1,with CE,ROHS,ISO etc 2,professional amplifier,with USB,TF,MPS input 3, ... , reducing potential distortion but reducing efficiency to 50 percent. Class D amplifiers, which use ultra-high frequencies to regulate switching operations ... 1 x Specification 1 x Power Adaptor With ROHS,CE,ISO 9001 certificate Rechargeable Portable Waist Hanged Voice Amplifier GP977 red