Mono cartridge classification

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