JPS6281109A - Loudness control circuit - Google Patents

Abstract

PURPOSE:To attain excellent loudness control by using an output signal of an output signal level detection circuit of an amplifier circuit so as to control a resistance value of a voltage controlled resistor circuit. CONSTITUTION:A signal level detection circuit 5 is provided, which grounds a feedback circuit 1a of an amplifier circuit 1 having a feedback circuit 1a amplifying a sound signal through a series circuit comprising a connection switch 2, a voltage controlled resistance circuit 3 and a series resonance circuit 4 and detects an output signal level of the amplifier circuit 1, and an output signal of the signal level detection circuit 5 is used to control the resistance of the voltage controlled resistance circuit 3. As the output signal level of the amplifier circuit 1 is decreased, the negative feedback quantity of a low frequency is decreased and the boosting quantity at the frequency is increased by it, then an excellent dynamic loudness control is attained. Since there is no problem that the sound signal is to be clipped, a sound source having a wide dynamic range is used and a powerful sound is reproduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a loudness control circuit used in audio equipment and the like.

[Summary of the invention]

The present invention relates to a loudness control circuit used in audio equipment, etc., in which an amplifier circuit having a feedback circuit for amplifying an audio signal is connected to the feedback circuit through a series circuit of a switch, a voltage controlled resistance circuit, and a series resonant circuit. A signal level detection circuit is provided for detecting the output signal level of this amplifier circuit, and the output signal of this signal level detection circuit is used to control the resistance value of this voltage control resistor circuit, thereby dynamically controlling the loudness. In addition, there is no worry that the signal will be clipped by the output amplification circuit even when inputting a large signal or using a tone control device, so you can use a sound source with a wide dynamic range and reproduce powerful sound. Furthermore, by changing the constants of this series resonant circuit, the boost frequency and boost amount can be set relatively freely.

[Conventional technology]

In general, the human ear has a characteristic that as the volume decreases, it becomes harder to hear low and high frequencies.

Therefore, conventional loudness control circuits have been proposed that electrically correct this problem so that even at low volumes, the sound can be heard in a well-balanced manner over the entire frequency range.

This conventional loudness control circuit is provided in connection with the volume, and as the volume is turned down (lower the volume), the degree of bass (treble) enhancement increases.

[Problem that the invention seeks to solve]

However, in conventional loudness control circuits, booth 1-1 was determined by the volume position (decrease II), so when a large signal is input or when used in conjunction with a tone control device, the audio output of the audio equipment is amplified. If there is a risk that the audio signal of the boost frequency part in the circuit may be clipped, and if the supplied audio signal level varies depending on the connected audio equipment (tape recorder, tuner, CD player, etc.), adjust the volume. Even if you listen at the same volume, the degree of enhancement is determined by the position of the volume, so there is an inconvenience that the degree of enhancement of bass (treble) sounds differs.

In view of this, the present invention enables good loudness control even when a large signal is input, when a tone control device is used together, or when the level of the input audio signal differs, and it is possible to use a sound source with a wide dynamic range. The purpose is to make it possible to use it to reproduce powerful sounds.

Means for Solving Problem C] The loudness control circuit of the present invention has an amplifier circuit (11 feedback circuits (1a) connected to each other) having a feedback circuit (la) for amplifying an audio signal as shown in FIGS. 1 and 2. switch (2
), a signal level detection circuit (5) is provided which is grounded via a series circuit of a voltage controlled resistance circuit (3) and a series resonant circuit (4) and which detects the output signal level of this amplifier circuit +1). The resistance value of this voltage controlled resistance circuit (3) is controlled by the output signal of the detection circuit (5).

[Effect]

According to the present invention, as the output signal level of the amplifier circuit (1) decreases, the resistance value of the voltage-controlled resistance circuit (3) is decreased, and the low frequency negative voltage determined by the series resonant circuit (4) is Since the amount of feedback is small and the amount of boost at that frequency is increased accordingly, good dynamic loudness control can be achieved, and when a large signal is input,
Even when a tone control device is used, there is no worry that the audio signal will be clipped by the audio output amplification circuit, so it is possible to use a sound source with a wide dynamic range and reproduce powerful sound. The level of the signal determines the degree of amplification of the audio signal, so even if the level of the input audio signal is different, if the volume is the same, the degree of amplification will be the same.Also, this series resonant circuit (4)
By changing the constant of , the boost frequency and boost it can be set relatively freely. Also, when this loudness control circuit is not used, the connection switch (2) is opened, but when this connection switch (2) is opened, the voltage control resistance circuit (3), the series resonant circuit (4), etc. are connected to the signal system. Since it does not become a load, there is no problem of worsening signal distortion at this time.

