Thermionic VST3

Thermionic VST3

What is Thermionic?

Thermionic is an FX VST3 Plugin.
It is waveshaping in nature by applying a custom dynamic range compression followed by a single-ended triode amplifier.
The single-ended triode circuit uses a SPICE algorithm to solve the circuit state.
It can do both very low THD and heavy distortion/waveshaping effects.

The idea for this plugin came after designing this waveshaping compressor in LTspice. Then I thought that it would be cool to add a final triode stage.

Custom compression :
The compression applies a linear-to-log conversion with an additional coefficient (parameter k) that alters the transfer function to provide varied waveshaping effects.
Also, the knee effect can be tailored to provide distortion at the knee level. It is roughly the digital implementation of the LTspice knee-breaker compressor that I discussed in a previous post.

As for the triode implementation, it uses a classic 12AX7 single-ended configuration circuit. with AC coupling at the input and output stages for the default preset, with additional presets available.
It features a cathode bypass resistor and capacitor, grid current emulation, and Miller capacitance.

The intrinsic triode parameters are based on Norman Koren’s model and allow the emulation of other models of triodes.
Grid current is based on Rydel’s model.
Non-realistic Vact parameter is added to start grid current distortion at an arbitrary voltage input level, disregarding biasing.

Since the state-based nature of the circuit, some parameter combinations may result in divergence and are non-recoverable, but it is rare, Some parameter combinations also require more CPU time to find a solution.
So, it is advised to tread carefully when modifying parameters.

Saving a preset / restoring a preset is possible and the simulation should start all right but with a delay of a handful of seconds to obtain convergence.

abstol defines the SPICE solution tolerance and improves quality at the expense of more CPU load.

The plugin also features an experimental routing of the gain reduction to some triode parameters.

Additional features :

  • Oversampling from 0x to 3x.
  • Auto Make-up gain on/off with trimming.
  • Compressor / Triode bypass.
  • Compressor Stereo Linking On/Off.

Beta Caveats / Bugs :

  • Not all parameters are suitable for automation.
  • In some cases, when CPU load is high, switching on/off checkboxes and a StringListBox parameter, (for instance, Oversampling, GR Routing) may not be taken into account. If that happens, Please stop audio processing and change the parameter state, and then resume audio processing.

Tests :

To ensure a quality product, we will try to test the plugin in the most varied configurations, including a wide variety of OS and Hosts configurations.
Most of the tests to date have been done on Renoise 3.41

We also plan to enroll users for beta testing. Nothing is better than field experience.

Release Date :
To be announced,
Probably June to August 2023.

Minimum OS/Software requirements :

  • Windows 8 to 11.
  • x64 OS.
  • A VST3 compatible host.

What about Mac users?

We envision a plugin for Mac users, but we need more time to port some functions.

Will there be a Demo version?

There will be a demo version available on our portal soon, to start the beta field testing phase. For now, there is a youtube video with a demo of the product for waveshaping applications.

Some Screencaps :

Triode operation, Default Settings, Harmonic content.
Triode operation while drawing grid current
WaveShaping operation.

For a more dynamic presentation, check the video :

Thermionic VST3 Demo Video


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