The Ortofon Replicant 100 geometry

ack

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In this thread post on down, we are discussing which side of the Replicant 100 stylus is relevant in calculating SRA off of vertical, and bblue said:

I had always assumed the right side of the tip was the actual angle of concern
and I had agreed. Here's my picture again, depicting vertical stylus:

a90-stylus-1..jpg

I thought continuing that investigation merits a new thread, so here it goes...

I am quite certain the Replicant 100 stylus is a variation of the Fritz Gyger stylus, with [major/minor radii] R/r 100/5 microns (hence the name), instead of the typical 80 (wasn't there a Replicant 80 before???). US patent US4855989 (pdf) is a translation of the original European and makes the following claims:

1. A stylus for tracking stereophonic and quadrophonic sound grooves of gramophone records, comprising:
a stylus body having a tip, the tip of the stylus having at least one substantially flat surface which forms a front side of the stylus facing forward along said sound grooves during tracking, the stylus being prismatic with a square cross-section and having a surface forming the tip defining a shaped section with tracking edges, the shaped section having facets disposed diagonally to a longitudinal axis of the stylus, the flat surface forming the front side of the stylus leading in the direction of tracking along the grooves.2. A stylus according to claim 1, wherein the shaped section of the tip has a cross-sectional shape defining an isosceles triangle.
3. A stylus according to claim 1, wherein the shaped section of the tip has a cross-sectional shape defining a trapezoid.
4. A stylus according to claim 1, wherein the shaped section of the tip has a cross-sectional shape defining a circular section.
5. A stylus according to claims 2, 3 or 4, wherein the tip has a facet which corresponds to a base line of said cross-sectional shape, defining said front side of the stylus.
The underlined is the most critical point here... Figures 4, 5, 6 and 7 are variations of the invention:

gyger-1..jpg
gyger-2..jpg

while the following figures show mounting options - figure 9 applies to how Ortofon mounts their stylus, and verifies my picture above:

gyger-3..jpg

The patent is short and very worth reading, as it also discusses its relation to a cutting stylus - Figure 3; notice the sole flat side:

gyger-4..jpg

Therefore, the SRA calculation technique for the A90 using trigonometry discussed in that other thread is sound (and applicable to all styli), if one can assert perfect stylus vertical to start with, and that requires a USB microscope.

I decided to look into all that after reading yet another confusing claim by Ortofon, this time on setting SRA on the new Anna:

The Stylus Rake Angle (SRA) is very important to the performance of the Replicant 100 stylus, and the long contact surface (the sharp edge) of the diamond should be close to perpendicular to the record surface when viewed from the side.
 

cjfrbw

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That is very interesting. It looks like the replicant has its right angle in the stylus itself rather than the cantilever/stylus like the other illustration. I does appear that it might be difficult to mount that way since trying to visualize a tiny stylus and its right angle at the tip is a lot harder than seeing the large bend in the cantilever.
 

ack

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I need to examine the stylus closer under my USB microscope, to see which implementation they've chosen. Unlike other shapes, I would imagine the Gyger is really susceptible to proper SRA, because looking at any figure, say figure 5, the flat facets 13 and 14 are the ones in contact with the grooves, and ideally they should be in contact in their entirety. Because they are flat, that means EXACTLY one ideal SRA angle for this to happen, per record - major OUCH.

I have to assume their implementation includes a trapezoid at the base, as in figures 5 and 7, so as to avoid touching the bottom of the groove - in fact, the A90 is exemplary at reducing surface noise and I suspect it's because of the whatever trapezoid they included in the cut. But clearly, because the contact facets (e.g. 13 and 14) are flat, this stylus can have really superior contact with the groove.
 

bblue

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I need to examine the stylus closer under my USB microscope, to see which implementation they've chosen. Unlike other shapes, I would imagine the Gyger is really susceptible to proper SRA, because looking at any figure, say figure 5, the flat facets 13 and 14 are the ones in contact with the grooves, and ideally they should be in contact in their entirety. Because they are flat, that means EXACTLY one ideal SRA angle for this to happen, per record - major OUCH.
Excellent analysis, ack. These types of patents seem to only say just enough to get the patent, but not enough that it answers all the questions.