〔Example〕

An embodiment of the loudness control circuit of the present invention will be described below with reference to FIGS. 1 and 2. FIG. 1 shows a block diagram of this embodiment, and FIG. 2 shows a specific example of FIG. 1. , will be explained here with reference to FIG.

In FIGS. 1 and 2, (6) indicates an input terminal for audio signals, and (7) indicates a common terminal. This audio signal input terminal (6) is connected to the non-inverting input terminal (■) of the operational amplifier circuit (1b) constituting the amplifier circuit t1) via a series circuit of a capacitor and a resistor, and this non-inverting input terminal Φ is connected to the resistor. Connect to the common terminal (7) through the device. The output terminal of this operational amplifier circuit (1b) is connected via a series circuit of a capacitor and a resistor to an audio signal output terminal (8) connected to a speaker via an audio output amplifier circuit, and this operational amplifier circuit ( The output terminal of lb) is connected to the inverting input terminal e of this operational amplifier circuit (1b) through a parallel circuit of a resistor (1c) and a capacitor (1d) that constitute a negative feedback circuit (1a), and this operation The inverting input terminal e of the amplifier circuit (1b) is connected to the capacitor (1e) that constitutes the negative feedback circuit (1a).
and a common terminal (7) through a series circuit of a resistor (1f)
Connect to. In this case, the operational amplifier circuit (1b) and the negative feedback circuit (1a) constitute a so-called flat amplifier circuit in which the frequency-output signal level is flat, as shown in FIG.

Further, in this example, this negative feedback circuit (1a) is connected to a connection switch (2), a voltage controlled resistance circuit (3) and, for example, a
It is grounded through a series circuit of a series resonant circuit (4) having a center frequency of 11z. In the example shown in FIG. 2, the connection point between the capacitor (le) and the resistor (if) of this negative feedback circuit (1a) is connected to the variable resistance element of the voltage controlled resistance circuit via the connection switch (2). It is connected to the drain of the channel MO3 field effect transistor (3a), and this drain is connected to the common terminal (7) through a resistor, and this drain is connected to this MO3 field effect transistor (3a) through a series circuit of a capacitor and a resistor. Connect to the gate of 3a). In this case MO3 field effect transistor (3a)
The drain-source resistance value of this MO3 field effect transistor (3a) is controlled by controlling the gate voltage of the MO3 field effect transistor (3a). In this example, the resistance value between the drain and the source is controlled according to the magnitude of the absolute value of the negative voltage supplied to the gate.

The source of this MO3 field effect transistor (3a) is connected to the base of the npn transistor (4a) via a series circuit of capacitors (4b) and (4C) of a semiconductor resonant circuit constituting a series resonant circuit (4), The collector of this transistor (4a) is connected through a resistor (4d) to the positive power supply terminal B to which a positive DC voltage is supplied, and the emitter of this transistor (4a) is connected through a resistor (4e) to a negative power supply terminal B. Connect to the negative power supply terminal -B to which DC voltage is supplied.

Also, the connection point of capacitors (4b) and (4c) is connected to the emitter of this transistor (4a) via a resistor (4f), and the base of this transistor (4a) is connected to a common terminal via a resistor (4g). Connect to (7). In this case, the center frequency of resonance of the semiconductor resonant circuit constituting the series resonant circuit (4) is set to a low frequency, for example, 100 Hz. Further, the output terminal (8) of the amplifier circuit (1) is connected to the common terminal (7) via a series circuit of two resistors (5a) and (5b) for detecting the signal level, and this resistor (5
Connect the connection point of a) and (5b) to the non-inverting input terminal ■ of the operational amplifier circuit constituting the control amplifier circuit (5C), and connect the output terminal of this control amplifier circuit (5C) to the capacitor (5e).
It is connected to the cathode of a diode (5d) which also constitutes a level detection circuit, and the anode of this diode (5d) is connected to a common terminal (7) via a parallel circuit of a capacitor (5e) and a resistor (5r).

