JP2006340121A - Amplifier for speaker and speaker system using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an amplifier for a speaker in which the connecting work of a user is easy, neither noise nor allophone is made and good voice regenerating is possible in relation with an amplifier for the vehicle-mounted speaker which drives the speaker for a sound reproduction and the speaker system constituted using this and to provide a speaker system using this. <P>SOLUTION: The amplifier for the speaker includes an input terminal into which an input voce signal is inputted, a detector which detects DC voltage values superimposed on the input voice signal, and a preamplifier circuit connected with the input terminal and the detector to amplify the input voice signal. The detector gives a gain switching control signal to the preamplifier circuit based on the detected DC voltage values, and the preamplifier circuit receives the gain switching control signal and switches the amplification gain of the preamplifier circuit. <P>COPYRIGHT: (C)2007,JPO&amp;INPIT

Description

  The present invention relates to a speaker amplifier for driving a speaker for in-vehicle sound reproduction, and a speaker system configured using the same.

  In an on-vehicle sound reproduction system, a speaker system including an amplifier may be added to improve acoustic characteristics. A speaker system including an amplifier is typically a subwoofer with a built-in amplifier for reproducing a low sound range. FIG. 3 is a diagram for explaining the connection between the head unit 3 and the speaker 4 constituting the sound reproduction system 2 and the conventional subwoofer 20 with a built-in amplifier. The amplifier built-in subwoofer 20 includes a preamplifier 21, a main amplifier 22, and a speaker 23. The amplifier built-in subwoofer 20 includes an input terminal for inputting an audio signal, a line level input terminal 25 corresponding to the line output signal terminal 33 of the disk player 31 or the like of the head unit 3, and an amplifier of the head unit 3 that drives the speaker 4. And a speaker level input terminal 26 corresponding to the output signal terminal 34 of the unit 32. That is, since the signal level of the audio output signal of the connected device is greatly different, the amplifier built-in subwoofer 20 is provided with two dedicated input terminals, a line level input terminal 25 and a speaker level input terminal 26, and the preamplifier 21. Are designed to give a predetermined amplification gain corresponding to each.

  FIG. 4 is a diagram for explaining the input terminals 25 and 26 and the preamplifier 21 of the conventional subwoofer 20 with a built-in amplifier. Specifically, the input terminal 25 is a terminal to which a pin plug can be connected, and the input terminal 26 is a terminal to which a speaker wire can be connected. This subwoofer 20 with a built-in amplifier does not have a changeover switch for switching between the line level input terminal 25 and the speaker level input terminal 26, and mixes the outputs of the preamplifier circuit portions corresponding to the preamplifiers 21, respectively. Output to the main amplifier 22. When the user connects the subwoofer 20 with a built-in amplifier to the sound reproduction system, there is a convenience that it is only necessary to input an audio signal to either the line level input terminal 25 or the speaker level input terminal 26.

  However, when connected to the speaker level input terminal 26 that is used in many cases, noise is mixed in the preamplifier output of the other line level input terminal 25 where the amplification gain is set large, and as a result, the subwoofer with a built-in amplifier. There is a problem that the S / N characteristic of 20 deteriorates. In order to avoid this problem, it is necessary to take measures such as connecting a short pin to the line level input terminal 25 or changing the line level input terminal 25 to an input terminal with a switch for cutting off the input. . If these measures are not taken, there may be a problem such as a loud popping sound when a foreign object comes into contact with the line level input terminal 25.

  In addition, a BTL (Balanced Transformer Less) amplifier that uses a vehicle battery as a power source is used as an amplifier constituting an on-vehicle sound reproduction system. Since a DC voltage based on a DC power supply is superimposed on the audio signal supplied from the BTL amplifier to the speaker, it is necessary to detect the on / off operation of the BTL amplifier in a device added to a conventional vehicle sound reproduction system. Some are performed by detecting this DC voltage. For example, by detecting a DC voltage superimposed on the output of a head amplifier including a BTL amplifier, operation on / off of the connected power amplifier device is switched (Patent Document 1). Also, there is one that determines whether the output is a BTL output or a non-BTL output, and switches the circuit configuration of the amplifier to correspond to either a BTL output or a non-BTL output according to the determination (Patent Document 2).