I had assumed (by picture comparisons) some time ago that the Replicant for all intents and purposes IS a Fritz Gyger-type stylus. And initially, at least, assumed it was a long straight-line whose vertical angle would be crucial to the SRA of the cutting stylus. And there does turn out to be a pretty sharp point (range) where the SRA is 'just right'. However, what has continually surprised me is how generally acceptable the sound is when the angle is fairly far off. It isn't 'right' but it isn't horrible, either. And you'd think it would be.

I have to assume their implementation includes a trapezoid at the base, as in figures 5 and 7, so as to avoid touching the bottom of the groove - in fact, the A90 is exemplary at reducing surface noise and I suspect it's because of the whatever trapezoid they included in the cut. But clearly, because the contact facets (e.g. 13 and 14) are flat, this stylus can have really superior contact with the groove.
Yes sir!

I have some additional bright side-lighting coming so I can use an overhead microscope on an articulating arm to really zero in on the tip. I'm not sure there's enough detail on the Dino-Scope types. And there may not be enough on my overhead either, but it might prove useful in some way.

--Bill
 

ack

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However, what has continually surprised me is how generally acceptable the sound is when the angle is fairly far off. It isn't 'right' but it isn't horrible, either. And you'd think it would be.

Excatly, my experience as well.

I have some additional bright side-lighting coming so I can use an overhead microscope on an articulating arm to really zero in on the tip. I'm not sure there's enough detail on the Dino-Scope types. And there may not be enough on my overhead either, but it might prove useful in some way.

--Bill

Eagerly awaiting to see these. Basically, what we need to see is that very trapezoid and hopefully measure the angles it forms with the side contact facets (13 and 14) as well as that vertical facet we are talking about (the patent only discusses ranges for these angles). Because when SRA is exactly correct, the entire trapezoid will fit at the bottom of the groove and the contact sides will have maximum contact with the sidewalls. Therefore, I suspect we will discover a very narrow trapezoid as in Figure 7 - as close to a rectangle as possible, without still touching the very bottom of the groove - because geometrically that's what would fit the groove best. At least that's the theory, subject to revision :)

We should then be able to calculate an SRA that would make all facets fit perfectly, and I still haven't thought what a good reference groove would look like (not sure that it matters either)

Basically, this is still all geometry to me, but still an approximation (because of the affected VTF et al discussed in the other thread, which affect the angle), but it's better to have an accurate mathematically-derived range to play with than nothing.
 
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ack

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Speaking of all major points raised in this and the parent thread:

  • the Replicant being a Gyger-variant profile;
  • calculating SRA mathematically using the arm's effective length & trigonometry; and
  • the stylus's profile being the ultimate determinant of proper SRA
I went back and re-read Fremer's article from 2009 in Stereophile, and I couldn't agree with him more on the following points below:

  1. Unfortunately, to properly set SRA you need to know the stylus-profile contact patch of your cartridge
  2. As recently pointed out in this column, the Ortofon Replicant stylus, a Geiger variant...
  3. What we need—what we should demand to know from every cartridge manufacturer—is the precise stylus profile and a drawing of the contact patch area, so that we can more accurately achieve the required 92° SRA
  4. One technique worth considering is to set the SRA to 90°—that is, with the shank of a symmetrically configured stylus sitting perpendicular (at a right angle, or 90°) to the record surface. Try using a mirror to achieve a straight line, much as you might to get an approximation of azimuth. Then, if your tonearm’s effective length is, say, 239mm (Rega, etc.) [ack: e.g. a 9 inch arm] and you move the arm pivot up (a considerable) 8.35mm from perpendicular, you’ve increased the SRA by 2°, to the desired 92°. Mathematically competent readers should be able to calculate how much to move the pivot for any tonearm’s effective length.
  5. if you don’t start close to the correct angle, you’ll never get it right—when you’re far off, you can’t possibly hear a difference until you somehow luck in to the correct zone.
Finally, the Replican't picture he includes in the article matches exactly what we said above - I don't know how I missed this... So all credit really belongs to Fremer... I just came from another angle with much more detail, plus we are now trying to extend on all this and figure out the tip's exact profile to determine the proper SRA range...

replicant-fremer&#4.jpg
 
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ack

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Gyger tip profile

Thanks Rich...

