Distortion
How much grind and saturation you get.
- Turn up Thicker, more saturated distortion.
- Turn down Leaner drive with clearer note attack.
Pedals / Filter-heavy RAT-style distortion
Black Rat
Filter-heavy RAT-style 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.
Filter
Cuts high frequencies after the distortion (this control darkens as you raise it).
- Turn up Darker, thicker, more muffled — tames fizz.
- Turn down Brighter and sharper — more buzz and edge.
Volume
Output loudness.
- Turn up Louder.
- Turn down Quieter.
Inspired by
Pro Co RAT (1978) — LM308 op-amp distortion with 1N4148 silicon diode hard clipping and a post-distortion Filter low-pass (475 Hz–32 kHz sweep, knob reversed vs most “tone” controls). Kurt used a RAT on In Utero sessions; Ninevolt profiles reference it for Nevermind studio tone and Metallica-style grind.
Signal path
| Step | What it does |
|---|---|
| Input HPF ~60 Hz | R7/C10 (560 Ω × 4.7 µF) — first leg of dual RC on op-amp input. |
| Pre-clip HPF ~1.5 kHz | R8/C11 (47 Ω × 2.2 µF) — second leg; bass rolled off before clip, mids into diodes. |
| Distortion gain | Distortion knob → up to ~79× (1 + distortion^1.08 × 78; analog ~2300×, scaled for digital). |
| Pre-clip soft LP | 100 pF feedback rolloff + LM308 slew; cutoff falls as gain rises (~1 kHz mid hump). |
| Silicon diode hard clip | Symmetric 1N4148 pair — knee at ~0.65 V then rational hard limit. |
| Filter one-pole LP | Filter inverted: CCW/ low knob = bright (~32 kHz); CW/ high = dark (~475 Hz). |
| Volume + clamp | Volume scales output (0.12 + volume × 1.25). |
How we modeled it
Classic RAT path: dual RC pre-clip EQ → gain → LM308-softened drive → diode clip → reversed Filter LP → Volume. Mid emphasis at high Distortion comes from the gain-dependent pre-clip LP (slew/100 pF), not from moving HPF corners. Factory In Utero preset targets moderate drive with mid Filter.
Simplifications
- No LM308 vs OP07 chip switch (Turbo RAT, You Dirty RAT, etc.) - Analog ~2300× max gain scaled to ~79× for digital headroom - 100 pF feedback LP applied post-gain, not inside a feedback loop - No JFET output buffer or volume-stage HPF