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the thin end of the wedge

On the SPHERICAL/CONICAL stylus

Postby flavio81 » 10 Nov 2009 16:33

Now, a few words on the Spherical Stylus:

The spherical stylus (also called "conical") is the oldest stylus design for LP play. It is used extensively and it was the only shape available until the elliptical was invented and manufactured.

The spherical stylus is simply ball-pointed shaped at the tip end. Thus it is a sphere of typical radius= 18 micron (uM) or 0.7mil.

Example of a real spherical - Stanton DJ stylus
Image

Spherical sometimes come in different radii, typically less than 18uM. In this way the stylus can trace the unworn parts of the vinyl groove. A good idea.

The 25uM stylus is made for mono records play. 65uM for 78RPM records.

So, what is the problem with the spherical? It is perfectly explained in this excellent web page by Jim Lesurf:
http://www.audiomisc.co.uk/HFN/LP3/aroundthebend.html

But i will hijack some of the pictures to summarize what is explained on that page.

The problem with the spherical is this:

Left blue spot - 12uM spherical
Right one - 8x18uM elliptical
The diagram shows a 20KHz 0dB groove at the start of the LP side. A very high frequency at a very loud level. The modulation is horizontal (mono).

Image

So, as you can see, the spherical stylus is too big to trace the 20KHz tone correctly. What will happen? The spherical will "jump" or ride the wave "vertically" and thus give "tracing distortion". Specifically we are showing what is called "the pinch effect".

Also note that the stylus on this diagram is of 12uM radius; usually they are bigger - 18uM being a typical value. But also note that 0dB is a very high (loud) recording level for a 20KHz tone!

The stylus at the right, 8x18uM (.3x.7mil) elliptical, fits much better and is not showing that problem. Thus you can see how the elliptical traces better.

In practice this problem does not appear (or it is not significant) at the beginning of the groove. It becomes a problem [mainly for sphericals] at the end of the groove, since the groove angular speed is much smaller and thus things are tighter!!

Here is a 20KHz 0dB at the end of the groove. Again, this is an extreme case; no sane cutting engineer would cut, at the end of the groove, such high levels at such high frequencies, though!!

Image

As you can see, the pinch effect would be extreme with a spherical and would even show with the elliptical, unless we use a narrower (smaller "r" radius) elliptical. Or a smaller spherical [not a good idea], or a more advanced stylus shape...

So what can be done to diminish this problem?? Alternatives for the cutting engineer:

(a) Tracing predistortion/ tracing compensation - while cutting the disk, a "tracing simulator" predicts the tracing distortion that will appear when the record is played, and adds, to the audio signal, the same distortion but in an inverse way so, when playing it with a spherical stylus of a specific radius , it will "cancel out".

Google "dynagroove". Tracing predistortion has been used in many records. If you have a clean, unworn record that sounds notoriously distorted with an elliptical, but sounds very well (undistorted) with a spherical stylus, you can bet it was cut with predistortion/tracing compensation. It will only sound good with a 0.7mil conical. Thus the importance of always having a spherical/conical stylus at hand.

(b) Introduce a strong cut-off (attenuation) of the high frequencies when approaching the end of the record and/or lower the cutting level significantly.

(c) Assume the listener will have a great tracking cartridge with an advanced stylus shape and be happy.

(d) I don't know. I'm not a mastering engineer.

However, again, this distortion will be much more evident:

- At the end of the record (inner grooves)
and
- At loud cutting levels

Returning to Jim Lesurf's article; he uses an estimate of the typical/max groove accelerations found on records (read his articles!) and makes the following graph:

Image

The curves shows what the maximum tip radius can be to safely "read" groove accelerations of a certain "g" (gravities), at the end of the record (red curve) and at the beginning of the record (blue curve).

As you can see, the problem -as i said before- is at the end of the record. But what about gravities? Jim Lesurf writes:

Looking back at the results in last month’s article we found that the largest peak accelerations observed were around 1000g. By using these results we can now assess what the demands may be on a replay stylus.


So he marks around 1200g with a green dotted line. That would be loudest level on a typical record. For 1200g at the end of the record you need 5uM (0.2mil) of side radius (r). And, coincidentally, the smallest profiled ellipticals sold are 0.2x0.7 mil!! But those narrow ellipticals also are the styli with the smallest contact areas (not a good thing); narrow profile and great contact area belong to... advanced stylus shapes.

Remember, a typical conical/spherical stylus is 18uM/0.7mil... Check out the graph and you will see that the typical conical will usually have a problem tracing the loudest parts at the end of the record, while performing fine at the beginning of the record.

That's why stylus comparisons should better be done using loud cuts at the end of the record!!

Again, this problem will be more or less noticeable depending on the cutting engineer choices at cutting the record. I have some records (usually from the start of the 60s) that perfectly OK at the inner grooves -- obviously because the cutting engineer knew everybody used spherical stylus (was there other choice before Grado's patent? :wink: ), and thus took care to significantly reduce cutting levels and high frequencies at the inner grooves.

