Where to find uni din protractor

Tawa,
If you want to try an alignment like UniDIN, you can use a two point protractor with similar nulls. The difference between the various alignments for a given arm basically amounts to setting up to different nulls, as explained here:
http://odysseytonearms.blogspot.co.uk/search/label/Formulae

I am sure that if you wish to experiment without spending a lot, it would be possible to use the free Chpratz protractor from VE.

Or, if not that, then have Yip make a Mint for a specific known effective length or mounting distance using given nulls.

The important thing with any protractor is to persevere with trying to obtain the required zero error degrees when the stylus is on the nulls.

Hi Nikola,

Some more boring stuff...

There is an RIAA standard from 1963 (and subsequent later revisions and metrications) which gives the record hole size as 0.286", with a tolerance of +0.001" and -0.002". This means that the hole can be between 0.284 and 0.287 (7.214mm to 7.289mm).

Why should this be? It seems a strange size until you remember that the standard was established in the age of imperial sizes, and the nearest fractional size is 9/32" which is 0.281" (7.14mm). This would have been the nominal size for a spindle, and the records were made to fit neatly on a typical spindle, not vice versa.

If a spindle diameter had been within the range for hole size, the record will be a push fit or an interference fit. It won't drop on or lift off easily.

The spindle should probably ideally be 0.282 +0 and -0.002 (7.11mm to 7.18mm)

From a quick internet survey of measured spindles, typical modern spindle sizes are around 7.1 to 7.2mm ie 0.279" to 0.283". In other words 9/32" +/- 0.002", which might be expected.

So, with regard to protractors, these are small amounts and the effect on set up is minuscule regarding the position of the nulls if the error in position is in that direction - variations in distortion in the hundredths of a percent (ie 0.01%)

For a protractor that uses the Dennesen principle, like the Smartractor/Unitractor, any variation in the overhang direction of 0.1mm would produce an error in offset angle in the order of 0.08 degrees, which, depending on the direction of the overhang variation, can actually reduce average distortion for a Lofgren A IEC alignment.

However all these numbers are tiny and bear no relation to the variation in accuracy normally achieved in practice (with whichever alignment). Usually the overhang is easiest to set and both the Mint and the Uni protractor, make much of how accurately their items are made, to within 0.01mm. So perhaps if you have an arm with a micrometer adjustment for overhang you could perhaps work to those tolerances with patience and time.

However, the restricting factor is usually how accurately the offset can be set, especially on an arm where adjusting the offset also affects overhang. If you get within a tenth of a degree you are an ace. Worrying about hundredths is silly.

Best wishes to you and all Audiogoners for 2015.
John
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Fleib,
Did you ever try nulls at say 70 and 124 for lower outer distortion?
Thanks for the Uni-Din nulls - I'd presumed they were around that, similar to FR66.

Tawa,
Do keep in mind that small errors in offset and overhang can lead to big errors in distortion at different points on the record, or not, depending on whether they add or cancel.

Fleib,
I have advised Rega owners to try a similar alignment which avoids having to slide the cartridge overmuch.
http://odysseytonearms.blogspot.co.uk/2011/09/stevenson-alignment.html
But as you say, it means more distortion on the outer inch or so.

For albums recorded right into the label, it also depends whether that last track or movement is a quiet one or a loud one, and what profile stylus is used.

I suppose it all does highlight the fact that every alignment is ultimately decided by the inner and outer recorded radii and LPs don't fare well in that regard: an alignment for seven inch singles played with an 8" arm will have less distortion than any LP set up...