The housing is 3D printed with self casted rubber pads for muffling vibrations or other mechanical sounds. Inside is the preamp PCB with low noise components and two good electret condenser microphone capsules. The preamp circuit is powered by a 9V battery mounted on the hot shoe of the camera. The preamp features a power saving circuit which senses the phantom power of the camera (or device the microphone is attached to) and switches off the 9V power supply completely when not sensing a voltage from the camera (when the camera is switched off). There's also an indicator circuit which turns on a low current LED for a short time (indicating switch-on with a full battery) or long time indicating (warning for) an almost empty battery.
There are two switches; one for the Gain (G) which can be High (H) or Low (L) and one for Power save (P) with a setting for Save (S) and None (N). The gain switch switches R14 in parallel with R2 to regulate the gain and the power save switch just bypasses the current sensing circuit for devices that do not have phantom power.