CatGirl Synth

CatGirl Synth or CGS is the popular name for the synthesizer designs of Ken Stone.

History
The CGS web page chronicled and supplied details of the construction of Ken's own modular synthesizer. The site itself was simply titled "Modular Synth". After other parties started referring to it as the "Catgirl Synth", Ken adopted the letters CGS as identifiers on his PCB designs.

The web page first came online in the late 1990s, and moved several times before settling at www.cgs.synth.net It closed down in September 2018, with Elby Designs taking over the CGS projects and the rest of the site archived at Archive.org

Format
CGS is based around the 4U format, with +/-15 volts supplied via 0.156 4 pin MTA connectors and either banana sockets or 3.5mm jacks.

Building a DIY synthesizer
Building a DIY synthesizer will be more expensive than buying one ready made. Synth DIY is for people who do DIY for the enjoyment and challenges involved in doing so.

Prerequisite skills
If you don't have the skills consider buying a pre-built synthesizer.
 * Must be able to read and understand a circuit diagram.
 * Must be able to readily identify components by looking at them. If you cannot read resistor colour codes, or if you cannot tell one component apart from another without it being in a labelled bag, DIY is NOT for you.
 * Must be able to identify which parts from the supplier's (e.g. Mouser) available selection are suitable.
 * Must be able to fault find and fix circuits.
 * Must be prepared to accept the full responsibility for whatever you do with these designs, or circuit boards based on them.

Support

 * If you have technical questions, please seek help on one of the many synth DIY forums, where there is plenty of assistance available from other builders.
 * If you have technical answers that you think others will find useful, please add them to the wiki.
 * DIY kits are presented as a convenience for those with the required knowledge as a way to save them hours hunting around for parts on their own. You are paying the kit supplier to spend hours of his time gathering those part, so you can devote yourself to the "fun bit". The price does NOT include hours of customer support to fix the mess caused by your own lack of skills. When a module you have constructed does not work because of your inexperience and lack of understanding, it is NOT the fault of kit supplier or designer. It is entirely your own fault, if not for the errors, then at least for buying something that was beyond your capability.

Disclaimer
All electronic projects and designs presented on this web site, or associated web sites should be considered dangerous if not lethal if not used safely. When working on projects based on these designs, use extreme care to ensure that you do not come into contact with mains AC voltages or high voltage DC. If you are not confident about working with mains voltages, or high voltages, or you are not legally allowed to work with mains voltages, or high voltages, you are advised not to attempt work on them. The author, host, and all people associated with these web pages disclaim any liability for damages should anyone be killed or injured while working on these projects, or projects based on these designs, or any other project or design presented on these web pages and any associated web pages. The author, host, and all people associated with these web pages also disclaim any liability for projects, or projects based on these designs, or any other project or design presented on these web pages and any associated web pages when used in such a way as to infringe relevant government regulations and by-laws.

Copyright
Individual construction of modules based on the original designs of Ken Stone is encouraged. Commercial production of these designs is prohibited without written permission from the designer, Ken Stone.

Note that no guarantees are given for any of these designs. Where a design is copyright by a third party, details of that design are not given, rather a way of researching the information or contacting the designer is given instead.

CGS includes adaptations of several classic Serge modules from the People's Synthesizer. These have been done with the permission and collaboration of Serge Tcherepnin himself.

The CGS modules
These designs are for advanced builders and experimenters. They have been built and they have worked satisfactorily. Obviously only very few from the the variety of available component brands have been tried in each design. This is Ken's hobby and he has shared what he has done with other interested parties.

CV processors

 * CGS26 Analog Logic voltage processor
 * This module is the analog implementation of some basic logic elements. Instead of dealing with binary inputs, the "logic" is applied to whatever voltages are present on the inputs. When the and element is fed several voltages, the output will equal the the lowest input voltage. The NAND output will be the inversion around 0 volts of the and output. When the OR element is fed several voltages, the output will equal the the highest input voltage. The NOR output will be the inversion around 0 volts of the OR output. Apparently the AND and OR functions are the same thing as "peak" and "trough" on old Serge synthesizers, though they are implemented somewhat differently.


