JPS6145621Y2 - - 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 generated when power is turned on and off.

A high-grade tape recorder called a tape deck is used by being connected to an amplifier with high output, so the noise generated by the tape recorder is amplified by the amplifier and then emitted from the speaker at a high level, causing no harm to the user. It will give you a sense of pleasure. Some of the noise output from a tape recorder is generated when switching operations, but if the noise generated when the power is turned on and off is especially large and severe, it may damage the speaker.

The present invention aims to provide a muting circuit that can suppress noise generated when power is turned on and off, 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 a magnetic head for reproduction, 2 is a preamplifier circuit for amplifying the signal reproduced by the magnetic head 1, and 3 is a preamplifier circuit for amplifying the signal reproduced by the magnetic head 1. position amplifier circuit 2
4 is a main amplifier circuit into which the signal level-adjusted by the variable resistor 3 is input; 5 is a main amplifier circuit into which the signal amplified by the main amplifier circuit 4 is input; It is an output terminal connected to an input terminal of an amplifier having a large output power. A mutating transistor 6 has a collector connected to the signal transmission line 7 and an emitter grounded, and has the function of bypassing the signal flowing through the signal transmission line 7 when in an on state. 8 is a power supply terminal connected to a commercial AC power source; 9 is a power switch that is closed when the power is turned on; and 10, when the power switch 9 is closed, the input AC power is rectified and the voltage is regulated. This is a constant voltage power supply circuit that outputs to the power supply line 11. 12 is a differentiation circuit consisting of a first capacitor 13 and a resistor 14; 15 is the constant voltage power supply circuit 10;
The direct current that is the output of the backflow prevention diode 1
A second capacitor 17 is supplied and charged through a Zener diode 18 and a resistor 19, and has an emitter connected to the power supply terminal of the capacitor 15 and a collector connected to the base of the mutating transistor 6 via a Zener diode 18 and a resistor 19. This is the first control transistor. A second control transistor 20 has a collector connected to the base of the first control transistor 17 and an emitter grounded, and its base is connected to the differentiating circuit 12 via a resistor 21. A bridge circuit 22 is connected between the power supply line 11 and the ground, and is composed of the reverse current prevention diode 16 and resistors 23, 24, 25 and 26. 27 is the resistor 23 and 24
A third control transistor whose emitter is connected to a balanced terminal A, which is the connection point of the resistors 25 and 26, and whose base is connected to the balanced terminal B, which is the connection point of the resistors 25 and 26, and whose collector is connected to the first control transistor 17. connected to the base of. 2
8 is a muting signal generation circuit that outputs a high-level muting signal during a muting operation, and the output signal is sent to the Zener diode 18.
and is connected to the base of the mutating transistor 6 via a resistor 19 so as to be applied thereto. In the circuit configured in this manner, the resistance values of the resistors 23, 24, 25, and 26 constituting the bridge circuit 22 are such that in a steady state where power is supplied, the third control transistor 27 is reverse biased and turned off. is set to .

The muting circuit of the present invention is constructed as described above, and the operation of this circuit will now be described. The illustrated state is a non-power supply state, and when the power switch 9 is closed in this state, a constant voltage power supply circuit 10 outputs a constant voltage power to the power supply line 11. As a result, power is supplied to the preamplifier circuit 2 and the main amplifier circuit 4, and the signals are differentiated by the differentiating circuit 12 and applied to the base of the second control transistor 20, and the backflow prevention diode is also applied to the base of the second control transistor 20. 2nd through 16
A charging current flows through the capacitor 15, and the second capacitor 15 is charged. When the differential signal from the differentiating circuit 12 is applied to the base of the second control transistor 20, the second control transistor 20 is in an on state and the second capacitor 15 is charged. 1 control transistor 17 is turned on. When the first control transistor 17 is turned on, a bias current is supplied from its collector to the base of the muting transistor 6 through the Zener diode 18 and the resistor 19, so that the muting transistor 6 remains on for a predetermined period of time. Therefore, since the signal transmission line 7 is grounded by the muting transistor 6, signals such as noise are not outputted to the output terminal 5. When a predetermined period of time elapses after the power switch 9 is closed, the second control transistor 20 is inverted to the OFF state.
The control transistor 17 and the muting transistor 6 are inverted to the off state, and the third control transistor 27 is reverse biased and is in the off state. When a reproduction operation is performed in such a state, the tape recorder enters a reproduction operation state, and the reproduction magnetic head 1 reproduces the signal recorded on the magnetic tape. The signal reproduced by the reproducing magnetic head 1 is amplified by a preamplifier circuit 2 and then applied to a variable resistor 3. The reproduced signal applied to the variable resistor 3 is level-adjusted and input to the main amplifier circuit 4, where it is amplified and output to the output terminal 5. The reproduced signal outputted to the output terminal 5 is amplified by an amplifier having a large output, and then applied to a speaker to emit sound. When a muting operation is performed in such a reproduction mode, a high-level muting signal is output from the muting signal generation circuit 28, and the muting signal is applied to the base of the muting transistor 6 via the Zener diode 18 and the resistor 19. . As a result, the muting transistor 6 is turned on and performs a muting operation, so that no reproduced signal or noise is output to the output terminal 5.

