... press for switching Modes .If have USB memory and SD card ,Switch USB→SD→FM→USB ,if only have USB memory ... , switch order USB→FM→USB , if only have SD card, switch order SD→FM→SD ,If no have USB Memory ... and SD card , switch order USB→FM→USB Previous /Vol- :short press ... number over 9 , just input the numbers in series . Amplifier mp3 player , digital audio player