"Pete Riggle is one of the
very few tonearm manufacturers with the foresight to supply with his arm a simple overhang gage. As I discovered, by using
that gage to set overhang early in the setup process, one needs to expend very little time and effort later on." Art
Alignment and Protractors
a lot of concern over alignment, and sometimes questionably expensive alignment protractors. Here is my take on these
There are two popular alignment
families, the Baerwald (or Lofgren A) family, and the Stevenson family. The Baerwald provides the lowest average tracking
distortion over the surface of the record. The Stevenson provides relatively low average distortion over the surface
of the record, not as low as Baerwald, but also provides zero tracking distortion at the lead-out groove (where surface speed
is lowest, and the groove geometry is more troublesome). Either of these families is fine. I happen to use the
For either of these alignment families, there are two so-called null points in the swing
of the tonearm where the cantilever plane of symmetry becomes tangent to the record groove. These points are different
for Baerwald and Stevenson. An alignment protractor provides a grid for cartridge alignment at each of these points.
The alignment protractor for the Baerwald alignment is different from the alignment protractor for Stevenson alignment. An
alignment protractor should be marked as Baerwald (or Lofgren A), or Stevenson.
The null points do not vary
with tonearm length. Therefore a given protractor can be used for any tonearm length. A protractor can be as simple
as paper or cardstock having a hole to snugly fit the spindle, and a radial line from the pivot, with a perpendicular
cross line at each of the null (or alignment) points. When the stylus is at either of the null points, the cantilver
vertical plane of symmetry must be in alignment with the cross line.
There is no compelling necessity for any protractor more complicated than the one described in the paragraph above.
Of course metal or plastic would be more durable than paper or cardstock, and less senstive to subtle dimensional change from
humidity variations. But beyond that, protractor battles seem to be a tempest in a teapot.
One can download
a protractor from the following web page: http://www.vinylengine.com/cartridge-alignment-protractors.shtml . For Baerwald I recommend one of the "Stupid Protractors." There is also a simple Stevenson
protractor shown. The scale must be adjusted to get the alignment points to be the correct radius from the spindle center.
I provide a simple card stock Baerwald protractor with my Woody tonearms.
To achieve an alignment consistent with either the Baerwald or Stevenson family, the overhang must have a specific
relationship to the mounting distance.
See the diagram at the bottom of this page for a depiction of overhang,
mounting distance (spindle-to-pivot distance), and tonearm effective length. Overhang is the horizontal distance between the
stylus and the spindle center when the stylus lies on an extension of the line between the turntable spindle axis and the
tonearm vertical pivot axis . Mounting distance is the horizontal distance from the tonearm vertical pivot axis to the
spindle axis. The tonearm effective length is sum of the mounting distance and the overhang.
In a typical situation, the manufacturer specifies the mounting distance,
the overhang, and perhaps the effective length (the sum of the two). The user then attempts to achieve the specified
mounting distance when mounting the tonearm, and then attempts to achieve the specified overhang by sliding the cartridge
in the headshell slots.
If mounting distance is not adjustable, and is off a little bit, one can accomodate
by changing overhang. More on this below.
If there are no headshell slots, one must be able to
adjust the mounting distance (example, SME tonearms).
When the overhang and the mounting distance are in proper relationship, alignment at one of the
two protractor alignment points guarantees alignment at the other alignment point. In principle, only one alignment
point is needed.
Alignment needs to be made between the cartridge cantilver and the cross line of the protractor. The
cantilver must be viewed from above and directly in front of the cartridge. Good vision (or magnification) and a bright
light are essential.
If one can not easily get the exact mounting distance specified by the tonearm
manufacturer, the overhang can be adjusted accordingly. To determine the proper overhang at a specified mounting
distance, one can use Alignment Calculator Pro. Go to www.vinylengine.com. Click on the
Data button. Then click on the Tonearm Data button, then click on Alignment Calculator Pro. Go to the data entry
boxes on the left, and input the mounting (or pivot to spindle) distance in all the boxes, then click the Calculate button.
Scroll down below the charts to find the calculated results.
In conclusion here, let me say that I believe
way too much emphasis is placed on perfection in alignment. We don't see perfectly. We don't measure perfectly.
A nearly aligned cartridge sounds very good. To demonstrate my point, consider the following: Although tracking error
varies throughout the play of an LP, in amounts varying from zero to about 1.5 degrees, we don't seem to hear a lot
of tracking distortion. Also, consider the "straight alignment" proponents (including Tom Fletcher at
Nottingham Analog) who set up a 12 inch arm with the cantilver aligned with the tonearm axis (zero offset angle). This
arrangement results in tracking angle errors several times those of the Baerwald and Stevenson alignments, but purportedly
sounds good. If a bit of tracking error causes so little noticible problem, is it possible that one can
give too much time and money to the pursuit of the perfect protractor?
|Diagram Showing Mounting Distance, Overhang, and Effective Length