As described above, the noise prevention operation and the normal muting operation are performed when the power is turned on.Next, the operation when the power is cut off by opening the power switch 9 will be explained. When the power switch 9 is opened, the potential of the power line 11 drops, so that the potential of the balanced terminal A of the bridge circuit 22 , that is, the emitter potential of the third control transistor 27, also drops.
On the other hand, the potential of the other balance circuit B of the bridge circuit 22 , that is, the base potential of the third control transistor 27, is delayed in falling by the charge stored in the second capacitor 15. Therefore, when the emitter potential of the third control transistor 27 drops due to power cut-off, the third control transistor 27 changes from a reverse bias state to a forward bias state, and the third control transistor 27 immediately turns on. When the third control transistor 27 is turned on, the first control transistor 17 whose base is connected to the collector of the third control transistor 27 is turned on, and the collector is connected to the base of the mutating transistor 6. A bias current is supplied. Therefore, the mutating transistor 6
is turned on and the signal transmission line 7 is grounded, so that noise caused by power cut-off is not output to the output terminal 5. The mutating transistor 6
Since the bias current to is supplied by discharging the charge stored in the second capacitor 15,
When the charge stored in the second capacitor 15 is discharged, the first control transistor 17 and the third
The control transistor 27 and the muting transistor 6 are turned off. Further, when the power supply is cut off, the charge stored in the first capacitor 13 constituting the differentiating circuit 12 is quickly discharged through the diode 29.

In this embodiment, the operation was explained in which the power was cut off and supplied by opening and closing the power switch 9. However, it is also possible to turn off and supply power by opening and closing the power switch 9. Similar operations can be performed when controlling.

As explained above, the muting circuit of the present invention has a simple configuration and can suppress the noise generated not only when the power is turned on but also when the power is turned off from being output as a signal, so it can be connected to an amplifier with a large output. If implemented as a muting circuit for a tape recorder that is used in

[Brief explanation of the drawing]

The illustrated circuit is one embodiment of the muting circuit of the present invention. Explanation of main drawing numbers, 4... Main amplifier circuit, 5... Output terminal, 6... Muting transistor, 7... Signal transmission path, 9... Power switch, 1
0... Constant voltage power supply circuit, 12 ... Differential circuit, 13
...First capacitor, 15...Second capacitor, 16...Reverse current prevention diode, 17...First control transistor, 20...Second control transistor, 22 ...Bridge circuit, 27...Third
Control transistor, 28...mutating signal generation circuit.

Claims (1)

[Scope of utility model registration request] A muting transistor whose collector-emitter path is connected between the signal transmission path and ground and which performs a muting operation when in an on state, and which is connected to control the operation of the muting transistor and which is in an on state. a first control transistor that turns on the mutating transistor; and a second control that turns on for a predetermined period of time by the output of a differentiating circuit including a first capacitor when power is turned on, and keeps the first control transistor on during that time. a second capacitor that is constantly charged through a reverse current prevention diode in a power supply state and is connected to the current supply side of the first control transistor;
Muting of a tape recorder comprising a third control transistor which is in an off state when power is supplied and is biased to an on state by the discharge current of the second capacitor when the power is cut off, thereby turning on the first control transistor. circuit.