Tube Harmonic Exciter
ZenTubeAnalog warmth. Harmonic precision.
Wave-digital 5670 triode
Modelled at 4× oversampling per channel, so the harmonic content comes from the circuit itself.
You can see what it does
A live drawer with the waveform, the harmonic spectrum in dBFS and the in → out transfer curve.
Cathode bias on hand
250–800 Ω moves the triode operating point and rebalances even against odd harmonics.
In detail
The 5670 dual triode
The pair of triodes running the wave-digital model at 4× oversampling. The glow follows what the stage is doing — the window is a display, not a control.
Gain-compensated Drive
Turning it up moves energy from the fundamental into the harmonics, so the fundamental gets quieter on purpose. Give the level back with the output trim and compare against bypass at matched level.
The analysis drawer
WAVE shows the peaks round off before you can hear it. HARMONICS is the honest picture of what the tube adds, in dBFS. TRANSFER is the in → out curve: a straight line is clean gain, the bend at the ends is the tube.
ZenTube is a tube harmonic exciter. Each channel runs through a wave-digital model of a 5670 dual triode at 4× oversampling, so the harmonics are the ones the circuit produces, not a waveshaper’s idea of them. Around the tube there is what you need to place it in a mix: input and output trims, a pad, an AIR shelf, a low cut, a dry/wet blend, and an analysis drawer that shows exactly what the stage is doing to your signal.
DRIVE is gain compensated, and that is deliberate: driving a triode harder compresses the peaks and moves energy from the fundamental into the harmonics, so the fundamental gets quieter — exactly as it does on a real unit. What you are buying with DRIVE is harmonic content, not loudness. The DRIVE meter reads push, not distortion: the mark near the top is the saturation threshold, where the second harmonic starts to come up out of the noise.
LOW CUT sits before the tube, so the bottom end never uses up the headroom the rest of the signal needs, and AIR is a shelf after it. MIX crossfades dry and wet with the dry path time-aligned to the wet, so blending the two does not thin the signal out — and the cathode BIAS trimmer (250–800 Ω) moves the operating point of the triode, shifting the balance between even and odd harmonics.
Controls
- Drive — −10 to +30 dB, gain compensated — the main control of the plug-in
- Drive meter — reads push, not distortion — the upper mark is the saturation threshold
- AIR — high shelf, +4 dB @ 10 kHz, after the tube
- Low Cut — 80 Hz Butterworth high-pass, before the tube
- Pad — −20 dB in front of the stage, for sources that arrive too hot
- Input / Output Trim — −60 to +12 dB each, stereo
- Mix / In Level — dry-wet crossfade, time-aligned · dry-side level ±12 dB
- Bias — cathode bias trimmer 250–800 Ω (390 Ω default)
- Link — channel 1 leads; channel 2 follows and locks
- Analysis drawer — waveform, harmonic spectrum and transfer curve, live
Specifications
- VST3, 64-bit — Windows 10 / 11
- 5670 dual triode modelled with wave digital filters, 4× oversampling per channel
- Drive −10 to +30 dB, gain compensated · PAD −20 dB
- AIR: high shelf +4 dB @ 10 kHz · LOW CUT: 80 Hz Butterworth
- Input / output trim −60 to +12 dB · IN LEVEL ±12 dB
- Cathode bias 250–800 Ω (default 390 Ω)
- Live analysis: waveform, harmonic spectrum and transfer curve
- No external runtime required