Mono cartridge classification

While researching various mono cartridges I notice that Ortofon makes specific reference to the cartridge (their SPU cartridges anyway) being best suited for playback of certain mono recordings. I don't recall seeing this mentioned for other manufacturers. These references are given in the form of a number (25 or 65 is what I've seen) followed immediately by a symbol that looks like a stylized letter "n" and then the letter "m". What does this symbol/abbreviation mean? How do I know which of these a certain recording is in? and I'm assuming its not that important to worry about since I don't see it mentioned by other manufacturers - or is it?
The only difference I know of between Mono records is early mono's, pre Stereo & the 60's the groove profile is differant than they are now and when stereo was introduced. So the needle profiles are differant. I have not had any problems with what I use but some feel there is a differance in sound between them the two. There are threads here on the subject.
Dear Pkemery: Why don't you ask Ortofon directly? Ortofon was your ask source, right?

Regards and enjoy the music,
Oooh, boy. This is a pretty complex area you're getting into. Google will be your friend. The wide range of contradictory information you find will be your enemy. I'm just learning about the world of mono myself, so take everything I say with a grain of salt. And I hope those more knowledgeable will double-check me. But here goes:

That symbol you're talking about is almost certainly the symbol for micron (also called a micrometer). The thing to remember is that 25.4 microns equal 1 mil. Generally, you will see today's typical elliptical stylus dimensions stated as .3 mil x .7 mil. These serve well for playing mono records. When you see a stylus specified in microns, just convert it.

Despite the fact that I said a .3 mil x .7 mil stylus is fine for mono records, many people maintain that it is best to use styli that are similar to those used at the time the recording was made. VERY GENERALLY speaking, records that are not labeled either "mono" or "stereo" are mono recordings. These, according to some, should generally be played with spherical (aka conical) styli of 1 mil (25.4 microns). If the record is labeled "mono," it was probably made during the early stereo era. Since the record grooves were narrowed at this time, it's GENERALLY best to play these records with spherical styli of .7 mil.

Modern high-end cartridge makers like Lyra are today making very expensive mono carts and maintain that variations of modern fine-line styli are best for playing mono records.

Also be aware that cartridges that are sold as mono carts actually do produce a mono signal (Denon DL-102, Grados). But some are called mono only because they have a bigger spherical/conical stylus appropriate for mono recordings——BUT their output is stereo (Ortofon D25M, I think). The signal must be summed by a mono switch on a preamp, by wiring the cart for mono, or by using a double-Y connector to sum the signals.

Keep in mind that in discussions of mono, the term "LP" is used to refer to 33-1/3 RPM records, as distinct from 78 RPM.

If this isn't confusing enough for you, I invite you to hit Google. A very good summary is offered here:

There's also a mono forum at Lenco Heaven:

Hope this helps, but I'm guessing it might not!
Sorry. The first sentence of my fourth paragraph, above, should read:

"Also be aware that SOME cartridges that are sold as mono carts actually do produce a mono signal (Denon DL-102, Grados)."

Hesson11, I've posted comments on selecting stylus size relative to the records to be played here and elsewhere and thank you for your added descriptions. I've also read the suggestion that Lyra narrow profile styli are recommend for mono playback. But then I ask if the Lyra recommendation was for modern mono reissues (cut with current stereo cutter heads as apparently no mono cutters remain) as compared to original '50s monos cut with a wider groove? So far, I've not seen an answer to that.

Also, you include mention of Grado as an example of "mono carts (that) actually do produce a mono signal". My understanding is that a true mono cartridge will only pick up lateral motion, not vertical. Several sources have suggested that Grado mono cartridges are merely stereo designs that have been strapped internally for mono output. In other words, they still pick up vertical signals, thus would be more susceptible to noise. Have you found a confirmation one way or the other?

