In high performance analog playback, azimuth and stylus rake angle ("SRA") are the two setup parameters most likely to have a major impact on the playback performance, yet they are the two that are usually implemented improperly and imperfectly.  This article focuses on what the ideal SRA is and why achieving it is so critical to playback performance.

​

When we playback our records with our fine-contact profile stylii (think Shibata, Geiger, microridge, line contact, etc.) we want the angle of the stylus contact edge to be at the same angle the lathe's cutter head was at when the lacquer was cut in order to keep distortions to an absolute minimum. Why? Because the turntable is a transcription instrument, so the closer we get it to read the grooves in the same manner in which they were cut by the lathe, we will enjoy lower playback distortions and higher playback quality.

​

THE LATHE AND LACQUER DEFINE THE IDEAL SRA RANGE

Setting the ideal SRA at home starts in the cutting room with the record lacquer on the lathe. The lathe's cutter head drops down into the soft lacquer and is modulated by the musical signal, cutting the spiraled groove that will later be pressed onto our LPs. The angle at which the cutter head's sharp edges meet the lacquer MUST be greater than 90 degrees in order to remove the "chip" that is cut out of the lacquer. Cutter heads of 90 degrees or less will result in some of that soft chip being pressed back into the freshly cut grooves - not good. 

​

So we know the cutter head needs to be greater than 90 degrees, but how much more? 

​

Imagine using a garden hoe in loose soil. When you drag the hoe through the soil you would notice that the hoe begins to dive into the ground as you draw it forward. It does this because the hoe's blade is at an angle greater than 90 degrees to the ground and when forward motion of the hoe's blade is met with the friction of the soil a downward vector force is created on the hoe, causing it to dive down.

​

If a lathe's cutter head is at too steep of an angle against the lacquer, this same downward vector force causes instability in the cutting process. This instability causes cutting distortions which will end up on our LPs. This cutting instability can be avoided by keeping the cutter head over, but barely over, 90 degrees. The greater the angle, the greater the cutting instability.

​

We can imagine that aiming for a 91 degree setting may not allow enough room for setup error and would not provide the engineer with enough confidence that the chip will always be kept away from the freshly cut groove. We also know from doing some calculations that anywhere over 94-95 degrees causes downward forces to increase to the point where distortions become an issue in the cutting process. By inference then, 92-93 degrees would be the ideal cutting angle and the ideal SRA for us to aim at.

​

But perhaps the inferential approach isn't enough?

​

A MEASURED STUDY

In 1981, Audio Magazine ran an article by Jon Risch and Bruce Maier entitled "More than One Tracking Angle". In this definitive analysis on VTA and stylus rake angle, the authors arrived at the conclusion that 92 degrees is the ideal stylus rake angle for most records. There is no need to go over the details in this space when you can read the article:

​

​

​

​