JP2921160B2 - Magnetic recording / reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[Table of Contents] The present invention will be described in the following order. Industrial Application Conventional Technology (FIGS. 8 to 11) Problems to be Solved by the Invention (FIGS. 8 to 11) Means for Solving the Problems (FIG. 1) Function (FIG. 1) Example (1) First Embodiment (FIGS. 1 to 3) (2) Second Embodiment (FIGS. 4 to 7) (3) Other Embodiments Advantages of the Invention

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording / reproducing apparatus, and more particularly, to a magnetic recording / reproducing apparatus which transmits and receives a recording signal and a reproducing signal to and from a rotary head through a rotary transformer.

[0003]

2. Description of the Related Art Conventionally, in a magnetic recording / reproducing apparatus, a recording tape is formed by helically scanning a magnetic tape running while being wound obliquely to a drum with a rotating head mounted on the drum. There is a type in which a predetermined information signal is recorded on a recording track and reproduced.

In such a magnetic recording / reproducing apparatus,
Various tracking methods are used in order for the rotating head to scan the recording track correctly.However, in a magnetic recording / reproducing apparatus for recording and reproducing a digital signal, rough tracking with a mechanical accuracy is performed roughly, and the reproduced signal is converted into a digital signal. A device using a so-called non-tracking method of processing and obtaining a reproduced digital signal has been proposed (Japanese Patent Application No. 2-169078).

[0005] In the case of such a non-tracking type magnetic recording / reproducing apparatus, as shown in FIG. 8, the rotating head 1 has double azimuths having different azimuth angles from each other for recording and recording. The second magnetic heads AR and BRP are arranged side by side, and for example, the first magnetic heads AR and BRP are arranged.
The third magnetic head AP for reproduction, which has a single azimuth having the same azimuth angle as the magnetic head AR, is arranged 180 ° opposite to the second magnetic head BRP for recording and reproduction. is there.

[0006] The magnetic tape 3 is mounted on the drum on which the rotary head 1 is mounted by guide rollers 2A and 2B.
At a winding angle of, for example, 90 °, and the first or second magnetic head AR or B is provided for each rotation of the rotating head 1 during recording.
As shown in FIG. 9, the recording tracks TA1 having different azimuth angles are recorded on the magnetic tape 3 by so-called azimuth solid recording by sequentially and alternately recording RPs.
TB1, TA2, TB2,... Are formed.

That is, at the time of recording, the first and second magnetic heads AR and BRP are, as shown by the logical "H" level in FIGS.
During the first 90 ° period of ヘ リ, the helical scan is performed while contacting the magnetic tape 3, whereby recording data is sequentially and alternately supplied to the first or second magnetic head AR or BRP for each rotation. The recording format described above with reference to FIG.

At this time, the third magnetic head AP is shown in FIG.
As shown by the logic "H" level in FIG.
During the 90 ° period 180 ° behind the first and second magnetic heads AR and BRP during one 360 ° rotation, the magnetic tape 3 comes into contact with the magnetic tape 3 to perform helical scanning.

At the time of reproducing, the third
And by reproducing with the second magnetic heads AP and BRP, the recording tracks TA1, TB1,
TA2, TB2,... Are reproduced.

That is, at the time of reproduction, the first, second and third magnetic heads AR, BRP and AP are shown in FIGS.
As shown by the logical "H" level, the helical scan is performed by contacting the magnetic tape 3 in the same manner as during recording, and the second and third scans are performed.
By sequentially taking in reproduction signals obtained from the magnetic heads BRP and AP, the recording track T of the magnetic tape 3 is read.
Play A and TB.

[0011]

In the magnetic recording / reproducing apparatus having the above construction, a recording signal generated in the signal processing section is transmitted to the rotary head 1 through a rotary transformer, or a reproduced signal fetched by the rotary head 1 is converted into a signal. The data is supplied to the processing unit.

However, if a small-sized rotary transformer is used and the drum itself is reduced in size and weight, the channel separation between adjacent windings becomes about 13 [dB]. For this reason, for example, the secondary side winding composed of the fixed primary side and the rotating head 1 side is sequentially connected to the first, second and third magnetic heads AR, BRP and AP.
When the channels are arranged so as to correspond to each of the above channels, there is a problem that the SN deteriorates during recording and reproduction due to crosstalk generated between adjacent channels.

