JPS6324714Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a low-frequency characteristic improvement circuit equipped with a bypass switch, and its purpose is to prevent low-frequency saturation of a power amplifier and damage to a speaker.

Conventionally, an acoustic device as shown in FIG. 1 is known. In Fig. 1, the input signal applied to the input terminal 1 is amplified by the preamplifier 2, and then sent to the volume 3 to which a loudness circuit is added, which performs high-frequency enhancement, high-frequency attenuation, low-frequency enhancement, and low-frequency attenuation. The output signal of the main amplifier 5 is applied to the main amplifier 5 via the tone control circuit 4 which performs the following, and the output signal of the main amplifier 5 is further applied to the speaker 6, where it is electrically and acoustically converted to generate sound.

Although the speaker 6 generally has a characteristic in which its frequency response drops sharply below the low cutoff frequency, it has a characteristic as shown by the dotted line A in Figure 2, which corrects the audibility of the human ear. The loudness circuit and the tone control circuit 4, which has characteristics as shown by the solid line B in FIG. I can't do that.

In addition, in addition to the loudness circuit and tone control circuit, there have recently been some audio devices equipped with a low-frequency boost main stage that has characteristics opposite to the low-frequency characteristics of the speaker and performs equivalent low-frequency compensation. However, this was not very desirable because of problems such as excessive input and an increase in low-frequency distortion components.

A circuit designed to improve the low-frequency characteristics is shown in FIG. 3. In Figure 3,
7 is an amplifier with a gain of 1, 8 and 9 are capacitors,
10 and 11 are resistors, and the whole constitutes a positive feedback type secondary system bypass filter. This circuit has the characteristics shown in Figure 2C, that is, for example, when the low cutoff frequency of a speaker is 100Hz, it has a single peak characteristic with a peak at the center frequency near 100Hz, and a flat characteristic in the higher frequency range. It has an attenuation characteristic of 12 dB/Oct in the lower frequency range, and is usually inserted between the volume 3 and tone control circuit 4 in FIG. However, since the circuit shown in Fig. 3 has the above-mentioned single-peak characteristic, it can vary from 5 dB to 13
It is possible to enhance the low frequency range by about dB, and
Since it has the above-mentioned attenuation characteristic, it has the advantage of being able to block at least signals outside the audible band and improving cross-modulation distortion and the like.

However, when the low frequency enhancement using the circuit shown in Figure 3 and the low frequency enhancement using the tone control circuit are performed simultaneously, the level of the low frequency component becomes too large, exceeding the dynamic range of the power amplifier and causing saturation. When using speakers with low input resistance, there is a risk of distortion or damage to the speaker.

The present invention has been developed in view of the above points, and will be described below based on embodiments with reference to the drawings. FIG. 4 is a circuit diagram showing an embodiment of the present invention, in which 12 is a volume equipped with a loudness circuit, 13 is an input transistor for impedance conversion, 14 is an amplification transistor 15, a capacitor 16 and 1
7, a circuit for improving the low frequency characteristics consisting of resistors 18 and 19, 20 a tone control circuit, and 21 a circuit 14 for improving the low frequency characteristics.
The switch 21 is controlled in conjunction with a variable resistor 22 of the tone control circuit 20 that enhances bass.

Assuming that the tone control circuit 20 is not operated and the contacts of the switch 21 are in the state shown in the figure, a voltage is applied from the volume 12 via the input transistor 13 to the input terminal of the circuit 14 for improving the low frequency characteristics. The signal transmitted through the circuit 14 is given the characteristics shown in FIG. Therefore, the sound generated from the speaker has low frequency extension due to low frequency enhancement, and has less distortion and noise due to the attenuation characteristics.

Next, operate the tone control circuit 20,
If bass enhancement is performed, the output signal of the input transistor 13 will be as follows:
The signal is applied to the tone control circuit 20 via the switch 21 without passing through the circuit 14 for improving low frequency characteristics. Therefore, double low-frequency enhancement by both the circuit 14 and the tone control circuit 20 is not performed, and saturation in the subsequent main amplifier (not shown) and excessive input to the speaker are prevented.

As described above, according to the present invention, it is possible to prevent double low-frequency enhancement by both the circuit for improving low-frequency characteristics and the tone control circuit, so that It is possible to prevent saturation and excessive input to the speakers, and in that case, the circuit for improving low frequency characteristics is bypassed depending on the position of the variable resistor in the tone control circuit. This has the advantage that there is no need to perform a special operation of switching a switch to bypass the circuit.

[Brief explanation of the drawing]

FIG. 1 is a circuit block diagram showing an example of an acoustic device, and FIG. 2 is a characteristic diagram for explaining the present invention.
FIG. 3 is a circuit diagram showing an example of a circuit for improving low frequency characteristics, and FIG. 4 is a circuit diagram showing an embodiment of the present invention. Explanation of main drawing numbers, 14 ...Circuit for improving low frequency characteristics, 20...Tone control circuit, 2
1...Switch.

Claims (1)

[Scope of utility model registration request] In an audio device equipped with a tone control circuit having a variable resistance for bass enhancement, the first function is to enhance the low frequency range with a center frequency near the low frequency cutoff frequency of the speaker, and the first function is to enhance the low frequency range with a center frequency near the low cutoff frequency of the speaker. A circuit having a second function of attenuating the range frequency and a switch for bypassing the circuit are provided, and the switch is switched according to the position of the variable resistor to bypass the circuit. Range characteristic improvement circuit.