JPS5915572B2 - Audio mute control circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to muting of an audio reproduction device having multiple audio signal sources, such as a system, a component, or a stereo.

Devices having a plurality of audio signal sources are configured so that the audio signal sources can be switched during use, and therefore may generate excessive noise when switching.

This kind of noise is called hop noise, and it becomes a big problem when the tie-up power is turned on and off.
In many cases, the signal is muted by cutting off the signal at the speaker input end using a relay or the like during F, and when switching between multiple audio signal sources, the level of hop noise that appears at the output of each signal source is not very large. Up until now, it has not been much of an issue, with only a small amount of consideration being given to it. However, as the level of sound reproduction equipment increases and the S/N improves, even the slightest hop noise becomes a problem, and the gain of the main amplifier reaches 30 to 40 dB like in normal reproduction equipment. Even if the level of hop noise at the output of each signal source is suppressed to about 1 mV,
The speaker has an output of 30 to 100 meters, and as speakers have become more efficient, it has become impossible to prevent significant hop noise from appearing. An object of the present invention is to provide an audio mute control circuit with a simple configuration for preventing transient noise such as hop noise from being reproduced during any operation in the above-mentioned sound reproduction device. .

In order to achieve this object, the present invention is characterized in that a signal obtained by selective power-on operation for each audio signal source is differentiated to obtain a mute control signal.

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

FIG. 1 is a block diagram showing one embodiment of the present invention, and 1, 2, and 3 are the power supply voltages applied when operating power is supplied to an audio signal source such as a tape deck, radio tuner, or television tuner. The input signal terminals 4 and 5 are used to mute during the operation of each audio signal source, such as when changing programs on a tape deck, fast forwarding or rewinding a tape, or when switching bands on a tuner, or when operating a channel. An input terminal to which a control signal is applied, 6 a power supply terminal, 7 an output amplifier circuit, 8 an audio input terminal, 9 an audio output terminal,
10 is a mute input terminal, 11 and 12 are adder circuits, 13
, 14 and 15 are differentiating circuits, 16 is a time constant circuit, 17 is a mute signal amplification circuit, and 18 is a relay with switching contacts.
19 is a power input terminal of the output amplifier circuit 7. Next, the operation will be explained.

First, terminals 1, 2, and 3 are connected to, for example, a tape deck, . The power input terminals of the radio tuner and the television tuner are connected, and terminal 4 receives input from, for example, a tape deck when the device is in an operating state other than the playback operation state, and terminal 5 receives input from, for example, the television tuner only when the channel is being switched. , control signals are applied to each of them.

Now, when the tape deck, tuner, record player, etc. are not in use, no input signal is applied to any of the terminals 1 to 5, so no current flows to the coil of the relay 18, and the slave contacts In the illustrated state, the voltage from the power supply terminal 6 is applied to the mute input terminal 10 via the break contact of the relay 18, the input of the adder circuit 12, the time constant circuit 16, and the amplifier circuit 17.
However, at this time, no power is being supplied to the power input terminal 19 and the output amplifier circuit 7 is not operating, so no output signal is generated at the output terminal 9, and the device is in an inactive state. . Next, in order to use one of the audio signal sources such as a tape deck, it is assumed that power is selectively supplied to that device (by operating a selection switch, etc.).

As a result, the power supply voltage is applied to any one of terminals 1 to 3, so current flows to the coil of relay 18 via adder circuit 11, and relay 18 operates to switch its contacts and close the make contact. Then, the power from the terminal 6 is supplied to the power input terminal 19 of the output amplifier circuit 7, and the output amplifier circuit 7 is put into operation. As a result, the audio signal from that audio signal source is applied to the input terminal 8 and supplied to the speaker from the output terminal 9, so if this continues, hop noise caused by that signal source will be reproduced, but the input The voltage applied to any of terminals 1 to 3 is applied to differentiating circuits 13 to 1.
5, and the differentiated output signal is supplied to the time constant circuit 16 via the adder circuit 12 as a pulse-like input signal. The time constant circuit 16 generates an output signal in response to this input signal for a predetermined period of time, that is, a period sufficient for the transient state to subside and a steady state to be reached after the power supply voltage is applied to the audio signal source. , this signal is applied to the mute terminal 10 of the output amplifier circuit 7 via the amplifier circuit 17.
Therefore, transient hop noise caused by applying the power supply voltage to the selected audio signal source is caused by the time constant circuit 16.
The mute signal of a predetermined time width supplied from the terminal 10 to the terminal 10 effectively erases the mute signal and prevents it from being reproduced from the speaker.

