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.
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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.
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.
Again... not a genius but I've designed a few phono amps. Lundahl make nice MC transformers, they also have quite a bit of technical info on their website. There is also this handy tech note that provides guidance on setting up the input impedance when used with an MM stage.
If I remember correctly the data sheets for the trafos are missing some information to do the calculation for yourself but I can probably dig out a spreadsheet I've used for the calculations in the past if you can't find what you're looking for in the tech note.
"If loaded too lightly it can ring, "
This can be a danger, or an area of mistakes, as we can mis-load and live off of the ringing, which exists as temporally shifted energies. (one way of explaining it)
We can mistake this noise for detail and lose actual detail in the spray of noise. It crushes dynamic range but leads to an impression of detail, to those who seek easy answers and use their minds to fill in, and are not actually listening. It is exactly why we have people who don't hear what power cords do or what rca cables do or what fuses do, and so on.
FYI, a core function of how the ear/brain works, is to fill in. Look up speech recognition, in time. We preload sound patterns via the ego loop, to speed up recognition, and some people are so bound to that, that they cannot hear what the equipment is actually doing. They can't shut it off and listen for real.
Listen for it. Try to isolate that aspect, via actual listening and learning.
It is a very critical thing to understand, it leads to a far greater dynamic range in a system as a whole, once a person ’groks’ it. Decisions in system building change to accommodate it, and then we start building our systems properly.