PLT LOSS RADIO CONTACT WITH ARTCC AS A RESULT OF HIS TURNING THE VOLUME TO LOW.

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I WAS CRUISING AT 7000 FT ON AN IFR FLT PLAN TO RWY 81J. WX WAS VFR ABOVE A FAIRLY SOLID CEILING AT APPROX 4000 FT. I HAD SOME STATIC HISS ON MY RADIO AND DECIDED TO TRY AND ELIMINATE IT. I TURNED MY MAIN RADIO DOWN - DIDN'T MEAN TO LEAVE IT DOWN - BUT THEN; AFTER CHKING OTHER RADIOS; FORGOT TO TURN IT BACK UP. WHEN I REALIZED WHAT HAD HAPPENED; I TURNED IT BACK UP AND HEARD ATC CALLING FOR ME; ASSUMING I HAD RADIO TROUBLE. I STATED WHAT HAD HAPPENED. ATC SAID THEY HAD TRIED TO CALL ME 6 TIMES; THEN SWITCHED ME TO THE NEXT CTR AND A LOWER ALT. AS FAR AS I KNOW THERE WERE NO TFC CONFLICTS AND I SAW NO ONE ELSE NEAR ME. CONTRIBUTING FACTORS WERE 1) COMPLACENCY; 2) LOW WORK LOAD AT THE TIME; SO I HAD TIME TO 'FIDDLE' WITH THINGS; 3) NOT STAYING FOCUSED ON THE JOB AT HAND UNTIL COMPLETED. IT WAS DISCOVERED BECAUSE IF I HAVEN'T HEARD SOMETHING ON THE RADIO IN AWHILE I PULL THE SQUELCH OUT TO MAKE SURE THERE'S AT LEAST STATIC GETTING THROUGH. LESSON - DON'T TURN DOWN THE RADIO WITHOUT TURNING IT RIGHT BACK BEFORE MOVING ON TO SOMETHING ELSE. HISS WAS FROM MY INTERCOM SQUELCH; DISCOVERED ON RETURN TRIP.