JPS6017046Y2 - Tape recorder muting circuit - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a tape recorder, and particularly to a muting circuit that suppresses noise generation.

A high-grade tape recorder called a tape deck is used by being connected to an amplifier with a high output, so the noise generated by the tape recorder is amplified by the amplifier and then emitted at a louder level than the speaker, causing discomfort to the user. It turns out.

To improve this point, this type of tape recorder is equipped with a muting circuit.

The present invention aims to provide a circuit that can suppress noise generated when power is cut off by using such a muting circuit, and will be described in detail below with reference to the drawings.

The illustrated circuit is an embodiment of the present invention, and in the figure, 1 is an input terminal to which a signal reproduced from a magnetic tape is applied, 2 is an amplifier circuit, and 3 is an input terminal of an amplifier having a large output. This is the output terminal to be connected.

4 is a muting transistor whose collector-emitter path is connected between the signal transmission path 5 and ground;
Its base is connected to a power supply line 8 via a Zener diode 6 and a resistor 7.

A first control transistor 9 controls the operation of the muting transistor 4, and its collector is connected to a ground point P between the Zener diode 6 and the resistor 7, and its emitter is grounded.

10 is a second control transistor that controls the operation of the first control transistor 9, and its collector is connected to the base of the first control transistor 9 via a Zener diode 11 and to the power supply line 8 via a resistor 12. and the emitter is grounded.

The base of the second control transistor 10 is connected to a muting operation control circuit 14 via a resistor 13 and to a power supply line 8 via a time constant circuit 17 comprising a capacitor 15 and a resistor 16.

18 is a capacitor that prevents malfunctions caused by fluctuations in power supply voltage, 19 is a constant voltage circuit that supplies power to the power line 8, and 20 is a main unit that controls power supply to the constant voltage circuit 19. It's a switch.

A capacitor 21 is charged through a diode 22 when power is supplied to the power line 8 from the constant voltage circuit 19, and a capacitor 23 is opened when the main switch 20 is closed, and closed when the main switch 20 is opened. This control switch is connected to apply the discharged charge of the capacitor 21 to the base of the muting transistor 4 when it is in a closed state.

In such a configuration, the Zener voltage of the Zener diode 11 is set to a value at which the first control transistor 9 switches from a conductive state to a non-conducting state as soon as the voltage of the power supply line 8 falls, that is, the voltage of the power supply line 8 exceeds the voltage value of the transistor 9. It is set to be approximately equal to the value obtained by subtracting the voltage value.

The present invention is constructed and implemented as described above, and its operation will be explained next.

The illustrated state is a power-off state, and when the main switch 20 is closed in this state, power is supplied from the constant voltage circuit 19 to the power line 8 and the control switch 23 is opened.

As a result, the charging current of the capacitor 15 constituting the time constant circuit 17 flows as the base current of the second control transistor 10, and the second control transistor 10 becomes conductive for a predetermined time, that is, until the capacitor 15 is charged.

Therefore, during that time, the first control transistor 9 is in a non-conducting state and the muting transistor 4 is in a conducting state.

Therefore, the noise generated until the amplifier circuit 2 etc. reach a steady operating state is bypassed through the collector-emitter path of the muting transistor 4, and no signal such as noise appears at the output terminal 3. .

Then, after a predetermined time, when the second control transistor 10 is reversed to a non-conductive state, the first control transistor 9 is reversed to a conductive state, and the muting transistor 4, which is in a conductive state, is reversed to a non-conductive state.

As a result, the signal amplified by the amplifier circuit 2 is outputted to the output terminal 3 without being bypassed, and a predetermined operation such as reproduction by a tape recorder is performed.

Next, normal muting operation will be explained.

When the fast-forward operation state is switched from the rewind operation state to the playback operation state, the noise generated by switching the switches of each part is input to the amplifier circuit 2 and amplified. A control signal is output for a predetermined period of time, thereby inverting the second control transistor 10 to a conductive state.

As a result, the first control transistor 9 becomes non-conductive, and the muting transistor 4 becomes conductive accordingly, so that no noise is output to the output terminal 3.

The muting operation of the muting circuit is performed as described above, but the operation when the main switch 20 is opened will now be described.

When the main switch 20 is closed and power is supplied to the power line 8 from the constant voltage circuit 19, the capacitor 21 is charged through the diode 22.

In this state, when the main switch 20 is opened, the voltage of the power supply line 8 will gradually decrease due to the influence of the smoothing capacitor, etc.
Zener diode 11 connected to the base circuit of
The Zener voltage value of is set to be approximately equal to the value obtained by subtracting the rising voltage value of the first transistor 9 from the voltage value of the power supply line 8. Therefore, as soon as the voltage of the power supply line 8 falls, the first control transistor 9 is reversed to non-conducting state.

In addition, when the main switch 20 is opened, the control switch 23
Since the capacitor 21 is closed and released, the charge stored in the capacitor 21 is discharged through the switch 23, and the muting transistor 4 to which the discharge current is applied to the base becomes conductive.

Therefore, when the main switch 20 is opened and the power is cut off, the muting transistor 4 becomes conductive, so that the noise generated from the amplifier circuit 2 and the like when the power is cut off is not outputted to the output terminal 3.

As explained above, the muting circuit of the present invention is
When the main switch that controls the power supply to the tape recorder is closed, the discharge charge of the capacitor that is charged when the power is supplied is controlled by a control switch that changes the discharge charge of the capacitor when the power is turned off. Since the voltage can be applied to the base of the switching transistor, it is possible to reliably suppress the noise generated when the power is cut off by opening the main switch.

In addition, since the operation of the control transistor connected to cut off the base bias of the muting transistor when it is in a conductive state is controlled by the voltage supplied to the amplifier circuit, the noise generated by the amplifier circuit due to power cut-off is reduced. The practical value of the present invention is very great as it can reliably suppress the

[Brief explanation of the drawing]

The illustrated circuit is one embodiment of the muting circuit of the present invention. Explanation of main drawing numbers, 2... Amplifier circuit, 4...
...Muting transistor, 5...
Signal transmission line, 8...Power line, 9...
First control transistor, 10... Second control transistor, 14... Muting operation control circuit, 17... Time constant circuit, 19...
- Constant voltage circuit, 20... Main switch, 23...
・Control switch.

Claims (1)

[Scope of utility model registration request] In a tape recorder having a muting transistor that conducts during muting operation and bypasses a signal flowing through a signal transmission path, the tape recorder includes a main switch that controls power supply to the tape recorder, and a power supply that is supplied by closing the main switch. When the main switch is open, the capacitor is charged through the diode, and when the main switch is open, the capacitor is connected to the muting transistor. A control switch connected to the base of the muting transistor is connected to cut off the base bias of the muting transistor when the main switch is in a conductive state, and is non-conductive when the supply voltage to the amplifier circuit drops as the main switch is opened. When the power is cut off by opening the main switch, the discharge charge of the capacitor is transferred to the base of the muting transistor by closing the control switch and reversing the control transistor to a non-conducting state. A muting circuit for a tape recorder, characterized in that a muting circuit for a tape recorder is configured to apply a voltage to the transistor, thereby making the transistor conductive.