JPH082803Y2 - Magnetic head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to an induction type magnetic head which is composed of a magnetic core around which a coil is wound and which magnetically records or reproduces information on a magnetic recording medium.

[Prior Art] Generally, in the above-mentioned induction type magnetic head, when recording is performed, an alternating bias current is applied to the magnetic head together with a recording signal current for recording. The characteristics of the magnetic head change depending on the magnitude of the bias current. For example, as shown in FIG. 3, the sensitivity of the magnetic head does not change much depending on the bias current, but the frequency characteristics and the harmonic distortion rate change as shown. Therefore, various characteristics of the magnetic head can be adjusted by adjusting the magnitude of the bias current.

Conventionally, in order to optimize and equalize various characteristics of the magnetic head, a bias current is applied on the circuit side of the device body in which the bias oscillation circuit is provided after the magnetic head is incorporated into the device in the assembly process of the magnetic recording / reproducing device. I was adjusting.

[Problems to be Solved by the Invention] However, according to such an adjusting method, the magnetic recording / reproducing apparatus incorporating the magnetic head, for example, a tape recorder is made to run the magnetic tape, and the adjustment is performed while monitoring the output level. There is a problem that the adjustment work requires a great deal of labor, the adjustment cannot be performed efficiently, and the assembling cost of the magnetic recording / reproducing apparatus increases.

On the other hand, in recent years, a method in which the bias current is fixed to a fixed value and the adjustment is not performed has become popular in, for example, a VTR audio signal head. However, this method has the advantage that the assembly cost is low because no adjustment is performed, but the characteristics of the magnetic head vary. In addition, when the material lot of the magnetic core is changed in the manufacture of the magnetic head, the magnetic permeability of the magnetic core is changed and the optimum bias current value is largely changed, so that the manufactured lot rarely satisfies the predetermined specifications. Occur.
A system that does not adjust the bias current cannot handle such a case.

Therefore, a structure has been proposed in which a variable resistor 4a for adjusting a bias current is provided on the magnetic head side as shown in FIG.

However, this structure has a problem that the manufacturing cost of the magnetic head is increased by the amount of the variable resistor 4a and the magnetic head is increased in size by the space occupied by the variable resistor 4a.

[Means for Solving Problems] In order to solve such problems, according to the present invention,
In a magnetic head in which a printed circuit board for connecting an external signal line is attached to a connection terminal of the magnetic head, a resistive film having a predetermined pattern is provided on the printed circuit board, and the resistive film is connected to a coil of the magnetic head. A structure is adopted in which the resistance value of the resistor film is changed by cutting out a part of the resistor film to adjust the bias current flowing through the coil during recording.

[Operation] According to such a structure, the bias current of the magnetic head can be adjusted very efficiently and inexpensively in the state of the magnetic head alone before the magnetic head is incorporated in the magnetic recording / reproducing apparatus. Further, the resistor film can be constructed at a very low cost as compared with the variable resistor and does not occupy an occupied space.

Embodiment An embodiment of the present invention will be described in detail below with reference to FIGS. 1 and 2.

FIG. 1 illustrates an embodiment of the present invention, and shows the structure of a printed circuit board 1 attached to the magnetic head according to this embodiment for connecting to the magnetic recording / reproducing apparatus. The surface of the printed circuit board 1 shown in the drawing is the back surface opposite to the surface facing the bottom surface of the main body of the magnetic head.

The printed circuit board 1 is attached to the main body of a magnetic head, which is composed of a magnetic core 2 and a coil 3 wound around the magnetic core 2 shown by broken lines. That is, the printed circuit board 1 has holes 1
a and 1a are formed, and the connection terminals (not shown) to which both ends of the coil 3 are connected in the body of the magnetic head are connected to the holes 1
The printed circuit board 1 is attached to the main body of the magnetic head through the connection terminals by inserting into the a and 1a and soldering.

On the surface of the printed board 1 shown in the drawing, a resistor film 4 shown by hatching is formed and provided as a point relating to the present invention.

In this case, the resistor film 4 is formed in a pattern obtained by adding a rectangular pattern to the horizontal bar at the center of approximately H.
The lower end portions 4a, 4a on both sides of the resistor film 4 are located in the regions of the holes 1a, 1a, and each of the end portions 4a, 4a is soldered to each of the connection terminals of the head described above. As a result, the resistor film 4 is connected to the coil 3 in parallel.

The resistor film 4 is connected to the coil 3 in accordance with the length 1 of the notch 5 by forming a notch 5 in the central portion 4b formed in a rectangular pattern in this case, for example, by laser trimming. The length and thickness of the path of the resistor film 4 between the formed end portions 4a, 4a are changed, and the resistance value therebetween is variably set.

The upper ends of the resistor film 4 on both sides in the drawing are formed as connection terminal portions 4c, 4c.
An external signal line (not shown) for connecting the magnetic head to the magnetic recording / reproducing apparatus is soldered and connected to each of 4c.

An equivalent circuit of the magnetic head of this embodiment provided with the printed circuit board 1 provided with the resistor film 4 is shown in FIG. As shown in FIG. 2, the resistor film 4 as a variable resistance is connected in parallel to the coil 3, so that the bias applied from the magnetic recording / reproducing device (not shown) via the connection terminals 4c, 4c. The current I _B is divided into the bias current I _BH flowing through the coil 3 and the bias current I _BR flowing through the resistor film 4. As described above, the length l of the notch 5 in the resistor film 4
The resistance value of the resistor film 4 is variably set by changing the ratio of the shunt current of the bias current to the coil 3
It is possible to adjust the magnitude of the bias current I _BH flowing in the.

