stylus for mono vs stereo grooves

[Bran Kulez]

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?

[Alec124c41]

I doubt it.

Cheers,
Alec

[Coffee Phil]

Hi Bran kulez,

There may be some truth to it but I don't think it is a big deal. For Lps my main cartridge is a Sonus Blue. It has a replacement stylus which is a genuine Sonus I'm not sure if is the more exotic type of the original but I'm pretty sure it is at least an elliptical. I also have an ancient "true mono" GE RPX which has a 1 mill conical for Lps. For mono I sum the channels actively in my mono phono stage. Other than the much greater output from the GE and its reduced tracking ability they sound remarkably similar.

If you are looking to get the ultimate from old records you will want an assortment of styli but for most mono Lps it will be difficult to tell. Also spending big bucks on a "true mono" cart is not necesary. My GE was a junk box find and a NOS GE styli assembly (Lp & 78) for it cost ~$20. Since it is a "classic" I wanted it in the arsenal. I do like the sound of it and I'm glad I restored it. Also now when the "true mono" zealots claim that you must have a "true mono" vs a strapped stereo body I know how serious to take that claim.

Phil

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?

[Ldg]

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 !

[Ldg]

Oops..a correction on that last post. Should read "Nominal contact location is higher from groove base apex for a mono (17.5um) verus stereo (12.5um).

[Bran Kulez]

Thank you Alec124c41, Coffee Phil and ld for your input, but ld, I'm going to have to unwrap this one carefully...

ld wrote: 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

That makes sense for the cartridge...

ld wrote: Groove width at nominal contact locations is 25um for stereo and 35um for mono

which means a larger diameter stylus tip for mono

ld wrote: Nominal contact location is higher from groove base for a mono (35um) versus stereo (25um).

o.k., I'm assuming that in section, mono and stereo lp's have the same distance from the bottom of the groove to the top of the groove as measured plumb, i.e perpendicular to the horizontal...

so if a 1 mil stylus is palyed in a stereo groove, the contact area of the stylus tip may not reach the nominal contact location of the groove.

If this is correct (I'm just guessing here) then it seems that there should be no damage done to the part of the stereo groove that matters because the 1 mil tip won't even reach it.

I'm still trying to wrap my head around base clearance and how it affects the stylus tip...

[Ldg]

ld wrote: 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

That makes sense for the cartridge...

Yes, consequences of restricted vertical motion follows the suspension. Rather than the stylus size/profile. My point is this can be the mechanism by which true stereo pressings might become damaged by playing with true mono cartridges, rather than fit of a 1 mil (25um) spherical stylus in a stereo groove. It does actually fit !

ld wrote: Groove width at nominal contact locations is 25um for stereo and 35um for mono

which means a larger diameter stylus tip for mono

Yes

ld wrote: Nominal contact location is higher from groove base for a mono (35um) versus stereo (25um).

o.k., I'm assuming that in section, mono and stereo lp's have the same distance from the bottom of the groove to the top of the groove as measured plumb, i.e perpendicular to the horizontal...

so if a 1 mil stylus is palyed in a stereo groove, the contact area of the stylus tip may not reach the nominal contact location of the groove.

If this is correct (I'm just guessing here) then it seems that there should be no damage done to the part of the stereo groove that matters because the 1 mil tip won't even reach it.

See my correction BK, nominal contact location is higher from groove base for a mono (17.5um) versus stereo (12.5um).

No, groove depth is nominally deeper for mono. Absolute min groove depth spec is c 1.5 mil for mono, and c 0.7 mil for stereo. So worst case, the nominal contact height for mono stylus in a stereo groove would be 25% of the depth up from the base, versus 18% for a stereo stylus in a stereo groove.

That's not significantly different in my book, and so if a 1 mil stylus is played in a stereo groove, the contact area of the stylus tip would be close but a little higher than the nominal contact location of the groove. It fits !

I'm still trying to wrap my head around base clearance and how it affects the stylus tip...

Mono spec groove base radius is 0.25 mil max, versus 0.2 mil max for stereo. There's not much in it. So a 1mil mono spherical stylus would have a nominal min clearance of about 5um, whereas for a 0.7mil stereo spherical that would be only 2um. This is significant in avoiding manufacturing imperfections/swarf in the groove base, and general crud in the groove base affecting surface noise.

HTH !

[KentT]

I like the .7 mil conical tip best for older mono records. And it is a good option to have. But traditional old school mono cartridges are not vertically compliant so will harm stereo records and post 1967 mono discs which require stereo compatibility due to being cut on Stereo cutter heads.

[Bran Kulez]

Thanks Ld! So here's my take on the MONO groove dimensions. I'm assuming 45 degree angles for the groove walls... Am I getting close?...

[Ldg]

Hi BK. Nice drawing. Looking at the NAB 1964 standard for mono grooves, I get the following dimensions :

A 1.1 mil (not less than)
B 0.7 mil
C 0.25mil
D 2.2 mil (not less than)
E 1.4 mil

Dimensions A and B strictly should be reference to the horizontal plane where the groove walls intersect, rather than the radiussed groove base.

Where this contradicts the figures I've posted on this thread, suggest use these revised ones. HTH !

[flavio81]

Nice drawing BK! What do you use ?

[Bran Kulez]

Thanks Ld!

ld wrote: Dimensions A and B strictly should be reference to the horizontal plane where the groove walls intersect, rather than the radiussed groove base.

I'm assuming you mean that A & B should be measured from the top of the groove. Is this correct?

flavio81 wrote: Nice drawing BK! What do you use ?

Thanks! Autocad 2000 that I've customized over the years.

[Ldg]

I'm assuming you mean that A & B should be measured from the top of the groove. Is this correct?

BK, if you extend the two groove walls they intersect at a point. The horizontal plane containing that point should be the datum for dimensions A and B.

Hey, now you can add a sphere of various radii to scale and see where the contact locations and check clearance between the base of the sphere and the groove bottom !

One additional point, the NAB spec defines absolute minimum limit groove dimensions rather than what might be common practice. Yosh's excellent site might have some further info for real grooves.

[vexorgtr]

Esoteric Sound is big into "Archiving" and being able to play any record ever made if it's flat and has a groove. Here's what they said about it... Seems logical. Their approach is always "Use the stylus that sounds best"

Mono LP and 45 RPM records when introduced in 1947 & 48 were made to be played with "microgroove styli" of 1.0 mils in radius. While modern stereo styli will play these records fairly well, their size varies from 0.5 to 0.7 mil in radius, thus placing them lower in the groove, in the area of most wear.

You will usually hear an improvement in noise and distortion when older mono records are played with their intended stylus the D5110J. For more worn records we offer the larger D5112J, a 1.2 mil stylus. Because it is larger we have made it elliptical to better trace the highs. It does wonders on beater 45s. On some occasions, these styli can even help some 78s and broadcast transcriptions.