Epoch Modular Benjolin User manual

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.

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