VTA method???

[rodman101]

This is a bit off topic but now vinyl is "in" I wonder how many beginners are duped by adding a turntable mat with no consciousness of how this changes VTA, most probably unaware of this specification, especially how many offerings come as plug and play with preset VTA. I just attended a Christmas party of wife's coworker and her husband was showing off his system using a Cambridge Audio Alva TT v2 which by appearance is solid and I see it has good reviews but nothing I consider to be in the same class as my deck. He added a funk firm mat which looked to be at least 2x LP thickness. I looked at the arm setup and didn't see any VTA adjustment, not wanting to be too intrusive didn't look super hard but there is no obvious VTA adjustment if it exists. It sounded OK but not impressed. I really wanted to tell him that a ~$500 used deck in good shape, eye candy!!, from the golden era, mated to a modern ~$700 cartridge would put him light years ahead of what he was hearing but not wanting to offend just nodded and smiled. Seems like this group is happy with the looks, simplicity, and reviews but it kind of reminds me of the 90's Bose crowd...

 

[AvFan]

It's wrong, because it would disregard the included error of perspective.

Simple example: Imagine you'd only have one eye and you'd walk up to a pole, that's not exactly upright/perpedicular relative to the ground, from a good bit away, so that you can't see it in detail yet. Now the two most extreme errors of perspective would be, if you'd happen to approach the pole exactly in line with its plane of inclination, so that it would actually lean either towards or away from you, while to you it would appear upright instead. So now you don't directly walk up to that pole anymore, but instead beging to walk around it in a circle - then the error of perspective will reduce more and more, until it reaches zero at the two spots on the circle, at which your view is perpedicular to the plane of the inclination of that pole, so you can now see its actual inclination relative to the ground.

The same goes for the SRA: For calculating the actual inclination along the groove tangent the perspective of that calculation needs to be perpendicular to the groove tangent, not perpendicular to the virtual arm axis - 'cause in the latter case the calculation would also contain an error of perspective, so that the result wouldn't quite equal the actual SRA (= inclination along the groove tangent). And hence, now referring back to my drawing and calculation formulas in post #80, the need for the two case-dependent correction factors:

One the left: change in SRA = arcsin (height change / (effective length / cos (offest angle)))

And on the right: change in SRA = arcsin (height change / (effective length * cos (offset angle)))

Well, and as already hinted to, the angle between the virtual tonearm axis and the groove tangent can be expressed as the offset angle +/- the remaining tracking error angle - with the latter being zero at the two null points, positive before the first and after the second null point and negative between the two null points. But due to the remaining tacking error angle being quite small compared to the offset angle, disregarding it doesn't introduce much of an error of perspective. So I'd suggest to forget about the slight variation of the SRA over playback radius - that's simply too small to be of any actual relevance.

Greetings from Munich!

Manfred / lini

Lots of distractions these past few days but I wanted to get back to this issue of perspective as it relates to setting the SRA. The analogy of the walking around a leaning post was helpful and I believe I understand your point. I've had a chance to consider the idea of perspective and while I think you are correct, I could find no other source that thought the SRA varied across the record or that visually setting the SRA at the edge of the record created an error. If you have any sources that say that I'd like to review them. I stepped back and asked what impact on the SRA would occur if it was set visually at the edge of the record.

Earlier we discussed that the correct place to set the SRA was at one of the two null points because of the relationship between the stylus and the groove. If I understand correctly if the stylus is leaning forward and from the perspective of the groove the stylus SRA would be reduced at other than the null points. I wanted to roughly determine the change in what the groove perceives as SRA at the edge of the record versus at the outer null point. For my example : eff length = 256.6, inner null 70.3, outer null 116.6, lead in at edge of record 150 and I roughly measured the arc between the outer null point and the edge of the record and it was about 7°. The 7° horizontal rotation equates to about 8% change in how the SRA is viewed so the perceived SRA would be 1.84° if the SRA was set at 2° at the null point. Even with the best microscopes this is insignificant given the tolerances of stylus fabrication and the ability of the person setting up the microscope.

All this minutiae is dwarfed by the changing SRA due to warps and since most records are not perfectly flat. Attempting to dial in the SRA to the accuracy we've assumed during our discussion is mostly wasted effort. Also, if we tried to allot distortion to SRA I believe it would be dwarfed by the distortions created by changing stylus zenith across the record as shown as tracking error in the VE calculator. I think this is why we see most cartridge manufacturers advise to set the tonearm, or some part of the cartridge, parallel to the record; it just doesn't need to be that accurate given the variabilities of vinyl records.

So set SRA as best you can per the manufacturer's instructions and if a microscope is used to view the stylus know that in either case there will be one more step: adjust SRA by ear so it sounds right. How often SRA is adjusted is up to the individual.

 

[lini]

Lots of distractions these past few days (...)

No problem - it's more important, that you've got the idea in the meantime.

And yes, not setting the SRA at on the the two null points would cause the tip to lean ever so slightly to the outside or inside rather than fully along the groove tangent - but the error introduced by not considering the offset angle at all already is anything but huge on the absolute scale, and hence, as already mentioned, I'd suggest to simply forget about the even smaller error due to the remaining tracking error angle, that one would get by setting the SRA with the needle placed at the edge of the record, as that error really is way too small to worry about.

Greetings from Munich!

Manfred / lini

 

[Thomas_AA]

SRA might be optimum at 92° but in reality it seems that it is not that sensitive. If VTA is off it might be better to opt for VTA. From Yosh pages:

"Once Mr. Shibata commented about his invented SHIBATA stylus tip: "Care should be taken on the inclination of tip at normal usage but its tolerance is about 5 degrees in all directions. So it is not too particularly severe compared with 7 degrees tolerance for elliptic tip and 10 degrees tolerance for spherical tip."

 

[tabarddn51]

Thomas, This is talking about an Inverted (turned through 180 degrees stylus) The Shibata also a curved stylus, so in standard position, the SRA is virtually impossible to set up to 92 deg's, because one never knows what part of the Shibata stylus curve is actually touching the LP grooves.
So inverting it would send all the standard norm's out the window.

Cheers

 

[Thomas_AA]

Thomas, This is talking about an Inverted (turned through 180 degrees stylus) The Shibata also a curved stylus, so in standard position, the SRA is virtually impossible to set up to 92 deg's, because one never knows what part of the Shibata stylus curve is actually touching the LP grooves.
So inverting it would send all the standard norm's out the window.

Cheers

Invented, not inverted. Yes it is slightly curved. But the change I made of a microline was around 7 degree but no effect on high frequency level. So how critical is it?

 

[tabarddn51]

Ha Well Thomas, It can be heard, but like so many many things in our Fancy, it can be heard, not measured.

Cheers