Above illustration: Effective Length
Def: The straight line distance from the tonearm pivot to the stylus.
Above illustration: SRA and VTA
Def: VTA, Vertical Tracking Angle describes the angle between the record surface and a line described by the cantilever pivot to the stylus contact area within the record groove.
Def: SRA, Stylus Rake Angle, or Scanning Rake Angle describes the angle between centerline of the stylus and the record surface. Alternately it can be measured as the angle between a plane that is perpendicular to the record surface and the stylus centerline.
Both of these elements are part and parcel of the same adjustment. If you say you are adjusting VTA, you are also altering the SRA. The distinction is offered to explain the need for the stylus and it's cantilever to duplicate the vertical swinging motion of the original cutter head used to cut the master. Critical for the fine tuning of elliptical and fine-line stylii, the closer the SRA can be adjusted to match that of the original cutter head, the more information the stylus will retrieve from the groove. If we could shrink ourselves small enough to climb into the groove and see the relationship between stylus and groove, we would begin thinking in terms of adjusting SRA because SRA describes the angle of the stylus. VTA describes the angle of the cantilever.
Using photography and a cad program to measure VTA and SRA
Above photo: The stylus and cantilever of a Shelter 501 type II as it rests within a record groove.
This is macro photography. Not the cleanest and with some difficulty. The macro lens I use needs to have very close proximity to its subject. This is not really possible without taking the record player down off its equipment rack and placing it onto a more suitable fixture to get the shot. (not going to happen today!) So I settled for further distance, less than adequate lighting and a less clean shot. But it is readable to get the general idea of the method. Using my preferred 3d CAD software (Rhino) I can overlay a photograph onto the screen. Then it is a matter of using the drawing and dimensioning tools within Rhino to create the above.
SRA is always measured on the inboard side of the stylus. It is generally accepted that 92° is the starting place.
All images copyright © Steve Clarke
3d geometry created in Rhino and then rendered with Moray-POVray.