JP6292614B2 - Sound quality adjustment circuit - Google Patents

Description

  The present invention relates to a sound quality adjustment circuit using an electron tube (vacuum tube) that can arbitrarily enhance or suppress, for example, a low frequency component and a high frequency component of an audio signal.

A PG feedback type sound quality adjustment circuit is known as one of the sound quality adjustment circuits using an electron tube, and a typical example is a so-called Lux type sound quality adjustment circuit.
This Lux type sound quality adjustment circuit is disclosed in, for example, Non-Patent Document 1, and the configuration of this sound quality adjustment circuit is shown in FIG.

As shown in FIG. 5, the Lux type sound quality adjusting circuit uses a triode as both the first electron tube Q11 and the second electron tube Q12, and between the plates of the first and second electron tubes Q11, Q12. The sound quality adjustment circuit unit TC11 is inserted.
The output impedance of the first electron tube Q11 is set low, and a part of the sound quality adjustment circuit unit TC11 is arranged in a state in which a negative feedback circuit is configured between the plate and the grid of the second electron tube Q12.

  Note that VR11 in the sound quality adjustment circuit unit TC11 is a potentiometer that enhances or suppresses the low frequency component of the audio signal, and VR12 is a potentiometer that enhances or suppresses the high frequency component of the audio signal.

Between the cathodes of the first and second electron tubes Q11 and Q12 described above and the reference potential point (ground potential) of the circuit, cathode resistors R11 and R12 having different values for generating self-bias are respectively provided. The plate resistors R13 and R14 having different values are also connected between the plates of the electron tubes Q11 and Q12 and the DC operating power source + B.
Therefore, DC cut capacitors C11 and C12 must be inserted at the input / output terminals a and b of the sound quality adjusting circuit unit TC11 connected between the plates of the electron tubes Q11 and Q12 because the DC potentials are different.

For this reason, not only the DC cut capacitors C11 and C12 described above are required in the circuit configuration of the sound quality adjusting circuit, but the DC cut capacitors C11 and C12 function as reactance fluctuation components depending on the input frequency.
Therefore, it is difficult to set the input / output characteristics of the sound quality adjustment circuit to be flat at the center positions of the potentiometers VR11 and VR12 that control the low frequency component and the high frequency component of the audio signal. Arise.

  In the conventional sound quality adjusting circuit shown in FIG. 5, since the first and second electron tubes Q11 and Q12 constitute a PG feedback circuit, the first and second electron tubes are used. The total gain (voltage gain) is “1”, and it is difficult to adjust the voltage gain in the sound quality adjustment circuit. Furthermore, since the PG feedback type circuit is configured, there is an inconvenient problem in circuit design that an inverted signal is output with respect to the input signal.

LUXMAN website "LUXMAN tube amplifier kit A1020 specifications" Internet <URL: http://audio-heritage.jp/LUXMAN/kit/a1020.html> [Search on March 25, 2014]

The present invention has been made paying attention to the above-mentioned problems of the sound quality adjustment circuit shown as the conventional example, and solves the conventional problems of the circuit configuration described above while using the first and second electron tubes. It is an object of the present invention to provide a sound quality adjustment circuit that can be used.
It is another object of the present invention to provide a sound quality adjusting circuit that can obtain a substantially flat frequency characteristic at the center position of a potentiometer that selects the degree of enhancement or suppression of the band frequency.

