JPH0320891Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Purpose of the Invention] (Field of Industrial Application) The present invention relates to a magnetic recording device that prevents recording of noise.

(Prior Art) As a magnetic recording device, one is conventionally known in which, for example, a magnetic head and a recording medium formed of a magnetic band are always kept in contact with each other. This configuration does not require a mechanism for separating the magnetic band and the magnetic head when stopped, so the configuration is simple and can be manufactured at low cost.

(Problem that the invention aims to solve) However, since the magnetic band and the magnetic head are in contact even when the power is turned on, there is a problem that the transient current that flows through the magnetic head when the power is turned on is also recorded in the magnetic band, resulting in noise. . Furthermore, since this phenomenon in which a transient current flows in the magnetic head when the power is turned on occurs in an unbiased state, even if the bias level of the recording bias signal is changed, as shown in Japanese Utility Model Publication No. 50-29466, noise will be generated. recording cannot be prevented.

The present invention was devised in view of the above problems, and it is an object of the present invention to provide a magnetic recording device that prevents recording of noise due to transient current when power is turned on.

[Structure of the idea]

(Means for Solving the Problems) The present invention provides a main switch for opening and closing the power supply in a magnetic recording device in which a magnetic head and a recording medium recorded by the magnetic head are always in contact with each other. , a recording switch that starts and stops the recording motor when the main switch is closed, a bias oscillation circuit that supplies a recording bias signal to the magnetic head when the recording switch is closed, and a bias oscillation circuit that supplies a recording bias signal to the magnetic head when the recording switch is closed; a time constant circuit that does not output the output of the bias oscillation circuit to the magnetic head; a transistor that is connected in parallel with the magnetic head and shorts the magnetic head; and a time constant circuit that biases the transistor for at least a predetermined period of time after the main switch is closed. A bias circuit includes a capacitor that supplies current to turn on the transistor, and a bias circuit that turns off the transistor when the recording switch is closed.

(Operation) In the present invention, after the main switch closes the power supply circuit, a bias current is supplied from the power supply to the transistor for at least a predetermined period of time until the capacitor is charged, the transistor is turned on, and the magnetic head is short-circuited. Also, by closing the write switch, the transistor is turned off and the magnetic head is made conductive. Further, after the recording switch is closed, the recording bias signal of the bias oscillation circuit is not outputted for a predetermined period of time by a time constant circuit.

(Embodiment) Hereinafter, the configuration of an embodiment of the present invention will be described with reference to FIG.

In Fig. 1, 1 is a power supply, and this power supply 1 is
It is connected to a capstan motor 2 as a recording motor via a main switch 3 and a recording switch 4 as a recording switch. Reference numeral 5 denotes a power supply stabilizing circuit, which is connected to the positive terminal of the power supply 1 via the connection point A and the main switch 3, and between the output terminal C and the negative terminal of the power supply 1. A capacitor 6 is connected. and,
A constant voltage is output from the output terminal C, and is supplied to the time constant circuit 7, bias oscillation circuit 8, amplifier 9, and bias circuit 10.

The time constant circuit 7 is composed of a transistor 11, a backflow prevention diode 12, a capacitor 13, and resistors 14, 15, 16, and 17. When a current is supplied from the power supply stabilization circuit 5, the transistor 11 is turned on. When the recording switch 4 is turned on, the transistor 11 is turned off.

The bias oscillation circuit 8 includes an oscillation transformer 1
9. Consists of a resonant capacitor 20, a transistor 21, a capacitor 22, resistors 23, 24, and a diode 25. When the transistor 11 of the time constant circuit 7 is on, it does not operate and the transistor 1
It operates after a predetermined period of time has passed after 1 is turned off.

The input end of the amplifier 9 is connected to a microphone, and the output end is connected to a coupling capacitor 27, an equalizer circuit 30 consisting of a parallel circuit of a resistor 28 and a capacitor 29, and a coupling capacitor 31.
The magnetic head 3
6, and is also connected via the coupling capacitor 27 to a monitor circuit 40 consisting of a variable resistor 37, a jack 38, and a resistor 39.

A collector of a transistor 41 is connected to a connection point between the equalizer circuit 30 and the coupling capacitor 31. The emitter of this transistor 41 is directly connected to the negative terminal of the power supply 1, and the base is connected to the bias circuit 10. In this bias circuit 10, the base of a transistor 41 is connected to a negative voltage terminal via a resistor 43, a connection point E, and a capacitor 44. Also, connection point E
is connected to the output terminal C via resistors 45 and 46, and to the negative voltage terminal via a diode 47, a connection point D, and a parallel circuit of a resistor 48 and a diode 49. Further, the connection point D is connected to the positive end of the power supply 1 via the capacitor 50 and the main switch 3. Furthermore, resistance 4
A connection point B between 5 and 46 is connected to the negative terminal via a backflow prevention diode 51 and the recording switch 4.

Further, the trap circuit 34 and the magnetic head 36
The connection point is connected to the negative terminal of the power supply 1 via the capacitor 52 and the secondary coil of the oscillation transformer 19.

Next, the operation of this embodiment will be explained with reference to FIG.

