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DESCRIPTION JPH10335961

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DESCRIPTION JPH10335961
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
bass amplifier for driving a subwoofer which reproduces a signal having a frequency of about
200 Hz or less, and more particularly to a bass amplifier suitable for a car audio system.
[0002]
2. Description of the Related Art In many on-vehicle audio devices, a pair of speakers are
disposed in front of and behind a driver's seat, and these speakers form an expansion of a sound
field around the driver's seat. In addition, in order to faithfully reproduce a deep bass, there is a
system provided with a loudspeaker (subwoofer) dedicated to deep bass reproduction of about
200 Hz or less and a bass amplifier for driving the speaker.
[0003]
By the way, in the middle to high tone region, if the volume is increased, the distortion is
increased and it is difficult to hear, so the volume is hardly increased until the distortion is
increased. However, there is a property that even if a clip occurs in the deep bass region, it does
not feel so much in the human ear. For example, even if the total harmonic distortion (THD)
becomes 10% or more, almost distortion is detected in the human ear Can not do it. For this
reason, the output may be excessively increased to cause a failure of the bass amplifier or the
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speaker.
[0004]
In order to avoid such problems, conventionally, in the low-frequency amplifier of an audio
device, an auto level control (Auto Level Control) circuit for automatically adjusting the output
level or a clipped waveform is made smooth. A soft clip circuit (waveform shaping circuit) or the
like to be shaped is provided. In a car audio system, the power supply voltage supplied from the
car battery fluctuates. Therefore, if auto level control or waveform shaping is not performed after
detecting the clip of the output waveform, the efficiency of the amplifier may drop or the effect
of the soft clip I can not get enough.
[0005]
FIG. 6 is a block diagram showing a conventional bass amplifier for a car audio system. The
signal input from the signal source 5 is input to the power amplifier 22 through the waveform
shaping circuit 21, amplified by the power amplifier 22, and supplied to the subwoofer. The clip
detection circuit 23 detects the presence or absence of a clip by comparing, for example, the
input signal and the output signal of the power amplifier 22. Then, when detecting that the
output signal of the power amplifier 22 is clipped, the clip detection circuit 23 limits the output
level of the waveform shaping circuit 21 via the level control circuit 24.
[0006]
FIG. 7 is a diagram showing the relationship between the level (input voltage) of the input signal
on the horizontal axis and the level (output voltage) of the output signal and the total harmonic
distortion (THD) on the vertical axis. Assuming that the waveform shaping circuit 21, the clip
detection circuit 23, and the level control circuit 24 do not exist, that is, if the input signal is
directly input to the power amplifier 22, the level of the output signal (solid line Output signal
level becomes almost constant when it reaches a certain level. On the other hand, the total
harmonic distortion (dotted line) decreases as the level of the input signal increases, and
increases significantly when the level of the output signal exceeds a substantially constant value.
As shown in FIG. 6, in the bass amplification device provided with the waveform shaping circuit
21, the grip detection circuit 23, and the level control circuit 24, the output level exceeds a value
at which the output level is substantially constant, as shown by the one-dot chain line in FIG.
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Even in this case, the increase in total harmonic distortion can be avoided.
[0007]
SUMMARY OF THE INVENTION However, in the case of the bass amplifier of the conventional
car audio system, as described above, the clip detection circuit 23 and the level control circuit 24
are used to cope with the fluctuation of the power supply voltage. There is a problem that the
circuit configuration is complicated. From the above, it is an object of the present invention to
provide a bass range amplifier which is capable of soft clipping with a relatively simple circuit
configuration and is suitable for driving a subwoofer of a car audio system.
[0008]
In the subwoofer driving bass range amplifying device, the above-mentioned subject is a
preamplifier for amplifying an input signal, a waveform shaping circuit for shaping the output
signal of the preamplifier, and the waveform shaping circuit And a power amplifier for
amplifying an output of the low-frequency amplifier.
[0009]
Hereinafter, the operation of the present invention will be described.
In the present invention, a preamplifier and a waveform shaping circuit are provided at the front
stage of the power amplifier. As a result, when the level of the input signal is high, the clip is first
generated in the preamplifier, and the output level of the preamplifier is limited. The waveform
shaping circuit shapes the waveform of the signal input from the preamplifier and outputs it to
the power amplifier. Since the signal input to the power amplifier is previously limited in level by
the preamplifier, clipping in the power amplifier is avoided, and as a result, overload of the power
amplifier and the speaker is reduced. In the present invention, when the power supply voltage
changes, the clip level at the preamplifier changes. Thereby, regardless of the fluctuation of the
power supply voltage, the optimum soft clipping effect can always be obtained.
[0010]
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Furthermore, in the present invention, the circuit conventionally required such as a clip detection
circuit connected to the output end of the power amplifier to detect a clip, a level control circuit,
etc. is not necessary, and the circuit configuration is simplified. Note that it is preferable to make
the power supply voltage supplied to the preamplifier lower (the absolute value is smaller) than
the power supply voltage supplied to the power amplifier in order to ensure that the clip is
generated by the preamplifier earlier than the power amplifier. .