JP 2001-189986 A (FIG. 2) Japanese Utility Model Publication No. 61-57708 (FIGS. 1 and 2)

  The present invention has been made to solve the above-described problems of the prior art, and an object of the present invention is to configure a speaker amplifier that drives a speaker for on-vehicle sound reproduction, and the same. An object of the present invention is to provide an amplifier for a speaker that can be easily connected by a user, can generate a good sound without causing noise or abnormal noise, and a speaker system using the same.

  The speaker amplifier of the present invention is connected to an input terminal to which an input audio signal is input, a detection circuit for detecting a DC voltage value superimposed on the input audio signal, and the input terminal and the detection circuit, and amplifies the input audio signal. A preamplifier circuit, the detection circuit applies a gain switching control signal to the preamplifier circuit based on the detected DC voltage value, and the preamplifier circuit receives the gain switching control signal and switches the amplification gain of the preamplifier circuit.

  Preferably, in the speaker amplifier according to the present invention, the detection circuit has a reference DC voltage value, and when the detected DC voltage value is greater than or equal to the reference DC voltage value, the preamplifier is less than the reference DC voltage value. A gain switching control signal for setting the amplification gain of the circuit low is applied to the preamplifier circuit.

  More preferably, the speaker amplifier of the present invention includes a DC power supply input terminal to which a DC power supply voltage is supplied from an external power supply, and a reference DC voltage value is a value of 9/20 or more and 11/20 or less of the DC power supply voltage. Set to

  More preferably, the speaker amplifier of the present invention includes a DC power supply input terminal to which a DC power supply voltage is supplied from an external power supply, and the reference DC voltage value is set to a value that is ½ of the DC power supply voltage.

  A speaker system according to the present invention includes any of the speaker amplifiers described above, a main amplifier circuit that amplifies an output signal of the preamplifier circuit, and a speaker connected to the main amplifier circuit.

  The operation of the present invention will be described below.

  The speaker amplifier of the present invention is connected to an input terminal to which an input audio signal is input, a detection circuit for detecting a DC voltage value superimposed on the input audio signal, and the input terminal and the detection circuit, and amplifies the input audio signal. And a preamplifier circuit. Since the speaker system of the present invention including the speaker amplifier includes a main amplifier circuit that amplifies the output signal of the preamplifier circuit and a speaker connected to the main amplifier circuit of the speaker amplifier, an audio signal is reproduced from the speaker. The

  Corresponding to the signal level of the input audio signal input to the input terminal, the preamplifier circuit amplifies the input audio signal with a predetermined amplification gain and outputs it to the main amplifier circuit. The signal level of the input audio signal is about 10 to 200 mVrms when the line level is input, and is about 1 to 20 Vrms when the speaker level is input. Therefore, the preamplifier is more input when the speaker level is input than when the line level is input. Set the gain of the circuit low.

  Here, when the input audio signal input to the input terminal is a line level input with a low signal level from a vehicle-mounted device such as a disc player, a DC voltage is not superimposed on the input audio signal. On the other hand, when the input audio signal input to the input terminal is a speaker level input supplied from the in-vehicle BTL amplifier to the speaker, the signal level is large and a DC voltage is superimposed on the input audio signal. Yes. Since this DC voltage is based on an external DC power supply supplied to the in-vehicle BTL amplifier, the speaker amplifier detection circuit provides a gain switching control signal to the preamplifier circuit based on the detected DC voltage value. The preamplifier circuit can switch the amplification gain of the preamplifier circuit in response to the gain switching control signal.

  That is, the speaker amplifier of the present invention can automatically switch the amplification gain of the preamplifier circuit by detecting the DC voltage superimposed on the input audio signal. The detection circuit has a reference DC voltage value, and when the detected DC voltage value is greater than or equal to the reference DC voltage value, gain switching control that sets the amplification gain of the preamplifier circuit lower than when the detected DC voltage value is less than the reference DC voltage value Apply the signal to the preamplifier circuit. For example, a preamplifier circuit that has received a gain switching control signal sets the amplification gain of the preamplifier circuit low assuming that the input signal is a speaker level input, and if it does not receive a gain switching control signal, the preamplifier assumes that the input signal is a line level input. Set the amplification gain of the circuit high. As a result, whether the input signal is a line level input or a speaker level input, it is set to a predetermined amplification gain, so that it is amplified to an appropriate signal level and output to the main amplifier circuit, and good sound reproduction is achieved. It becomes possible.