First, when the main switch 3 is closed at time _T0 , the voltage at the connection point A becomes equal to the voltage value of the power source 1, as shown in FIG. 2A. Then, the current from the power supply 1 flows through the base of the transistor 41 via the diode 47, so that the transistor 41 is turned on at the same time as the main switch 3 is closed. In this way, the voltage at the connection point D once reaches the voltage value of the power source 1, and then gradually decreases over a predetermined period of time due to charging of the capacitor 50, as shown in FIG. Note that transistor 4
The predetermined time for supplying current to the base of the capacitor 50 is set by the charging time of the capacitor 50, and the change curve that determines this charging time is determined by the capacitance of the capacitor 50. Further, in the power supply stabilizing circuit 5, when the main switch 3 is closed and the voltage of the power supply 1 is applied, the voltage at the output terminal C increases to a specified value as shown in FIG. Then, the output voltage of the power supply stabilizing circuit 5 is applied to the amplifier 9, and at this time, a transient current is output from the output terminal of the amplifier 9. However, this transient current is caused by the coupling capacitor 2
7, 31 and the equalizer circuit 30, the signal is bypassed to the transistor 41 which is in an on state, and does not flow to the magnetic head 36, so that it is not recorded on the magnetic band as noise.

Note that even if the voltage at the connection point D drops due to charging of the capacitor 50, when the voltage at the output terminal C of the power supply stabilization circuit 5 increases, the transistor 41
The diode 47 prevents the voltage at the connection point E from dropping below a certain voltage as shown in E in the same figure, so the on state is maintained. Further, the voltage at the connection point B increases as the voltage at the output terminal A increases, as shown in FIG.

Also, at this time, the transistor 1 of the time constant circuit 7
1 is on, the bias oscillation circuit 8
is in an inactive state and does not reach the recording bias level, so no recording is made.

Next, when the recording switch 4 is closed at time T ₁ ,
Capstan motor 2 is started. Also, since connection point B is connected to the negative pole of power supply 1, connection point E
The voltage drops due to discharge of the capacitor 44, and the transistor 41 is turned off. Therefore, the output current corresponding to the microphone input of the amplifier 9 flows through the coupling capacitor 27, the equalizer circuit 30, the coupling capacitor 31 and the trap circuit 34 to the magnetic head 36, and is recorded on the magnetic band. Note that at this time, the time constant circuit 7
The transistor 11 is turned off because its base is connected to the negative electrode of the power supply 1. Then, after a predetermined time,
That is, after the capacitor 13 is charged to a predetermined voltage, the bias oscillation circuit 8 becomes operational and supplies recording bias. Here, the time from when the recording switch 4 is closed until the recording bias is supplied is set equal to the time from when the capstan motor 2 is completely started until the rotational speed reaches a constant speed. .

Next, when the recording switch 4 is opened at time _T1 , the capstan motor 2 is stopped and the connection point E
The voltage gradually rises as the capacitor 44 is charged, which turns on the transistor 41, and no current flows through the magnetic head 36 again, and the bias oscillation circuit 8 also becomes inactive and no longer supplies recording bias.

Next, when the main switch ₃ is opened at time T3, the voltage at the connection point E does not drop due to the capacitor 44 until the capacitor 6 is discharged and the voltage at the output terminal C drops to some extent, and the transistor 41 remains on. maintain. Therefore, a transient current that becomes a noise current due to opening of the main switch 3 does not flow to the magnetic head 36 and is not recorded.

The oscillation level of the bias oscillation circuit 8 is gradually increased and decreased at the start and stop of recording, so that a predetermined recording bias level can be supplied only while the capstan motor 2 is fully started and at a constant speed. By doing so, you can obtain even better recording results.

Although the above embodiment has been described for the case of recording, the same effect can be achieved if magnetic recording is performed using a magnetic head.

Further, even if the magnetic head and the recording medium are in constant contact with each other, since no head current flows through the magnetic head except during the recording operation, microphone connection noise and drop impact noise are not recorded.

[Effect of idea]

According to the present invention, the capacitor of the bias circuit supplies bias current to the transistor for a predetermined time after the main switch is closed, and the time constant circuit does not supply the recording bias signal of the bias oscillation circuit to the magnetic head for a predetermined time. , it is possible to prevent noise from being recorded due to transient current when the power is turned on.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the magnetic recording device of the present invention, and FIG. 2 is an explanatory diagram of the same operation. 1...Power supply, 2...Capstan motor as a recording motor, 3...Main switch, 4...
Recording switch as a recording switch, 7... Time constant circuit, 8... Bias oscillation circuit, 10... Bias circuit, 36... Magnetic head, 41... Transistor, 50... Capacitor.

Claims (1)

[Scope of Claim for Utility Model Registration] In a magnetic recording device in which a magnetic head and a recording medium recorded by the magnetic head are always in contact with each other, a main switch that opens and closes the power supply, and a main switch that closes the main switch. a recording switch that starts and stops a recording motor when the recording switch is closed; a bias oscillation circuit that supplies a recording bias signal to the magnetic head when the recording switch is closed; and a bias oscillation circuit that supplies the recording bias signal to the magnetic head when the recording switch is closed; a time constant circuit that does not output an output to the magnetic head; a transistor connected in parallel with the magnetic head to short-circuit the magnetic head; A magnetic recording device comprising: a bias circuit that has a capacitor that turns on a transistor and turns off the transistor when the recording switch is closed.