This distortion unit uses three MOSFET gain stages followed by a simple Big-Muff style tone control. It is a positive-ground circuit, so it should be powered with a battery. It doesn't draw much power anyway.
It's important to build the circuit on a breadboard first, as the MOSFETs will usually require re-biasing. Adjust the 3.9k resistors until the drains are at approximately 4.5v. This doesn't have to be exact, anywhere between 4-5 volts is fine.
The circuit may also be built in a normal negative-ground configuration, using 2N7000 or BS170 devices. However, there will be a higher level of background noise.