Doepfer A-136 Distortion/Waveshaper Tutorial Videos by Raul Pena

Raul Pena published new videos demonstrating the A-136 Distortion/Waveshaper Module

Module A-136 is a distortion and waveshaping module with extensive control possibilities. The incoming audio or cv signal is internally divided into 3 sections:
- positive component of the signal with adjustable clipping level (even externally via jack socket) and positive or negative amplification (+/-) of this component
- negative component of the signal with adjustable clipping level (even externally via jack socket) and positive or negative amplification (+/-) of this component
- original signal with positive or negative amplification (+/-)

Different settings of 5 distortion/waveshaping parameters enable a lot of very complex and extreme waveform modifications. The range of modifications reaches from simple soft or hard clipping to completely altered waveforms where the original signal is no longer recognizable.
The sketch below shows only a few examples when using a triangle as input signal.

Applications: audio distortion (especially in combination with filters very interesting), waveform modification for audio signals as well as for control voltages (LFO, ADSR, random etc.).

Video: Doepfer A136 Distortion/Waveshaper Basics and Demos (Full Playlist)

A-136 Pre-amp Modification

I discovered another nice light-weight DIY-project on the Doepfer DIY-page.

Locating the R2 resistor

It seems that the A-136 Distortion/Waveshaper module contains an internal pre-amplifier that is used to amplify the input signal by about 3.5 before it is processed by the A-136.
Especially for low level audio signals (e.g. output from a VCF) this is useful.

But for all signals with a level beyond ~ 7V this causes clipping before the internal processing takes place. 

Especially for the processing of LFOs or unfiltered VCOs this may cause a problem.

The wiring, additional pictures
on the PatchPierre Facebook page

To totally bypass the internal pre-amplifier, resistor R2 can be removed (e.g. by pinching off).

R2 is the resistor in the upper third of the pcb which is very close to the rear edge.
When R2 is removed the amplification of the internal pre-amplifier becomes "1" (which means that it does no longer amplify).

Finished modified A-136 

Because i love to keep myself busy (I'm slightly ADD-ish), i decided to add a switch to the module, so i can switch between pre-amplifier on and off modes.
It looked like an easy project, so... what could go wrong? ;-)

Besides the front-panel it was a pretty easy job;
I desoldered one side of the R2 resistor, bent it over towards the switch, and wired it with black wire.
After that i soldered another wire (red) from the switch to the hole where R2 used to be. Easy as that.

Now i can manually switch the internal amplifier on and off when required.
The clipping did annoy me at times and now i prevent that and try the un-amplified signal with alternate settings*.
it's not a groundbreaking project, but a nice extra.

* In addition one has to pay attention that the knob positions may vary a bit from the front panel printing because of mechanical tolerances of the potentiometers and knobs (i.e. "0" is not always exactly the neutral position for "A", "+A" or "-A")

The modifications described on this site will most likely void any warranty and, if not done carefully, can damage the circuit board, IC chips, and faceplates.
PatchPierre can not be held responsible for any damage.

A-137 Wave Multiplier

I might have underrated the A-137-1 Voltage Controlled Wave Multiplier a bit. Until lately...

The basic idea of a wave multiplier is to multiply the waveform of an incoming signal and add harmonics to a signal that contains none or only a few harmonics (e.g. sine or triangle waveform)
The A-137 can be used with signals rich in harmonics too (e.g. saw) but the effect is not as remarkable as for triangle or sine waves.
For rectangle signals none or only little effects are obtained.

The A-137 is a very interesting module, in a way it is quite similar to the A-136 Distortion/Waveshaper
You can compare it with four simple A136 modules in series. (The A136 is basically like a guitar distortion stompbox with different distortion levels for the positive and the negative parts of the signal.)
Only in this module you do not have separate access to the two half waves and to the parameters of the individual stages.

The parameters of the A-137 are:
- Multiples: defines the number of basic wave multiplications within one period.
- Folding Level and Symmetry: the upper and lower clipping levels of the wave folder units are controlled.
- Harmonics: adds some harmonic content by sharpening the waveform edges and adding overshoot peaks. It works a little bit like the resonance control of a VCF.

All 4 parameters can be manually adjusted and controlled by external voltages.

It is a lot of fun to experiment with this module, with all different parameters controlled by different CV sources like LFO, ADSR's, Ribbon Control pressure and sequenced triggers for example.

The only thing i dislike about this module is the unpredictability factor.
You should be carefull for a 'damping' effect that can occur when different parameters interact with eachother.
But on the other hand; the module is fully DC coupled, so even CV signals can be messed up with this module.

Check out the audio examples on the Doepfer site that explain the function of the module and its parameters.

Video Synthesis - A-136 Solarization Tests

Besides for audio, some Doepfer (and other (analog modular) synthesizer modules can be used for other purposes too.
For example this A-136 Distortion/Waveshaper in combination with an LZX analogue modular video synthesizer.

LZX Visionary (by LZX Industies) is a line of EuroRack format synthesizer modules designed for creating and manipulating video and images.
Their range consists of 9 different modules so far: a Color Video Encoder, Video Sync Generator, Video Waveform Generator, Triple Video Fader & Key Generator, Video Blending Matrix, Voltage Interface I, Video Ramps, Triple Video Processor and a Voltage Bridge.

It looks like a very versatile range of products that will probably make a lot of video-editors happy.
For modular synth-geeks the layout, functions etc. looks quite familiar with what we do, and i like the idea of video-mixing, LFO-controlled color-swapping, and adding other effects to video with Eurorack modules.
The possibility of adding synthesizer modules that were intended for audio to this system is IMO just brilliant, i can imagine what different LFO's, noise generators and other modulators/waveshapers or perhaps a video sampler will do with video.
The LZX webpage is full with interesting info, basic patch-examples, video's and links to other resources.

I couldn't find a lot of info on the video below, but it is quite new and i found it interesting enough to post it here on my blog.

Video: A-136 Solarization Tests*
http://vimeo.com/35069251

" Sean Hannan processes video through the Doepfer A-136 Audio/CV shaping module."
*video has no audio

For more info on video-synthesis check out

- Video Synthesis subforum on Muffwiggler
- EuroRack Modular Synth Planner

A-136 Distortion / Waveshaper

The A-136 Distortion/Waveshaper module is a nice distortion/wave-shaping module with external CV control possibilities. It can be used for audio-distortion, but also to modify control voltages ( create new control waveforms made from LFO, ADSR, or Random voltages ) with it.

The module divides the incoming signal into 3 different components; the positive, the negative and the original signal. The 5 knobs and the 2 CV inputs let you adjust the positive and negative amplification and the clipping levels.

With all the different different settings you can create complex wave-shapes and impressive sounds, but to be fair, i have heard better (extended?) distortions. This might perhaps be the reason why Doepfer advices you to use it in combination with filters... not sure though...

For mild and subtle distortions this module sounds alright, but the wilder, clipping distortions are a bit too extreme for me.
Personally i prefer the A-137 Wave Multiplier or the A-116 WP Waveform Processor controlled by random voltages, for the more interesting ( subtle and extremer ) wave-shaping.