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Latest Version: 
Last Update: 
28 Jan 2013

CharBooster is a composite overdrive effect tailored specifically to be used as booster in front of any virtual amplifier model. It essentially consists of a pre-emphasis filter section designed to provide a variation of voicings for your instrument followed by a saturation circuit that excites the signal with harmonics while still being as transparent as possible. The UI is not trying to look like a hardware stomp box but rather has a range of meters and scopes to provide an insight on what is going on with your signal.


The effect's controls are broken down into 3 sections:

1. Character

  • Amount – sets the amount of the filtering applied.
  • Character – selects one of the pre-configured filters:

    - Shrill – boosts the top frequencies enhancing the presence of the signal
    - Bright – boosts the high frequencies adding clarity and brightness
    - Tight – rolls-off the low end to reduce the muddiness of the high-gain amps
    - Flat – bypass of the filtering stage
    - Fat – boosts the middle frequencies for the best high-gain tone
    - Warm – rolls-off the high frequencies (good for taming single-coil pickups)

2. Saturation

  • Harmonics – sets the amount of the harmonics introduced by this stage.
  • Mode – selects the configuration of the stages:

    - Off – bypass the saturation stage
    - Tube – pre-amp stage based on a single 12AX7 triode
    - Tape – simple magnetic tape model
    - T-n-T – tube preamp followed by the tape model

3. Boost

  • Level – sets the output gain of the booster from -6dB to +24dB.

On the top of the effect's window there are 5 more buttons (from left to right):

  • Enable the effect.
  • Stereo mode.
  • 16x oversampling.
  • About.
  • Check for updates.

The tube model used in the saturation stage is similar to the one used in Softamp 3OD, however the modeled circuit is different.

The tape model is a very simplified one. It has only the nonlinear transfer curve and dynamic frequency response modeled. Wow & flutter effects as well as phase smearing were omitted keep the CPU consumption low. It is loosely based on the Ampex ATR-102 tape recorder.


Unzip the archive and put the "AXP CharBooster.dll" or "AXP CharBooster x64.dll" to your VST folder. Make sure to select the one appropriate for your system (Win32 or x64).


  • The effect is able to produce high level output signal (up to +24dB). Make sure that there will be something in your processing chain that limits the output signal. The assumed use case is that CharBooster is followed by the amplifier model that is pushed into saturation.
  • Not all amplifiers will sound pleasing while being overdriven at the input. Experiment.
  • CharBooster expects to be driven by a full-swing 0dB input signal. If pushed further the sound quality will degrade.
  • The CPU consumption in the most complex mode (T-n-T saturation, Stereo mode with 16x oversampling) could be a bit high. There's a plan to optimize it later, but it's a low priority task unless I'm specifically asked to do it.


This software is licensed for an unlimited usage by everyone, including personal, commercial and scientific applications. You are NOT allowed to modify it (including both the binary code and the copyright information) or sell it, in either stand-alone or bundled form. The plugin is provided "as is" without a warranty of any kind. In no event I shall be liable for any damage associated with the usage of this software. I encourage further distribution by sharing a link to this page.

Please send your questions and suggestions.

VST is a registered trademark of Steinberg, GmbH




Has a nice quality sound to it. Is useful for increasing the overall versatility of amp chains.

Mastrcode (not verified):

This is a great plugin. I use it to fatten up my trance kicks and this plugn does it's job great.

AXP's picture


This plugin is often overlooked, and is less popular than my amp sims. It's great to hear it has found its use.

Homero (not verified):

Very versitile preamp model. I'm also using it to warm up my tracks. When you hit the 16X mode man, it sounds analogbeautiful!!!!

Jon (not verified):

As soon as I heard the boost/saturation was partially based on a 12AX7 tube emulation I had to look into this thing. Do you think it could be used as a poor man's virtual BK Butler Tube Driver?

AXP's picture

I haven't heard the BKB Tube Driver myself, so I can't really help you here. But it depends a lot on the whole circuit, not just the tube model. Give it a go, and also look at SoftAmp 3OD for more tube tones.

poo (not verified):

im gonna need you to make this for mac

AXP's picture

Would be cool, but I neither own any Apple device (not even a phone) nor have any MacOS programming experience. So there should be either:

1) an opportunity to learn it while I do my paid work or
2) a cool multi-platform framework that would allow cross-compiling with minimal changes.

Both remain a possibility, but not in the near future.

Jonathan Dozesoph (not verified):

I really love whatever you are doing behind the scenes in your plugins.i've always had this problem with software tube models making the sound brittle,small and static.for some reason,yours do not suffer from any of would probably be a little exotic based on your current sonic repertoire,but i would really like to see you do a tape model.more low end like cassette as i am very interested in the phase smearing it produces,it seems like a lot of this stuff is constantly omitted in any kind of circuit modelling,when i personally think it is a large part of the sound.if anybody could do a model like that justice,it would be you.30D and Charbooster are literally on every single one of my projects,albeit sparingly.just to add a bit more meat and size to sterile digital elements

Keep doing what you are doing

AXP's picture

Hi Jonathan, 

thanks for the kind words! You have no idea how close you are to what I have on my radar. Really, the low end cassette, phase smearing and all that ;)

And keep an eye out on the upcoming KVRAudio developer challenge!

AM (not verified):

I also would love to see a tapelike or even better a complete tape machine emulation from You. It would be a dream come true! Thank You very much AXP for all Your absolutely awesome free plugins. They are very much appreciated and cherished! =)

Joao (not verified):

This is the best, most versatile and musical overdrive emulation I've found in vst format, period.
No other free or paid plugin has given such a wide variety of options.
It absolutely rocks, as your other works.
I hope you keep at it!