Twiolins

hi, i have nearly read everything i found about the pin connections and resistors. i use CO-8WD headset mics and sound quality is nearly perfect - but the output level of the mics is not very high and it would be great to boost the level for the tbp12 transmitters... as far as i understood, there is no way to do this without an external batterypowered preamp - or can you adjust the gain of transmitter by changing some smd resistor or something? thank you :-) chris