JPH0635535Y2 - Click sound prevention circuit in direct-coupled amplifier - Google Patents

Description

[Detailed Description of the Invention] [Industrial field of application] The present invention relates to a click sound prevention circuit in a direct-coupled amplifier, and in particular, a click noise in a direct-coupled amplifier that prevents the load from being affected when the power switch is turned on and off. Regarding sound prevention circuit.

[Conventional technology]

This type of amplifier is known to be capable of driving a speaker by amplifying an output signal of a pickup cartridge, a tape recorder, a tuner, etc. of a record player. Such an amplifier includes a front-stage amplifier circuit that amplifies an input signal, a single-ended push-pull circuit that power-amplifies the signal from the amplifier circuit, and a bias voltage that supplies a bias voltage to the single-ended push-pull circuit. A supply circuit and a power supply circuit for supplying DC power to the single-ended push-pull circuit and the like are provided, and the single-ended push-pull circuit is configured to drive a speaker that is a load.

Since such an amplifier does not use an output transformer, it has a wide frequency band and a small distortion, and is therefore widely used at present.

In particular, recently, with the progress of miniaturization of circuit elements along with the progress of semiconductor technology and the like, it has become difficult to obtain an amplifier which adopts a dual power supply system and has no output capacitor. For this reason, the speaker circuit is provided with a protective relay contact because it is necessary to prevent the speaker from being burned due to the destruction of the element that constitutes the single-ended push-pull circuit.

However, such a protective relay has a drawback in that it requires a large amount of current because it passes a considerable amount of current through its contacts, and occupies a considerable place in the device. Further, if the contacts of the protective relay are present in the speaker circuit, the sound quality is deteriorated. Therefore, it has been desired to eliminate the protective relay contacts in the speaker circuit.

[Problems to be solved by the invention]

Therefore, by making full use of recent semiconductor technology, etc., a protector circuit to prevent the burnout of the speaker is electronically configured, and the speaker is directly connected to the output of the single-ended push-pull circuit. By using an amplifier, the above two drawbacks could be overcome.
However, according to the above-mentioned direct-coupled amplifier, since there is a difference in operation time between the amplifier circuit in the previous stage and the single-ended push-pull circuit, the influence is exerted when the power switch is turned on and off, and the speaker that is a load is driven. As a result, there is a problem that the sound is output as a special sound or the speaker is destroyed in some cases.

The present invention has been made in order to solve the above-mentioned problems of the prior art, and it is an object of the present invention to provide a click noise prevention circuit in a direct-coupled amplifier that does not affect the load when the power switch is turned on and off. To aim.

[Means for solving problems]

The click noise preventing circuit in the direct-coupled amplifier according to the present invention which achieves the above object inputs the operation signal from the differential amplifier circuit of the preceding stage to the input terminal of each constituent element of the single-ended push-pull circuit, and the single-ended push-pull circuit. A load is connected between the output end of the circuit and the common potential point, the potential at the connection point between the load and the output end is taken in, and a feedback signal for maintaining the potential at this connection point at the same potential as the common potential point is formed. A direct-coupled amplifier circuit provided with a DC servo amplifier circuit for feeding back to the differential amplifier circuit, the input signal of the DC servo amplifier circuit when an output signal from the differential amplifier circuit is turned on / off. It is characterized in that a detection circuit to be introduced into is provided.

[Action]

According to the present invention, when the power switch is turned on / off, the detection circuit introduces the output signal from the differential amplifier circuit to the input terminal of the DC servo amplifier circuit. Then, the output signal from the differential amplifier circuit is immediately fed back through the DC servo amplifier circuit, and the differential amplifier circuit converges to the stable region very quickly when the power switch is turned on or relatively when the power switch is turned off. Since the stability is maintained for a long time, the output end of the single-ended push-pull circuit is also maintained at the potential of the common potential point.

Therefore, even if the power switch is turned on and off,
The effect does not appear on the speaker, which is the load.

〔Example〕

 Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram showing a basic configuration of an embodiment of a click sound prevention circuit in a direct connection amplifier according to the present invention.

An embodiment of the click sound prevention circuit in the direct-coupled amplifier shown in FIG. 1 includes an operation amplification circuit 2, a bias voltage supply circuit 4,
A single-ended push-pull circuit 6 composed of two complementary transistor elements Tr1 and Tr2, a direct-coupled amplifier 10 composed of a DC servo amplifier circuit 8 and a negative feedback circuit 9, and a power supply for an output signal from the differential amplifier circuit 2. The power supply circuit 30 includes a detection circuit 20 which is introduced into the input terminal of the DC servo amplifier circuit when the switch is turned on and off.

That is, the configuration of the direct coupling amplifier 10 is as follows. The circuit configuration is such that the operation signal from the differential amplifier circuit 2 at the preceding stage can be input to the input terminals of the respective constituent elements Tr1 and Tr2 of the single ended push-pull circuit 6. A load 40 is connected between the output terminal OUT of the single ended push-pull circuit 6 and the common potential point G. The potential of the output terminal OUT is taken into the DC servo amplifier circuit 8 and the normal negative feedback circuit 9. In the DC servo amplifier circuit 8, the output terminal OUT has a common potential point G
A feedback signal for maintaining the same potential as the potential of 1 is formed and fed back to the input terminal of the differential amplifier circuit 2. Further, the normal negative feedback circuit 9 divides the output from the output terminal OUT with resistors 90 and 91 and supplies the divided signal from the voltage dividing point J to the input terminal of the differential amplifier circuit 2. .

