A magnetic cartridge such as a pick-up or cutter, whose magnetic circuits are at least partly hollow, the cavities extending mainly in the direction of the magnetic flux. Each magnetic circuit and in particular each polepiece is formed at least partly with a slot communicating with the cavity and extending substantially in the same direction. This reduces eddy-current losses in the magnetic circuit, thereby improving the treble reproduction of the pick-up.

BACKGROUND OF THE INVENTION 
The invention relates to a pick-up and/or cutter cartridge for scanning 
and/or cutting information in a track of a disk-shaped record carrier, 
comprising a stylus holder which carries a stylus at one end and is 
attached to an omnidirectionally pivotal movable element at its other end, 
and two magnetic circuits, one for each of two mutually perpendicular 
directions of oscillation, which magnetic circuits each comprise at least 
one pole-piece, each of which co-operate with the pivotal element. 
Such a pick-up is known from British Pat. No. 1,505,884. The known pick-up 
has the disadvantage that its output signal suffers some loss of 
high-frequency signal components. 
SUMMARY OF THE INVENTION 
It is an object of the invention to provide a magnetic cartridge (as used 
herein, the term magnetic cartridge will be understood to refer both to 
pick-ups and cutters) which mitigates this loss. To this end the 
cartridge, according to the invention, is characterized in that the 
magnetic circuit contains one or more cavities which extend substantially 
in the direction of the magnetic flux or lines of force and the magnetic 
circuit has at least one slot which extends substantially in the direction 
of the magnetic lines of force. 
The invention is based on the recognition that the loss of high-frequency 
signal components in the output signal is mainly caused by eddy-current 
losses in the magnetic circuit of the cartridge, the magnitude of the 
eddy-current losses being proportional to the square of the frequency. By 
applying the invention to the magnetic circuit and, in particular, to a 
polepiece, eddy currents, which are caused by variations of the magnetic 
field in the magnetic circuit and which mainly propagate in the part of 
the magnetic circuit lying close to the surface in a direction 
perpendicular to the direction of the magnetic lines of force, are 
reduced. 
Another embodiment of the cartridge in accordance with the invention is 
characterized in that the slot (slots) extend (extends) into the cavity. 
This step leads to a further reduction of eddy currents and the consequent 
reduction of the loss of high-frequency signal components. Suitably, the 
slot (slots) is (are) made to coincide with the cavity, because this 
simplifies manufacture and is therefore cheaper. 
A further embodiment of the cartridge in accordance with the invention is 
characterized in that the polepiece is made of a sheet material, the 
polepiece being obtained by mechanical deformation. This step has the 
advantage that the material costs for this embodiment are very low. Thus 
the polepiece may be stamped out of a flat sheet of a thin material and be 
mechanically deformed in such a way that the desired exterior shape of the 
polepiece is obtained. By the use of a sheet material a hollow polepiece 
is obtained which is formed with at least one slot which extends up to the 
cavity, so that a very high resistance to eddy currents is obtained.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIGS. 1a and 1b show a pick-up and/or cutter in accordance with the 
invention, FIG. 1a being a sectional view of the pick-up taken on the line 
Y--Y in FIG. 1b and FIG. 1b a sectional view of the pick-up taken on the 
line X--X in FIG. 1a. 
The polepieces of the pick-up consists of U-shaped magnetic conductors 1 
and 2, the one limb of each U, 3 and 4 respectively, cooperating with an 
omnidirectionally pivotal movable element 5 which is attached to one end 
of a stylus, holder whose other end carries a stylus and arranged on the 
other limb electric coils 8 and 9 which are cylindrical in this 
embodiment. The ends which cooperate with the movable element are located 
in recesses in a plastic block 13, while the coils 8 and 9 engage in 
grooves in that block. The ends of the limbs of the U-shaped round 
conductors 1 and 2 which do not cooperate with the movable element 5 are 
interconnected by a U-shaped yoke 10 of a magnetic material whose limbs 
are connected to the housing 11. The underside 12 of the housing 11, which 
consists of a soft-magnetic material, constitutes a third polepiece and is 
flat in this case. This third polepiece is common to both directions of 
oscillations. The two magnetic circuits, one for each of the two mutually 
perpendicular directions of oscillation, are now constituted by: the 
polepiece 1, the limb 3, the movable element 5, the underside 12 of the 
housing 11, the U-shaped yoke and the polepiece 1 and by the polepiece 2, 
the limb 4, the movable element 5, the underside 12 of the housing 11, the 
housing 11, the U-shaped yoke 10, and the polepiece 2 respectively. The 
connection pins 14 are mounted in the plastic block 13. 
The movable element 5 is made of a permanent magnetic material, but it is 
alternatively possible to make this element of a soft magnetic material 
and to arrange a permanent magnet between the yoke 10 and the housing 11, 
or to make the yoke 10 of a permanent magnetic material. 
The polepieces 1 and 2 need not necessarily be U-shaped, but may just as 
easily have a different shape. They may, for example, be Z-shaped. 
Furthermore, the idea of the invention is not limited to a pick-up as 
shown in FIG. 1, in which the magnetic circuit comprises only one pole 
piece for each direction of oscillation with the underside 12 of the 
housing 11 functioning as a common conductor for the magnetic flux in both 
circuits. It is equally possible to provide each magnetic circuit with two 
associated polepieces, which both cooperate with the movable element 5. 
The step in accordance with the invention, which in fact may also be 
applied to other parts of the magnetic circuit, will be explained by means 
of a number of examples shown in FIGS. 2 to 6. These Figures show some 
polepieces to which the step in accordance with the invention has been 
applied. 
FIG. 2 shows a hollow polepiece 21, whose limb 22 cooperates with the coil 
8 or 9 of FIG. 1. The other limb 23 of the polepiece cooperates with the 
movable element 5 of FIG. 1. The polepiece is formed with a slot 24 which 
extends over the entire length of the polepiece. It need not necessarily 
extend up to the cavity although this is desirable for an optimum effect. 
The polepiece of FIG. 2 has a slot which does extend up to the cavity. The 
polepiece of FIG. 2 can for example be obtained by a mechanical operation, 
such as stamping and folding, so that ultimately a slit tube is obtained. 
FIG. 3 shows a part of the limb 22 of another polepiece having a slot 25, 
which may be formed in the solid rod, for example by cutting, before it is 
bent into the U or Z-shape. Thus the slot and the cavity then coincide. 
FIG. 4 shows yet another polepiece, made of a thin flat sheet, whose 
development is shown in FIG. 5. The polepiece of FIG. 4 is obtained by 
bending the sheet of FIG. 5 along the lines A--A, B--B and C--C. The 
portions 29 and 30 in FIG. 5 then constitute the limb 22 of FIG. 4, which 
is hollow and formed with two slots 32 which extends in the longitudinal 
direction of the limb. The portion 31 in FIG. 5 constitutes the limb 23, 
which is formed with a slot 33 on one side only. 
It is to be noted that the invention is not limited to polepieces of the 
shapes shown here, but that the invention is equally applicable to 
polepieces whose shapes differ from those of the polepieces shown with 
respect to points which are not relevant to the invention. An example of 
this is the polepiece of FIG. 6, of which only one limb is shown in 
sectional view, which polepiece is also made of a thin sheet material and 
is formed with a slot 34.