Zlob Modular - VC F3DB

VC F3DB stands for Voltage Controlled Fixed Filter Feedback Distortion Bank — a long but very accurate name. Its analogue filter bank divides the spectrum into six fixed frequency bands from 88 Hz to 7 kHz, all clearly labelled on the panel. Drawn from the Moog 914 filter bank, these frequencies were selected for their ambiguous, dissonant relationships rather than a neatly musical spread. The circuit is not a direct clone, however: the F3DB replaces the original’s passive inductor-based cells with active op-amp filters inspired by YU Synth.

Each band has an illuminated level slider, CV control, mute and clipping switches, plus its own audio output and envelope follower. It can shape a sound like a graphic equalizer, animate individual parts of its spectrum or split it into six related audio and control signals.

Its gain and feedback stages take the F3DB well beyond conventional filter-bank duties. The input section provides plenty of gain, hard or soft clipping and a local gain-feedback circuit, while a second voltage-controlled feedback path sends the combined filter output back around to the beginning. At restrained settings this adds emphasis and resonant movement. Push it further and the circuit begins to fold in on itself, with the signal becoming increasingly fractured and unpredictable. It can even run without an input as a wonderfully unstable, pseudo-chaotic feedback oscillator.

The VC F3DB can be a spectral processor, multiband distortion, envelope-follower bank, crude vocoder or an instrument in its own right. It begins with the familiar idea of a fixed filter bank, then gives you enough gain, CV and feedback to make it behave like something entirely different.

Features:

• Analogue six-band voltage-controlled fixed filter bank
• Frequency selection derived from the Moog 914 filter bank
• Fixed bands at 88 Hz, 250 Hz, 750 Hz, 1 kHz, 2.8 kHz and 7 kHz
• 24 dB/oct low- and high-pass outer bands
• Four 12 dB/oct band-pass filters with a Q of approximately 4
• Illuminated level slider and CV input for each band
• Individual mute and VCA clipping switches
• Separate audio and envelope-follower outputs per band
• Sum, Odd and Even audio outputs
• Two audio inputs
• High-gain input stage with hard and soft clipping
• Gain-feedback circuit for additional fuzz and instability
• Voltage-controlled global feedback with external feedback input
• Capable of self-oscillation without an input signal