I've used the Juice Box on many projects. It's a great sounding D.I. that works well on guitar, bass, vintage keyboards and synths.
"The Juice Box's audio circuitry is class "A" from start to finish. That and the absence of a transformer explain the conspicuously low distortion spec. It also employs a low impedance high voltage power supply, and a D.C. filament circuit just to keep things nice and quiet.
Then retrospec took one significant step further and included enough gain and headroom to be able to drive a 10k input at professional line level. Now you can go from instrument to console channel line in or direct to tape machine in one sweet clean step!"
"The “-20” position is for a traditional direct box situation, intended to feed a low level signal, typically the signal from an electric musical instrument, to a microphone input. The “0” position turns the unit into a unity gain buffer; the musical instrument signal can be driven into a mic input or a low level line input. The “+20” position raises the signal to professional line level for those fans of the “direct to the tape machine” mode of recording. The “VARI” knob allows continuously variable gain adjustment between 0 dB and +20 dB".