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RE: Background...

Hi Tom:

Wow! Those reference posts are extremely technical and tedious. Yes, I've read them before and I am very familiar with the mathematics and methodology employed by Löfgren and Baerwald. Unfortunately, I don't see a connection between those posts and the question as to whether the numbers in your SME 309 manual are simply mistakes or valid parameters from a previous design. However, I have found a reasonable alignment that can be formed with those numbers rather than the absurd alignment I presented in my previous post.

It appears that all modern SME tonearms use Löfgren A (Baerwald) methodology to define their geometry. Although there are slight geometric differences in the 300 Series compared to the Series IV and V, the differences can be explained by the choice of innermost and outermost groove radii. For example, the IV and V use 60.325-mm and 146.05-mm for inner and outer groove radii whereas the 300 Series use 58.0-mm and 146.0-mm. Plugging those numbers into Löfgren A equations yield slightly different alignment null-point radii. Now, if we change the innermost groove radius from 58.0-mm to 62.975-mm, we can get an alignment with effective length of 232.2-mm and mounting distance of 213.4-mm. Below are graphs of this possible previous SME 309 alignment along with the current SME 309 alignment. It is clear that the possible previous alignment has greater inner groove distortion when the inner groove radius goes all the way in to 60-mm.

So, the question still remains: Was there a possible previous alignment or are those numbers simply mistakes?

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  Kimber Kable  

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