JPS6210057B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an audio muting device that can be used to prevent the generation of noise when turning on the power or switching channels in audio equipment such as television receivers. The purpose of the present invention is to provide a device that can effectively prevent this.

In television receivers, noise is generated due to transient operation of the circuit when turning on the power or switching channels. In order to prevent such noise, conventionally, a muting circuit is provided in the transmission path of the audio signal to suppress the signal, and the switching element of this muting circuit is operated when the power is turned on or when changing channels to mute the audio. It is made to be. However, in such an audio signal muting circuit, the switching element does not turn on and off completely, so if a high gain audio output circuit is used, a small amount of audio will remain even during muting, and the switching element will not turn on or off completely.
When it is off, it is not possible to completely remove transient signals, leaving a small amount of noise behind.

Therefore, the present invention solves such conventional drawbacks, and
The purpose is to provide a muting device that can completely eliminate voices and noise, and for this purpose, the volume can be adjusted by muting the control voltage to a voltage-controlled volume control circuit at the same time as muting the audio signal. It is characterized by suppressing the

EMBODIMENT OF THE INVENTION Hereinafter, the present invention will be described in detail with reference to the drawings showing one embodiment thereof. Figure 1 shows the power supply circuit and part of the audio circuit of a television receiver.
Here, 1 is a power supply circuit, 2 is a voltage-controlled volume control circuit, 3 is an audio output circuit, 4 is a control voltage muting circuit, 5 is an audio muting circuit, and 6
is a mutating pulse generation circuit. The audio signal is input from the input terminal 7 to the base of one transistor of the differential amplifier 8 in the volume control circuit 2, and the amplitude is controlled, taken out from the collector, and output from the emitter follower transistor 9. The signal is then added to the audio output circuit 3 via capacitors 10 and 11, where it is further amplified and then emitted from the speaker 12. In the volume control circuit 2, the degree of amplification is controlled by the volume control voltage applied from the level shift circuit 13 to the base of the differential amplifier 8, thereby controlling the volume. This volume control voltage is set by a variable resistor 14 for volume control, and is applied to the level shift circuit 13 via the transistor 15 of the control voltage muting circuit 4. The level shift circuit 13 converts the volume control voltage applied from the transistor 15 to a level suitable for controlling the differential amplifier 8 and converts it into two control voltages that change in opposite directions to be applied to the differential amplifier 8. It is something.

In this device, a transistor 16 for suppressing the volume control voltage to the minimum volume value is provided on the output side of the transistor 15 in the path for supplying the volume control voltage, and the volume control circuit 2 controls the volume. An audio muting circuit 5 is connected to the connection point between the capacitors 10 and 11 in the middle of the transmission path of the audio signal, and a transistor 17 for suppressing the audio signal is connected thereto.

On the other hand, in the mutating pulse generation circuit 6,
The power supply voltage generated when the power switch 18 of the power supply circuit 1 is turned on is differentiated by the capacitor 19 and the resistor 20, and the first voltage for power-on as shown in FIG. 2A is obtained.
Create a mutating pulse. In addition, this muting pulse A is connected to a constant voltage diode 21.
Then, the level is shifted by the level shown by the one-dot chain line, and a second muting pulse having a narrower pulse width than the muting pulse A is generated as shown in FIG. 2C. The diode 22 is for removing the differential signal of negative polarity. This first muting pulse A is then passed through the diode 23 to the control voltage muting transistor 16.
In addition to the base of the second mutating pulse C
is the transistor 17 for audio signal muting.
Add to the base. In this way, the transistor 16 becomes conductive as shown in FIG. 2B during the period when the threshold level shown by the broken line in FIG. suppress the sound volume generated from the speaker 12 to a minimum.

Further, the transistor 17 is in the second state during the period in which it exceeds the threshold level shown by the broken line in FIG. 2C.
It conducts as shown in Figure D, and suppresses the audio signal so that it is not transmitted during that period. Here, the length of time that the transistor 17 conducts and mutes the audio signal is set to be longer than the time that each circuit becomes unstable and generates undesirable audio or noise when the power is turned on or when switching channels. It is necessary to set the differential time constant to make it longer. Note that 24 is a terminal to which a muting command pulse is applied at the time of channel switching.

In this way, by suppressing the volume control voltage and suppressing the audio signal, noise can be effectively prevented by the synergistic effect of the suppression effects of both. In particular, even when a large gain and large output circuit is used as the audio output circuit 3, residual audio during muting can be eliminated, and a sufficient muting effect can be achieved.

Moreover, even if a situation arises in which the audio signal is transiently distorted when the audio signal muting circuit 5 is turned on or off, the control voltage muting circuit 4 mutes the volume control voltage to suppress the volume to the minimum value. Because of this, the influence of the inconvenient state does not appear, and there is an advantage that the generation of transient noise can be effectively prevented.

Furthermore, at this time, if the muting pulse A applied to the control voltage muting circuit 4 is made to end later than the muting pulse B applied to the audio muting circuit 5 as described above, the audio mutating circuit 5 The transient inconveniences that occur can be more completely eliminated.

As described above, according to the present invention, since both the control voltage for the volume control circuit and the audio signal are suppressed, it is possible to effectively prevent noise when the power is turned on or when switching channels. Since the muting pulse applied to the control voltage muting circuit ends later than the muting pulse applied to the audio muting circuit, transient inconveniences that occur in the audio muting circuit (harmonic noise caused by switching) are avoided. ) can be completely removed.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an audio muting device according to an embodiment of the present invention, and FIGS. 2A, B, C, and D are waveform diagrams of each part thereof. 1...Power supply circuit, 2...Volume control circuit, 3...
Audio output circuit, 4... control voltage muting circuit, 5... audio muting circuit, 6... muting pulse generation circuit.

Claims (1)

[Claims] 1. A volume control circuit that controls the volume by changing the amplification degree of the audio signal according to the applied DC volume control voltage, an audio output circuit that amplifies and outputs the volume-controlled audio signal, and the volume control voltage. a control voltage mutating circuit that suppresses the volume-controlled central voice signal, a first muting pulse during voice muting, and a second muting pulse that ends later than the first muting pulse. and a muting pulse generation circuit that generates a muting pulse, wherein the first muting pulse operates the audio muting circuit, and the second muting pulse operates the control voltage muting circuit. Audio mutating device.