Now, all this analysis has been with horizontal modulation (mono only). In stereo reproduction we have vertical and horizontal components, and things get more complex!
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Postby flavio81 » 10 Nov 2009 18:37

Now, on that ca. 1000g typical max acceleration value. On the very same web page (Jim's page):

Their [Shure's] chief engineer of the time also wrote an article that appeared in Hi Fi News. This said that they had surveyed a number of LPs and that the highest accelerations they could find were around 1500g, so they designed the V15 series to track these discs. From the values in the above table we can see that the requirements include a tip mass of less than or equal to 0·6 milligrams and a minor radius of less than or equal to 3·5 microns


Note that:

- The "Hi-fi" news article cited is from 1966. We can assume records were cut louder on the 70s and beyond, when the elliptical stylus was commonplace!! Telarc 1812 overture anyone?

- 0.60mg of tip mass has been bettered. For example Ortofon quotes X5-MC having 0.40mg tip mass, although the X1-MCP has 0.75mg tip mass. But the X1 is supposed to be a good tracker. Still, that's a truckload of ballast compared to (imho) the king of all cartridges, the Technics EPC-100CMK3 (moving magnet):

http://audio-heritage.jp/TECHNICS/etc/epc-100cmk3.html

Using high tech to achieve 0.098mg tip mass. Frequency response 5Hz-100KHz!! Take that, Ortofon...
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horizontal

Postby 1200y3 » 10 Nov 2009 19:20

I believe the spherical is best used with mono (lateral/horizontal) and is the only one to use on mono. (Any modern stylus should work, but imagine a sharp edge hitting the sidewall of the groove.) Lateral records provide us with an opportunity to experience sound as if it was played back on the best tonearm in existence, provided it is a linear tracking arm.

Ancient monos were vertiacally cut, laterally cut is the accepted, and stereo (and I would think modern monos) were cut at 45 degrees in a V-groove that allows even centering and immunity to pinch effect under normal circumstances. 45 degree groove won't pinch, it is mistracking.

Parabolic ellipticals are somewhat spherical.
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Re: horizontal

Postby flavio81 » 10 Nov 2009 20:18

1200y3 wrote:I believe the spherical is best used with mono (lateral/horizontal) and is the only one to use on mono. (Any modern stylus should work, but imagine a sharp edge hitting the sidewall of the groove.)

But styli do not have sharp edges. There is no sharp edge on the sides of the groove.

Stereo records also have lateral/horizontal modulation too, just like mono records. But they also have vertical modulation.

1200y3 wrote:Ancient monos were vertiacally cut, laterally cut is the accepted, and stereo (and I would think modern monos) were cut at 45 degrees in a V-groove

All mono LP records also have a V-groove, same as stereo. The 45-45 degree (stereo) system is also a vertical-horizontal system. The horizontal component is L+R (the sum of both channels) and the vertical component is L-R (the difference.) Any instrument that is placed on the center will be L+R and thus will mainly be modulated horizontally.

1200y3 wrote:that allows even centering and immunity to pinch effect under normal circumstances. 45 degree groove won't pinch, it is mistracking.

"Pinch effect" is also a kind of mistracking. Please read the above post, it explains the pinch effect and explains it happening in a MONO groove. It happens on mono and stereo grooves. When the stylus is too big for the waveform, then it bounces up, since it cannot follow the horizontal waveform. That bouncing is the "pinch".
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Postby flavio81 » 10 Nov 2009 20:39

More on the problems of the spherical. From this very excellent page:
http://www7a.biglobe.ne.jp/~yosh/recspecs.htm

Distortion ratio in %, calculated using the vertical velocity that appears from bad tracking of the horizontal velocity:

Left: 18uM radius spherical
Right: 5uM radius spherical
ImageImage

But note that the "distortion" quoted there is mainly 2nd harmonic distortion, which does not sound terrible to the ears.

As you can see, a smaller side tracing radius is better.
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Postby bauzace50 » 10 Nov 2009 20:45

Oh, my goodness,

we didn't deserve all this information trove [-o< :!:
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Arms and pinch effect

Postby 1200y3 » 10 Nov 2009 20:52

Does tonearm quality have anything to do with the pinch effect and can an arm add to the effect?

Any pinch effect information I have read is in the Radiotron Designers Handbook, and is readily noticeable with a saphire stylus at too high of a VTA and too little weight. It is easy to demonstrate.
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Postby flavio81 » 10 Nov 2009 21:01

bauzace50 wrote:Oh, my goodness,

we didn't deserve all this information trove [-o< :!:
b50

Yes you do deserve it!

Now... GREAT NEWS!! More stylus pics!! (borrowed from other VE members...)

Now the differences will be more evident!!

From user "Ernie L", paperweight models of the VDH, Shibata, and FG! Yes, a FG!
Image

Although that Shibata looks too stylished to be realistic.

