The fastest way to damage a record is to play it back with a worn or damaged cartridge. A stylus that is worn is believed to have burnished, flat facets with sharp corners that place far greater pressures on the record than usual, causing permanent deformation and in some cases, outright recutting of the surface.
Worn stylii are anecdotally believed to cause audio distortions such as sibilance, harmonic distortion, etc. When these distortions occur at all locations on a record, and are evenly distributed through loud and soft passages, the stylus may be suspected.
Unfortunately, there are no hard and fast rules for determining when a stylus is too worn. Manufacturers usually provide lifetime figures, measured in hours of playback. However, these numbers can be affected by any number of factors, including the dirtiness of the played records, the tracking force, etc. A microscope of 200X power or higher is useful to visually inspect stylii. Again, no distinct rules exist for determining stylus quality, but any sort of flat surface on the stylus is a clear sign of wear.
Every time the turntable is used for playback, the cantilever should be inspected to see if it is visibly damaged or bent. When using a conical stylus,
The azimuth of the stylus on the cartridge in the horizontal plane (as opposed to the VTA) should be within 5 degrees of straight. If the