bran kulez wrote:I just read the following in AK:
"I have 2 mono carts and they make a world of difference on pre-1957 albums. Later mono albums (usually say "mono" on them as there was no choice before 1957), were cut on a stereo lathe, hence they are a stereo groove with the same information on both sides of the groove wall, thus sound excellent with a stereo cart and should NOT be played with the larger mono cart as the larger needle will damage the narrower groove."
Is there any truth to this?
My 2p worth :
The explanation is mostly nonsense, of course. And records with mono programme material are playable on true mono carts without risk of damage, even if cut on a stereo lathe.
But that 'one ought to be careful with playing true stereo records on true mono carts to avoid damage' has a good basis. Bona fide mono carts often had restricted vertical compliance, ie were pretty stiff for vertical stylus tracing motion. But records with stereo programme material encode both vertical and lateral stylus movement. Mono just lateral movement, even if cut with a stereo cutter head. Hence records with stereo programme material would meet far higher resistance to vertical motion than intended, and might be damaged by the stylus effectively pressing with more vertical force than was intended or healthy. So it depends on the cartridge suspension, and specifically the vertical motion arrangement.
In principle, mono and stereo groove shapes are similar in cross section. Base clearance and min width at groove top is different. As is intended seperation between the stylus contact locations on the groove walls. Groove width at nominal contact locations is 25um for stereo and 35um for mono. Base clearance nominally 10um for mono, 7um for stereo in a perfect cut groove without base radius, but spec for stereo base clearance is 2um absolute min IIRC. Nominal contact location is higher from groove base for a mono (35um) verus stereo (25um).
So yes, for optimal mono playback a stylus which contacts at the 'correct' location on the groove, and has adequate base clearance (given true mono can tolerate more swarf in the groove base) seems the ticket.
But much of the benefit of mono playback can also be obtained from an electronic arrangement that ignores vertical stylus motion. There are various ways to arrange this of differing merit. In combination with a 'correct' profile stylus and suitable arm/suspension arrangement, one then ends up with a far more realistic presentation of the sound as it was intended to be heard, IMO. And mastered for, including compensations.
And playback of stereo records on a 25um spherical on a stereo cartridge suspension doesn't damage records per se, and I sometimes intentionally do this for worn/damaged stereo records, or to obtain improved base clearance and reduce surface noise of a certain type. Most stereo sphericals are 18um radius or smaller, and offer a good compromise. 25um (1 mil) stylii still fit stereo grooves, stereo grooves aren't narrower - just not necessarily as deep, so risk fouling the groove crown on peak vertical excursions, but that never seems to happen IME !