This circuit can be used when the audio equipment is connected to a power amplifier and the sound is small. It is suitable for small audio signal amplification. The amplification multiples are 8 times (18db) and comes with a USB charging cable. It cannot drive headphones and can be connected to audio amplifiers. It can be charged with a mobile phone charging head. It can be used continuously for 60-70 hours on a single charge. Using the classic Dual OP AMP NE5532, high frequency electrolytic capacitor, noise reduction circuit design, no background noise, effective gain audio, improve sound quality. The audio input and output are 3.5mm interface and RCA Lotus interface. The two interfaces are to adapt to different occasions and cannot be used at the same time. Just choose one. Input: RCA (L / R) + 3.5mm, Output: RCA (L / R) + 3.5mm + headphones. With volume adjustment knob, the volume can be adjusted freely. Small size, easy to carry and use. It is a preamp and cannot be used as a power amplifier to drive passive speakers working. Widely compatible with all audio devices. Input: DVD, CD, set-top box, MP3, TV, mobile phone, computer, tablet, microphone, phono turntable, sound card, guitar, bass, electronic instrument, game console or other devices. Output: speakers, subwoofer, Sound Blaster, reverberator, AV receiver, Post-Amp, Headphones, etc. Colour:Black Material:Metal Package Contents: 1 x Audio Preamplifier 1 x USB charging cable Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.