Great pedal for getting that Marshall tone. There are two different circuits built into the pedal for two distinct tones. An internal slider switch controls which circuit is active. Choices are either a Super Lead setting, which is based on Marshall Super Lead, which has more gain than the second setting. The second setting is the Super Bass setting, which emulates a Marshall Super Bass tone, similar to a JTM or Plexi.
The pedal can be powered via either a 9-volt battery or by power supply with a negative tip DC from 9 to 18 volts. Running the pedal at 18 volts will give you more headroom and volume.