Suppose that after this, the audio signal source is switched from, for example, a tape deck to a radio tuner.

At this time, for example, the power supply voltage signal applied to input terminal 1 disappears, and the power supply voltage signal is switched to be applied to terminal 2. Since this switching is normally done instantaneously, the relay 18 does not once recover and operate again, but continues to operate using the voltage from terminal 2 even after the voltage from terminal 1 disappears. Therefore, the power of the output amplifier circuit 7 continues to operate without being turned off. However, the signal from the terminal 2 is differentiated by the differentiating circuit 14, becomes a pulse-like signal, and is supplied from the adding circuit 12 to the time constant circuit 16, and the time constant circuit 16 again generates an output signal with a predetermined time width and amplifies it. A signal is applied from the circuit 17 to the mute terminal 10, and the output amplifier circuit 7 is muted for a predetermined period of time. Therefore, hop noise from the next selected audio signal source, such as a radio tuner, is also effectively muted and is no longer reproduced from the loudspeaker.

Hereinafter, the same operation is performed every time a new power supply voltage signal is supplied to any of input terminals 1 to 3, and the hop noise caused by a new power supply voltage being supplied to the audio signal source is Everything is effectively muted. By the way, audio signal sources such as tape decks, radios, televisions, and FM tuners not only generate transient hop noise when the power switch is turned on and the power supply voltage is applied, but also when switching operations, for example, when switching programs. Noise is also generated during tape forwarding or rewinding, hand switching, or channel selection.

Therefore, when these operations are switched, a mute control signal is generated from the audio signal source, and these mute signals are supplied to the input terminals 4 and 5. As a result, when any of the audio signal sources switches operation, a mute control signal is applied to the terminals 4 and 5, and the mute control signal is applied to the mute terminal 10 via the adder circuit 12, the time constant circuit 16, and the amplifier circuit 17.
A mute signal is applied to the signal, and muting is performed during the period in which noise may be generated.
When you turn off the power to the audio signal source that is in use, input terminal 1
The power supply voltage signal applied to any of the points 3 to 3 also disappears, and the relay 18 is restored.

This opens the make contact and closes the break contact, so that the voltage from the power supply terminal 6 is no longer supplied to the power supply input terminal 19 of the output amplifier circuit 7 and is instead supplied to the adder circuit 1.
2 is supported by a voltage from the power supply, and this is supplied as a mute signal to the mute terminal 10 via the time constant circuit 16 and amplifier circuit 17, so that the output amplifier circuit 7 is immediately muted. Therefore, it is possible to prevent the hop noise of the output amplifier circuit 7, which occurs transiently when the power supply voltage is cut off, from being reproduced from the speaker. In this way, according to this embodiment, the muting is complete in all operating conditions that may generate transient hop noise, resulting in a high quality level and therefore good SA. system. component. Sufficient muting can be performed even in stereo etc. FIG. 2 shows a more specific embodiment of the present invention, which is a more specific embodiment of the embodiment shown in FIG.

The parts 1 to 19 are the same as the embodiment shown in FIG. In the figure, 21 is a diode that constitutes the adder circuit 11, 22 is a diode that also constitutes the adder circuit 12, 23 and 24 are capacitors and resistors that constitute the differentiator circuits 13, 14, and 15, and 25, 26, and 27 are timepieces. A transistor, a resistor, and a capacitor that constitute the constant circuit 16,
28 and 29 are transistors and resistors that constitute the amplifier circuit 17.