 * CGS34 Analog Shift Register
 * Is three stages in length, duplicating the functionality of the Serge ASR, but doing it in a very different way. It is great for producing "arabesque-like" sequences, trills etc., when used with VCOs. Of course it's use is not limited to VCOs only.


 * CGS98 Bus Driver
 * The Bus Driver is a buffered bus for distributing CVs, or even audio to several modules, or even to several cabinets. In the basic configuration, it has four buffers, each of which (through the use of a CGS99 bus expansion port) also offers inversions of these voltages. In the advanced configuration, input 1 is added to the signals of inputs 2, 3 and 4. As such, a root note can be fed into input 1, while sequencers are fed into the other inputs. Changing the voltage on input 1 would then change the root of all three of the sequences, allowing them to follow the root pitch. This was developed due to the drastic shortage of CV inputs on many Eurorack VCO modules.


 * CGS43 Cascade Mixer
 * The Cascade Mixer is an experimental mixer that can be built in one of several ways - a unity gain cascaded mixer, a binary weighted (or scaled) mixer, or as a staircase generator when coupled with a binary counter.


 * CGS37 CV Cluster
 * The CV cluster is an unusual kind of mixer. It takes two input voltages - a base control voltage, and a modulating control voltage, and creates the sum and differences of them, as well as a range of voltage in between.


 * CGS23 CV Mega Mixer
 * This module is an enhanced version of the DC mixer designed for both audio and CV mixing. It has both non-inverting (adding) and inverting (subtracting) inputs, as well as a master level control. It also features two inverting outputs, one that is offset by the master level control, and the other which has independent offset and center inputs.


 * CGS04 DC mixer and SMT04 DC Mixer SMT version
 * Mix synthesizer level audio signals or control voltages with this DC coupled mixer.


 * CGS70 Dev-mod Mixer/Inverter block
 * A universal DC mixer and/or analog inverter for use in developing custom modules, or as a stand alone DC mixer.


 * CGS81 Dual Voltage Processor/Mixer
 * This module is a variation on the standard two-inverting-stage op-amp DC Mixer. It has provision for an offset pot, four DC mixer inputs, processor style inputs, with both inverting and non-invering outputs, though the inverting output cannot be used with the processor function.


 * CGS81 Stereo Mixer
 * How the CGS81 PCB can be used as the basis for a basic stereo mixer.


 * CGS04 Joystick Controller
 * This module uses a pair of CGS04 DC mixers with a two-axis joystick to control various synthesizer funtions.


 * CGS33 Matrix Mixer
 * The matrix mixer is a five input, five output bipolar or unipolar DC coupled mixer, for mixing control voltages or audio signals. In cases where you require several different mixes from a common set of signals, this module is ideal.


 * CGS33EUR Matrix Mixer Eurorack
 * The matrix mixer is a four input, multiple output bipolar or unipolar DC coupled mixer, for mixing control voltages or audio signals. In cases where you require several different mixes from a common set of signals, this module is ideal. Eurorack format.


 * UNI33 Matrix Mixer (UNI format)
 * The matrix mixer is a multiple input, four output bipolar or unipolar DC coupled mixer, for mixing control voltages or audio signals. In cases where you require several different mixes from a common set of signals, this module is ideal. This variant of the matrix mixer is designed for use behind Serge 4U panels.


 * CGS40 Modulo Magic
 * A CV and signal processor based on the mathematical modulo principle. Makes a great wave multiplier too!


 * CGS80 Multi-Mixer
 * This module is a multi-purpose mixer that can be used for both synth-level audio and control voltages. There are eight input channels, each which has AC coupled and DC coupled inputs and a level control, as well as AC and DC coupled outputs.


 * CGS82 Negative Slew
 * This is the Serge Negative Slew which was part of the original line of modules. Ultimately this would go on to be replaced by the Dual Universal Slope Generator
 * It can be used as a falling sawtooth LFO, VCO, or as the name suggests, a lag/slew for falling voltages. Rising voltages are passed unhindered.


