JPS5834573Y2 - Muting circuit - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a muting circuit suitable for application to, for example, a tape recorder or a stereo reproduction amplifier, and is particularly intended to eliminate pop noise that occurs when the power is turned on and off.

Generally, in tape recorders, etc., a muting switch is operated in conjunction with the recording/playback switching mechanism, and the muting switch shorts out the signal path of the amplifier in response to switching between recording and playback, which occurs when switching. This prevents noise from being emitted from the speakers.

In small stereo amplifiers, etc., a muting circuit is used that shorts out the signal path of the amplifier for a certain period of time from when the power is turned on, so that the pop noise generated when the power is turned on is not output as sound from the speakers.

Conventional muting circuits have only been designed to operate in conjunction with the operation of a recording/reproduction switch, or to remove pop noise when the power is turned on.

However, in practice, pop noise occurs even when the amplifier is turned off.

The purpose of this invention is to be able to perform muting operations both when the power to the amplifier is on and off.
Another object of the present invention is to provide a muting circuit that can perform a muting operation even when switching between recording and reproduction when applied to a tape recorder.

An embodiment of this invention will be described in detail below with reference to the drawings.

The figure shows an example of a muting circuit according to this invention. In the figure, 1 and 2 are signal input terminals, and this example shows a case where this invention is applied to a tape recorder for stereo reproduction.

That is, stereo signals are supplied to input terminals 1 and 2, respectively, and each stereo signal is amplified by amplifiers 3 and 4. Although not particularly shown, the amplified signals are sent to speakers or recording heads connected to the output sides of amplifiers 3 and 4. Output is supplied.

First switch elements 5 and 6 are connected between the signal paths of amplifiers 3 and 4 and ground, respectively.

This example shows a case where first switch elements 5 and 6 are connected between input terminals 1 and 2 of amplifiers 3 and 4 and ground.

These first switch elements 5 and 6 are, for example, NP
An N-type transistor can be used, the collector of which is connected to the signal path of the amplifier, the emitter connected to ground, the bases connected in common, and the second switch element 7 connected between the common connection point of the bases and ground.

A capacitor 9 constituting a time constant circuit 8 is connected between the base and emitter of the second switch element 7, and the connection point between the capacitor 9 and the base of the second switch element 7 is connected to the time constant circuit 8.
It is connected to the power supply terminal B through the resistor 10 that constitutes the power supply terminal B.

A series circuit consisting of a diode 11 and a resistor 12 is connected in parallel to the capacitor 9 constituting the time constant circuit 8, and a muting switch 13 is connected in parallel to the resistor 12.

Further, a series circuit including a diode 14, a resistor 15, and a capacitor 16 is connected between the connection point between the diode 11 and the resistor 12 and the positive power supply terminal B.

Further, a resistor 17 is connected between the connection point between the diode 14 and the resistor 15 and the connection point between the collector of the second switch element 7 and the bases of the first switch elements 5 and 6.
Connect capacitor 1 between the connection point between 7 and diode 14 and ground.
Connect 8.

According to such a configuration, when the power supply to the amplifiers 3 and 4 is first turned on, a positive voltage is applied to the power supply terminal B.

At this time, since the charging voltage of the capacitor 9 is zero volts, the second switch element 7 is held off.
The first capacitor 18 is rapidly charged through the diode 14 and the first switch elements 5 and 6 are turned on, shorting the signal paths of the amplifiers 3 and 4.

From the time the power is turned on, the charging voltage of the capacitor 9 constituting the time constant circuit 8 gradually rises in accordance with the time constant with the resistor 10, and the second switch element 7 is turned on after the time elapsed from the time the power is turned on.

When the second switch element 7 is turned on, the first switch element 5
and 6 are shunted through the collector-emitter of the second switch element 7, the first switch elements 5 and 6 are turned off and the signal paths of amplifiers 3 and 4 are disconnected from ground and the input terminals 1 and 2 When the power is turned on, the stereo signal supplied to the first circuit 8 is amplified and the stereo signal supplied to the first circuit 8 is amplified.
Switch elements 5 and 6 are kept on, and a muting operation is performed to eliminate pop noise that occurs when the power is turned on.

When the muting switch 13 is turned on during operation, the charge in the capacitor 9 is rapidly discharged through the diode 11 and the muting switch 13, and the second switch element 7 is turned off.

As a result, the first switch elements 5 and 6 are turned on and a muting state can be achieved.

Therefore, in a tape recorder or the like, by interlocking the recording/playback operation mechanism and the □auto switch 13, the muting state can be set each time the recording or playback state is changed.

On the other hand, when the power is turned off, the potential at the connection point between the diode 11 and the resistor 12 suddenly becomes negative due to the charging voltage of the capacitor 16, and the charge charged in the capacitor 9 is rapidly discharged through the diode 11 and the resistor 12. Then, the second switch element 7 is turned off.

Therefore, the discharge current of the capacitor 18 is supplied to the bases of the first switch elements 5 and 6 through the resistor 17, turning on the first switch elements 5 and 6 and placing them in a muting state.

The discharge of capacitor 18 is connected to diode 1 on the power supply side.
4, it is applied only to the base side of the first switch elements 5 and 6, and maintains the muting state for a certain period of time after the power is turned off, thereby making it possible to eliminate pop noise that occurs when the power is turned off.

As explained above, according to this invention, it is possible to enter the muting state by turning on the muting switch 13 when the power is turned on, when it is turned off, and even during operation, and pop noise can be removed in all conditions. , its effectiveness is of great practical importance.

Although the above explanation has been given by exemplifying the application of this invention to a stereo regenerative amplifier, it is easy to understand that this invention can also be applied to a monaural signal system.

Furthermore, although an example has been described in which the muting switch 13 is added and applied to a tape recorder, it is easy to understand that this muting switch is not necessarily required in cases other than tape recorders.

In the above description, the first switching elements 5 and 6 for muting are
are connected to the input terminals 1 and 2 of amplifiers 3 and 4, but they can also be connected between the stages of amplifiers 3 and 4.

BRIEF DESCRIPTION OF THE DRAWINGS The figure is a connection diagram showing an embodiment of this invention. 3.4... Amplifier, 5, 6... First switch element,
7... Second switch element, 8... Time constant circuit, 14... Diode, 18... Capacitor.

Claims (1)

[Scope of utility model registration request] A first switch element for muting connected in parallel to the signal path, a second switch element connected between the control electrode of the first switch element and ground, and a control electrode of the first switch element are powered off. a first capacitor for supplying a discharge current to hold the first switch element on at 1 for a period of time consisting of its off point;
a diode that supplies a charging current to the capacitor when the power is turned on and blocks a discharging current from discharging from the first capacitor to the power supply when the power is turned off; a time constant circuit that holds the element off for a certain period of time and then turns on; and a muting switch that is connected between the control electrode of the second switch element and ground and that is turned on each time the recording or reproducing mechanism is switched. A muting circuit that is fully equipped with.