Update : jul. 10, 2006

Wavefolder
En français
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Description

This circuit is a device which provides wonderful sonic possibilities. This module performs a non-linear transformation of a simple waveshape (triangle or sawtooth) into a complex waveform rich in overtones.
This module is based on Jürgen Haible's wavefolder B  that I have associated to a VCA at the input to dynamically control wavefolding, and with an amplifier to adjust the output level.

Some sound samples :
    example 1 : progressive variations of CV2         
    example 2 : envelope modulation. I say, there is no filter involved !!!!!    
  
Some scope images :

Schematics
sch
This circuit is made of three parts : the first one is based on U2, Q1 and Q3 and is a voltage controlled amplifier (VCA) and accepts an input signal ranging from -10V et +10V with a control voltage (CV1) ranging from 0 to 15V.  The second part made of U1b, U1c and U1d and diodes D1 à D20 is actually Jürgen Haible's walvefolder B . Next, the third part is a level amplifier which gain is set to obtain an ouput signal in the range -10V to 10V.
By the way, if you need to modify the voltage range of the input and output signals, it is just a matter of changing the values of R20 & R21 for the input signal and that of R17 & R18 to adjust the output level.

Printed circuit boards and component layout
PCB design
Component layout



 Download the schematic as a PDF file
Download the PCB as a PDF file

WARNING ! The document is formatted to be printed directly on a mylar for photo-etching or a "press & peel" paper. Make sure that when the printed face of mylar is in contact with the copper side of the PCB, the lettering can be read normally.
Get the silkscreen as a PDF file

Components and building details
reference
 value
 number
U1
 TL074 / LM324
 1
U2
 TL072 / LM358
1
Q1, Q2, Q3
 BC547C or equivalent (Q1 & Q2 must be matched)
 3
D1 to D20
 1N4148 (should be matched by pairs)
 20
R19
 470 ohms
 1
R21
 680/330 ohms to selected depending on the input levels
 1
R3
 2k7
 1
R14,R15
 5k6 2
R17
 6k8 1
R22,R23
 10k 1%
 2
R5,R6,R7,R8,R9,R10,R11,
R12,R26*,R27*,R29
 15k, *1%
 12
R33,R34
 22k
 2
R13
 27k
 1
R4,R28
 33k
 2
R16,R18
 56k
 2
R30
 68k
 1
R1,R2,R20,R24,R25,R31,R32
 100k
 8
A1
 1K 10 turn trimmer
 1
A2
 50K/47K 10 turn trimmer
 1
C2,C3
 100nF ceramic or polyester
 2
C4,C5
 22µF 35V polarised
 2
P2
 47k/50k Lin potentiometer
 1
P1,P3
 100k Lin potentiometer 2
J1,J2,J3
 jack socket
 3
 Note that there is no C1 !...
Wiring


Front panel
Panel design


 Silk-screening
 

Download the silkscreen mask as a PDF file

Download the silkscreen mask as a  JPEG file

Setting and trimming
Trimming is quite easy if you use matched NPNs for Q1 and Q2, and 1% tolerance resistors for R22 to R27. You will need a dual trace scope, a DVM and a sinewave generator. Using 10 turn trimmers is a little bit more expensive than using 1 turn but makes it easier to adjust with high accuracy.
  1. Set A1& A2 to mid-range.
  2. Connect the sinewave generator (freq. 1KHz, 10Vpp) to input 1, P1 turned fully clockwise (maximum signal).
  3. Connect the sinewave generator to the first input of your scope.
  4. Connect CV1 to 0V and turn P3 fully clockwise (maximum gain).
  5. Connect the output to the second input of the scope.
  6. Adjust the trimmer A1 in order to have a perfectly symmetrical sine wave at the output (the best way is to superimpose the trace of the sinewave at input and the one at the output). You may have also to play slightly with A2 as well to reduce gain if you have saturation on both the positive and negative crests of the output sinewave.
  7. Next, turn P3 fully counter-clockwise (no CV). Adjust A2 in order to completly mute the output signal.

References
There are many different variant of wavefolder,  here are some valuable links:
Jurgen Haible's WaveFolder  : http://home.debitel.net/user/jhaible/jh_wavefolder.html
Grant Richter's WaveWarper  : http://www.musicsynthesizer.com/DIY/Grant/CVtwister2.html
Ken Stone's WaveMultiplier  : http://www.cgs.synth.net/modules/cgs29_wave_multiplier.html
Ian Fritz's Wavolver  : http://home.earthlink.net/~ijfritz/sy_cir6.htm

The DIY builders' gallery
Here are the photographs of the yusynth Wavefolder modules built by other synth geeks around the world.
Thank you  guys for sending me these nice photos.
Name : Czaba ZVEKAN
Modular project :
Location : Basel, Switzerland
Website :  		Name : Oliver ABPLANALP
Modular project : Cave studio
Location : Schaffhausen, Switzerland
Website : http://www.cavestudio.ch
Name  : Patrick
Pseudo : Baronrouge
Modular project: JHC live lab
Location Toulon, France
Web site : http://myspace.com/patjhc
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