Depending on the setting of the effect control, it can go from classic "fuzz face" sounds and beyond - achieving the sustain of a big muff. It's a three stage, high gain, low voltage solid state amplifier circuit.
I was unable to to find any videos of it, but as soon as I saw the words Sunn and Fuzz together I knew I had to take a crack at this pedal.
The circuit runs off of +1.5V, just like the FZ-1A. The problem with this is that we would need either a dedicated power supply or run it off a AA battery, and you wouldn't be able to wire up an indicator LED. So what I've done is made a board for the original, and did some digging to see how to get +1.5V from a +9V source.
What I found was that using an LM317 regulator you can get the voltage down to +1.5V with the right resistors. After doing some calculations with the regulator board you should get +1.516V. If my calculations are right, that means you can run it just like any other pedal and have an indicator LED.