Bluetooth mode cannot be used when a MicroSD card is inserted.
DO NOT LEAVE THE CHARGING CABLE ATTACHED TO THE BLUETOOTH RECEIVER WHEN IT'S TURNED OFF AND NOT CHARGING. THERE'S A BUG WHICH DRAINS THE BATTERY AND YOU HAVE TO USE A DIFFERENT CHARGER OR POWER BANK TO RESET OR IT WILL NOT RECHARGE EVEN THOUGH THE RECHARGE LIGHT IS ON. YOU'LL KNOW AS IT WILL KEEP PLAYING A "LOW BATTERY RECHARGE" NOTIFICATION. VERY DISAPPOINTING FIRMWARE BUG. DIDN'T HAVE THIS PROBLEM WITH OLDER AND CHEAPER BLUETOOTH RECEIVERS I HAVE USED. THE SOUND QUALITY IS QUITE GOOD FOR THE PRICE BUT THE BUILT-IN PLAYER IS REALLY LOUSY, DON'T BOTHER USING IT. THE BASS SETTING BOOST UP THE BASS TO SUCH AN EXTEND THAT YOU CANNOT EVEN HEAR THE VOCALS PROPERLY. THE GAIN SETTING BOOST UP EVERYTHING UNTIL IT SOUNDS DISTORTED DUE TO OVER PEAK PLAYBACK. I'D RATHER IT DIDN'T HAVE THE BASS AND GAIN BUTTONS AND ALSO THE MP3 PLAYER SO I DON'T HAVE TO PAY FOR FEATURES THAT ARE COSMETIC AND USELESS IN PRACTICAL USE.