The "Distortion" channel on a JC-120 is often misunderstood. It is not a modern high-gain preamp. Examining the schematic reveals a simple clipping stage. It typically uses a set of diodes (often silicon signal diodes like 1S1588 or 1N4148s) to hard-clip the waveform.
Following the gain stages, the signal enters the Equalization (EQ) section. The schematic reveals a Baxandall-style tone control circuit (or a variation thereof). jc-120 schematic
Pro Tip: Locate the serial number on the back panel. If you see "MA" (Roland Japan), you likely have the discrete power amp. If you see "FI" (Roland Italy), you have the later European revision. The "Distortion" channel on a JC-120 is often misunderstood
Purists ignore it, but the JC-120 includes a distortion circuit. The schematic shows a separate gain stage using an op-amp with clipping diodes (usually 1S1588 or 1N4148) in the feedback loop. Following the gain stages, the signal enters the