JPH11289228A - Amplifying device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the distortion of an internal power amplifier and to eliminate an unfavorable effect such as distortion on a signal outputted from a pre-out terminal, by providing an amplification varying circuit which reduces the amplification level of a preamplifier at the time of detecting an output that is a prescribed level or more. SOLUTION: An input signal is amplified by a preamplifier 2 and the signal which is further amplified by a voltage amplifier circuit 5 of a power amplifier 4 is inputted to the built-in power amplifier 4. When an input signal of a level that is higher than a fixed level is inputted, it exceeds a power amplifiable signal level in the circuit 5 and exceeds the voltage of power supply voltage ±B of the amplifier 4, distortion occurs and noise gets mixed with an output signal of an output terminal 7 because it is amplified by both the preamplifier 2 and the circuit 5. Therefore, an output signal is outputted as a control signal from a comparator 10 which compares a signal attenuated by an attenuator(ATT) 9 with a signal inputted to the amplifier 4, an amplification control circuit provided in the preamplifier 2 is controlled and the amplification is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amplifying device such as a multi-channel audio amplifier.

[0002]

2. Description of the Related Art Conventionally, it is impossible for an audio amplifier to output an output signal having an amplitude close to a power supply voltage without distortion. If an excessive signal is input, the waveform is changed to the power supply voltage of the amplifier whose power is amplified. Greatly affected by Conventionally, the input and output waveforms of a power amplifier are compared, and when the difference is large (that is, the output waveform is distorted), the amplification of the preamplifier, which is the preceding stage, is varied to lower the amplification from the input to the output. Thus, circuits for preventing waveform distortion have been used.

[0003]

However, when a conventional amplifying device having a power amplifier is provided with a pre-out terminal for outputting a pre-amplifier output (hereinafter referred to as "pre-out") and is connected to an external power amplifier, the power amplifier that has been used is used. Despite that, the amplification degree of the preamplifier is controlled by the output distortion due to the voltage clip, the signal output from the pre-out terminal contains a distortion component, and a large level fluctuation occurs.

In order to solve this problem, a buffer amplifier may be added between the preamplifier and the power amplifier to eliminate a change in the output of the preamplifier. There were problems such as the need to add and the need for space.

[0005]

According to the present invention, an input terminal to which a signal is input, a preamplifier for amplifying a signal input to the input terminal, a preout terminal for outputting a signal of the preamplifier to the outside, A power amplifier that power-amplifies the signal amplified by the preamplifier, a detection circuit that detects an output of the power amplifier, and an amplification variable circuit that lowers the amplification of the preamplifier when an output equal to or more than a predetermined value is detected by the detection circuit. An amplifying device comprising:

Further, the present invention provides an input terminal to which a signal is input, a preamplifier for amplifying the signal input to the input terminal, a preout terminal for outputting the signal of the preamplifier to the outside, and an amplifier amplified by the preamplifier. Power amplifier that power-amplifies the output signal, a comparison circuit that compares input and output signals of the power amplifier and outputs a signal proportional to distortion, a current detection circuit that detects an output current of the power amplifier, and the current detection circuit. And a control circuit for lowering the degree of amplification of the preamplifier in accordance with the output of the comparison circuit when the output current of the power amplifier is detected by a predetermined amount or more.

The present invention also provides an input terminal to which a signal is input, a preamplifier for amplifying a signal input to the input terminal, a preout terminal for outputting a signal of the preamplifier to the outside, and an amplifier amplified by the preamplifier. A power amplifier that amplifies the amplified signal, an amplification control circuit that controls the amplification of the preamplifier, and compares an input signal input to the power amplifier and an output signal output from the power amplifier and is proportional to the distortion. A comparison circuit for outputting a signal; a switch for turning the output of the comparison circuit on or off to the amplification control circuit; a detection circuit for detecting the output of the power amplifier; When the output is smaller, the switch is turned off, and when the output of the detection circuit is equal to or more than a predetermined value, the switch is turned on and the output of the comparison circuit is controlled by the amplification degree control. An amplification device comprising a switch control circuit connected to the circuit.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the amplifying device of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing one embodiment of the amplifying device of the present invention. The audio signal input to the input terminal 1 is voltage-amplified by the preamplifier 2, and a signal is output from the preout terminal 3 for connection to an external amplifier or the like.

