ticking noise connecting an external audio source

Hi all!

I’m tryng connect to MICin and external (“active”?) audio source like some chead FM radio or PC sound board, etc…
The problem is that I’m getting too much “GSMmodem” brust ticking noise while in communication (that “trr trrr trr tt ttt ttt” sound) If i use an ordinary microphone it works ok… but other wise no :\

Any ideia how can I get ride of the ticking sound when connect some external source? Is any kind os circuit or chip I can add to make isolation?

I’m using in my case the same ground in boot circuits (and have it connected to mic-)

I supose the noise comes from pre-micamp that when connecting to an external source doesnt works right… (well it wasnt made for that at all! :neutral_face: )


Thanks in advance!

well maybe some electrical induction in the mic,
a good way to determine that it is take your mic closer to the modem (cable mainly) then if you go away from the modem with and the noise goes lower you know that the modem it is making some induction on the mic, the solution it will be protect the mic from this induction