 * CGS83 Positive Slew
 * This is the Serge Positive Slew which was part of the original line of modules. Ultimately this would go on to be replaced by the Dual Universal Slope Generator
 * It can be used as a rising sawtooth LFO, VCO, a simple envelope generator or as the name suggests, a lag/slew for rising voltages. Falling voltages are passed unhindered.


 * CGS84 Dual Peak and Trough
 * This module is a variation on the 1973 Classic Serge Peak and Trough module. It is much like the Analog Logic voltage processor, though a little less precise. It is presented here for those who want to build themselves a classic Serge.


 * CGS92 Serge Smooth and Stepped Generator and CGSSSG Serge Smooth and Stepped Generator (previous version)
 * The Serge Smooth and Stepped Function Generator (SSG) is s a complex multi-functional module to provide various slew and sample functions


 * CGS88 Serge Triple Bi-Directional Router
 * The Serge Triple Bi-Directional Router is a group of three switches each of which can route one input to either of two outputs, or either of two inputs to one output according to a pulse or control voltage level. It can also be assembled to sequentially route one input to one of four outputs, or one of four inputs to one output.


 * CGS55 Analog Switch Matrix
 * The Analog Switch Matrix is a complex router, allowing one input to be switched between four outputs, or vice versa, or even to route one signal through one of four external effects (e.g. wave multipliers, filters etc.). It can also be used as four independent analog switches.


 * CGS56 Gate Converter
 * The purpose of the Gate Converter is to turn standard positive gate signals into negative to postitive going gate signal. This is particularly handy when interfacing to other manufacturer's modules that require a zero crossing singal to operate. It can also be used to convert assorted LFO or VCO signals to square or rectangular waves, to extract some form of gate signal from an envelope and so on.


 * CGS122 Switched Matrix and CGS123 Switched Matrix Eurorack
 * 8x8 switched mixing matrix. Eurorack format.


 * CGS51 Weighted Random Switch
 * The weighted random switch is another module for introducing unpredictability into synthesizers. The original requirement was for a circuit that would, upon receiving a clock signal, randomly direct a single input to one of four outputs, but with a twist. Four knobs or control voltages could be used to sway the likelihood of one or more outputs being selected over the others.


 * CGS64 VCA
 * Voltage Controlled Amplifier, suitable for both audio and control voltage modulation.


 * CGS65 TubeVCA/ Timbral Gate
 * Tube based Voltage Controlled Amplifier / timbral gate. While this module basically operates as a VCA, it does add a degree of distortion to the signal. How much distortion depends on how hard it is driven. Add feedback and it begins to oscillate, syncing to the incoming signal to some extent. All this while running on a standard synthesizer power supply, with no extra heater supply required.

CV generators/controllers

 * CGS41 Diatonic Converter
 * The Diatonic Converter is an adapter for projects such as the Infinite Melody and Gated Comparator, constricting their outputs to the notes of a major or minor diatonic scale instead of the chromatic scale. A single control line selects between major and minor. It can also be used as a stand-alone module when driven from other systhesizer gate events.


 * CGS42 Gate Sequencer CV Adapter
 * The CV Adapter is an addition to the CGS07 Gate Sequencer (obsolete) converting it to a traditional eight-step control voltage sequencer.


 * CGS32 Infinite Melody
 * The name of this module is a play on its function. Put simply, it generates a series of semi-random or themed stepped control voltages, or if you prefer, white and pink control voltages. The pink function is probably better known as 1/f.


 * CGS10 Pedal Board/Mini Keyboard
 * A simple circuit that can be used to make a small monophonic 1V/octave keyboard, or pedalboard.


 * CGS03 Psycho LFO
 * This is a bizarre little LFO that produces a wide range of pseudo random effects from random timed stepped, to smooth flowing. One of the most popular CGS modules.


 * CGS59 Programmer/Sequencer
 * The Programmer/Sequencer is a Serge inpired multi-stage sequencer. Unlike most sequencers, this one makes no use of binary counters. Rather, it uses a set of individual stages, each one directly accessible.