That is, assuming that the resistance value of the resistor film 4 is R and the impedance at the bias frequency of the head element composed of the coil 3 and the magnetic core 2 is Z _fB , the bias current I _BH shunted to the coil 3 is as follows (1) Given by the formula.

Therefore, set the resistance value R to an appropriate value and set the bias current I
By properly adjusting _BH , various characteristics of the magnetic head such as frequency characteristics and harmonic distortion can be adjusted optimally and uniformly.

In this embodiment, as shown in FIG. 2, the signal current I _S applied from the magnetic recording / reproducing apparatus is the signal current I _SH flowing through the coil 3 and the signal flowing through the resistor film 4 as well as the bias current I _B. Although it is shunted to the current I _SR , the shunt flow to the resistor film 4 is extremely smaller than that in the case of the bias current and has almost no effect, so it is not a concern. The reason will be described below.

Here, assuming that the head of this embodiment is a magnetic head for audio, its bias frequency is usually a high frequency of 60 to 80 KHz, and the signal frequency is an audible frequency, so it is a low frequency band of 20 Hz to 20 KHz. Moreover, the signal frequency of the VTR voice signal head is about 50 Hz to 12 KHz. Below, it is assumed that the bias frequency is, for example, 70 KHz, and the typical signal frequency is 12 KHz.

First, the adjustment range of the bias current I _BH flowing in the coil 3 is set to 20.
When the ratio of the resistance value R of the resistor film 4 to the impedance Z _fB at the bias frequency of the head element is calculated as%, from the equation (1), And from this, R = 4Z _fB (2).

Also, the impedance Z at the bias frequency of the head element
_If the ratio of _fB to the impedance Z ₍ 70KHz) at 12KHz of the signal frequency is calculated, the impedance of the head element changes by 6dB / O _ct depending on the frequency and is proportional to the frequency, so Z _fB = Z _(70KHz) = 70 / 12Z _(12KHz) = 5.8Z _(12KHz) … (3). Therefore, when the ratio of the resistance value R of the resistor film 4 and the impedance of the head element at 12 KHz is calculated from the equations (2) and (3), R = 4 × 5.8 × Z _(12KHz) = 23.2Z _(12KHz) ( 4) Here, the signal current I _SH shunted to the coil 3 is obtained by the following equation similar to the equation (1).

Substituting the value of R in equation (4) into equation (5), Becomes That is, it can be seen that 96% of the signal current I _S is shunted to the coil 3 and only 4% to the resistor film 4, which is hardly affected.

According to the magnetic head of the present embodiment as described above, the bias current can be adjusted through the resistor film 4, various characteristics of the magnetic head can be optimized and made uniform, the yield of the head can be improved, and the cost can be reduced. Further, the bias current can be adjusted extremely efficiently and inexpensively in a state where the magnetic head is not installed in the magnetic recording / reproducing apparatus, and the adjustment of the bias current in the assembly process of the magnetic recording / reproducing apparatus is unnecessary, and the magnetic recording / reproducing apparatus is assembled. Cost can be reduced.

Moreover, the resistor film 4 can be constructed at a much lower cost than a general variable resistor, and the cost of the magnetic head can be reduced accordingly. Further, the resistor film 4 does not take up an occupied space as compared with the variable resistor, and the magnetic head can be miniaturized accordingly.

[Effects of the Invention] As is apparent from the above description, according to the present invention, in a magnetic head in which a printed circuit board for connecting an external signal line is attached to a connection terminal of the magnetic head, the printed circuit board has a predetermined size. A resistance film of a pattern is provided, the resistance film is connected to a coil of a magnetic head, and a part of the resistance film is cut out to change the resistance value of the resistance film so that the coil is used for recording. Since the structure that adjusts the bias current to flow is adopted, the bias current can be adjusted very efficiently and inexpensively in the state of the magnetic head alone, and the various characteristics of the magnetic head during recording can be optimized and made uniform. The head yield can be improved and cost can be reduced. Further, since the resistor film can be constructed at a low cost, the cost of the head can be further reduced and the size of the head can be reduced.

[Brief description of drawings]

1 is an explanatory view showing the structure of a printed circuit board attached to a magnetic head according to an embodiment of the present invention, FIG. 2 is a circuit diagram of an equivalent circuit of the head of FIG. 1, FIG. 3 is a magnetic head sensitivity, and FIG.
FIG. 4 is a diagram showing the relationship between the frequency characteristics and the harmonic distortion rate and the bias current, and FIG. 4 is an explanatory diagram showing the structure having a conventional variable resistor. 1 ... Printed circuit board, 2 ... Magnetic core 3 ... Coil, 4 ... Resistor film 5 ... Notch

Claims (1)

[Scope of utility model registration request] 1. A magnetic head in which a printed circuit board for connecting an external signal line is attached to a connection terminal of the magnetic head, wherein the printed circuit board is provided with a resistor film having a predetermined pattern, and the resistor film is used as the magnetic head. And a part of the resistor film is cut out to change the resistance value of the resistor film to adjust the bias current flowing in the coil during recording. head.