SUTs are as diverse in their sound as phono stages are (maybe even more so), so it’s difficult to put all the stages with built-in SUTs into a bucket. And as mentioned by chakster, any given SUT is not nearly as adaptable to a wide range of cartridges as a typical active MC stage would be - so when picking a SUT you generally also have to select either a single target cartridge, or a narrow window of target cartridges for best results. It’s not going to work great if you have a low output MC, medium MC, and high MC in your collection. It’s not going to work great if you have a cartridge with high coil impedance for its output level, like a Benz Ruby. You must keep that in mind when choosing a phono stage with a SUT MC stage. Of course you can always do what I do - bypass the stage’s internal SUT and use outboard SUTs of your choice coupled to its MM mode.
SUTs are generally paired with tube MM stages to keep the tube rush noise down. Kind of the "best of both worlds" approach. But there’s no reason they can’t also work great with SS MM stages - it just seems less common probably for market factors more than anything else.
In my experience, two ends of the SUT sonic spectrum would be Bob’s Devices blue label CineMags with a warm, meaty, fleshy and seductive sound - and then Lundahl LL1931 amorphous cores with a crystalline, fast, detailed sound. Both of these have found their way into many phono stages. Personally I’ve found the CineMags to work better for me so far.
I chose my VAC Renaissance phono stage because its tube MM stage was by far the best I’ve heard, even though it uses Lundahl SUTs for MC mode. I just bypass them to favor my various outboard SUTs :)
As for transformer SUT vs. active MC stage (JFET), I have definitely preferred the sound of SUT so far. It’s generally more tactile, more dynamic, more alive sounding. JFET sounds more like a reproduction to me; I feel emotionally more distant to the music (slightly). But at this point I’ve heard only a few JFET stages and have a lot more experience with SUTs.
And one annoying thing with SUTs (especially outboard) is tracking down various hum / grounding issues. At least with built-in SUTs they usually get that right for you.
SUTs are generally paired with tube MM stages to keep the tube rush noise down. Kind of the "best of both worlds" approach. But there’s no reason they can’t also work great with SS MM stages - it just seems less common probably for market factors more than anything else.
In my experience, two ends of the SUT sonic spectrum would be Bob’s Devices blue label CineMags with a warm, meaty, fleshy and seductive sound - and then Lundahl LL1931 amorphous cores with a crystalline, fast, detailed sound. Both of these have found their way into many phono stages. Personally I’ve found the CineMags to work better for me so far.
I chose my VAC Renaissance phono stage because its tube MM stage was by far the best I’ve heard, even though it uses Lundahl SUTs for MC mode. I just bypass them to favor my various outboard SUTs :)
As for transformer SUT vs. active MC stage (JFET), I have definitely preferred the sound of SUT so far. It’s generally more tactile, more dynamic, more alive sounding. JFET sounds more like a reproduction to me; I feel emotionally more distant to the music (slightly). But at this point I’ve heard only a few JFET stages and have a lot more experience with SUTs.
And one annoying thing with SUTs (especially outboard) is tracking down various hum / grounding issues. At least with built-in SUTs they usually get that right for you.