Microphone preamp schemeThis series uses low noise transistor types, namely BC 650 C, this transistor can be found hard degan replaced 109 BC that is not less good. Or EMC (electric condenser mic) microphone there are elements that are very sensitive and a series of internal FET preamp, so the voltage needs to EMC is between 2-10 volt, for that we can love resistor 1 K-10 K ohm to send the EMS.