 * CGS87 Programmer/Sequencer
 * This is a redesigned circuit board for the CGS59 Serge Programmer/Sequencer. Unlike that version, this one has no panel-format specific PCBs. The column boards have been replaced with boards that contain 8 stages. These can be used to drive pots or switches in any panel configuration you wish.


 * CGS82 Negative Slew
 * This is the Serge Negative Slew which was part of the original line of modules. Ultimately this would go on to be replaced by the Dual Universal Slope Generator
 * It can be used as a falling sawtooth LFO, VCO, or as the name suggests, a lag/slew for falling voltages. Rising voltages are passed unhindered.


 * CGS83 Positive Slew
 * This is the Serge Positive Slew which was part of the original line of modules. Ultimately this would go on to be replaced by the Dual Universal Slope Generator
 * It can be used as a rising sawtooth LFO, VCO, a simple envelope generator or as the name suggests, a lag/slew for rising voltages. Falling voltages are passed unhindered.


 * CGS97 Serge Noise
 * The Serge noise module can be built in several ways. In it's simplest form, it contains three basic outputs, white noise, pink noise, and a random voltage suitable for use with sample and hold modules. An optional sample and hold circuit is included on the PCB. Alternatively, the basic version may be coupled with the CGS92 Serge Smooth and Stepped Generator to make the Random Voltage Generator module.


 * CGS92 Serge Smooth and Stepped Generator
 * CGSSSG Serge Smooth and Stepped Generator (previous version)
 * The Serge Smooth and Stepped Function Generator (SSG) is a complex multi-functional module to provide various slew and sample functions.


 * CGS86 Touch Responsive Keyboard
 * This module is a variation of the Serge Touch Responsive Keyboard published in the Synapse magazine January/February 1977.


 * CGS21 Super Psycho Modulation Source
 * This module is a much expanded version of the Psycho LFO, featuring six free-running oscillators, each variable between LFO and audio ranges, two of which can be switched to have triangular wave outputs. Each oscillator can be switched between low and high ranges, as well as off, and also has a rate LED, to allow visual determination of the frequency at which it is running. As per the original, there are also level and glide controls.


 * CGS58 Utility LFO
 * The Utility LFO is a dual manually controlled LFO offering a number of standard and combined outputs for general low frequency work, such as filter and phaser sweeps, clocking sequencers and so on.


 * CGS75 Voltage Controlled Slope and CGS775 Voltage Controlled Slope Eurorack
 * Adapted from the Serge DUSG, this is a general purpose version of the VCS made popular by Bananalogue. Produced under licence from Serge.


 * CGS114 Serge Dual Universal Slope Generator
 * Another adaptation of the original Serge DUSG. Produced under licence from Serge.


 * CGS76 Serge 1973 Envelope Generator
 * This is an adaptation of the original Serge Envelope Generator from the early "R" series PCBs. Produced under licence from Serge. This is NOT an ADSR style generator, and can be used as an LFO.


 * CGS78 Utility Envelope Generator
 * This is a basic envelope generator of the ADSR variety.


 * CGS116 Serge Extended Adsr Envelope Generator
 * This is an adaptation of the original Serge Extended ADSR (voltag controlled). Produced under licence from Serge.

Clock/gate/trigger processors

 * CGS06 Burst Generator
 * A rhythm and timing accessory that generates a burst of gate or trigger pulses at various speeds. Used for washboard, maracas or similar rapid-burst percussive effects when connected to the appropriate sound generating device.


 * CGS13 Gated Comparator
 * This module can be used as a simple gate delay, a semi-random melody generator, a comparator, and a gate/clock controlled comparator. All in all, a very versatile module.


 * CGS96 Serge Triple Comparator
 * The Serge Triple Comparator consists of three independent functions which are useful in the production of square waves and variable pulse waves. The Comparator reference level can be a time-varying control voltage, a complex audio signal, or a fixed preset voltage. Additionally, the comparators are useful for level detection and for logic decisions based on amplitude. The module also contains a single, non-adjustable, Schmitt trigger.