Lastly, I'm not aware of any manufacturer who claims a cartridge is mono simply because it has a conical stylus. Do you have an example? Many early stereo cartridges had conical styli, the current survivor being the Denon 103.
Thanks for checking me, Pryso. I need it! Still learning.

Here is a post by Jonathan Carr of Lyra that says Lyra listened to a wide range of mono recordings in developing their stylus. He says the records were both pristine and well-worn, but he doesn't cite the eras they represented. I assumed that by well-worn, he meant they listened to records from many eras, but he doesn't explicitly say that:

About Grado, I was careful to say that they produce a mono signal. As you said, I believe they are "mono carts" in that they are strapped to sum the L and R signals. Like you, I believe I've read that they do have vertical compliance, but I can't be sure. So they probably can't be considered TRUE mono carts like the Denon DL-102.

For your last question, the KAB website states that the KAB/Ortofon OM-1M is a stereo cart with a 1.1 mil stylus for mono playback. I believe this cart is the same as or similar to the Ortofon OM D25M, but I may be wrong about that. Do you know for sure?

I wish I had time to track down and post all the references I've drawn from——but I don't. So I hope others like you will continue to fact-check me. Not that we'll ever solve all the contradictions of mono! THANKS.
Hesson11, thanks for the link to Carr's information. Nothing like going to the
horse's mouth! Here is information I posted on VA some time ago. Mr. Carr's
information seems to correct part of that -

"I believe you must first consider which records you will be playing before
buying a mono cartridge. From reading I've done, here are my conclusions.
Note this applies only to 33 LPs, not 78s. Dates refer to master cutting, not
performance date for reissues. This is a function of the groove shape created
by the cutter head.

Pre-stereo era monos (roughly '48-'57), select a 1.0 mil conical stylus.

Early stereo era monos (roughly '58-'68), select a 0.7 mil conical stylus.

Recent mono reissues (mid '90s to present), select a mono cartridge with a
modern narrow stylus profile.

Lyra may have been the first to promote narrow profile stylus tips for better
performance in mono cartridges. I suggest this may be true for playback of
the many mono reissues, but not as good for older originals. I've heard that
mono cutter heads are no longer available so reissue monos are now cut with
stereo heads, but with lateral motion only. This is not to say a mono cartridge
with a narrow profile stylus would not sound OK on earlier pressings, it
simply would not be optimal."

I've since purchased a mono Denon 102 but installation awaits the
completion of a new plinth for a two-arm table.

I'm not familiar with Ortofon cartridges so no help from me there.

If you think there are lots of contradictions with mono lps, start doing some
research on 78s! I have a 4-record 78 album of Louis Armstrong and the All
Stars at Town Hall, a very famous concert from 1947. I began researching 78
cartridges and that is where the waters really become muddy, and deep.
You've got to add speed and EQ variations to the various tip dimensions. At
least the situation was a little more standardized by the late '40s for my
Thanks, Pryso. Your understanding of which styli to use for which recording era matches mine. Perhaps I got it from you! Have you checked out the Esoteric link I posted above? There's some pretty good info there that seems to match yours (and it's pretty clear, too!).

I'm confused enough about mono, so I'm scared to even think about 78s!

Not to open another can of worms, but do you use any kind of equipment to match the pre-RIAA EQ curves (Esoteric Re-Equalizer, KAB Souvenir, etc.)? I just use the tone controls on my integrated amp, at least for now. Works pretty well.

Hesson11, I've looked into EQ devices, including the Re-Equalizer, but have not purchased anything as yet. I began a major change in my system last year, going to HE speakers and a 300B PP amp. I've also picked up a few cartridges following inspiration from Raul's lengthly post. But one component at a time, and after I settle on an amp (still evaluating), I'll choose a new preamp/line stage, then decide on the EQ. I don't have anything with tone controls but I've read they can work fairly well.

