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STYLUS TRACKING
The basic stylus is conical, with a spherical tip; the included angle of the cone is 60 degrees. Most modern styli are elliptical: i.e. they look the same from the front, but from the side they have a much narrower angle. This enables them to track movements in the groove more easily (as the groove moves from side to side it effectively narrows - not across its direct width but across the diameter of the conical tip, at an angle to the direction of travel: consequently a spherical tip will ride up in the groove).
The illustrations below could apply equally to a spherical tip and an elliptical tip seen from the front: in practice I would always recommend elliptical.
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A modern record groove should be a neat 90 degrees, with the stylus making contact at only two points part-way up the groove wall, thus avoiding any debris in the bottom of the groove. (Some modern microgroove styli have a flat section at the contact point, giving a wider area of contact which reduces wear: however it can also increase noise from worn or damaged groove walls and I would be dubious about its use for 78s). |
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In the case of microgroove records the specification for the stylus tip is 1 thousandth of an inch for mono, or 0.7 thou. for stereo (with variations for ellipticals). For 78s the mid-1950s specification is 2.5 thou, and this works well enough in a properly cut groove. However older 78s were cut to be used with steel needles, on the assumption that the needle would wear down to fit the groove in the first few seconds: when this wider groove is tracked with a 2.5 thou stylus the result is 'bottoming' as can be seen here. |
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Here the combination of a larger basic size - 2.8 thou. works on the majority of records, although larger sizes may be helpful with very old records - and the truncated tip (which is spherical down to the contact points but truncated below) result in vastly better tracking. If the stylus is elliptical this also brings a considerable improvement in distortion. |
