|Posted by "AudioAficionado" on June 17, 2018 at 4:05 PM|
The vinyl record master is cut horizontally, meaning there will always be distortion when using a pivoted tonearm. The trick to reduce this problem is to adjusting phono cartridge offset (cartridge alignment on the tonearm head shell). If done correctly, groove and surface noise will be reduced, and music will have a greater sense of space and dynamics.
Correct cartridge geometry is primordial for maximum sound performance. This geometry is dictated by the effective arm length (the distance between the platter spindle and the tonearm pivot point, plus the tonearm overhang). Most manufacturers provide a protractor with their turntable to set your cartridge offset, if not, you may look for a template online or buy a commercially available one, like Dr. Feickert Protractor.
What is the science behind it?
A pivoted tone arm in contrast to the tangential tone arm tracks the record in an arc, it cannot follow the exact path of the cutter head, but it can be set to track two null points throughout that path. Aligning the cartridge to these points, which are generally near the beginning and end of the disc, will eliminate all errors at this point and greatly decrease distortion across the disc. If this is not done correctly, even by a couple of degrees, the null point will move away of the record surface and distortion will increase.
Can you tell me more about the null points?
There are three generally use equations to establish the null points:
Baer Wald - minimizes and equalizes distortion across the record.
Lofgren - minimizes distortion between the inner and outer grooves resulting in the lowest average distortion, but there is slightly higher distortion close to the inner and outer grooves.
Stevenson - optimized for lower distortion at the inner groove, but there is increased distortion elsewhere.
Dr. Feickert Protractor offers the parameters to set up the offset using any of the three equations, so the user can experiment.
How do I use the Protractor?
First, we need to make sure that the effective length (distance from de spindle to the tonearm pivot) is set to the manufacturers recommendation. This protractor should work with most tone arms from 9” to 14” with minimal error. To measure the length, adjust the ruler to slide down the pointer over the tonearm pivot. Tables with an adjustable tonearm base may need adjustment. While tables with a fix tonearm should have the correct length from the factory. Anyhow, I always check these parameters as any deviation will affect the geometer and positioning of the null points. If the effective length is correct proceed to the next step.
Now adjust the cartridge body until the stylus drops exactly over the markings of your desired alignment, in the center of the protractor. Then move to the outside markings to set the cartridge offset. Make sure the cantilever rather than the body is in line with the markings.
Last step, move to the inner markings to confirm your alignment. If everything matches you are finished. If it is not aligned with the markings repeat the procedure from the start.
This is not a cheap accessory, but it is effective at simplifying the phono cartridge mounting process. It improves accuracy and repetition, while providing flexibility to try different alignments. Also, it would last a life time! If you are serious about turntable set up or a dealer that provides this kind of service, it is well worth the investment.
If you liked this article you may be interested in our Turntable Set-Up Guide.
Dr. Feickert Universal Protractor
Estimated Price: $259
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