MM or MI Cartridge?

Way back in the Days of Yore (late 70's) I had to choose between two cartridges - an MC and an MI type. The GAS Sleeping Beauty and the Grado Signature One. Both cost the same - $240. I went with the Sleeping Beauty mc cartridge - though I had to put it aside for a few months until I could afford a Mitchell Cotter SUT. The Sleeping Beauty gave much pleasure, though the Signature One would have probably served just as well! I just didn't want to pay so much for a Grado cartridge. The lowly Grado FTE ($15!) was praised by Harry Pearson. The Signature One ($240) was Grado's premium - and most expensive! - cartridge. I shake my head in disbelief when I read of a Grado Epoch costing $12K! 

I went through that phase just recently. I have owned Grados and Clearaudios, but the best so far overall was the Soundsmith Voice. It punches way above it's price point with exceptional tracking and remarkable neutrality. I gave it to a friend for his birthday and he greatly prefers it to his old Spectral (really a Lyra) cartridge. My current phono stage will not handle a high output cartridge.

I remain an mc cartridge fan and user because no mm or mi type I have tried can equal the "liveliness" and detail retrieval of a good mc cartridge. Even the lowly Denon 103 is capable of astonishing sound quality! Why don't you consider an upper-tier mc cartridge like a Miyajima Madake? After all, that Ortofon SPU is rather long-in-the-tooth for an mc design!

Nagaoka MP500 is about as good as it gets IMHO, but it’s subjective and very system dependent. It does a lot of things extremely well, and doesn't have any bad habits.  Technically it’s moving permalloy, but I wouldn’t let semantics be the reason to stop you from trying it. 😎

Soundsmith makes a strain-gauge cartridge. This type does not use an RIAA network/phono stage. It does the equalization mechanically. It can drive a line stage - eliminating the phono stage. I listened to the Panasonic strain gauge at a friend's house. It fed the line stage of a Marantz 7 tube preamp into a pair of Futterman H3aa OTL amps into Quad 57's. I was impressed! Soundsmith claims their strain gauge cartridge is a superior improvement over the Panasonic.