[ARSCLIST] historical stylus rake angles (SRA)

[Eric Jacobs <ericj@xxxxxxxxxxxxxxxxxxx>]

Does anyone know of a reference where I might find historical stylus rake
angles?  Even some rough guidance on this list would be useful.

Note that SRA (the angle the stylus makes with the record surface) is not to
be confused with the Vertical Tracking Angle (VTA) which is the angle the
cantilever makes with the record surface.  Of course, VTA and SRA are
directly related by the angle at which the stylus is mounted to the
cantilever.

Modern cartridges and tonearms are designed for SRA values of zero (ie. a
vertical stylus, perpendicular to the record surface) or slightly positive
to about 3 degrees or so.  I realize that SRA values, like VTA, will vary by
record label and need to be adjusted for each record for optimal playback if
you are a perfectionist.  SRA and VTA are primarily affected by record
thickness and cartridge height.

Variations in SRA (fractions of degrees) are most audible on LPs with their
lower noise, wider frequency response and narrower grooves making VTA an
important adjustment for each LP.

How critical is SRA for accurate playback on acoustic or electric 78s or
transcription discs?  Am I making a mountain out of a mole hill?

The reason behind my question is that the 1-2 inches of VTA adjustment on a
tonearm will only compensate the SRA by a few degrees.  In fact, tonearm VTA
adjustment is best suited to compensate for variations in cartridge height
and record thickness since it is assumed that the cartridge SRA is correct
when the tonearm is level.  If historical SRAs used rakes of 5 degees or
greater, some sort of custom cartridge mount would need to be devised (a
wedge shaped block or shim) to achieve the correct SRA.

Because of the limitations of tonearm VTA adjustment, it is not possible for
me to experiment with large variations in SRA and listen for differences.
Optical measurements of SRA are not possible with my 150x microscope with
0.01 mm measurement reticle.

Thanks in advance to anyone who can shed some light on this question.

Eric Jacobs
The Audio Archive
San Jose, California