JPH0437206A - Power amplifier - Google Patents

Abstract

PURPOSE:To suppress noise at the time of low-outputting and to improve the distortion factor and the noise characteristic by providing a sound volume adjusting variable resistor, a buffer circuit for impedance matching and a current amplifier circuit whose voltage gain is 0dB to an output of a voltage amplifier circuit whose voltage gain is set to a desired gain. CONSTITUTION:An audio signal is amplified by a voltage amplifier circuit 8 and fed to a current amplifier circuit 11 through a sound volume adjustment variable resistor 9 and a buffer circuit 10. Then the signal is amplified by the current amplifier circuit 11 and fed to a speaker 12 or the like. Thus, the level of the audio signal after voltage amplification is changed by the sound volume adjusting variable resistor 9 and noise generated in the voltage amplifier circuit 8 is changed attended with the level change. Thus, the noise included in the output is suppressed at the time of low-outputting when the resistance of the resistor 9 is increased and the distortion factor of the output and the noise characteristic are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a power amplifier for an audio amplifier having a volume adjustment volume.

[Conventional technology]

Conventionally, this type of power amplifier is constructed as shown in FIG. 6, and an audio signal supplied to an input terminal (1) is first supplied to a volume adjustment volume (2).

Then, the audio signal whose level has been adjusted by the volume control (2) is sequentially subjected to voltage amplification in the voltage amplification circuit (3) and current amplification in the current amplification circuit (4), and is power amplified to a desired level, e.g. The signal is supplied to the speaker (5).

At this time, in order to stabilize the output, etc., a current amplification circuit (
A part of the output signal of 4) is passed through the negative feedback path (6)? Negative feedback is provided to the voltage amplification circuit (3) via the voltage amplification circuit (3).

[Problem to be solved by the invention]

In the case of the conventional power amplifier shown in FIG.
) does not change with operation, but increases at low output, as in the case of a general voltage amplification circuit.

Since the generated noise is directly propagated to the subsequent stage and added to the output, the distortion rate characteristics that affect the output noise, that is, the distortion rate and noise characteristics, are as shown in Figure 7, the harmonic distortion T
There is a problem that noise N increases and deteriorates when the power PO is low in output as HD decreases.

The present invention suppresses noise and reduces distortion at low output.

The object of the present invention is to provide an overall power amplifier with significantly improved noise characteristics.

[Means to solve the problem]

In order to achieve the above object, the power amplifier of the present invention includes a voltage amplification circuit set to a desired voltage gain;
A volume adjustment volume provided on the output side of the voltage amplification circuit, a buffer circuit for impedance matching provided after the volume, and a voltage gain provided after the buffer 7 circuit.
B current amplification circuit.

When improving distortion characteristics and DC output characteristics at high output, a current amplifier circuit is connected to an operational amplifier circuit for input via a bias circuit for driving, and a push-pull connected emitter follower circuit for current output. At the same time, the output of the emitter follower circuit that is supplied to the load is directly injected into the inverting input terminal on the reference side of the operational amplifier circuit for input to form a 100% negative feedback total voltage gain of 1 odB. , a correction signal corresponding to a fluctuation in the midpoint potential of the output of the emitter follower circuit, which is composed of a Miller integrator configured as an operational amplifier circuit whose to-off frequency is set to be lower than the input signal frequency; It is desirable to add a DC servo circuit that supplies the non-inverting input terminal on the input side.

[Effect]

In the case of the power amplifier of the present invention configured as described above, the audio signal is voltage amplified by the voltage amplification circuit, and then
The signal is supplied to a current amplification circuit via a volume adjustment volume and a buffer circuit, and the current is amplified by this amplification circuit before being supplied to a speaker or the like.

Then, the level of the audio signal after voltage amplification changes with the volume adjustment volume, and the noise generated in the voltage amplification circuit changes with this change.Secondly, at low output when the volume adjustment volume is turned down, The noise contained in the output is suppressed, and the distortion rate and noise characteristics of the output are improved.

At this time, the buffer circuit prevents fluctuations in the input impedance of the current amplification circuit due to volume operation, and stable power amplification is performed regardless of the magnitude of the output.

In addition, 100% is applied to the operational amplifier circuit for the input of the current amplifier circuit.
When the voltage gain of the current amplifier circuit is set to 10 dB by applying all negative feedback, and a DC servo circuit is added, harmonic distortion at high output can be suppressed due to 100% negative feedback of the current amplifier circuit. The DC servo circuit stabilizes the DC output of the follower circuit, which serves as the output stage of the current amplifier circuit, and suppresses DC drift in the output.

〔Example〕

One embodiment will be described with reference to FIGS. 1 to 5.

In FIG. 1, (7) is an audio signal input terminal;
(8' is a voltage amplification circuit, (9' is a volume adjustment volume, (10 is a buffer circuit for high novitance matching, (111 is a current amplification circuit, +12 is a speaker as a load, VI3 is a DC servo circuit) It is.