  The reference DC voltage value of the detection circuit is set to a value of 9/20 or more and 11/20 or less of the DC power supply voltage when a DC power supply input terminal to which a DC power supply voltage is supplied from an external power supply is provided. The value is set to ½ of the DC power supply voltage. The DC voltage superimposed on the input audio signal is about half the value of the external power supply supplied to the in-vehicle BTL amplifier, and the speaker amplifier circuit of the present invention is also supplied with power from the same external power supply. Because. Therefore, if the reference DC voltage value is within this range, the amplification gain of the preamplifier circuit can be set almost automatically according to the signal level of the input signal.

  In addition, the amplification gain of the preamplifier circuit can be switched automatically regardless of whether the input signal is line level input or speaker level input, so there is no need to provide separate input terminals corresponding to each, and user connection work Becomes easier. In addition, since the preamplifier circuit is unified, the conventional noise and noise caused by the unused preamplifier circuit do not occur, and good sound reproduction is possible. Since a separate input terminal can be omitted, there is no problem such as a loud popping sound caused by a foreign object coming into contact with the terminal, and there is no need to provide an accessory such as a short pin.

  The speaker amplifier according to the present invention can realize a speaker system that can be easily connected by a user and can reproduce sound without causing noise or abnormal noise.

  The speaker amplifier of the present invention is an input terminal to which an input audio signal is input for the purpose of providing a speaker system that can be easily connected by a user and can reproduce sound without causing noise or abnormal noise. And a detection circuit that detects a DC voltage value superimposed on the input audio signal, and a preamplifier circuit that is connected to the input terminal and the detection circuit and amplifies the input audio signal. Based on this, the gain switching control signal is given to the preamplifier circuit, and the preamplifier circuit receives the gain switching control signal and switches the amplification gain of the preamplifier circuit.

  Hereinafter, a speaker amplifier and a speaker system using the same according to preferred embodiments of the present invention will be described, but the present invention is not limited to these embodiments.

  FIG. 1 is a diagram illustrating a speaker system including a speaker amplifier according to a preferred embodiment of the present invention. In this embodiment, the speaker system is an amplifier built-in subwoofer 10. The subwoofer 10 with a built-in amplifier is connected to an acoustic reproduction system 1 including a head unit 3 and a speaker 4 and reproduces a low frequency component (for example, about 300 Hz or less) of an audio signal. The sound reproduction system 1 is an in-vehicle audio system. The head unit 3 and the amplifier built-in subwoofer 10 constituting the sound reproduction system 1 are respectively supplied with a DC voltage VCC from a DC power source 5 formed of a vehicle battery. Yes. The DC voltage VCC of the DC power supply 5 is a positive DC voltage, and the power supply + 12V or + 24V is frequently used. In the present embodiment, the case where there is only one channel of the audio signal (that is, a monaural signal) is shown in the figure. However, the audio signal is not limited to a monaural signal, but in the case of a stereo signal including left and right signals. A reproduction channel corresponding to the number of audio signal channels may be provided. Further, when the reproduction band is a low-frequency component, the subwoofer 10 with a built-in amplifier may mix a stereo signal into a monaural signal.

  The head unit 3 includes a disc player 31 and a BTL amplifier 32, a line output signal terminal 33 that outputs an output signal VL of the disc player 31, and a speaker that outputs an output signal VH of the BTL amplifier 32 that drives the speaker 4. An output signal terminal 34 is provided. For example, the level of the output signal VL from the line output signal terminal 33 is about 10 to 200 mVrms, while the level of the output signal from the speaker output signal terminal 34 is about 1 to 20 Vrms. Here, although the output signal VL of the disc player 31 does not include a direct current component, the output signal VH from the BTL amplifier 32 has a direct current voltage having a value about ½ of the power supply voltage VCC supplied to the BTL amplifier 32. It is superimposed. For example, when the DC voltage VCC from the DC power supply 5 is + 12V, a DC voltage of about 6V is included in the output signal VH from the BTL amplifier 32.

