status Draft
drc ok
erc ok
unconnected ok
github

welle

Wavefolder for siusoidal and triangle waves

Danger

This is a preview of the elektrophon website, the content may not be accurate and is subject to change without any notice.
Folding waves is another way to add timbre to the sound. This is a very interesting way and creates richer results than a filter.

Danger

This is a work in progress module and might not work as expected. Feel free to file a bug report on the github page.

construction

There are various wavefolder circuits out there. the most famous is the serge wave multiplier middle section. Welle is implemented using the basic idea from Jürgen Haible [1] and the modifications from Yves Usson [2].

Figure 1: Block Diagram

There are three sections in this circuit. First, there is a simple discrete VCA with a long-tailed pair. This circuit was analysed in the ringmod article. The second part is the wavefolder and the third is mixing the signals together.

The folding itself is done with a diode ladder, where the diodes select different voltages. I think Jürgen has the best explanation of that concept [1].

5


1V: 450 (1), 1300 (3), 2200 (5), 3100 (7), 3950 (9), 4850 (11), 5700 (13), 6600 (15), 7500 (17), 8350 (19), 10999 (25), 
2V: 450 (1), 1300 (3), 1750 (4), 2200 (5), 3100 (7), 3950 (9), 4850 (11), 5700 (13), 6600 (15), 7500 (17), 8350 (19), 9250 (21), 10099 (23), 10999 (25), 11899 (27), 
3V: 450 (1), 950 (2), 1300 (3), 1750 (4), 2200 (5), 3950 (9), 4850 (11), 5700 (13), 6600 (15), 7500 (17), 8350 (19), 9250 (21), 10099 (23), 10999 (25), 11899 (27), 12749 (29), 13649 (31), 14499 (33), 15399 (35), 
4V: 450 (1), 950 (2), 1300 (3), 1750 (4), 2200 (5), 3100 (7), 4850 (11), 5700 (13), 6600 (15), 7500 (17), 8350 (19), 9250 (21), 10099 (23), 10999 (25), 11899 (27), 12749 (29), 13649 (31), 14499 (33), 15399 (35), 16299 (37), 17149 (39), 18049 (41), 
5V: 450 (1), 1300 (3), 1750 (4), 2200 (5), 3100 (7), 3950 (9), 5700 (13), 6600 (15), 7500 (17), 8350 (19), 9250 (21), 10099 (23), 10999 (25), 11899 (27), 12749 (29), 13649 (31), 14499 (33), 15399 (35), 16299 (37), 17149 (39), 18049 (41), 18899 (43), 19799 (45), 20699 (47), 21549 (49), 22449 (51),

BOM

main

#referencevaluedescription
2C1 C222uAluminium Electrolytic Capacitors (50V, D=6.3 mm, LS=2.5 mm)
4C3 C4 C5 C60.1uMultilayer Ceramic Capacitors MLCC (50V, L=4 mm, W=2.5 mm, LS=2.5 mm)
2C7 C810p*Multilayer Ceramic Capacitors MLCC (50V, L=4 mm, W=2.5 mm, LS=2.5 mm)
18D1 D2 D3 D4 D5 D6 D7 D8 D9 D10 D11 D12 D13 D14 D15 D16 D17 D18DSmall Signal Diode (DO-35)
2D19 D20DSmall Signal Diode (DO-35)
1J101x06 FemaleBoard to Board Connectors (2.54 mm)
1J201x03 FemaleBoard to Board Connectors (2.54 mm)
1J410 PosPin Header IDC (2.54mm)
3Q1 Q2 Q3BC547Package_TO_SOT_THT:TO-92_Inline_Wide
7R1 R3 R8 R17 R18 R23 R24100kMetal Film Resistors - Through Hole (L=3.6 mm, D=1.6 mm, 1%)
1R268kMetal Film Resistors - Through Hole (L=3.6 mm, D=1.6 mm, 1%)
1R5680Metal Film Resistors - Through Hole (L=3.6 mm, D=1.6 mm, 1%)
2R6 R710Metal Film Resistors - Through Hole (L=3.6 mm, D=1.6 mm, 1%)
2R9 R1022kMetal Film Resistors - Through Hole (L=3.6 mm, D=1.6 mm, 1%)
11R11 R13 R14 R19 R20 R21 R22 R25 R26 R27 R2815kMetal Film Resistors - Through Hole (L=3.6 mm, D=1.6 mm, 1%)
2R12 R3033kMetal Film Resistors - Through Hole (L=3.6 mm, D=1.6 mm, 1%)
2R15 R1610kMetal Film Resistors - Through Hole (L=3.6 mm, D=1.6 mm, 1%)
1R2927kMetal Film Resistors - Through Hole (L=3.6 mm, D=1.6 mm, 1%)
1R312k7Metal Film Resistors - Through Hole (L=3.6 mm, D=1.6 mm, 1%)
2R32 R335k6Metal Film Resistors - Through Hole (L=3.6 mm, D=1.6 mm, 1%)
2R34 R3656kMetal Film Resistors - Through Hole (L=3.6 mm, D=1.6 mm, 1%)
1R356k8Metal Film Resistors - Through Hole (L=3.6 mm, D=1.6 mm, 1%)
1R37470Metal Film Resistors - Through Hole (L=3.6 mm, D=1.6 mm, 1%)
1RV450kTrimmer Resistor, Bourns 3296Z
1RV51kTrimmer Resistor, Bourns 3296Z
1U1TL072Package_DIP:DIP-8_W7.62mm_Socket
1U2TL074Package_DIP:DIP-14_W7.62mm_Socket

For mounting the LED's the long lead has to go to the round pad.

The diodes should be matched in pairs, otherwise, it could be that the folding is not symmetrical (TBH I have not matched them).

schema

main

PCB

main panel

gerber

main panel

calibration

The discrete VCA in this circuit needs to be calibrated. This is done in two steps. first set the gain of the differential pair and then the control current in the tail.

  1. set the two trimpots to some middle position
  2. close the control pot (CCW) and fully open the range pot (CW)
  3. connect a sine wave to the input jack
  4. connect the scope first channel to your sine wave and the second to the output of the VCA. This is pin1 from U1 or the Resistor R23.
  5. adjust RV5 until both sine waves are the same, maybe also RV4 has to be changed to get a match
  6. turn the range pot to silent (CCW) and adjust RV4 until the output is silent too

Now connect your scope to the output. when the wave passes 0V there will be folding. when these foldings look like filled areas there is self-oscillation in the circuit. This can be removed by adding capacitors to the opamps feedback loop. Try using 22-47pF ceramic capacitors for C7 and/or C8.

usage

A sine or triangle wave can be connected to the module, other waveforms will not work or give strange results. The range controls the amount of folding, this can also be controlled with a CV. For example from an LFO or ADSR. There is a nice effect if the output is connected to a LPG, this results in nice percussive bass sounds.

References

  • Jürgen Haible Wavefolder A+B. The missing images were just still images, there are versions on archive.org with the images. Look for the PDF's on the page.
  • Yusynth The wavefolder from Yves Usson.