From "Ernie L", another Fritz Gyger stylus:
Image

From "Ernie L": A line contact from Audio Technica
Image

Again let's compare with Ortofon OM30 "Fine Line":
Image

From user "shrice51": "JICO Stylus for Shure V15 III". Seems to be the SAS stylus...
Image

From user "juud": A denon DL103 stylus. Supposedly conical. Beautiful!
Image

An unidentified elliptical "Diamond_Needle_4760_Styli" from user "irwan_su". Typical elliptical:
Image
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Postby flavio81 » 10 Nov 2009 21:50

Another stylus: Ortofon Replicant 100

Looks almost exactly as a FG design. There are no stylus patents assigned to Ortofon. Major radius ("R") is 100uM, minor radius ("r") 5uM.
Used on Ortofon's best cartridges.

Image

Image

Looks like a Fritz Gyger. Ortofon also uses the FG stylus, so this one ought to be a slight variation on the FG.

So, to recollect all major/minor radii data again:

23uM for HE according to Canadian Astatic,
38uM for HE in Shure V15V-P according to Shure
40uM for the Ortofon OM30 Fine Line according to Ortofon,
50uM for the Shibata on the Ortofon 2M Red, also for the Shibata on the Jubilee (*)
70uM for Stereohedron
70uM for the VDH according to Audio Technica
70uM for the Fritz Gyger 70 [FG70] according to Ortofon.
75uM for the Shibata according to many other sources (*)
75uM for SAS and MicroLine according to Namiki and Audio Technica.
80uM for Fritz Gyger 80 [FG80], according to Ortofon.
100uM for Ortofon Replicant according to Ortofon.

(*) Patent for Shibata shows two versions with different R radii.
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Postby lini » 10 Nov 2009 23:07

flavio81 wrote:Very interesting observation on the AT, Manfred. Do you have pics? (...)


Don't think so - but I could try to make some, maybe also of a couple more shapes like Philips' SST and Nagaoka's Ultra-EX. Might take a while, though - 'cause, frankly, I'm a rather lousy photographer and have next to zero experience with macro shots yet...

Greetings from Munich!

Manfred / lini
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Postby Thomas_A » 10 Nov 2009 23:54

flavio81 wrote:
Thomas_A wrote:
flavio81 wrote:[quote="Thomas_A"]Thanks flavio, good review.

A note on the Shibata. I think that the contact area is curved, which has some effects not observed with later fine-lines.


But what effects can it have? Has this been studied?


I've read that the curved align causes a force that pushes the stylus upwards during play, which in turn, may cause a not-so-smooth pattern of groove riding, and in the end, increased wear. The straight line-types do not have the same upward force.


Hi Thomas!!

This sounds like the "pinch effect" typical of the Sphericals, but this is caused only because the side radius ("r") is too big.

I don't think this would happen with all the other types (elliptical, HE, shibata, etc) which have a narrow "r" radius.

Source?[/quote]

Don't have a scientific source, only from another forum. So I do not know whether this has been published or if it is true. I can only imagine that a straight (or symmetrical) contact line is forced to go sideways in vertical* modulation, while a contact area that is shaped like an inverted plough tend to ride a bit up on the groove flanks (the force is on an arc, and depending on the angle it will either dig (a resultant small downforce, like ploughs) or move upwards.)

*Edit: should be lateral (and/or vertical ?). I usually mix up the diff movements...
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Postby 1200y3 » 11 Nov 2009 00:15

Would that not be similar to another offset angle (the need for antiskating), only vertically?
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Postby flavio81 » 11 Nov 2009 04:25

1200y3 wrote:Would that not be similar to another offset angle (the need for antiskating), only vertically?


Mmm i'm not sure if i understand your question. There is already a vertical "compensating" force: The vertical tracking force itself.

If Ortofon uses the Shibata on his most high priced models (when not using the FG/Replicant), then it should be very good... Ortofon people know what they're doing.
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Postby Thomas_A » 11 Nov 2009 08:16

flavio81 wrote:If Ortofon uses the Shibata on his most high priced models (when not using the FG/Replicant), then it should be very good... Ortofon people know what they're doing.


I asked Ortofon why they changed from the more modern FG to the older Shibata in their top model when they switched from OM to 2M.

They agreed that the Shibata was an older design but that it is not a poorer one, and pointed to their highly praised Jubilee model. I am not 100% convinced though, since I did not get any technical argument as to why the Shibata was chosen over FG or microridge models. The Shibata is simpler so it may be cheaper in production than other more advanced designs.
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Ortofon FG

Postby 1200y3 » 11 Nov 2009 14:20

I believe the FG has the ability to "sense" the better part of the groove. (It works best with records in excellent shape.) The problem may have something to do with inconsistent record sound on worn records (comparing first and last tracks).

Any pics of the Shure MR?

Re:Ortofon -Stylus companies still have to deal with manufacturing compromises.
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