BACKGROUND OF THE INVENTION 
     The present invention relates to a magnetic head for a digital video cassette tape recorder (VCR), and more particularly to a video magnetic head being jointly usable in a VHS-VCR and a digital VCR, by using a double azimuth four head drum for VHS-VCR to record two tracks when the head drum rotates every 180 degrees. 
     Generally, as shown in FIG. 1, the double azimuth four head drum is manufactured such that a first standard play channel head (hereinafter, referred to as SP1) 10 and a second extended play channel head (hereinafter, referred to as EP2) 20 are mounted in a pair on the surface of a head drum base 1, and a first extended play channel head (hereinafter, referred to as EP1) 30 and a second standard play channel head (hereinafter, referred to as SP2) 40 are mounted in a pair on the surface of head drum base 1 opposite the pair 10, 20. Since the heads having the structure as illustrated in FIG. 1 are attached on the surface of the head drum base 1, the positions of the heads are fixed, thus rising a drawback that necessarily requires a use of digital VCR head and a rotary transformer so as to record and reproduce the digital video signals. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a double azimuth four-head drum which may be jointly used for a VHS-VCR and a digital VCR to record and reproduce digital signals. Between the head drum and a first standard play channel head and a first extended play channel head which are mounted thereon, is respectively installed a piezoelement. And, switch is coupled to the piezoelement in order to selectively apply voltage thereto. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings, in which: 
     FIG. 1 is a view of head positions according to a conventional VCR head drum; 
     FIG. 2 is a partially magnified cross sectional view of a head according to the present invention; 
     FIG. 3 is a plan view of head positions while serving for a digital VCR according to the present invention; and 
     FIG. 4 is a plan view of head positions while serving for a VHS-VCR according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 2, the structure of an EP1 head 30 and SP1 head are described in detail, in which a piezoelement 2 is mounted on a head drum base 1. The piezoelement 2 is coupled to a terminal 50 of a switch SW1. The switch SW1 is normally put in a condition that the terminal 50 is switched to a terminal 60 in order to provide the piezoelement 2 with a voltage input while a terminal 70 is disconnected from the terminal 50. 
     Referring to FIG. 3, a reference level 100 of the heads is represented on the surface of the head drum base 1. The SP1 head 10 with a track width of 60 μm is mounted 10 μm above the reference level 100. An EP2 head 20 with a track width of 30 μm is mounted on the reference level 100, the EP2 head 20 making a pair with the SPl head 10. In similar manner, the SP2 head 40 with a track width of 20 μm is mounted on the reference level 100 and the EP1 head 30 is mounted 10 μm above the reference level 100, the EP1 head 30 making another pair with the SP2 head 40. 
     Referring to FIG. 4, the SP1 head 10 of which track width is reduced to 50 μm because the piezoelement attached thereto is lowered by 10 μm below the reference level 100 is mounted on the reference level 100. The EP2 head 20 with a track width of 30 μm is mounted on the reference level 100, so that the SP1 head 10 and the EP2 head 20 are formed in a pair. The SP2 head 40 with a track width of 20 μm is mounted on the reference level 100 and the EP1 head 30 with a track width of 30 μm is mounted on the reference level 100 due to the piezoelement being attached to the head, so that the SP2 head 40 and the EP1 head 30 are formed in a pair. 
     Since a track width of the standard play is 59 μm, 60 μm is used as reference, and since a track width of expended play is 19.3 μm, 30 μm is are commonly used. SP1 head 10 and EP2 head 20 are a pair of heads with different azimuth from each other. Therefore, when the head drum makes one rotation EP2, SP1, EP1, and SP1 tracks are recorded in turn, and when the head drum rotates in a 180 degrees arc, the pair of the SP1 and the EP2 heads 10, 20 and the other pair of the EP1 and the SP2 heads 30, 40 record video signals on their corresponding tracks. Hence the piezoelement 2 does not operate while the head drum serves for a digital VCR, because no voltage is applied to the above piezoelement through the switch SW1. Therefore, when the SP1 and the EP2 heads 10, 20 record video signals on the tape as shown in FIG. 3, the EP2 head 20 records the video signals on the tape with a track width of 30 μm. However, the recorded video signals will be deleted except for the video signals recorded on the tape area where the SP1 head 10 is dislocated by 10 μm relative to the EP2 head 20. 
     The SP1 head 10 records the video signals on the tape with a track width of 60 μm. However, only a track width of 29 μm remains on the tape, the rest being deleted by means of the EP1 head 30 and the SP2 head 40. Also, the SP2 head 40 and EP1 head 30 record the video signals with the track width of about 20 μm and 9 μm on the tape in the same method. 
     However, hence the piezoelement 2 operates while the head drum serves for a VHS-VCR, because voltage is applied to the above piezoelement 2 through the switch SW1. Therefore, the piezoelement 2 is contracted by means of the its characteristics, and thus the SP1 head 10 is lowered by 20 μm and the EP1 head 30 is lowered by 10 μm while the head drum serves for a VHS-VCR, as shown in FIG. 4. When two tracks are recorded on the tape while the head drum rotates in a 180 degree arc in a digital VCR, recording frequency can be reduced by 1/2. For example, when a video signal with 8 bits sampled at 10 MHz is recorded on the video tape, its data processing bit rate will be 80 Mbps. In practice, this data processing bit rate is so high that the recording of video signals will be restricted according to the reactance component of the rotary transformer. However, when two tracks are recorded on the tape with two heads, it becomes 40 Mbps and recording is possible. Furthermore, if the data is compressed by 1/8, only 5 Mbps is required per channel, thus making recording possible with an existing VHS deck. 
     As described in the foregoing, this invention has an advantage of implementing a video magnetic head for a joint use of a VHS-VCR and a digital VCR by using a piezoelement. 
     While the invention has been particularly shown and described with reference to a preferred embodiment, it will be understood by those skilled in the art that modifications in detail may be made without departing from the spirit and scope of the invention.
A double azimuth four-head drum may be made to be jointly usable in a digital VCR and VHS-VCR. A piezoelement is respectively installed between the head drum and the first standard play channel head and the first extended play channel head, and a switch is coupled to the piezoelement to apply a control voltage thereto.