JPS6151322B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording/reproducing device, and in particular to a signal erasing magnetic head (hereinafter referred to as an "erasing head") that erases signals already recorded on a magnetic tape by applying a high frequency voltage. ).

As is well known, in a magnetic recording/reproducing device, an erasing head and a signal recording/reproducing magnetic head (hereinafter referred to as a "recording/reproducing head") that record and reproduce signals on the magnetic tape are arranged sequentially in the running direction of the magnetic tape. death,
When recording new signals on a magnetic tape, first a high frequency voltage is applied to the drive coil of the erasing head to erase signals already recorded on the magnetic tape. Afterwards, a new signal is recorded on this magnetic tape by a recording/reproducing head. On the other hand, when reproducing a signal recorded on a magnetic tape, the magnetic tape signal is reproduced by the recording/reproducing head without applying a high frequency voltage to the drive coil of the erasing head.

Below are two types of channels (Channel: CH)
A magnetic recording and reproducing device for recording and reproducing signals will be explained as an example.

FIG. 1 is a circuit diagram showing an example of a conventional magnetic recording/reproducing device.

In the figure, 1 surrounded by a dashed line is a high frequency oscillator, and the oscillation frequency of this high frequency oscillator 1 is determined by the resonance frequency of a coil L and a capacitor C forming a tank circuit. 2 is the first CH signal (hereinafter referred to as "CHl signal") source, and 3 is the CHl signal source 2 whose input side is connected to the recording side contact r of the changeover switch _S11 .
A CHl amplifier 4 is connected to the CHl amplifier for amplifying the CHl signal output from the CHl signal source 2, and a CHl recording/reproducing head 4 for recording and reproducing the CHl signal on the magnetic tape. When recording in this CHl recording/playback head 4, the drive coil passes through contact r of the changeover switch _S12 , passes through the resistor _R11 , and then connects to the CHl.
It is connected to the output side of the amplifier 3, as well as to the output side of the high frequency oscillator 1 through the contact r of the changeover switch _S12 and the resistor _R12 . At the same time as the CHl signal is supplied, an alternating current bias current is supplied from the high frequency oscillator 1. In addition, CHl recording/playback head 4
During reproduction, the drive coil is connected to the input side of the CHl amplifier 3 through the reproduction side contact p of the changeover switch _S12 and the contact p of the changeover switch _S11 ,
A monitor (handset) M ₁ to which the CHl signal reproduced by the CHl recording/playback head 3 is connected to the output side of the CHl amplifier 4.
is output from. 5 is a CHl erasing head for erasing CHl signals already recorded on the magnetic tape. The drive coil of this CHl erase head 5 is
When the recording/reproducing head 4 is recording, a high frequency voltage is applied from the high frequency oscillator ₁ to the drive coil of the CHl erasing head 5, which is connected to the output side of the high frequency oscillator 1 through the contact r of the changeover switch S13. It is becoming more and more common. At this time, the oscillation frequency of the high-frequency oscillator 1 varies depending on the inductance of the drive coil of the CHl erase head 5, so a compensation capacitor is used to compensate for this variation.
C ₁₀ is connected to the output side of the high frequency oscillator 1 through the contact r of the changeover switch S ₁₄ . Note that the changeover switches S ₁₁ , S ₁₂ , S ₁₃ , and S ₁₄ are configured to be switched simultaneously in conjunction with the respective contacts r or p. 6 is the second
CH signal (hereinafter referred to as "CH2 signal") source, 7 is
CH2 amplifier, 8 is CH2 recording/reproducing head, and 9 is CH2 erasing head. CH2 signal source 6, CH2 amplifier 7,
CH2 recording/playback head 8, CH2 erasing head 9, resistor
R ₂₁ , R ₂₂ , changeover switch S ₂₁ , S ₂₂ , S ₂₃ , S ₂₄ ,
Compensation capacitor C ₂ and monitor M ₂ are connected to CH1 signal source 2, CH1 amplifier 3, CH1 recording head 4, CH1 erasing head 5, resistors R ₁₁ , R ₁₂ , changeover switches S ₁₁ , S ₁₂ , S ₁₃ , S ₁₄ , compensation capacitor C ₁₀
and serves as a counterpart to monitor M ₁ .