 * CGS89 Gate Sequencer and CGS07 Gate Sequencer (obsolete).
 * A sequencer designed for controlling pulsed or gated events, for rhythm and percussion.


 * CGS24 Gate to Trigger Converter
 * This module contains a pair of two gate to trigger converters, allowing key-down gate signals, or those from gate sequencers etc. to be converted into a much narrower trigger signal as required by some percussive effects. These may come in handy when adapting various drum sound generators to synthesizer use.


 * CGS69 Dev-mod Gate/Trigger block
 * A universal gate and/or trigger processor for use in developing custom modules, or as a stand alone gate to trigger converter.


 * CGS22 Master Divider
 * The purpose of this module is to divide down a system master clock (e.g. a VCLFO) to drive an array of sequencers or other timed events. The different phase outputs are to allow for modules that may trigger from the falling edge of a wave, or to allow for deliberate lagging of an event. It would for example be possible to have two sequencers running from this unit, one at 1/8 of the frequency of the other, their outputs being mixed to give a sequence that changes fundamental pitch each eight notes.


 * CGS36 Pulse Divider and Boolean Logic
 * This module consists of several parts, a pulse divider with integer divisions between 2 and 8, and several logic elements. The divider is used to generate interrelated pulses for use in creating poly-rhythms, and unusual sequences or as a sub-oscillator/sub harmonic generator. As well as the pulse divider, there are also four Boolean logic elements, two inverters an OR gate and an AND gate for the processing of gate and trigger signals.


 * CGS54 XOR/XNOR logic
 * This board is an add-on for the CGS36 Pulse Divider and Boolean Logic module, adding XOR and XNOR funtionality. It can also be used to compare two analog signals, either positive or negative in value.


 * CGS39 Quad Logic Gate
 * The Quad Logic Gate is a very simple module that can be built in one of five flavors : XOR, OR, AND, NOR and NAND. It is a simple way to gain additional control of gate and trigger pulses within a system. It can also be used for some simple signal multiplying. The XOR is well known as a square wave "ring modulator", though interesing effects can also be generated using the other configurations. Each gate has an inbuilt LED to indicate the status of the outputof that gate.


 * CGS62 Slope Detector
 * The slope detector is an event-driven gate/trigger generating device. It monitors a control voltage, and triggers one of three "gate" output dependent on what the control voltage is doing.


 * CGS01 Sub-Oscillator/Harmonic Sequencer and UNI01 Sub-Oscillator/Harmonic Sequencer (UNI format), designed to fit on a 4U Serge style panel.
 * Use this twin sub-oscillator with one or two VCOs for fat sounding lead or harmonies, or with a VCO and an LFO for harmonic sequences, or as a pattern based sequencer.


 * CGS78 Utility Envelope Generator
 * This is a basic envelope generator of the ADSR variety.


 * CGS121 Quad Comparator and Memory Cell
 * This module is the combination of a quad comparator "voting system" and memory cell (flip-flop). It can be built in many ways to suit the builder's needs. For example, if the memory cell functions are not required, they can be omitted. Alternatively, the panel presence of the comparators can be greatly reduced if the memory cell is the primary interest.
 * The comparator "voting" circuits can be used as OR, AND or 2 of 3, 2 of 4, 3 of 4 etc. type gates, depending on construction. Both positive responding and negative responding inputs are available.
 * Master AND and OR outputs monitor the four voting circuits. The four voting circuits are used to drive the flip-flop memory cell, providing SET, RESET, CLOCK and DATA inputs.
 * The purpose of the module is to allow the combination of various gate events and CVs to generate responses, rhythms, etc.

Signal processors

 * CGS67 Active Real Ring Modulator
 * The Real Ring modulator now has buffered inputs and outputs, and a pre-amp stuitable for guitar use.


 * CGS30 Bandpass Filter
 * A utility bandpass filter for creating artifical instrument resonant cavities etc.


