Hello and thank you for using the Rottnest Voltage-Controlled Oscillator for 4U modular. We hope you will
find its tones most pleasing!
Technical Specifications (4U, Loudest Warning standard)
Width: 2”
Depth: 25mm
Current Draw: 40mA @ +12V, 33mA @ -12V
Saw/Ramp, Pulse, Triangle output voltage range: +/-2.5V (5Vpp)
Complex output voltage range: +/-4.2V (8.4Vpp)
1. Connecting your Rottnest
Connect a power cable to the MTA-156 header at the top of the Rottnest pcb. The +12V side of the
connector must be aligned with the silkscreen indicator that says “+12V” for proper use. This module is
reverse diode protected, but it is still not recommended that you plug it in backwards to see what
happens.
2. Theory of Operation
The Rottnest is, at its core, a simple oscillator designed around the FatKeys SSI2131 VCO-on-a-chip and
made possible by the incredible
provided by Sound Semiconductor. This chip performs
outstandingly well both in terms of technical performance and sound, which makes it easy to design a
great oscillator.
With this in mind, we set out to create an oscillator in 4U which can complement the many great designs
by Serge, CGS and others in this format, while taking advantage of the superlative tracking and waveform
features of the SSI2131 to avoid some of the known issues and quirks in some of those older designs.
The feature-set is designed to slot right into existing 4U setups and uses the same voltage ranges as
typical Serge designs, but offers something new in terms of range and performance.
3. Summary of Functions
Coarse Tune:
Sets the starting frequency of the oscillator over a 10-octave range.
Fine Tune:
Adjusts the starting frequency of the oscillator over approximately 1.5 semitones.
Lin FM Amt
: Amount of Linear Frequency Modulation. Full CCW = 0 modulation.
Lin FM:
Control Voltage input which changes the oscillator’s frequency linearly.
Expo FM Amt:
Amount of Exponential Frequency Modulation. Full CCW = 0 modulation.
Expo FM:
Control Voltage input which changes the oscillator’s frequency exponentially.
Lo/Hi/Super Lo Switch:
Sets the frequency range of the oscillator. (Lo = .02 Hz-30Hz; Hi = 10 Hz-20kHz;
Super Lo = 0.0015 Hz-2Hz approx)
S-Sync Amt
: Sets the amount of control input from the “S-Sync” jack.
1V/Oct:
Control Voltage input offering equal-temperament tracking with 1V/Oct scale.
S-Sync:
Input for Soft Sync pulses, which will reset the Rottnest’s waveform if it is close to the end of its
own cycle.
Pulse Width:
Adjusts Pulse Width present at “Pulse” output jack and acts as an offset for the “PWM CV”
input. With no CV input, full CCW = 0% Duty Cycle and full CW = 100% Duty Cycle.
H-Sync:
Pulse input which will reset the Rottnest’s waveform. Note that the waveform will only partially
reset at lower frequency settings.