  The amplifier built-in subwoofer 10 includes a preamplifier 11, a main amplifier 12, and a speaker 13, and includes a DC power supply input terminal 14 to which a DC voltage VCC is supplied and an input terminal 15 to which an audio signal is input. The input terminal 15 connected to the preamplifier 11 is supplied with an output signal VL from a line output signal terminal 33 such as a disk player 31 of the head unit 3 or an output signal 34 of the amplifier unit 32 of the head unit 3 that drives the speaker 4. The output signal VH is input. The main amplifier 12 is connected to the output signal from the preamplifier 11 and includes a low-pass filter (not shown) that passes only the low frequency signal of the audio signal and a volume (not shown) that controls the output voltage to the speaker 13. .

  FIG. 2 is a diagram illustrating the input terminal 15 and the preamplifier 11 of the amplifier built-in subwoofer 10. The preamplifier 11 includes a preamplifier circuit P and a detection circuit K described later. The input terminal 15 is composed of a set of a terminal 151 and a terminal 152, and the terminal 151 and the terminal 152 are connected to the preamplifier circuit P via capacitors C1 and C2, respectively. The low-frequency noise component of the input signal is removed by the capacitors C1 and C2, and only the audio signal component is input to the preamplifier circuit P. The output of the preamplifier circuit P is connected to the main amplifier 12 as the output of the preamplifier 11. In FIG. 2, a terminal for inputting the DC voltage VCC supplied from the DC power source 5 to the preamplifier 11 is omitted.

  The preamplifier circuit P includes an operational amplifier OP1 to which a DC voltage VCC is supplied, FET1 and FET2. The preamplifier circuit P includes a resistor R11 connected to the capacitor C1, a resistor R12 connected to the capacitor C2, a resistor R21 connected to the input of the resistor R11 and the operational amplifier OP1, and a resistor connected to the other input of the resistor R12 and the operational amplifier OP1. R22, a resistor R31 connected to the resistor R21 and the output of the operational amplifier OP1, a resistor R32 connected to the resistor R22 and a terminal to which half the DC voltage VCC is supplied, and a resistor connected to the output of the operational amplifier OP1 R41. The drain and source of FET1 are connected to the resistor R31, the drain and source of FET2 are connected in parallel to the resistor R32, and the gates of the FET1 and FET2 are connected to the detection circuit K. That is, the preamplifier circuit P includes gain switching means for amplifying the input signal with a predetermined gain according to the signal level of the input signal, and a gain switching control signal is given from the detection circuit K to each gate of the FET1 and FET2. It is done.

  The detection circuit K includes a low-pass filter composed of resistors R51 and R52 and capacitors C3 and C4 connected to either the terminal 151 or the terminal 152, an operational amplifier OP2 whose input is connected to the low-pass filter, and the other of the operational amplifier OP2. Resistors R61 and R62 connected to the input of the amplifier, resistors R63 and R64 connected to the output of the operational amplifier OP2, diodes D1 and D2 connected to R64, and a capacitor C5. Resistors R61 and R63 are connected to power supply voltage VCC, and capacitors C4 and C5 and resistor R62 are grounded. Diodes D1 and D2 are connected to respective gates of FET1 and FET2 of preamplifier circuit P, and provide a gain switching control signal to FET1 and FET2. The resistors R61 and R62 are set to have the same resistance value.

  An input signal is input to the detection circuit K from either the terminal 151 or the terminal 152 (in the case of FIG. 2, the terminal 152). The low-pass filter of the detection circuit K outputs a DC voltage component of the input signal and inputs it to the operational amplifier OP2. The power supply voltage VCC (+12 V) is equally divided by resistors R61 and R62 having the same resistance value, and is input to the other input of the operational amplifier OP2. Therefore, the operational amplifier OP2 compares the reference DC voltage (+ 6V), which is a half value of the external power supply voltage VCC, with the DC voltage component of the input signal, and outputs a gain switching control signal from the output. . For example, when the input signal is an output signal VL that does not include a DC voltage, the detection circuit K outputs a gain switching control signal: GH for setting the amplification gain high, and an output signal VH on which the DC voltage + 6V is superimposed. In this case, a gain switching control signal GL for setting the amplification gain low is output. Here, the gain switching control signal may be a voltage sufficient to turn on FET1 and FET2, and is, for example, a DC voltage signal having a DC voltage value of GH: about 5V or GL: about 0V.