I do have several hundred mono LPs so optimizing their playback will be a high priority. Thanks for your interest and adding your thoughts.
As seen from the front, the 70~75um radius stylii that we (Lyra) use on our mono cartridges are anything but narrow, and are intended to "fill up" the LP groove as completely as possible without requiring a fiendishly accurate setup which would be too difficult for most users. "Long contact patch" is a much better phrase to describe these stylii than "narrow profile" (which is a completely wrong phrase to describe our engineering choices). However, as seen from the side, these stylii are narrow (2.5~3um), because to be otherwise would create unnecessary time-smear (at best), and at worst would result in impaired ability to track high frequencies. The grooves of vinyl LPs are able to withstand 2.5um~3um, but styrene records should be played with larger side-radius stylii.

In our mono cartridge testing, we've played everything from Microgroove LPs from the late 1940s, to mono LP's from the 1950s, to modern mono LP reissues. In all cases I've felt that a properly dimensioned wide, long-footprint line contact stylus gave much better results than traditional options like 1 mil or 0.7mil spherical stylii.

Our hands-on testing has not shown that a properly dimensioned wide, long-footprint line contact stylus is particularly sensitive to the width of the groove. What we have seen is that the important parameter that changed over the years is groove depth. Groove angle would also be important if it varied according to the time of LP pressing, but the groove angle of a Microgroove LP (as well as modern LPs) is defined to be 90 degrees, and as long as it doesn't deviate from 90 degrees, the stylus will simply keep its natural distance (as defined by the stylus shape) from the groove bottom. The stylus should therefore have no problem with remaining in full contact with the groove walls or tracking, regardless of groove width. But if the groove bottom is shallower than the groove width would suggest (which could be the case with earlier Microgrooves and mono LPs), or filled with dirt (not an uncommon condition with second-hand mono records), the tip of the stylus may "bottom out" if it is too acute and/or goes too deep.

Our mono stylii retain a long contact patch with the groove wall, which is essential for top performance, but are designed to not go so deep into the groove and therefore don't get into problems with grooves that are shallower or filled with dirt.

hth, jonathan carr
Thanks so much for the information, Jonathan. Glad we're no longer talking behind your back! I'm glad you cleared up the question on which types of records you used in developing your stylus shape. I've certainly never heard of anyone doing such extensive comparisons of stylus shapes with mono records, so your findings are especially valuable.

Am I correct in understanding that you now use that stylus shape on ALL your cartridges, both stereo and mono?

I hope we haven't scared off our original poster, but I fear we have!

Hey sorry I'm late to the party.

The Ortofon CG 25 DI MKII and CG 65 cartridges are SPU-styled (although SPU technically stands for Stereo Pick Up). Some places refer to these as MPU cartridges (M meaning 'Mono').

The CG 25 has a 25 micrometer diameter conical diamond, and the 65... Well, 65 micrometer. 25um is best for your general mono/microgroove recordings whereas 65 is for 78rpm recordings. These are TRUE mono designs built as closely to the original mono cartridges from the 1950s/60s. The SPU Mono GM MKII, by contrast, is a strapped design - it's a stereo cartridge wired to run in mono.

Yes, Lyra has some very interesting diamond profiles, and for some people this will be the ticket to high performance reproduction of mono recordings.

Ortofon feels that the CG25 and CG65 represent the true artisan style of playback of mono recordings, and consequently these cartridges find their way primarily in modern-vintage systems with removable-headshell-style tonearms. Your Thorens, Garrard, etc crowd. You might not get a highly detailed listen, but mind you these cartridges are designed to provide everything but the HiFi sort of sound. They're meant to provide body, rich and syrupy midrange, and slam.

Depends what you like... Lyra also makes a stellar product.

I work for Ortofon.
Hesson11. No problem. Glad to be of help. I am lucky to be in a position where I can do my own controlled experiments, and decide if previously-published literature is worth accepting or not (smile).

