The importance of VTA, SRA and Azimuth - pics
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There are many big name arms that claim to be SOTA, but do not have easy to use, very fine, indexed adjustments, of SRA and azimuth.
I do not think the arm designers know of the absolute need of a micrometer head height adjustment with index marks for SRA.
This adjustment is very, very fine, and you need to zero in on the optimum setting by ear. Adjust -on- the fly is just not practical. Too easy to move past the optimum. Setting to 92 degrees with a camera is too difficult and only a starting point. You must move around the optimal height by listening by ear.
Many diamonds like micro ridge require this fine adjustment.
If you find the optimal SRA, for a typical record of same weight , 80% of your records will playback great, as per an article in Audio magazine from the early 80’s and it is true today.
Without these very fine, indexed adjustments, can an arm truly be SOTA??
I do not think the arm designers know of the absolute need of a micrometer head height adjustment with index marks for SRA.
This adjustment is very, very fine, and you need to zero in on the optimum setting by ear. Adjust -on- the fly is just not practical. Too easy to move past the optimum. Setting to 92 degrees with a camera is too difficult and only a starting point. You must move around the optimal height by listening by ear.
Many diamonds like micro ridge require this fine adjustment.
If you find the optimal SRA, for a typical record of same weight , 80% of your records will playback great, as per an article in Audio magazine from the early 80’s and it is true today.
Without these very fine, indexed adjustments, can an arm truly be SOTA??
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Hi,
it's a shibata stylus (made by Namiki I believe) which makes it hard to measure SRA. when it's measured based on shank boundaries SRA is around 96.5 degrees. since it's a shibata stylus which has an asymmetrical profile I don't think that measurement is accurate. when I measure only the edges that touch the groove SRA is around 91.7 degrees, but it's hard to be sure. with micro ridge and super fine line it's much easier.
stylus landed on a cd with green marker on the edge but it can not be seen on the picture. I hope mirror image is sufficient. I know there are a lot of members using usb microscope for SRA measurement and I want to ask,
what is your SRA estimate of this stylus?
it's a shibata stylus (made by Namiki I believe) which makes it hard to measure SRA. when it's measured based on shank boundaries SRA is around 96.5 degrees. since it's a shibata stylus which has an asymmetrical profile I don't think that measurement is accurate. when I measure only the edges that touch the groove SRA is around 91.7 degrees, but it's hard to be sure. with micro ridge and super fine line it's much easier.
stylus landed on a cd with green marker on the edge but it can not be seen on the picture. I hope mirror image is sufficient. I know there are a lot of members using usb microscope for SRA measurement and I want to ask,
what is your SRA estimate of this stylus?
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Above is the Shibata datasheet. Based on the angle (24+-1 deg, i.e. 23-25 deg) circled in red, your cantilever should be at an angle of 25-27 degrees with the record surface for SRA = 92 deg. While it is extremely difficult to measure SRA accurately for any stylus profile, it is much easier to measure the aforementioned cantilever angle. Needless to say, one needs that 24 deg angle for any stylus accurately. Even Shabata manufacturer specifies +-1 deg. At least, we have a useful guide if we have that angle.
I have yet to find a USB scope with a large enough receptor to image Shibata profiles. It's not a matter of pixel density and almost entirely to do with the receptor size. The WallyScope is about to be released and has only 2.0 megapixels but a very large receptor so the images are fantastic. I'll offer it for rent to WallyTools owners in order to save them the $$ on a purchase.
As for the photo, without a horizontal reference to measure the angles against I'd normally declare this an impossible photo to do work from (you need to get the stylus RIGHT ON the edge of the CD). However, the reflected image is so excellent that we can use that to find the bisection line - that would be your horizontal line to measure from ASSUMING that the photo was taken perpendicular to the cantilever. By way of reference: a six degree off-perpendicular photographic angle results in about a 3 degree error in your MEASURED (but not correct) rake angle.
The WallyScope uses an approach where you can take a close-up photo of the stylus without resting on any surface at all to get the first of two data points needed to calculate the dynamic rake angle.
Speaking of which: don't forget to measure the dynamic effect before arriving at your final rake angle! I've seen as much as 2.25 degrees change to rake angle under dynamic conditions.
As for the photo, without a horizontal reference to measure the angles against I'd normally declare this an impossible photo to do work from (you need to get the stylus RIGHT ON the edge of the CD). However, the reflected image is so excellent that we can use that to find the bisection line - that would be your horizontal line to measure from ASSUMING that the photo was taken perpendicular to the cantilever. By way of reference: a six degree off-perpendicular photographic angle results in about a 3 degree error in your MEASURED (but not correct) rake angle.