The built-in power amplifier 4 of this embodiment is
Transistor 6a of voltage amplification circuit 5 and power amplification circuit 6
And a circuit having emitter resistors 6c and 6b are connected between power supplies + B and -B. The output of the power amplifier 4 is output from the output terminal 7 to the speaker 8.

At this time, if there is no distortion in the output signal, the input signal of the voltage amplification stage 5 of the power amplifier 4 and the signal output to the output terminal 7 are brought to the same signal level via an attenuator (hereinafter referred to as ATT). And the signals are compared by the comparator 10. At this time, the output of the comparator 10 has no distortion in the power amplifier 4 and no variable control output of the amplification degree of the preamplifier 2 is output regardless of whether the switch 11 is opened or closed. Therefore, the amplification of the signal output from the pre-out terminal is constant.

Next, the operation when the output is distorted when the built-in power amplifier 4 is used will be described. The input signal is amplified by the preamplifier 2 and further amplified by the voltage amplifier circuit 5 of the power amplifier 4 is input to the built-in power amplifier 4. Since the signal is amplified by the preamplifier 2 and the voltage amplifying circuit 5, when an input signal having a level larger than a certain level is input, the signal level exceeds the signal level that can be amplified by the voltage amplifying circuit 5 and the power supply voltage of the power amplifier 4 ± When the voltage exceeds the voltage of B, a negation (clip of the output signal) occurs. The output signal of the output terminal 7 is mixed with noise due to distortion.

Therefore, the comparator 10 that compares the signal whose output signal has been attenuated by the ATT 9 with the signal input to the power amplifier 4 receives a different signal and outputs a signal proportional to the distortion (clip amount) of the output signal. Is output as a control signal, and this control signal controls an amplification degree control circuit provided in the preamplifier 2 to lower the amplification degree.

The control output of the comparator 10 is connected to the amplification control circuit of the preamplifier 2 via the switch 11,
When the switch 11 is turned on, the amplification control circuit of the preamplifier 2 is variably controlled. That is, the switch 11
Is ON and the output of the comparator 10 is large, the amplification of the preamplifier 2 is set to be small, and the amplification of the preamplifier 2 is reduced, so that the output distortion is automatically reduced.

Next, the ON / OFF setting of the switch 11 will be described. Although not shown, the amplifying device of the present embodiment is provided with an input terminal, a pre-out terminal, and an output terminal so that a plurality of channels can be reproduced, for example, as a surround reproduction channel, and a speaker is connected to the plurality of output terminals to output a signal. You.

When the signal of each output channel is being reproduced, a current proportional to the output signal flows through the resistor 6c of the power amplifier of one channel.
A potential difference occurs at both ends of c. This potential difference is input to the output current detection circuit 12, and the attenuator resistance R
1 or R2 and a transistor TR1 that performs a switching operation via a capacitor C1 that bypasses a high frequency, is turned ON or OFF.
An FF is set, and the switch 11 is controlled to be ON or OFF.

The output current detection circuit 12 is connected to the output resistance 6c when the signal is not being reproduced or when the speaker 8 is not connected and the light load is not shown (not shown). Does not flow the current due to the output signal,
There is no potential difference between both ends of the resistor 6c due to the signal. Therefore, the output of the output current detection circuit 12 is in the OFF state, and a control signal for turning off the switch 11 is output.