By the way, in such conventional equipment, CH1
When recording a signal, when the erasing head 5 is connected to the output side of the high frequency oscillator 1 via the changeover switch _S13 and the compensation capacitor _C10 is connected via the changeover switch _S1D , the changeover switch _S13 ,
A large current flows through _S14 . Similarly, CH2
When recording a signal, if the erasing head 9 and the compensation capacitor C ₂₀ are connected to the output side of the high frequency oscillator 1,
A large current flows through the changeover switches S ₂₃ and S ₂₄ .
For example, the oscillation frequency of high frequency oscillator 1 is 60KHz
Then, the voltage applied to each drive coil of erase heads 5 and 9 is 50V, and the inductance of each drive coil of erase head 59 is
If the internal resistance is 7.5Ω at 0.4mH, the reactance of each drive coil of erase heads 5 and 9 is 150Ω, and the changeover switches S ₁₃ and S ₁₄
The current flowing through the command and changeover switches S ₂₃ and S ₂₄ has a large value of approximately 50V/150Ω=300mA. Therefore, in this conventional device, it is necessary to increase the capacitance of the switches S ₁₃ and S ₂₃ of the erase heads 5 and 9, and the compensation capacitor is also required.
The disadvantage is that C ₁₀ , C ₂₀ and changeover switches S ₁₄ , S ₂₄ are required. However, it is possible that the changeover switches S ₁₄ and S ₂₄ are not provided, but in this case, when recording either the CH1 signal or the CH2 signal, or when recording the CH1 signal and the CH2 signal at the same time, Since the inductance loads connected to the output side of the high-frequency oscillator 1 are different, the oscillation frequency and oscillation voltage amplitude of the high-frequency oscillator 1 are different, which impedes proper signal recording and signal erasure.

This invention has been made in view of the above-mentioned drawbacks, and a resonant capacitor is directly connected in parallel to the drive coil of the erasing head, so that the resonant frequency of the parallel resonant circuit of the drive coil and the resonant capacitor is set to a high frequency oscillator. The oscillation frequency of An object of the present invention is to provide a magnetic recording/reproducing device that can use a changeover switch.

FIG. 2 is a circuit diagram showing the basic configuration of the magnetic recording/reproducing apparatus of the present invention.

In the figure, C ₁₁ and C ₂₁ are connected in parallel to the drive coils of CH1 erase head 5 and CH2 erase head 9, respectively, and are used for resonance such that the parallel resonance frequency with these drive coils matches the frequency of high frequency oscillator 1. It is a capacitor.

The device shown in Figure 2 consists of a resonant capacitor C ₁₁
and C ₂₁ are provided, and the changeover switches S ₁₄ and S ₂₄ of the conventional device shown in FIG. 1 are omitted, but the device is substantially the same as the conventional device.

In the device shown in FIG. 2, the drive coils of the CH1 erase head 5 and CH2 erase head 9 and the resonance capacitors _C11 and _C21 constitute a parallel resonant circuit. When connected to the output side of the high-frequency oscillator 1 via changeover switches S ₁₃ and S ₂₃ , respectively, the currents flowing in each of these parallel resonant circuits, that is, the currents flowing in the drive coils constituting each of these parallel resonant circuits, are This results in a large current limited by the reactance of the drive coil. On the other hand, the current flowing through the changeover switches _S13 and _S23 is transmitted to the erase heads 5, which constitute these parallel resonant circuits.
The current becomes a small current that is limited by the combined impedance of the reactance of each of the drive coils 9 and the reactance of each of the resonance capacitors C ₁₁ and C ₂₁ . These combined impedances are expressed as the product of q of each parallel resonant circuit and the reactance of each drive coil. for example,
As in the case of the conventional example explained in FIG. If the inductance of each drive coil of 9 is 0.4mH and the internal resistance is 7.5Ω, then erase head 5,
The reactance of each of the 9 drive coils is 150
Ω, and the q of the parallel resonant circuit composed of each of these drive coils and each of the resonance capacitors C ₁₁ and C ₂₁ is 150Ω/7.5Ω = 20, and the combined impedance of these parallel resonant circuits is 150Ω×20=3000Ω. Therefore, the current flowing through each of these drive coils is approximately 50V/150Ω, similar to the current in the conventional example shown in Figure 1.
In addition to the large current of 〓300mA, the current flowing through the changeover switches S ₁₃ and S ₂₃ becomes a small current of approximately 50V/3000Ω/〓15mA. In this way, the resonance capacitors C ₁₁ and C ₂₁ corresponding to the compensation capacitors C ₁₀ and C ₂₀ are directly connected in parallel to the respective drive coils of the erasing heads 5 and 9 to form a parallel resonant circuit. Since the combined impedance of the resonant circuit is a large value of 3000Ω, even if this parallel resonant circuit is connected to the output side of the high-frequency oscillator 1, it will hardly affect the high-frequency oscillator 1. It is not necessary to provide the switching switches S ₁₄ and S ₂₄ as in the conventional example shown, and these switching switches S ₁₄ and S ₂₄ can be omitted.

