The Experiment resumes .....

Written by Steve Poskitt Print Email

After a long time with no input finally decided to revisit the blog and continue with the quest!

Thanks to the Guitarix team there has been a major update to some of the tools used to simulate circuits using the DK method.

What were once experimental tools and used to generate filters to simulate the linear parts of a circuit have been expanded by brummer to enable simulation of the non-linear elements in a circuit ( by far the most important in guitar amplifiers and effects ! ).

 I have followed Brummer's lead and am in the process of setting up a Github repository to host my experiments as firstly the Guitarix project is in danger of getting to large, and I have also some interest in simulation of other studio effects.

The tools in question are in the tools/ampsim directory and enable the generation of Faust DSP scripts directly from circuits with the linear elements being represented by filters and the non-linear by look up tables. 

Some experimentation is necessary to break the circuits into manageable blocks that can be solved and also do not cause problems with the filters. Once that has been achieved the resulting blocks can be tweaked and optimised to achieve the required results. I have now spent several months with this and am impressed with the results. Seems a big improvement to the previous methods both in terms of the sound produced and  the efficiency of the code ( CPU usage is minimal ).

My initial experiments with this new method seemed to be having problems with the higher frequencies, but on a suggestion from brummer to use the faust freq_split function to process the audio in preset frequency bands, that has mostly been sorted. Another option would be to use oversampling but that could have CPU use implications.


For the user interface I have been experimenting with the DISTRHO DPF Framework with good results. I like the idea of of using the Open GL for the graphics as this is available on all platforms and makes use of the hardware acceleration of modern graphics cards. Have to admit that have never been a fan of either GTK or Qt. The DPF Framework should also allow Mac OS and Windows users to build and use the plugins.

As a taster there are some screens shots below of my work so far with brief description.

Redeye F2-B


Yet another attempt at this classic Alembic preamp, previously the Studio Pre in Guitarix. This version does seem to have a little something missing from previous versions. Bright channel does not work 100% as in real circuit due to nature of the simulation.

Redeye AC4TV

Based on the Vox AC4TV with additional option of an old EF86 pentode based preamp. Was basically experiment to see if single ended tube/transformer combinations could be reasonably simulated with the ampsim tools.


Redeye Clubman

Another simple circuit based on the Watkins.WEM clubman amplifier. My first ever amplifier was a Watkins and stupidly I sold as did not really appreciate it at the time. Like the real versions relatively dark amplifier.

Redeye Deluxe

No prizes for guessing the inspiration for this one ! An attempt to simulate the strange interaction of the older "tweed" circuits. For such a simple circuit the quirky controls give a wide range of sounds.


Redeye Echorec

This is a much more ambitious attempt to simulate this famous echo machine. Much time taken tweaking the various stages and getting everything working together, still some work to be done on the feedback loop. Due to the sheer amount of controls this is a beast of a machine to play with. Endless possibilities for creativity an, of course, to just get lost!

Redeye Overdrive Special

Another of the more ambitious circuits based around the famous Dumble Overdrive Special circuits as far as they are possible to clone. So far pleased with the variety of sounds available here, the cleans are varied and clean most of the way up, the overdrive dirty but controlled. More tweaking required but definitely a good result with this one.


Redeye Princeton

Another of Fenders finest was the base for this one. Really the same as the Guitarix "Chump" as based on the single ended Princeton circuit. A very usable basic amplifier.

Redeye Treble-n-Bass

Another blast from the past, for many years I played through one of the old Crocodile skin covered Selmer Treble-n-Bass amplifiers and a pair of Goodmans 15" speakers. This is based on teh circuit from that era and like the Watkins inspired circuit is relatively dark. Goes well with a treble booster like the Guitarix Rangemaster clone.

Redeye TiltDrive

Latest incarnation of this effect that I produced for the Guitarix project. Is basically a tube overdrive with some interesting tone controls. Lots of work on the second stage of the circuit so that it produced a more usable overdrive tone.

Redeye TubeDriver

This circuit was a revelation to me ! Past experience with real tube circuits that ran at "starved" voltages have always been bad, they just sound wimpy and give non of the benefits of a real tube . This is certainly different, based on the Butler Tube Driver it is an awesome overdrive. From subtle creamy to outright offensive, which from the demos I have seen online is exactly what the real version does.