Liquid filter Overview Ripples delivers a classic, big-sounding analog four-pole filter in a small 8-HP package, continuing Mutable Instruments’ lineage of warm and tasty filters started by the Shruthi SMR4 mkII and 4-Pole Mission. 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. Specifications Inputs • 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. Controls • Cutoff frequency, 18Hz to 18kHz • Resonance (self oscillation at 80%) • Attenuverter on Frequency CV Outputs • 2-pole BP • 2-pole LP • 4-pole LP • 4-pole LP 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. • 8-HP. • Current consumption: +12V: 35mA ; -12V: 35mA.
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