I wanted to document a bit more Figure 7 of the Gyger tip, so I drew the following profile (sideview) diagram, to see how it works:

gyger-drawing-si&#1.jpg

  • Angle A0 = 15-30 degrees as per patent; unknown yet what Ortofon may have chosen
  • Trapezoid width: 5um at the tip, 100um at the other wide end - I assume this is what Ortofon refers to as the R/r radii
  • We don't really know where the top of the groove is
Also refer to this image I borrowed from vinylengine.com:
ortofonreplicant&#.jpg

Observations:

  • As SRA is adjusted - and because the trapezoid (facet 38) facing the groove bottom widens at the back - the cartridge tip should be raised further away from the bottom of the groove - probably less surface noise
  • Correcting what I said earlier, there is no reason why Facet 38 - the trapezoid - should be parallel to the bottom of the groove, for proper SRA
  • Because Facet 33 is flat and because it shrinks at the back (on the left), adjusting SRA results in slightly varying contact area - not sure this has much audible effect.
  • Facet 33 must shrink to be able to adjust SRA (don't want a rectangle)
  • We hope that for SRA range 0-2 degrees the contact is anywhere between the tip and the back of Facet 33. One probably must not adjust SRA beyond the back of Facet 33. Thus, proper SRA adjustment looks like an extremely narrow range
Hopefully we can get a drawing of the actual Replicant 100 for further analysis...
 
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bblue

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Something is wrong here. SRA should have the stylus pointing back toward the arm pivot up to 2 degrees. That's a requirement of the cutter head to produce a smooth and catchable 'thread' of acetate while it's cutting. VTA is also the same direction but is variable based on the pivot angle of the cutter stylus assembly, independent of SRA. VTA can only be mimicked by the pivot angle movement of the stylus. SRA is the most audible of the two and the only one you can accurately set per record.

If I'm understanding the picture above, the supposed facet 39 angle is the wrong direction. I don't see what it would be accomplishing. In the drawing, the vertical reference is actually the one that would tilt ccw (tip toward pivot) up to 2 degrees to mimic the SRA of the cutting stylus.

Am I missing something?

--Bill
 

ack

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Something is wrong here. SRA should have the stylus pointing back toward the arm pivot up to 2 degrees. That's a requirement of the cutter head to produce a smooth and catchable 'thread' of acetate while it's cutting. VTA is also the same direction but is variable based on the pivot angle of the cutter stylus assembly, independent of SRA. VTA can only be mimicked by the pivot angle movement of the stylus. SRA is the most audible of the two and the only one you can accurately set per record.

If I'm understanding the picture above, the supposed facet 39 angle is the wrong direction. I don't see what it would be accomplishing. In the drawing, the vertical reference is actually the one that would tilt ccw (tip toward pivot) up to 2 degrees to mimic the SRA of the cutting stylus.

Am I missing something?

--Bill

In a way, the drawing is a bit misleading, but I think it is depicting exactly what you said; increasing the real SRA off vertical by lifting the arm results in a counter-clockwise motion, which effectively "drops" or decreases the angle I show as the SRA angle range. Keep in mind, in geometry the same angle can appear in many places. I put the angle there to indicate such a range and actually show that you may not want to go beyond a point where the trapezoid facet 38 is parallel to the groove bottom (because there would be no real tip tracking the grooves anymore).

On the other hand, admittedly, it's not entirely clear whether the tip and facet 39 are to the right and close to the vertical reference as shown in my diagram, or the opposite left side. However, I put the tip and facet 39 close to the vertical reference as shown, based on two things:

  1. Putting the tip on the left means the larger 100um side of the trapezoid would be on the right, thus it might be awkward for that kind of cartridge to track with that larger side of the trapezoid, _until_ one adjusts SRA higher - surely, this might be a big assumption
  2. My interpretation on the patent's claim that: a stylus body having a tip, the tip of the stylus having at least one substantially flat surface which forms a front side of the stylus facing forward along said sound grooves during tracking, the stylus being prismatic with a square cross-section and having a surface forming the tip defining a shaped section with tracking edges, the shaped section having facets disposed diagonally to a longitudinal axis of the stylus, the flat surface forming the front side of the stylus leading in the direction of tracking along the grooves

"Front side" and "Leading in the direction of tracking" to me implies facet 39 as shown - I took that to be the "substantially flat surface" because: a) it's the only such facet marked in the patent drawings; and b) it's a derivative of (i.e. a continuation of) the vertical reference - which to me is also "leading" and is the only such facet that's meaningful in measurements - when you go from Figure 3 to Figure 7 (F7 is a specialization of F3). If that's not the case, the patent doesn't make it obvious to me.