 * CGS57 Bi-N-Tic Voltage Controlled Filter/Oscillator
 * This is a strange mixture of a VCO and a switched capacitor filter based on the filter presented by Jan Hall in Electronotes. If you are after something different, this fits the bill. After all, how many filters have a sync input?


 * CGS43 Cascade Mixer
 * The Cascade Mixer is an experimental mixer that can be built in one of several ways - a unity gain cascaded mixer, a binary weighted (or scaled) mixer, or as a staircase generator when coupled with a binary counter.


 * CGS44 Delay Development Board
 * The Delay Development Board has been designed to allow people to experiment with the Princeton Technologies PT2395 Enhanced Digital Echo IC.


 * CGS45 Dome Filter
 * The dome filter is a 90 degree phase difference network, as used in frequency shifters. It is not a project in itself, and will be of no use to most people. Ken Stone designed this board simply because he needed some dome filters for his own experimentation.


 * LPG Low Pass Gate
 * Peter Grenader's Buchla style Low Pass Gate.


 * CGS40 Modulo Magic
 * A CV and signal processor based on the mathematical modulo principle. Makes a great wave multiplier too!


 * CGS90 Serge Phaser and Audio Mixers
 * This module is a variation on the classic Serge Phaser module. On the PCB are also two AC coupled audio mixers.


 * CGSRRM Real Ring Modem
 * Someting to try out with your Real Ring Modulators. Two are required.


 * CGSRR Real Ring Modulator
 * This is a pre-assembled classic diode ring modulator for when a four quadrant multiplier simply won't do.


 * CGS95 Reverb
 * This is a basic reverb module constructed around the Belton BTDR-2H Reverb Module. From a single input, two channels of raw reverb are generated. Mix outputs are also provided, allowing the input/reverb mix to be controlled via a panel pot. An additional feedback function is provided for emphasizing the effect, or even for generating screaming feedback.


 * CGS38 Saw Pitch Shifter/Wave Multiplier
 * The Saw Pitch Shifter is an experimental combination of op-amp summers and comparators with surprising results, ranging from complex wave shaping to pitch shifting of saw tooth waves.


 * CGS77 Serge 1973 Voltage Controlled Filter
 * This is an adaptation of the original Serge VCF from the early "R" series PCBs. Produced under licence from Serge.


 * CGS101 CGS Serge quad VCA
 * This module is a variation on the Serge Quad Voltage Controlled Amplifier (QVCA) module, built using the CGS108 VCA.


 * CGS101 Serge Dual Channel Stereo Mixer (DCSM).
 * This module is a variation of the Serge Dual Channel Stereo Mixer, built using the CGS108 VCA and the CGS102 Equal Power Panner drivers. Produced under licence from Serge.


 * CGS102 Serge Equal Power Panner
 * Serge Equal Power Panner driver. Produced under licence from Serge.


 * CGS108 Serge Voltage Controlled Gain Cell
 * This is an adaptation of the original gain cell used in many of Serge's later designs. Produced under licence from Serge.


 * CGS202 Serge Resonant Equalizer
 * The Serge Resonant Equalizer (EQ) is a unique ten-band filter designed specifically for electronic sound synthesis and processing. Except for the top and bottom frequency bands, all other bands are spaced at an interval of a major seventh. This non-standard spacing avoids the very common effect of an accentuated resonance in one key, as will be the effect from graphic equalizers with octave or third-octave spacing between bands. Spacing by octaves will reinforce a regular overtone structure for one musical key, thereby producing regularly spaced formants accenting a particular tonality. The Resonant Equalizer's band spacing are much more interesting, producing formant peaks and valleys that are similar to those in acoustic instument sounds. Produced under licence from Serge.


 * CGS79 Serge Ring Modulator
 * This module is a variation on the 1973 Classic Serge R6 Ring Modulator.


 * CGS88 Serge Triple Bi-Directional Router
 * The Serge Triple Bi-Directional Router is a group of three switches each of which can route one input to either of two outputs, or either of two inputs to one output according to a pulse or control voltage level. It can also be assembled to sequentially route one input to one of four outputs, or one of four inputs to one output.