That is, at the time of recording, as shown in FIG. 10, first and second magnetic heads AR and BRP (FIG. 10)
(A) and (B)) one of the paused magnetic heads A
Noise from R, BRP is crosstalk CT0, CT1
As a result, there is a problem that the recording signal is superimposed and recorded on the recording signal of the other magnetic head BRP or AR channel, and the SN of the recording signal eventually deteriorates.

At this time, the second and third magnetic heads BRP
And AP (FIGS. 10 (B) and 10 (C)), crosstalk CT2 and CT3 occur with each other, but have no effect because they are not in contact with the magnetic tape 3 or are not in use.

On the other hand, at the time of reproduction, as shown in FIG. 11, noise generated when the unused first magnetic head AR (FIG. 11A) comes into contact with the magnetic tape 3 causes crosstalk CT4.
As a result, the signal is superimposed on the reproduction signal of the channel of the second magnetic head BRP (FIG. 11B), and the SN of the reproduction signal is eventually deteriorated.

At this time, the second and third magnetic heads BRP
And AP (FIGS. 11B and 11C), crosstalk CT5 and CT6 occur with each other, but this has no effect because the other magnetic heads BRP and AP are not in contact with the magnetic tape 3.

The present invention has been made in view of the above points, and it is an object of the present invention to propose a magnetic recording / reproducing apparatus which can prevent the deterioration of the SN of a recording and reproducing signal due to the influence of crosstalk in a rotary transformer. Things.

In order to solve such a problem, in the present invention, the magnetic tape 3 is provided on a drum around which the magnetic tape 3 is wound.
A first magnetic head AR for recording and a second magnetic head BRP for recording and reproduction, which are adjacent to each other and have different azimuth angles, and a predetermined distance from and apart from the first and second magnetic heads AR and BRP. A first magnetic head AR and a third magnetic head AP having the same azimuth angle are provided, and recording tracks TA1, TB1, TA2, TB2,... Are recorded on the magnetic tape 3 by the first and second magnetic heads AR and BRP. The rotating head 1 that is formed and scans the recording tracks TA1, TB1, TA2, TB2,... With the second and third magnetic heads BRP and AP, and the channel corresponding to the first magnetic head AR is the outer circumferential winding 12A. , 13A, a channel corresponding to the second magnetic head BRP is allocated to the inner circumferential windings 12C, 13C, and a channel corresponding to the third magnetic head AP is allocated. Peripheral winding 12A, 13A and the inner peripheral side winding 12C, the intermediate winding 12B between 13C, a rotary transformer 11 assigned to 13B, the recording signal AR during recording
EC and BREC are sequentially and alternately supplied to the first or second magnetic heads AR and BRP via the rotary transformer 11, and the second or third magnetic heads BRP and ARP are reproduced during reproduction.
Recording / reproducing means 14 to sequentially and alternately receive reproduction signals APB and BPB obtained from P through the rotary transformer 11
16 and supply of recording signals AREC and BREC to recording / reproducing means 14-16 based on head switching signal SWP or reproduction signals APB and BPB from recording / reproducing means 14-16.
And the recording control signal SR.
Recording / reproducing means 1 based on EC and reproduction control signal SPB
Control means for controlling operations 4 to 16; a head switching signal SWP; a recording control signal SREC; and a reproduction control signal SPB.
Based on the first or second magnetic head AR at the time of recording,
BRP sequentially and alternately places a magnetic track TA on the magnetic tape 3.
1, TB1, TA2, TB2,.
The channel corresponding to the magnetic head AP is shorted, and the second magnetic head BRP is applied to the magnetic tape 3 during reproduction.
.. When scanning the recording tracks TA1, TB1, TA2, TB2... Of the third magnetic head AP.
0 is provided. In the present invention, the switching means 30 comprises a first logic circuit 32 for ANDing the signal obtained by inverting the head switching signal SWP and the reproduction control signal SPB.
And the operation result of the first logic circuit 32 and the recording control signal SR
There is provided a second logic circuit 33 for taking a NOR with the EC, and a switching circuit Q1 for shorting a channel corresponding to the third magnetic head AP based on an output signal from the second logic circuit 33. .

[0019]

A plurality of magnetic heads AR and BR of the rotary head 1 are provided.
P, AP, at least during a period in which it is not used for recording and / or reproduction, by causing the channel corresponding to the unused magnetic head AP to be shorted,
Crosstalk caused by the magnetic head AP when not in use can be prevented.