Let me know if I misunderstood something, which is quite possible...

EDIT: BTW, I just got confirmation from Ortofon that the vertical reference is indeed the one we've been talking about and shown in our pictures, and SRA is naturally off of that
 
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bblue

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In a way, the drawing is a bit misleading, but I think it is depicting exactly what you said; increasing the real SRA off vertical by lifting the arm results in a counter-clockwise motion, which effectively "drops" or decreases the angle I show as the SRA angle range. Keep in mind, in geometry the same angle can appear in many places. I put the angle there to indicate such a range and actually show that you may not want to go beyond a point where the trapezoid facet 38 is parallel to the groove bottom (because there would be no real tip tracking the grooves anymore).

On the other hand, admittedly, it's not entirely clear whether the tip and facet 39 are to the right and close to the vertical reference as shown in my diagram, or the opposite left side. However, I put the tip and facet 39 close to the vertical reference as shown, based on two things:

  1. Putting the tip on the left means the larger 100um side of the trapezoid would be on the right, thus it might be awkward for that kind of cartridge to track with that larger side of the trapezoid, _until_ one adjusts SRA higher - surely, this might be a big assumption
  2. My interpretation on the patent's claim that: a stylus body having a tip, the tip of the stylus having at least one substantially flat surface which forms a front side of the stylus facing forward along said sound grooves during tracking, the stylus being prismatic with a square cross-section and having a surface forming the tip defining a shaped section with tracking edges, the shaped section having facets disposed diagonally to a longitudinal axis of the stylus, the flat surface forming the front side of the stylus leading in the direction of tracking along the grooves
Well this is where I start losing what the text says. The large flat side which is currently shown on the right, is at the rear of the stylus, with the groove meeting it first as the record turns CW.

Given that, then A0 and what you have marked as the SRA are the wrong angle, flipped backwards. Or perhaps I'm just not seeing the 2D lines in the right context.

And with the flat side seeing the groove first, exactly what is the function of the additional slope show as facet 39, which would be at the front of the stylus and not relevant to contact to the groove walls?

Do you see what my issue is? Also, when you say that an angle moves the stylus up in the groove, how is that accomplished? I don't see any mechanism for that other than the rounded off tip of the stylus. It doesn't seem like we would have any control of the height at which the stylus rides, only the angle at which it follows the (almost) up and down vertical movement of the stylus, as well as nesting perfectly with the groove wall while moving laterally.

"Front side" and "Leading in the direction of tracking" to me implies facet 39 as shown - I took that to be the "substantially flat surface" because: a) it's the only such facet marked in the patent drawings; and b) it's a derivative of (i.e. a continuation of) the vertical reference - which to me is also "leading" and is the only such facet that's meaningful in measurements - when you go from Figure 3 to Figure 7 (F7 is a specialization of F3). If that's not the case, the patent doesn't make it obvious to me.

Let me know if I misunderstood something, which is quite possible...

EDIT: BTW, I just got confirmation from Ortofon that the vertical reference is indeed the one we've been talking about and shown in our pictures, and SRA is naturally off of that
I wonder why, then, they state that it should be perpendicular rather than raked slightly. Just dumming down for simplicity, or it's close enough, or what? Maybe I'm just taking things too literally. It wouldn't be the first time...

--Bill
 

ack

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Well this is where I start losing what the text says. The large flat side which is currently shown on the right, is at the rear of the stylus, with the groove meeting it first as the record turns CW.

Given that, then A0 and what you have marked as the SRA are the wrong angle, flipped backwards. Or perhaps I'm just not seeing the 2D lines in the right context.

And with the flat side seeing the groove first, exactly what is the function of the additional slope show as facet 39, which would be at the front of the stylus and not relevant to contact to the groove walls?

A0 has nothing to do with SRA - it's a somewhat random angle; rather, the vertical reference is sloped near the tip as per Fig7, by 15-30 degrees as specified in the patent, forming Facet 39 and the angle A0 shown. It's that facet (along with the vertical reference by extension) that first meets the grooves about to be tracked, and its purpose is to pick up and move away dirt. See also the vinylengine picture. The SRA range simply depicts a range where, when adjusting SRA, groove contact along Facet 33 could be anywhere between the tip area and the opposite wider end of the trapezoid (see Facet 38); you probably don't want to adjust SRA beyond a certain point where contact would fall beyond the wider end of the trapezoid, that's all.

