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RE: "I make and use alignment protractors that aren't based on null-point theory" ...

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In Reply to: RE: "I make and use alignment protractors that aren't based on null-point theory" ... posted by andyr on October 07, 2015 at 17:34:17

It's actually not really complicated. The protractors are based on equations from the 'Radiotron Designer's Handbook' published by RCA, which were meant to be used for tonearm design, but can be used to design alignment protractors.

When you're done, you don't end up with two "null-point" alignment grids, like you see on most downloadable protractors. You get an overhang value and an offset angle for one-point alignment. No wiggling back and forth.

This is just a pet project of mine. I'm not recommending that other people abandon null-point protractors. But the Handbook is a free download, in case anyone's curious.
----------------------------
"We should look beyond the measurements." ~ From 'Engineering for Poetry Majors, 3rd Edition'
"Use adjectives instead of numbers, and you'll never be wrong again." ~ Audio Glinda

Follow Ups:

How do you adjust overhang and offset?... - John Elison 19:35:12 10/07/15 (5)
The goal of any protractor is to adjust overhang and offset to specific values. Those two parameters in conjunction with mounting distance establish a desired alignment geometry. To achieve minimum distortion with a pivotal tonearm, there must be two points on the record playing surface where tracking error equals zero.

I believe the simplest and most accurate alignment protractor has an arc for setting overhang and two alignment grids for setting offset angle. As long as the stylus follows the arc exactly, only one alignment grid is required for setting offset. The second alignment grid is provided for redundancy and confirming accuracy.

How does your protractor work?

Thanks,
John Elison
- see page 725 - ringwear 01:35:25 10/08/15 (4)
  First edition printed 1934.
  - Radiotron Designer's Handbook (Open in New Window)
  - RE: see page 725 - John Elison 03:27:52 10/08/15 (3)
    This particular edition was printed in 1953. What exactly do you wish to emphasize. I've read pages 725 through 727. They talk about tracking error and distortion for a straight 8-inch tonearm without headshell offset versus one with offset. The straight tonearm should be aligned with underhang to minimize distortion whereas the offset tonearm should be aligned with overhang to minimize distortion. The book says the straight 8-inch tonearm will have about 18.6-degrees tracking error with approximately 6.7-percent distortion. I don't know how they arrived at their figures, but they claim the offset tonearm will produce only 0.76-percent distortion. Is this what you're referring to?
    My question to Poinzy was "how does his protractor work if it doesn't have an arc for adjusting overhang and an alignment grid for adjusting offset." Here is what Poinzy wrote in one of his posts above:
    > When you're done, you don't end up with two "null-point" alignment grids, like you see on most downloadable protractors.
    > You get an overhang value and an offset angle for one-point alignment. No wiggling back and forth.
    Well, there is no wiggling back and forth with an arc protractor. You adjust overhang with the arc and you adjust offset with either one of the two grids. You only have to "wiggle" back-and-forth if you disturb one adjustment while making the other. How does Poinzy go about adjusting overhang and offset? In other words, how does Poinzy's protractor work if it doesn't have an arc and an alignment grid?
    On the other hand, if Poinzy is suggesting a straight tonearm without offset in order to simplify the alignment process, that would be both unnecessary and absurd. If you want to simplify the alignment process, you can simply attach the cartridge to the headshell without doing an alignment at all. You will achieve much greater accuracy that way than using a straight tonearm without offset.
    Thanks,
    John Elison
    
    Edits: 10/08/15 10/08/15 10/08/15
    - What exactly do you wish to emphasize. - ringwear 04:27:52 10/08/15 (2)
      nothing. just trying to be helpful.
      - RE: What exactly do you wish to emphasize. - John Elison 06:05:47 10/08/15 (1)
        
        In Reply to: RE: What exactly do you wish to emphasize. posted by ringwear on October 08, 2015 at 04:27:52
        
        Okay! Thanks! I think I have a fairly good understanding of tonearm alignment geometry and there are more recent papers written on the subject.
        
        Thanks again,
        John Elison
        
        attaboy. good for you. - ringwear 12:34:37 10/08/15 (0)
        
        In Reply to: RE: What exactly do you wish to emphasize. posted by John Elison on October 08, 2015 at 06:05:47
        
        you really are a big asset in this little pool we have.

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