In the grand tradition of waste not, want not, Chainsaw is a precision VCO designed around the idea that all those unused Schmitt-Trigger inputs in a normal CD40106-based VCO can be put to use building a weirder VCO.
A typical design for a CD40106-based VCO only uses one of the six Schmitt-Trigger inverters, leaving the other five lonely and bored. We’ve decided to press them into service as variable-rate oscillators that can be used to modulate the primary oscillator.
Independent rate and mix control over each modulation oscillator allows you to dial in highly complex waveforms and evolving animations. Basic CV control over two of the modulation oscillators adds the flexibility to use outside voltage sources–such as sequencers, LFOs or audio-rate oscillators–to control the pitch of the modulation.
Notes: The schematic shows only one of the five possible modulation oscillators. This section can be duplicated up to five times to maximize usage of the CD40106. A different capacitor value should be used for C3 in each iteration, creating different pitch ranges. Some recommended values are provided.
In the BOM, any part marked with an asterisk (*) is part of the modulation oscillator and will need to be multiplied by the number of oscillators you intend to build.
Schematic
As with any schematic found on the internet, exercise caution when building. Test the build before plugging it into your case. If you find mistakes in the schematic, or you have recommendations for improving the design, feel free to contact us and let us know.
BOM
BOM lists part count as reflected in the schematic above. Parts marked with an asterisk will need to be multiplied by the number of modulation oscillators built.
- Capacitors
- 4.7pf (2) C6, C7
- 2.2nf (1) C1
- 1uf (3) C2, C4, C5*
- Choose your own adventure! (1) C3* – see notes above
- Resistors
- 22R (1) R26*
- 1k (1) R27
- 1.5k (1) R8
- 6.8k (1) R29
- 10k (7) R7, R9, R17, R19, R22, R25, R28
- 12k (1) R23*
- 33k (1) R2
- 47k (3) R12, R13*, R18*
- 100k (9) R1, R3, R4, R6, R11, R14, R16*, R20*, R21
- 150k (1) R24
- 1M (3) R5, R10, R15
- Transistors
- BC548 (1) Q2
- BC558 (1) Q1
- Potentiometers
- 1k (1) RV5*
- 1k trimmer (1) RV3
- 100k (2) RV1, RV2
- 500k (1) RV4*
- ICs
- TL074 (3) U1, U3, U4
- CD40106 (1) U2
- 10k Thermistor (3) TH1, TH2, TH3
- 1N4148 diodes (2) D1, D2*
- Audio jack (2) J1, J3
- Switched audio jack (1) J2