Also, when you say that an angle moves the stylus up in the groove, how is that accomplished?

Don't forget Facet 38 which is a *trapezoid*, that gets _wider_ away from the tip... does this cross section help?

gyger-cross-sect&#10.jpg

In the bottom drawing you are looking at the wide side of the trapezoid, therefore the tip (5um side) has also moved up (it can't possibly sit lower than the 100um side). Am I making sense?

I'll grant you one thing... if you look at Figure 7 closely, the trapezoid shown face up is in fact Facet 38, and although there is an arrow pointing to it, the actual text is missing - but, if you read the patent's text further down, it describes how the tip 31 is formed by facets 33, 34, 38 and 39 (and thankfully all others are marked)... this is confirmed by the vinylengine picture. Contrast with Figure 5 which clearly annotates the trapezoid (as facet 18).

I wonder why, then, they state that it should be perpendicular rather than raked slightly. Just dumming down for simplicity, or it's close enough, or what?

If you go back to the original post of the thread, the Anna manual text reads "should be close to perpendicular" - vague as always; then I asked them if the side they are talking about is the vertical one in my original picture taken with the microscope, and they confirmed that, as expected. They did not provide any more detail on what "close to" means; probably dumbing down as you said.

I find the stylus's design incredibly well thought-out from a geometry standpoint; I mean it's fascinating how simple it looks, yet how many problems it solves with geometry. What I don't know is how it compares with respect to intermodulation distortion against other profiles... There are times I wish I had an IMD measuring device to set SRA and measure overall IMD and be done with it.

So what we haven't discussed yet is this stylus's drawbacks and advantages - the tip, the shank, and overall mounting...
 
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MylesBAstor

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I don't know what's spinning faster: the record or my head ;)
 

ack

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bblue

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A0 has nothing to do with SRA - it's a somewhat random angle; rather, the vertical reference is sloped near the tip as per Fig7, by 15-30 degrees as specified in the patent, forming Facet 39 and the angle A0 shown. It's that facet (along with the vertical reference by extension) that first meets the grooves about to be tracked, and its purpose is to pick up and move away dirt. See also the vinylengine picture. The SRA range simply depicts a range where, when adjusting SRA, groove contact along Facet 33 could be anywhere between the tip area and the opposite wider end of the trapezoid (see Facet 38); you probably don't want to adjust SRA beyond a certain point where contact would fall beyond the wider end of the trapezoid, that's all.
emphasis mine. I think you're over thinking it. There is nothing that the groove meets whose intentions are to move away dirt. The very first thing encountered by the groove is the leading flat wall (15 in fig 5 and 39 in fig 7). The edges of that wall (16 and 17 in fig 5, 36 and 37 in fig 7) actually make contact to the groove wall. Their rounding (contour) affects the size of the scanning radius of the stylus which affects how high a frequency and amplitude it can scan. Fig 3 has the smallest scanning radius and would likely have the highest resolution, followed closely by the shape of Fig 5 and Fig 7. All the other angles are likely designed to help with cutting the surfaces to produce a rugged stylus shape. I don't believe facet 33 would ever have contact with a groove wall unless high frequency and amplitude exceeded its scanning capability.

I really don't see the relevance of the height of the tip from the bottom of the groove, and don't see how it would change significantly other than with gross misalignment of SRA. All we can do with SRA is optimize the matching of motion between the cutting stylus and playback stylus, which if it was perfect would be the lowest to the bottom of the groove, limited by the radius of the tip.

I'm no geometry expert (at all) so perhaps I'm oversimplifying some more subtle points, but it all seems pretty straightforward.

Don't forget Facet 38 which is a *trapezoid*, that gets _wider_ away from the tip... does this cross section help?

In the bottom drawing you are looking at the wide side of the trapezoid, therefore the tip (5um side) has also moved up (it can't possibly sit lower than the 100um side). Am I making sense?
Neither of these points are making sense to me.

