Put a small value unbypassed emitter resitor between the emitter of the Darlington and gnd.
I recently needed a carbon mic equivalent for an aircraft radio. Aircraft radios expect a specific, preset level. I converted a 500Ω dynamic CB mic for that use with the following circuit:
I experimentally found a value of the emitter resistor that provided the correct level. I settled on 16Ω
The 22K resistor is the majority of the negative feedback. Adjusting it adjusts the audio gain. It also shifts the circuit's operating point, so start with small steps, like a 20K resistor and a 5K pot in series.