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be
described below with reference to the attached drawings. (First Embodiment) FIG. 1 is a block
diagram showing a bass range amplifying apparatus according to a first embodiment of the
present invention.
[0012]
The signal input from the signal source 5 is input to the preamplifier 1, and the output end of the
preamplifier 1 is connected to the input end of the waveform shaping circuit 2. The output end of
the waveform shaping circuit 2 is connected to the input end of the power amplifier 3, and the
output end of the power amplifier 3 is connected to the subwoofer. Power supply voltages of +
Vcc and -Vcc are supplied to the waveform shaping circuit 2 and the power amplifier 3 from a
power supply circuit (not shown) connected to the on-board battery. On the other hand, positiveside power supply voltage is supplied to preamplifier 1 from the power supply voltage supply
circuit formed of NPN transistor Q1 and resistors R11 and R12, and negative voltage is
generated from the power supply voltage supply circuit formed of PNP transistor Q2 and
resistors R21 and R22. A side power supply voltage is supplied. The collector of the transistor Q1
is connected to the power supply line + Vcc, and a resistor R11 is connected between the
collector and the base. Further, a resistor R12 is connected between the base of the transistor Q1
and the ground, and the emitter is connected to the positive power supply line of the
preamplifier 1. The collector of the transistor Q2 is connected to the power supply line -Vcc, the
resistor R21 is connected between the collector and the base, and the resistor R22 is connected
between the base of the transistor Q2 and the ground. The emitter of the transistor Q2 is
connected to the negative power supply line of the preamplifier 1.
[0013]
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FIG. 2 is a circuit diagram showing an example of the preamplifier 1 and the waveform shaping
circuit 2. The preamplifier 1 is constituted of an amplifier 10, a capacitor C1 and resistors R1 to
R3. The input signal is input to the noninverting input (+) of the amplifier 10 via the capacitor
C1. A resistor R1 is connected between the non-inverted input end and the ground, and a resistor
R2 is connected between the inverted input end (-) and the ground, and between the output end
of the amplifier 10 and the inverted input end. Is connected to the resistor R3. The positive and
negative power supply lines of amplifier 10 are connected to the emitters of transistors Q1 and
Q2 shown in FIG.
[0014]
On the other hand, the waveform shaping circuit 2 is composed of an amplifier 20, capacitors C2
and C3, and resistors R4 to R7. The resistors R4, R6 and R7 are connected in series between the
non-inverting input terminal (+) of the amplifier 20 and the output terminal of the preamplifier 1,
and the resistor R5 is connected between the connection point of the resistors R4 and R6 and the
ground. Is connected. A capacitor C2 is connected between the output of the amplifier 20 and the
connection point between the resistors R6 and R7, and a capacitor C3 is connected between the
noninverting input and the ground. Furthermore, the output end of the amplifier 20 and the
inverting input end are connected.
[0015]
The positive and negative power supply lines of the amplifier 20 are supplied with power supply
voltages ± Vcc from the power supply circuit. In the bass range amplification device of the
present embodiment configured as described above, the signal input from the signal source 5 is
amplified by the preamplifier 1 and then input to the waveform shaping circuit 2. In this case, the
amplification factor of the preamplifier 2 is determined by the resistors R2 and R3. However, if
the level of the input signal is excessively high, clipping occurs in the output signal of the
preamplifier 1. The voltage generated by the clip is determined by the power supply voltage
supplied to preamplifier 1. However, in this embodiment, the voltage drop by transistors Q1 and
Q2 is lower than the power supply voltage ± Vcc supplied to power amplifier 3 (absolute value
Because the voltage is supplied to the preamplifier 1, the clip level of the preamplifier 1 is lower
than the clip level of the power amplifier 3.
[0016]
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The waveform shaping circuit 2 is a kind of low pass filter, and the clipped signal is waveformshaped by the waveform shaping circuit 2 to be shaped into a smooth waveform having no edge.
The power amplifier 3 amplifies the signal input from the waveform shaping circuit 2. However,
even if the signal level of the signal source 5 is excessively high, a clip is generated in the
preamplifier 1 and the signal level is limited. In 3, it is possible to avoid the occurrence of a clip.
[0017]
In the present embodiment, conventionally required circuits such as a clip detection circuit and a
level control circuit for checking whether or not a clip is generated in the signal output from the
power amplifier are unnecessary, and compared with the prior art. Thus, the circuit configuration
is simplified. In addition, even if the power supply voltage (± Vcc) changes, the power supply
voltage supplied to the preamplifier 11 also changes accordingly, and the clip level of the
preamplifier 11 changes. For this reason, even if the power supply voltage fluctuates, the
optimum soft clipping effect can always be obtained.
