This picture shows part of GECOM-Technologies' extensive HF-measurement facility.
A comparison of phono alignment protractors for cartridge alignment
Published July 26th, 2014 by gecom-tech, Germany
As generally agreed, the process of aligning a phono cartridge “right” is a fairly complex one and anything but easy.
The magazine “Stereophile” published a well written and very informative article on the topic:
www.stereophile.com/reference/arc_angles_optimizing_tonearm_geometry/index.html
I will take this article as the basis of my comparison of phono alignment protractors.
In this comparison I will concentrate on minimizing tangential error and thus minimizing tracking distortions.
There are 2 major versions of protractors:
One features 2 separated points (version 1) where the cartridge has to be aligned.
The other features 1 single mark point (version 2) for the orientation of the cartridge and the cantilever - which needs to be aligned to make sure the later is in-line with the pivot of the tonearm.
With version 1 you need to know both “null points” of the given tangential curve.
This allows you to choose them by measuring the offset angle at the given mark point.
Version 2 usually offers different mark points for several tangential curves to choose from.
One of the least expensive protractors is from Ortofon.
With this protractor the spindle hole was way too large.
The protractor is made from very thin material.
Prior to start the alignment, you should support it by a layer of strong cardboard to simulate the thickness of the LP.
This protractor is a member of version 1 - sporting 2 null points.
The thickness of each line is approx. 0.25 mm.
The mark points - null points - are even larger.
A precise routine with a derivation less than 0.5 mm and error smaller than 0.5° is very hard under these circumstances.
Please note:
this photo - as well as all pictures taken of the protractors featured in this article - were shot with macro lens and in identical distance.
You see clearly the very prominent outline of the “arrow” - more than 0.5 mm, which makes the actual alignment very difficult.
It is enough however for a first “general” positioning.
Another member of version 1 is the protractor made by van den Hul.
This protractor is made from mirrored plastic and features approximately the thickness of a standard LP.
The hole for the spindle is quite accurate and has only very little “play”.
The lines are approx. 0.5 mm “strong”.
The picture clearly shows the “double lines” - an effect of the mirrored surface.
Due to the way too broad lines, a precise alignment is however practical impossible.
A member of version 2 is the protractor made by Clearaudio.
The effective length of the tonearm is marked in steps of 1 mm - with a resolution of 0.2 mm.
The center drill for the spindle has significant play - approximately 0.5 mm.
There is a choice of 4 different tangential curves - made possible by easy-to-change mounting of the main plate.
The stroke width of the lines is 0.4 mm.
The main plate has approximately the thickness of a standard 140 gram LP.
-
Because of the stroke width plus the 0.5 mm play of the spindle hole a precise alignment is not possible. The price for this protractor is approximately EURO 200.
Another member of variant 2 is the SMARTractor by Acoustical Systems.
This is a mirrored plastic plate with a choice of 5 tangential curves.
The plate itself features the thickness of a modern 180 gram LP.
The center hole has absolutely no play - all the user has to do is to select the fitting center insert from a choice of 3 different inserts coming with the protractor.
The effective length of a given tonearm can be precisely read out with an accuracy of 0.01 mm.
If the pivot isn’t clearly marked on the bearing house, there is a special crosshairs / reticule coming with this protractor which is very helpful to align to the pivot. Further to this, there is also the supplied choice of a needle pointer for the pivot.
The marking lines are explicitly fine - with a mark width of only 0.1 mm.
This is the only protractor under review featuring single laser-shot alignment point for the stylus tip of the cartridge.
There is a very precise read-out possible here, tanks to the supplied metal and glass magnifier in its dedicated frame.
For a comparable precise read-out the other protractors in this survey all would need a USB-microscope.
In summary this is a real precision-tool.
The red pointer marks the laser-shot indention for the stylus tip.
The larger point below is the mirrored image.
Same applies to the lines - the thinner line is the laser-engraved mark line, the slightly thicker the mirrored image.
Despite its retail price of approximately EURO 500, I can recommend this protractor with a clear conscience.
Precision, easy operation and operational reliability justify the price.
The result of the more precise alignment was reviewed with a test record with a constant 1kHz test tone over the full record side.
First we made a measurement of a combined alignment with the Ortofon and Clearaudio protractors. The output of the phono preamp was connected to a Rohde & Schwarz UPD Audioanalyzer. The summary klirr factor (distortion factor) was measured and weighted over the whole record side.
The result was 1.22 % distortion.
Following this we aligned the very same tonearm/cartridge combination with the SMARTractor and repeated the measurement.
The result was 0.48% distortion.
This improvement is significant and was clearly audible verified in listening tests.
This is the SMARTractor set-up during alignment.
A sensible and effective product.
All rights and Copyright: GECOM-Technologies GmbH, Germany
Druckversion 