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tonearm geometry question

I've followed the linear vs pivoted thread with some interest. Itt raises a question that someone with greater technical expertise may be able to clarify for me.

At rest, both a pivoted arm tube and an LTT tube share a common position tangent to the platter ( call it the CP line) and a common anchor ( or pivot) point (call it CAP). From there, a pivoted arm tube defines an arc across the record, while the LTT tube slides on its anchor point from the CAP along a line perpendicular to the CP line and tangent to the platter until it hits the inner groove. Call this the LTT anchor journey.

My question: Why is the pivot point on a pivoted arm not located halfway along the LTT anchor journey. Wouldn't this reduce the pivoted arm's error by half? Surely loading/removing the record can't be the reason. What am I missing?

Thanks in advance.

Marty
martykl

Showing 2 responses by 04rdking

04rdking's avatar
04rdking
178 posts
 
Marty,
"For any length tube it would seem that the geometry is the same (save the headshell offset), no?"

I don't follow that. A longer arm will have a larger radius. The larger the radius, the less the tracking error/distortion between the null points.
04rdking's avatar
04rdking
178 posts
 
Marty,
I believe you're missing the forest because of the trees. A radius is not a radius. A 9" radius is not the same as a 12" radius. They are both arc's, but not the same. You keep saying "the particular radius tracked by an LTT". A LTT has no radius. It is linear.

Point is. If one were to put the pivot point in the center of the null points on a fixed head/arm, the tracking error would be gratly increased. In fact, I believe with this configuration, one would only be able to achieve one null point....... Stevenson geometery.
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