[0020]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.

(1) First Embodiment In FIG. 1, in which parts corresponding to those in FIG. 8 are assigned the same reference numerals, reference numeral 10 denotes a magnetic recording / reproducing apparatus as a whole, and an outer peripheral side of a rotary head 11 of a rotary transformer 11. Sequentially to the first, second and third windings 12A, 12B and 12C,
First, third and second magnetic heads AR, AP and BRP
Is connected to the corresponding channel.

Correspondingly, at the time of recording, the input RF signal RFIN for recording is input to the A head recording buffer 15A through the input end of the recording switching section 14A of the head switching circuit 14 and the A head output end a. The output of the first winding 13 from the outer periphery of the rotary transformer 11 on the main body side together with the driving power supply + V is output as an A head recording signal AREC.
A (that is, the outermost periphery).

In addition to this, an input RF signal RFI for recording
N is input to a B head recording buffer 15B through an input terminal of a recording switching section 14A of the head switching circuit 14 and a B head output terminal b, and its output is a B head recording signal B.
The REC is supplied from the outer periphery of the rotary transformer 11 to the third winding 13C (that is, the innermost periphery) together with the driving power supply + V.

At the time of reproduction, the A-head reproduction signal APB and the B-head reproduction signal BPB sent from the second and third windings 13B and 13C from the outer periphery of the rotary transformer 11 on the main body side are converted to the A-head reproduction buffer 16A. The head input terminal a and the head input terminal b of the reproduction switching section 14B of the head switching circuit 14 are input to the A head input terminal a and the B head input terminal b of the head switching circuit 14 through the B head reproduction buffer 16B, and are selectively output at a predetermined timing and output as the output RF signal RFOUT. You.

The A head recording buffer 15A and the B head recording buffer 15B are turned on at a timing corresponding to recording by a recording control signal SREC.
The head reproducing buffer 16A and the B head reproducing buffer 16B are turned on at a timing corresponding to the reproduction by a reproduction control signal SPB.
The recording switching section 14A and the reproduction switching section 14B are switched by a head switching signal SWP.

In the above configuration, the magnetic recording / reproducing apparatus 1
At the time of recording 0, as shown in FIG. 2, a first magnetic head AR for recording and a second magnetic head BRP for recording / reproducing.
2A and 2C, noise from one of the magnetic heads AR and BRP at rest is the crosstalk CT.
Unused third magnetic head AP adjacent as 10
(FIG. 2B) is superimposed on the channel.

The noise generated when the unused third magnetic head AP comes into contact with the magnetic tape 3 is generated by the first and second adjacent crosstalks CT11 and CT12 on the outer circumferential side and the inner circumferential side, respectively. Magnetic head AR and BRP
During the rest of the channel.

Thus, during recording, the rotary transformer 11
Adjacent windings 12A and 13A, 12B and 13B,
Crosstalk CT10 generated between 12C and 13C,
Noise due to the effects of CT11 and CT12 is reduced to the recording signal A.
The timing can be shifted to a timing irrelevant to REC and BREC. Thus, the deterioration of the SN of the recording signals AREC and BREC can be prevented.

On the other hand, during reproduction of the magnetic recording / reproducing apparatus 10,
As shown in FIG. 3, the noise from one of the paused magnetic heads AP and BRP of the third and second magnetic heads AP and BRP for reproduction (FIGS. 3B and 3C) is as follows. The crosstalks CT13 and CT14 are superimposed on adjacent channels of the magnetic heads AP, BRP, and AR at rest and not in use.

The noise generated when the unused first magnetic head AR (FIG. 3A) comes into contact with the magnetic tape 3 is the third magnetic head adjacent to the inner peripheral side as the crosstalk CT15. This is superimposed during the pause of the channel of the head AP.

As a result, at the time of reproduction, the rotary transformer 11
Adjacent windings 12A and 13A, 12B and 13B,
Crosstalk CT13 generated between 12C and 13C,
Noise due to the effects of CT14 and CT15 is reproduced signal A
The timing can be shifted to a timing irrelevant to PB and BPB, and thus the deterioration of the SN of the reproduction signals APB and BPB can be prevented.

