so even if you want to slightly change the frequency characteristic. , which has the disadvantage of significantly deteriorating sound quality.

This is thought to be due to the complexity of the frequency characteristic adjustment circuit and the resonance phenomenon of the capacitors present in this circuit. The present invention has been made in view of the above points, and has a configuration in which a signal that has passed through a frequency characteristic adjustment circuit and a signal that does not pass through this circuit are combined, thereby improving sound quality when the amount of control is relatively small. The present invention aims to provide a tone control circuit that can minimize deterioration. The details of the present invention will be explained below with reference to the drawings.

FIG. 4 is a diagram showing the basic configuration of the tone control circuit according to the present invention, in which an audio input signal and a signal obtained by passing this signal through a frequency characteristic adjustment circuit 11 are synthesized by a synthesis circuit 12, and the synthesized output is The configuration is such that the signal is extracted as an output signal via an amplifier 13 having flat frequency characteristics. If you do this, as the amount of tone control decreases,
A signal that passes through the frequency characteristic adjustment circuit 11 accordingly;
In other words, since the frequency characteristic adjustment circuit 11 reduces the amount of signals with deteriorated S/N, distortion rate, and other characteristics relative to the input signal amount, the deterioration of the output signal, that is, the deterioration of the audio, is relatively small. FIG. 5 is a circuit configuration diagram showing a specific embodiment of the present invention.

The audio input signal supplied to the input terminal 21 is applied to a buffer amplifier 22 consisting of an emitter follower using a transistor TR3, and the output of this amplifier 22 is branched into three paths, some of which are connected to the amplifier via a resistor R. 23
is led to the inverting input terminal T, of. The amplification degree of this amplifier 23 is determined by the ratio of its negative feedback circuit R4 to the parallel combined resistance of resistors R, , R2, and R3. Note that the non-inverting input terminal L of the amplifier 23 is grounded. The output of the buffer amplifier 22 is further guided to a frequency characteristic adjustment circuit 24.

This circuit 24 is constructed as follows. That is, the output of the buffer amplifier 22 is first passed through the frequency characteristic adjustment circuit 24 to a low frequency signal passing circuit 25 consisting of a variable resistor VR, a capacitor C, a capacitor C2, and a variable resistor V.
Transistors TR constituting the first and second phase dividing circuits via the Takagi signal passing circuit 26 consisting of R2,
, TR2 is added to each base. Note that VR,,VR
2 are for adjusting the turnover frequency on the low-frequency side and the high-frequency side, respectively. Signals having opposite phases to each other are obtained at the collectors and emitters of the transistors TR, TR2, respectively, and these signals are sent to the first and second combining circuits via capacitors C3, C4 and C5, C6, respectively. As shown in FIG. And VR3
, VR4 are led to the inverting input terminal T of the amplifier 23 via resistors R2 and R3, respectively. Therefore, a signal appears at the sliding terminal of VR4, the voltage value of which changes linearly in the in-phase direction and the anti-phase direction with respect to the signal passing through the resistor R, depending on the contact position. In this case, if the center taps of VR3 and VR4 are grounded as shown in the figure, the signal voltage at this point becomes completely zero, and if the sliding terminal contact is aligned with this point, the frequency characteristic adjustment circuit 24 The signal that has passed through does not appear at the output terminal 27, resulting in a state of tone cancellation. In the above configuration, VR3, V
Depending on the adjustment direction of R4, that is, in which direction you adjust it around the midpoint position, you can enhance or attenuate the low range or high frequencies, and the amount of tone control can be changed depending on the amount of adjustment. I can do it.

Note that the circuit composed of the resistors R, to R4 and the amplifier 23 corresponds to the combining circuit 12 and the amplifier 13 in FIG. Next, the operation of this tone control circuit will be explained in more detail using mathematical expressions.

First, the transfer function of the low-pass signal passing circuit 25 is expressed as follows. 1 1 T (S) = ▽Hajaku = ▽Hei ÷...'1l (However ~ R: Resistance value of VR, 7 = C, R) Therefore, the frequency characteristics of this circuit 25 are shown in Figure 6 a. As shown, when the angular frequency of the input signal becomes equal to 1, it decreases, and at frequencies higher than that, it decreases by B/oct.

The output of this circuit 25 is converted by a transistor TR into an in-phase component and an anti-phase component with respect to the world power, and then combined by a variable resistor VR3 via capacitors C3 and C4, and further passed through a resistor R2 to a resistor R. Vector calculation is performed on the passed signal, amplified by amplifier 23, and sent to output terminal 2.
7 as an output signal. This output signal is connected to the resistor R2
If the ratio of the signal current flowing through the resistor R to the signal current flowing through the resistor R is k, then for the input signal T〆'(S)=10kTso(S)-(10kZ+S...■-1 It has a frequency characteristic of 10S7.

Here, of course, when k=0, TZ'(S)il.

