JPH0566642B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a rotating head type magnetic recording/reproducing device having a magnetic head, a head amplifier, a rotary transformer, etc. on a rotating drum, and specifically relates to a configuration of a recording/reproducing switching circuit. It is related to.

[Conventional technology]

Figure 7 shows, for example, Proceedings of the 1985 National Conference of the Television Society 7-5 "Circuit mounting system in rotating cylinder of VTR" (Ochi, Tomita, Hashirama, Matsushita Electric)
This figure shows part of the circuit configuration of the rotating drum in the conventional device of this type shown in FIG.

In the figure, 1 is a magnetic head that records and reproduces signals, 2 is a head amplifier that amplifies the reproduction output of magnetic head 1, and 3 is a device that transmits the output signal of head amplifier 2 to the fixed side, and transmits the recording signal from the fixed side during recording. A rotary transformer transmits the signal to the rotating side; 28 is a recording/reproducing switching circuit that short-circuits or opens the input and output of the head amplifier 2; 27 is a recording/reproducing switching signal input terminal that controls the recording/reproducing switching circuit 28;

Note that one of the winding terminals A of the magnetic head 1 is connected to the input of the head amplifier 2, and the other B is grounded. One of the rotating winding terminals C of the rotary transformer 3 is connected to the output of the head amplifier 2, and the other terminal D is grounded.

Next, the operation will be explained. First, during recording, a recording mode signal is applied to the recording/reproducing switching signal input 27 by a slip ring (not shown) or the like, and the recording/reproducing switching circuit 28 is closed. The recording signal transmitted to the rotating side by the rotary transformer 3 passes through the recording/reproduction switching circuit 28.
A recording current is applied to the magnetic head 1, and a recording current flows therethrough.

Next, during playback, a power supply voltage is applied to the head amplifier 2 by a slip ring or the like, and at the same time a playback mode signal is applied to the recording/playback switching signal input terminal 27, the recording/playback switching circuit 28 is placed in an open state, and the head amplifier 2 is turned on. Input and output are separated. The reproduced output of the magnetic head 1 is amplified by a head amplifier 2, then transmitted to a fixed side by a rotary transformer 3, and video and audio are reproduced in a signal processing circuit (not shown).

[Problem that the invention seeks to solve]

Since the conventional rotating head type magnetic recording/reproducing apparatus is constructed as described above, the recording signal is applied to the magnetic head 1 via the recording/reproducing switching circuit 28 at the time of recording, and is also applied to the input of the head amplifier 2 at the same time. Ru. For this reason, the semiconductor element in the first stage of the head amplifier 2, which is designed to receive a minute signal, may be destroyed by the recording signal having a large amplitude.

Furthermore, the recording signal transmitted to the rotation side by the rotary transformer 3 is applied to the recording/reproducing switching circuit 28 side and at the same time, is also applied to the output of the head amplifier 2, and the head amplifier output is a low impedance circuit such as an emitter follower. Therefore, there were problems such as part of the recording signal flowing in and causing distortion in the recording signal.

This invention was made to solve the above-mentioned problems, and the recording signal is not applied to the input and output of the head amplifier in a state of large amplitude, so that the head amplifier can be protected, and the recording signal is not distorted. It is an object of the present invention to provide a rotating head type magnetic recording/reproducing device which can eliminate the possibility of occurrence of such problems.

[Means for solving problems]

The rotating head type magnetic recording and reproducing apparatus according to the present invention includes a first switch means interposed between the head amplifier input and the ground, a second switch means interposed between the head amplifier output and the ground, and a magnetic head winding. a third switch means inserted between the other of the wire terminals and the ground; a fourth switch means inserted between the other of the rotating side winding terminals of the rotary transformer and the ground; A recording/reproducing switching circuit is constituted by a fifth switch inserted between the other terminal and the other rotating side winding terminal of the rotary transformer.
and closes the fifth switch means and opens the third and fourth switch means, and during regeneration, closes the third and fourth switch means and closes the first, second and fifth switch means. It is set to open up the means.