I'll grant you one thing... if you look at Figure 7 closely, the trapezoid shown face up is in fact Facet 38, and although there is an arrow pointing to it, the actual text is missing - but, if you read the patent's text further down, it describes how the tip 31 is formed by facets 33, 34, 38 and 39 (and thankfully all others are marked)... this is confirmed by the vinylengine picture. Contrast with Figure 5 which clearly annotates the trapezoid (as facet 18).
Yes, but that angle only helps define the scanning radius of the edges, and seems to be there more for mechanical support and to help with smooth and gradual wearing of the radius (edges).

If you go back to the original post of the thread, the Anna manual text reads "should be close to perpendicular" - vague as always; then I asked them if the side they are talking about is the vertical one in my original picture taken with the microscope, and they confirmed that, as expected. They did not provide any more detail on what "close to" means; probably dumbing down as you said.

I find the stylus's design incredibly well thought-out from a geometry standpoint; I mean it's fascinating how simple it looks, yet how many problems it solves with geometry. What I don't know is how it compares with respect to intermodulation distortion against other profiles... There are times I wish I had an IMD measuring device to set SRA and measure overall IMD and be done with it.
You and me both!

So what we haven't discussed yet is this stylus's drawbacks and advantages - the tip, the shank, and overall mounting...
To me, the tip's major strength is its robustness, at a slight compromise in high frequency high amplitude scanning. Fig 3 tip has the edge there, but would not be as rugged.

This cartridge/stylus does have high amplitude lateral tracking/tracing issues which are very difficult to tame down. I'm not sure of the cause and you don't hear it (or see it on XY) on most well recorded records. But those that are pushed hard in the center channel (mono, lateral movement) with sibilance or other HF content will cause it to lift upwards (not stay seated) in the groove. In both of my A90's in three different arms and a variety of adjustments and tuning I've never yet gotten that tendency to go completely away. Yet a cartridge/Stylus like a Zyx Airy 3 has no problems with the same passages. They claim very close to the same horizontal/vertical compliance.

--Bill
 

ack

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I think you're over thinking it. There is nothing that the groove meets whose intentions are to move away dirt. The very first thing encountered by the groove is the leading flat wall (15 in fig 5 and 39 in fig 7). The edges of that wall (16 and 17 in fig 5, 36 and 37 in fig 7) actually make contact to the groove wall. Their rounding (contour) affects the size of the scanning radius of the stylus which affects how high a frequency and amplitude it can scan. Fig 3 has the smallest scanning radius and would likely have the highest resolution, followed closely by the shape of Fig 5 and Fig 7. All the other angles are likely designed to help with cutting the surfaces to produce a rugged stylus shape. I don't believe facet 33 would ever have contact with a groove wall unless high frequency and amplitude exceeded its scanning capability.

I can see clearly now what you are saying - you are correct. Contact is only made by edges 16/17 or 36/37 indeed; they are rounded to 3-8um per patent and polished. Therefore, Facet 39 is actually the vertical reference. And the tip is rounded to 5um per patent to provide clearance from the groove bottom. Moreover, the vinylengine picture is correct as is my marking of Facet 39, except that I missed that the shank of the stylus is mounted perpendicular to the cantilever which is angled - and the patent makes it explicit that Figures 6 and 7 have the advantage of mounting the stylus perpendicular to the cantilever, as is shown in my picture in the original post.

Therefore the vinylengine picture tells the whole story and clearly shows the two edges that make contact - however, all of that means that what I've been reading about this stylus having larger contact area is actually not true: it touches the groove with very narrow edges... correct?

Here's the corrected diagram which now matches Fremer's paperweight model:

gyger-drawing-si&#1.jpg

Finally, here's something else I just noticed... recall, the patent says such a stylus can be mounted perpendicular to the cantilever, as in my original picture at the start of the thread... Well, it's tough to achieve that, so as you can see, I measure an angle TA1 of roughly 93.8, or 3.8 degrees off prescribed vertical. I wonder if that error, in turn, is in fact responsible for the VTA (TA2) measuring ~25.9, instead of Ortofon's claim of ideal 23 degrees (and at that point my VTF was ~2.4g).

One thing is quite clear - one needs a microscope to get that vertical reference, and from there adjust SRA.

@Mike - I will post a summary soon...
 