In the case of this embodiment, the reproduction signals APB and B having a low level of about several μV are compared with the recording signals AREC and BREC having a high level of about several V.
The channels for handling the PB are connected to the second and third channels on the inner peripheral side of the rotary transformer 11 which are relatively resistant to noise from an external magnetic field.
The arrangement of the windings 12B and 13B, 12C and 13C makes it possible to further prevent the deterioration of the SN of the reproduction signals APB and BPB.

According to the above configuration, the rotary transformer 1
The first, second, and third windings 12A and 13A, 12B and 13B, 12C and 13C are sequentially applied to the first, second, and third magnetic coils for recording, reproduction, and recording / reproduction from the outer peripheral side of the first magnetic field. By allocating channels according to the heads AR, AP and BRP, it is possible to effectively eliminate the influence of noise due to crosstalk from adjacent channels during recording and reproduction, and thus to connect the windings of the rotary transformer 11. With a simple configuration that only optimizes the recording signal A
It is possible to realize the magnetic recording / reproducing apparatus 10 that can prevent deterioration of the REC and BREC and the SN of the reproduction signals APB and BPB.

Further, according to the above configuration, the reproduction system channel is assigned to the inner peripheral side of the rotary transformer 11 which is more resistant to noise from the external magnetic field than the outer peripheral side of the rotary transformer 11. It is possible to realize the magnetic recording / reproducing apparatus 10 that can further prevent the deterioration of the SN of the reproduction signals APB and BPB.

As described above, even if the rotary transformer 11 is downsized, the influence of noise due to crosstalk can be effectively removed, so that the magnetic recording / reproducing can be made smaller, lighter and more reliable as compared with the conventional case. The device 10 can be realized.

(2) Second Embodiment In FIG. 4, in which parts corresponding to those in FIG. 1 are assigned the same reference numerals, reference numeral 20 denotes a magnetic recording / reproducing apparatus as a whole. The channel corresponding to the unused third magnetic head AP is short-circuited at a predetermined timing during recording and reproduction, thereby effectively removing the influence of noise due to crosstalk from the adjacent channels. It has been made like that.

That is, in the magnetic recording / reproducing apparatus 20,
The collector of the short-circuit transistor Q1 is connected between the second winding 13B and the A-head reproducing buffer 16A from the fixed outer periphery of the primary side of the rotary transformer 11 to the second winding 13B. The emitter of the transistor Q1 is connected to the power supply + V, and the base is connected to the collectors of the switching transistors Q2 and Q3 via the resistor R1.

The emitter of the transistor Q2 is grounded, a recording control signal SREC is inputted to the base through a resistor R2, a head switching signal SWP is inputted to an emitter of the transistor Q3, and the base is reproduced through a resistor R3. The control signal SPB is input.

In the above configuration, the magnetic recording / reproducing device 2
0, as shown in FIG. 5, the recording control signal SREC
(FIG. 5 (A)) shows the first and second recording / reproducing media.
In response to the timing at which the magnetic heads AR and BRP contact the magnetic tape 3, the A and BRP rise to a logical "H" level so that the A head recording buffer 15A and the B head recording buffer 15B are turned on.

At this time, the head switching signal SWP is
As shown in (B), the frequency has a logic "H" level and a logic "L" level alternately at half the frequency of the rotating head 1,
As a result, the first or second rotation is alternately performed every rotation of the rotation head 1.
Of the magnetic head AR or BRP is selected.

Here, the second transistor Q2 is shown in FIG.
As shown in FIG. 5C, the recording control signal SREC is turned on during a period having the logic "H" level, and in response to this, the first transistor Q1 is turned on as shown in FIG. 5D. .

Thus, the first and second magnetic heads AR
5B, the recording signals AREC and BREC are recorded on the magnetic tape 3 and the recording tracks TA1, TB1, TA2, TB2,... Are sequentially formed as shown in FIG. The channel corresponding to the head AP is shot.

Thus, the magnetic recording / reproducing apparatus 20
Then, the channel corresponding to the third magnetic head AP which is not used at the time of recording is short-circuited, so that the first and second magnetic heads AR and BRP cause crosstalk from the channel according to the BRP. It is designed to effectively remove the effects of noise.