The operation of the embodiment shown in FIG. 2 is the same as that shown in FIG. and operates the relay 18. The diode 22 is also the same as the diode 21, and is used for addition so that the signals from the differentiating circuits 13 to 14 and the signals from the terminals 4 and 5 can be added to the input of the time constant circuit 16 without mutual interference. Configure the circuit. capacitor 23 and resistor 24
constitute the differentiating circuits 13, 14, 15, and the input terminals 1 to 15
The signal from 3 is shaped into a pulse. transistor 25
is made conductive by the input signal from adder circuit 12, and capacitor 2
7 is discharged, and when the input signal disappears, it is cut off, and the capacitor 27 is charged from the power supply via the resistor 26, and the time width determined by the constants of these capacitors 27 and resistor 26 is negative This constitutes a time constant circuit 16 that generates a signal. The transistor 28 is cut off by the negative direction signal from the time constant circuit 16, and constitutes an amplifier circuit 17 that performs muting by applying the voltage from the power supply terminal 6 to the mute terminal 10 via the resistor 29. When the capacitor 27 is charged and reaches close to the power supply voltage, it becomes conductive again, its collector voltage becomes O, and the mute signal is no longer applied to the mute terminal 10.

In this way, the embodiment shown in FIG. 2 operates in exactly the same way as the circuit shown in FIG. 1, and effective muting can be performed.

FIG. 3 shows another embodiment of the present invention, which has a simpler configuration.

In this embodiment, the time constant circuit 16 in the embodiments of FIGS. 1 and 2 is omitted, and the same effect can be achieved.
is directly connected to the output of the adder circuit 12 via a bias current limiting resistor 30.

Although not shown in the figure, the other configurations are exactly the same as those of the embodiment shown in FIGS. 1 and 2. In this embodiment, the capacitor 2 constituting the differentiating circuits 13 to 14 is
3 and the resistor 24 are set to relatively large values so that when the input signal charged in the capacitor 23 is discharged, it is discharged relatively slowly.
The output signal is a rectangular wave with a relatively long duration, and the duration of this rectangular wave signal is approximately comparable to the period during which transient hop noise may occur. By doing so, the same effect as when using the time constant circuit 16 can be obtained, and thereby the time constant circuit 16 can be omitted and the configuration can be simplified.

As explained above, according to the present invention, a high quality system with a high quality level and a good S/N ratio can be obtained. component. In stereo etc., it is possible to perform extremely complete muting, further improving the quality, and
An excellent effect can be expected in that only a slight increase in the necessary cost is required.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an audio mute control circuit according to an embodiment of the present invention, and FIG. 2 is a wiring diagram of an audio mute control circuit according to an embodiment of the present invention that further embodies the embodiment of FIG. 1. FIG. 3 is a wiring diagram of an audio mute circuit according to another embodiment of the present invention. 1 to 3... Power supply voltage signal input terminal from the audio signal source, 4, 5... Mute control signal input terminal,
6...Power supply terminal, 7...Output amplifier circuit, 10...Mute terminal, 11, 12...
... Addition circuit, 13-15 ... Differentiation circuit, 16
...Time constant circuit, 17...Amplification circuit,
18...Relay 19...Power input terminal.

Claims (1)

[Scope of Claims] 1. In an audio mute control circuit of a composite sound reproduction device having a plurality of audio signal sources that share an output amplification circuit, the audio mute control circuit of a composite audio reproduction device has a plurality of audio signal sources that share an output amplification circuit. means for generating a plurality of control signals corresponding to the plurality of control signals; a relay circuit that operates in response to one of the plurality of control signals from the means and supplies power to the output amplification circuit; and a plurality of control signals from the means. It consists of a plurality of differentiating circuits which take each of the differentiating circuits as inputs, an adder circuit which takes the outputs of the plurality of differentiators as inputs, and a time constant circuit which takes the outputs of the adder circuits as inputs, and the output of the time constant circuits An audio mute control circuit characterized in that the output amplification circuit is muted. 2. Multiple audio signal sources that share an output amplification circuit are tape decks, AM, FM, or television tuners, and when switching the operation of these audio signal sources, switching tape deck programs, fast forwarding the tape, or It has a circuit that generates control signals only during rewinding, switching tuner bands, tuning operations, etc.
2. The audio mute control circuit according to claim 1, wherein the control signal is applied in addition to the input of the adder circuit. 3. The relay circuit is configured to generate a control signal when the relay circuit is not in operation, and the control signal is added to the input of the adder circuit and applied from the normally closed side terminal inside the relay of the relay circuit. An audio mute control circuit according to claims 1 and 2, characterized in that: