JP2530594Y2 - Muting circuit of tape recorder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to a tape recorder, and more particularly to a muting circuit that suppresses output operation of unpleasant reproduced sound.

(B) Conventional technology Portable tape recorders used outdoors are widely used, and such tape recorders use a battery as a power source. Such portable tape recorders have been miniaturized in order to make them easy to carry, and the miniaturization of batteries, reduction of power supply voltage, and motor Has been downsized. Further, the tape recorder is provided with a speed control circuit for keeping the rotation speed of the electric motor constant since it is necessary to keep the running speed of the magnetic tape constant during the reproducing operation.
As such a speed control circuit, there is a circuit called an electronic governor. However, the speed control circuit has been formed into an IC (integrated circuit) for reasons such as a reduction in power supply voltage. Such
As a technology of an IC-based speed control circuit, for example,
There is one disclosed in JP-A-56-25392. The motor incorporated in the tape recorder needs to rotate at a constant speed when performing a reproducing operation, but does not need to rotate at a constant speed when performing a fast-forward or rewind operation. There is a technology in which the rotational speed of the motor is increased in consideration of the shortage of the transmission torque of the drive mechanism, etc.
There is one disclosed in Japanese Patent No. 47960.

(C) Problems to be solved by the present invention If a tape recorder performs a fast-forward or rewind operation in the reproducing operation state, the fast-forward or rewind operation is performed with the magnetic head in contact with the magnetic tape. There is a tape recorder that is configured to return to the playback operation state when canceling the fast forward or rewind operation.
In such a tape recorder, the signal sound reproduced by the magnetic head when in the fast forward or rewind state becomes an unpleasant sound. The present invention seeks to provide a circuit in which this point is improved.

(D) Means for Solving the Problems The muting circuit of the present invention is connected to a muting transistor for bypassing a signal flowing through a signal transmission line when in a conductive state, and to control the operation of the muting transistor. And supplying a constant voltage to the motor connected between the drive terminal and the power supply irrespective of fluctuations in the power supply voltage, and a control transistor for causing the muting transistor to be non-conductive when the power supply voltage is in the conductive state. A speed control circuit for making the rotation speed of the motor constant, a speed switching switch that is closed during fast-forward or rewind operation, grounds the drive terminal of the speed control circuit, and makes the control transistor non-conductive. It is composed of

(E) Operation The muting circuit of the present invention is provided with a speed switching switch for switching the rotation speed of the motor by grounding the drive terminal of the speed control circuit provided to keep the rotation speed of the motor constant. The switching operation is controlled by a switch.

