Radial Engineering JDI Stereo Passive direct box - The Radial JDI Stereo is a passive stereo direct box designed to handle extreme signal levels without distortion of any kind. Unlike an active DI that is limited by the buffering amplifier's rail voltage, the JDI employs a pair of Jensen audio transformers that at once balance the signal and lower the impedance to drive long cables. No power is required. You simply plug in and it works.