The amount of tone control normally required is up to ±IM.
Since the value of k is calculated from this, 10INB corresponds to approximately Tso'(S)=3, so if S7<<1 in the low frequency region, then (10k) From /1=3, k=2 can be found. That is, it is sufficient that the signal current passing through the resistor R2 is twice the signal current passing through the resistor R. on the other hand,
Since the 11th place old corresponds to T〆'(S)31/3, k in this case can be found as k=-2/3. That is, the signal current passing through R2 is in opposite phase to the signal current passing through R, and is -2/
If it's a needle sound, it's fine. Considering the overall frequency characteristics in this case, first of all, in the case of 110 years ago, T〆'
〈S) = skewer meeting...{3, and when the mountain = 2　'7, M(S): IT from the vessel〆'(S)l=nomori = 2.236 (about 16. Mother B )
Therefore, the overall frequency characteristic at this time is as shown by the dashed line in FIG. 6b.

On the other hand, in the case of the old 11th Q, Tso'(S) = Ki-sanou seize;...
…[41, w = 2′? When , from Bi(S) Hi band, Bi(S)l = Yesterday.

-75 Column-2 Since this is the second position, the overall frequency characteristics are as shown by the broken line in Figure 6b.

The above is an explanation for the low frequency side, but for the high frequency side, the transfer function of the Takagi signal passing circuit 26 is expressed as a shelf, and its frequency characteristics are shown by the solid line in Figure 6. The overall frequency characteristic is also opposite to the one-dot chain line and the broken line in FIG.

That is, in this circuit, variable resistors VR3 and VR4
By adjusting , it is possible to obtain a change in the gain-frequency characteristic as shown in FIG. 2, similar to the conventional circuit. As described above with reference to one embodiment, the tone control circuit of the present invention synthesizes (adds and subtracts) the signal passed through the frequency characteristic adjustment circuit 24 and the input signal, and adjusts the frequency characteristic adjustment circuit 24 to create a tone. Since control is performed, it is possible to reduce deterioration in sound quality, especially when the amount of control is small.

In other words, in the conventional feedback type tone control circuit as shown in FIG. Negative feedback always had to be applied, and as a result, a relatively large amount of signal passed through the frequency characteristic adjustment circuit, resulting in a significant deterioration in sound quality. On the other hand, according to the present invention, the signal itself passing through the frequency characteristic adjustment circuit 24 is affected by the resonance phenomenon of the capacitor existing in the frequency characteristic adjustment circuit 24, so signal deterioration is unavoidable. However, it is not necessary for the mid-range components that do not need to be controlled to pass through the frequency characteristic adjustment circuit 24 at all. Furthermore, when the amount of control is small, the amount of low-frequency or high-frequency signals passing through the frequency characteristic adjustment circuit 24 only needs to correspond to the amount of control. Therefore, according to the circuit of the present invention, the deterioration in sound quality is significantly reduced compared to the conventional circuit. In addition, in the above embodiment, the frequency characteristic adjustment circuit converts the input signal into the low frequency component and the high frequency component and the opposite phase component, and synthesizes them at an arbitrary ratio using the variable resistors for adjusting the low frequency and high frequency levels. The structure is simpler than that of a frequency characteristic adjustment circuit in which the low-frequency and high-frequency gains can be adjusted in both positive and negative directions around zero. Sariko In the above embodiment, a variable resistor with a center point tap was used as the variable resistor for adjusting the low and high level levels, and the center point tap was grounded, so the port terminal should be aligned with the center point tap position. Can be in complete tone cancellation state,
Another advantage is that there is no need for a special tone cancel switch as in the conventional case.

[Brief explanation of the drawing]

FIG. 1 is a circuit configuration diagram showing an example of a conventional tone control circuit, FIG. 2 is a diagram showing changes in its frequency characteristics, FIG. 3 is a block diagram showing another example of a conventional tone control circuit, and FIG. The figure is a block diagram showing the basic configuration of the tone control circuit according to the present invention, FIG. 5 is a circuit configuration diagram showing one embodiment of the present invention, and FIG. FIG. 4 is a diagram showing the characteristics and the overall frequency characteristics during low-frequency tone control in terms of the relationship between the angular frequency of the input signal and the transfer function. 11, 24... Frequency characteristic adjustment circuit, 12...
Synthesizing circuit, 13, 23...Amplifier, 22...
...Buffer amplifier, 25...Low frequency signal passing circuit, 26...Takagi signal passing circuit, VR.・・・・・・
Variable resistor for adjusting low frequency turnover frequency, VR2...
・…Variable resistor for high frequency turnover frequency adjustment, VR3
・・・・・・Variable resistor for adjusting low level level, VR4...
...Variable resistor for high frequency level adjustment. 1 figure, 2 crabs. Sha 3 boxes * Mugu * 5 boxes Figure 6

Claims (1)

[Claims] 1. In a tone control circuit that introduces an audio input signal and extracts the low-frequency component and high-frequency component by optionally emphasizing or attenuating the same, the low-frequency and high-frequency components that pass the low-frequency and high-frequency signals of the audio input signal, respectively, are used. a frequency signal passing circuit, first and second phase dividing circuits for extracting in-phase components and anti-phase components of respective outputs of these low-frequency and high-frequency signal passing circuits, and each of these first and second phase dividing circuits. It includes first and second synthesis circuits that synthesize output in-phase components and anti-phase components at arbitrary ratios, and a circuit that synthesizes the outputs of these first and second synthesis circuits and the audio input signal. The tone control circuit is characterized by: