... so on. Function:1,with USB,TF,MP3 input2,FM radio with antenna3,with echo Features:The Rechargeable Voice Amplifier adopts ABS engineering ... lithium battery) use time long, can reach 15 hours ,Battery life can reach 2-3 years Cooperate with wearing type microphone Amplification ... completely when so signal reaches them, yielding up to 70 percent efficiency. Class A/B amplifiers allow the switching ...