Tuesday, 23 June 2020

Synthesizer Build part-34: TRIPLE WAVEFOLDER.

A wavefolder with three folding stages which produces amazing sounds and it's very easy to build too!

I came across this project on YouTube when I watched a video by YouTuber Adamski A. called "DIY analog synth project part 18 - The Wavefolder".

So I set about building it and it came out very well so I asked Adam for permission to write an article for my website, based on his project, to which he very enthusiastically replied in the affirmative so here it is; The Triple Wavefolder.
Like I said, it's a very simple design and in my experience those work the best. This wavefolder produces sounds that I would describe as sharp or hard and accurate. In some settings it almost resembles a Harpsichord or an electric piano. They can be real speaker rippers too. If you watch the video by Adamski A. (see link above) you can listen to the wavefolder in action. The latter part of the video is full of sound samples in different settings. I also made a little demo video myself which is at the bottom of this article. The sound is very different from that of the filters we've become so used to, with their resonance and cut-off frequency. It sometimes almost sounds like an FM synthesizer. That's why this is a very useful addition to any modular set-up because diversity in sound is what we all want don't we?
Now, I built the Yusynth Wavefolder after first building this because I thought that this triple wavefolder was more of an experimental thing and the Yusynth one would be the official implementation to go into my synthesizer. But the Yusynth one only has a single folding stage and eventhough that sounds amazing too, I found that this one actually sounded even better. So I made a panel for it and mounted it in my synthesizer. Btw, you can add as many wavefolding stages as you wish to this circuit. You can easily build this on a breadboard and experiment with the number of stages. The voltage it runs on also influences the number of folds you can get so changing the value of the 22K resistors going to the emitters of the transistors also influences the behaviour of this circuit.

This wavefolder works best with Triangle or Sawtooth waves or even Sinewaves but Squarewave pass through almost unchanged. That's convenient because squarewaves are best used for conventional filters.
This wavefolder has in it's original form only three controls; the input level or 'Amount', the Dry/Wet control and a Saturation control. I added voltage control to two of those, the Amount and Saturation by means of two self-made Vactrols connected between pins 2 and 3 of the respective potmeters.
These vactrols are made up of a bright white LED and a Light Dependent Resistor (LDR) connected together with some heat-shrink tubing that seals it off from any light from the outside.
These Vactrols both have their own level potmeter too so you can dial in the effect it has very accurately. You can also use a VCA before the Wavefolder, That way you can control the level and thus the Amount by means of the VCA. That's what Adam also demonstrates in his video.
The other thing I addressed was the fact that the Amount control is also the Level or Volume control so turning it up increases the volume and turning it down decreases it. For that reason I added a Gain potmeter to the output opamp which increases the volume by a factor of 2 to 5 times. It's not a perfect solution but it works and helps to keep the volume the same through-out even-though you have to do it by hand. But you need to keep in mind the simplicity of the design and that it is therefor not perfect but it sounds so good that I had to include it in my synthesizer set-up.
The Dry/Wet control is a bit temperamental in that it only works well if the other controls are at a certain setting. It's not a big deal and you'll find it out when you test it but I just thought I'd mention it.

Here's the schematic drawing of the Triple Wavefolder by Adamski A. I have re-drawn it and added the Vactrols to it. I mention on the schematic that you can also use BC transistors instead of the 2N trannies I used but that will influence the sound or the number of folds you get because BC transistors have a greater multiplication factor. You can of course experiment with that by setting up the circuit on a breadboard first.

Here's the stripboard layout. It's verified because I used this for my own build:
(Wiring diagram)

Print only:

Bill of Materials:

15V vs 12V and de-coupling:
As you can see a very simple and easy to build project and it sounds amazing so I can really recommend trying this one out. The circuit is meant to work on a dual 15V powersupply but I tested it on 12V and it works just fine but changing the voltage does influence the number of folds you get so it sounds a bit different but it still works fine, trust me =)
I did not include any de-coupling capacitors in the schematic because I didn't use any but if you need to have those included just put a 100nF from plus to ground and a 100nF from ground to minus and place them as near to the TL chip as possible. Should you have problems with hum, you can also add a few electrolithic caps (22µF or 33µF) on the plus and minus rails like the other caps and you can also try putting Ferrite Beads in series with the plus and minus power supply input, or if you don't have them, a few 10 Ohm resistors. There's plenty of room on the stripboard for that.

Here's a picture of the finished panel:

Here's a look at the stripboard: I see from these pictures I added an extra opamp to the output but because I actually built this module a while ago I can't remember why I did that. Probably to have more room to experiment with the output and add the Gain potmeter. Anyway, it works the same so you don't have to include that.

And, to close off this article, I made a video demonstrating the different settings and the sounds they produce:

Okay that's an other project done. I hope you enjoyed it. Check out Adamski A. 's youtube channel. It is full of awesome synthesizer projects and electronics tutorials. It's an enormous source of inspiration for anyone interested in building synthesizers.
As always, any questions or remarks, please put them in the comments below or contact me on Facebook. 
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  1. hello eddy,
    what photo resistance do I need, there are different resistances here, or it doesn't matter!

    1. Hi Maik. I'm not exactly sure. I took mine from some bicycle LEDs that turn on when it's dark so I don't know what types they are. The dark resistance should be above 1 Mega Ohm if possible and when fully exposed to light as low resistance as possible. I don't know what else to tell you. Most LDR's will work fine I think.

  2. Replies
    1. LOL, well I'm sorry I couldn't be more precise but you'll get it to work, no problem ^___^

  3. Hello Eddy,
    I have a somewhat unusual question for you and I found this page on the Internet:

    I was looking for the VCF74 filter, here on this Dutch website the module is offered at an exceptionally low price, normally the module costs € 240, what do you think?


    1. That site looks a bit sketchy. Really low prices and loads of template text in some pages.

      Let me know if they delivered to you. I am a bit fearful of ordering with them.

  4. Replies
    1. Yes it looks like a bargain to me, High and Lowpass in one for 88 euros. I haven't heard of the VCF74 before but I don't think you can go wrong with that.

  5. Hi Eddy,

    Thanks for sharing the schematic and stripboard layout. Loving Adam’s channel, so nice to see some of his work being shared here as well.



    1. Yes he does excellent work. I love his videos. He was really enthusiastic about me using his design too. Maybe, in the future, I'll write about some more of his projects.

    2. What doe you recon I need to modify if I turn this into an eurorack compatible module?

    3. You don't need to modify much I think. Only the 22K resistors. I'd replace those with 18K resistors to counteract the drop in voltage from 15V to 12V. But that's all. It will work on 12V as it is now too btw.