The WallyScope uses an approach where you can take a close-up photo of the stylus without resting on any surface at all to get the first of two data points needed to calculate the dynamic rake angle.
Speaking of which: don't forget to measure the dynamic effect before arriving at your final rake angle! I've seen as much as 2.25 degrees change to rake angle under dynamic conditions.
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I sure
I know there are the 'by ear', 'by sight' and 'by electrical output' measurement camps but please know that I really appreciate the fact that you care and are doing all this research and development!
Thanks, @Solypsa!
Keep in mind that rake angle *on its own* has to undergo a pretty significant change (usually about 2 degrees or more) before making audible changes good or bad. Of course, in analog there are scant few parameters you can change without affecting another important parameter (and then ONLY on true azimuth tonearms or linear trackers). The point is: rake angle error is a multiplier of zenith errors. In other words, the three types of very obvious mechanical problems that are caused by zenith error (tracing error is similar but refers to a slightly different condition - look for more to come on this clarification). Adding a rake error makes those mechanical zenith error problems WORSE.
Some people claim to hear significant differences when changing SRA by small amounts. I would add that what they are hearing is the multiplying effect of rake angle changes on their already existing zenith error. If they use a free rolling unipivot then there are at least FOUR other conditions that are changing as well when tonearm height is changed.
Videos and mathematical proof to come soon
Thanks for bringing out the importance of that horizontal line. I always have difficulty determining exactly where that line is even if I place a toothpick lined up (?) with the long edge of the cartridge body.
I'll show everyone soon how to measure the rake without having a platform from which to generate the horizontal reference line at all. I need time to finish the WallyScope.
Until then, get that stylus on the VERY PRECIPICE of your platform. This is one of three good reasons why I always use a "stylus slide" (as shown in my webinar) to drop the stylus onto. You can use a tiny strip of a playing card but make sure the edge facing the scope is a clean, new cut. Don't touch that edge so as to keep the fibers down and laying nicely.
The stylus slide:
1. allows the cantilever to fully relax since it will slide forward when the stylus lands on it
2. keeps the stylus from generating a chip of the platform material at its leading edge. It even takes a divot out of aluminum!!! This is why you don't lower a stylus to a non-moving record. If it makes it into the groove you have an instant pop you'll hear every time you play that record in that spot.
3. It allows you something to bring the stylus to the VERY, VERY edge of without worry about sliding off and down into some abyss. It will drop a total of 0.25mm or so. Big deal!
The reason you need that stylus at the VERY edge of the stylus slide is so that the stylus AND the horizontal reference (the stylus slide) can be simultaneously in focus.
I have seen some people focus first on the platform, place the horizontal reference line and then focus on the stylus with the horizontal reference line already laid down and then the angles of the stylus measured against the horizontal reference line. This will NOT work. Something called telecentricity error makes this process very inaccurate.
J.R. Boisclair,
do you know this tool being more exact than the Fozgometer.
best
E.
www.AudioCirc.com
do you know this tool being more exact than the Fozgometer.
best
E.
www.AudioCirc.com
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Hello @airbearing
I have no direct experience with the Audio Circ unit so I couldn't tell you what I think of it. It sure looks cool!
The quality and engineering of the test record itself is also very important. The test is disadvantaged if the tone track was done at the wrong amplitude (since varying coefficient of friction will cause axial forces on the coil assembly to vary) or the wrong radius. Further, the azimuth test results will not be optimized if zenith error is present.
For a lot less you could get a digital oscilloscope and then you'd be able to use that for many other things.
As for stencils to determine angular relationships of the armwand and cantilever, I consider them to be not at all valuable. The only thing that matters is the angular relationship between the contact edges of the stylus and the groove wall as that is where and how the information is collected from the groove. A stencil will tell you nothing about that. Use of a stencil is putting blind faith in the cartridge manufacturers precision - which we know is not particularly good. Further, I have seen several cases where the armwand was not parallel with the underside of the headshell - which is where your angular reference for "level" should be. So, putting your faith in the tonearm manufacturer's precision is iffy too.
I hope that helps.
Hello J.R.,
the test tone was done at correct amplitude. The test LP is cut for 33 on one side and for 45 at the other side. The PDA works pretty well. Nevertheless you may correct a bad Azimut by ear too. It may need some experience but it is possible. In case you need clarity the PDA is a helpful instrument and much more serious than the Fozgometer (I have it and tried it).
i do have a digital oscilloscope. The only problem is you cannot compensate a wrong needle-zenith. All experiments in compensating cause too much collateral damage in other variables.
