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Cartridge tests - Vertical Tracking Angle

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Cartridge tests
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vta-2m-black

Vertical tracking angle measurement is made by recording intermodulation sum at 1kHz of 370Hz and 630Hz test tones on DIN 45 452 test disc, with tracks that progressively increase in cut angle.


VERTICAL TRACKING ANGLE


WHAT IT TELLS US

Vertical tracking angle, if it is wrong, is a source of distortion. It is the angle subtended by the cantilever to the record surface, as our diagram shows, and it is meant to be the same as the vertical cutting angle, set to 22 degrees. If it strays from this value, distortion results. Few cartridges actually achieve 22 degrees or anything close, most measuring out at 30 degrees or higher. The reason is that achieving 22 degrees means using a long cantilever and suffering limited disc clearance, causing the cartridge body to hit disc warps.


What does this tell us? It means high distortion on vertical modulation, affecting left and right images, but not centre images. The amounts can be large, from around 1% second harmonic if VTA is right, up to 5% or more with incorrect VTA, as measured on the +15dB vertical cut of CBS-STR112.


It has hard to pin down the subjective impact of low order distortions but incorrect VTA does seem to slightly mess the sound, degrading a sense of clean precision. As VTA is also linked to cartridge azimuth (see our Adjust+ measurement system review) there is quite a lot going on here.



HOW WE MEASURE IT

We measure VTA using the German DIN 45 542 test disc. The 1kHz sum product of 370Hz + 630Hz test tones, cut at successively increasing angles, is measured with a spectrum analyser. The result is graphed to find where the sum tone reaches a minimum, which gives the VTA figure.


We also measure distortion on vertical modulation with CBS STR-112 and this correlates well with the vertical tracking angle error provided by DIN 45 5452.


vta-graph-2

Vertical tracking angle is determined by plotting measurements on a graph. Shown are results for a Denon DL103R MC cartridge, showing it has correct VTA of 22 degrees.



 

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