The voltage amplification circuit (8, for example, is an operational amplification circuit (8).
a) and a negative feedback path (8b) with an appropriate amount of feedback? Consists of a general constant gain voltage amplification circuit combined with an input terminal (7)
The audio signal is set to the desired voltage gain Vc
(dB) and output to the volume (9°).

This volume (9) is similar to the volume (2) in Figure 6,
It is operated based on the output adjustment to the speaker (12).

Then, by operating the volume control (9:), the voltage amplification circuit (
The output signal containing noise generated in the circuit (8) of 8) is variable-divided and output from the volume (9).

At this time, the magnitude of noise contained in the output signal of the volume (9) changes in proportion to the output signal, that is, in proportion to the output of the power amplifier.

Furthermore, is the output signal of the volume controller (9) a change in the input impedance of the current amplification circuit (11) based on volume manipulation? To prevent this, a buffer circuit (10) is provided.

This buffer circuit (Itl) is formed, for example, by a transistor transistor circuit in order to reduce the total input impedance.

Furthermore, a current amplifier circuit (11 is a human-powered operational amplifier circuit (lla)) to which the output signal of the volume controller (9) is supplied via a buffer circuit (10) is supplied with a bias circuit i% (11
b) An emitter follower circuit (llc) with a push-pull connection of transistors for current output through the circuit (connected to 10).

Then, the drive bias value of the bias circuit (llb) changes in proportion to the output signal of the buffer circuit (10), and based on this change, the emitter follower circuit (llc) converts the output signal of the volume (9) into a predetermined current gain. Amplify the current with G+ (dB).

At this time, in order to make the voltage gain OdB, the output of the epitaxial follower circuit (11) is connected to a negative feedback path (lid) for direct connection.
) is directly feedback-injected to the inverting input terminal (-) on the reference side of the operational amplifier circuit (lla) through k.

Through this feedback injection, 100% negative feedback is applied to the current amplification circuit (++), eliminating any voltage amplification that causes noise, and also absorbing harmonic distortion of the output signal of the emitter follower circuit (11C). .

And the emitter follower circuit (11c) after current amplification
The output signal is supplied to the speaker (12) as a power amplified audio signal.

At this time, if you close down the volume (9) all the way and adjust the low output by 1, the noise generated in the voltage amplifier circuit (8) will be less propagated to the subsequent stage, and the noise of the power supplied to the speaker (12) will be reduced. This is significantly suppressed compared to the case shown in the figure.

The second one has the same distortion rate and noise characteristics as in Figure 7.
As shown in the figure, noise at low output is suppressed and significantly improved.

By the way, when omitted from the DC servo circuit Q31', 1
Even if 00% negative feedback is applied, the operational amplifier circuit (,
The DC potential of the non-inverting input terminal (+-) of 1la) is unstable, and the DC potential (midpoint -) of the output of the emitter follower circuit (IIC) becomes unstable.

Therefore, for example, when building a high-grade power amplifier that also requires stabilization of the DC characteristics of the output, it is necessary to use a DC servo circuit (
13 is added.

This subcircuit I3 is an operational amplifier circuit (13a)
and a DC level setting hole that generates the reference voltage Vref2.
) It consists of a Miller integrator with an operational amplifier configuration using a ram (13b), and is it affected by power supply fluctuations in output adjustment? In order to eliminate as much as possible, for example, an amplifier circuit, 8. ,．． 11 and the buffing circuit, a power supply separate from that of Io is supplied.

Then, the operational amplifier circuit (13a) forms a correction signal according to the difference between, for example, the reference voltage ~'ref of OV and the midpoint potential of the output of the emitter follower circuit (IIC), and this correction signal is used as the bias signal. As an operational amplifier circuit (]la)
is supplied to the non-inverting input terminal (+) of

The DC drift of the output is suppressed, and the DC characteristics are significantly improved and stabilized.

Note that the cutoff frequency of the mirror integrator is set to a number 1-(Z) lower than the signal frequency so as not to affect the audio signal.

An example of a specific circuit connection of each part shown in FIG. 1 is shown in FIG. 3.

In the same figure, (Ql) to (Q9) are voltage amplification circuits; 8
It is a transistor that forms a transistor (Ql)
~ (Q3) constitutes the input stage, and the transistor (Q4) ~
(Q7) constitutes a drive stage and a negative feedback path (8b),
Transistors (Q8) and (Q9) constitute an output stage.

(QIO) to (Q13) are transistors connected to Turlington that form the buffer circuit (lo'), (Q14) to (Q
18), (Q19) to (Q22) are current amplifier circuits (11
) bias circuit (llb).

This is a transistor forming an emitter follower circuit (llc).

In addition, (Dl) to (D4), (D7) to (Dl3) are rectifier diodes, (D5) and (D6) are Zener diodes, (C1) to (C22) are capacitors, (G) is a coil, ( R1) to (R56) are resistors.

Furthermore, DVI), (-Vl) hat1 width times i%fs)
, [++] and Hihanofa circuit (positive and negative DC power supplies supplied to lot +VCC't-vccl) terminals, (+
V2), (-V2) are the terminals of the positive and negative DC power supplies +VCC2 and -VCC2 supplied to 131.

