This machine adopts attenuated tone circuit + NE5532 preamplifier compensation, When not powered, the attenuation is -15db, When the power is supplied, the amplifying part of the NE5532 works for compensation, and the gain is 0db, that is, the input and output signals are equal. When the switch is bounced, no power supply is required, and the working state is an attenuating tone circuit, which is -15db, the switch when power is supplied, there is an internal amplifier circuit for compensation and the gain is 0db. DC power supply should use low-ripple high-quality power supply as much as possible. When the input signal amplitude is less than 1V, 12V power supply is sufficient. When the input signal is 1V, please increase the power supply voltage, and the maximum power supply voltage is 24V. Plug Type:EU Plug,it applies to Indonesia, Germany, France, Spain, Italy and so on Voltage:AC220V Color: Black Material: plastic Package Contents: 1 set * TO-10A volume adjustment controller 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.