JPS5931046Y2 - Muting circuit - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a muting circuit for preventing abnormal sounds when operating various changeover switches in an acoustic amplifier or the like.

Conventionally, a muting circuit as shown in FIG. 1 has been used to prevent clicking sounds when turning the power on and off and when operating various changeover switches.

In the figure, when the switch 2 is closed, AC voltage is supplied from the plug 1 to the transformer 3, so that the capacitor 7 is charged to the negative polarity with a short time constant by the diodes 5 and 6, and the transistor 11 is turned off.

On the other hand, the capacitor 13 is charged to the positive polarity via the resistor 12 by the voltage of 10 B from the DC power supply 4 for driving the acoustic amplifier 24, so that after a predetermined time t1 seconds, the transistor 15 is turned on, and therefore the transistor 16 is also turned on. The relay 25 is driven by the coil 17 of the muting relay to turn on the output of the acoustic amplifier 24, and the speaker 26 is turned on.

Here, the predetermined time t1 seconds is set to the time required for the acoustic amplifier to stabilize.

Furthermore, since the relay 25 is off when not driven, no abnormal noise is generated due to abnormal operation of the acoustic amplifier immediately after the power switch is turned on.

On the other hand, the capacitor 19 is also charged via the resistor 18, and is set to turn on the transistor 21 after a predetermined time of 12 seconds.

For example, when operating a changeover switch (not shown) for switching between MC and MM cartridges, if the switch 20 is simultaneously turned on for a moment, the capacitor 19 will be discharged, the L transistor 21 will be turned off, and the base of the transistor 16 will be turned off. The voltage increases and transistor 16 is turned off.

Therefore, since the speaker 26 is also turned off, no abnormal sound is generated during the switching operation.

Here, the predetermined time t2 required for muting when operating various changeover switches is shorter than the predetermined time t1 required for muting immediately after the power is turned on, so it is necessary to provide two time constant circuits as described above. The configuration is complicated.

The present invention provides a time constant circuit that can set two time constants with a simple configuration, and will be described in detail below according to embodiments.

FIG. 2 shows an embodiment of the present invention.

In the figure, parts having the same functions as those of the conventional example shown in FIG.

In the present invention, a parallel circuit consisting of a series circuit of capacitors 29 and 30 and a series circuit of Zener diodes 27 and 28 is inserted in place of capacitor 13 in FIG. 20
It is designed to be grounded through.

Note that the emitter of the transistor 15 is a diode 31.3.
2 to ground.

Further, the resistors 18, 22, capacitor 19, transistor 21 and diode 23 in the conventional example shown in FIG. 1 are not used.

Here, the Zener voltage ■1 of the Zener diode 27 is set lower than the threshold voltage between the base and ground required to turn on the transistor 15, and the Zener voltages ■1 and ■2 of the Zener diodes 2T and 28 are Keep the total large.

In the above configuration, when the power switch 2 is turned on, the transistor 11 is immediately turned off as in the conventional example described above, and the resistor 12 charges the series circuit of the capacitors 29 and 30 for a predetermined period of time 41 determined by this charging time constant. After a second, transistor 15 turns on, and speaker 26, which had been off until then, turns on.

Next, set the various changeover switches to time T.

When switching by smell, switch 2 is activated in conjunction with this switching.
0 is turned on for a moment to completely discharge the charge in the capacitor 30 as shown in Fig. 3A, and then the switch 20 is turned off.The Zener voltage 1 is applied to the base of the transistor 15, and the transistor 15 is turned off, and the speaker 26 is turned off.

After that, the series circuit of the capacitors 29 and 30 is charged again, and the transistor 15 is charged again after a predetermined time of 42 seconds as shown by the dotted line.
reaches the threshold voltage of , and the speaker 26 is turned on.

Also, when power switch 2 is turned off, capacitor 1 is immediately turned off.
is discharged and the potential rises, so transistor 11 is turned on, transistors 15 and 16 are turned off, and speaker 26 is also turned off.

Therefore, since the speaker is turned off immediately after the power switch 2 is opened, no abnormal sound is generated.

As described above, the present invention has the excellent effect that the muting circuit can be operated with two types of time constants suitable for the purpose with a simple configuration.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram showing a conventional muting circuit, Figure 2 is a circuit diagram showing a conventional muting circuit.
The figure is a circuit diagram showing the muting circuit of the present invention, and FIG. 3 is a diagram asking questions about the operation of the present invention. In the figure, 2 and 20 are switches, 7, 29.30 are capacitors, and 25 is a relay.

Claims (1)

[Scope of utility model registration request] The terminal voltage of the capacitor in the charging/discharging circuit is 1 immediately after the power is turned on.
In an amplifier muting circuit having a relay that performs a muting operation until reaching a first level after a time period of By short-circuiting all but one of the capacitors in conjunction with the operation of various changeover switches of the amplifier, and lowering the terminal voltage of the capacitor of the charge/discharge circuit to the second level, A muting circuit that performs a muting operation until a second time period shorter than the first time period elapses.