JPS634292Y2 - - Google Patents

Description

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

A high-grade tape recorder called a tape deck is connected to an amplifier with a 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, making it difficult for the user to hear. It will make you feel uncomfortable. Some of this noise occurs when switching operations, but the noise that occurs when the power is cut off by opening the power switch is particularly large.
Various circuits have been developed to suppress this noise.

The present invention aims to provide a muting circuit with a simple configuration that suppresses such noise.
A detailed explanation will be given below with reference to the drawings. The illustrated circuit is an embodiment of the muting circuit of the present invention, in which 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. A variable resistor 4 adjusts the level of the output signal of the preamplifier 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 4; This is an output terminal to which an amplified signal is applied and is connected to an input terminal of an amplifier having a large output. 6
is a mutating transistor whose collector is connected to the signal transmission path 7 and whose emitter is grounded, and has the function of bypassing the signal flowing through the signal transmission path 7 when in the on state. 8 is a power terminal connected to a commercial AC power supply;
9 is a power switch that is closed when power is supplied to the tape recorder; 10 is a constant voltage that rectifies the input AC power when the power switch 9 is closed, and outputs the regulated voltage to the power supply line 11; This is a power supply circuit. 12 is a capacitor 14 to which DC current, which is the output of the constant voltage power supply circuit 10, is supplied through the backflow prevention diode 13 and charged;
is a control transistor whose emitter is connected to the power supply terminal of the capacitor 12 and whose collector is connected to the base of the mutating transistor 6 via the Zener diode 15 and resistor 16, and between the base and ground. Resistors 17 and 18 are connected in series. 1
A control switch 9 is connected between the connection point A of the resistors 17 and 18 and the power line 11, and is configured to be switched in conjunction with the power switch 9. Reference numeral 20 denotes a muting signal generation circuit that outputs a high-level muting signal during a muting operation, and is connected so that the output signal is applied to the base of the mutating transistor 6 via a Zener diode 15 and a resistor 16. .

The muting circuit of the present invention is constructed as described above, and the operation of the circuit thus constructed will now be described. The illustrated state is a state in which power is not supplied, and both the power switch 9 and the control switch 19 are in an open state. In this state, when the power switch 9 is closed, a constant voltage DC voltage is output from the constant voltage power supply circuit 10, and the control switch 19 is closed. As a result, power is supplied to the preamplifier circuit 2 and the main amplification circuit 4 and they become operational, and a charging current is supplied to the capacitor 12 through the backflow prevention diode 13, so that the capacitor 12 is charged. Further, when power is supplied, a high voltage is applied to the base of the control transistor 14 through the control switch 19, so that the control transistor 14 is reverse biased and in an off state. In such a state, when a playback operation is performed, a playback operation state is entered, and the signal recorded on the magnetic tape is played back by the playback magnetic head 1. 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. If a muting operation is performed while in such a reproducing operation state, the muting signal generation circuit 2
A muting signal having a level higher than 0 is output, and the muting signal is applied to the base of the muting transistor 6 via the Zener diode 15 and the resistor 16. 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.

Although the reproducing operation and the normal muting operation are performed as described above, the operation when the power is cut off by opening the power switch 9 will be explained next. When the power switch 9 is opened, the potential of the power line 11 on the anode side of the backflow prevention diode 13 drops and the control switch 19 is opened. When the control switch 19 is opened, the base potential of the control transistor 14 drops to ground potential. On the other hand, since the emitter potential of the control transistor 14 is held at a high potential by the charge stored in the capacitor 12, the control transistor 14 becomes forward biased and turns on immediately when the control switch 19 is opened. do. When the control transistor 14 is turned on, a bias current is supplied from its collector to the base of the mutating transistor 6. Therefore, the muting 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. Since the bias current to the mutating transistor 6 is supplied by discharging the charge stored in the capacitor 12, the capacitor 1
When the charge stored in the transistor 2 is discharged, both the control transistor 14 and the muting transistor 6 are turned off.

As explained above, the muting circuit of the present invention can suppress the noise generated when the power is cut off by opening the power switch, so it is ideal as a muting circuit for a tape recorder connected to a high-output amplifier. be.
In addition, the operation of the control transistor that controls the operation of the muting transistor is controlled by a switch that is switched in conjunction with the power switch, which simplifies the circuit configuration and ensures reliable and quick switching operation when the power is cut off. The muting circuit of the present invention has the advantage of being able to perform the following functions.

[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... Capacitor,
13... Backflow prevention diode, 14... Control transistor, 19... Control switch, 20...
Muting signal generation circuit.

Claims (1)

[Scope of utility model registration request] a mutating transistor having a collector-emitter path connected between the signal transmission path and ground; and a muting transistor connected to control the operation of the muting transistor and turning on the mutating transistor when in the on state. a control transistor; a 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 control transistor;
It consists of a control switch that is switched in conjunction with a power switch and is connected to reverse bias the control transistor in the power supply state, and forward bias the control transistor when the power switch is opened and the power is cut off. A muting circuit for a tape recorder, characterized in that the controlling transistor and the mutating transistor are turned on by the discharge current of the capacitor.