Tuesday 21 April 2020

Synthesizer Build part-28: WAVEFOLDER (Yusynth design).

Here's an alternative way to create awesome synthesizer sounds! It's a pretty easy project to build too.

After first experimenting with a wavefolder design I found on YouTube I decided to build the Yusynth version because I wanted this option in my synth. This circuit produces some awesome and very divers sounds and waveforms.
This is a really good sounding wavefolder with a VCA on the input so there will be no changes in audio level when you turn the 'Shape' knob. It has a different approach to wavefolding than the Triple Wavefolder and the Metalizer circuits which you can also find on this website. The addition of the diode ladder and the clamping diodes on the output opamp give this wavefolder a very distinctive sound which I personally really love. See the demo video further down the article.
The build was pretty straight-forward and it doesn't need to take up much room in your modular set-up either. This is a beginner to medium difficulty project but you do need to have a scope available to calibrate the circuit. A 20 dollar cheap one will do nicely. Make sure you use multi-turn trimmer potmeters for this. That will make it easier to calibrate later on. You can use normal trimmer pots if you have no multi-turn ones but it won't be as accurate. The schematic says to used matched pairs of diodes in the diode ladder but when I measured them they were almost all the same voltage drop. So as long as they come from the same batch I think you needn't bother with matching. The two transistors Q1 and Q2 need to be matched also but you can use the transistor tester in your multimeter. I recently built an adapter to change the pinout of my power supply bus system so I can test modules on dual 12 Volt and I'm happy to report the wavefolder works just as well on 12V as it does on 15V without any changes.

Here's the schematic I used from the Yusynth website:

Here's the (verified) layout I made for it and which I used for this project. These layouts have been updated on June 12th 2023. I made some cosmetic changes to them and colour-coded the wirebridges and removed the coloured bands from the resistors so the values are easier to read.
Wiring diagram:

Stripboard only. Beware that some stripboards are sold with 56 instead of 55 holes horizontally. The layout is 55 holes wide:

Cuts and Wirebridges seen from the COMPONENT SIDE! As always, mark the cuts on the component side with a waterproof Sharpie and then stick a pin through the marked holes and mark them again on the copper side where the pin sticks through. Then cut the marked holes with a sharp 6 or 7mm handheld drill bit.

Bill of Materials:

This wavefolder works best if you feed it a triangle- or sine-wave from an analog VCO or waves from a Wavetable Oscillator. This is convenient because an analog filter works best with square-waves and ramp- or sawtooth-waves, they have the most harmonic content and triangle- or sine-waves don't work that well in a filter. So with the wavefolder we have a use for those triangle and sinewaves. Ramp- or sawtooth-waves will sound good too through the wavefolder but square-waves pass through the wavefolder unchanged.
Here's a video demonstration of the type of sounds I'm getting from this module using a triangle-wave only. There's also a very low frequency LFO ramp signal going into the CV input.:

To calibrate this Wavefolder you will first need to set the two trimmers in their middle position. Turn the Shape potmeter all the way counter clockwise and Range all the way open (fully clockwise). Connect a sinewave from your VCO to the input and a scope to the output and turn the 1K trimmer (above the two transistors) to get the best looking sinewave possible.  It will probably not be a perfect sinewave but try to get the top and bottom part to look the same. Once you set this, turn the Range potmeter all the way counter clockwise and turn the 50K trimmer so as to just mute the signal, so the level is 0 when the Range potmeter is turned all the way left (counter-clockwise).
That's the calibration done.

Here are some pictures of the finished product:

This is what your soldering should look like:

Finally, here's a video I found on YouTube demonstrating the Wavefolder:

Okay, that's an other one done. A very worth while addition to the synthesizer. I can really recommend it and all you need to build it are some very common parts.
As always, please put any questions or remarks in the comments below.
Thanks for checking it out. See you on the next one!

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