Any electronic geniuses here?

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

Thanks everyone for all the great info and advice.  I am looking for a 10:1 SUT so it looks like load shouldn't be unmanageable from what I've read here.  Anyone familiar with the Bryston TF-2?

Yes, assuming an ideal transformer, the measured impedance is related to the impedance at the output by the ratio of winding on the input vs. the output. 

http://www.vias.org/matsch_capmag/matsch_caps_magnetics_chap6_04_04.html