I am curious in learning from you what correction attempts you are proposing?
best
E.
www.AudioCirc.com
the test tone was done at correct amplitude. The test LP is cut for 33 on one side and for 45 at the other side. The PDA works pretty well. Nevertheless you may correct a bad Azimut by ear too. It may need some experience but it is possible. In case you need clarity the PDA is a helpful instrument and much more serious than the Fozgometer (I have it and tried it).
i do have a digital oscilloscope. The only problem is you cannot compensate a wrong needle-zenith. All experiments in compensating cause too much collateral damage in other variables.
I am curious in learning from you what correction attempts you are proposing?
best
E.
www.AudioCirc.com
Attachments
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I would be very interested to know how they determined the proper amplitude for a 1kHz signal to replicate the coefficient of friction of an "average" amplitude groove with musical content. I know how it could be done, but it requires a laboratory setup and some experimentation. Perhaps there is a simpler way I do not know of.
Actually, it IS possible to correct for the +-5 degree zenith tolerance that at least one high-end stylus/cantilever assembly manufacturer had the guts to admit to. (I have shared that link in this forum before.) Unfortunately, measuring zenith error needs a very expensive microscope and a good deal of training to remove distortions caused by illumination and polarization. I've been doing this for the past year in my lab. I am, however, working on an alternative for everyone else who does not have a microscope that costs the same as a nice car.
Once the zenith angular error is known, the WallyZenith offers the ability to correct for it. Most headshells offer 4.5 to 5.0 degrees of correction but I have seen multi-thousand dollar cartridges with more error than 5 degrees that I had to condemn.You could probably get "in the neighborhood" of a cartridge's zenith error with a basic high-school level microscope (not a USB) but you couldn't reliably measure the angle at all due to microscope telecentricity error and other problems with focus stacking.
So, I don't think I understand your comment that "All experiments in compensating cause too much collateral damage in other variables." I assume you are referring to zenith error compensation.
I invite your thoughts.
One other thing: your usb scope is angled upward so the measurable facets of the stylus are obscured from view by the platform edge. Check out our webinar for more tips, but you could wait for the WallyScope that is just a couple weeks out from release and it will give you far better resolution, magnification and control.
JR and all,
Ian, I've used a pencil lead placed behind the stylus. Long leads are better for visual guesswork.
I've used the Dino-Lite microscopes as their software will give angle measurements. Getting the lens parallel to the stylus and perpendicular to the platform requires a fine degree of adjustment that is very difficult, frustratingly difficult - to the point that I alwalys have doubt about stylus rake angle measuments using that method. It would be nice if the USB camera had even a horizontal and vertical bubble level.
JR, It would seem you are saying that correct zenith is a necessary condition to optimal SRA.
Zenith is a confusing word for me. When you talk about zenith (zenith error, zenith tolerance, etc.), what is the object of your sentence?
Are you talking about the yaw axis of the cantilever relative to a line on your tractor of choice? Or the yaw axis of the stylus tangent to the groove? Or something else entirely?
The language of pitch, roll, and yaw seems more straightforward, imo.
Hi @tima. I'd put it another way: slight rake angle errors aren't terribly problematic in the absence of zenith and/or tracing error (see below on what the difference is). If zenith/tracing error is present then any rake error makes the zenith/tracing mechanical errors a good deal worse. We'll soon share the formula defining what "slight" and "a good deal" means.
I don't care much for the term either. Since very few people are talking about it right now (though I think it will be common knowledge amongst vinylphiles in the near future) perhaps we can coin a better term. I'm open to suggestions.
Zenith Error: the two-dimensional angular deviation from perpendicularity between the cantilever and the groove contact edges of the stylus when the stylus is viewed with its apex (technically, "vertex") aiming directly at the viewer. Zenith error is FIXED in the immutable bond between stylus and cantilever. It cannot be changed or affected by the user.
which is different from...
Tracing Error: the two-dimensional angular deviation from perpendicularity between the radial line of the record and the groove contact edges of the stylus when the stylus is viewed with its apex ("vertex") aiming directly at the viewer. Tracing error is DYNAMIC and changes as a pivoted tonearm traverses the record surface. Theoretically, tracing error is FIXED on a linear bearing tonearm if setup has been done properly and the tonearm design is a good one (many are not!).
Here's a more advanced consideration for those interested: Tracing error is also affected by Zenith error. For example, if a cartridge that is mounted to a 9" tonearm has a 2 degree clockwise zenith error then the tracing error at the null points will be 2 degrees and will go down to as little as 0.9 degrees error at the innermost point of maximum angular error and up to 3.8 degrees error at the outermost point of maximum angular error.
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