1022 Chapter 27
pivot point of the tonearm. Older tonearms suffered
from a tangent error because the cartridge was aligned
properly at only one point on the record. Today’s piv-
oted tonearms have a built-in offset angle at which the
cartridge is positioned so it is always perpendicular
within a couple of degrees to the radius of the disc. This
reduces distortion in the lateral plane and improve
tracking. There are many protractors available today
using different approaches to help position the cartridge
as accurately as possible in the tonearm to minimize
tracking error.
When a disc is being cut, the cutting head is carried
across the face of the recording disc following the
radius. However, when in playback, the pickup is at the
right angle to the radius of the disc only at two points,
because the pickup arm is pivoted in such a manner that
it swings across the face of the disc in an arc, as shown
in Fig. 27-8.
Generally, the manufacturer of the arm supplies a
template and mounting instructions for a particular arm.
In the absence of such information, the pickup arm is
mounted in such a manner that the tangent error is at a
minimum. One method of mounting the arm is shown in
Fig. 27-9. Regardless of where the pivoted arm is
placed, a tangent error cannot be eliminated entirely.The error can be made so small, however, that it can
be neglected. In offsetting the tonearm by bending it
into an S or J shape, Fig. 27-10, it is possible to position
the cartridge so that at two points on the record the error
shall be zero. The deviation from this ideal
groove-cartridge interface will be only 2–3° in the hori-
zontal plane.Figure 27-7. Tonearm classification.
A. Pivoted tonearm.B. Tangential tracking tonearm.Lead screw
or servoPhono
cartridgeFigure 27-8. Tangent error in a reproducing arm. The error
is zero at point A only.Figure 27-9. Typical mounting for an offset pickup arm.Pivot point
of reproducer
armCutting head
travelRecord AAverage center of
recorded area90 o90 o