Description

The GS1-F low pass/high pass filter module is based on Roland’s 4-pole filter design using the classic BA662 circuit. Modelled after the Roland System 100M VCF, this module gets that lovely buttery 1970’s Roland VCF into your Eurorack system.

The GS1-F acts as a three input mixer with gain control on each input, so you can layer your patch with up to three gain-controlled audio sources for a nice thick sound. 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.

At full resonance with no audio input, the filter will self-resonate, and it can be calibrated via the frequency and width controls so that the filter plays in tune with your V/Oct input supplied in the first CV modulation input marked “key”.

The cutoff and resonance pots provide the usual controls over the filter manually, and of course an LFO or other CV modulating the filter will automate this based on the starting position of the pots.

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). All partial kits include a bonus passive multiple panel/pcb set.

GS1-F Features: 

• Audio Inputs: 3x each with gain pot
• CV Inputs: 3x each with attenuation pot
• Audio Outputs: 1x filter out
• Pot controls for Frequency and Resonance
• LPF on/off toggle switch (fixed)
• Bonus passive multiple panel/pcb set included
• Width 8HP

This Panel & PCB set includes the following rare parts (Green in BOM):

• 4 x 2SK30A-GR
• 3 x 2SA1015-GR
• 6 x 2SC1815-GR
• 4 x BA6110
• 1 x RC4558
• 4 x 470pF Polystyrene capacitors
• 1 x 10K NTC
• 2 x 10uF Bipolar electrolytic capacitors

GS1-F – BOM & Build Guide