The sound quality adjusting circuit according to the present invention, which has been made to solve the above-mentioned problems, includes a first and a second one in which the same bias voltage is applied to each grid and the same load circuit is connected to each plate. An electron tube, and a sound quality adjusting circuit unit connected between the plates of the first and second electron tubes and returning the plate output of the second electron tube to the grid of the second electron tube; An input signal is supplied to the grid of the electron tube, and a sound quality adjustment circuit that outputs a signal whose sound quality is adjusted from the plate of the second electron tube, and the sound quality adjustment circuit unit includes a first terminal, a second terminal, and a slide. A low-frequency adjustment potentiometer and a high-frequency adjustment potentiometer each having a moving terminal are provided, and a first terminal of the low-frequency adjustment potentiometer is connected to a first electron tube via a first resistor. The second terminal of the potentiometer for low-frequency adjustment is directly connected to the plate of the second electron tube via the second resistor, and the first terminal of the potentiometer for high-frequency adjustment is connected to the first electron tube. The second terminal of the high range adjustment potentiometer is directly connected to the plate of the second electron tube, and the sliding terminal of the high range adjustment potentiometer is connected in series with the third resistor and the first capacitor. The circuit is connected to the second terminal of the low-frequency adjustment potentiometer, and a second capacitor is connected between the first and second terminals of the low-frequency adjustment potentiometer so that the low-frequency adjustment potentiometer slides. The terminal is connected to the grid of the second electron tube through a third capacitor .

In this case, preferably, the cathodes of the first and second electron tubes are connected in common, and a voltage drop element that generates a common self-bias between the cathode and the reference potential point is connected, and the first and second electron tubes are connected. A configuration in which a grid resistor is connected between each grid and the reference potential point can be employed.
Preferably, the first and second constant current sources functioning as the load circuit are respectively connected between the plates of the first and second electron tubes and a common DC power source. Can do.

Further, a DC cut capacitor and a negative feedback resistor are connected in series between the plate and grid of the first electron tube, and an input-side negative feedback resistor is connected in series between the grid of the first electron tube and the signal input terminal. A connected configuration can also be suitably employed.
In addition, it is desirable that the first and second electron tubes described above are constituted by bitriode electron tubes.

  According to the above-described sound quality adjusting circuit according to the present invention, the same bias voltage is applied to the grids of the first and second electron tubes, and the same load circuit is connected to each plate. The plate potentials of the electron tubes can always be set to the same value.

Therefore, it is not necessary to provide a DC cut capacitor between the sound quality adjusting circuit unit connected between the plates (points a and b) of the first and second electron tubes. Can be reduced.
In addition, since the output impedance of each plate of the first and second electron tubes is the same, setting the sound quality adjusting potentiometer to the midpoint ensures that the input / output frequency characteristics are flat (flat). be able to.

  Further, since the first electron tube functions as an inverting amplifier, a negative feedback resistor is inserted from the plate to the grid side, and an input side negative feedback resistor is connected in series between the grid and the signal input terminal, thereby providing a voltage gain. Can be adjusted. The sound quality adjustment circuit including the first and second electron tubes can make the input / output characteristics non-inverted output.

1 is a circuit configuration diagram showing a first form of a sound quality adjustment circuit according to the present invention; FIG. It is a characteristic view when the sound quality adjustment control in the 1st form shown in FIG. 1 is set flat. It is a characteristic view showing the control range (MAX-MIN) of the sound quality adjustment control in the first embodiment. It is the circuit block diagram which showed the 2nd form of the sound quality adjustment circuit which concerns on this invention. It is a circuit block diagram which showed an example of the conventional sound quality adjustment circuit.

A sound quality adjusting circuit according to the present invention will be described below based on the embodiments shown in the drawings. FIG. 1 is a circuit configuration diagram showing the first embodiment. In the first embodiment, bitriodes are used as the first and second electron tubes Q1 and Q2.
The cathodes of the first and second electron tubes Q1 and Q2 are connected in common, and a voltage drop element (Zener diode) ZD1 that generates a common self-bias with the reference potential point (earth) of the circuit, A cathode bypass capacitor Ck is connected.

In addition, grid resistors Rg1 and Rg2 are connected between the grids of the first and second electron tubes Q1 and Q2 and the reference potential point, respectively, and each grid is set as a reference potential point.
The circuit configuration shown in FIG. 1 employs a self-bias method. For example, the cathodes of the first and second electron tubes Q1 and Q2 are directly connected to a reference potential point, and the grid resistors Rg1 and Rg2 are connected. It is also possible to adopt a fixed bias system in which the same bias voltage is connected to each grid and the same bias voltage is applied to each grid.