[Effect]

In this invention, the recording/reproducing switching circuit includes:
Since the first and second switch means are configured to close during recording, the input and output of the head amplifier are grounded, and the recording signal is not applied to the input and output of the head amplifier in a state of large amplitude. Therefore, there is no risk of destroying the semiconductor element in the first stage of the head amplifier, and a recording signal with less distortion can be obtained.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the basic structure of the main parts of a rotating head type magnetic recording and reproducing apparatus according to the present invention.
In the figure, 1 is a magnetic head, 2 is a head amplifier, and 3 is a rotary transformer, which are the same as in the conventional example, so their explanation will be omitted. 4 is a first switch means inserted between the head amplifier input and the ground, 5 is a second switch means inserted between the head amplifier output and the ground, and 6 is a switch between the other winding terminal B of the magnetic head 1 and the ground. the third one inserted in between
A fourth switch means 7 and 8 is inserted between the other winding terminal B of the magnetic head 1 and the rotary transformer 3. It is a fifth switch means inserted between the other side D of the rotating side winding terminals, and these first to fifth switch means 4
.about.8 constitute a recording/reproduction switching circuit 100.

Next, a transistor (hereinafter abbreviated as Tr) is used as each switching element of the first, second and fifth switching means 4, 5 and 8, and each switching element of the third and fourth switching means 6 and 7 is used. A specific example of a circuit using FET as an element will be explained using FIG. 2.

In FIG. 2, 9 is a Tr in the first switch means 4, 10 is a base resistor of Tr9, 11 is a Tr in the second switch means 5, and 12 is a Tr1
1 base resistor. 13 is a FET in the third switching means 6; 14 is a capacitor for cutting off direct current; 15 is a source resistor of the FET 13; 16 is a bypass capacitor for the resistor 15;
7 is a resistor that applies a reverse bias to the FET 13 during recording, and 18 is a gate resistor of the FET 13.

19 is an FET in the fourth switch means 7;
20 is a capacitor for blocking direct current, 21 is
Source resistor of FET19, 22 is a bypass capacitor of resistor 21, 23 is FET19 when recording
A resistor that gives reverse bias to , 24 is FET19
This is the gate resistor.

25 is Tr in the fifth switch means 8, 2
6 is the base resistor of Tr25.

The base resistor 10 of Tr9, the base resistor 12 of Tr11, the base resistor 26 of Tr25,
A resistor 17 that applies a reverse bias to the FET 13 and a resistor 23 that applies a reverse bias to the FET 19 are connected to a recording/reproduction switching signal input terminal 27.

Also, the gate resistor 18 of FET13 and FET19
The gate resistor 24 is connected to the power supply of the head amplifier 2.
Connected to Vcc.

Next, the operation will be explained using FIGS. 2 to 6.

First, during recording, the recording/reproduction switching signal is “H”
level, and power to head amplifier 2 is not supplied. Therefore, Tr9, Tr11, and Tr25 are in a short-circuited state, and FET13 and FET19 are in an open state.
This is equivalent to the situation in FIG. The recording signal transmitted to the rotating side of the rotary transformer 3 is transmitted from the other side D of the rotating side winding terminal of the rotary transformer 3 to
Tr25 → Magnetic head 1 → Tr9 → Ground → Tr1
1→A current flows through the current loop of one C of the rotating side winding terminals of the rotary transformer 3 (I _REC in FIG. 3), and the signal is recorded. At this time, since the input and output of the head amplifier 2 are grounded, a recording signal with a large amplitude is not applied to the input and output of the head amplifier 2.

Here, the third and fourth switch means 6, 7
As each switching element, FET13, 19
Explain the advantages of using For example, as shown in FIG. 4, when commonly used NPN type transistors 60 and 70 are used as switching elements of the third and fourth switching means 6 and 7, the recorded signal shown in FIG. In the negative half cycle of , the collector potential becomes lower than the base potential, which is approximately 0V. As a result, conduction occurs between the base and the collector, and the recording signal becomes a waveform in which a part of the negative half cycle is collapsed as shown in FIG. 5b, making it impossible to perform normal recording. On the other hand, if FETs 13 and 14 are used as the switching elements of the third and fourth switching means 6 and 7, the current flowing from the drain to the gate is very small, so that the recording signal can be recorded well without being distorted. It is.

