I'm new to Step Up Transformers

It is moving iron, but it has a .4 Mv output.  

The approach of using a hybrid transistor and tube to supply the needed gain for low output cartridges is to reduce the level of noise from using tubes exclusively.   

The use of a SUT also reduces noise as an issue and adds the sonic signature of a transformer.  If you want tube only amplification (no transistor stage or no SUT) you have far few alternatives.  I mentioned Aesthetix earlier as an all-tube design that sounds good (if a bit noisy); another good sounding example is made by Lector (quiet for an all-tube design).

Yes, it's a moving iron but a very low output, similar to a low output Moving Coil. 

I have two low-output MI cartridges, one of 0.4mV output, which requires an MC input or external SUT, and the other with 1mV output sounds better that way (but could be connected via an MM input and the gain turned way up).

I have three ways of doing it - using the Musical Fidelity NuVista Vinyl and setting the input to MC, using the Quad 24p set to MC (with internal SUTs), or using an external SUT and the Quad set to MM. The last of these sounds the best of the three, so that is what I do.

Atmasphere is also all tube high gain phono, as I mentioned earlier. I’ve owned an MP1 for two decades upgrading along the way. I also owned an Aesthetic Rhea Signature but not the Io. The Rhea is amazing for its remote controlability but was a tad noisy compared to the MP1 when I cranked up the gain. 

Most SUTs, the gain and impedance load are inter-related, some SUTs have optional but not separate settings, like my Fidelity Research FRT-4, but the 4 optional choices are still inter-related, i.e. more gain = lower load. (Load = typical 47,000 ohm phono input divided by the chosen x factor squared), 

SUTs or Phono Stages with separate gain and separage load settings are needed for some cartridges, as the standard ratios don’t fit properly.

Soundsmith says Paua output 0.4mv signal strength, it’s coil is 10 ohm resistance, (very much like my AT33PTGII 0.3mv/10 ohm coil). The strange to me part is they advise a load of greater than 470 ohms?????

industry guidance for MC impedance load says try coil impedance x 10, i.e. try 100 ohms. anybody know why they advise 470 ohms for their 10 ohm coil?

GAIN: they advise a TOTAL gain of 58-64db, keep in mind, that is total, including whatever your MM phono is doing AFTER you pre-boost with a SUT.

i.e. my SUT boosts my AT33PTG 0.3mv x 20.68 x factor (+26db) thus up to 6.20 mv that I then send into my MM Phono input for RIAA EQ and it’s gain. Luckily it does not over-load the MX110z’s phono stage, not sure what it’s limits are.

My SUT has a 10.55x gain option, (+20db), the load is 423 ohms, closest to Soundsmith’s stated 470 ohms.

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btw, My experience: my SUT does NOT have a sound characteristic of it’s own, it is dead silent, simply and passively boost a too weak signal, allows me to use my existing preferred MX110z Tube MM Phono Stage