The output terminal of this level detection circuit, that is, the diode (5d)
and the connection point of the capacitor (5e) is connected to the gate of the MO5 field effect transistor (3a) via the resistor (3b).

Since this example is configured as described above, when this loudness control circuit is not used, the connection switch (
2) Open. At this time, the operational amplifier circuit (lb) and the negative feedback circuit (la) become an amplifier circuit with flat frequency characteristics, regardless of the output signal level, as shown in Figure 3, and in this case, the connection switch (2) is opened. Therefore, the voltage controlled resistance circuit (3), the series resonant circuit (4), etc. do not become a load on the signal system, and at this time, the distortion of the audio signal is not worsened.

Further, when using this loudness control circuit, this connection switch (2) is closed. At this time, the resistance value between the drain and source of the MO3 field effect transistor (3a) is controlled according to the output signal level obtained at the output terminal (8) of the amplifier circuit (1), that is, as shown in FIG. As the output signal level of the circuit (11) becomes smaller, the resistance value of this MO3 field effect transistor (3a) becomes smaller, and the amount of negative feedback at a low frequency, for example, 10011z, determined by the series resonant circuit (4) is accordingly reduced. When the boost [1 at the frequency, for example, 100 Hz, becomes that large, and the output signal level is large, the resistance value of this MO3 field effect transistor (3a) becomes large, and this negative feedback circuit (1a)
The γ-reverberation becomes smaller, and in this case, the frequency characteristic becomes flat, and good cloudiness control can be achieved. In addition, in this example, the frequency characteristics become flat when the output signal level increases, so the audio signal will not be clipped by the audio output amplifier circuit even when a large signal is input or when a tone control device is used together. It is possible to play back powerful music using a sound source with a wide dynamic range. In addition, in this example, since the degree of amplification of the audio signal is determined by the output signal level of the amplifier circuit (1), the input audio signal is There is an advantage that even if the level of the sound is different, the degree of amplification will be the same when the volume is the same. In addition, in this example, it is relatively easy to change the constant of the series resonant circuit (4) and change the resistance value between the drain and source of the MO3 field effect transistor (3a), so you can use it relatively freely. This boost frequency and boost t-
There is an advantage in being able to set i.

It goes without saying that the present invention is not limited to the above-described embodiments, and that various other configurations may be adopted without departing from the gist of the present invention.

〔Effect of the invention〕

According to the present invention, it is possible to perform good dynamic loudness control, and there is no fear that the audio signal will be clipped by the audio output amplification circuit even when a large signal is input or when a tone control device is used together, and the dynamic range is wide. You can use the sound source to play powerful music, etc., and even if the level of the input audio signal varies depending on the connected audio equipment (tape recorder, record player, CD player, etc.), the volume remains the same. , the degree of enhancement will be the same. Further, according to the present invention, there is an advantage that the boost frequency and boost m can be set relatively freely. Furthermore, in the present invention, when the loudness control circuit is not used, the connection switch (2) is opened, so that the voltage control resistance circuit (3), the series resonant circuit (4), etc. do not become a load on the signal system. There is no inconvenience that worsens the distortion of the audio signal.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the loudness control circuit of the present invention, FIG. 2 is a connection diagram showing a specific example of FIG. 1, and FIGS. 3 and 4 are diagrams for explaining the present invention. It is. (11 is an amplifier circuit, (la) is a negative feedback circuit, (2) is a connection switch, (3) is a voltage controlled resistance circuit, (4) is a series resonant circuit, and (5) is a signal level detection circuit.

Claims (1)

[Claims] A signal level detection circuit that connects the feedback circuit of an amplifier circuit having a feedback circuit that amplifies an audio signal to ground via a series circuit of a connection switch, a voltage controlled resistance circuit, and a series resonant circuit, and detects the output signal level of the amplifier circuit. A loudness control circuit characterized in that the resistance value of the voltage controlled resistance circuit is controlled by the output signal of the signal level detection circuit.