JPS6076005A - Magnetic tape erasing device - Google Patents

Abstract

PURPOSE:To obtain an AC eraser of a low power consumption type by using an AC erasing head having an azimuth and then using a coil wound round the core of said erasing head as an oscillating coil of an oscillating circuit which supplies an erasing current. CONSTITUTION:The oscillation frequency of an oscillating circuit 36 is decided by a capacitor 45 and a coil 35 wound round a core 31 of a magnetic material having high permeability of an AC erasing head 46. The coil 35 functions as an oscillating coil and at the same time produces AC magnetic fields at gaps 33 and 34. Then the coil 35 impresses the AC magnetic fields leaked out of the gaps 33 and 34 to a magnetic tape and erases them. In this case, a remaining magnetization pattern obtained after erasion is reproduced by a reproducing head with an azimuth loss since the gaps 33 and 34 have azimuths. Thus the erasion frequency can be set within an audio band, and the impedance of the head 46 is lowered. Therefore the erasion power is also reduced. Furthermore the voltage impressed to the circuit 36 can be reduced less than the conventional level.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a magnetic tape erasing device for audio tape recorders, particularly portable type tape recorders powered by dry batteries.

Conventional Structure and Problems Conventional methods for erasing all signals recorded on a magnetic tape can be roughly divided into DC erasure methods and AC erasure methods.

The DC erasure method applies a strong DC magnetic field to a magnetic tape.
This is a method of erasing residual magnetization, which is a recorded signal, by magnetizing it to the magnetic saturation point. In this method, a coil is fully wound around a core of high magnetic permeability material with a gap, and a large DC current is passed through the coil to cause leakage from the gear sawn part. There are two types of erase heads: DC erase heads that use a DC magnetic field and magnetic erase heads that use ferromagnetic magnets. This DC quenching method does not require an oscillation circuit and has the advantage of low power consumption, unlike the AC quenching method described next. However, this has the disadvantage that it appears as noise during playback, and that the playback signal recorded after erasing becomes distorted.

On the other hand, the alternating current erasing method is a method in which an alternating current magnetic field is applied to a magnetic tape to converge residual magnetization, which is a recording signal, to a magnetic neutral point and erase the residual magnetization. FIG. 1 shows the above-mentioned conventional AC erasing head, and FIG. 2 shows an oscillation circuit that supplies an AC current to the AC erasing head.

In FIG. 1, 11a and 11b are high magnetic permeability material cores, 1
2.13 is the gap provided between the high magnetic permeability material cores 11a and 11b, 14 is the coil wound around the high magnetic permeability material core 11a, 16 is the oscillation circuit shown in FIG. 2, and 16 is the advancement of the magnetic tape. It is the direction.

In FIG. 2, 21 is a negative power supply terminal, 22 is a positive power supply terminal, 23&, 23b is a transistor, 24 is a capacitor, 25 is an oscillation transformer, and 26 is an oscillation transformer 26.
This is the next coil. 27a.

27b is a resistor, and 28 is a terminal for connecting an AC erasing head.

Figure 2 is an example of a push-pull connection oscillation circuit, in which a voltage of about ±15V is applied to the power supply terminals 21 and 22, and the resistor 26
DC operation is performed by applying bias to the bases of the transistors 23a and 23b through &, 26b'i, and the oscillation frequency is determined by the inductance of the secondary coil 26 of the oscillation transformer 25 and the capacitor 24. The alternating current generated in this oscillation circuit is passed through the alternating current erasing head terminal 27 to the coil 14 wound around the high permeability material core 11a, and the alternating current magnetic field leaking from the gap 12.13 is applied to the magnetic tape passing through the gap 12.13. is applied to and erased.

The erasing frequency is selected to be 3 to 4 times the audio band or higher so as not to be reproduced by the reproducing head, and an alternating current of 6olIh or higher is usually used.

Comparing the AC erasing method using this AC erasing head and the DC erasing method, erasing using the AC erasing head has the advantage that there is less noise during reproduction after erasing and less distortion of the recorded signal.

However, the erasing method using an AC erasing head consumes a large amount of power, and the power consumption is even greater when using tapes with high coercive force (for example, metal tapes). However, it was difficult to mount an AC erase head on a dry battery-powered portable type cassette tape recorder.

OBJECTS OF THE INVENTION The present invention solves the above-mentioned conventional problems by providing a low power consumption AC erasing device, making it possible to mount an AC erasing head on a dry battery-powered portable type cassette tape recorder, and eliminating noise and noise. The purpose is to realize audio recording and playback with less distortion.

