Uni-Protractor Set tonearm alignment

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.

I tried the Uni-Pro on my Thorens TD-316. I love this simple table and is my 1st table I bought as a kid. Got it new in the mid 80's.

I chose the Baerwarld IEC for this table which comes with the TP-21 arm. I used Benz Micro MC20E2 cartridge.

I had to level the spring suspension a bit after placing the Uni-Pro on the platter. No big deal. The cartridge had to be scooted all the way to the front of the headshell in order for the stylus to hit the point precisely. The Uni-Pro makes sighting the cantilever a simple procedure.

Listening to some Keith Jarrett LPs and I have to say, this modest table does hold quite well against my main table which costs much much more. It's been running just like new for close to 30 years with just a belt swap. Including several home moves! Too bad Thorens ain't what it used to be.

Halcro

I haven't used it, but I'm sure you are correct in assuming a different principle for the Feickert. If it has the facility to set or measure mounting distance, it is because it uses arcs which have to be referenced to a known pivot point.

You are correct in saying that headshell type cartridges having no facility for adjustment need to have the effective length of the arm with the cartridge fitted known or measured. Also the true cartridge offset angle (which will depend on the arm/cartridge combination) also known or measured. Then an appropriate mounting distance can be calculated, and precisely set.

Alternatively, using an arm with a known alignment, you can use (if it has the same alignment) a two point protractor to set up. By sliding the base the offset will be given automatically. Swapping different kinds of these cartridges would depend on them having the same headshell mounting collar to stylus distance.

You are also right in saying that swapping headshells could be problematic. It looks to me that swapping headshells between arms would require them to be set up initially with one headshell/ cartridge combination which remained set once the first arm was done, and which was then used to set the remaining arms with adjustment achieved at the bases of the others, assuming they were different arms.

The alignment chosen would have to also be the same for each set up, irrespective of the arm design, but the arms could be different lengths. Then any cartridge/ headshell combination could be set up to suit these alignments without moving the bases. This would depend on the headshells having slots, though the initial headshell could have holes as long as the arm used was designed to the chosen alignment.

I think that covers most of the difficulties..... please feel free to point out a simpler way, any mistakes or anything I've overlooked.

John
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Dear Halcro: My mistake. That 15mm on overhang is not what help me but the distance between the cartridge stylus and the rear part on the headshell that if I remember is 50mm on some of my tonearms.

Raul.

Dear Halcro: I don't think you noted yet. Several of my hedashell removable tonearms design have the manufacturer overhang spec at 15mm, I choosed on porpose due so many tests cartridge/tonearm combinations I have. This similar overhang characteristic help me to mount with almost none change any cartridge in any of those tonearms.

Yes, this is not exactly what you are talking about but an idea that could help.

Btw, now that you and other people are so in " deep " about cartridge/tonearm set up through accurate protractors seems to me adequate for you and every one that want to " explore " and learn on the subject to make a simple ( no money need it.! ) experiment:

- in one or two of your cartridge/tonearm combinations move the cartridge 1mm forward ( no protractor need it. ) and mantain the same cartrridge/headshell offset angle. After re-set the VTF and VTA/SRA and if you want azymuth and antiskate ( not need it for the experiment but if you want to be more " even " with today set-up. ) push the playback " button " and listen for a while.

After that and if you have the time and patience move the cartridge an additional 1mm forward and the same process but moving the cartridge 1mm and 2mm rearward.

Compare what you listened on those four different set ups against each to other and against what you are listening in your rigth now set ups.

IMHO this is a un-expected ( because the quality performance ) experiences where we could learn what is happening down " there ", I mean on playback against no-play status.

All of you that decide to " explore " in this " jungle " will be appreciated what you experienced.

Thank you in advance.

Regrads and enjoy the music,
Raul.