The sound of SPU

Friends, I have never heard an SPU but have heard a lot about it. It has an amazing following. The general impression I get from reading various opinions is, SPU has a big, bold sound which is somewhat rolled off on the top and is not too detailed. It is musical in the traditional analogue way but not very transparent or extended.

Recently a friend of mine lent me an old (1970) Ortofon SL15 ELL cartridge which was suppose to have been built on the SPU engine of that time, but is naked and with some modifications to sound more open. Nevertheless it was still aimed at the SPU listeners. Since my tonearm cannot take a regular SPU it was a good way of getting a taste of SPU sound. It is a very low output cartride (0.125 mv) and comes with its own SUT. I have been listening to this cartridge for the last 7 days or so. To my surprise I find it to be a very open, detailed, fast and neutral cartridge. It doesnt have the dynamics of my ZYX but it has a warmer midrange which makes it sound more humane. It is also not as detailed as the ZYX but there is still a lot of it. This is coming from a 40 year old MC cart which was not a top end cart even at that time, has been borrowed from SPU, has only a "normal" aluminium cantilever. The SUT is very good but still not all that great so I am sure it is eating some resolution, still the cartridge makes for such a fulfilling experience, better than most cartridge costing $1k today and many costing much more.

The question is, what is the sound of an SPU ? Is it really fast, detailed and extended compared to other cartridges of its price point or is this SL15 experience is kind of exception ? Moreover today we have much more advanced SPUs like the Meister Silver and SPU90, what can be expected from them ?