SRA Versus VTA???

In our video series The 7 Alignment Targets for Vinyl Playback Optimization, we discuss the difference between and the details of Stylus Rake Angle (SRA) and Vertical Tracking Angle (VTA). Please watch!

The common “wisdom” of adjusting your tonearm height for SRA/VTA states that as you raise the arm, the sound will become brighter and more bass lean. As you lower the arm, the bass will sound heavier. These exact sonic attributes associated with raising or lowering are not universally experienced. This is largely due to tonearm design variation with respect to the vertical location of the center of gravity for the tonearm relative to the horizontal axis pivot. However, in most cases this dogma is exactly what we experience when changing tonearm height but there are at least two big problems with this effort to "improve" our turntable's performance. The first problem is

WHAT you hear when you change the arm height IS NOT WHAT CHANGING SRA AND VTA SOUNDS LIKE!

YES, when you change arm height you are changing SRA and VTA, but the sonic attributes that materialize specifically because of SRA and VTA changing are absolutely swamped by other mechanical parameters.

What you are hearing when you raise and lower the tonearm are the sonic attributes of changing vector forces in the tonearm.

The second problem is that when you knock your tonearm out of level position, you are playing loose with dynamic playback vector forces. Your tonearm will perform its best with a level armwand. 

Avoid being more than 1° from level armwand on the front/back (SRA/VTA) angle (azimuth can go up to 2.5° depending upon stylus profile) and make any changes to SRA/VTA at the headshell using a corrective shim. Contact WAM Engineering for corrective shims or make your own shimming method, using the WallyReference Front/Back Blade to measure the angle of the corrective shim to within 0.05° accuracy (on the newly released version).

Optimal VTA is 18° with the stylus under friction. This is what most cutterheads cut at after lacquer springback and vertical modulation pre-distortion (DMM recording) are taken into account. Anywhere from 15° to 20° VTA on playback is excellent. Unfortunately, few of you will get your VTA down this far. There are two very bad reasons for this. Watch the VTA video from the The 7 Alignment Targets for Vinyl Playback Optimization video series to learn more about these two reasons. For the record, we find these two reasons totally unacceptable!

Optimal SRA is less certain as playback rake angle HAS NEVER BEEN SCIENTIFICALLY STUDIED. The only paper written on the subject was not detailed enough to be peer reviewed and their claim of 92 being the optimal angle did not articulate whether this is to be measured statically or dynamically. Given what we know of the rake angle most engineers cut at (typically between ~85° to 90°) plus the effect of lacquer springback, it is plausible that the optimal range for SRA is between 90° and 93°.

Until we perform a controlled study on SRA at WAM Engineering and release it for peer review, this is the best available information we know of. Further, it is highly likely that VTA is more important than SRA (watch for our upcoming videos on this) so we suggest if you have to err with one of the two parameters, err in favor of VTA.

If you can get within these two target ranges, you are optimizing your playback performance in these important parameters. Getting your cartridge’s SRA and VTA to equal the effective cutting rake and vertical modulation angles used to cut the lacquers which made your record will result in greater sonic clarity, focus, transient speed, inner detail, soundstaging and imaging.

What you see above are the mechanical distortion characteristics that occur when VTA is different from the cutting modulation angle. Notice the variation in velocity of the stylus when it goes up versus when it goes down? You may recall that moving coil and moving magnet cartridges are velocity sensitive devices. This mechanical distortion creates harmonic and intermodulation distortion.