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Flextron DC14

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Flextron DC14

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Flextron is a virtual-analog guitar amp made for KVR DC14. It's based on a concept of the hybrid guitar distortion pedal I've built for myself a while ago. The prototype pedal in its turn was based on two commercial tube emulation technologies – Flexwave by Crate and Cooltron by VOX.

This combination was discovered by accident when I was repairing my bandmate's VOX Bulldog distortion pedal. I didn't like the Bulldog that much, however I got interested in its low-voltage tube design so I assembled a copy on a test bench. On its own it has provided very little overdrive, just as expected, but when combined with the Crate Flexwave preamp (my favorite solid-state distortion) it has completed its already great tone, giving it more fullness and presence. I've used this arrangement for rehearsals and some gigs and got complemented for the tone.

Flextron goes a step further and accurately models a range of Crate solid-state amps powered by the Flexwave circuit. Every stage of the preamp signal path is carefully analyzed and modeled with the same attention to details as my previous SoftDrive GV and SoftAmp FM25 plugins.

The Flexwave amp design has evolved over the years. I counted 6 different variations. After careful analysis, I've narrowed down the scope to 3 models. The one I've played with was made in the late 90's and I think it's ahead of the pack. However in 2000's they have changed the gain channel structure significantly and after some consideration I've decided to model all three.

The Cooltron circuit in its turn stayed the same across their pedal range. I've tried a couple of different approaches to modeling it before settling on the final one. Since I've had a real physical implementation at my disposal I was able to successfully verify the accuracy of the digital model.

Interestingly, both Flexwave and Cooltron follow exactly the same idea – they essentially are an asymmetric clipping stage biased by the low-passed feedback signal. Having made my own SoftAmp 3OD model I can say that this is exactly how a real guitar amp triode stage works. The main difference is that Cooltron uses a 12AU7 tube running on 6V anode voltage for the authentic tube waveshaping, while Flexwave relies on an asymmetrically configured "rubber diode" pair to achieve the same effect.

In addition to the fully featured 3-channel preamp and a tube saturation stage, Flextron offers a dual-mode stereo reverb (algorithmic and convolution-based), a speaker simulator with two cabinet models and an ambience control (intended mainly for practicing in headphones), a switchable order oversampling and a set of visualization instruments, such as an EQ curve plot and stage bias meters.

Just as with my previous plugins, every single control is remapped to produce linear response on a dB scale.

Additional details can be found in the bundled manual.

This plugin was made for KVRAudio Developer Challenge 2014:

“Crate” and "Flexwave" are registered trademarks of LOUD Technologies Inc.

“VOX”, “Bulldog”, and “Cooltron” are registered trademarks of VOX Amplification LTD.

AXP is not affiliated with or endorsed by neither LOUD Technologies Inc., nor VOX Amplification LTD. The names are used only for reference and benchmarking.

AXP Flextron (c) 2014 Alexander Petrov-Savchenko


Sound clip:

An instrumental track composed and recorded by a Czech musician and producer Martin Linda using AXP Flextron (also check out his site):

Demo videos kindly created by Pete Kelly to showcase the Flextron:

Long and detailed playthrough by Amner Hunter (make sure to listen to the track at the end of the video):

Version History: 

1.0.03 Bugfix:
- Fixed a bug that caused no output upon plugin loading with Tube stage enabled

1.0.02 Bugfix:
- Fixed a bug that caused a crash in 64 bit mode on the latest Intel "Devil's Canyon" CPUs
- Fixed a wrong redraw behavior of the Tube Saturation plot

1.0.01 Bugfix:
- Fixed a bug that may cause high CPU load on some systems

1.0.00 Initial version for KVR Developer Challenge 2014


Dmitry (not verified):

Greetings from Moscow! Awesome amp. I voted for you.

AXP's picture

I'm glad to hear that, thanks!

Alex Irae (not verified):

Awesome man!, you really know how recreate analog distortion in digital domain!, 5 stars for you in the KVR DC 2014 contest.

