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Overview
Type Burst Generator
Size 10HP Eurorack
Depth .8 Inches
Power 2x5 Eurorack
+12 mA 50
-12 mA 5
Variatic Erumption is a dual-burst generator. When triggered, it produces a
controllable sequence of gates synchronized to a LFO. A 1v/8va LFO is
included. Any external LFO/clock may optionally be used. Bursts can be
terminated early with the choke. Burst length can be controlled as well as the
pattern used for the burst.
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Noise Engineering
Variatic Erumption
Dual-Burst Generator with built-in LFO
Page 2
Patch Tutorial
Put INT/EXT switch into the INT position. Put FST/SLW switch into the SLW
position.
Set PAT knob fully CCW. Set le CNT fully CW.
Connect the le OUT and END to two gateble modules such as an envelope or
Basimilus Iteritas.
Hit the le HIT switch. A long burst will be generated which will blink the orange
LED and trigger the attached device. At the end of the burst the red LED will blink
and any device attached to the end out will trigger.
Adjusting the TMP knob while hitting HIT will change the burst speed. e tempo
can be controlled by CV (CLK IN). Send an envelope or LFO to modulate the
burst rate. e tempo range can be changed with the FST/SLW switch. It has three
positions each is half tempo of the position above. e CNT knob/jack controls
the number of gates in the burst. e PAT knob/jack controls the pattern of the
burst.
Connect an external trigger source to the HIT jack to trigger the burst externally.
Hitting the CHK switch or sending a trigger to the CHK jack will terminate the
burst.
To use an external clock ip the clock switch to EXT and send a clock into the INLFO. Everything will work the same except it will use the external clock for output
timing. In this mode the DIV knob acts as an adjustable divider to the clock input.
To match the external clock without division put DIV in the fully CCW position.
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Noise Engineering
Variatic Erumption
Dual-Burst Generator with built-in LFO
Page 3
Interface - LFO
Int/Ext
is switch selects the burst clock source between the internal LFO or an external
clock.
In - Jack 0-8v
In internal LFO mode this jack is a 1v/8va CV for the internal LFO and has 8
octaves of range. In external mode, it is a clock input. Burst gate length follows
both rising and falling edges so clock duty cycle is maintained between LFO, Out
and End.
Tmp/Div - Knob
In internal LFO mode, this knob controls the LFO tempo. It allows 4 octaves of
control. In external mode, it is a controllable clock divider with 1-32 divisions.
Fst/Slw - Toggle
is switch controls the base tempo of the internal LFO. It is a three-position
switch. Each position is half tempo of the position above. e lowest tempos in
each range are: 1/2Hz (30 BPM), 2Hz (120 BPM) and 8Hz (480 BPM).
Out - Jack
is jack outputs the LFO used for burst generation.
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Noise Engineering
Variatic Erumption
Dual-Burst Generator with built-in LFO
Page 4
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Hit - Jack
is gate input will start the burst on a rising edge. If using internal clock mode, it
will also reset the phase of the internal LFO to match the HIT phase.
Hit - Tactile
is tactile switch will start the burst when depressed. If using internal clock mode
it will also reset the phase of the internal LFO to match the HIT phase.
Chk - Jack
is gate input will terminate the current burst on a rising edge.
Chk - Tactile
is tactile switch will terminate the current burst when depressed.
Cnt - Jack 0-8v
is jack allows to control the burst count with a control voltage.
Cnt - Knob
is knob allows the control of the burst count. It acts as a scalar when using an
external CV.
Out - Jack
is gate output sends a burst based on the clock when triggered with a Hit. ere
is an orange LED to indicate the current output state.
End - Jack
is gate output sends a pulse based on the clock at the next clock following the
end of a burst.
Pat - Jack 0-8v
is jack allows CV control over the pattern.
Pat - Knob
is knob controls the current pattern used for the burst. Built-in patterns are
documented in detail on the following page. When rotated fully CW this knob will
double the maximal length of the pattern to 64 gates. When in double length mode
the bust pattern is the same as when fully CCW (every clock outputs a gate).
Interface - Burst
Noise Engineering
Variatic Erumption
Dual-Burst Generator with built-in LFO
Page 5
Patterns
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Variatic Erumption’s patterns are based off of the bit-reversed concatenation of
two 16-bit prime numbers. Prime numbers are always odd so in binary the lowest
bit is always set. Reversing these will always generate a pattern who’s rst beat is
set. Note the rst two patterns are not prime as they are all bits set since this is the
most simple burst pattern.
Noise Engineering
Variatic Erumption
Dual-Burst Generator with built-in LFO
Page 6
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Special Thanks
Kris Kaiser
Aaron Funk
Cyrus Makarechian
Richard Devine
Rodent516
Baseck
Shawn Jimmerson
William Mathewson
Mickey Bakas
Tyler Thompson
Alex Anderson
Design Notes
Variatic Erumption started in Cyrus Makarechian’s lo when Aaron Funk asked
me why there was no burst generator in Eurorack. I responded: “What is a burst
generator?”. Cyrus sent me some links to existing products and a few days later I
had a rudimentary prototype designed and ordered. Many features were suggested
by the testers of that rst prototype which led to the second prototype. e second
prototype is nearly identical to the nal module you hold in your hand.
I had very little to do with the overall formulation of the module. It was very much
a community product based on the ideas and feedback of friends.
First
Prototype
Noise Engineering
Variatic Erumption
Dual-Burst Generator with built-in LFO
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