On the other hand, at the time of reproduction by the magnetic recording / reproducing apparatus 20, FIG.
As shown in FIG. 6, the reproduction control signal SPB (FIG. 6A) is used for reproducing the A head according to the timing at which the third and second magnetic heads AP and BRP for reproduction and recording and reproduction come into contact with the magnetic tape 3. Rises to a logic "H" level so that the buffer 16A for reproduction and the buffer 16B for head reproduction are turned on.

At the same time, the head switching signal SWP is
As shown in FIG. 3B, the signal has a logic "H" level and a logic "L" level alternately at a frequency corresponding to the rotation head 1, and as a result, the third or second rotation is performed every 1/2 rotation of the rotation head 1. Are alternately selected.

Here, the third transistor Q3 corresponds to FIG.
As shown in (C), the reproduction control signal SREC has a logic "H" level and the head switching signal SWP is at a logic "L" level, that is, the second magnetic head BRP is turned on during a period during which the BRP is selected. In response to this, the first transistor Q1 is turned on as shown in FIG.

As a result, the second magnetic head BRP is set as shown in FIG.
As shown in (E), when the reproduction signal BPB is obtained from the recording tracks TB1, TB2,... By abutting on the magnetic tape 3, the channel corresponding to the third magnetic head AP is shot.

Thus, the magnetic recording / reproducing apparatus 20
At the time of reproduction, at the same time as the second magnetic head BRP during reproduction, the effect of noise due to crosstalk from the channel corresponding to the unused first magnetic head AR that comes into contact with the magnetic tape 3 is effectively removed. .

According to the above configuration, the rotary transformer 1
The first, second, and third windings 12A and 13A, 12B and 13B, 12C, and 13C are sequentially applied to the first, second, and third magnets for recording, reproduction, and recording / reproduction from the outer periphery of In addition to allocating the channels of the head AR, AP and BRP, the channel corresponding to the unused third magnetic head AP is short-circuited at a predetermined timing at the time of recording and reproduction. And the effect of noise due to crosstalk from adjacent channels and adjacent channels during playback can be effectively removed,
Thus, the recording signals AREC and BREC and the reproduction signal AP
The magnetic recording / reproducing apparatus 20 that can prevent the deterioration of the SN of B and BPB can be realized.

As described above, even if the rotary transformer 11 is downsized, the influence of noise due to crosstalk can be effectively removed, so that the magnetic recording / reproducing can be made smaller, lighter and more reliable as compared with the related art. The device 20 can be realized.

(3) Other Embodiments (3-1) In the above-described embodiment, channels corresponding to the magnetic heads AR and BRP for recording and recording / reproducing are provided on the outer and inner peripheral sides of the rotary transformer 11, respectively. The channel corresponding to the magnetic head AP for reproduction, which is disposed 180 ° opposite to the winding, is allocated to the intermediate winding. Alternatively, if external noise does not pose a problem during reproduction, the magnetic head is used. Even if channels corresponding to AR and BRP are assigned to the inner and outer windings of the rotary transformer 11 respectively, the same effect as in the above-described embodiment can be realized.

(3-2) In the above-described second embodiment, the switching transistors Q2 and Q3 are used to control the short-circuit transistor Q1, but instead, for example, a logic circuit as shown in FIG. The short-circuit transistor Q1 may be turned on / off by the short-circuit control circuit 30 having the configuration.

In the short control circuit 30,
The head switching signal SWP is inverted by the not circuit 31 and input to the AND circuit 32 together with the reproduction control signal SPB. The logical operation result is input to the NOR circuit 33 together with the recording control signal SREC, and the logical operation result is shorted through the resistor R1. Is supplied to the base of the transistor Q1.

As a result, at the time of recording, the recording control signal SRE
At the rising timing of C, the transistor Q1 is turned on and short-circuited. At the time of reproduction, the transistor Q1 is turned on and short-circuited at the rising timing of the reproduction control signal SPB and the falling timing of the head switching signal SWP. The operation is the same as that of the embodiment.

(3-3) In the above embodiment, the case where the magnetic head for reproduction is arranged 180 ° opposite to the magnetic head for recording and recording / reproduction has been described. The arrangement of the magnetic heads is not limited to this, and the magnetic heads may be arranged at predetermined angular intervals with respect to the recording and recording magnetic heads.

