Distortion
Main gain into the crunch circuit.
- Turn up Heavier distortion and more compressed sustain.
- Turn down Milder overdrive, more of your pick attack survives.
Pedals / Dual-mode turbo distortion
Turbo Crunch
Dual-mode turbo distortion · play-tested
seth — fish
seth@ninevolt:~$
Knobs
In the TUI each knob runs from low (left / 0%) to high (right / 100%). Start near noon, then nudge while you play.
Tone
Dark-to-bright balance of the distorted sound.
- Turn up Brighter and sharper.
- Turn down Darker and smoother.
Level
Output volume.
- Turn up Louder into the rest of your chain.
- Turn down Softer overall level.
Turbo
Switches between the milder and hotter gain modes (treat low as mode A, high as mode B).
- Turn up Hotter, more aggressive turbo character.
- Turn down Classic, slightly tighter crunch mode.
Inspired by
Boss DS-2 Turbo Distortion (1987–present) — DS-1 core (transistor booster, op-amp, hard diodes, scooped tone stack) plus a Turbo mode with higher gain and LED-style clipping. Kurt Cobain used DS-2 on the In Utero tour; Ninevolt profile nirvana-in-utero stacks it ahead of SansAmp and Polychorus.
Signal path
| Step | What it does |
|---|---|
| Input HPF ~60 Hz | Blocks DC / sub rumble (C1 coupling). |
| Transistor booster | Q2 soft asymmetric pre-clip — shared by both modes. |
| Turbo knob | Turbo > 0.5 selects the Turbo path (higher gain, LED clip, post LP). |
| Mode I op-amp gain | Distortion → up to ~22.3× (1 + distortion^1.04 × 21.3) — same curve as Crazy Tone. |
| Pre-clip HPF / LP | Mode I only — bass rolls off before clip; grain mellowed ~7.2 kHz. |
| Mode I hard clip | 1N4148 pair at ~0.7 V — fizzy DS-1 knee. |
| Turbo op-amp gain | Distortion → up to ~75× linear — hotter LED feedback path. |
| turbo_clip | Asymmetric bias, lower threshold (~0.58 V) — compressed upper mids. |
| Post-clip LP | Turbo only — one-pole ~5.2–6.1 kHz tames fizz after LED clip. |
| Tone LP / HP blend | Tone blends 234 Hz LP vs 1063 Hz HP — scoop ~500 Hz at noon (both modes). |
| Level + clamp | Restores tone-stack loss; output trim. |
How we modeled it
Mode I reuses the Crazy Tone (DS-1) chain so In Utero presets with Turbo off behave like DS-1. Turbo skips pre-clip filtering, runs hotter linear gain, LED-style asymmetric clip, optional post LP, then the same tone stack.
Simplifications
- Turbo is a knob threshold, not a dedicated footswitch - No separate Mode I / II diode pair footswitch — Turbo knob picks one of two modeled paths - Mono only; no battery sag or buffer stages