The Finish Line for your Phono Cartridge- Stylus Wear by Mike Bodell

To help folks understand the results I've been showing, I put together the 600-hour contact images and the front profile into a composite image, with the contacts projected onto the profile, to show where the contacts are forming. Also see the detail with the profile drawn to better show the shape of the profile at the tip. As you can see, there are no real "flats" yet, so the dark areas we're seeing are just polished regions of the curved contact region. This gives some idea also of the contrast selectivity of this ringlight photographic method.

 

What would be neat to see, but might be beyond your facilities, is a little video or animation of what this contact patch looks like, and how the reflection changes, when the stylus tip is pivoted on-axis - to get lighting at different angles.

Since you have a p-mount that can simply plug into a universal adapter you might already have:



On another topic - wearing some vinyl out (not styli) and measuring the results:

Let's say you have the "Ultimate Analogue Test LP". The first track on side 2 is 315Hz with modulation increasing up to +12dBu. This track is as ill-conceived for antiskate adjustment as the next track for "demagnetizing" - so a good record to destroy by putting that single track on repeat, which many linear trackers can do.

Press record on your computer, and let it go for days. One can then measure the harmonic distortion before and after (pitch shifting to 997Hz if your software is not versatile), discovering even slight increases in groove wear and waveform shape at low and high modulations, the rate of distortion increase over time, and additionally, analyze for additional non-harmonic noise similar to cue burn.

 

If I interpret you correctly, you want me to rotate the cartridge in the contact plane, such that the contact remains flat, but light comes in from different "clock positions", is this correct? Note that the lighting I use for these images is a ringlight, so it is coming in simultaneously from all sides, so the result won't change from what I'm showing. Now, if you're asking for the angle of the lights to sweep, that's a different story. The ringlight shines at the contact from 45-53deg (IIRC). If I tilt the contact away from 45-deg, then the "apparent" contact patch will shift with the angle of the tilt.

One further note that may make things more clear is that instead of a small, flat wood block like you show in your photo, I use a wood wedge cut at 45-deg with the universal adapter mounted on the 45-deg surface.

Regarding the test LP, I have an STR-100 on the way. It could be used to check the stylus wear, and as you say may be useful as a vehicle for further record wear tests.

 

If the diamond stylus were to pivot around the green axis, we can see how the lighting on the wear spot changes. At a certain angle, it should reflect the ringlight into the camera, and the transition of this "specular" would let one understand when the diamond is changing from "polished" to "faceted".

Above is the apparatus I imagined to do that.

 

Turns out this photo did tell a lot. The stylus was not mounted correctly on the cantilever.






The stylus is off center and tilted. Looks like it's buried in mounting adhesive. Poor mfg and QC

The next one the cuts don't line up

 

Next



Uneven wear.

 

The areas you have circled are not the wear patches.

 

The apparatus you showed looks straight down onto the stylus tip, and then rotates the stylus on the green axis, correct? This would rely on the Shure method of lighting, which reflects the light off the contact surface. I'm not using that method since it is only qualitative and can't really be used for contact measurements.

I'm thinking about a slightly different approach...more later.

 

Well after I got back from my camping adventure in the Sierra Nevada mountains (note new avatar), I received this email from John Wright in the UK (I sent the cartridge just before leaving on vacation)...

"I have examined your Reference cartridge.

1. London reference cartridge serial no.LR-35.
Paratrace stylus badly worn.
Overhaul and replace stylus assembly, clean, recalibrate and test...........................£685.00 inclusive

Regards
John Wright"

So I finally got the cartridge back (remember I have used this cartridge since 2008!) and carefully mounted it. Wow! Everything was so loud! The output must have increased a lot with that re-tip, because now the average position on my amps' volume control is about ten o'clock, whereas before the average setting was at 12 noon! So now that I'm adjusting to it, it just sounds so powerful yet smooth. Amazing detail and realism! And the bass, my God the bass! Also before I could not see the stylus tip with my naked eye, but now I can actually see something there -- a kind of white mass, which is the new stylus.

