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 8step shift register that takes its data input from one
oscillator (OSC A) and its clock input from the other (OSC B). The output of the
shift register is then fed into a primitive, digitaltoanalogue 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 voltagecontrolled filter expands these possibilities further into
the audio realm. Its design includes Hordijk’s signature, Zplane modulation
circuitry, which produces an allharmonic distortion. This gives the filter the kind
of warm, organic character, reminiscent of classic tube amplifiers. This 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.
Oscillator Manual Controls: Two knobs at the top center of the panel (OSC A
and OSC B) are the manual controls for each oscillator. They determine the
central rate/frequency/pitch of each respectively. Both oscillators cover around
18 octaves, spanning From LFO into VCO range.
Filter Cutoff Manual Control: Third knob down at center (FREQ), dictates
central cutoff frequency of filter. As is the case with SVFs in general, maximum
cutoff for High Pass and Low Pass are located at either end of the knob’s
rotation. Both have 12db curves, while the band pass is 6db. Like the
oscillators, the cutoff frequency range is around 18 octaves.
Filter Resonance Control: Fourth knob down, to the right (RES). This knob
controls the amount of resonance or damping of the filter. It is designed to have
a slight antilogarithmic curve. In addition, you will notice a significant increase
in the loudness when resonance approaches the max setting. This is due to the
interplay between the filters resonance and allharmonic distortion.
External Modulation Controls: Three knobs to the left of the panel (MOD A,
MOD B and MOD F) are basic attenuators for their corresponding CV input.
Without CV inputs, they control the level of internal modulation via their
normalized inputs. Again these are: Triangle A to MOD B, Triangle B to MOD A
and Triangle B to MOD F.
Rungler Modulation Controls: Three knobs to the right of the panel (RUN A,
RUN B and RUN F) are standard attenuators that interface the Rungler with the
three other function blocs in the circuit.
Rungler Loop Controls: Both the offset knob (LOOP) and the toggle Switch, to
its right, serve to augment the looping function of the rungler. When the rungler
enters loop mode, the data contents of the shift register are recirculated, thus it
no longer accepts new data from Oscillator A. This effectively, removes the
benjolin from the chaotic domain, cutting pieces out of the rungler pattern, and
using them to feed repetitive drones, beatlike patterns and so on.