EM-402 | III/VI Pole Cascade Filter

Sunless City is a discrete transistor cascade filter combining selectable III/VI pole architectures, voltage-controlled resonance, and variable input drive. Designed for exceptional tonal depth and harmonic integrity, its architecture delivers fluid spectral movement, 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 through 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 resonance, 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.

SPECIFICATIONS

• Discrete transistor cascade filter architecture
• Selectable III/VI pole operation (18 / 36 dB per octave)
• Cutoff frequency range: 10 Hz–35 kHz
• Dual exponential FM inputs with calibrated V/oct and bipolar attenuation
• Voltage-controlled resonance via dedicated Q input
• Variable Drive Level with progressive analog saturation
• Resonant self-oscillation with low-distortion sine-wave output
• Pitch tracking through exponential frequency modulation
• 12 HP anodized aluminum front panel

LA CIRCUITS, INC.

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

https://circuits.audio/

• 75 mA +12V
• 75 mA -12V
• ? mA 5V
• 40 mm Depth

This Module is currently available.