  First and second constant current elements (constant current diodes) Ic1 and Ic2 functioning as the same load circuit are connected to the plates of the first and second electron tubes Q1 and Q2, respectively. The constant current elements Ic1 and Ic2 are connected to a common DC operating power source + B. Further, a sound quality adjustment circuit unit TC1 is connected between the plates of the first and second electron tubes Q1 and Q2, and the output of the second electron tube Q2 is part of the sound quality adjustment circuit unit TC1 from the plate. The PG feedback type sound quality adjustment circuit is configured to be fed back to the grid via the.

The sound quality adjustment circuit unit TC1 is provided with a potentiometer VR1 for enhancing or suppressing the low frequency component of the audio signal and a potentiometer VR2 for enhancing or suppressing the high frequency component of the audio signal.
The grid of the first electron tube Q1 constitutes an audio signal input terminal In, and the plate of the second electron tube Q2 constitutes an audio signal output terminal Out via a DC cut capacitor C4.
Further, as shown in FIG. 1, the sound quality adjustment circuit unit TC1 includes a low-frequency adjustment potentiometer VR1 and a high-frequency adjustment potentiometer VR2 each having a first terminal, a second terminal, and a sliding terminal. The first terminal of the band adjustment potentiometer VR1 is directly connected to the plate of the first electron tube via the first resistor R1, and the second terminal of the low band adjustment potentiometer VR1 is connected to the second terminal via the second resistor R2. Directly connected to the electron tube plate.
The first terminal of the high frequency adjustment potentiometer VR2 is directly connected to the plate of the first electron tube, and the second terminal of the high frequency adjustment potentiometer VR2 is directly connected to the plate of the second electron tube.
In addition, the sliding terminal of the high-frequency adjustment potentiometer VR2 is connected to the second terminal of the low-frequency adjustment potentiometer VR1 through the series circuit of the third resistor R3 and the first capacitor C1, and the low-frequency adjustment The second capacitor C2 is connected between the first and second terminals of the potentiometer VR1, and the sliding terminal of the low-frequency adjusting potentiometer VR1 is connected to the grid of the second electron tube via the third capacitor C3. Yes.

It should be noted that the values of the respective elements constituting the above-described sound quality adjustment circuit unit TC1 are preferably as follows, and the first and second electron tubes Q1 and Q2 are preferably bitriodes “E88CC” Can be suitably used.
VR1 = 500KΩ, VR2 = 500KΩ, R1 = 100KΩ, R2 = 100KΩ, R3 = 200KΩ, C1 = 680pF, C2 = 4400pF, C3 = 0.1μF

  According to the sound quality adjusting circuit shown in FIG. 1, the same grid bias is applied to the grids of the first and second electron tubes Q1 and Q2, and the same load circuit is connected to each plate. Therefore, the sound quality adjustment circuit unit TC1 connected between the plates does not need to have a DC cut capacitor at points a and b as in the conventional example shown in FIG. Therefore, the circuit can be simplified.

  In the example shown in FIG. 1, it is necessary to provide a DC cut capacitor C3 immediately before the grid of the second electron tube Q2 that performs PG feedback, that is, at point c. However, since the DC cut capacitor C3 has a high input impedance of the electron tube Q2, its capacitance value is small and it can sufficiently function.

  Further, according to the sound quality adjustment circuit shown in FIG. 1, since the output impedances of the plates of the first and second electron tubes are the same, by setting the potentiometers VR1 and VR2 for sound quality adjustment to the middle points, The input / output frequency characteristics can be reliably set flat.

FIG. 2 shows measured values of frequency characteristics when the potentiometers VR1 and VR2 for low-frequency and high-frequency control in the sound quality adjustment circuit shown in FIG. As shown in the actual measurement values, according to the embodiment shown in FIG. 1, it can be said that the input / output frequency characteristics can be reliably set flat.
FIG. 3 also shows measured values showing the sound quality adjustment range when the potentiometers VR1 and VR2 in the sound quality adjustment circuit shown in FIG. 1 are set to the maximum value (MAX) and the minimum value (MIN).