AXP's picture

That's great, thank you!

Sergey (not verified):

Thanks for great plugin.

AXP's picture

You are welcome!

Dash (not verified):

Two words: Tremendous. Thanks

AXP's picture

You are welcome :)

Cody (not verified):

thanks for following through man, you've made your best plugin yet! the hall reverb in particular is great for the Taurus vsti's lead type sounds. and it works great for sub-bass too. great work!

Antiphase (not verified):

Nice amp! It`s really natural and has something of rectifier (or Crate), jcm800 and even maybe orange dark terror) shape function does this! However it`s too fuzzy or so... Do you plan another types of sound, e.g. Engl Invader or similar? That would be awesome)

STU KARLSSON (not verified):

This new Flextron Amp is "AWESOME" it is a must have amp sim vst "JUST GET IT" enuff said

Rafa (not verified):

Hi, Alexander...CONGRATULATIONS!!!!....Your plugin is probably the best!!...I work with music and musicians, and tried with many other VST' one like yours!!....You're a genius!!!....(The only thing to "retouch" is CPU consumption, is so high)......By other side.....AWSOME!!, BRILLIANT!!, INCREDIBLE!!....Congratulations again and go on!!!!....Best regards from Spain....

AXP's picture

Wow, thanks for such an emotional response! I'm glad you like it. I suggest lowering the oversampling ratio to 4x or switching it off completely (1x). It may be good enough for playing/mixing and you can always switch it back to 16x for the final rendering.

coconuts (not verified):

I love sending drums through this plugin, it makes them sound like a bunch of gremlins bouncing around in a trashcan in the best way possible. Thank you!

AXP's picture

haha, what a description, I should name a preset like that!


Leo (not verified):

wow, i've stumbled uppon your site by accident, really. and i'm glad i have! this amp sounds amazing an it's by far the lightest amp sim for the cpu. i have a crate gtx65 combo, and this sounds a lot better :D

AXP's picture

Thanks a lot! Very cool to hear that from an actual prototype amp owner :)

Pilvi (not verified):

Hello Alexander!

I love the Flextron! It's been my favorite preamp/amp/cab plugin since I discovered it. I have a request: my friend uses a Mac and he's a fan of the Flextron but is sad that there is no Mac version. How hard would it be to make a VST for the Mac?

AXP's picture

Hi Pilvi,

thank you, I'm pleased to hear that! 
I plan to release something completely new later this year that would be cross-platform. Depending on that experience I might redo all my plugins to work on Mac as well. Can't give you an ETA, or even guarantee that it will be done, but I hear you (and others) loud and clear on the Mac request.

Anonymous (not verified):

Добрый день, Александр.
От всей души хотел Вас поблагодарить за потрясающую работу.
Перелопатив за все эти годы тонны шлака, я так и не нашёл ни одного нормального софтового усилителя. Ваш - единственный!
Мне нужно было в качестве основы хоть что-нибудь отдалённо напоминающее по звуку Bogner Ecstasy 101b. Ничего такого и в помине нет. Вокруг - сплошные жужжалки и перделки отвратного качества, независимо от того платные они или нет.
Единственный "Bogner" - LeXtac от LePou -это жалкая поделка по сравнению с Вашим Flextron.
Ещё раз - огромное Вам спасибо. Пожалуйста, продолжайте Ваш гениальный труд, даже если он не приносит желаемых дивидендов в виде финансов и человеческого отклика.
С огромный уважением и наилучшими пожеланиями, Михаил.

AXP's picture


Большое спасибо за столь теплый отзыв, я правда тронут! Рад, что Flextron Вам так понравился. Это то, ради чего я и работаю. К слову, рекомендую обратить внимание на очередной конкурс плагинов KVRAudio developer challenge - я готовлю новый проект, должен получиться еще интереснее! Открытие - 1 декабря, 

Еще раз спасибо,

esd (not verified):

how to download ?

AXP's picture

There's a blue "download" button under the effect screenshot.

