JPH0118487B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a video tape recorder (hereinafter referred to as VTR).
It is called. ) relates to a magnetic tape erasing device.

In a VTR, two sets of erasing heads are used so that the video and audio signals recorded on the magnetic tape can be independently erased. this is,
Using magnetic tape that has already been recorded,
This is useful for so-called audio dubbing work in which only the audio signal is replaced without erasing the video signal. In other words, a helical scan type VTR uses a full-width erasing head that can erase the entire width of the tape, including the video signal track, and an audio erasing head that can erase only the audio signal track. The circuit is formed so that the erasing current flows through both the erasing head and the audio erasing head, but during audio dubbing, the erasing current is configured to flow only through the audio erasing head to prevent the video signal portion from being erased. This is something that is taken into consideration.

Conventionally, to achieve the above configuration, a changeover switch such as a relay and a dummy coil were used to avoid load fluctuations on the erase oscillation circuit, resulting in high costs and the need for a small, lightweight set.
There was a problem with power saving. One such conventional example is shown in FIG. In FIG. 1, 1 is an erase oscillator circuit, 2 and 3 are a full-width erase head and an audio erase head, respectively, which are connected in series. 4 is a dummy coil, the inductance of which is selected to be approximately the same as the inductance of the full-width erase head 2. Reference numeral 5 denotes an audio dubbing switch, and in this example, when current flows through the relay coil 6, the contact switches from the A side to the B side. A transistor switch 7 has an emitter directly grounded, a collector connected to the power supply _Vcc through the relay coil 6, and a base connected to the audio dubbing command application terminal 8 through a resistor 22. A positive voltage is applied to the audio dubbing command application terminal 8 only during dubbing.

Now, in the normal recording mode, the contacts of the audio dubbing switch 5 are closed on the A side as shown in FIG. That is, in this case, both the full-width erase head 2 and the audio erase head 3 are enabled for erase operation.

On the other hand, when a positive voltage is applied to the audio dubbing command application terminal 8, the transistor switch 7 becomes conductive, so current flows through the relay coil 6 and the contact of the audio dubbing switch 5 closes to the B side. . In this case, the signal from the erasing oscillation circuit 1 flows through the dummy coil 4 to the audio erasing head 3. Therefore, since no erase current flows through the full-width erase head 2, the video signal is not erased during audio dubbing. Although not shown, the audio erasing head 3 is directly connected to the output terminal of the erasing oscillation circuit 1, and either the full width erasing head 2 or the dummy coil 4 is selectively connected to the audio erasing head 2 by using a switch. The same applies even if it is connected in parallel.

The present invention is configured to remove the relays and dummy coils used in the conventional example as described above, and the following is a second example of the present invention.
This will be explained with reference to the drawings in the figures.

FIG. 2 is a circuit diagram showing the main parts of an embodiment of the magnetic tape erasing device according to the present invention, and parts similar to those shown in FIG. 1 are given the same reference numerals.

In FIG. 2, reference numeral 1 denotes an erase oscillation circuit, to whose output terminal an audio erase head 3, which is a first erase head, is directly connected. Reference numeral 2 denotes a full-width erase head, which is a second erase head, to which the output signal of the erase oscillation circuit 1 is supplied through a buffer amplifier 9 and a capacitor 10. 11 is a transistor switch, and 12 is an audio dubbing command application terminal. Note that 20 is an oscillation transformer included in the erase oscillation circuit 1, and a tap 2 is provided on its secondary side.
1.

A feature of the magnetic tape erasing device according to the present invention is that the audio erasing head that needs to perform erasing operation during audio dubbing (in the case of two audio channels, one channel is not erased as necessary) is always directly connected to the erasing oscillation circuit. In addition, an erase head (full-width erase head 2 in Fig. 2, which does not allow audio operation during audio dubbing, but in the case of audio 2 channels,
If necessary, an audio cancellation head for one channel is also included. ) is connected to the erase oscillator circuit via a buffer amplifier, and the erase signal passage consisting of the buffer amplifier is opened and closed by an electronic switch, and the erase mode during audio dubbing is set by a purely electronic switch. The point is that it is controlled. In the embodiment of FIG. 2, the buffer amplifier 9 is shown as an emitter follower type amplifier using complementary transistors, the transistor 13 being an NPN transistor, and the transistor 14 being a PNP transistor. The collector of transistor 13 is directly connected to the power supply V _cc
The emitter is connected to ground through a series circuit of capacitor 10 and full-width erase head 2, and is also connected to the emitter of transistor 14. Further, the base of the transistor 13 is connected to the power supply V _cc through a resistor 15 and grounded through a series circuit of diodes 16 and 17 and a resistor 18, and further connected to the collector of the transistor switch 11 through a resistor 24. There is.

