How to set SRA after determining true vertical?

Dear Doug, Gregm,

Base on what I understand from your answers, it is the SRA that is important, not the VTA (of course, the SRA and VTA are interrelated). As long as you can adjust the SRA to fit the angle of the cutting heads, it would be ok. So, any cartridge (no matter whether it has a build-in VTA of 20 degrees or 22 degrees) can be adjusted to fit any cutting angle. Am I correct?

Now, my friend’s “theory” actual goes one step further, which I have hinted but didn’t really state out clearly in my original question. It goes like this:

Going back to my original example “say an Ortofon, with 20 degrees build-in VTA, will fit the Decca, and another brand of cartridge, say a Clearaudio, with 22 degrees of build-in VTA, will fit the EMI etc.”, his theory is that with a Decca LP, an Ortofon (due to the fit of it’s build in VTA) will always sounds better than a Clearaudio no matter how you adjust the arm/cartridge (even if you adjust the SRA/VTA for individual records), assuming the cartridges are in a similar price range. And vice versa, an EMI LP will always sound better with a Clearaudio. So, if you want to ideally play back all the LPs, you will need one cartridge with a 20 degrees build-in VTA, and another one with 22 degrees build-in VTA.

Well, based on the answers I got from you guys, I guess this theory is false.

Thanks again,

Michael

SRA is very easy to match to the cutter head rake angle. True, there is/was no absolute standard, but the range of variation is very small, and so even if you don't have a tonearm with on-the-fly adjustable arm height, you can usually find a happy setting that fits most record grooves at least 90% perfectly if not 100% all the time. The trick once again is to find the absolute vertical point described at the beginning of this thread and then go from there.

VTA is another matter altogether. It is the angle of travel described by the cutter head as it moves up and down and depends on the design of cutter's torque tube (something like a cartridge cantilever.) There is some variation here also, but the big (and impossible to match) variation is among cartridges themselves. Cantilever length is all over the place among different cartridges, so it always struck me as folly to even attempt to match cutter VTA. A mismatch wil only create forth order harmonic distortion (if I remember my reading correctly) which is virtually inaudible, and so any attempt to "dial in" VTA by ear would be futile anyway. That's why I get upset when I hear the term "VTA adjustment" in any context. Call it whatever, but what's really going on is SRA adjustment.

Greg, adjusting arm height (in the range we're talking about here) has no effect on stylus overhang. That's function of the position of the tonearm base relative to the platter spindle -- with fine adjustment available via slotted headshell mounting holes, or in the case of SME, a sliding tonearm base.

Well, based on the answers I got from you guys, I guess this theory is false.

That's wasn't my answer or Nsgarch's. I said the theory was true but that attempting to apply it would be ridiculous. Nsgarch elaborated by explaining why matching VTA between individual cutting lathes and cartridges would require too many cartridges and would be virtually inaudible anyway.

Gregadd,
Put a stick of soft butter flat on a plate.
Hold a sharp, pointed knife straight vertical, with the edges of the blade oriented across the stick.
Lower the point into the butter and drag it the length of the stick, moving it left and right as you go.

Now rotate the butter to put a fresh side on top.
Hold the knife edges across the stick as before, but angle the point sharply either point-forward or point-back.
Cut a modulated groove as before.

Compare the two grooves. They are clearly different. The modulations cut with the vertical knife have straight vertical sides. The modulations cut with the angled knife have angled sides. The only way to accurately re-trace either groove is to use a blade with the same size and shape and hold it at the same angle (SRA). Any other angle will cause the blade to slur past parts of each modulation, creating playback timing errors.

We adjust arm height for each LP. The changes we hear are consistent with SRA-matching theory. Some people do not hear the differences as readily as others. That's normal, but it doesn't change the shape of the butter!

Doug- given that stylus rake angle is such a well accepted theory somebody must have done this already. With far more accuracy than I can. From what I have gathered so far the head is more like a plow than a knife. It cuts forward and to the side. The cutting head digs down into the vinyl cutting ahead and side to side. The master is rotating underneath the head.
To further complicate matters the cutting is now being heated. This means that there is some melting going on. The articles all swear by SRA again providing no proof.

Greg, maybe you (or Doug or I) can find some microscopic groove photos that will show this rake or slant in the groove undulations clearly. I know Last used to show such photos with their products. I'll see what I can find.

Neil

.