work very good with 16mm capsule
This is an amplifier for electret mics that with internal FET, the only problem is unacceptably high level of noise, but it can be significantly improved if one adds an electrolytic capacitor (470 microfarads * 10V) parallel to the zener diode in the circuit (small red-black glass tube). There is enough space on the other side (where no elements are places). Used to replace standard amplifier in BM800 when upgrading it...