(3-4) In the above-described second embodiment, the channel corresponding to the reproducing magnetic head AP assigned to the intermediate winding of the rotary transformer is shorted during nonuse and / or at rest. Although the case was described, when a plurality of magnetic heads are mounted on the rotating head,
If the shot is made as needed during periods of non-use and / or periods of non-use, the present invention can be widely applied to magnetic recording / reproducing apparatuses using a so-called multi-channel magnetic head.

[0057]

As described above, according to the present invention, among the plurality of magnetic heads of the rotary head, at least during a period not used for recording and / or reproduction, a channel corresponding to the unused magnetic head is used. , It is possible to realize a magnetic recording / reproducing apparatus capable of preventing crosstalk caused by a magnetic head not in use beforehand.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of a magnetic recording / reproducing apparatus according to the present invention.

FIG. 2 is a schematic diagram for explaining a recording process of the magnetic recording / reproducing apparatus of FIG. 1;

FIG. 3 is a schematic diagram for explaining a reproducing process of the magnetic recording / reproducing apparatus of FIG. 1;

FIG. 4 is a block diagram showing a second embodiment of the magnetic recording / reproducing apparatus according to the present invention.

FIG. 5 is a schematic diagram for explaining a recording process of the magnetic recording / reproducing apparatus of FIG. 4;

FIG. 6 is a schematic diagram for explaining a reproducing process of the magnetic recording / reproducing apparatus of FIG. 4;

FIG. 7 is a block diagram showing another embodiment of the magnetic recording / reproducing apparatus of FIG.

FIG. 8 is a schematic diagram used for describing a configuration of a rotary head.

FIG. 9 is a schematic diagram for explaining a format of a recording track.

FIG. 10 is a schematic diagram for explaining a recording process by a conventional magnetic recording / reproducing apparatus using the rotary head of FIG. 8;

11 is a schematic diagram for explaining a reproducing process by a conventional magnetic recording / reproducing apparatus using the rotary head of FIG. 8;

[Explanation of symbols]

1 ... rotating head, 3 ... magnetic tape, 10, 20 ...
Magnetic recording / reproducing device, 11: rotary transformer, 12
A, 12B, 12C, 13A, 13B, 13C ... winding, 14 ... head switching circuit, 15 ... recording buffer, 16 ... reproduction buffer, AR, BRP, AP ...
Magnetic head.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G11B 5/02

Claims (2)

(57) [Claims] A first magnetic head for recording and a second magnetic head for recording and reproducing, which are provided on a drum around which a magnetic tape is wound and have mutually different azimuth angles, and the first and second magnetic heads; A third magnetic head having a predetermined distance from the second magnetic head and having the same azimuth angle as the first magnetic head; and forming a recording track on the magnetic tape with the first and second magnetic heads. the outer peripheral side winding and rotary head for scanning the recording tracks in the second and third magnetic head, a channel corresponding to the first magnetic head as well as
And a channel corresponding to the second magnetic head.
Allocated to the inner circumference side winding, the the rotary transformer of the third channel corresponding to the magnetic head of the assignment to an intermediate winding between the outer peripheral side winding and the inner peripheral winding, said recording signal during recording The first and second magnetic heads are sequentially and alternately supplied to the first and second magnetic heads via the rotary transformer, and the reproduction signals obtained from the second and third magnetic heads via the rotary transformer are sequentially and alternately reproduced during reproduction. Receiving and reproducing means, and selectively switching supply of the recording signal to the recording / reproducing means or transmission / reception of the reproduction signal from the recording / reproducing means based on the head switching signal, and switching to a recording control signal and a reproduction control signal. Control means for controlling the operation of the recording / reproducing means on the basis of the head switching signal, the recording control signal, and the reproduction control signal; When the first or second magnetic head forms the magnetic track on the magnetic tape alternately and sequentially, the channel corresponding to the third magnetic head is shorted, and the second magnetic head is used during the reproduction. A magnetic recording / reproducing apparatus comprising: switching means for shorting a channel corresponding to the third magnetic head when scanning the recording track of the magnetic tape. 2. The switching means according to claim 1, wherein said switching means comprises: a first logic circuit for inverting said head switching signal and said reproduction control signal; and a calculation result of said first logic circuit and said recording control signal. 2. The semiconductor device according to claim 1, further comprising a second logic circuit for taking a NOR circuit, and a switching circuit for short-circuiting a channel corresponding to the third magnetic head based on an output signal from the second logic circuit. 3. The magnetic recording and reproducing device according to claim 1.