Based on the Mutable Instruments Ripples.

The DIY Ripples kit includes the Eurorack panel, a limited edition PCB (blue w/gold immersion finish), Rogan knobs, Alps potentiometers, all necessary components, mounting hardware and power cable. 
Don't worry if you drop an SMT part-- for 0603, 0805 and 1206 packages, we include an extra !! If you don't lose SMT parts, keep the spares to build up your shop inventory

3 filter modes are available: 2-pole band-pass, 2-pole low-pass, and 4-pole low-pass.
Self-oscillation is available for all modes and produces a clean sine-wave on the LP4 output. Unlike many classic 4-pole designs, this filter does not suffer from “loudness drop” when resonance is increased. The resonance loudness compensation circuit brings a slight tone coloration reminiscent of the Roland SH/Jupiter filters, with a very round and “liquid” resonance.
The 4-pole low-pass output is additionally sent to a VCA. This makes Ripples a good “final stage” module for an inexpensive/space-constrained subtractive synthesis synth voice.

Controls

• Cutoff frequency, 18Hz to 18kHz
• Resonance (self oscillation at 80%)
• Attenuverter on Frequency CV
   

Inputs and outputs

• Signal in
• Frequency CV 1 (1V/Oct)
• Resonance CV. Self oscillation starts at 4V. Control voltages above 5V are non-linearly compressed, for fine control of resonance overdrive
• Frequency CV 2 (with bipolar attenuator, from -1V/Oct to 1V/Oct)
• VCA level. Control voltages above 5V are non-linearly compressed.
• 2-pole BP output
• 2-pole LP output
• 4-pole LP output
• 4-pole LP output attenuated by VCA
   

Technical characteristics

• Fully analog, based on SSM2164 low noise/distortion quad VCA chip, and LM13700 OTA for that extra bit of non-linearity.
• Frequency CV inputs impedance: 100k.
• Audio input impedance: 75k.
• Resonance and VCA CV input impedance: 30k.
• Open-source hardware.

PCBs produced by synthCube.
We are delighted to be able to offer these for the diy community.
Courtesy of the circuit designer, certain synth module designs are now available via creative commons licensing.