(F) Embodiment The illustrated circuit is an embodiment of the matching circuit of the present invention. In the figure, (1) is a magnetic head for reproducing a signal recorded on a magnetic tape, and (2) is a preamplifier circuit for receiving a signal reproduced by the magnetic head (1) and amplifying the signal. , (3) are variable resistors to which the signal amplified by the preamplifier circuit (2) is applied and the level of the signal is adjusted, and (4) is level-adjusted by the variable resistor (3). A main amplifier circuit that receives the signal and amplifies the signal, and (5) is a speaker that receives the signal amplified by the main amplifier circuit (4) and emits the signal. (6) is a battery for supplying power to the preamplifier circuit (2) and the main amplifier circuit (4), etc., and (7) is provided to keep the rotation speed of the electric motor (8) constant and is integrated into an IC. The speed control circuit includes a power input terminal (10) and a drive terminal (11) connected to a power supply via a resistor (9). In such a configuration, the motor (8) is connected between the drive terminal (11) provided in the speed control circuit (7) and the power supply, so that even if the voltage of the battery (6) decreases, the motor (8) The output voltage of the drive terminal (11) changes so that the voltage applied to both ends of (8) becomes constant. When the voltage of the battery (6) as the power supply drops to a voltage at which the tape recorder cannot operate normally, the speed control circuit (7) reduces the voltage output to the drive terminal (11) to a predetermined voltage. It is configured to lower.
(12) is a muting transistor whose collector is connected to a signal transmission line (13) through which the output signal of the preamplifier circuit (2) flows, and whose emitter is grounded, and whose base is a resistor (14). Connected to the power supply. (15) is a control transistor having a collector connected to its base and an emitter grounded to control the operation of the muting transistor (12), and having a base connected to the first diode (16).
And a power supply via a resistor (17). Also,
A second diode (18) is connected between a connection point (A) between the first diode (16) and the resistor (17) and a drive terminal (11) provided in the speed control circuit (7). Have been. (19) is a capacitor connected between the base of the control transistor (15) and ground, and has a function of preventing malfunction. A speed switching switch (20) is closed when a fast-forward or rewind operation is performed, and is connected between the drive terminal (11) of the speed control circuit (7) and the ground. In such a circuit configuration, when the voltage of the battery is equal to or higher than a predetermined voltage value, that is, a minimum voltage value at which the operation of the tape recorder can be performed normally, the voltage is output to the drive terminal (11) of the speed control circuit (7). When the voltage is equal to or higher than a predetermined value, the second diode (18) is reverse-biased to turn on the control transistor (15), and when the voltage falls below the predetermined voltage, control is performed by turning on the second diode (18). The transistor (15) is set to be non-conductive. The present invention is configured as described above. Next, the operation of such a circuit will be described. First, the operation when the voltage of the battery (6) as the power source is sufficiently high will be described. When the reproducing operation of the tape recorder is performed, the driving mechanism is in a state of performing the reproducing operation, and the battery from the battery (6) is replaced by the preamplifier circuit (2)
It is supplied to a main amplifier circuit (4) and a speed control circuit (7). When power is supplied to the speed control circuit (7), a voltage for making the voltage applied to the electric motor (8) constant is output to a drive terminal (11) provided in the speed control circuit (7). . As a result, the motor (8) is driven to rotate at a constant speed by the speed control circuit (7), and the magnetic tape is driven at a constant speed by the reproducing drive mechanism. And
In such a state, the output voltage of the drive terminal (11) provided in the speed control circuit (7) is sufficiently higher than a predetermined voltage, and the second diode (18) is in a reverse-biased state. Accordingly, a bias current is supplied to the base of the control transistor (15) through the resistor (17) and the first diode (16), and the control transistor (15) is turned on. When the control transistor (15) is in a conductive state, the potential of the collector thereof is at the ground potential, so that the muting transistor (12) is in a reverse-biased state and is in a non-conductive state. In such a state, the signal recorded on the magnetic tape is input to the preamplifier circuit (2) after being reproduced by the magnetic head (1). The reproduced signal input to the preamplifier circuit (2) is amplified and applied to the variable resistor (3) without being bypassed. After the level of the reproduced signal applied to the variable resistor (3) is adjusted, the reproduced signal is input to the main amplifier circuit (4) and amplified. The reproduced signal amplified by the main amplifier circuit (4) is applied to the speaker (5) and emitted, so that the user can listen to the reproduced signal. In this manner, the reproducing operation is performed, but the voltage output to the drive terminal (11) of the speed control circuit (7) decreases in accordance with the decrease in the voltage of the battery (6), and the electric motor (8) The rotation speed of the motor (8) for making the applied voltage constant becomes constant, and the reproducing operation of the tape recorder can be performed without any trouble. The reproduction operation is performed when the voltage of the battery (6) is equal to or higher than the voltage value at which the tape recorder can operate normally, but the voltage of the battery (6) cannot operate normally next. The operation when the voltage value decreases will be described. When the voltage of the battery (6) drops below a predetermined value, the drive terminal (1) provided in the speed control circuit (7)
The output voltage of 1) drops below the predetermined value and the second diode (1
8) becomes conductive. When the second diode (18) conducts, the first diode (16) and the second diode (18)
The potential at the connection point (A), which is the anode of the control transistor (15), drops below a voltage value that causes the control transistor (15) and the first diode (16) to be in a conductive state, and the control transistor (15) is inverted to a non-conductive state. The control transistor (15)
Is inverted to a non-conducting state, the potential of its collector becomes high, so that the muting transistor (12) is biased to a conducting state. A signal transmission line (13) when the muting transistor (12) is in a conductive state;
The signal flowing through the muting transistor (1
2) To be bypassed through the collector / emitter road,
An unpleasant sound reproduced with a decrease in the running speed of the magnetic tape or the like is not emitted from the speaker (5).

