The diaphragm of a condenser microphone is the movable plate of a capacitor. WHen properly polarized the vibration of the diaphragm in relation to the back plate produces an ac audio-output voltage. The condenser capsule has a capacitance of 10 to 60 pF; thus, you should connect it to an impedance converter with extremely high input impedance for a flat frequency response. The conventional impedance converter is a JFET source follower with an additional amplifying and power-decoupling circuit.
The balanced audio pair at the XLR connector’s pins 2 and 3 both carry both power (phantom power) and audio signal. Typically the amplifying/decoupling circuit contains an audio transformer or a couple of capacitors to separate the dc power from the audio signal.
High-value dc-blocking capacitors can generate measurable and audible distortion. Audio signal transformers have also their limitations. The circuit shown at Condenser microphone uses dc-coupled impedance converter article eliminates transformers and coupling capacitors using self-balancing microphone interface circuit.
This is an interesting circuit idea to look at. I have not tried this in practice, but looks interesting.