Jagged24

Cartridge alignment with an arc protractor

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For years I have aligned cartridges on my 9” and 12” PU7 arms (both use Linn-type mounts) using the handy single-point universal cartridge protractor that comes with them.

However convenient, universal single-point (or even 2-point) alignment protractors work by simplifying the arm’s actual tracking geometry, and are therefore a bit hit-and-miss.

Arc protractors, on the other hand, are in theory more accurate because they specify a made-to-measure arc for any arm with a given pivot-to-spindle distance, with bespoke alignment grids calculated specifically for that arm.

I therefore invested some time this BH weekend to find a simple way to create and use arc protractors for cartridge alignment, with simple DIY tools. This post is to share my experience in the hope that others will find it useful. (I haven’t searched the forum – it may be that I’m repeating what’s already covered elsewhere). This note only covers the steps I took for cartridge alignment; it assumes that you already have adjusted azimuth, VTA and VTF correctly.

I used the latest version of Conrad Hoffman’s free Arc Protractor template generating programme – link here http://www.conradhoffman.com/chsw.htm

Choose “Custom arc template generator …..”. I found it extremely easy to use, and very accurate. The download comes with detailed instructions.

All I had to do was to measure the pivot-to-spindle distance for each arm accurate to 0.5mm or better, choose the alignment algorithm (the programme calculates Lofgren A (Baerwald) or Lofgren B or Stevenson) and print out the calculated arc protractor on photo paper using my cheap home inkjet. The printout comes with alignment marks at 100 and 200mm – I checked them with a steel ruler to make sure the printout was at exactly the right scale. It was, without any printer adjustment whatsoever.

Alignment using the included instructions was equally simple. Interestingly – for both arms and two different cartridges with quite different construction – the arc protractor’s optimal alignment had about 3-5mm difference to the universal protractor I used to use. It took about 20 min to complete.

Did it make a difference? Yes – particularly on records with grooves stamped closer to the spindle. There was a clearly audible decrease in end distortion, particularly on the 12” arm, and background noise was lower right through the records.

Very well worth trying IMO!

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Interesting! Though 3-5mm difference seems hell of a lot. Not surprised it made a difference esp on the 12".

I had a loan of a Dr Feickert to check my alignment and it was spot on after using one of the universal ones. Must give it a try though, at least as a check on what I have at the moment.

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I printed out Hoffmann's arc protractor and aligned my cartridge with it (an easy task).  The dealer who installed and set up my turntable (Michell Gyro SE with TecnoArm) came around with a Dr Feickert device to check the alignment and found it to be spot-on.  Neither method gave the same result as a conventional 2-point protractor.

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1 hour ago, wino2020 said:

Though 3-5mm difference seems hell of a lot.

As Logan notes - the Hoffman arc protractor does appear to give different results from the universal ones. I think the reason for this could be the difference from "default" in the pivot-to-spindle distance  - the universal protractors work I assume on a default value. For example, I found the P2S distance for the 12" PU7 was exactly 288.5mm, and so was able to print out a very accurate alignment arc customized for this measurement.

The sound is now spot-on, though, allaying any initial concerns.

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No question; even a degree or two out makes a significant difference to the dynamics (ergo, the s.q.). I got fed up with cardboard and paper for my 12" Ace Anna and PU7, do got an original Dr. Feickert.  Magic (but still a heart-stopping faff with £3 -4000 cartridges !)

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 All of the effective best with YOUR chosen compromise - we prefer our Sept.-Oct. 1987 HI FI REVIEW heavy plastic protractor-rectangle-thingie, with hearing to prove it ...

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Super Wammer
On 8/29/2016 at 07:40, Logan said:

I printed out Hoffmann's arc protractor and aligned my cartridge with it (an easy task).  The dealer who installed and set up my turntable (Michell Gyro SE with TecnoArm) came around with a Dr Feickert device to check the alignment and found it to be spot-on.  Neither method gave the same result as a conventional 2-point protractor.

I use a two point given free with practical hifi in the 70s .. i measured the length of my arm spindle to pivot and keyed in the data .. printed out the template for lofgren A  and surprise surprise it was bang on .. .  So that was a pleasant few minutes and a quick check only to find all was A OK and that my freebie protractor from the dinosaur age has been serving me well over many years (what is nice about it is it is plastic the same thickness as a 180 gram vinyl record so arm height can be done at the same time)..

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