So I am following this thread with interest of course. Great work by Ray and Bill and the rest.

In regards to Ray's test here, I mischievously speculate that once there is enough diamond dust scraped off the stylus, then the resultant abrasive wear on it will finally start to accelerate, which of course will produce more diamond dust, which then continues to speed up the stylus wear, and so on until both record and stylus are both completely trashed not too many hours afterwards...

 

Good grief!!! Talk about a groove chewer!

 

Good to hear and not because it vindicated any view of mine. I think the issue-- and I find it true of tubes too-- is that we get used to what we hear and the degradation is incremental. I agree that Ray's little 'project' here is fascinating-- I'm learning as much as anybody in the course of this.

 

I was only demonstrating how to pivot the stylus. Still observing from the sides like your pictures, but rotating to extract more details about the nature of the dark contact patch.

Looking straight down, the contact areas are 12um from the center; all the contact is happening within a few scale ticks. You need to use higher magnification and focus on the tip of the stylus. You also might face the sample more into the beam so there is less shadow, or try a coating.

It is enough to discover strange-looking cuts. The tilt is compensated by VTA alignment if it does not deviate much from the plane of the coils. Off-center should be of little consequence, if this is not simply misinterpretation of the view angle.

The stylus is not "buried". A lot of what you are seeing is likely detritus from inadequate cleaning. Try preparation with Magic Eraser.

 

Hmmm...looks to me more like the cantilever is rotated in the suspension. That's bad enough, but is probably fixable.

 

The cantilever was in the correct position. I made sure before the photo. The stylus was placed incorrectly from my perspective. I should have returned it. It’s not even cut symmetrically.

Very disappointed in the quality of what should be a precision instrument.

 

My standard technique of holding the stylus at 45-deg puts the opposite contact in profile view. By adding an auxiliary light shining onto the opposite contact, I can illuminate the surface such that the profile is visible. I first tried this on a well-worn LTD290 stylus with extreme wear, and the technique clearly shows the extent and shape of the wear flat. I then tried it on the 600-hour 480LT stylus and it looks like only the smallest amount of flat formation is occurring. Indeed the surface still seems to have some texture like it hasn't been completely polished.

Here are the images:

LTD290


600-hour 480LT

 

Here's a picture of your line contact stylus that I enhanced, by correcting the "picture of a screen" distortion and blurriness.



1) I transposed the scale up (red), so we can see the size of the stylus from the center (providing the instrument is calibrated at working distance).
2) Then I overlaid the ellipses of contact areas for a .7 mil conical stylus (17.8 um), for comparison (contact areas actual start as a tiny point on a new "ideal" conical stylus).
3) Besides the faceting, it looks like there are final finishing cuts with a cylindrical tool. I noted their observed axis and numbered them (white/orange).


Cuts #1 and #3 apparently turn what would otherwise be a isosceles trapezoid contact area into a line (rectangle), and perhaps extend the life of the line contact.

I simply cannot talk myself out of seeing that both cut #2's on the line stylus are concave and dished. This could be an effect of the electron charge buildup or such, but the debris in the 40um scale picture seems to also depict that the "line" is also finished with a cylindrical tool, and actually forms two contact lines.

What's notable is the lack of wear, which I expect would be a rounding and widening of the line contact area.

The debris on the left line contact area is gone in another picture, and this debris looks similar to another STEM thread's before-cleaning picture.

I think the major error is that cut #1 on the right side is too deep, and/or both #1 and #3 are shifted. Contact is still 45 degrees; simply made longer on one side. Compared with the potential tracing error for a conical or elliptical stylus, I don't think this would be of large concern, as the disproportionate cuts only lift the contact higher in the groove wall (and away from bottoming-out on the tip), and ultimately the contact area still transcribes the groove pretty well. 10kHz audio is 1537um wavelength at 33rpm/7", giving us under 1 degree phase shift for one side being "behind" 4um.

