C208 TAKES OFF AFTER MISSING THE TWR'S AMENDED HOLD SHORT CLRNC DUE TO IMPROPER AUDIO PANEL SETUP. CONFLICTING TFC IS GIVEN A GAR BY TWR.

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TYPICALLY; I SET TWR/APCH AIRBORNE FREQS ON THE #1 COM AND GND/CLRNC DELIVERY FREQS ON THE #2. AT THE TIME; I WAS TAXIING OUT TO DEPART RWY 26. THERE WAS AN ULTRA-LIGHT ACFT THAT WAS DEPARTING RWY 21 AND STAYING IN THE PATTERN. WITH THIS IN MIND; I HAD RECEIVED IFR AND TAXI CLRNC ON THE GND CTL FREQ SET ON THE #2 COM RADIO. DURING READBACK OVER THE #2 COM RADIO THERE WAS A LOUD (FEEDBACK?) SQUEAL SO I PUSHED 'OFF' THE #1 COM RECEIVE BUTTON WHICH ELIMINATED THE SQUEAL. TWR THEN GAVE ME TKOF CLRNC OVER THE GND FREQ AS I APCHED THE RWY. I CONSIDERED THE ULTRA-LIGHT ACFT FOR RWY 21 BUT THOUGHT HE WAS ON DOWNWIND. SINCE I WAS TAXIING S FOR RWY 26 DEP I WAS UNABLE TO VISUALLY CONFIRM HIS POS. DURING THE TKOF I NOTICED THE ULTRA-LIGHT ON GAR FROM THE CONVERGING RWY AND WONDERED WHY TWR GAVE ME CLRNC TO TAKE OFF. I THEN NOTICED THE AUDIO SELECTOR WAS STILL SET TO THE #2 (GND) AND THE AUDIO BUTTON FOR #1 WAS OUT. QUICKLY SWITCHING; I INFORMED THE TWR OVER THE PROPER TWR FREQ. TWR SAID THEY HAD TRIED TO CONTACT ME TO CANCEL MY TKOF CLRNC AND HAD TO GIVE THE OTHER AIRPLANE A GAR. THANKS TO THE TWR; THERE WAS ADEQUATE ACFT SEPARATION. A PRIMARY FACTOR IS MY EFFORT TO HURRY MY DEP AND FAILURE TO RESET/RECHK THE AUDIO PANEL. ALTHOUGH ACCOMMODATING; ATC PROBABLY SHOULD NOT HAVE ISSUED ME TKOF CLRNC; CONSIDERING THE OTHER ACFT IN THE PATTERN; BUT SINCE I WAS IN A HURRY I WAS ALL TOO HAPPY TO ACCEPT. ALSO; THE TWR PROBABLY SHOULD HAVE ISSUED THE AMENDED HOLD SHORT INSTRUCTIONS OVER BOTH FREQS. THE AUDIO PANEL IS NOW PART OF MY PERSONAL 'LAST CHANCE' TKOF CHKLIST.