Uni-Protractor Set tonearm alignment

Dear Jazzgene, thank you for your impressions.
In the 2nd production run we will produce too a different version of the round reticle with black cross-hairs.
It will be much easier to read when spotting silver colored bearing houses.
This is available as an option side by side with the white engraved reticle that come with the UNI-Protractor ( which in contrary is easier to read on black tonearms).
Cheers,
D.

As an aside:

Halcro,

you asked (16th April):

although something tells me that whilst the UNIprotractor 'arm' is not centred on the Spindle, there might be some mathematical formula which, when the micrometer is wound down to its minimum position, could still be used to check Spindle to Pivot dimensions?

I don't know how the device works, how it differs from the Dennesen, or what the various fine adjustment features are, but presumably they allow the device to be set up for Baerwald IEC nulls, (and whatever other nulls are supplied).

If the principle is Dennesen, which it appears to be, then arm mounting distance (pivot to spindle distance) can be obtained by finding two dimensions:

First:
The distance to the arm pivot as measured along the axis of the perspex arm from the point where the null radius crosses it.
Call this X.

Second:
The distance from the centre of the spindle along the null radius to the centre line of the perspex arm that terminates on the arm pivot.

This distance varies depending on the alignment, and must adjust for each, but you don't have to measure it if the device can be set for Baerwald IEC as it is given by:

Outer null minus Inner null, then divide by 2,
Call this Y.

(For Baerwald IEC this is 27.45. If the device is set for another alignment, then the same calculation applies with the appropriate nulls.)

This gives a right angled triangle, so the mounting distance is given by:

the square root of: X squared plus Y squared.

This applies to the Dennesen also, of course, but only for the Baerwald alignment for which it is set up, unless modified.

The accuracy of the method depends on how well you can measure the distance along the perspex arm to the pivot.

It does beg the question, though, of why one would need to know the mounting distance, as the Dennesen principle allows correct alignment with any existing and unknown mounting distance. If the distance has been set wrongly for a particular arm, this would be corrected (for a slotted headshell) by adjusting the effective length and cartridge offset (assuming enough adjustment) to match the null on the protractor.
.

It does beg the question, though, of why one would need to know the mounting distance, as the Dennesen principle allows correct alignment with any existing and unknown mounting distance. If the distance has been set wrongly for a particular arm, this would be corrected (for a slotted headshell) by adjusting the effective length and cartridge offset (assuming enough adjustment) to match the null on the protractor.

Thanks for that explanation John.
Then the Feikert alignment tool works on a different principle where Spindle to Pivot distance and Overhang are critical to achieving correct geometry? Is that correct?

Good point here. That's the reason for the micrometer driven linear stage carrying the positioning arm - it sets "Y" precisely for whatever null point the specific UNI-template sets.

My initial thoughts when designing the UNI-Pro were similar.
If a phono protractor really is universal, it must automatically align regardless of the given mounting distance.

In most cases the tonearm is already mounted when one starts to align the tonearm/cartridge. Then there are a good many situations where the P2S simply can't be altered by the user (pre-drilled mounting hole, fixed armboards/plinth).
The UNI-Pro does follow the smart idea of Francis Dennesen and adapts to whatever P2S a given tonearm is mounted.
Setting the mounting distance is done before aligning the tonearm. It is a "conditio" already set before starting the alignment.
If however the user does wish to align the given tonearm exactly to the geometry (especially the offset angle) the tonearm was designed with, then knowing the P2S and setting it precisely (IF possible ...) is important.
Important only if one wants to avoid an additional breakdown torque and thus another source for skating force in a pivot tonearm with a fixed offset cartridge mounting.
With tonarms like the Schroeder, Reed or Talea however we won't run into this problem at all.
Cheers,
D.

Dear Daniel and John,
I accept that the majority of tonearms in use today are 'fixed' to their turntables and cannot be adjusted.
The accuracy of the positioning of these tonearms vis-a-vis the spindle to pivot distance is often not the greatest and I appreciate that the UNIprotractor achieves the correct cartridge alignment regardless of the accuracy of the tonearm placement.
Having said that however, I believe that the cost of the UNIprotractor can best be amortized by someone possessing multiple arms and often in such a situation, some of those tonearms will have removable headshells?
If each tonearm is 'inaccurately' positioned in terms of S to P distance, the swapping of headshells+cartridges between arms, will result in multiple accumulating errors......no?
Additionally, if one is using fixed headshell/cartridge combinations such as the FR-7 series or some EMTs, adjustments within the headshell/cartridge are simply not possible and correct spindle to pivot dimension is essential to extract the best performance n'est pas?
It is obviously ideal to have the tonearm set at the correct S to P dimension and an accurate method for achieving this is desirable.