SUT With a Manley Steelhead RC?

It’s a complicated question, because the steelhead’s "Z" inputs uses autoformers (primary only) rather than a traditional SUT (primary + secondary windings). I don’t think most of us have a good understanding of autoformers in this application lol. I’m not even sure anyone else is using them here.

The description on Manley’s site is fairly good but still kinda hard to parse out. It sounds (perhaps) a bit more like a "current injection" head-amp in electrical function, versus a traditional SUT - where the "optimal" level Manley speaks of is going to be loading the cartridge pretty heavily (and that’s OK).

The "rough" gain range listed of 3 - 12dB is much lower than most head-amps and SUTs, but the extremely high "base" Steelhead gain (up to 65dB) covers for that.

If you get a SUT - it’s going to sound different than the autoformers, that’s for sure. Even SUTs can sound wildly different to each other! All you can do is try a SUT and decide which you like better. If you do, the SUT should be run at the lowest gain level (50dB) on the R input set to 47K and minimal capacitance load (0 is fine). Even 50dB is quite high, so you don’t want to push past the usually recommended SUT gain ratio for your cartridge. For an MSL Platinum at 0.5mV, I think a 10x SUT would be perfect here.

The "Sky" SUT Bob sells is excellent, and in your shoes - yeah I’d give it a shot against the Manley’s autoformers. The "Sky" has a warm, vibrant, rich sound with superb dynamics and big bass response. It’s not as refined or nimble as some of the other top tier SUTs (more expensive), but it’s a fun listen. Fantastic for rock. It really reminds me of a classic tube amp’s sonic style. And it absolutely clobbers the cheaper SUTs (entry level Lundahls, CineMag 3440A) IMO. My main complaint is the little metal boxes can be microphonic and they're also easily bullied around by stiff cables (both solve-able, but a PITA).

When I look at SUTs / cartridge pairings, I first consider "are SUT’s good for this cartridge?". For that, you look at the ratio of a cartridge’s output voltage over its coil ohms. This is proportional to how much current the cartridge can supply (in theory). Since a SUT essentially converts current to voltage gain, this is a good indicator of its match to both a SUT, AND to current injection stages (SUT is passive and current injection is active). Of course there’s more to it than that, but this is a good rule of thumb IMO.

To keep nice integer (rounded) numbers, express the output in micro-volts uV. For for example, Koetsu lists 0.3mV = 300uV for 5 ohm coils. That’s a ratio of 300 / 5 = 60. That’s a "very good" ratio for a SUT. Koetsus yield very strong output levels for relatively small coils, and are a known good match to SUT’s.

Benz iron cross models are not quite as efficient, but they still yield 400 uV / 12 ohms = 33. That’s still a good ratio for SUT’s.

Benz ruby core models suck with SUT’s. They have 380 uV / 40 ohms = 9.5
Van den Hul Colibri is another tough one, with very similar specs to the Benz ruby. But again, their lower models’ generators (Crimson, Frog) are more efficient and work great with either SUT or current injection. Why do some cartridge motors have so much less efficiency? Because they’re either doing something weird with the magnet (Colibri positions its coils in a monopole layout rather than the typical dipole) or they’ve made a choice for the coil’s core to be a non-magnetic (or less magnetic) material than the usual iron / permendur. Ruby, air, polymer (IIRC Ortofon said they use these in Anna?) - these all sacrifice output efficiency in order to reduce magnetic flux disruptions during playback conditions (essentially they are reducing the magnetic complexity).

Most LOMC’s will have a ratio somewhere between the Benz iron-cross and Koetsu. A few have ratios even higher than Koetsu: Ortofon Cadenza Red / Blue / Bronze and all My Sonic Labs cartridges (by a LOT there!).

So once you know a cartridge is "good" for a SUT, then what you want to do is match step-up ratio so that the resulting "MM level" is around 5mV. Now I like to go even higher to de-emphasize the MM stage’s noise floor, but at some point you do risk MM stage overload. With tube MM stages though (generally good overload margins), I’ve found anything ~ 10mV and below is perfectly fine. If you’re falling below 4mV then sometimes dynamics and "punch" can suffer. So just match step-up ratio and never worry about loading - if you have a good cart for SUT and a 47K ohm MM input impedance, it always works itself out fine :) I’ve also never found any value in additional loading on the SUT’s primary or secondary.

I think it’s well known Koetsu never wound their own SUT’s, but sourced them from a Japanese maker - the question is "who"? Haven’t seen an answer on that, yet. The new metal-box SUT shows some additional components inside there too (resistors) along with damping materials - so they’re probably doing something to "optimize" sonics for Koetsu. The old wood box SUT’s are different - and they lean towards the "detailed / fast" side of the sonic spectrum, with a little extra energy in treble and without destroying the midrange romance (like Lundahls do). It is a VERY good match for Koetsu carts. Can sound great with other carts too, but you have to watch that treble getting too hot. I don’t know how the metal boxes ones sound. 

For Ortofon - their Verto shows Lundhals inside. Pretty much any transformer with that distinct flat rectangular metal box is going to be a Lundahl. Lots of component manufacturers use them (line inputs too). I’d be surprised if Ortofon wound any of their modern SUT’s. I’d be surprised if ANY cartridge manufacturer did.

EAR is impressive for winding their own transformers (and their MC-3 / MC-4 SUT’s are superb), but they’re a component maker, not a cartridge maker.