JPH0617218Y2 - Audio amplifier - Google Patents

Description

[Detailed Description of the Invention] [Industrial application] The present invention relates to an audio amplifier, and in particular, one of a plurality of input sources is selectively selected, amplified and output, and a predetermined time is elapsed after power is turned on. The present invention relates to an audio amplifier in which the output is muted only during the period.

[Conventional technology]

Generally, an audio amplifier (hereinafter, simply referred to as "amplifier") is a user-specified one from a plurality of input sources.
The output is muted for a predetermined time (about 4 seconds) from when the power of the amplifier is turned on to when the gain becomes stable. This prevents the speaker from producing unnatural sound.

A schematic configuration of a conventional amplifier is shown in FIG.

A selector circuit (analog function switch I array I) is connected to input terminals IN _{1 to} IN _n to which a plurality of audio sources such as PHONO, CD, and TUNER are individually input.
C) 10 is connected, and one input source designated by the user is alternatively selected and output.

The output of the selector circuit 10 is amplified by the amplifier 12 and output from the output terminal OUT to, for example, the external speaker 14.

On the input side of the amplifier 12, a muting transistor Tr is provided between the signal input line of the amplifier 12 and ground, and the transistor output can be muted by turning on the transistor Tr if necessary. It has become.

The selector circuit 10 and the transistor Tr are controlled by the microcomputer 16.

The microcomputer 16 is connected with a source changeover switch 18 for a user to specify a desired source, a power switch 20, a display 22 such as an FL tube or an LED.

The microcomputer 16 executes an initial process according to an ON operation of the power switch 20 and a source switching process according to an operation of the source change switch 18 according to a predetermined program stored in the ROM.

Regardless of whether the power switch 20 is on or off, the microcomputer 16 is always supplied with power from a sub power supply circuit (not shown). On the other hand, power is supplied to the amplifier 12 and the selector circuit 10 when the microcomputer 16 turns on the main power supply circuit.

Specifically, according to the flowchart shown in FIG. 4, when the power switch 20 is first turned on, YES is determined in step 30 to turn on the main power supply circuit to turn on the amplifier 12 and the selector circuit 10 and Step 3
2) The control output of "H" level is output to the transistor Tr to turn it on, the input signal of the amplifier 12 is dropped to ground, and the output of the amplifier is muted (step 34).

Subsequently, a 4s timer for muting and a 0.5s timer for display are set (step 3).
6, 38).

Then, it waits until the 0.5s timer expires (step 40).

When the 0.5 s timer times out, the microcomputer 16 determines YES in step 40, determines the initial setting source from the switching position of the source changeover switch 18 at that time, and creates and displays source display data related to this source. It is output to the instrument 22 and the initial setting source is displayed (step 44).

For example, if the source changeover switch 18 has been previously switched to the CD position, the display 22 will display <CD>, and immediately after the power switch 20 is turned on, it is possible to visually confirm what the initial setting source is.

Subsequently, the microcomputer 16 creates the source data for controlling the selector circuit related to the initial setting source and outputs it to the selector circuit 10, closes the analog function switch related to the input of the initial setting source, and closes the analog function switches related to other input sources. The function switch is opened, and only the initial setting source is selected and output to the amplifier 12 side (step 46).

Thereby, for example, the audio signal of the CD is transmitted to the amplifier
It is output to the side.

After that, when the 4s timer times out, the microcomputer 16 determines YES in step 42, outputs an "L" level control output to the transistor Tr to turn it off, and sets the input signal of the amplifier 12 to the original level. The mute is released by returning it (step 48).

As a result, the sound related to the initial setting source is reproduced and output from the speaker 14.

Of course, if the user operates the source selector switch 18 to switch the source, the microcomputer 16
Source display data and selector circuit control data relating to the newly designated source are created and output to the display 22 and the selector circuit 10 to change the display of the source and the output from the selector circuit 10 (steps 50 and 52). .

In this way, after the power is turned on, the output of the amplifier is muted until the gain of the amplifier 12 stabilizes, thereby preventing generation of an unnatural sound.