 * CGS85 Triple Wave Shaper
 * This module is a variation on the 1973 Classic Serge Triple Wave Shaper. This design started off as a wave shaper for the original Serge VCO, and has persisted as an available module since that time.


 * CGS112 Serge Voltage Controlled Resonance Filter
 * The Serge Variable Q VCF (VCFQ) is an excellent general-purpose VCF offering simultaneous low-pass, high-pass, band-pass and notch (band-reject) outputs. The resonance (Q) of this filter is dynamically variable by manual or voltage control.


 * CGS113 Serge Voltage Controlled Wave Multiplier
 * This is an adaptation of the original Serge VCM containing three distinct sections for the addition of harmonics to a signal. Produced under licence from Serge.


 * CGS52 Simple Wave Folder
 * The Simple Wave Folder is an ideal beginners project for two reasons - it is simple to build, and its effect is powerful - far beyond what could be suspected from such a simple circuit. The effect it produces is not like unlike that of the Serge middle wave multiplier - harmonically rich waveforms that can be swept for filter-like effects.


 * CGS35 Steiner Voltage Controlled HP, LP and BP Filter
 * This module is a "tribute" module, based on the awesome Steiner-Parker Synthacon VCF. Despite not being a big VCF fan this one really appealed to Ken Stone. Its sound is quite unlike the Moog ladder, and has a lot of character.


 * CGS35EURO Steiner Voltage Controlled HP, LP and BP Filter Eurorack
 * Like the above, this module is a "tribute" module, based on the awesome Steiner-Parker Synthacon VCF. Some circuit improvements such as input level controls and expanded response have been made, as well as a new set of PCBs designed for use in Eurorack and Frac rack formats.


 * CGS28 Sequential Switch
 * A basic switching/sequencing module with many uses.


 * CGS49 Twin CMOS Filter
 * A dual version of the popular CMOS based Wasp VCF, featuring adjustable distortion.


 * CGS27 Tube VCA and Wave Folder
 * This circuit board was designed to allow for easier assembly of 7 pin tube based synthesizer circuits. It is a tube module that runs on ±15V, a simple VCA that doubles as a wave folder/distortion unit. There are no dangers in connection this to solid state modules due to the voltages in use, and the fact that this is really a voltage controlled attenuator, and not an amplifier. There is about 50% signal level loss.


 * CGS29 Wave Multiplier
 * The idea for this project came from the fabled middle section of the Serge wave multipliers. It could equally be described as a wave folder or a timbre modulator.


 * CGS64 VCA
 * Voltage Controlled Amplifier, suitable for both audio and control voltage modulation.


 * CGS65 TubeVCA/ Timbral Gate
 * Tube based Voltage Controlled Amplifier / timbral gate. While this module basically operates as a VCA, it does add a degree of distortion to the signal. How much distortion depends on how hard it is driven. Add feedback and it begins to oscillate, syncing to the incoming signal to some extent. All this while running on a standard synthesizer power supply, with no extra heater supply required.


 * CGS09 Voltage Controlled Divider
 * Use this as a timing accessory for sequencers, or with a VCO for frequency trills like those of the old 8-bit computer games. Unilke other voltage controlled dividers, this one preserves the pulse width of the incoming signal.

Signal generators

 * CGS19 Chime Simulator
 * This module contains a pair of two or three tone chimes that are suitable for connection to modular synthesizers. Each chime sound is created by modulating two or three square wave oscillators together, and applying an envelope to the result. Each chime is individually triggered.


 * CGS47 Cynare Drum Simulator
 * The Cynare drum simulator is the third in the series of CGS drum simulators. It generates a single drum sound that can be adjusted to sound like a cymbal, hi-hat, snare drum, electronic drum, or numerous other percussive sounds. It is a complete dedicated synthesizer in its own right, including six oscillators, a noise source, a mixer, an envelope generator, a VCF and a VCA.


