Arm geometry and null points

Null points (Baerwald and otherwise) are defined by measuring a specified distance along a radius centered on the TT spindle. The tonearm has nothing to do with their location.

Null points do not change whether you adjust spindle-to-pivot or overhang correctly or incorrectly. They do not change regardless of which tonearm you use, or even if you use no tonearm at all! The null point is the null point.

This literal answer is so simple that I suspect you intended to ask some other question than the one you actually wrote. :-)

Here's another way of putting it: with a single pivot tonearm, the stylus scribes an arc. This arc will have at most two points where it intersects the straight line which corresponds to zero tracking error

The various schemes set these two points at different disc radii according to formulations which attempt to minimise either simple errors or the consequences of these errors.

Different tonearm lengths change the curvature of the arc but the position can always be adjusted so the arc has the same two intersection points..

This last statement assumes the radius of the arc is not made impracticably small.

Mark Kelly

Thanks guys, that's what I thought.
The reason I had to ask Doug, is that I have just bought from Yip the Mint Tractor made for the Graham Phantom II standard arm which is, as you have said, the best template on the market IMHO.

For my other arms, the Copperhead and the DaVinci 12" Ref, I have the WallyTractor and the Feickert respectively.

I wanted to use the Mint Null Points inscribed lines to align the styli in my other arms after I had set up the correct Spindle to Pivot distances and Overhang adjustments using the other templates and I asked Yip if the null points were in the same positions and he did not know!!??...a bit worrying?

Regards
Henry

Henry,

Still not sure why you had to ask moi in particular, but thanks for clarifying.

Yes, you can use the Mint's null grids after setting S2P and overhang by other means. As Mark noted and you obviously understand, the Mint's arc won't be useful for any other arms, but the null grids will. Neither the null points nor the intercept angle of the grid (cantilever) at those points ever varies.

I wanted to use the Mint Null Points inscribed lines to align the styli in my other arms after I had set up the correct Spindle to Pivot distances and Overhang adjustments using the other templates and I asked Yip if the null points were in the same positions and he did not know!!??...a bit worrying?

Is it possible that he said that simply because he didn't know which geometry these other tools uses? Löfgren A and B for example have null points in different places.