Max potential difference that can be created in an analog signal using a microphone
It's unclear what you are really asking.  Most microphones produce quite small signals relative to usual audio voltage levels inside audio equipment.  Audio "line" is about 1 V.  That level is easy to handle but large enough so that various subtle sources of noise are small enough relative to the signal to not cause much trouble.

Dynamic microphones directly convert sound power from the air into a electrical signal.  They usually put out a millivolt or less.  Piezo microphones are similar.  Electret microphones are common now, and when properly powered, usually produce up to a few millivolts.  Old telephone mouthpieces worked by having the sound pressure squish and squash graphite powder.  This varied the resistance across the powder, which could cause quite a significant signal.  You could apply a few volts directly to the series combination of such a carbon microcphone and a dynamic earpiece, and be able to hear quite well in the earpiece what the microphone picked up.

Since microphone signal levels are much smaller than what is required to drive a speaker or even line level, amplification is required.  This is what a microphone preamp does.  it amplifies the bare signal from a microphone and produces line level audio out, which can then be fed into other equipment.