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Cartridge Alignment to Protractor Extremes

Discussion in 'Audio Hardware' started by avanti1960, Apr 3, 2021.

  1. Ingenieur

    Ingenieur Forum Resident

    Location:
    PA
    Delta 20 deg F
    Aluminum 1 m to 1.0002, 0.2 mm
    Plastic 0.6

    over a 100 mm span
    Al 0.02 mm
    Plastic 0.06 mm

    a stylus diameter > 0.08 mm
     
  2. avanti1960

    avanti1960 Forum Resident Thread Starter

    Location:
    Chicago metro, USA
    FYI it is made out of glass. At one point I thought about selling it believing that the technics white diving board was good enough, geez.
     
    Brucedgoose likes this.
  3. missan

    missan Forum Resident

    Location:
    Stockholm
    The Technics gauge is perfectly fine IME, but it will yield slightly different null-points to a Lofgren A (Baerwald). The only thing is if the arm isn´t within tolerance; then a gauge isn´t that reliable.
     
    JackG and avanti1960 like this.
  4. Brucedgoose

    Brucedgoose Forum Resident

    Location:
    Hawaii
    Congratulations! You’ve officially made it to the Hard Core!
    Remember, too, that you’ll need a new Mint LP protractor every time you change cartridges or arms! It never ends! Also, you’ll have to wait awhile for it, since this guy (who’s in Japan, I think) makes each one to order and he’s apparently pretty busy.
    There is someone else on Ebay who is selling pre-made protractors specific to certain popular arm/cartridge combinations, and these may be cheaper than the Mint LP system. They may or may not be easier to use; I haven't tried those.
     
    Last edited: Apr 3, 2021
  5. Brucedgoose

    Brucedgoose Forum Resident

    Location:
    Hawaii
    While you’re waiting for it to arrive, you may find this interesting, “Understanding Phono Cartridges,” from Audio Magazine (back issues available free at World Radio History);
    https://worldradiohistory.com/Archive-All-Audio/Archive-Audio/70s/Audio-1979-03.pdf
    Written by a noted cartridge designer,
    And this one on tonearms by the same author;
    https://worldradiohistory.com/Archive-All-Audio/Archive-Audio/80s/Audio-1980-06.pdf
    There are more along these lines in old issues of Audio, but these are two of the best.
     
    doctor fuse likes this.
  6. Brucedgoose

    Brucedgoose Forum Resident

    Location:
    Hawaii
    He uses glass so he can easily etch the correct grid lines into the surface for each different arm/cartridge combination. A nice system. Glass is reasonably stable dimensionally, but for really good dimensional stability, special “low thermal expansion” glasses are used, for things like spacecraft windows. “Zerodur” is the trade name for one of these LTE glasses.

    When you buy your next $10,000+ cartridge, get a custom Mint LP protractor made from Zerodur. That way, your protractor can cost as much as your cartridge! :)
     
    avanti1960 likes this.
  7. Jimi Floyd

    Jimi Floyd Forum Resident

    Location:
    Pisa, Italy
    After alignment I always perform a check.

    I have a very clever tool, devised in the 70s by IAF (Istituto Alta Fedeltà), which allows for an easy measurement of the tracking error angle (measured in degrees) as a function of the stylus distance from the pivot (measured in cm).

    Example: SME V + Dynavector xx2 mkII. The nominal null points for the SME V are at 6.6 and 12.0 cm from the centre, it is a Stevenson-kind of alignment very similar to the Technics SL-1200 arm. First alignment with the clever supplied SME protractor. The following check is however independent of the chosen alignment.

    Then I measure the error angle each cm in radius and plot it (dots)

    [​IMG]

    The error curve can then be fitted by computer or by eye if errors are small, and the tool is good, since the measured points are not scattered around very much from the curve. The null points are now checked with confidence to be at 6.2 and 12.0 cm, pretty close to the specs. Alignment seems OK. Maximum tracking error is below 2° at 14.5 cm which is the outer groove radius.

    Last and final check, the smart one. A good choice to define a perfect alignment is to set the same distortion limit for positive and negative tracking error angles. For a Stevenson alignment the inner grooves are not a problem, one should balance the distortion in the outer grooves (positive tracking error) against the center grooves (negative tracking error). Now, the tracking distortion is proportional to the tracking error divided by the tracking radius. Believe me, this means that the two straight lines from OO to the curve 1) at the outer groove and 2) tangent to the bottom of the curve, must then have the same slope. In this case I got it exactly so, and stopped worrying.

    11 points allows for redundancy in measurement, and a safer procedure than just relying on 2 null points.

    Alignment done. Alignment checked. Let the music play
     
    Last edited: Apr 3, 2021
    avanti1960, Ingenieur and Brucedgoose like this.
  8. Brucedgoose

    Brucedgoose Forum Resident

    Location:
    Hawaii
    Very nice!
     
  9. Ingenieur

    Ingenieur Forum Resident

    Location:
    PA
    Clever!
    How do you measure the 11 tracking error angles? 2 are the null points, how about the other 9?
     