The single ended push-pull circuit 6 is, for example, NP
The emitters of the N-transistor Tr1 and the PNP transistor Tr2 are connected to each other so that the signals from the preceding stage operational amplifier circuit 2 are input to each base, and
The collector of Tr1 is used as the positive output of the power supply circuit 30, and the transistor T
The collector of r2 is connected to the-output of the power supply circuit 30, respectively, and the connection point between the emitters and the power supply circuit
The speaker 40 can be connected to the common potential point (neutral point) of 30.

Further, the detection circuit 20 for introducing the output signal from the differential amplifier circuit 2 into the input terminal of the DC servo amplifier circuit 8 when the power switch is turned on and off is configured as follows. A resistor having the same resistance value between both outputs of the differential amplifier circuit 2.
Connect a series connection of 200 and 201. Further, the input signal from the output terminal OUT is input to the input terminal of the DC servo amplifier circuit 8 via the resistors 202 and 203. Connection point of the C _a resistor 200 and 201, the resistors 202 and 203 and the connection point C _b, the power switch 50
It is connected by the switch means 204 which is interlocked with the power switch 50 and is turned on for a fixed time from the on / off of the power switch 50 as shown in FIG.

The power supply circuit 30 has large-capacity capacitors 31 and 32 connected in series,
Transformer 3 with the connection point of the capacitors 31 and 32 as the neutral point
3 is connected to the intermediate point G ₀ , the electrode of the capacitor 31 is connected to the A ₁ point of the transformer 33 via the diode 34, and the A ₂ point of the transformer 33 is connected via the diode 35 to the electrode of the capacitor 32. It is connected to the A ₁ point of the transformer 33 via the diode 36 and to the A ₂ point of the transformer 33 via the diode 37, and the electrode of the capacitor 31 is used as a positive output and the electrode of the capacitor 32 is a −.
As an output, the primary side of the transformer 33 is connected to an AC power source via a power switch 50.

The operation of the embodiment thus configured will be described.

First, when the power switch 50 is turned on, the switching means 204, as shown in FIG. 2, for a certain time period t _a,
Turn on. Then, the signal from the differential amplifier circuit 2 is input to the DC servo amplifier circuit 8 via the resistors 200, 201 and 203. As a result, the DC servo amplifier circuit 8
Forms a feedback signal so that the connection point Ca of the resistors 200 and 201 has a common potential, and feeds the feedback to the differential amplifier circuit 2. Then, the differential amplifier circuit 2 reaches a stable point relatively quickly, so that the output terminal OUT of the single-ended push-pull circuit 6 also has a common potential (neutral point potential). Therefore, from the speaker 40,
No clicking sound is generated even when the power switch 50 is turned on.

On the other hand, when you turn off the power switch 50, the switching unit 204, as shown in FIG. 2, a certain period of time t _b,
Turn on. Then, the signal from the differential amplifier circuit 2 is input to the DC servo amplifier circuit 8 via the resistors 200, 201 and 203. As a result, the DC servo amplifier circuit 8
Forms a feedback signal so that the connection point Ca of the resistors 200 and 201 has a common potential, and feeds the feedback to the differential amplifier circuit 2. Then, the differential amplifier circuit 2 is kept stable for a relatively long time, so that the output end OUT of the single-ended push-pull circuit 6 is also maintained at the common potential (neutral point potential). Therefore, from the speaker 40,
Even if the power switch 50 is turned off, no click sound is generated.

FIG. 3 is a circuit diagram showing a configuration example of a DC servo amplifier circuit used in the same embodiment.

This DC servo amplifier circuit 8 is an operational amplifier.
OA ₁ , capacitor C and resistor R ₁ form an integrator circuit, and diodes D ₁ and D ₂ connected in antiparallel to the input terminal of this operational amplifier OA ₁ are connected for protection. resistor R ₂ to R ₅ and op-amp output
The signal is amplified by the amplifier circuit composed of OA ₂ and can be input to the input terminal J of the differential amplifier circuit 2.

In this way, the speaker 40 is prevented from being affected when the power switch 50 is turned on / off.

The single-ended push-pull circuit 6 has been described as the most basic circuit, and it is needless to say that the single-ended push-pull circuit having a complicated structure can naturally obtain the above-described effects. Absent.

[Effect of device]

Since the present invention is as described above, there is an effect that even if the power switch is turned on / off, the load is not affected.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a basic configuration of an embodiment of a click sound prevention circuit in a direct-coupled amplifier according to the present invention, and FIG. 2 is a time chart shown for explaining the operation of a power switch and a switch means of the same embodiment. 3 is a circuit diagram showing the DC servo amplifier circuit of the same embodiment. 2 ... Differential amplifier circuit, 4 ... Bias voltage supply circuit, 6
...... Single-ended push-pull circuit, 8 …… DC servo amplifier circuit, 10 …… Direct connection amplifier, 20 …… Detection circuit, 30
...... Power supply circuit, 50 ...... Power switch.

Claims (1)

[Scope of utility model registration request] 1. An operating signal from a differential amplifier circuit at a preceding stage is input to an input end of each constituent element of a single ended push-pull circuit, and a load is applied between an output end of the single ended push-push circuit and a common potential point. , A DC servo amplifier that takes in the potential at the connection point between the load and the output terminal, forms a feedback signal for maintaining the potential at this connection point at the same potential as the common potential point, and feeds it back to the differential amplifier circuit. A direct-coupled amplifier having a circuit, characterized in that a detection circuit for introducing the output signal from the differential amplifier circuit to the input end of the DC servo amplifier circuit when the power switch is turned on and off is provided. Click sound prevention circuit in a direct-coupled amplifier.