Frank Ventimiglia (not verified):

I recently installed this VST on my computer and have been using it through Ableton Live Lite 9, and I love it. It is by far my favorite amp plugin. But I just installed Reaper, and it is not showing up in my available VSTs'. Does it not work with Reaper? Or is there something I need to do. I really want to use this VST. It is the closest tone I have found for my actual Fender HRD3.

AXP's picture

It sure works with Reaper. Make sure you are using appropriate DLL (32 or 64 bit) if you are running 32-bit Reaper.

Anonymous (not verified):

Thank you, sounds incredible!

rc (not verified):

Thank you very much for Flextron, it's hand-down the most easy to use, dynamic sounding amp sim I've ever tried. This has been my to go plugin for a few months now, far better than any of the overpriced commercial plugins. Hats off to you sir!

kluihom (not verified):

thank you

ben zukerman (not verified):

work grate for bass as well!

Steve (not verified):

Thanks for this plugin. You've captured something quite natural here to my ears, that many amp sims lack.On lead tones the Flextron excels. Many thanks for this release. You are a talented and gracious gentleman, to make this available.

Steve (not verified):

Thanks for this plugin. You've captured something quite natural here to my ears, that many amp sims lack.On lead tones the Flextron excels. Many thanks for this release. You are a talented and gracious gentleman, to make this available.

AXP's picture

My pleasure to share it, thank you!

James (not verified):

IMO one of the best amp sim vst's available at any price especially for free. Thanks for making this and freely releasing it to the public. Happy holidays and happy new year to you!

AXP's picture

Thanks a lot! I've found myself using it a lot for my own tracks, just as I did with its prototype many years ago. 

Dolurum (not verified):

Tried your PSA last night - loved it. Tonight the Flextron - loved that too! Your plugins are a cut above - the sound seems smooth and analogue even though we are running the in PC. You have something special here! Thank you!

AXP's picture


QMetalMan (not verified):

I've been struggling to find great guitar tones for a while now. I knew I liked my crate GX-15's tones a lot, so I searched "Crate amp sim". I want you to know: you have ended my struggle. The tones I get from this are perfect! Thank you so much!

AXP's picture

Thanks! Their "Flexwave" circuit is indeed quite nice. I was attracted to their thick but smooth sound myself so I had to model it!

Alejandrobp (not verified):

I just used it for a couple of minutes and got impressed with the sound. It brought alive my cheap guitar again!

Thank you Alexander

AXP's picture

Thanks, keep playing!

Евгений (not verified):

Здравствуйте! Ваш плагин - единственный бесплатный, который удовлетворил мои потребности. Это просто чудо, всё прекрасно звучит - хоть клин, хоть драйв, хоть метал-лид. Не сочтите, пожалуйста, за дерзость, но у меня есть один вопрос по поводу самого плагина - обновления, получаются, дальше не планируются, разработка подошла к логическому концу? А так выражаю вам огромную благодарность за столь шикарный усилитель!

AXP's picture

Спасибо за добрые слова!

Каких-то прямо критических апдейтов не назрело, со своими целями плагин вроде справляется (сам им постоянно пользуюсь!). Сейчас у меня совсем мало свободного времени. В качестве развлечения и отдыха портирую конкретно этот плагин на аппаратную платформу (копеечная open-source платка) для игры в нашуниках вдали от компьютера. Когда найду время для новых VST плагинов, это будет скорее всего что-то совсем новое (есть пара насущных потребностей).

Russ (not verified):

Thanks for the great tools.

I think the spring reverb offers better sounds than commercials ones. It would be great to have a separate spring reverb effect, I think it would be popular.

AXP's picture

Interesting take, thanks. Frankly speaking I just sampled the reverb unit in the Randall amp I had at hand. I've toyed the idea of a procedural spring reverb in the beginning (the one based on the physical model that you can tweak), but concluded that it offers little value in terms of quality at the expense of high processing cost. However I can think of an IR-based one still with decent morphing capabilities.

RonnieTub (not verified):