EM-402 | III / VI Pole Cascade Filter

SUNLESS CITY is a fully discrete transistor cascade filter combining selectable III/VI pole architectures, voltage-controlled resonance, and variable input drive. Its architecture provides smooth resonant transitions, substantial low-frequency presence, and a distinctive saturation character.

Two selectable slopes provide markedly different responses. The 18 dB/octave (III pole) configuration maintains an open, harmonically rich character, preserving body and definition across resonant sweeps. Switching to 36 dB/octave (VI pole) produces a steeper, denser response with increased spectral separation and pronounced low-frequency weight.

Cutoff extends from 10 Hz to 35 kHz, with two independent exponential frequency modulation inputs. FM I incorporates calibrated V/oct attenuation for pitch-oriented control, while FM II provides bipolar modulation depth. A dedicated Q CV input enables external control of resonance, and Drive Level adjusts the signal entering the filter core, ranging from restrained harmonic coloration to dense, musical saturation.

At elevated regeneration levels, the filter enters self-oscillation, producing a low-distortion sine wave capable of melodic tracking through its exponential FM inputs. The combination of selectable pole configurations, voltage-controlled resonance, and variable drive allows SUNLESS CITY to operate as both a precision spectral processor and an independent tonal source.

01 / FILTER ARCHITECTURE

Discrete transistor cascade filter architecture
Selectable III/VI pole operation (18 / 36 dB per octave)
Cutoff frequency range — 10 Hz–35 kHz

02 / VOLTAGE CONTROL

Dual exponential FM inputs with calibrated V/oct and bipolar attenuation
Voltage-controlled resonance via dedicated Q input
Pitch tracking through exponential frequency modulation

03 / DRIVE & RESONANCE

Variable Drive Level with progressive analog saturation
Resonant self-oscillation with low-distortion sine-wave output

POWER & CONNECTIVITY

±12 V. 10-Pin IDC / Keyed Headers. Red Stripe: −12 V.

LA CIRCUITS, INC.

Official Website — https://circuits.audio
Instagram — https://instagram.com/lacircuits
Email — contact@circuits.audio

https://circuits.audio/