JPH0139034Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an audio circuit for, for example, a television receiver.

Conventionally, in this type of circuit, since the speaker built into the receiver is generally small, the low range of the frequency characteristic is enhanced, so-called low boost is applied, so that the characteristic is audibly flat.

However, if you try to connect a large external speaker to this type of circuit, as mentioned above, if the signal is still low boosted, the low range will be enhanced too much, resulting in extremely unpleasant sound. There is.

Taking these points into consideration, the present invention has been designed to eliminate low boost with a simple configuration, and even with low boost removed, when the volume is reduced, the low range is enhanced, so that a flat characteristic is always obtained. This is what I did. Referring to the drawings below,
Let us explain one embodiment of the present invention.

In FIG. 1, an input terminal 1 is connected to one end of a capacitor 2, and the other end of the capacitor 2 is grounded through the resistance components of a resistor 3 and a variable resistor 4. The slider of this variable resistor 4 is a capacitor 5,
It is connected to the input terminal of an operational amplifier 7 through a resistor 6 . The output terminal of this amplifier 7 is connected to a speaker 8. At the same time, the output terminal of the amplifier 7 is connected to one end of a capacitor 10 and a resistor 11 through a resistor 9.
1 is grounded through a resistor 12 and a capacitor 13, and the other ends of the capacitor 10 and resistor 11 are connected to the inverting input terminal of the amplifier 7.

A switch 14 is also provided in parallel to the capacitor 2.

In this circuit, when the switch 14 is on, a signal from the input terminal 1 is supplied to the amplifier 7 through the variable resistor 4 etc., and a signal from the amplifier 7 is supplied to the speaker 8. At the same time, the signal from the amplifier 7 is negatively fed back through a circuit such as the resistor 9, and is low-boosted. By operating the variable resistor 4, the volume from the speaker 8 is controlled.

On the other hand, when the switch 14 is off,
A high-pass filter is configured by the capacitor 2, a circuit such as the variable resistor 4, and the input impedance of the amplifier 7.

Here, the roll-off frequency _c of this high-pass filter is, assuming that the impedance on the input terminal 1 side is 0, _c = 1/2πC | Zin | However, C is the capacitance value of capacitor 2 Zin is the resistor 3 seen from the capacitor 2 side The impedance is as follows.

In this case, the value of Zin changes by operating the variable resistor 4. That is, when the slider of the variable resistor 4 is set to the upper limit, the input impedance of the amplifier 7 is connected in parallel to the resistance component of the variable resistor 4, and the overall resistance value becomes small. As the slider of the variable resistor 4 is lowered, the influence of the input impedance becomes smaller and the overall resistance value becomes larger.

Therefore, the roll-off frequency _c of this high-pass filter becomes higher when the slider of the variable resistor 4 is raised, and becomes lower when it is lowered.

In this circuit, the roll-off frequency _{c nax} when the slider of variable resistor 4 is set at the upper limit
is equal to the roll-off frequency of the low boost of the amplifier 7, and by making the absolute values of the slopes of the characteristics equal, when the slider of the variable resistor 4 is set to the upper limit, that is, the volume is maximized, Frequency characteristics become flat.

Further, as the slider of the variable resistor 4 is lowered, the roll-off frequency _c becomes lower, and the influence of the low boost becomes larger, and the low frequency range is enhanced.

That is, in this circuit, when the switch 14 is on, normal low boost is performed, and when the switch 14 is off, the frequency response is flattened at maximum volume, and as the volume is lowered, the low range is enhanced. Ru.

This is how the acoustic circuit is constructed.
According to the present invention, when using a built-in speaker or a small speaker, turning on the switch 14 performs low boost, and when using a large speaker, turning off the switch 14 flattens the frequency response. In this state, when the volume is further reduced, the low range is enhanced, producing a so-called loudness effect, and the audible characteristic can always be flat.

Note that in the conventional circuit, the capacitor 10,
A switch was installed between both ends of the resistor 11, and low boost was removed by turning on this switch, but in that case, the switch must be installed on the circuit board or wired using a shielded wire. In addition, if it is provided on the board, it becomes impossible for the user to switch it arbitrarily, and wiring the shield wire has the drawback of increasing the number of manufacturing steps.

In this regard, according to the present invention, the switch 14 and the capacitor 2 are located near the input terminal 1, which eliminates the need for extra wiring, facilitates manufacturing, and allows the user to switch safely. Become.

Furthermore, an example of the values of each element of the specific circuit is shown below.

Capacitor 2: 0.015μF Resistor 3: 39kΩ Variable resistor 4: 100kΩ Capacitor 5: 4.7μF Resistor 6: 56Ω Resistor 9: 5.6kΩ Capacitor 10: 0.15μF Resistor 11: 12kΩ Resistor 12: 100Ω Capacitor 13: 100μF According to this circuit, when the switch 14 is turned on, the frequency response is low boosted as shown in curve A in Figure 2, and when the volume is at maximum and the switch 14 is turned off, it becomes flat as shown in curve B in Figure 2. If the volume is lowered in this state, the low range will be enhanced as shown by curve C in Figure 2.

[Brief explanation of the drawing]

FIG. 1 is a connection diagram of an example of the present invention, and FIG. 2 is a waveform diagram for explaining the same. 1 is an input terminal; 2, 5, 10, and 13 are capacitors; 3, 6, 9, 11, and 12 are resistors; 4 is a variable resistor; 7 is an amplifier; and 8 is a speaker.

Claims (1)

[Scope of utility model registration request] The input terminal to which the audio signal is supplied is connected to one end of a capacitor, this capacitor and a variable resistor constitute a high pass filter, and the slider of this variable resistor is connected to the input terminal of an amplifier with low frequency enhancement. terminal and connect a switch in parallel to the capacitor, and when the switch is off, the resistance value of the variable resistor is increased to reduce the level of the audio signal and increase the cutoff frequency of the high-pass filter. and an acoustic circuit in which the level of the audio signal is increased by decreasing the resistance value, and the cutoff frequency of the high-pass filter is lowered, so that the frequency characteristics can be changed according to the level of the audio signal.