This Lab Series is based on the classic MXR Distortion + circuit. It's also the same circuit as the DOD 250 and MXR Micro Amp.
To act like a volume boost, just put Volume knob at max and the gain knob will be your volume setting (exact same circuit as the MXR Micro Amp). This particular unit is silicon diodes to match the spec of the grey DOD250.
Link to the production model : Shark + Distortion