In FIG. 3, especially the operational amplifier circuit (ll
The power supply circuit configuration a) has the following characteristics.

That is, the operational amplifier circuit (lla) has a breakdown voltage of less than ±20V, similar to an operational amplifier circuit having a general integrated circuit configuration.

On the other hand, the voltage of the terminals (10~'1) and (-Vl) CC1 is, for example, ±50V-+ in the case of 100W output.
The voltage is close to 0 to ', which far exceeds the withstand voltage of the operational amplifier circuit (lla).

Based on the voltage drive of VCCI, the voltage of the human input signal of the operational amplifier circuit (lla) changes over a wide range of ±vCC1, as shown by the solid line l in the diagram Q4.

For example, the terminals (+V1), (-V2
) are connected to the positive and negative power supply terminals (10V'') j (-Vl) of the operational amplifier circuit (lla) via a voltage dividing resistor, and the midpoint of the power supply voltage of the operational amplifier circuit 1 (lla) is If it is set as the ground point of QV, the operational amplifier circuit (lla) will be destroyed.

Therefore, in FIG. 3, a Zener diode (D) is used.

(D6) and capacitors (C13) and (C14) form a constant voltage source (El) and (R2) of a voltage VB lower than the withstand voltage of the operational amplifier circuit (lla) in FIG. ) power supply terminals (+Vi) and (-'1) are connected to the non-inverting input terminal (
-1-).

At this time, the operational amplifier circuit (lla) operates floating from the ground point, and the power supply voltage becomes ~'B above the voltage midpoint of the input signal of the non-inverting input terminal (+).

Then, the voltage terminal (+V1) of the operational amplifier circuit (lla)
.

(-~'1) changes (sinks) according to the voltage of the input signal, as shown by the solid lines +v and -v in Figure 4, so destruction of the operational amplifier circuit f% (lla) is prevented. Ru.

The circuit connections in each circuit (8., (105,:n, Q3i) are not limited to those in the embodiment.

〔Effect of the invention〕

Since the present invention is configured as described above, it produces the effects described below.

A volume adjustment volume is provided on the output side of the voltage amplification circuit, and the output signal of the voltage amplification circuit via this volume is supplied to a current amplification circuit via a buffer circuit, and this current amplification circuit converts the input signal with a voltage gain of OdB. Second, when the output is low, the propagation of the noise generated in the voltage amplification circuit to the subsequent stage is reduced by the volume adjustment volume, and the distortion rate and noise characteristics of the output are reduced. Significantly improved.

Also, an operational amplifier circuit for all inputs of the current amplifier circuit.

Formed by a bias circuit and emitter follower circuit,
Apply 100% negative feedback from the emitter follower circuit to the operational amplifier circuit to make the voltage gain of the current amplifier circuit 10 dB.
Furthermore, when a DC servo circuit is added, harmonic distortion is absorbed and improved by the negative feedback, and furthermore, the DC servo circuit prevents DC drift of the output and improves DC characteristics.

[Brief explanation of drawings]

1 to 5 show one embodiment of the power amplifier of the present invention, FIG. 1 is a circuit block diagram, and FIG. 2 is a pressure distortion factor,
Noise characteristic diagram, Figure 3 is a specific wiring diagram of each part in Figure 1, Figures 4 and 5 are waveform diagrams for explaining part of the power supply in Figure 3, 2 equivalent circuit diagrams, Figure 6, FIG. 7 is a circuit block diagram, output distortion rate, and noise characteristic diagram of a conventional example. 8 Voltage amplification circuit, (9 Volume adjustment volume, ila
Buffer circuit, 11 Current amplification circuit, (lla) Input arithmetic intensifier circuit, (lib), -t<Ias circuit, (IIC) Emitter follower circuit, 113.・
DC servo circuit. Figure 1

Claims (2)

[Claims] (1) A voltage amplification circuit set to a desired voltage gain,
A volume adjustment volume provided on the output side of the voltage amplification circuit; a buffer circuit for impedance matching provided after the volume; and a voltage gain provided after the buffer circuit.
A power amplifier for an audio amplifier, characterized in that it is equipped with a current amplification circuit of B. (2) a voltage amplification circuit set to a desired voltage gain; a volume adjustment volume provided on the output side of the voltage amplification circuit; a buffer circuit for impedance matching provided after the volume; A push-pull connected emitter follower circuit for current output is connected to the operational amplifier circuit for input via a bias circuit for driving, and the output of the emitter follower circuit is provided at the rear stage of the buffer circuit and is supplied to the load. Feedback is directly injected into the inverting input terminal on the reference side of the operational amplifier circuit for input, and 100% negative feedback is applied to reduce the voltage gain.
dB, and a Miller integrator configured as an operational amplifier circuit whose cutoff frequency is set lower than the input signal frequency. A power amplifier for an audio amplifier, comprising: a DC servo circuit that supplies a signal to a non-inverting input terminal on the signal input side of an operational amplifier for the audio amplifier.