Zenith

The next parameter is called the zenith. This refers to the horizontal rotation of the stylus relative to the groove path. (See figure 1). Most cartridge alignment tools give you some method of determining zenith. Some align the sides of the cartridge body to a parallel lines, and others have a line traced which is meant to line up with the cantilever. The first method makes the assumption that you have straight parallel sided on your cartridge, and that the cantilever is perfectly parallel to those sides. Both methods assume that the long axis of the actual stylus is perfectly perpendicular to the cantilever. Look for an alignment tool that will allow you to check the setting relative to the cantilever, not the cartridge body. That method makes fewer assumptions, and will allow a more precise setting. To properly set zenith, you will generally have to rotate the cartridge body relative to the cartridge mounting holes in either the armtube or headshell.

Improperly set zenith will result in a small but possibly significant phase shift between channels. In a linear tracking arm, this error will be present equally across the entire record, and is therefore more critical to set precisely. Due to the nature of pivoted arms, there is going to be some error in zenith everywhere but the null points, and as such very small errors in zenith are less critical than on linear arms. You should still strive for as precise an alignment as possible whichever arm type you have. The most precise method of setting the zenith is to use a dual trace oscilloscope, using one trace for each channel on a mono track. When the zenith is just right, the two sine waves showing on the screen will be exactly in sync.

View of stylus in groove from top. The stylus footprint is in red, and the black line is an imaginary line along the long axis of the stylus. Ideally, this axis should be perfectly perpendicular to the groove walls at the point of contact. The arrows represent the plane in which zenith can be adjusted. This is usually done by twisting the cartridge body in the horizontal plane relative to the tonearm tube