Not to be even more pedantic (I apologize) but my first exposure to a "mag amp" was inside an early DC-DC switching supply, back in the 1960s. The mag amp was used in a power supply current limiting circuit. Mag amps can indeed provide gain as a small current can modulate a much higher current, but they are clearly active (electromagnetic) not passive, or electronic.
Passive transformers do not have power gain****. If anything there will be small internal losses. Primary and secondary turns ratios can step up an AC voltage, but since the transformer output power is roughly equal to the transformer input power, the output will be higher impedance and have much lower drive capability.
Just to make my point if you were to connect a dynamic microphone to a step up transformer and then the output of that step up transformer to a very sensitive loudspeaker it might just make a barely audible sound, but not likely.
Every mic preamplifier I ever designed involved an active electronic amplifier stage.
JR
PS; I look forward to seeing schematics of a magnetic amplifier (saturable reactor) mic preamp
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**** it is extremely convenient to think of transformer turns ratios in terms of dB ( a power measure)... it is a bad habit to get into.