The Arcturus Natural Overdrive is based on the Nobels ODR-S Overdrive Special, first released in 1993 as a sibling of their more famous ODR-1.
Compared to the ODR-1, the ODR-S has a nearly identical drive section, except that the hard-clipping diodes are germanium instead of silicon. The main difference is in the tone stack. The ODR-1’s Spectrum control has been replaced by a full 3-band EQ. The midrange control uses the same transistor gyrator concept as the Spectrum control, though it’s tuned very differently, while the bass and treble controls are a standard Baxandall arrangement.
The Arcturus is a direct adaptation of the ODR-S, but with the JFET switching removed in favor of true bypass. We have also added an optional correction for what has been seen as an error in the original design related to the input bias of the second op-amp stage. This is described in detail in the build documentation if you’re curious.
In 2023, Kai Tachibana, the original designer of the ODR-1 and ODR-S, released a pedal called the ODR-CS Custom Special under his company Nordland Electronics in honor of the original pedal’s 30th anniversary. The ODR-CS is a re-engineered version of the ODR-S that uses better quality components than the original Nobels unit as well as true bypass switching. It also has a few editorial changes, primarily in the three bands of the tone stack.
The Nordland ODR-CS has not been traced as of this writing, so we are not sure what exact schematic changes were made. But Nordland makes a fantastic product, so we strongly recommend buying one from them if you are interested!