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Description 1, title of the invention
Power amplifier for musical instruments
3. Detailed Description of the Invention The present invention relates to a power amplifier for
musical instruments, and by supplying a power supply voltage corresponding to a change in load
impedance to an amplifier, it is possible to effectively use the maximum power capacity of the
power supply and to change the load. The purpose is to effectively output the maximum power.
Usually, a speaker is generally used as a load for a power amplifier in the audio frequency band,
and the speaker is driven at a constant voltage by the amplifier although its impedance is not
constant due to the frequency as shown in the impedance characteristic diagram of FIG. Since a
flat sound pressure output characteristic is obtained in the desired reproduction band, there has
been no problem in faithful reproduction of the input audio signal. However, since amplification
devices for musical instruments are often used by changing the above-mentioned sound pressure
output characteristics depending on the characteristics of the used musical instruments, etc., the
power amplifier can be loaded to obtain such characteristics. Or a constant current amplifier that
detects the current flowing through the speaker and feeds it back to the amplifier and supplies
an output voltage corresponding to the impedance fluctuation to the load, and the speaker is
driven at constant power to obtain a desired sound pressure output characteristic, Although an
amplification device having a desired frequency characteristic has conventionally been employed,
in the power amplifier described above, when amplifying a frequency band where the load
impedance has risen, in order to supply the same power as the band where the load impedance is
low, Although high output voltages are required, generally the maximum output voltage of the
amplifier is limited by the supply voltage of the amplifier, so the load impedance is high. The
main that amplifier compared to the bandwidth of the low impedance quickly saturated, the
dynamic range of the maximum output power load impedance at the higher-band had the
disadvantage of can not be secured. Therefore, in order to solve the drawbacks in the
conventional example, the applicant detects a change in load impedance and copes with the load
impedance fluctuation.-A power amplifier for musical instruments provided with a power supply
device for supplying a power supply voltage to a power amplifier (Japanese Patent Application
No. 55-182414), but since such a device obtains a predetermined power supply voltage by pulse
width modulation means, its efficiency is high in terms of effective use of power, but the circuit
configuration becomes complicated, and This has led to a new defect that the problem of
unwanted radiation of electromagnetic waves also occurs. The present invention solves the
above-mentioned drawbacks, and one embodiment of the present invention will be described in
detail based on the block diagram shown in FIG. A power amplifier (Al) operated by a pair of
positive and negative power supplies (+ B) (−B) is generally connected to the first positive and
negative via a positive / negative overcurrent detector (CD) (CD ′) than the power supply (PS).
Power supply voltage (+81) (-Bt) is supplied to output to the load (RL) an output signal (vO)
obtained by amplifying the input signal (Vi) by A times. An error detector (A2) for detecting and
amplifying a difference between a signal (vo ') obtained by multiplying an output signal (vO) by 1
/ A with a resistor (B +) and a resistor (R2) and an input signal (Vi); The detector (A2) is
connected via a gate controlled by the output signal (CVI) (CV'l) of the overcurrent detector (CD)
(CD ′ ′) via a device (Gl), the detector (A2) ) @ Output signal corresponding to positive and
negative control signal ('CV2) (C A control signal generator (CG) generating V2 ') and a control
signal (CV2) (CV2') from the control signal generator (CG) respectively respond and supplied
from the power supply (PS) The second positive and negative power supply voltages (+ B2)
(−B2) higher than the first positive and negative power supply voltages (+ B1) (−BS) are added
to the first voltage (+ BI) (−B +) respectively. And a voltage controller (G2) (G #) for supplying a
power supply voltage to the power amplifier (A1) via a current detector (CD) (CD '), the power
amplifier (A1) having a larger signal than usual It amplifies and detects that the impedance of the
load (RL) rises and the excessive power supply current is not supplied by the overcurrent
detector (CD) (CD ′ ′), and the power supply voltage (+ B of the power amplifier (A1) ) (-B) to
the normal first voltage (+ B +) (-B +) More higher second voltage (+ B2) (- 82) was changed to
one in which allowed to ensure the desired dynamic range.
