All transformers require excitation current before they will pass any signal. Where do you think the S.U.T. gets its excitation current from?
Has it a power supply? No. So obviously it uses some of the signal as excitation current.
That would be OK but for the fact that magnetic cartridges don’t have a linear response – their bass is much weaker than the highs, and so more is ‘stolen’ from the lows.
That’s the reason you’ll often see additional components inside a S.U.T.’s casing – these being used to straighten-out the frequency response.
I think you’ll agree by now that the Elevator EXP step-up amplifier is the better option.