In this way, in the device shown in FIG. 2, the current flowing through the changeover switches S ₁₃ and S ₂₃ can be reduced, so that the current flowing through the changeover switches S ₁₃ and S ₂₃ can be reduced.
can be converted into electronic circuits. In addition, the withstand voltage and current of the changeover switches S ₁ A, S ₁ B, S ₂ A, and S ₂₂ are smaller than those of the changeover switches S ₁₃ and S ₂₃ , so these changeover switches S ₁₁ and S ₁₂ ,
It is even easier to convert S ₂₁ and S ₂₂ into electronic circuits. Therefore, an electronic circuit-based changeover switch
S ₁₁ , S ₁₂ , S ₁₃ are linked and switched by a CH1 common changeover switch when recording and reproducing CH1 signals, and electronic circuit changeover switches S ₂₁ , S ₂₂ , S ₂₃ is linked to the CH2 signal when recording and playing back the CH2 signal.
The switching can be performed by a common switching switch. Such CH1 common changeover switch and CH2 common changeover switch are much more effective than the triple interlocking switch of changeover switches S ₁₁ , S ₁₂ , S ₁₃ and the triple interlocking switch of changeover switches S ₂₁ , S ₂₂ , S _23, respectively. Can be operated easily.

FIG. 3 is a circuit diagram showing a main part of an embodiment of the present invention in which the changeover switch of the CH1 erase head of this basic configuration is computerized.

In the figure, C ₁₄ is a DC blocking capacitor, T ₁
and D ₁ are npn transistors and diodes connected antiparallel to each other. This inverse parallel body of npn transistor T ₁ and diode D ₁ is connected to the DC blocking capacitor C ₁₄ between the CH1 erase head 5 connected to the high frequency oscillator 1 shown by the dashed line and the ground.
connected via. _S15 is a CH1 common changeover switch, and this CH1 common changeover switch _S15 is connected to the base of the npn transistor _T1 via a base resistor _R13 . E ₁ is contact r (for recording) of CH1 common changeover switch S ₁₅ and npn transistor T ₁
This is a DC power supply inserted between the emitter of the
When this DC power source E ₁ is applied to the base of the npn transistor T ₁ through the contact r of the CH1 common changeover switch S ₁₅ and through the base resistor R ₁₃ , the npn transistor T ₁ is turned on, and the drive coil of the erase head 5 is turned on. is connected to the output side of the high frequency oscillator 1.
By connecting electronic circuitized changeover switches S ₁₁ and S 12 to the illustrated point of the common changeover switch S ₁₅ , these changeover switches S ₁₁ and _{S 12 can} be operated. Similarly, the CH2 erase head changeover switch can be implemented as an electronic circuit.

In this embodiment, a magnetic recording and reproducing apparatus that records and reproduces two types of CH signals is explained as an example, but the present invention is applicable to recording and reproducing only one type of CH signal, an audio signal or a video signal, or an audio signal, The invention can also be applied to magnetic recording and reproducing devices that record and reproduce two or more types of CH signals, such as VTRs that have video signals and control signals.

As explained above, in the magnetic recording/reproducing apparatus of the present invention, a resonant capacitor is directly connected in parallel to the drive coil of the erasing head to form a parallel resonant circuit, and the resonant frequency of this parallel resonant circuit is set to the oscillation frequency of the high-frequency oscillator. A DC cutoff capacitor and an anti-parallel connection of a switch transistor and a diode are inserted in series between the parallel resonant circuit and the ground to match the frequency, which not only simplifies the switching operation but also makes it easier to erase the erase head. It is possible to efficiently transmit high frequency components while blocking direct current from flowing to the electronic switch, and to ensure reliable operation when the electronic switch is turned off.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an example of a conventional magnetic recording and reproducing device, FIG. 2 is a diagram showing the basic configuration of the magnetic recording and reproducing device of the present invention, and FIG. 3 is a diagram showing the switching of the CH1 erase head in the above basic configuration. 1 is a diagram showing the main part of an embodiment of the present invention in which a switch is computerized. In the figure, 1 is a high frequency oscillator, 4 and 8 are magnetic heads for recording and reproducing signals, and 5 and 9 are magnetic heads.
are magnetic heads for signal erasure, C ₁₁ and C ₂₁ respectively.
are each a resonance capacitor, _S13 and _S23 are each a changeover switch, _C14 is a DC cutoff capacitor, _T1 is a switching transistor, and _D1 is a diode. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] 1. A signal erasing magnetic head having a drive coil and erasing signals recorded on a magnetic tape, and a high frequency oscillator inserted between the magnetic head and ground and supplying a high frequency voltage to the magnetic head. and a parallel resonant circuit consisting of the drive coil and a capacitor connected in parallel thereto, the resonant frequency of which is the same as the oscillation frequency of the high frequency oscillator, and a parallel resonant circuit connected in series with a DC interrupting capacitor between the parallel resonant circuit and ground. 1. A magnetic recording and reproducing device comprising an anti-parallel connection body inserted into a switching transistor and a diode connected in anti-parallel to the switching transistor.