I should understand this subject better than I do, but here goes. The problem with using a stereo cartridge on a mono record is that the stereo cartridge has both vertical and horizontal compliance, which on a mono record having music only in the horizontal plane opens up the possibility for picking up a significant amount of surface noise. On new reissues of mono LPs this is really not a problem, or at least it shouldn't be. For old and well used mono LPs, though, the noise difference is frequently quite pronounced. If the wiring in the cartridge is set up to ignore the vertical information, the net effect is identical to using the mono button on preamps so equipped, and is also identical to using Y cables as already discussed. I have a mono cartridge and can attest that it sounds significantly better on old mono records than using a stereo cartridge, but on new re-issues, the advantage is less pronounced. One of my stereo cartridges is an Ortofon 2M Black, which has a shibata stylus. The shibata shape is not easy to set up for quiet tracking with the vertical tracking angle being particularly critical. For that reason, I prefer the much more forgiving conical stylus geometry for mono. I hope that helps.