[Problems to be solved by the invention]

However, in the above-described conventional technique, the on-resistance of the transistor Tr does not always become zero at the time of mute. Therefore, in the selector circuit 10, when the analog function switch related to the input source selected in the initialization process of the microcomputer 16 is closed. A part of the audio signal of the initial setting input source is input to the amplifier 12.
Therefore, in the case where the amplifier 12 has a high gain, there is a problem that the sound of the input source leaks from the speaker 14 even when muted.

In view of the problems of the prior art, the present invention has an object to provide an audio amplifier capable of reliably preventing sound leakage during mute.

[Means for solving problems]

In the audio amplifier according to the present invention, a selector circuit that selectively selects and outputs one from a plurality of input sources, and controls this selector circuit. When the source is specified, the specified one is selected. A selector control circuit that outputs an input source, an amplifier that amplifies the output signal of the selector circuit, a mute circuit that sets the input of this amplifier to zero as necessary, and a mute circuit that controls the mute circuit A mute control circuit for activating the mute circuit to mute the amplifier input and deactivating the mute circuit for a predetermined time after the power is turned on to release the mute; The output of the selector circuit is kept open until the time elapses, and the preset value is set after the elapse of the predetermined time from the power-on. It is characterized by a certain one of the input source and so as to output from the selection circuit.

〔Example〕

One embodiment of the present invention will be described with reference to FIG.

FIG. 1 shows a block diagram of an amplifier according to the present invention.

A selector circuit (analog function switch array I) is connected to input terminals IN _{1 to} IN _n to which a plurality of audio sources such as PHONO, CD, and TUNER are individually input.
C) 10 is connected, and one input source designated by the user is alternatively selected and output.

An amplifier 12 is connected to the output side of the selector circuit 10, and the audio signal related to the source selected by the selector circuit 10 is amplified and output to the output terminal OUT.

For example, a speaker 14 is externally connected to the output terminal OUT, and sound is reproduced based on the output of the amplifier.

On the input side of the amplifier 12, a muting transistor Tr is provided between the signal input line of the amplifier 12 and ground, and the transistor output can be muted by turning on the transistor Tr if necessary. It has become.

A microcomputer 16A is connected to the selector circuit 10 and the transistor Tr, and receives predetermined source switching control and on / off control.

The microcomputer 16A is connected with a source changeover switch 18 for a user to specify a desired source, a power switch 20, a display 22 such as an FL tube or an LED.

The microcomputer 16A executes an initial process when the power switch 20 is turned on, a source change process when the source change switch 18 is operated, and the like according to a predetermined program stored in the ROM.

The microcomputer 16A is always supplied with power from a sub power supply circuit (not shown) regardless of whether the power switch 20 is on or off. On the other hand, power is supplied to the amplifier 12 and the selector circuit 10 by turning on the main power supply circuit by the microcomputer 16A.

Next, the operation of the above embodiment will be described with reference to the flowchart shown in FIG.

It is assumed that the power switch 20 has been turned off and the source selector switch 18 has been switched to the CD position in advance.

When the power switch 20 is off, the microcomputer 16A repeatedly determines whether or not the power switch 20 is on (step 60).

When the user turns on the power switch 20 to operate the amplifier, the microcomputer 16A proceeds to step 60.
In step 62, the main power supply circuit is turned on to activate the amplifier 12 and the selector circuit 10 (step 62), and an "H" level control output is output to the transistor Tr to turn it on. The input signal of 12 is dropped to ground to mute the output of the amplifier (step 64).

Then, after setting the 4s timer for muting and the 0.5s timer for display (steps 66 and 68), the selector circuit control all-off data for cutting off all the source inputs is subsequently set. It is created and output to the selector circuit 10, and all the analog function switches of the selector circuit 10 are opened (step 69).

As a result, the selector circuit 10 and the amplifier 12 are electrically disconnected from each other, and no audio signal related to any input source is output to the amplifier 12 side.

Therefore, the input signal level of the amplifier 12 during mute becomes zero, and even if the amplifier 12 having a high gain is used, the speaker 14
There is no sound leakage from.

In this state, the microcomputer 16A waits until the 0.5s timer expires (step 70).

When the 0.5 s timer times out, the microcomputer 16A determines YES in step 70, determines the initial setting source from the switching position of the source changeover switch 18 at that time, and creates and displays the source display data related to this source. It is output to the instrument 22 and the initialization source is displayed (step 74).

