150 µm
78 RPM
Goove depth and radii
33 1/3 RPM microgroove LP
130 µm
13 µm
Minimum depth
1 mil = 25 µm
Typical depth
~
38 µm
Maximum depth
5 mil = 127 µm
~
70 µm
~
250 µm
~
50 µm
0.036 mm
0.7 mil
0.5 mil
Conical
(Spherical)
Elliptical
0.2 x 0.7 mil
0.026 mm
0.036 mm
78 RPM
75 µm radius
0.15 mm
Line Contact
Figure 3.15: Dimensions of example styli, drawn to scale. The figure on the left is typical for a 78 RPM steel needle. The four examples
on the right show di
ff
erent examples of tip shapes. These are explained in more details in the text. (For comparison, a typical diameter
of a human hair is about 0.06 mm.)
There have been a number of di
ff
erent
designs following Shibata’s general
concept, with names such as
MicroRidge (which has an interesting,
almost blade-like shape “across” the
groove), Fritz-Geiger, Van-den-Hul, and
Optimized Contour Contact Line.
Generally, these designs have come to
be known as
line contact
(or
contact
line
) styli, because the area of contact
between the stylus and the groove wall
is a vertical line rather than a single
point.
Originally, the Beogram 4002 was
supplied with an MMC 6000 cartridge,
which featured a stylus tip designed by
Subir K. Pramanik, an engineer at Bang
& Olufsen. This became known as the
Pramanik diamond, and was designed
to ensure maximum surface area with
the groove wall on its vertical axis
while maintaining a minimum contact
along the horizontal axis.
Figure 3.16: An example of an elliptical
stylus on the left vs. a line contact Pra-
manik grind on the right. Notice the dif-
ference in the area of contact between
the styli and the groove walls.
3.4 Bonded vs. Nude
There is one small, but important point
regarding a stylus’s construction.
Although the tip of the stylus is almost
always made of diamond today, in
lower-cost units, that diamond tip is
mounted or
bonded
to a steel pin which
is, in turn, connected to the cantilever
(the long “arm” that connects back to
the cartridge housing). This bonded
design is cheaper to manufacture, but
it results in a high mass at the stylus
tip, which means that it will not move
easily at high frequencies.
Figure 3.17: Scale models (on two dif-
ferent scales) of di
ff
erent styli. The ex-
ample on the left is bonded, the other
four are nude.
In order to reduce mass, the steel pin
is eliminated, and the entire stylus is
made of diamond instead. This makes
things more costly, but reduces the
mass dramatically, so it is preferred if
the goal is higher sound performance.
This design is known as a
nude
stylus.
3.5 Tracking force
In order to keep the stylus tip in the
groove of the record, it must have
some force pushing down on it. This
force must be enough to keep the
stylus in the groove. However, if it is
too large, then both the vinyl and the
stylus will wear more quickly. Thus a
balance must be found between “too
much” and “not enough”.
1920
1930
1940
1950
1960
1970
1980
1990
2000
2010
2020
Year
0.1
1
10
100
Typical tracking force (g)
Figure 3.18: Typical tracking force over
time. The red portion of the curve shows
the recommendation for Beogram 4002
and Beogram 4000c.
As can be seen in Figure
, the
typical tracking force of phonograph
players has changed considerably
since the days of gramophones playing
shellac discs, with values under 10 g
being standard since the introduction
of vinyl microgroove records in 1948.
The original recommended tracking
force of the Beogram 4002 was 1 g,
however, this has been increased to
1.3 g for the Beogram 4000c in order
to help track more recent recordings
with higher modulation velocities and
displacements.
3.6 E
ff
ective Tip Mass
The stylus’s job is to track all of the
vibrations encoded in the groove. It
stays in that groove as a result of the
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