Structure of the Invention The present invention comprises an AC erasing head having an azimuth angle in which a gap for generating an erasing magnetic field is inclined with respect to a direction perpendicular to the traveling direction of the magnetic tape, and a coil wound around the core of the AC erasing head. This is a magnetic tape erasing device consisting of an oscillation circuit used as an oscillation coil. By setting an azimuth angle to the gap of the AC erasing head, the residual magnetization pattern after erasing will not be reproduced by the reproducing head due to azimuth loss, so it is possible to set the erasing frequency within the audio band, and AC erasing. The impedance of the head is lowered, requiring less erasing power, and as a result, the voltage applied to the oscillation circuit can be lower than that of conventional systems, and the oscillation coil uses a coil wrapped around the core of the AC erasing head. This has the unique effect that the oscillation circuit can be miniaturized and that a magnetic tape erasing device using an AC erasing head can be installed even in a portable type cassette tape recorder driven by dry batteries.

Description of examples An embodiment of the present invention will be described below.

FIG. 3 shows an embodiment of the AC erasing head of the present invention. 3
1.32 is a high magnetic permeability material core, 33.34 is a git knob provided on the high magnetic permeability material core 31.32, 35 is a coil wound around the high magnetic permeability material core 31, 36 is an oscillation circuit, 37
is the traveling direction of the magnetic tape.

FIG. 4 shows an embodiment of the oscillation circuit of the present invention.

41 is a power supply terminal, 42 and 43 are resistors, 44 is a transistor, 45 is a capacitor, and 46i'j is the AC erasing head shown in FIG.

Azimuth loss LA is given by the following equation.

Here, W is the gap width, λ is the recording wavelength, θ is the azimuth angle, and π is the circumference. FIG. 6 shows a characteristic curve of azimuth angle and azimuth loss according to equation 0).

In Figure 6, if the curve connecting the tops of the mountains is *LA/, then L' is calculated as follows in equation (1): s 1n(7tan θ)=±1 -------・<2
), therefore LA' is L'
=201 og 101- tanθI ・=-(3
)A λ. LA' indicates the minimum guaranteed level of azimuth loss. Recording wavelength λ, tape speed V, and recording frequency f
The relationship with is λ=v/f (4). Now w = 0, 6 mm, v = 4 a
8cm/s %f = 5klh, 101Jh120
Figure 6 shows the characteristic trends of LA/ in animals. The azimuth angle is 100 or more and the recording frequency is 5 kJ (z
or more, the azimuth loss is at least 13 dB lower than the residual magnetization level (-30 dB) caused by a conventional AC erase head.
It can be seen that odB is guaranteed.

For these reasons, the AC erasing head of the present invention allows the erasing frequency to be set lower than that of the conventional one.

Furthermore, since the magnitude of the magnetic field leaking from the gap required for erasing is the same whether a conventional AC erase head is used or an AC erase head according to the present invention, the erase current required for erasing is The same level applies to inventions, but
Since the impedance of the AC erasing head can be set to a low erasing frequency in the case of the present invention, power consumption is smaller in the case of the present invention.

In this experiment, the impedance of the AC erase head was approximately 19 Ω at an erase frequency of 8 kHz, and the erase current of the metal tape was 130 mA, so the AC erase head had an impedance of approximately 2.5 V.
Since the applied voltage is sufficient, the oscillation circuit may be one with low power consumption.

According to this experiment, the azimuth angle is 100 or more and 6o0 or less,
The erasing frequency was 6 kHz or higher, and no practical problems occurred.

Effects of the Invention As described above, according to the present invention, by using a coil wound around the core of an AC erasing head as an oscillation coil, it is possible to downsize and reduce costs of a magnetic tape erasing device.

In addition, the same erasing effect as the conventional one can be obtained with the voltage of about two dry batteries, and since the erasing power is lower than the conventional one, the battery life is longer. It becomes possible to install a magnetic tape erasing device.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a schematic configuration of an AC erasing head of a conventional magnetic tape erasing device, FIG. 2 is an oscillation circuit diagram of the same, and FIG. 3 is an AC erasing head of a magnetic tape erasing device according to an embodiment of the present invention. 4 is a perspective view showing the schematic configuration of the oscillator circuit,
FIG. 6 is a diagram showing the characteristic curve of the azimuth angle and azimuth loss, and FIG. 6 is a diagram showing the characteristic mill m of the azimuth angle and the minimum guaranteed level of azimuth loss. 31.32... High permeability material core, 33.34.
...Gap, 35...Coil, 36.
...Oscillation circuit, 41...Power supply terminal, 4
2.43...Resistor, 44...Transistor, 45...Capacitor, 46...AC erase head. Name of agent: Patent attorney Toshio Nakao and 1 other person 2nd
Figure 4 Azimuth angle [θ (radian angle)

Claims (1)

[Claims] A magnetic tape erasing device using an AC erasing head that erases information recorded on the magnetic tape by applying an AC erasing magnetic field generated from a gap portion of a core to the magnetic tape, the magnetic tape erasing device being perpendicular to the traveling direction of the magnetic tape. An AC erasing head with a gap inclined with respect to the direction is provided, and a coil wound around the core of the AC erasing head is used as an oscillation coil of an oscillation circuit that supplies an erasing current to the AC erasing head. A magnetic tape erasing device characterized in that the magnetic tape is set within an audio band.