[0018]
Hereinafter, the result of actually producing the circuit shown in FIG. 2 and examining the
electrical characteristics will be described. However, the capacitance value of the capacitor C1 is
10 μF, the capacitance value of the capacitor C2 is 0.11 μF, and the capacitance value of the
capacitor C3 is 0.056 μF. The resistances R1 to R7 are all 10 k.OMEGA. In this case, the
waveform shaping circuit 2 acts as a low pass filter with a cutoff frequency fc = 200 Hz. Also, the
input signal is amplified about twice by the preamplifier 1. Further, ± 15 V was applied as a
power supply voltage to both the amplifier 10 of the preamplifier 1 and the amplifier 20 of the
waveform shaping circuit 2. Furthermore, a sine wave signal with a frequency of 100 Hz was
input from the signal source 5 to the preamplifier 1.
[0019]
FIG. 3 is a waveform diagram showing the output of the preamplifier 1, and FIG. 4 is a waveform
diagram showing the output of the waveform shaping circuit 2. As shown in FIG. As shown in
FIG. 3, the output of the preamplifier 1 has a waveform clipping when the input signal reaches a
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certain level. When this clipped waveform is input to the waveform shaping circuit 2, the
waveform is shaped as shown in FIG. In this waveform shaping circuit 2, since the cutoff signal fc
is set to twice the frequency of the input signal, the third or higher harmonic components of the
clipped signal are cut, and as shown in FIG. The signal of a complex waveform is output.
[0020]
In the above example, although the power supply voltage supplied to the preamplifier 1 and the
power supply voltage supplied to the power amplifier 3 are the same, as shown in FIG. 1, the
transistors Q1 and Q2 and the resistors R11, R12, R21 and R22 By providing the configured
power supply voltage supply circuit and setting the power supply voltage of preamplifier 1 lower
than the power supply voltage of power amplifier 3, the clip level of preamplifier 1 can be
reduced more reliably than the clip level of power amplifier 3 It is preferable to
[0021]
Second Embodiment FIG. 5 is a block diagram showing a bass range amplifying apparatus
according to a second embodiment of the present invention.
In the present embodiment, the present invention is applied to a single power supply type bass
range amplifier. The signal input from the signal source 5 is input to the preamplifier 11, and the
output end of the preamplifier 11 is connected to the input end of the waveform shaping circuit
12. The output terminal of the waveform shaping circuit 12 is connected to the input terminal of
the power amplifier 13, and the subwoofer is connected to the output terminal of the power
amplifier 13.
[0022]
A power supply voltage of + Vcc is supplied to the waveform shaping circuit 12 and the power
amplifier 13 from a power supply circuit (not shown) connected to an onboard battery. On the
other hand, a driving voltage is supplied to the preamplifier 11 from a power supply voltage
supply circuit constituted by an NPN transistor Q3 and resistors R31 and R32. The collector of
the transistor Q3 is connected to the power supply line + Vcc, and a resistor R31 is connected
between the collector and the base. Further, a resistor R32 is connected between the base of the
transistor Q3 and the ground, and the emitter is connected to the power supply line of the
preamplifier 11.
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[0023]
Also in this embodiment, the basic operation is the same as in the first embodiment, and when
the level of the input signal is excessively high, a clip is generated in the preamplifier 11. Then,
the clipped waveform is shaped into a smooth waveform without edges by the waveform shaping
circuit 12, amplified by the power amplifier 13, and output to the subwoofer. This can prevent
the power amplifier 13 and the speaker from being overloaded. Also in the present embodiment,
as in the first embodiment, the circuit is simplified, and when the power supply voltage changes,
the clip level of preamplifier 11 changes, so that the optimum soft clip effect is always obtained.
Be
[0024]
As described above, according to the bass amplifier of the present invention, since the
preamplifier and the waveform shaping circuit are connected to the front stage of the power
amplifier, when the level of the input signal is high, the preamplifier clips , And the clipped signal
is waveform-shaped by the waveform shaping circuit and supplied to the power amplifier.
Therefore, it is possible to avoid the occurrence of clipping in the power amplifier, and to avoid
overloading of the power amplifier and the speaker. In addition, when the power supply voltage
changes, the clip level of the preamplifier changes, so that the optimum clipping effect can
always be obtained. Furthermore, according to the present invention, the conventionally required
circuits such as the clip detection circuit and the level limit circuit are not required, and the
circuit configuration can be simplified.
[0025]
Brief description of the drawings
[0026]
1 is a block diagram showing a bass range amplification device of the first embodiment of the
present invention.
[0027]
FIG. 2 is a circuit diagram showing an example of a preamplifier and a waveform shaping circuit
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of the low frequency range amplifier of the same.
[0028]
3 is a waveform diagram showing the output of the preamplifier.
[0029]
4 is a waveform diagram showing the output of the waveform shaping circuit.
[0030]
5 is a block diagram showing a bass range amplification device of the second embodiment of the
present invention.
[0031]
6 is a block diagram showing a bass range amplification device of the conventional car audio
system.
[0032]
7 is a diagram showing the relationship between the input signal level and the output signal level
and total harmonic distortion.
[0033]
Explanation of sign
[0034]
1, 11, 22 preamplifier 2, 12, 21 waveform shaping circuit 3, 13 power amplifier 5 signal source
10, 20 amplifier 23 clip detection circuit 24 level control circuit
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