Dual SSI2130 analog triangle VCO

Fully analog dual analog triangle core voltage controlled oscillator (VCO) 16HP Eurorack module with through zero FM modulation based on SSI2130 ICs. Module features precision analog exponential converters, triangle oscillator cores, waveshapers as well as high quality voltage controlled amplifiers for wave mixing.

Multiple wave outputs and control knobs

Each VCO in the module outputs sine, triangle, saw and square/pulse waves, also voltage controlled mix of them plus a sub oscillator an octave below controlled with integrated crossfader mixer.

There are also knobs for shape, pulse width, pitch and fine tuning.

When paired with analog filter harsh pulse, saw and sub oscillator wave forms sound excellent in subtractive synthesis. Find out how to patch and control it:

Subtractive synthesis

Integrated crossfaders

Module features 3 integrated crossfaders, two for mixing variable wave outputs with sub oscillator and a master crossfader.

Master crossfader allows mixing final outputs of the two oscillators.

Frequency modulation (FM) options

Both oscillators can be modulated with exponential and linear FM, as well as through zero FM/PM, wave shape and pulse width CV.

To ease modulation for each oscillator we have added separate sine outputs with variable gain controlled with modulation knob.

FM audio synthesis

Through zero FM

Through zero FM is a n advanced linear frequency modulation available only to triangle core oscillators.

When modulation index is increased to swing below zero hertz it sends the wave backwards maintaining pitch with back and forward toggling wave form.

Each modulation CV has its dedicated input, being analog design shape and all FM modulations can be performed simultaneously. They all accept both audio and CV signals with endless sonic possibilities to explore.

Complex analog voice

Tuning and octave switch

Each oscillator is equipped with high precision 8 position octave selector switch configured for a  wide range from -3 to +4 octaves.

Pitch is controlled with Tune and Fine knobs for precise pitch adjustment and detuning when needed.

Precision and temperature stability

Precision 1 volt per octave pitch tracking

Module is designed using precision voltage reference and other high quality components to achieve +/-1ct (+/-0.01 semitone) tuning across 10 octaves- well below human ear pitch sensitivity which is around 3-5ct.

Temperature stability

VCO module offers excellent temperature stability, each VCO IC has integrated temperature compensated exponential converter, all external resistors and voltage reference are rated at 0.1% and 25ppm/c.

Module versions and improvements

2023 version 2.1

High end audio grade precision Burr-Brown CMOS OpAmps on all outputs, board connectors with gold plated contacts, improved reference voltage and sine offset, removed octave switch trimmers for easier tuning – instead used precision parts for fixed octave switching accurate within 1ct.

2024 version 2.2

Octave switch changed from 6 to 8 positions for more modulation options, added startup circuit to prevent VCO lockup on start for those with asymmetric power supplies, modern JFET/CMOS OpAmps – slightly improved accuracy and reduced power consumption, extra components for accurate sine outputs with virtually no offset, high end trimmers for even more accurate pitch tracking.

2025 version 2.3

Removed external +5V rail, now module is powered from +/-12V rails. +5V is generated using internal voltage regulator, this improves stability and sub oscillator noise. Module is now also easier to install as +5V power supply is not needed.

Sine wave offset trimmers were added as well to finetune sine wave outputs for perfect TZFM.

Plan your Eurorack synthesizer on ModularGrid

Our dual VCO is available on ModularGrid where  you can visually build your own Euroack synthesizer rack, also view synthesizers that other artists have built using this module.

Our dual VCO on ModularGrid

VCO module video demo