Can I replace a NPN with a darlington at input stage ?

[Tedyp]

I have an LM386 based amplifier, and a 1 transistor preamplifier connected to an electret mic. It is supposed to be very sensitive: the tr. base and collector are conected by a 2.2M rsistor, the collector to VCC by a 10k, the emitter grounded and the base, via a 0.1uF to the electret. The problem is that this paricular electret is not very sensitive, but relative small (about 6mm diameter). With other inserts, the circut works OK, it can pick up a wisper from about 10m or even more, with larger electrets. With the little one, barely 2m or less. I've tried to play with the electret bias resistor (the whole circuit works from a 9V battery)- the best one was 10k, but it's not enough... I thought that I can replace the 3904 tr. with a mpsa 14 darlington, but it stopped working. Is ther any way to increase the sensitivity of the input by a darlington tr.? If so, how? (I cannot add an additional transistor, because I have no place on he PCB, and cannot use the larger electret as I have no room in the box). Any idea please?
TIA,
Tedy

 

[IanP]

You can replace standard NPN with Darlington, but to make it operating in is linear region you will need to add a base-GND resistor .. see picture below ..
If the base-collector resistor is 2.2MΩ you can try 1MΩ base-ground resistor of ..

Regards,
IanP