Next, during reproduction, power is applied to the head amplifier 2, and an "L" level is applied to the recording/reproduction switching signal input terminal 27. Therefore, Tr9,
Tr11 and Tr25 are open, FET13 and FET19 are short-circuited, and the other magnetic head winding terminal B and the other rotating winding terminal D of the rotary transformer 3 are grounded. If this is equivalently shown, the state shown in FIG. 6 will be obtained. The reproduced output of the magnetic head 1 is amplified by a head amplifier 2, then transmitted to a fixed side by a rotary transformer 3, and video and audio are reproduced in a signal processing circuit or the like.

In addition, in the above embodiment, an example was explained in which semiconductor switching elements were used as each switching element of the first to fifth switching means 4 to 8.
A device having a small mechanical contact such as a reed relay may also be used.

Further, as the switching element of the first switching means 4, a device whose stray capacitance when opened is smaller than the stray capacitance when the switching elements of the other switching means 5 to 8 are opened, such as a transistor with a small collector capacitance, may be used. Since this reduces the capacitance component added to the head amplifier input, it is more effective in expanding the reproduced signal transmission band.

〔Effect of the invention〕

As described above, according to the present invention, the first to third recording signals are provided at specific positions so that the recording signal is not applied to the input and output of the head amplifier in a state of large amplitude.
Since the recording/reproduction switching circuit is constructed using the fifth switch means, there is an effect that the risk of destroying the semiconductor element in the first stage of the head amplifier is eliminated, and a recording signal with less distortion can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the basic configuration of the main parts of a rotating head type magnetic recording/reproducing apparatus according to an embodiment of the present invention, FIG. 2 is a circuit diagram showing a specific example of a recording/reproducing switching circuit, and FIG. FIG. 4 is a circuit diagram showing the basic configuration of the recording current loop during recording in the apparatus of the present invention, and FIGS. FIG. 7 is a circuit diagram showing the basic structure of the operating state of the apparatus of the present invention during reproduction, and FIG. 7 is a circuit diagram showing the structure of the main part of a conventional rotary head type magnetic recording and reproducing apparatus. 1 is a magnetic head, 2 is a head amplifier, 3 is a rotary transformer, 4 is a first switch means, 5 is a second switch means, 6 is a third switch means,
7 is a fourth switching means, 8 is a fifth switching means, 9, 11, 25 are semiconductor switching elements,
13 and 19 are FETs, 100 is a recording/reproduction switching circuit, A and B are magnetic head winding terminals, and C and D are rotating side winding terminals of the rotary transformer 3. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Scope of Claims] 1. A magnetic head for recording and reproducing signals, a head amplifier to which one of the winding terminals of the magnetic head is connected to an input and amplifying the reproduction output of the magnetic head, and a head amplifier whose output is connected to a rotating side winding. A rotary transformer that is connected to one of the wire terminals and transmits the output signal from the head amplifier during playback from the rotating side to the fixed side, and transmits the recorded signal during recording from the fixed side to the rotating side is housed in the rotating drum. In a rotary head type magnetic recording/reproducing device in which a recording/reproducing switching circuit inserted between the magnetic head side and a rotary transformer side is controlled by a recording/reproducing switching signal, a recording/reproducing switching circuit is inserted between the head amplifier input and the ground. a first switch means inserted between the magnetic heads, a second switch means inserted between the head amplifier output and the ground, and a third switch means inserted between the other of the magnetic head winding terminals and the ground. , a fourth switch means interposed between the other of the rotation side winding terminals of the rotary transformer and the ground, and a fourth switch means interposed between the other of the magnetic head winding terminals and the other of the rotation side winding terminals of the rotary transformer. The inserted fifth switch means constitutes the recording/reproduction switching circuit,
During recording, the first, second and fifth switch means are closed and the third and fourth switch means are opened, and during reproduction, the third and fourth switch means are closed and the first switch means is closed. A rotary head type magnetic recording/reproducing apparatus characterized in that the second and fifth switch means are set to be open. 2. The rotating head type magnetic recording and reproducing apparatus according to claim 1, wherein each switching element of said first, second, third, fourth and fifth switching means is a semiconductor switching element. 3. The rotating head type magnetic recording and reproducing apparatus according to claim 1 or 2, wherein FETs are used as each switching element of the third and fourth switching means. 4. Claims 1, 2, or 3, wherein the stray capacitance of the switching element of the first switching means when the switching element is open is smaller than the stray capacitance of the switching element of the other switching means when the switching element is open. The rotating head type magnetic recording/reproducing device described above.