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

Discussion in 'Audio Hardware' started by Bill Hart, May 24, 2019.

  1. Ray Parkhurst

    Ray Parkhurst Forum Resident

    Location:
    Santa Clara, CA
    Bought the Behringer box. It's supposed to arrive 8/19-22. The 480LT will be at 480-576 hours around that time.
     
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  2. Soopahmahn

    Soopahmahn Well-Known Member

    Location:
    Pittsburgh
    This thread has inspired me to bust out my USB microscope and try to image my stylus tip. Hopefully 1000x isn't overkill and I can get the lighting right. :thumbsup:
     
  3. Ray Parkhurst

    Ray Parkhurst Forum Resident

    Location:
    Santa Clara, CA
    Excellent! Let's see some photos...
     
  4. Soopahmahn

    Soopahmahn Well-Known Member

    Location:
    Pittsburgh
    Alright, I tried, but the tip was very dirty and I'm not sure the focal length of this camera allows me to get close enough. I'll try again tomorrow.

    I have a ring of LEDs around the lens for lighting and am adding side lighting from an iPhone - any tips on lighting? I am pretty much lighting the whole diamond up and can't see contrast in the surface.
     
  5. Ray Parkhurst

    Ray Parkhurst Forum Resident

    Location:
    Santa Clara, CA
    For the contact surface images I hold the stylus at a 45-deg angle so that the contact patch is flat vs the camera sensor. Under those conditions the ringlight will reflect off the contact surface and produce a dark patch surrounded by bright reflections.
     
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  6. Thomas_A

    Thomas_A Forum Resident

    Location:
    Uppsala, Sweden
    Thnaks for info. It is then not a true elliptical but some kind of hyperelliptical but only one-sided. My concern was that there appears to be very little polish of that one side cut. One can imagine that a break-in period would polish that cut but then it may increase record wear during that period. After all, perhaps there is a point using a break-in record with pink noise the first 50 hours before playing the real stuff?
     
  7. Ray Parkhurst

    Ray Parkhurst Forum Resident

    Location:
    Santa Clara, CA
    It looks to me like the stylus is a true elliptical, but maybe was 0.3x0.7mil originally, and then the small cut was added to justify a re-specification to 0.2x0.7mil. Or something like that.

    Note that the small cut is not a contact surface. The cut is on the front (trailing edge) face of the stylus, so it cuts across from one groove wall to the other. Polishing of that cut surface thus does not matter much.
     
  8. Ray Parkhurst

    Ray Parkhurst Forum Resident

    Location:
    Santa Clara, CA
    Another 96 hours completed, now 384 hours total. The inner/left contact has grown slightly from 0.27mil to 0.28mil, and right/outer from 0.25mil to 0.27mil. The contact patches also have a more uniform darkness so they are a bit flatter and/or better polished, though I still don't really see much change in the Profile view.

    Honestly, If I had purchased this cartridge as "new" from an ebay seller I would have no complaints, yet this is ~400 hours of play time already, a very unexpected result.

    Here are the pics:

    Inner/Left
    [​IMG]

    Outer/Right
    [​IMG]

    Front Profile
    [​IMG]
     
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  9. Thomas_A

    Thomas_A Forum Resident

    Location:
    Uppsala, Sweden
    Yes, I realise this is the front. But my concern is that since the contact area varies during play around the axis of the tip, you will reach the sharper edge during play. The back side is smooth/round elliptical (due to polish of the first front/back cut) the front side shows half as smooth, and half as a sharp edge. See picture. I am a bit concerned if this may cause some extra record wear.

    [​IMG]
     
  10. harby

    harby Forum Resident

    Location:
    Portland, OR, USA
    Here's imagery of an elliptical (bi-radial) stylus.

    [​IMG]
    [​IMG]

    It starts as a "turned" conical stylus, and then the facet or dual facets are polished into it, the idea being that the contact area point has a reduced-width, especially as it traverses more complex passages, but obviously the taper means the optimization is less as we get further from the tip. This and other more optimized cuts keeps the stylus from transcribing music ahead or behind the desired contact area. As we can see and imagine, the contact in lower modulation tends to be solely in the conically-polished areas, until the worn contact area expands in width to the facets.

    Does it cause increased wear on a record? I don't think that is a concern, as the wear is spread over a mile of vinyl groove per hour of play, vs the wear we see on .0002 inches of diamond. The facet edge will be slowly rounded over also, as only a silent groove is perpendicular with the contact patches. In fact, we see in the pictures of the stylus being tested how little elliptical shaping the particular stylus has actually received, and it still acts as a conical except for high frequencies at a high modulation that would give a large angle of contact.

    That brings up another thing we are seeing here, not simply the grinding away of a flat facet contact patch, but rather, the smoothing of the coarse crystal polish. There is less frequent contact in front of or behind the center of the patch, but these areas are also smoothed gradually by music. One should not immediately conclude that the smoothed darkened areas are "worn", or are evidence of a new completely flat growing contact facet. In fact, smoother may mean a less coarse shape being dug through the groove, with less macro-mechanical friction and wear, and less surface noise.
     
  11. Ray Parkhurst

    Ray Parkhurst Forum Resident

    Location:
    Santa Clara, CA
    I think this is similar to the various discussions regarding MR/SAS type styli, which rapidly develop very sharp edges on both front and rear of the contacts. My understanding is that these are not considered to cause increased record wear, though personally I can't imagine they would not. Note that the line where you write "sharp" is actually not all that sharp. The center of the brightest area surrounding the contact patch is at ~23deg from horizontal, so even on that trailing edge there is a significant chamfer to the edge between the cut and the contact patch. The cut is also on the trailing edge, so would presumably cause less wear than if it were on the leading edge. This is all presumption as no one really knows the right answer.

    Unfortunately those images are artist's renderings and don't look much at all like a real stylus tip, nor are they in correct proportion to the groove, so it's hard to make any conclusions from them.

    I've always been under the impression that true biradial/elliptical styli do not require the front or rear cuts to achieve their goals, and that these cuts are indicators of cost-cutting methods of achieving similar goals. That said, it could also be the case that their minor radius is indeed smaller than their major radius, and thus the contact patch is elliptical in shape, even if the front and/or rear cuts are made, so you can't always make the conclusion that if the cuts are present that the stylus is not a true elliptical/biradial.

    Regarding wear due to the cuts, I believe the bigger concern would be the edges of the contact patch itself after the stylus has worn significantly. These edges are indeed fairly sharp. It would seem that groove modulation would cause them to be rounded, but the well-worn styli I've imaged don't show this, instead showing a very flat contact patch surface.
     
  12. Thomas_A

    Thomas_A Forum Resident

    Location:
    Uppsala, Sweden
    I am not sure that the MR/SAS is sharp like that due to following polish. It just seems that the stylus shown above has made a normal back/front cut for an elliptical, then polished, and then a third small cut was made after the polish. But since the cut is on the trailing part it may not give problems.
     

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