Manual for protractor

Preface

Dear customer. First of all let us thank you for your confidence in our products. The protractor that you hold in your hands is a precision device that enables you to set up tonearms with an effective length from 8,6 up to 17,7 inches.

The calculation of parameters were carefully carried out according Løfgren’s equations aiming in reduction of the overall RMS distortion level caused by deviations from the ideal tangential position of your cartridge while tracking your records. Please read this manual carefully to have full benefit from this unique tool.

A little bit of theory

The general geometrical correlation of a tracking device based on a fixed pivot point are well known since the fundamental publications of Baerwald and Løfgren back in the first half of the 20th century. The conclusion of both publications was that such a tracking device must have a cranked head with a defined overhang. The offset and the overhang vary with the effective length of the tonearm itself. While tracking the record the stylus matches tangential position in the groove at two points – the inner and outer Null points.

But what does this mean? Have a look at the picture below:




Everybody of us listening to Vinyl records at least once has heard of terms like “effective length”, “overhang”, “offset” etc. The sketch above shall give you an overview on the correlation of theese terms.


What does the real-life tracking curve look like? Have a look at the following two images that show the tracking curves of a REGA, a Scheu Cantus 12 inch and a virtual 14 inch tonearm.




One can easily see that the larger the effective length the flatter the tracking curve gets. In terms of geometrical distortions we have the following situation:





The REGA tonearm at 57 mm tracking radius shows 1,6% in distortions whilst the 14 incher still is below 1%!

At inner and outer Null points the distortions disappear as the tracking there is tangential. The distortions mentioned so far are only a result of misalignment that cannot be avoided in pivoted tracking devices! What your cartridge does additionally is a completely different thing.

Another point to mention is that with growing effective length the tracking and distortion curves converge towards the x-axis and therefore one can say that the tangential tonearm is the border case of a pivoted tonearm with infinite effective length ;-)Characteristics of the template

The major goal was to find a tracking geometry that suits LPs in a perfect way. Out of a 100 records we checked the inner and outer radii and found out that the IEC recommendations of 60,325 and 146,05 mm were matched well by the large majority of records determined. After Løfgren’s equations this results in 70,2 and 116,6 mm for the Null points and a linear offset of 93,445 mm.

Older records dated back in the late 50s and early 60s sometimes have recorded grooves at down to 56 mm! Taking this into account we have calculated a second set of parameters and printed another template on the backside. There you can also find a strobe to adjust 33 1/3 und 45 rpm with light of 50/100 Hz.


Setup – an easy task

Caution: Always bear in mind that cartridges are very fragile equipment and therefore must be treated extremely carefully. We are not liable for any damage caused by using this template!.

The template was developped for absoute easiness in use. The thickness of 3 mm simulates the 180 gr pressings sold nowadays perfectly. This means that you can also preadjust the VTA.

 

Please put the template on the platter and put the liner on the template. Carefully press the liner with the adjust pin into the hole that corresponds with the pivot-spindle distance given by the manufacturer of your tonearm (i.e. Abstände von 200-235 mm for a REGA [222 mm]).

 

Twist the liner towards the pivot point of your tonearm.

 

Measure the distance pivot-spindle.

The next step is to adjust the overhang. The stylus must touch the line on the template at the point that you measured with the liner. The template has 1 mm marks. If you cannot move the cartridge to touch the matching point on the template in any way than anything might be wrong with the data given by your tonearm manufacturer.

 

The next step is to adjust the offset. First of all check at the inner Null and twist the cartridge to make the cantilever aligning with the lines. In some cases this can also be done by using the housing of the cartridge. Please also take care that antiskating compensation is set to zero force as otherwise the result is falsified! In case the cantilver aligns in both – inner and outer Null – the setup work is done. If this is not the case please check again the overhang. For sure the position was altered! Then repeatedly check the Null points.

 

Have fun listening to your records!