Therefore, when the power amplifier (, + N) amplifies a small signal or a signal in a band in which
the impedance of the load (R, L) is low, predetermined power is positive or negative from the
power supply (PS) as in the conventional example. Provided by the first power supply voltage (+
B +) (-B +), the output signal (vO) supplies the desired power to the load (RL) without causing
waveform distortion below a predetermined maximum output power. -10,000, since the error
detector (A2) receives the divided output signal (vo ') at the same level as the input signal (VS)
and no detection signal is output, the control signal generator (CG C) without generating the
control signal (CV2) (CV2 '), the voltage control device (G2) (G2') blocks the power supply from
the higher second voltage (+82) (-B2). If the output signal (.0) causes waveform clipping at an
output voltage corresponding to the first power supply voltage (+ BI) (-Bl) due to an excessive
input, the error detector (A2) detects a detection signal Because the amplifier (A +) outputs a
power greater than or equal to the predetermined maximum output, the overcurrent detector
(CD) (CD ') supplies an excessive current to the amplifier (A1) EndPage: 2 Detects that the
connection to the detection signal is cut off to block the supply of the second power supply
voltage (+ B2X-B2), and the amplifier (A1) and the load (RL) are not supplied with power of a
predetermined power or more. And protect. Next, when amplifying a signal in a band in which
the impedance of the load (RL) has risen, a higher voltage output is required to supply the same
power as the low impedance to the load (RL). Since the amount of current may be small, the
overcurrent device (CD) (CD ') does not operate, so the gate device (G1) becomes conductive, and
an output signal is generated when the cylinder 1 is supplied with the power supply voltage (+
B1) (-Bl). The voltage controller (CV2) (CV2 ') is generated by the control signal generator (CG)
corresponding to the detection signal output from the error detector (A2) corresponding to the
waveform clip (vO). G2) (C2 ') is controlled to supply the second power supply voltage (+ B2) (B2) from the power supply (PS) to the power amplifier (AI), and the output voltage (? 0) is
clipped by the supply voltage Do not want the desired power And supplies to the load (RL).
Therefore, the power supply apparatus (PS) is configured to supply the first power supply
voltage (ten B +) (−11 N) of the output current capacity for supplying predetermined power as
in the prior art, and the second power Since it is sufficient to supply a high power supply voltage
(+ B2) (-82), as shown within the dotted line in FIG. 2 (but simplified for illustration), the
secondary winding of a normal power supply transformer (T) The line output is rectified by the
diode (DI) (DI 'XD2) (D2') and the capacitor (CI) (CI) (CI ') (C2) (C2') respectively, and the pair of
first positive and negative power supply voltages (ten B1) (-B +) and the second power supply
voltage (+82) (-B2) can be simply output, and moreover, when a high power supply voltage (+ B2)
(-82) is supplied, the output current is Because it is small, it obtains high output voltage of
transformer (T) The capacity of the added secondary winding can be reduced, and the structure
can be made similar to that in the case of supplying only the power supply voltage (ten B +)
(−Bl) for ordinary power supply. is there.
Furthermore, when a high supply voltage (+ 82X-82) is not supplied to the amplifier (A1), the
amplifier (AI) is consumed at a low supply voltage (10B + X-BI) L or no supply · ^ ° Reactive
power can be reduced. According to the above description, the present invention supplies a
power supply voltage corresponding to a change in load impedance to a power amplifier with a
power supply apparatus having a simple configuration similar to that of the prior art and
effectively supplies a desired maximum power output to a load over a wide band. It is possible to
reduce the reactive power consumption as well.
4. Brief Description of the Drawings FIG. 1 is a diagram showing an example of an impedance
characteristic of a speaker, and FIG. 2 is a block diagram showing an embodiment of the present
invention. In the drawing, (AI) is a power amplifier, (A2) is an error detector, (G +) is a gate
device, (CG) is a control signal generator, (CD) (CD ') is an overcurrent detector, (G2) (62'-) is the
voltage control FIG. 1 EndPage: 3
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