Analog Liquid Filter

Ripples is a classic, big-sounding analog four-pole filter in a small 8-HP package. Over the years it has earned its reputation as a no-fuss, elegant choice. Ripples has two input paths: one with a drive control, allowing the signal to be distorted (or providing enough gain for the processing of line-level signals), and the other totally transparent, preserving the clean-sounding character of the original version of the module. Three filter modes are available: high-pass, band-pass, and low-pass. The slope (2 or 4 poles) of the band-pass and low-pass outputs is switchable.

Self-oscillation is available for all modes and produces a clean sine-wave on the low-pass 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 Japanese classics from the 80s, with a very round and liquid resonance. The low-pass output goes through an internal VCA. This makes Ripples a good final stage module for an inexpensive, or space-constrained, subtractive synthesis synth voice.

A MultiMode Filter
• High-pass, band-pass, and low-pass outputs.
• Switchable slope control for the band-pass and low-pass outputs. The slope of the high-pass output varies with resonance.
• The low-pass output goes through an internal VCA - the perfect “end of subtractive chain” output!

All the CV inputs you need
• Un-attenuated frequency CV, calibrated for 1V/Oct tracking of the self-oscillation tone over 4 octaves.
• Frequency CV with attenuverter.
• Resonance CV. Self oscillation starts at 4V. Control voltages above 5V are non-linearly compressed, for fine control of resonance overdrive.
• VCA level for the low-pass output.

Specifications
• Cutoff knob range: 20Hz to 20kHz.
• Fully analog, based on the V2164 low noise/distortion quad VCA chip, and LM13700 OTA for that extra bit of non-linearity.
• Frequency CV inputs impedance: 100k, Audio input impedance: 100k.
• Resonance input impedance: 22k.
• VCA level input impedance: 39k.
• All CV inputs handle audio-rate modulations.

In the Box
• The module itself
• Eurorack Power Cable