The Graviton Metal Distortion is a clone of the BOSS® HM-2 Heavy Metal, first released in 1983 and discontinued in 1991. The HM-2 was largely overlooked while it was in production, but in the mid-1990s it got the attention of a few bands in the Swedish death metal scene who developed something of a signature guitar tone by turning all the knobs to 10, often running it into a cheap solid state amp. Here is the video that first exposed this technique:
Despite the reputation it enjoys in the extreme metal community, it is far from a one-trick pony. It’s a very flexible pedal with a balanced high-gain distortion tone that works well in many styles of music.
This circuit also made an appearance as the DOD FX-56 American Metal, released in 1984. While the pedals don’t really sound the same, the American Metal has almost the exact same circuit layout, just with different parts values and with the two tone knobs combined into one. You can build the American Metal with the Graviton PCB.