Low-gain overdrive. Works perfectly. I've been using this pedal and really liked it, but I'm selling it because I don't use it as often anymore. It's a popular Zen Drive, and this Supreme model is quite rare. Compared to previous Zen Drives, it has slightly less compression and a more subdued gain. You can get plenty of gain by stepping on both switches, allowing for some pretty heavy sounds. The two circuits use different op-amp configurations, resulting in different sound nuances. Combined with the 3-tone switch, you can create a wide variety of sounds. You can also choose between 9V and 18V power, allowing you to experience the difference in sound due to voltage variations.