Step Up Transformer with Moving Iron Cartridge?

Output voltage is 5 mV - should not need step-up.

No. But you do need a phono amplifier with a MM 47k input.

No, but Grado made a low-output MI cartridge (.3mv) that could use a stepup device.

Low output moving iron (MI) cartridges usually do not mate well to SUTs because even though they can have very low internal resistance, they exhibit high inductance, 100 to 1000 times higher than LOMC cartridges. Manufacturers of such cartridges will usually offer guidance. But anyway I agree no step up is needed in this case.

What is your phono stage? … and the rest of your system for that matter.

In addition to what Lew said, The LOMI carts still have appreciable inductance and the step up ratio needs to be kept low (generally under 10) to avoid issues at the top end of the audio band.  

dave

Soundsmith's Hyperion Mk2 (moving iron) cartridge recommends a 470 ohm loading for optimal performance.  Coincidentally - that equates to a 10:1 step up ratio.

The Hyperion Mk2 has an internal resistance of "10-11 ohms" to quote from Soundsmith directly.  Thus if it was an MC cartridge, you might expect it could be loaded with 100 ohms or higher.  The recommended 470 ohm load (or higher) not only suggests a SUT with a 1:10 step up ratio but also tells you that because of its inductance, loads below 470 ohms might result in loss of gain and in some cases treble rolloff.  The Hyperion has a stated coil inductance of 2.75mH (milliHenries).  Whereas a typical LOMC cartridge with a 10-ohm internal resistance would have an inductance of around 10 uH (micro-Henries), or less.  The inductance of the Hyperion would add 172 ohms of reactance at 10kHz, for example.  Which is why you don't want to load it down too much.

the key with LOMI and SUT's is the LC resonance gets to be too close to the top of the audio band for my liking.   assuming 2.75mHy and a 150pF load the 1:10 will reflect back 15nF which will resonate with the 2.75mHy @ 25kHz.  The typical 47kΩ load will go a long way to damp that resonant peak to something between 1-2dB which is actually a bit better than the 1-2dB drop @ 20kHZ from a simple 470Ω resistive load.

All of the above is simply the cartridge L resonating with the reflected capacitance and does not take into account the behavior if the SUT being thrown into the mix.

dave

What Dave said.