Precision cartridge alignment can be a tedious, time-consuming task, and it takes someone with a steady hand, a keen eye, a good deal of previous experience, and the patience of Job to do it accurately, safely, and thoroughly.
Step five is setting stylus rake angle (SRA)—a variant of what we used to call setting VTA (vertical tracking angle) back in the day. ’Course back in the day we adjusted VTA solely by ear. Received wisdom was that it should generally be set so that the tonearm was parallel to or slightly below parallel to the LP’s surface. In practice, this always seemed to give you a richer, fuller sound with less treble bite, and in those days reducing treble bite was a good thing given the state of tonearms, moving-coil cartridges, and LPs (particularly Mercury LPs).
However, it turns out this formula, for all its salubrious effects in listening, was technically incorrect. In March 1981, Jon M. Risch and Bruce R. Maier published an article in Audio magazine titled “More Than One Vertical Tracking Angle,” in which they pointed out that, in order to play back an LP properly, in theory the playback angle of the stylus ought to be the same as the angle of the stylus in the cutting head, and their research determined that the cutting angle on most of the LPs listened to was typically 92o (not the 90o or less that we had always assumed was right).
The article didn’t have much effect until Michael Fremer of Stereophile, bless his analog heart, rediscovered it. Since then there has been a bit of a mini-revolution in cartridge setup, in which measuring SRA and adjusting VTA to get SRA theoretically right—or close to right—have come to the fore.
The process of measuring SRA is not for the weak of spirit. To do it you must have a digital microscopic camera, a stand to put it on, a computer with a good deal of processing power, and, as is the case with every aspect of cartridge setup, a dedicated tweaker’s spirit, nerve, and patience.
Pictured on the previous page is one of Andre’s digital microscopic cameras, sitting beside an Acoustic Signature Ascona turntable with a Kuzma 4Point tonearm in which an Ortofon MC Anna has been mounted. The microscopic camera is a USB device that plugs into a laptop computer, whose screen you will see shortly. What it does—once you get the stylus in precise focus (a process so demanding that I literally couldn’t stand to do it on my own)—is take a close-up picture, like the one below this paragraph, of the stylus sitting on a perfectly flat surface with, in this case, a cylinder of pencil lead, which also must be focused, sitting behind it to provide a flat horizon line.
Software, which comes with the camera, allows you to adjust two perpendicular lines so that one of them runs straight through the shank of the stylus to the contact patch at its tip (In case you’re wondering why the perpendicular line in the photo above is not running straight through the stylus’ shank to the contact patch, this is because, unlike typical moving-coil styli, the tip of the Ortofon Replicant 100 stylus of the MC Anna is not centered below the vertical shank of the diamond. The geometry of this Giger-type stylus is asymmetrical; thus, measurements are not taken down the center of the stylus, as would normally be the case. Instead the rear edge of the stylus provides the reference, for which see the photo below.)
Once the perpendicular lines of the measuring software are properly adjusted, they are then rotated from a position perpendicular to the record surface to a position parallel to the record surface. The computer then calculates the stylus rake angle (symbolized by the little white curve running from the black line at the back edge of the stylus to the flat surface the stylus is sitting on). In this case the measured SRA was 89.725o.
To adjust SRA for theoretical correctness, you then raise (or lower, depending on your reading) VTA until the SRA (which must be measured again—often repeatedly) is somewhere between 91o and 92o. (The slop built into this setting allows you to season by ear and by typical record thickness.) In the screenshot above, you see that SRA has been adjusted, by raising the back of the tonearm, to a closer-to-theoretically-correct 91.477o (which is where I liked it best).