GS-Euro Series 1

Ge0sync Series One (GS1)

Inspired by the BA662 IC used in classic Roland analog synths, the Ge0sync (GS) series 1 is a DIY option to get small hp equivalents to some of the Roland System 100M into your Eurorack. Making use of the BA662 clone available from Open Music Labs (OML) or in some cases the almost equivalent BA6110 IC which is not yet un-obtainium. The GS series 1 provides everything you need to build a classic analogue synth voice including utility and modulation modules including VCO, VCF, VCA, ENV and LFO. The VCO make use of the CEM3340 VCO IC as many of the original parts used in the 100M VCO are long since discontinued. The series also adds a simple mixer than can average or sum the inputs (so works for both CV and audio). DIY kits and pre-built modules come with a bonus passive multiple.


The GS1-A provides a selectable linear or exponential VCA using the differential BA662 op-amp.

The PCB actually has a dual footprint for using either the BA662 clone or an original BA6110 IC if you can find one – these are not yet completely un-obtainium and are reasonably priced. The DIY partial kit option includes a BA6110.

The module acts as a three input mixer with gain control on each input. In addition up to three modulation sources can be used to shape the amplifier via CV.

Modeled after the Roland System 100M VCF circuit, this module gets that lovely buttery 1970’s Roland VCF into your Eurorack system.

The module acts as a three input mixer with gain control on each input. In addition up to three modulation sources can be used to shape the filter via CV.

The module includes a simple high pass filter that can be enabled by means of the toggle switch.

The GS1-E provides a small 4hp single fast triggering envelope modeled after the envelopes in the dual envelope module available for the Roland System 100M.

The envelope has pot controls for the usual ADSR portions and a manual gate trigger momentary push button.

A CV gate can be used to trigger the envelope as expected and the module provides 2 copies of the same envelope and one inverted copy of the envelope.

The GS1-L provides a single selectable LFO with ranges from 0-10v and -5v to +5v depending on the waveform. Based off the LFO included in the Roland System 100M dual envelope module.

The LFO can output a Sine and Triangle wave that oscillate from -5v to +5v. In addition a square, ramp and sawtooth wave can be selected which all output between 0 and 10v.

By using the toggle switch the LFO can be switched between L, M and H frequency ranges. The LFO does not go into audio range, but can go as low as approx 2s.

NEW! The GS1-NR provides an X-Y input for ring modulation between the two input signals. Based off the Ring Modulator in the Roland System 100M utility module.

The module also provides two noise sources, white and pink making use of the 2SC828 ‘legendary’ noisy transistor. However in reality any NPN like a 945 can work just as good!

The GS1-A2 is a smaller 6hp version of the GS1-A.

This module provides all the same circuitry as the larger GS1-A but reduces the inputs and modulation sources to two of each.

GS1-U Utility

COMING SOON! The GS1-U builds on the GS1-NR module and adds a gate delay function.

The delay allows for the delay time and threshold to be tweaked as well as the gate time itself.

In addition to the gate delay function the module contains the same white and pink noise generators as the GS1-NR and the same Ring-modulation capabilities.

COMING SOON! The GS1-O completes the GS Series 1 module family with the classic CEM3340 integrated VCO chip at its heart.

The CEM3340 is a well known classic IC from Curtis Electronics and has recently been re-issued (RevG) as well as the Alfar AS3340 clone. Either of these can be used in the module which provides 5 octave ranges for ‘feet’ with fine tune capability.

The CEM3340 includes hard and soft sync capabilities and the module provides both sync in and out jacks as well as attenuatable FM and PW controls.

Four outputs provide triangle, sawtooth, ramp and pulse waveforms.

GS1-M Audio/CV Mixer

COMING SOON! The GS1-M adds a mixer to the GS1 series. A simple module with 4 CV or Audio inputs, each with individual gain control.

The overall output signal has gain control.

The mixer can be run in two modes, either “averaging” or “summing”. Typically audio would be averaged, and CV would be summed.

GS Series 1