The Dorian uses a 2.5x75um microridge for both the mono and stereo versions. The Delos also uses a 2.5x75um microridge - at the present time the Delos is stereo-only, but in the future I hope that there can also be a mono version. All of our other cartridges, both stereo and mono, use a stylus with a 3x70um profile. As I indicated in my previous post, it is a line-contact with a contact patch that is vertically long and horizontally narrow, but has a "raised-bottom" architecture so that it doesn't get into trouble with some of the older LPs. IMO, those are the three conditions that are desireable for a high-quality mono stylus. If you want to play styrene records (either stereo or mono), forget the "horizontally narrow" requirement.

Ldorio: Hi and thanks for the input. It's always useful to hear the perspective of people that have their own product development philosophies.

Do you mind if I ask you a technical question about something that I find confusing in what you wrote above?

Using the word "strapped" or "strapping" in connection with mono and stereo cartridges indicates a situation where the sensor coils are oriented to the LP groove to have both vertical and horizontal sensitivity, but the electrical outputs of the coils are run either in series or parallel to cancel out as much of the vertical sensitivity as feasible. So strapping is a bit of a bastard solution - essentially the same as using a stereo cartridge and engaging the "mono" button on the preamp.

For fixed-coil cartridges (MMs, MIs, IMs) strapping the coil outputs makes a great deal of sense, because otherwise the coil and polepiece arrangement would have to be reshaped to have horizontal sensitivity only, and that could imply a serious overhaul of the MM or MI's basic structure (due to the fact that the coils and polepieces are rather tightly integrated into the physical structure of an MM or MI cartridge). IOW, most fixed-coil cartridges start out life with a designed-in preference for either stereo or mono operation, and this makes it easy to understand when the manufacturer decides to choose coil strapping over a full physical conversion.

With most MCs, however, the physical structure of the cartridge is independent from the coils, and the polepiece orientation has nothing to do with whether a cartridge is sensitive to vertical modulations, horizontal modulations, or both. The key factor is the angle of the sensor coils. IOW, most MCs start out life with no preference for either mono or stereo operation. Incorporate a set of stereo sensor coils into the MC and it will be a stereo device. Incorporate a mono sensor coil into the MC and it will be a real mono device with no sensitivity to vertical modulations, and therefore no strapping required. And since either stereo or mono sensor coils can be incorporated into most MC designs without needing to tear up and revise the physical structure (including the magnet and polepiece arrangement), there shouldn't be much penalty for using a sensor coil arrangement which is optimised for the intended playback task (mono or stereo).

So with all of that preamble out of the way, here is my question. Why did Ortofon decide to configure the SPU Mono GM MKII as a stereo cartridge wired to run in mono, rather than giving it coils with horizontal sensitivity only?

Apologies if I have misunderstood anything that you have written.

cheers, jonathan carr
Jonathan, thank you so much for your clarifications and added information. I was guilty of using the term "narrow profile" but in my own defense, I was thinking front to back, not side to side for stylus dimensions.

Your information makes me wish even more that I could try one of your Lyra models. But that is not in the budget at the current time. Perhaps if the Denon pleases me enough once I have experience with it, I'll be able to save for one of yours.
Jonathan--the only thing I would quibble with is that it really is essential to clean the LPs thoroughly, both for sonics and to avoid extra stylus wear.
CG25 and CG65 are the only true mono models that Ortofon makes, and they have no vertical compliance whatsoever. In theory, a spin on a stereo record would not have positive consequences for the vinyl.

In the SPU Mono GM MKII, not only is it a high output moving coil with suggested loading of 47k (3mV output at 5cm/sec). The coil assembly is rotated 45 degrees so that only lateral motion is sensed.

Why they have done this rather than making a true mono design... Not sure. But for the true mono heads who want the cartridge to be made the same as it was back in 1948, the CG 25 and CG 65 should satisfy you. We even sell a dedicated trafo for them.

I work for Ortofon
Thanks a lot Ldorio.

So the Ortofon OM D25M puts our a stereo signal, right?