Module Width: 18hp
Module Depth: 22mm, Skiff friendly
Current draw: ~45 mA@+12V
Price: 400 USD
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 his 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.
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 anti-logarithmic 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 all-harmonic 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, beat-like patterns and so on.
Modulation CVs: The three top most CV inputs, corresponding to MOD A, MOD B and MOD F. Each of these approximates a 1V/O curve, however the range for accurate tracking limited to around two octaves. Fine for a sequencer, or simple quantizer, but not ideal for tracking a keyboard.
Rungler Loop CV: Input allows for triggering rungler loop mode externally via CV. Nominal threshold, at +.7V (See Rungler Loop Controls above)
Pulsed Outputs for Oscillators A and B.
Triangle Outputs for Oscillators A and B.
XOR Output: Logic output from rungler.
Rungler Output: Chaotic Navel
PWM Output: Pulsed wave produced by comparing Triangle Waves A and B.
Filter Outputs: Lowpass, Highpass & Bandpass
The chaotic character of the benjolin is anchored in Hordijk’s rungler circuit. In essence, the rungler is an 8-step 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, 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.
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 imparts a type of all-harmonic distortion to the filter outputs. This distortion has a warm, organic feel—reminiscent of that classic tube, “break up” sound. Its effect is most palpable when the filter’s resonance is turned to its maximum setting and with both of the oscillators running in the audio range.
The 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.
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