Moritz Klein’s EDU DIY Wavefolder, to add extra harmonics to a simple waveform.
- FOLD knob – intensity of wave-folding effect.
- SIG IN – audio input, ideally a symmetrical triangle or sine waveform signal.
- SIG OUT – audio output, the folded waveform signal.
This is a compact 4HP perfboard module.
Circuit
This is not my work, so I will not reproduce the circuit. Please see Moritz Klein’s WAVEFOLDER MANUAL and this video for a full description.
I omitted the sawtooth-to-triangle convertor, because the ShedSynth VCO module already has a triangle output. But immediately afterwards I built a version of Moritz’s VCO which doesn’t do triangles…
The pairs of PNP/NPN transistors at each stage can be placed on the perfboard almost exactly as they appear in the original schematic.
I replaced two 20K resistors (between the emitters of each BC558 transistor and +12V) with 100K multiturn preset pots, so the output waveform could be calibrated accurately.
Construction
The whole thing is built on a single 7 hole x 42 hole piece cut from a 12cm x 8cm perfboard. All components are wired point-to-point with green 30 AWG kynar wire.
The 10-pin boxed power connector and the low-profile electrolytic capacitors (directly soldered to the pins of the power connector) are fitted across the top of the board to locate the knobs down from the very top of the panel. These should be soldered first for easier access before the other components are added. Here, yellow and blue wire is used for +12V and -12V respectively.
A single Alpha 9mm vertical pot and two PJ398SM mono jack sockets are placed directly on the board, mounting directly to the aluminium front panel. The other circuit components fit easily into the space between these.
The two preset pots are mounted on the reverse side of the board, so they can be adjusted when the panel is assembled.
Ideas & rethinks
First, I’m grateful to Moritz Klein for making his designs available to us all, thank you.
I followed through his careful explanation of its operation on breadboard first, learning all the way, then fiddled with some component values to see what happened, then went back to the original values that worked. Then realised that my transistors had been backwards all along so I started again.
Finally, having rehearsed the circuit connections on breadboard, transferring the layout to perfboard was fairly straighforward.
The easiest way to build this module is to buy the complete DIY kit from Erica Synths or perhaps from Thonk in the UK.
At first it seems strange that there is no separate voltage control input for the intensity. However it quickly becomes clear that the output effect is directly controlled by the input level, so a VCA ahead of this unit is all you need.
One idea I tried on breadboard: I added a vactrol to the input circuit to provide separate voltage control, but that made no improvement so I left it out of the final design.
The wavefolder works surprisingly well as a woodwind voice for the ShedSynth Wind Instrument, using a single triangle waveform through a VCA controlled by breath intensity – the output does not increase in volume over most of the breath range, but becomes psychoacoustically louder as more harmonics are added.
Another surprise: plug a guitar in via an INSTRUMENT INPUT and the wavefolder makes a nice smooth overdrive, distorting gracefully as you play harder without clipping.
ShedSynth 