Also, when the built-in power amplifier 4 is used, a large distortion does not occur in the case of a signal having a normal input signal level, but a distortion occurs in an output signal when a signal larger than the normal level is input, Then, a large current flows through the resistor 6c, the potential difference between both ends of the resistor 6c increases, the transistor TR1 of the output current detection circuit 12 is turned on, the switch 11 is turned on by the output current detection circuit 12, and the comparator 10 serves as a distortion prevention circuit. , The amplification degree of the preamplifier 2 is reduced.

When an external power amplifier and a speaker are connected to the pre-out terminal 3 for reproduction without using the built-in power amplifier 4, the output current of the built-in power amplifier 4 does not flow. The output is always off, and the switch 11 is always off. Therefore, there is no fear that the output signal from the pre-out terminal 3 includes distortion due to the power amplifier 4.

Even if the output is distorted in the voltage amplifier circuit 5 and the power output circuit 6 of the built-in power amplifier 4 due to the input over, power is not consumed. The effect of the distortion caused by the above does not affect other amplifier circuits. Further, the variable control of the amplification degree of the preamplifier 2 is not performed, and an unnecessary change in the output level of the output signal of the preout terminal 3 does not occur.

According to the distortion preventing device for an audio amplifier of this embodiment, the unnecessary output change of the pre-out terminal, which has been caused by the operation of the distortion preventing device in the past, can be reduced by the output current of the built-in power amplifier. Since the switch is controlled so as to prevent distortion by detection by an output current detection circuit for detection, there is little possibility that harmonics due to distortion from the power supply or output cord will be mixed into the output signal of the pre-out terminal 3. This embodiment can improve the distortion of the output of the pre-out terminal in a multi-channel amplifier such as a stereo amplifier and an AV amplifier.

[0021]

According to the present invention, the distortion of the built-in power amplifier can be prevented, and the signal output from the pre-out terminal can be prevented from being adversely affected by the influence of the distortion at the time of power amplification.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of an amplifying device of the present invention.

[Explanation of symbols]

 Reference Signs List 1 input terminal 2 preamplifier 3 preout terminal 4 power amplifier 5 voltage amplifier 6 output circuit 7 output terminal 8 speaker 9 ATT 10 comparator 11 switch 12 detection transistor circuit

Claims (3)

[Claims] An input terminal to which a signal is input; a preamplifier that amplifies a signal input to the input terminal; a preout terminal that outputs a signal of the preamplifier to the outside; A power amplifier for amplifying, a detection circuit for detecting an output of the power amplifier, and an amplification variable circuit for lowering the amplification of the preamplifier when an output of a predetermined value or more is detected by the detection circuit. Amplifying device. 2. An input terminal to which a signal is input, a preamplifier that amplifies a signal input to the input terminal, a preout terminal that outputs a signal of the preamplifier to the outside, and a power amplifier that amplifies the signal amplified by the preamplifier. A power amplifier that amplifies, a comparison circuit that compares input and output signals of the power amplifier and outputs a signal proportional to distortion, a current detection circuit that detects an output current of the power amplifier, An amplifying device comprising: a control circuit that reduces an amplification degree of the preamplifier according to an output of the comparison circuit when an output current is detected by a predetermined amount or more. 3. An input terminal to which a signal is input, a preamplifier for amplifying a signal input to the input terminal, a pre-out terminal for outputting a signal of the preamplifier to the outside, and a power amplified by the preamplifier. A power amplifier that amplifies, an amplification control circuit that controls the amplification of the preamplifier, and compares an input signal input to the power amplifier and an output signal output from the power amplifier to output a signal proportional to distortion. A comparison circuit, and an output of the comparison circuit to the amplification degree control circuit is turned on or off.
F, a switch for detecting the output of the power amplifier; and a switch for turning off the switch when the output of the power amplifier is smaller than a predetermined value, and for the switch when the output of the detection circuit is higher than a predetermined value. An amplification device comprising: a switch control circuit that turns on and connects an output of the comparison circuit to the amplification control circuit.