Fangrui Product Details 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 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 Lotus Interface. The Two Interfaces Are To Adapt To Different Occasions And Cannot Be Used At The Same Time. Just Choose One. Input: (l / R) + 3.5mm, Output: (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 W