  When the gain switching control signal GH from the detection circuit K is given to the respective gates of the FET1 and FET2, the preamplifier circuit P bypasses the resistor R31 and the resistor R32 so that the amplification gain is increased. Switch. That is, the gain switching means of the preamplifier circuit P receives the gain switching control signal GH or GL from the detection circuit K, and is the gain switching control signal GH (that is, the input signal is the output signal from the line output signal terminal 33). When the gain switching control signal GL is amplified (that is, when the input signal is the output signal VH from the output signal 34 of the amplifier unit 32), the gain is low and the gain is low. The gain of the preamplifier circuit P is switched so as to amplify. The amplification gain of the preamplifier circuit P is proportional to (R21 + R31) / R11 at high gain, and is proportional to (R21) / R11 at low gain.

  The amplification factor of the preamplifier circuit P is set by a combination of the values of the resistors R11, R12, R21, R22, R31, and R32. The difference in gain between the high gain and the low gain of the preamplifier circuit P is set by the difference in the input signal level. Specifically, for example, the level of the output signal VL that does not include the DC voltage is about 100 mVrms, while the level of the output signal VH on which the DC voltage + 6V, which is about ½ of the power supply voltage + 12V, is superimposed. Is about 1 Vrms, the amplification factor of the preamplifier circuit P is based on the difference between the input signal levels, and is higher than that of the low gain (that is, the output signal VH) (that is, the output signal VL). Is set higher by about 20 dB. Further, for example, when R11 = R12 = 33 kΩ, R21 = R22 = 5.1 kΩ, and R31 = R32 = 100 kΩ, the difference between the amplification gain at the high gain and the low gain is set to about 26 dB.

  In the detection circuit K, when the reference DC voltage value is ½ of the external power supply voltage VCC, the DC voltage value of the input signal output from the low-pass filter of the detection circuit K is the reference DC voltage value. If this is the case, it is detected that the input signal is a signal VH on which a DC voltage is superimposed, and the value of the DC voltage of the input signal output from the low-pass filter of the detection circuit K is less than the reference DC voltage value. For example, it is detected that the input signal is a signal VL on which no DC voltage is superimposed. The reference DC voltage value that is ½ of the power supply voltage VCC is set to a value that is not less than 9/20 and not more than 11/20 of the DC power supply voltage in preparation for a case where the power supply voltage VCC fluctuates. May be. For example, when the DC power supply voltage is + 12V, the reference DC voltage value may be set to + 5.4V or more and + 6.6V or less.

  That is, when a DC voltage value equal to or higher than a DC voltage value in a range of ± 10% of the reference DC voltage value is detected from the input signal, the input signal is determined as the output signal VH from the output signal 34 of the amplifier unit 32, When a DC voltage value less than a DC voltage value in the range of ± 10% of the reference voltage is detected from the input signal, the input signal is set to be determined as the output signal VL from the line output signal terminal 33. Specifically, by setting the values of the resistors R61 and R62 of the detection circuit K, the reference DC voltage value is set to a value between 9/20 and 11/20 of the DC power supply voltage. For example, when the reference DC voltage value is 9/20 of the DC power supply voltage, the resistance ratio of R61 and R62 is 11: 9, and the reference DC voltage value is 11/20 of the DC power supply voltage. The ratio of the resistance values of R61 and R62 may be 9:11.

  For example, when the connection to the input terminal 15 of the amplifier built-in subwoofer 10 is changed by the user and the detection circuit K of the preamplifier 11 outputs a gain switching control signal, the amplification gain of the preamplifier circuit P changes greatly. The low-pass filter composed of the resistor R64 and the capacitor C5 may be configured such that the amplification gain changes gradually or the amplification gain is held for a while.

