Any electronic geniuses here?

Of course, yes.  And I am no electronics genius.  The impedance seen by the cartridge will be equal to the input impedance of the phono stage divided by the square of the voltage step-up ratio afforded by the SUT.  In other words, if the phono stage has the typical MM standard 47K ohms input resistance, and if you use a 1:10 SUT, the cartridge will see 47K/100 or 470 ohms.  If you change that 47K resistor to some other value, that would make a corresponding change to the load on the cartridge.

Here are a few other technical issues.

Don't worry about the load on the cartridge. That is really only for the benefit of the phono section (ask if you need explanation). But you do have to worry about ringing from the transformer itself. If the transformer is designed for particular cartridge, its probably not going to ring if connected to a standard 47K input, unless the manufacturer of the SUT states otherwise.

But if you change the cartridge to one of a different impedance, you may well have to change the load on the output of the SUT to make sure its properly loaded. If loaded too lightly it can ring, which is to say it will make distortion, if loaded too hard (IOW with a load of too low an impedance) it will roll off the highs. 'Critical Damping' is where the load is just right.


Transformers **transform** impedance in both directions so change the load on the output definitely affects the source- and vice versa.

The only thing I can possibly add to the above comments is that good transformer companies like Sowter in the UK will make a range of transformers suited to specific cartridge impedances. These are "loose" transformers that should be wired internally into the preamp which turns out to be the best way to add a transformer. No added contacts or interconnects and the transformer has additional shielding within the preamp. You just have to keep it away from AC devices like the power transformer. A good technician can make the addition 100% reversible.  

Call Big Ears Stereo out of Tempe Arizona he has a degree in electrical engineering and is very easy to talk to hope this helps you all the best