Doppio serves as the smaller, simpler, and cheaper little brother to the Moka Harmonic Percolator. It features NOS Russian Germanium transistors, but can also be built with silicon. To sweeten the pot, the Magic switch brings a new level of versatility. At its core, Doppio is a truthful representation of the classic harmonic percolator. Just the basic controls, Harmonics (gain) and Level. It is the Magic switch that keeps things interesting. When Magic is engaged the low frequency response of the pedal changes dynamically with the Harmonics control. At low gain levels, the input is full range and fat. As the gain increases, the bass response is trimmed to keep it tight, resulting in a bright and focused distortion at its peak. If the traditional HP is what you're after, turning off Magic changes the value to the standard vintage spec. This will also give you access to a thinner low gain sound and a much fatter high gain sound. If Moka is too much to handle or you're trying to save room on your board, Doppio is the answer.