  In the case of the amplifier built-in subwoofer 10 according to the embodiment, the head unit that drives the speaker 4 even when the output signal VL from the line output signal terminal 33 such as the disk player 31 of the head unit 3 is input to the input terminal 15. Even when the output signal VH from the output signal 34 of the third amplifier section 32 is input, the output signal level supplied to the power amplifier 12 and the speaker 13 does not change. Therefore, the signal level of the audio signal reproduced from the amplifier built-in subwoofer 10 does not change depending on the difference in connection with the sound reproduction system 1, and the user's connection work becomes easy. In addition, it is not necessary to provide separate input terminals corresponding to each of them, so that noise and noise are not generated, and it is not necessary to provide accessory parts such as a short pin.

  The preamplifier 11 of the speaker amplifier included in the subwoofer with built-in amplifier according to the present invention amplifies based on the detection circuit K that detects the DC voltage value superimposed on the input audio signal and the gain switching control signal output from the detection circuit K. The detection circuit K and the preamplifier circuit P are not limited to the above-described embodiment, as long as the preamplifier circuit P that amplifies the input audio signal by switching the gain is included. The switching of the gain is not limited to the FET, and other switch elements may be used. The detection circuit K for the speaker amplifier according to the present invention has a gain for setting the amplification gain of the preamplifier circuit P lower when the detected DC voltage value is equal to or higher than the reference DC voltage value than when the detected DC voltage value is lower than the reference DC voltage value. The switching control signal may be supplied to the preamplifier circuit P.

  Further, the speaker system including the speaker amplifier according to the preferred embodiment of the present invention is not limited to the subwoofer with built-in amplifier. As long as it is a vehicle-mounted amplifier built-in speaker to which external DC power is supplied, it may be a speaker system that reproduces not only the low frequency component of an audio signal but also all the bands used for stereo reproduction or multi-channel surround reproduction. Further, the speaker amplifier according to the present invention may be only an amplifier portion that does not include a speaker.

  The speaker amplifier of the present invention can also be applied to portable electronic devices that are used with an external DC power supply such as an AC adapter.

It is a figure explaining the speaker system containing the amplifier for speakers by preferable embodiment of this invention. Example 1 It is a figure explaining the input terminal and preamplifier of the speaker system containing the amplifier for speakers by preferable embodiment of this invention. Example 1 It is a figure explaining the speaker system containing the conventional amplifier for speakers. It is a figure explaining the input terminal and preamplifier of the speaker system containing the conventional amplifier for speakers.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 2 Sound reproduction system 3 Head unit 31 Disc player 32 BTL amplifier 33, 34 Signal output terminal 4 Speaker 5 Battery 10, 20 Amplifier built-in subwoofer 11, 21 Preamplifier 12, 22 Main amplifier 13, 23 Speaker 14, 24 DC power supply Input terminal 15, 16, 25 Input terminal

Claims (5)

An input terminal to which an input audio signal is input;
A detection circuit for detecting a DC voltage value superimposed on the input audio signal;
A preamplifier circuit connected to the input terminal and the detection circuit to amplify the input audio signal,
The detection circuit provides a gain switching control signal to the preamplifier circuit based on the detected DC voltage value,
The preamplifier circuit receives the gain switching control signal and switches the amplification gain of the preamplifier circuit;
Speaker amplifier. The detection circuit has a reference DC voltage value, and when the detected DC voltage value is greater than or equal to the reference DC voltage value, the amplification gain of the preamplifier circuit is lower than when the detected DC voltage value is less than the reference DC voltage value. A gain switching control signal to be set is given to the preamplifier circuit.
The speaker amplifier according to claim 1. A DC power supply input terminal to which a DC power supply voltage is supplied from an external power supply
The reference DC voltage value is set to a value of 9/20 or more and 11/20 or less of the DC power supply voltage.
The speaker amplifier according to claim 2. A DC power supply input terminal to which a DC power supply voltage is supplied from an external power supply
The reference DC voltage value is set to a value that is 1/2 of the DC power supply voltage.
The speaker amplifier according to claim 3. A speaker amplifier according to any one of claims 1 to 4,
A main amplifier circuit that amplifies the output signal of the preamplifier unit, and a speaker connected to the main amplifier circuit,
Speaker system.

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