Calculation verification please

I always thought loading was to dampen the stylus against any 'ringing' which may occur...

@quincy Nope! Especially with LOMC cartridges, which have a very high 'Q' factor in their coils (so as to minimize mass) the result is that the peak I mentioned can be as much as 30dB higher than the signal level. That will mess with a lot of phono sections- it can cause distortion and overload, which is why they sound better when the 'loading' resistor is installed.

When an SUT is involved you have a different situation! The RFI can't make its way past the transformer, but the loading of the transformer becomes critical to prevent it 'ringing' (distorting). If the load is too high an impedance value this will happen; if the value too low the transformer will roll off. If you change the source impedance (the cartridge) that impedance is magnified by the transformer in this case (because its a stepup) so the load value will change with the source impedance.

@lewm I suspect this is why small differences in loading the SUT can be heard.

This process is thus best done with a squarewave generator and an oscilloscope to see how well the squarewave is passing thru the transformer. Most audiophiles don't have access to such equipment and if they did, may not understand how to do this particular critical measurement. So as a result, most of the time its by gosh and by golly unless a lot of care is taken to eliminate variables (like cable capacitance) and also if the manufacturer was careful to specify exact values.

Atma, Skos wrote: "I’ve been experimenting into a MC section and the manufacturer says to load between 100 - 800 ohms. I’ve tried 250, 324, 368, 404, 500 & 600 ohms and found I like best the 368 ohm loading. So now want to try using my SUT."

IOW, he heard differences in SQ among those listed load resistances BEFORE he decided to implement a SUT. So, using a step-up had nothing to do with his observation.  So many hear differences using load resistances that differ by only a few tens of ohms that I am convinced the observations are valid.  I just don't hear it, or better to say I do hear subtle differences between widely different loads (e.g., 100 ohms vs 47K ohms, with LOMCs that can drive 100 ohms) but none worth a damn. In those cases I slightly prefer 47K ohms. I do think my system is low enough in distortion that I should hear it if my brain says it's there.  That suggests my ears and brain are tuned differently or are superannuated or both.