Early at5555 sounded flat as a fart in thick fog,
they have a compression or vogad circuit in the mic amplifier with shitty time constants,
when you put a power mic on them without doing anything else & keyed up to talk the initial thump from a power mic would hammer the compressor shut & your audio was low at first then got louder as the gain slowly came back up,
i came up with a quick fix for locals by putting attenuation between mic & rig then turning the power mic up so the initial thump did not hammer the compressor shut.
not tried a later version but i have heard them on air & they sound like the time constants have been changed so it releases faster & maybe does not clamp down so hard,
to me they sound more dynamic than early versions.