Handbook for Sound Engineers

Analog Disc Playback 1031

27.6.1 Cartridge Styli

Stereo Disc Groove. The playback stylus is the first
link between the information stored in the record groove
and the playback system. The quality of the reproduced
sound is influenced by the precision with which the sty-
lus follows the groove modulation.

In stereophonic recordings with 45°/45° modulation,
the two channels are isolated from each other because
modulation of each channel is at 90° to the other,
Fig. 27-25.

To minimize the effects of vertical excursions at low
frequencies, the phase of both channels is adjusted so
low-frequency signals are in phase in order to produce
lateral modulation. The phase relationship of the two
channels determines the location of the sound image
between the two loudspeakers, and in some cases the
phase is a deciding factor as to whether there is going to
be a signal reproduced at all.

Stylus Tip. The function of the playback stylus of the
cartridge is to follow all deflections of the groove. Since
the stylus is attached to the end of the cantilever, any
motion of the stylus tip is transmitted to the other end of
the tube or shank, where the electrical signals are gener-
ated by a moving magnet, a moving coil, or a crystal.
The stylus has rounded off edges that are polished for
smooth tracking. Ideally, the playback stylus should be
centered in the groove, and its centerline should match
that of the cutting stylus. There are always minute
imperfections in the alignment of the stylus and of the
groove. Therefore the shape of the playbacd stylus is
made to compensate ans allow some misalignment of
the stylus in the record groove.

The stylus touches the groove walls at two points. The
contact area is curved and is a part of the tip radius so

that if the stylus is slightly tilted due to misalignment of

the cartridge or the tonearm, tracking will not be affected.

Spherical Stylus. There are several types of styli today.

The simplest and the oldest one is the spherical tip. The

spherical stylus is a tiny diamond or sapphire cylinder

with one end ground to a cone shape with its tip pol-

ished to an accurate sphere. The included angle of the

cone is about 55°, and the tip radius is about

0.0007 inch or 0.7 mil. Because grooves can be as nar-

row as 0.001 inch, the stylus tip has to be equal to or

smaller than the groove in order to track it. The standard

tip radius dimensions for today’s spherical styli range

from 0.0005–0.0007 inch (12.7–17.7μm).

Elliptical Stylus. The second type is the elliptical sty-

lus. From the front it looks like a spherical stylus; how-

ever, there are two flats polished in the front and the

back of the stylus. The side radius of the elliptical tip is

much slimmer than that of the spherical stylus. The

intersections of the two flats are polished to form small

radii called the tracing radii, which measure about

0.0002 inch (5μm). These small side radii are actually

in contact with the modulation of the groove and,

Figure 27-24. Networks for equalizing ceramic cartridges.

p p p

p p

1000 pF

5000 pF

10 k 7

560 pF

1000 pF

68 k 7

10 k 7

100 pF

47 k 7

380 mH

500 k 7

10 k 7

Figure 27-25. Comparison of 45°/45° stereophonic

groove with standard lateral groove.

2D

A'

2

A'

2

Lateral

2D + 2A'

A

0

Maximum groove excursion

Relative output per channel

Relative dB per channel

45-45 Stereo

2D + 2A'

3.0A'

A' A'

A

D

A' 2D A'

D

A'

2

A'

2

A'

2

Lateral

45–45 Stereo