Tube Drive

A stereo tube-saturation effect that models the warm, asymmetric clipping of a valve preamp. It runs from a gentle harmonic glow to full overdriven grind, and saturates each channel independently so the stereo width you feed in comes out untouched.

How it works

The signal is pushed through a biased sigmoid waveshaper — the curve a tube uses to round off and soften transients. Drive sets how hard you push into it. Bias offsets the signal before it clips, bending the curve asymmetric: at zero it stays symmetric and generates mostly odd harmonics; wound up it leans into even harmonics, the source of that "preamp glow." Crucially, bias is independent of drive, so you can dial heavy even-harmonic colour at low gain, or keep it clean at high gain. The output is loudness-compensated and DC-blocked, so the level holds steady as you sweep.

Controls

Drive

  • Drive — how hard the signal hits the tube, from subtle warmth to saturated grind.
  • Bias — even-harmonic asymmetry; up for thick preamp glow, down for a symmetric, odd-harmonic edge.

Voice

  • Presence — pre-emphasis: boosts the highs going into the tube so they distort harder. Adds bite and air — the more you drive, the more it bristles. At 0% it's transparent.
  • Tone — post-saturation brightness. A lowpass on the distorted signal that rolls off fizzy upper harmonics: 100% (default) is wide open, lower is progressively darker and warmer.
  • Sag — power-supply sag. Loud passages momentarily dip the tube's output and recover slowly, so the sound compresses and notes "bloom" as they decay — the breathing feel of an overworked valve amp. At 0% it's off.

Output

  • Level — output makeup on the saturated signal (1.0× unity), on top of the automatic drive compensation. Push it past unity to drive whatever follows.
  • Mix — dry/wet blend; 100% is fully wet, lower values fold the clean signal back in.

Inputs & outputs

  • In L / In R — the stereo signal to drive.
  • CV inputs — every knob has one: Drive / Bias / Mix / Tone / Presence / Sag / Level CV. Patch an envelope into Drive or Sag for dynamic grit, an LFO into Tone for a sweeping filter, or modulate Bias for shifting harmonic colour.
  • Out L / Out R — the saturated stereo pair.

Tips

  • Pull Mix back for parallel saturation: blend grit underneath the dry signal to add harmonics while keeping the low end tight.
  • High Bias at low Drive is the sweet spot for subtle tube warmth across a full mix or drum bus.
  • Presence + Tone together act like a tube amp's tone stack — push Presence for bite into the distortion, then pull Tone down to tame the result.
  • A touch of Sag on sustained or percussive material adds movement and "bloom"; patch an envelope into Sag CV to control it per note.