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I wonder if the little down?minus VTA adjustment that the Blue Angel Mantis needs to sound at its best has to do with this geometry analysis... great and informative reading! Thanks ack.
 

ack

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Summary of observations

Here's my summary - others feel free to post your own:

  1. The Gyger stylus, which the Replicant is a variant of, attempts to closely mimic a cutting head at the tip
  2. The cutting head has a flat, vertical facet (CF) facing the grooves about to be cut, and the Gyger has a similar facet (GF) facing the grooves about to be tracked
  3. CF has two sharp edges that form the groove walls, forming some angle CA between them (probably CA=90)
  4. Gyger's GF tracks with similar but rounded edges (3-8um radius, polished), which form an angle between them GA < CA
    • They must be rounded so as to not damage the grooves and the tip itself
    • Contact area with the grooves is likely smaller than the cutting head's, because GA < CA
    • The low life expectancy of the stylus (up to 1000hrs) is probably related to it tracking with edges and not a larger surface area
  5. The cutting head - and consequently CF - is then tilted off vertical, forming some SRA S1, and so must be the Gyger's GF
Refer to the following images before adjusting SRA (thanks to vinylengine and the patent):

gyger-tip-2..jpg
gyger-3-1..jpg

To set SRA with the Gyger:

  1. Use a USB microscope to assert vertical reference (vertical GF) - side profile works well
  2. Adjust SRA from there
    • I like and use the mathematical model discussed in the parent thread and the original A90 thread from2010
    • The model maps _desired_ SRA to arm travel, based on a calculated effective arm length - it simply enables one to very predictably adjust things
    • However, it is still an approximation, because VTF is also inevitably affected, which imposes its own change in the SRA angle. Fremer claims that, generally speaking, a 1g of VTF change results in a ~1 degree SRA angle change; you can probably use a linear formula for this
    • I contend SRA adjustment should still be within the recommended VTF range
    • It was hard for me to adjust SRA with the microscope, due to its low resolution, and it's really time consuming
Refer to the following images:

a90-vertical..jpg
a90-stylus-2..jpg

Fremer's article is a great reference and he makes points that I completely subscribe to...
 

bblue

Well-Known Member
Apr 26, 2011
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San Diego, CA
I can see clearly now what you are saying - you are correct. Contact is only made by edges 16/17 or 36/37 indeed; they are rounded to 3-8um per patent and polished. Therefore, Facet 39 is actually the vertical reference. And the tip is rounded to 5um per patent to provide clearance from the groove bottom. Moreover, the vinylengine picture is correct as is my marking of Facet 39, except that I missed that the shank of the stylus is mounted perpendicular to the cantilever which is angled - and the patent makes it explicit that Figures 6 and 7 have the advantage of mounting the stylus perpendicular to the cantilever, as is shown in my picture in the original post.

Therefore the vinylengine picture tells the whole story and clearly shows the two edges that make contact - however, all of that means that what I've been reading about this stylus having larger contact area is actually not true: it touches the groove with very narrow edges... correct?
Well, yes, but the height of the contact area is quite high vertically, so that is the key issue. The sharp 'edges' determine the scanning radius, not (directly) the contact area.

I'm totally lost on what your new diagram is supposed to be showing. It certainly doesn't seem to be depicting the operational position of the stylus at all.

Here's the sharpest closeup I can make with this Dino-scope showing a floating A90 stylus:

a90 129 vtf 0g_cr..jpg

Note that the total flat surface (with no facet 39) is riding in the groove. If there is a facet 39 it's on the trailing edge of the stylus. The entire flat edge is the vertical face that should reflect SRA adjustment. I can't tell what the shadow is at the very bottom of the tip.

My overhead scope lights should be here in a few days, so maybe I can get closer and more detailed then.

Finally, here's something else I just noticed... recall, the patent says such a stylus can be mounted perpendicular to the cantilever, as in my original picture at the start of the thread... Well, it's tough to achieve that, so as you can see, I measure an angle TA1 of roughly 93.8, or 3.8 degrees off prescribed vertical. I wonder if that error, in turn, is in fact responsible for the VTA (TA2) measuring ~25.9, instead of Ortofon's claim of ideal 23 degrees (and at that point my VTF was ~2.4g).
I don't know if that assumption can be made when the stylus in the right position.

One thing is quite clear - one needs a microscope to get that vertical reference, and from there adjust SRA.
Quite so.

Incidentally, this detail is how I initially set up any cartridge. Sometimes it's not so obvious as the A90 and you have to look for reflective edges or little fins as the contact points, but it's the same principle. For ellipticals you really can only guestimate based on the center line perpendicularity of the whole tip.

--Bill
 

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