PLT OF SMA TOOK OFF WITHOUT CONTACTING TWR. PLT ASSUMED TWR WAS NOT ACTIVE. PF NOT NAMED AS PLT ON IFR PLAN.

Narrative

I DEPARTED GAINESVILLE REGIONAL ARPT WITHOUT PERMISSION OF GND AND TWR. THIS WAS ACCIDENTAL CAUSED BY A MALFUNCTION OF THE MICROPHONE. I WAS ACTING AS THE PIC OF THE FLT EVEN THOUGH THE INST FLT PLAN WAS FILED UNDER ANOTHER PLT'S NAME. I WAS ALSO RENTING THE PLANE FOR THE RETURN FLT. AS I WAS PERFORMING THE PREFLT OF THE ACFT; I ASKED THE OTHER PLT TO FILE AN INST FLT PLAN FOR ME. HE DID SO ACCIDENTALLY UNDER HIS OWN NAME EVEN THOUGH HE WAS FLYING IN THE BACK SEAT AS A PAX. I WAS ATTEMPTING TO CONTACT GND AND TWR FROM THE FBO RAMP; AND I RECEIVED NO REPLY. I ASSUMED THE AIRFIELD WAS UNCTLED AT THE TIME BECAUSE OF A LACK OF COM ON THIS FREQ. THE PROBLEM OF NO OTHER TFC ALSO COMPLICATED MATTERS. SINCE NO ONE ELSE WAS IN THE VICINITY TALKING TO GND OR THE TWR WE DIDN'T PICK UP THEIR TRANSMISSIONS. I THEN CALLED THE UNICOM FREQ AND ADVISED TFC THAT I WAS DEPARTING ON RWY 6. I THEN TRIED TO CONTACT JACKSONVILLE APCH AND WAS UNABLE TO XMIT ON THIS FREQ UNTIL I USED A PAIR OF HEADSETS. THIS MADE ME REALIZE THAT THE MICROPHONE WAS INOP AND THAT I HAD TAKEN OFF WITHOUT CLRNC. I BELIEVE THIS OCCURRENCE COULD HAVE BEEN AVOIDED IF I TRIED TO TROUBLESHOOT THIS PROBLEM ON THE GND. I SHOULD HAVE STOPPED THE ACFT AND CALLED THE FSS TO SEE IF THE FIELD WAS INACTIVE INSTEAD OF ASSUMING SO.