Epoch Modular Benjolin User Manual (English)

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INTRODUCTION:

The benjolin is a multifunction

synthesizer designed by Rob Hordijk.

The module consists of four separate

function blocks: two VCOs, a state

variable filter and an additional circuit,

invented by Hordijk himself, called a

rungler. This particular arrangement

emerged from Hordijk’s efforts to design

a synthesizer that was, as he puts it,

"bent by design". As such, the module

functions according to principles of chaos

theory, where short to long sputtering

patterns spontaneously transform

themselves, at times, gradually, at

others, quite suddenly, morphing into

new pattern doublings and bifurcations.

The chaotic character of the benjolin is

anchored in Hordijk’s rungler circuit. In

essence, the rungler is an 8-step shift

oscillator (OSC A) and its clock input

from the other (OSC B). The output of

the shift register is then fed into a

primitive, digital-to-analogue converter,

creating a stepped voltage pattern of

variable length and depth, what Hordijk

terms a “stepped havoc wave”. This

rungler wave is then wired back into the

oscillators, via the attenuator knobs (Run

A and Run B), creating the complex

interference system that lends the

benjolin its unique, aleatoric character.

The inclusion of a voltage-controlled filter

expands these possibilities further into

the audio realm. Its design includes

Hordijk’s signature, Z-plane modulation

circuitry, which produces an all-harmonic

distortion, lending the filter a kind of

warm, organic character—reminiscent of

that classic tube amp sound. This

distortion is most palpable when the

resonance of the filter is turned to the

maximum, with both oscillators running in

the audio range.

The filter’s input is a mix of a PWM wave

(derived from the triangle waves of each

oscillator) and the rungler signal itself.

And as with each of the oscillators, a

rungler attenuator (RUN F) allows

modulation of the filter as well.

To round things out, CV inputs for both

the oscillators and filter are normalized,

each via their respective attenuators.

This allows for cross modulation between

the oscillators and a “sweeping” effect for

the filter, hitched to Triangle B.

Module Width: 18hp!

Module Depth: 22mm

Current draw: ~45 mA@+12V

~45 mA@-12V !

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Epoch Modular Benjolin Specifications

General

Brand	Epoch Modular
Model	Benjolin
Category	Synthesizer
Language	English

Summary

Introduction to Benjolin

Benjolin Design Principles

Describes the benjolin as a chaos theory-based synthesizer with VCOs, VCF, and the unique 'rungler' circuit.

The Rungler Circuit Explained

Explains the rungler's 8-step shift register, its input/output, and how it creates a 'stepped havoc wave' for feedback.

Voltage-Controlled Filter (VCF)

Details the VCF's Z-plane modulation, harmonic distortion, and its audio input mix.

Modulation and CV Inputs

Covers normalized CV inputs for oscillators/filter, enabling cross-modulation and sweeping effects.

Manual Controls

Oscillator Manual Controls

Manual controls for OSC A and OSC B determine their central rate/frequency/pitch over 18 octaves.

Filter Cutoff Control

Manual control for the filter's central cutoff frequency, with 12dB/6dB curves.

Filter Resonance Control

Controls filter resonance/damping with a slight anti-log curve, affecting loudness at max.

External Modulation Controls

Attenuators for CV inputs (MOD A, B, F), controlling internal modulation via normalized inputs.

Rungler Modulation Controls

Attenuators (RUN A, B, F) interfacing the rungler with other circuit blocks.

Rungler Loop Controls

Controls for the rungler's loop function, using an offset knob and toggle switch.

CV Inputs

Modulation CV Inputs

Details the three main CV inputs (MOD A, B, F) and their 1V/O approximation.

Rungler Loop CV Input

Input for externally triggering rungler loop mode via CV, with a nominal +.7V threshold.

Epoch Modular Benjolin User Manual