On the other hand, the collector of the transistor 14 is directly grounded, and the base thereof is connected to the cathode side of the diode 17. Here, a series circuit consisting of resistor 15, diodes 16 and 17, and resistor 18 includes transistor 13 and transistor 14.
It functions as a bias circuit to provide an appropriate operating bias to the circuit. The erase signal of the erase oscillation circuit 1 is applied from the tap 21 to the cathode side of the diode 16 via the capacitor 19.
The emitter of the transistor switch 11 is directly grounded, and its base is connected to the audio dubbing command application terminal 12 through a resistor 23. now,
It is assumed that the potential of the audio dubbing command application terminal 12 is a ground potential in the normal recording mode and is a positive potential in the audio dubbing mode. Therefore, the transistor switch 11 is turned off in the recording mode and turned on in the audio dubbing mode. Therefore, in the audio dubbing mode, from resistor 15 to resistor 24,
Since current flows to the transistor switch 11, by appropriately selecting the value of the resistor 24, the base potential of the transistor 13 can be lowered to a state where the transistor 13 is cut off.

In the audio dubbing mode as described above, the transistor 13 is turned off, and therefore the transistor 14 is also turned off, so the erase oscillation circuit 1
The erase signal from the full-width erase head 2 is blocked by the buffer amplifier 9, and no erase current flows through the full-width erase head 2. In the normal recording mode, the transistor switch 11 has no effect on the buffer amplifier 9, so the erase signal is supplied from the tap 21 of the erase oscillator circuit 1 through the buffer amplifier 9 to the full width erase head 2. Note that the buffer amplifier 9 may be of any type, and may have a gain of 1 or more than 1. Furthermore, the method of supplying the signal from the cancellation oscillation circuit to the buffer amplifier is not limited to this embodiment, and the signal may be supplied from both ends of the audio cancellation head 3 via a suitable attenuator, or It may be pulled out from inside. Further, a capacitor 10 was used to supply a signal from the buffer amplifier 9 to the full-width erase head 2. In this case, it is convenient to cause series resonance between the capacitor 10 and the inductance of the full width erase head 2, but a transformer may be used instead of the capacitor 10. Furthermore, in this embodiment, the transmission of the erase signal is controlled by controlling the transistors forming the buffer amplifier 9, but the attenuator is formed by the transistor switch 11 without changing the operating state of the buffer amplifier. It is clear that the same effect can be obtained by attenuating the erasure signal.

As described above, according to the present invention, it is possible to effectively control the erasing operation during audio dubbing even with a purely electrical switch, and it is possible to effectively control the erasing operation during audio dubbing using a purely electrical switch. Since it also eliminates the need for a coil, it greatly contributes to the use of ICs in devices, making them smaller and lighter, and reducing power consumption.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of the main parts of an example of a magnetic tape erasing device used in a conventional VTR.
The figure is a circuit configuration diagram of a main part showing an embodiment of the present invention. 1...Erase oscillation circuit, 2...Full-width erase head,
3...Audio cancellation head, 9...Buffer amplifier, 11
...transistor switch.

Claims (1)

[Claims] 1. A magnetic tape erasing device for a video tape recorder having an audio dubbing function, in which the first erasing head that requires an erasing operation in the audio dubbing mode is connected to the output terminal of an erasing oscillation circuit, and the erasing operation is performed in the audio dubbing mode. The second one that eliminates the need for
The erase head is connected to the oscillation circuit via a buffer amplifier, and controls the supply of erase current to the second erase head on and off by controlling the buffer amplifier to be in an active state or in an inactive state. What is claimed is: 1. A magnetic tape erasing device characterized in that the device is configured to perform the following operations.