Photo of Left Channel Groove Wall - Ortofon Test Record

J.R. Boisclair

Well-Known Member
Jun 30, 2020
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Here is a photo I took a couple days ago of the end of a frequency sweep test track on the Ortofon Test record. What is truly amazing about vinyl playback is that such TINY undulations in the groove wall result in something we can hear. The distance between each peak is about 11 microns (about 100th the width of a human hair).

Conicals usually have about 25 micron radius at the contact point, so no way they can reach down into these undulations. They'd read the groove as nearly a featureless straight edge. Ellipticals aren't a great deal better. They are usually around 12 micron radius so they'd dive slightly between the peaks but they'd never hit the bottom of the basins between peaks, essentially dropping stylus velocity and therefore the output. A fine line contact stylus would reach down all the way *IF* it had insignificant zenith error. As zenith error is introduced, the fine-line contact stylus begins behaving like an elliptical.

This is just a high frequency track, but when musical content gets complex the distance between the peaks REDUCES. Of course, the distance between peaks also reduces the closer you get to the center of the record. This means that you don't necessarily need to have very high frequency content for a fine line contact stylus that exhibits zenith error to not be able to reach down into the groove basins.

Further, not being able to reach into the groove basins necessitates that the stylus has to perform a vertical excursion to make it past the "pinch point". This "pinch effect" then causes the cartridge motor to create an electrical signal that is NOT directly related to groove content.

This is just part of the story. I find it fascinating. I hope you enjoy.

The first person who calculates the error in this photo gets a Gold Star!
 

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Here is a photo I took a couple days ago of the end of a frequency sweep test track on the Ortofon Test record. What is truly amazing about vinyl playback is that such TINY undulations in the groove wall result in something we can hear. The distance between each peak is about 11 microns (about 100th the width of a human hair).

Conicals usually have about 25 micron radius at the contact point, so no way they can reach down into these undulations. They'd read the groove as nearly a featureless straight edge. Ellipticals aren't a great deal better. They are usually around 12 micron radius so they'd dive slightly between the peaks but they'd never hit the bottom of the basins between peaks, essentially dropping stylus velocity and therefore the output. A fine line contact stylus would reach down all the way *IF* it had insignificant zenith error. As zenith error is introduced, the fine-line contact stylus begins behaving like an elliptical.

This is just a high frequency track, but when musical content gets complex the distance between the peaks REDUCES. Of course, the distance between peaks also reduces the closer you get to the center of the record. This means that you don't necessarily need to have very high frequency content for a fine line contact stylus that exhibits zenith error to not be able to reach down into the groove basins.

Further, not being able to reach into the groove basins necessitates that the stylus has to perform a vertical excursion to make it past the "pinch point". This "pinch effect" then causes the cartridge motor to create an electrical signal that is NOT directly related to groove content.

This is just part of the story. I find it fascinating. I hope you enjoy.

The first person who calculates the error in this photo gets a Gold Star!
Its amazing how it works.
 

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