In this case, since the source selector switch 18 has been switched to the CD position in advance, the display 22 will display <CD>, and the user will not be able to select the initial setting source immediately after turning on the power switch 20. You can see it.

After that, when the 4s timer expires, the microcomputer 16A determines YES in step 72,
The source data for controlling the selector circuit related to the initial setting source is created and output to the selector circuit 10 to close the analog function switch related to the input of the initial setting source, and the analog function switches related to the other input sources are opened. Then, only the initial setting source is selected and output to the amplifier 12 side (step 76).

Subsequently, the microcomputer 16A causes the transistor T
An "L" level control output is performed to r to turn it off, and the input signal of the amplifier 12 is returned to the original level to cancel the mute (step 78).

As a result, the audio signal of the CD is output to the amplifier 12 side.

This audio signal is amplified by the gain-stabilized amplifier 12 and output to the speaker 14 side.

Then, the sound related to the intended setting source is reproduced and output.

Of course, if the user operates the source selector switch 18 to switch the source, the microcomputer 16A
Creates source display data and selector circuit control data relating to the newly designated source, and outputs the source display data and selector circuit control data to the display 22 and the selector circuit 10 to display the source and select the selector circuit 10.
The output from is changed (steps 80, 82).

In this way, after the power is turned on, the mute is surely applied until the gain of the amplifier 12 becomes stable.

According to this embodiment, when the power switch 20 is turned on, the microcomputer 16A controls the transistor Tr to be turned on and mutes, and the selector circuit 10
Off control all analog function switches, and perform selector circuit control to switch to the initial setting source after a lapse of a predetermined time after turning on the power to turn on only the analog function switches related to the initial setting source and control the transistor Tr to turn off. By canceling the mute, the source side and the amplifier 12 side are completely separated by the selector circuit 10 while the transistor Tr is turned on and the mute is applied.
The input of the audio signal component to 2 is surely blocked, and the speaker 14 does not leak the sound of the input source even if the amplifier 12 has a high gain.

[Effect of device]

According to the audio amplifier of the present invention, a selector circuit for selectively selecting and outputting one from a plurality of input sources and a selector circuit for controlling the selector circuit, and when the source is specified, A selector control circuit that outputs one input source, an amplifier that amplifies the output signal of the selector circuit, a mute circuit that sets the input of this amplifier to zero as necessary, and a mute circuit that is controlled to turn on the power. And a mute control circuit for activating the mute circuit to mute the amplifier input and deactivating the mute circuit after a lapse of a predetermined time after the power is turned on. The output of the selector circuit is kept open until the predetermined time elapses, and the preset value is set after the predetermined time elapses after the power is turned on. By making one select input source output from the select circuit, the source side and the amplifier side are completely separated by the selector circuit while the mute is applied, so it is certain that the source signal component enters the amplifier. Therefore, there is an excellent effect that the sound leakage of the input source from the speaker can be surely prevented.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an amplifier according to an embodiment of the present invention, FIG. 2 is a flowchart explaining the operation of the microcomputer shown in FIG. 1, and FIG. 3 is a block showing the configuration of a conventional amplifier. 4 and 5 are flowcharts for explaining the operation of the microcomputer shown in FIG. 10: Selector circuit, 12: Amplifier, 14: Speaker, 16A: Microcomputer, Tr: Transistor.

Claims (1)

[Scope of utility model registration request] 1. A selector circuit for selectively selecting and outputting one of a plurality of input sources, and controlling the selector circuit so that when the source is specified, one specified input source is selected. A selector control circuit that outputs the signal, an amplifier that amplifies the output signal of the selector circuit, a mute circuit that makes the input of the amplifier zero when necessary, and a mute circuit that controls the mute circuit and turns on the power. And a mute control circuit for activating and muting the amplifier input, and deactivating the mute circuit by deactivating the mute circuit after a lapse of a predetermined time from power-on, and the selector control circuit passes the predetermined time after the power is turned on. Until the output of the selector circuit is kept open, and after the lapse of the predetermined time from power-on, a certain preset input source An audio amplifier, characterized in that so as to output from the select circuit.