 

ML/MR/SAS styli have a reasonable range of tolerance of azimuth error. This stylus looks to be perhaps 5-deg off (perhaps a bit more?), while the cantilever itself appears to be square. If the cantilever and magnets are well-aligned, and indeed the cantilever is aligned with the cartridge body, then the only issue with this stylus would be a bit shorter life than would be expected from a perfectly-aligned one.

I believe that cuts 1 and 3 in the diagram above were laser cuts. The actual ridge looks OK, but is very badly worn. It looks like this stylus "hit bottom" long ago.

 

Thanks Harby. I made the effort to SEM the stylus without sputtering in case I was going to reuse it. Even though I made a conductive path from the cantilever to the SEM ground, I was still getting excessive charging during the photo scan so I photo'ed the screen.
Ray, your optical photographs are amazing. I know how difficult it is. I have about 35 years optical and SEM experience. My initial photo in this thread was taken with a Keyence digital 3D scope. Your excellent photos prompted me to SEM an old stylus.

My complaint besides the low quality mounting and possible stylus cutting problem on my stylus, is where are the stylus wear photos from the stylus manufacturers? Why can't they show clear, before and after wear on an SEM? It's really not a lot of money to get this SEM service.
All I read are "replace after X hours" with no examples. I searched for a line contact or Shibata before and after SEM, nothing. Why is this so difficult? Where is their data?

 

Oh I must have been unfollowed automatically. If I may ask, have we found some interesting information in the last 10 pages or so?

 

There is one thing I don't get with the image/stylus, and that is the razor-sharp ridges. My impression was that these should be rounded.

MicroRidge | Adamant Namiki Precision Jewel Co., Ltd.

 

I would say 500 hours maximum.
My ears tell me all i need to know.
It works like this.
When all is well i am totally relaxed
With music.
When little things about reproduction
Start to annoy me and i feel the need to tweak arm settings i send the Mc off to Expert Stylus Co for examination
Free if they need to retip
Anywhere between 400 500 wesr is audible.
Increase in VTF may help, but probably best to have it checked

 

It's hard to know what is due to wear. A bit of hunting and we can find a diagram of the AT150MLX stylus from Audio-Technica.


Depicted is the necessary tip rounding (because worn cutter tips aren't laser-sharp at the bottom of the groove), and we can see the same cuts thinning the facet edge into a line. You can see the cut-away from the line that was misinterpreted as contact area.

Here's @Koptapad 2010 SEM pictures of what looks like the same stylus (with the same funky facet wiggles near the tip), and we get a better appreciation of the dimensions of the finishing cuts that make the microline:


The tip may be worn to a more precise "triangle" shape now from continued groove wear, and the point more pointy, but we don't have the same angle depicted in 2019 (yet) to see how wear has progressed (if he's been using the stylus for nine more years).

Skating force may have worn one line more than the other, so the stylus might have looked more balanced when new.

(one wonders if it is possible to rejuvenate a stylus worn to a point by re-blunting the tip with abrasives on a flat surface...)

 

It the sharp edges is due wear, the stylus must have been forgotten in a run-out groove for a year or so. It is impossible to get sharp edges like that when you play a groove with a signal.

 

All of the well-worn styli I've imaged have "flats", ie the wear patches are indeed almost completely flat, without much rounding to the corners, so I believe that flat wear pattern is the norm. This flat wear pattern results in a relatively sharp edge between the remaining diamond and the contact surface. I don't think that it is required to have anything like being stuck in a run-out groove or similar to give this result. Keep in mind that the power spectral density of music is heavily weighted to low frequencies, such that most of the time the grooves are hitting against a fairly flat surface, so my hypothesis is that playing typical records has a similar result to playing an unmodulated groove.

 

Wasnt the idea of the microridge that it wore down but kept its shape until the critical point where the ridge is almost entirely gone?