I am currently trying to make a preamp for an electret mic pair, which are placed physically in antiphase. The main idea is to subtract one mic's signal from another and therefore boost the signal amplitude while reducing the noise.
Caution: in the schematics below the nominals of resistors and capacitors are totally wrong, only the topology of preamp is what matters. The FETs in all schematics are just the FETs that are included in the electret mics.
A typical solution for this would be using a differential amp (number 4 on pic). However, I am not sure if this solution is good enough and if it is better to pre-amp the signal of each mic individually before subtraction. For a single-mic preamp I have found three solutions on the internet (see number 1-3 on pic): a simple non-inverting amp (1), a transimpedance amp (2) and a weird schematic which implies getting rid of the DC offset by precisely calibrating the R8 resistor, not by using a capacitor (3).
My question: should I subtract the microphones' signals immediately (using a differential preamp) or after some basic amplification and if the second option is preferable, which one of the preamp topologies (1-3) should I use? What are the pros and cons of each approach?