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 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.

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

 

MANUAL CONTROLS: Oscillator Manual Controls: These 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: These 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: These 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.

This is how the Loop function works. Both the offset knob (-5V/+5V) and the CV input meet at a critical node in the rungler circuit. Once the sum voltage at this node reaches +.7 volts, the rungler locks into the looping pattern described above. Conversely, when the voltage drops below this threshold, the pattern breaks.

The benefit of having an offset knob is not only that it provides a means of triggering loop mode manually, but also, since the offset and the Loop CV are summed at same node, they can be used in concert to change when or where the rungler will enter into loop mode, independent of the nominal .7V threshold.

Lastly, the addition of the toggle switch allows one to add (or subtract) the offset control from this equation, e.g., if one were inclined to use the nominal CV .7V threshold. But it can also be used in tandem with the offset knob, to push the rungler in or out of loop mode with a flick.

CV INPUTS: 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 for more details) Note: regarding the range of the CV inputs, all are positive voltage rectified, so you need not worry about damaging the module with errant, negative voltages. This being stated, I would not recommend regularly exceeding anything beyond -/+ 9V or 18V P/P. OUTPUTS: Pulse A and B: Average -/+ 8V or 16V P/P. Triangle A and B: Average -/+ 4.5V or 9V P/P. XOR: Logic output from rungler. Averages -/+ 5.5V or 11V P/P. Rungler: Averages -/+ 5.5V or 11V P/P. PWM: Averages -/+ 8V or 16V P/P. Filter Outs: Filter outputs are around line level (approx. -/+ 1.5V or 3V P/P)

WARRANTY:

Modules come with a one-year warranty for parts and repair (proof of purchase/invoice required), providing there are no obvious signs of abuse that would indicate malfunction is due to "external trauma" or that the user accidentally reversed the polarity of the power supply. Visit www.epochmodular.net for more details.