FIG. 4 is a circuit configuration diagram showing a second embodiment of the sound quality adjusting circuit according to the present invention, which improves the voltage gain (Gain) of the first electron tube Q1 and increases the overall gain of the sound quality adjusting circuit. An improved example is shown. That is, a DC cut capacitor C5 and a negative feedback resistor Rf are connected in series between the plate of the first electron tube Q1 and the grid, and the input side negative is connected between the grid of the first electron tube Q1 and the signal input terminal In. A feedback resistor Rs is connected in series.
The other circuit configuration as the sound quality adjustment circuit is the same as that shown in FIG.

In this second embodiment, the signal applied to the grid through the resistor Rs is amplified by the electron tube Q1 and appears on the plate, which forms a PG feedback circuit that is fed back to the grid through the resistor Rf. . According to this configuration, the voltage gain by the electron tube Q1 can be determined approximately by Rf / Rs. Therefore, by appropriately selecting the values of the negative feedback resistor Rf and the input-side negative feedback resistor Rs, the overall gain of the sound quality adjusting circuit including the first and second electron tubes Q1 and Q2 can be improved by several times. It becomes possible.
In the second embodiment shown in FIG. 4 as well, similar to the first embodiment shown in FIG. 1, the operational effects as described in the column of the effect of the invention described above can be obtained.

Q1 First electron tube Q2 Second electron tube Ic1, Ic2 Constant current source (load circuit)
Rg1, Rg2 Grid resistance ZD1 Zener diode (voltage drop element)
Ck Cathode bypass capacitor TC1 Sound quality adjustment circuit VR1 Low-frequency adjustment potentiometer VR2 High-frequency adjustment potentiometer R1-R3 resistors C1-C5 capacitors Rf, Rs Negative feedback resistors

Claims (5)

The same bias voltage is applied to each grid and the same load circuit is connected to each plate. The first and second electron tubes are connected between the plates of the first and second electron tubes. And a sound quality adjustment circuit unit that feeds back the plate output of the second electron tube to the grid of the second electron tube.
A sound quality adjusting circuit for supplying an input signal to the grid of the first electron tube and outputting a signal whose sound quality has been adjusted from the plate of the second electron tube ;
The sound quality adjustment circuit unit includes a low-frequency adjustment potentiometer (VR1) and a high-frequency adjustment potentiometer (VR2) each having a first terminal, a second terminal, and a sliding terminal.
The first terminal of the low-frequency adjustment potentiometer (VR1) is directly connected to the plate of the first electron tube via the first resistor (R1), and the second terminal of the low-frequency adjustment potentiometer (VR1) is connected to the first terminal. Directly connected to the plate of the second electron tube via two resistors (R2),
The first terminal of the high frequency adjustment potentiometer (VR2) is directly connected to the plate of the first electron tube, the second terminal of the high frequency adjustment potentiometer (VR2) is directly connected to the plate of the second electron tube,
In addition, the sliding terminal of the high frequency adjustment potentiometer (VR2) is connected to the second terminal of the low frequency adjustment potentiometer (VR1) through a series circuit of the third resistor (R3) and the first capacitor (C1). In addition, a second capacitor (C2) is connected between the first and second terminals of the low-frequency adjustment potentiometer (VR1),
A low-frequency adjustment potentiometer (VR1) has a sliding terminal connected to a grid of a second electron tube via a third capacitor (C3) .   The cathodes of the first and second electron tubes are connected in common, and a voltage drop element that generates a common self-bias is connected to a reference potential point. The grids of the first and second electron tubes and the reference The sound quality adjusting circuit according to claim 1, wherein a grid resistor is connected between each of the potential points.   The first and second constant current sources functioning as the load circuit are respectively connected between the plates of the first and second electron tubes and a common DC power source. The sound quality adjusting circuit according to claim 1 or 2.   A DC cut capacitor and a negative feedback resistor are connected in series between the plate and grid of the first electron tube, and an input-side negative feedback resistor is connected in series between the grid of the first electron tube and the signal input terminal. 4. The sound quality adjusting circuit according to claim 1, wherein the sound quality adjusting circuit is provided.   5. The sound quality adjusting circuit according to claim 1, wherein the first and second electron tubes are constituted by a bitriode electron tube. 6.

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