As described above, the reproducing operation in the present embodiment is performed. Next, the operation when the fast-forward or rewind operation is performed in the reproducing operation state will be described. If a fast-forward or rewind operation is performed while the tape recorder is in the above-described reproduction operation state, the drive mechanism performs a fast-forward or rewind operation while the magnetic head (1) is in contact with the magnetic tape, and the speed is increased. The switching switch (20) is closed. When the speed changeover switch (20) is closed, the drive terminal (11) of the speed control circuit (7) is grounded, so that the speed control operation by the speed control circuit (7) is canceled and the electric motor (8) Is in a state where the voltage of the battery (6) is applied as it is. As a result, the voltage applied to the electric motor (6) increases, and the rotation speed of the electric motor (6) increases.
Therefore, the magnetic tape is fast-forwarded or rewound by the high-speed rotation of the drive mechanism and the electric motor (8). Then, when in such a state, the speed switching switch (20)
Is closed, the cathode of the second diode (18) is grounded, so that the second diode (18) is conducting and the control transistor (15) is non-conducting. When the control transistor (15) is in a non-conductive state, as described above, the muting transistor (12) is biased to be in a conductive state to bypass a signal flowing through the signal transmission line (13). Therefore, a signal reproduced from the magnetic head (1) is applied to the speaker (5) even when the magnetic tape is run at high speed while the magnetic head (1) is in contact with the magnetic tape by the fast forward or rewind operation. It does not cause any discomfort to the user. The operation when the fast-forward or rewind operation is performed in this manner is performed. The same operation is performed even when the voltage of the battery (6) drops to a voltage at which the reproduction operation cannot be performed normally. Done. When the fast forward or rewind operation is performed, the voltage of the battery (6) is applied to both ends of the electric motor (8) by switching the speed switching switch (20), so that the voltage of the battery (6) is used efficiently. Can be done.

In this embodiment, the first diode (16) connected to the base of the control transistor (15) functions to set the operation level of the control transistor (15). Use of a germanium diode is effective in lowering the power supply voltage.

(G) Effects of the present invention In the present invention, a motor is connected between a drive terminal provided in a speed control circuit and a power supply, and a constant voltage is supplied to the motor to make the rotation speed of the motor constant. Thus, the rotation speed of the electric motor can be kept constant even if the power supply voltage fluctuates. Also, a speed changeover switch which is closed by a fast-forward or rewind operation is provided between the drive terminal of the speed control circuit and the ground, and one end of the motor is grounded by the speed changeover switch during the fast-forward or rewind operation. That is, since the motor is connected between the power supply and the ground, the maximum voltage obtained from the power supply can be supplied to both ends of the motor. Therefore, according to the present invention, the rotation speed of the electric motor can be maximized, and the power supply voltage can be used effectively. The present invention has been implemented in a portable tape recorder using a battery as a power supply. In such a case, a very large effect is achieved.

Further, the present invention provides a method for controlling the operation of a control transistor for controlling the operation of a muting transistor provided to bypass a signal flowing through a signal transmission line, a signal output to a drive terminal of the speed control circuit and a speed switching. Since the control is performed by the switch, that is, when the power supply voltage drops to a voltage value at which normal operation cannot be performed, or when a fast-forward or rewind operation is performed, the muting transistor is turned on and the muting is performed. Since the playing operation is performed, unpleasant sounds reproduced by abnormal reproduction or high-speed reproduction can be suppressed, and the practical value of the present invention is very high.

[Brief description of the drawings]

The circuit shown is an embodiment of the inventive muting circuit. Description of main figure numbers (2) ... preamplifier circuit, (4) ... main amplifier circuit, (6) ...
Battery, (7) Speed control circuit, (8) Electric motor, (11)
… Drive terminal, (12)… Muting transistor, (13)… Signal transmission line, (15)… Control transistor, (20) Speed switching switch.

Claims (1)

(57) [Scope of request for utility model registration] 1. A speed control circuit for supplying a constant voltage to a motor connected between a drive terminal and a power supply irrespective of fluctuations in a power supply voltage to thereby keep the rotation speed of the motor constant, and the speed control circuit A speed change-over switch connected between a drive terminal provided in the circuit and ground and closed at the time of fast-forward or rewind operation, and a muting for bypassing a signal flowing through the signal transmission line when in a conductive state. A driving circuit connected to the transistor for controlling the operation of the muting transistor and causing the muting transistor to be in a non-conductive state when the transistor is in a conductive state, and the operation being provided in the speed control circuit; And a control transistor connected so as to be controlled by the output voltage of the terminal. When the voltage decreases to a level that cannot be performed, the output voltage of the drive terminal is reduced to cause the control transistor to be in a non-conductive state, so that the muting transistor is in a conductive state, and a fast-forward or rewind operation is performed. The drive transistor is grounded by closing the speed changeover switch, thereby causing the control transistor to be in a non-conducting state and one end of the motor to be grounded, thereby causing the muting transistor to be in a conducting state. A muting circuit for the tape recorder, wherein the motor is rotated at a high speed.