Stylus Rake Angle

Although my own experiments and experiences cause me to doubt some of the charts and statements on Yosh's webpage about VTA, overall it remains worth reading.

http://www7a.biglobe.ne.jp/~yosh/vta.htm

I will add that speaking as a cartridge designer, I find SRA and VTA to be different. For example, designing a cartridge with increased VTA will allow a shorter cantilever to be used, but doing so has the side-effect of stiffening the suspension vertically while leaving the horizontal compliance more or less unaffected.

As a rough guide, at 0 degrees VTA, horizontal compliance and vertical compliance of the suspension wire will be the same. At 90 degrees VTA (which no cartridge does), the vertical compliance will be 0, while the horizontal compliance will remain the same as it was at 0 degrees. For all angles in between, you can figure out how the ratio of horizontal to vertical compliance changes in the suspension wire by calculating the cosine of the VTA angle.

Note that I have deliberately not included compliance of the suspension dampers, therefore you should not jump to conclusions from the above. Some suspensions have linear characteristics, while other types have progressive characteristics, making it impossible to generalize.

kind regards, jonathan

Which type of lathe do you have?

Its an old Scully (well, *all* Scully lathes are old...) equipped with a Westerex 3D cutterhead. The cutterhead does not need a lot of power and has a moderate impedance, we are easily able to drive it with our M-60 amplifiers.

Kiddman, it helps to take a look at what is happening in the groove with a microscope. Of course every lathe has one, you can't do the work without it! We have a multi-color LED light source that we installed, so we get different colors depending on what we are seeing- the lands, the groove wall, or the bottom of the groove. As I said before, the defining quality of groove depth is the center of the groove.

If you have high frequency modulation, that shows up under the 'scope like a groove with modulation on the walls. If you have bass information, the *entire* groove moves from side to side with the bass modulation. If the bass is out-of-phase, the groove will stay in one spot and seem to vary in width and depth. This sort of condition will knock the stylus right out of the groove and so has to be avoided. In natural 2-mic recordings it does not show up- only if the recording is multi-tracked to start with.

I Googled for images of this stuff. Without a multi-color light source it can be a little hard to see, but there is a photo that appears at this link that is not bad for what I am talking about http://en.wikipedia.org/wiki/Gramophone_record

Scroll down aways, the photo appears on the right hand side about half way down, just above the heading 'vinyl quality'. If you look closely at the grooves, you will see that they squiggle a bit. Those larger squiggles are bass notes. This is why I say the groove depth does not vary all that much, as the *entire* groove has to move to make the in-phase bass note.

Google 'record groove modulation photo'

I'm still wondering why, if slant angle varies not only from record to record but by the signal itself, by a cutter who's VTA is for all intents and purposes static, does cartridge VTA/SRA need to match VMA? Does it not stand to reason that in the same way variations are produced, the same information will be retrieved? Albeit once external influences such as adverse lacquer/cutter interactions are compensated for via SRA adjustment? Once adjusted, will the play back stylus not follow the same behavior as the cutting stylus. Same VTA constant.

When I adjust SRA to where it sounds correct, how close is it to (average?) VMA? It sure sounds like the entire frequency spectrum is correct, not just parts of it.