Proteus compared to MSL ultra eminent ex

To be clear, I don’t think you can say that low signal output per se is a goal of a moving coil cartridge designer. It’s more like that is a byproduct of designing the cartridge to have very low moving mass and very low internal resistance, both of which are desirable in a moving coil cartridge. Unfortunately, it is hard to achieve those goals or move toward them without also ending up with a low signal voltage output.

I have an early proteus, I think there were two revisions after mine the second being the diamond cantilever. It’s 5 years old now and seen a lot of vinyl so I started to look for a replacement. I was also on the verge of retirement so rebuild costs of any replacement become more important. Before the Trans I ran a series of Dynavector 17Ds and moving to the proteus from a 3 I didn’t miss anything of the Karat’s speed and gained more body to the sound, and improved dynamics, that was on a Naim Aro.  I didn’t want a lesser Proteus or I could go back to my part worn DV or the newer Dx. I was considering whether it was time to try a Koetsu and had picked out the Vermillion as the most likely candidate but ideally I’d prefer not to spend that much this time. Somehow the thought arrived that an SPU Royal N would make an interesting experiment, different enough from the Proteus that it was unlikely to be less of the same. The tracking force looks alarmingly high at 3g but the stylus isn’t as fine as a Proteus’ so pressure on the grooves probably not too much higher. My current arm, purchased after I’d started using the Proteus, is a Schröder Reference with an effective mass of 13g using an aluminium cartridge mounting plate, change it for a brass one and that goes up to 18g plus a bit for moving the counterweight further back. With the Royal N that’s quite a long way back.
So to my impressions, there was yet another increase in substance to the sound, orchestral music had more depth and a greater sense of scale and it seemed notes were being strung together in a more meaningful fashion. It’s all a bit more relaxed than the Proteus and detail not as prominent but on the whole I think I prefer it. I do get a bit more static build up from playing a disc.

Ana Mighty Sound in France will rebuild a Proteus and I had a quote just pre lockdown for about the same cost as a new Royal N but haven’t yet followed it up, I think I will though as I’m wondering if I’ve just got better at setting up the arm since I installed the Proteus.

I also have a certain curiosity about the Ortofon Anna with the same stylus profile but selected styli and more sophisticated materials than the Royal N but would it keep what I like about the SPU? The idea of a Koetsu Vermillion hasn’t entirely gone away either but both of those options might be unsustainable past the first rebuild.

That’s a nice simple question.

yeti42, assuming that the SPU's stylus is OK to run at 3 grams because it has a different shape is a mistake. I do not know what the difference in record wear is but it is certainly higher than the Proteus. 
You have a wonderful arm but it is too light for either the SPU,  Koetsu or Anna. This will effect tracking and low bass performance.
The Proteus is a good match and Ana has a great reputation. I would certainly consider getting it rebuilt. You want to stick to cartridges with compliances in the 12 to 20 um/mN. Your cartridge mounting plates will work great in this range. The Lyra cartridges are a great choice. The Ortifon WIndfeld Ti, any Clearaudio MC cartridge would also work. From a value perspective given your apparent preferences the Kiseki Purple Heart would be perfect.

Thanks guys. Interesting discussion. I would love to hear more comments, especially from anyone who has had the opportunity to actually hear the Proteus and the ultra eminent EX in some sort of comparison. I realize that will be tough but I welcome any and all opinions. Thanks again.