  10. avanti1960

    avanti1960 Forum Resident Thread Starter

    Location:
    Chicago metro, USA
    exactly right, which is another reason to use a protractor.
     
  11. avanti1960

    avanti1960 Forum Resident Thread Starter

    Location:
    Chicago metro, USA
    nicely done, i assume you are plotting the tracking error based on the measured null points?
     
  12. SCM

    SCM Forum Resident

    Location:
    Fl
    I use a Mint too.
    I remember the first time I used it...WOW what an endeavor !
    My eyes were going cross looking down that 'Runway' after about 3 hours and I still wasn`t done yet ! :laugh:

    Now I can get it done in about 45 minutes to an hour, I`m waay to finicky to just be close enough :)
     
    Shawn, avanti1960 and Ingenieur like this.
  13. Jimi Floyd

    Jimi Floyd Forum Resident

    Location:
    Pisa, Italy
    I use this since 45 years, self drawn on thick cardboard:

    [​IMG]

    place the needle on any arc such as the cartridge (or cantilever, at your preference) is parallel to the horizontal (here) lines, read the radial error directly on the arc scale.
     
    Bob_in_OKC, Brucedgoose and Ingenieur like this.
  14. Jimi Floyd

    Jimi Floyd Forum Resident

    Location:
    Pisa, Italy
    No, I measure each point independently. That is the strength of this method.
     
  15. avanti1960

    avanti1960 Forum Resident Thread Starter

    Location:
    Chicago metro, USA
    this is where a detachable headshell really helps, you can make the minor adjustments off the arm.
     
    SCM and Shawn like this.
  16. avanti1960

    avanti1960 Forum Resident Thread Starter

    Location:
    Chicago metro, USA
    Ottimo!
     
  17. Ingenieur

    Ingenieur Forum Resident

    Location:
    PA
    It's official
    I am not the biggest nerd on here.
    :D
     
    rogertheshrubber and Shawn like this.
  18. Jimi Floyd

    Jimi Floyd Forum Resident

    Location:
    Pisa, Italy
    I am a Physicist, what can I do?
     
  19. Erm no,in my workplace you heat a bearing to 120 degrees C which will allow the bearing to shrink fit onto a shaft with a -0.002" interference fit,you then make a cup of tea and have a few biscuits,by that time the bearing has cooled down so the said bearing/shaft will fit into to the bearing housing with a +0.002 tolerance.
    Not that it matters anyway.
     
    ubiknik likes this.
  20. Ingenieur

    Ingenieur Forum Resident

    Location:
    PA
    interference fit
    I've seen it done on 16" shafts for large conveyor drive rollers.
     
  21. ubiknik

    ubiknik Forum Resident

    Location:
    Chicago, IL USA
    This makes no sense, you get a protractor like the mint so you can mount and align a cartridge.
    Unless the cartridge needs to be specified when it's ordered, I have one that came with a Clearaudio table and I never heard of that aspect being restrictive.
    I would assume the main numbers used by the maker of the mint are the pivot to spindle distance and effective length of the arm, so if you switch arms and they have the same effective length then I don't know why that would require a new one either, as long as they are not radically different (if the new arm had only slightly more length available, I don't know why the Mint would not still give a nice alignment).
    The Mint I have is printed on frosted vinyl adhesive backed substrate similar to what is used in the sign mfg business, and then applied to the glass mirror -the mirror is not etched.
    Now that I think about it I sure hope the vinyl is a higher quality grade like 3M or Avery and that it is applied properly, I know 3M will not warranty their product (from de-lamination or severe shrinkage) unless the proper application fluid is used when applied, in that industry a lot of shops just use water w/a drop of dish soap and maybe some alcohol to help speed drying instead of the prescribed application fluid.
     
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  22. ubiknik

    ubiknik Forum Resident

    Location:
    Chicago, IL USA
    I've seen my mechanic heat up old parts on old crunchy (a rust belt term) cars with a torch to get the parts to free up after years of being welded together by rust and whatnot, I guess this is a pretty common mechanics trick.
    It usually works, anyway.
     
  23. avanti1960

    avanti1960 Forum Resident Thread Starter

    Location:
    Chicago metro, USA
    thank you. i was going from memory and did not look up any coefficients for thermal expansion.
     
  24. Ingenieur

    Ingenieur Forum Resident

    Location:
    PA
    Regardless, moot

    Linear Thermal Expansion
     
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  25. blakep

    blakep Forum Resident

    You are correct on both counts.

    You will not need a new Mint if you only change the cartridge and you will not need a new Mint if you change tonearms to another tonearm which utilizes the same pivot to spindle distance. Unless the tonearm geometry is such that the new arm uses a different alignment protocol (ie. Stevenson vs. Baerwald) and you want to align specifically to the alignment the new arm is designed for, which is not necessary (and may not be desirable IMO).

    New arm with different pivot to spindle distance = new Mint required.
     
    ubiknik likes this.

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