AXP SoftAmp 3OD
Vacuum Triode Stage simulator.

A single triode stage circuit typical for guitar preamps is captured in this plugin. The model engine is based on a system of non-linear ODEs. Some smart calculation techniques are used to reduce the computational load.

This effect could be used to apply mild tube overdrive to add some presence to your tracks, or you could chain a couple of instances together for a full-blown high-gain overdrive. You may want to throw in some EQ as well to better shape the signal and use a poweramp/speaker simulator afterwards.

The plugin UI has a real-time transfer characteristic plot display. It provides an overview of the things going on inside the tube. It also has a peak-detecting algorithm that will flash a line when the level exceeds 0dB. You can monitor stereo channels separately or at once by clicking the corresponding buttons under the plot display.

16x switchable oversampling is also implemented to reduce the aliasing effects. Please note that for the most time the aliasing is low enough to switch off the oversampling. When oversampling is enabled, the plot display will not be of much use, because of the phase smearing introduced by the oversampling filters. Still good enough for monitoring the in/out levels.

The model has 3 core controls to configure the circuit:

• 3 different triode models: 12AX7, 12AU7, 12AT7.
• 3 different plate voltages: 150v, 250v, 350v.
• 3 different cathode capacitors: 0.47uF, 1uF, 22uF.

The gain/level controls are combined into a single knob that is operated with left and right mouse buttons.

The "Normalize Output" control enables the normalization of peak-to-peak output voltage swing across all triode configurations, particularly different plate voltages. By default it's turned off to reflect the natural triode stage behavior, which could be regarded as a normalized small-signal gain.

Please note that output signal is not clipped at 0dB to let you overdrive chained stages using more that one plugin instance connected in series. Make sure to watch the output level or use a hard limiter somewhere in your signal chain.

Clicking on the SoftAmp logo in the plugin will bring up the "About" window with a version number and contact details.

Thanks to everyone who has voted for SoftAmp 3OD in the Developer Challenge and used it in their work.

Change history:

1.0.5 (20-Dec-2012):

• Fixed a bug with UI not opening if another instance of the plugin is closed.

1.0.4 (10-Dec-2012):

• Significantly reduced the amount of "clicks" during the parameter change. More user feedback is appreciated.
• Reworked GUI code to fix some drawing problems. The plugin scanning/loading should be come much smoother across different hosts. Thanks to Martin LeFever for reporting this one and helping to narrow-down the issue.

1.0.3 (5-Dec-2012):

• "Normalize" feature wasn't working as intended. Fixed, added description.

1.0.2 (16-Nov-2012):

• Prevented possible floating-point underflow.

1.0.1 (10-Nov-2012):

• Fixed dependency on MS CRT library.
• Changed signal phase to allow external dry/wet mixing.
• Fixed UI buttons half-lit at startup.
• Optimized CPU load (should no longer cause audio dropouts during parameter change) and model accuracy.
• Slightly reduced audible clicks during triode mode/plate voltage change.

1.0.0 (20-Oct-2012):

• Initial release for DC-12.