Hm-2 Schematic

Search for "Boss HM-2 service notes" (PDF). This includes the official schematic, parts list, and voltage readings. The voltages are critical: The op-amp inputs should read 4.5V DC (half supply). If they don't, the pedal won't clip correctly.

| Component | Value | Function | Interesting Mod | | :--- | :--- | :--- | :--- | | | 10k | Feedback resistors (gain) | Increase to 22k for more saturation | | D3, D4, D5 | 1S2473 | Clipping diodes | Swap for LEDs for louder, less compressed sound | | C21, C22 | 0.047uF | Gyrator caps (Low control) | Increase to 0.1uF for even more bass | | C23, C24 | 0.0039uF | Gyrator caps (High control) | Decrease to 0.0022uF for more extreme highs | | IC1 | M5218L | Op-amp | Socket it. Try NE5532 (tighter), LM833 (smoother) | hm-2 schematic