 * CGS31 Digital Noise
 * This module is a very standard pseudo-random digital noise source with a few enhancements. Instead of running a fixed high frequency clock, a VCO is used instead, allowing for unusual sweeps, and for reducing the speed right down to a series of random pulses. The internal linear VCO can also be bypassed so an external source such as a 1V/octave VCO or LFO can be substituted. It has pink and white noise outputs, and two separate (unique) digital outputs for use in triggering other circuits.


 * CGS18 Drum Simulator
 * This module is the embodiment of the classic twin-T circuit in a form that is suitable for connection to modular synthesizers. It contains two separate drum sounds, each individually triggered, as well as something unique - adjustable harmonic content.


 * CGS82 Negative Slew
 * This is the Serge Negative Slew which was part of the original line of modules. Ultimately this would go on to be replaced by the Dual Universal Slope Generator
 * It can be used as a falling sawtooth LFO, VCO, or as the name suggests, a lag/slew for falling voltages. Rising voltages are passed unhindered.


 * CGS83 Positive Slew
 * This is the Serge Positive Slew which was part of the original line of modules. Ultimately this would go on to be replaced by the Dual Universal Slope Generator
 * It can be used as a rising sawtooth LFO, VCO, a simple envelope generator or as the name suggests, a lag/slew for rising voltages. Falling voltages are passed unhindered.


 * CGS97 Serge Noise
 * The Serge noise module can be built in several ways. In it's simplest form, it contains three basic outputs, White noise, Pink noise, and a random voltage suitable for use with Sample and Hold modules. An optional Sample and Hold circuit is included on the PCB. Alternatively, the basic version may be coupled with the CGS92 Serge Smooth and Stepped Generator to make the Random Voltage Generator module.


 * CGS08 V8 Engine Simulator
 * A V8 engine sound simulator for revving up your music. A sound-effect module.


 * CGS48 VCO
 * This VCO started out life as a replacement for the original VCOs in Ken Stone's '73 Serge, so it replicates a lot of the functionality of that module. Of course there have been numerous enhancements to the design as well, making it right at home in a 1V/octave synthesizer.


 * CGS02 Wavetable For VCOs
 * Feed this module with a high frequency from a VCO or DCO for a range of selectable waveforms/tones. ROMs are available that contain 4 or 8 banks of eight waveforms per bank.

General and accessories

 * Multiple
 * This is a tiny board allows easy wiring of banana jack multiples.


 * CGS14 ±15V 7x15 Power Supply
 * A simple PSU for use with modules that don't require a more expensive alternative. This is suitable for the gate sequencer, burst generator, V8 simulator and a number of other CGS projects.


 * CGS66 ±15V LM3x7 Power Supply
 * A PSU suitable for use with both digital or analog modules. It can actually be varied to cover a fair range of voltages. It is suitable for use with Eurorack standard modules or Modcan and MOTM standard modules.


 * CGS124 Breadboard
 * This is a 6 inch x 2 inch, double-sided prototyping board designed to be compatible with other CGS format PCBs.


 * PAN000 Generic 4U x 4¼" panel
 * This is a PCB based panel primarily intended for prototyping and testing of new designs, although there is nothing to stop it being used in a permanent set-up. Four of these panels will fit side by side, in a standard rack boat. The 8mm holes are suitable for banana sockets and Cliff-style insulated 3.5mm jacks.


 * CGS98 Bus Driver
 * The Bus Driver is a buffered bus for distributing CVs, or even audio to several modules, or even to several cabinets. In the basic configuration, it has four buffers, each of which (through the use of a CGS99 bus expansion port) also offers inversions of these voltages. in the advanced configuration, input 1 is added to the signals of inputs 2, 3 and 4. as such, a root note can be fed into input 1, while sequencers are fed into the other inputs. changing the voltage on input 1 would then change the root of all three of the sequences, allowing them to follow the root pitch. This was developed due to the drastic shortage of CV inputs on many Eurorack VCO modules.


 * CGS99 Bus Expansion Port
 * The Bus Expansion Port is a simple PCB carrying three 16 pin (2x8) headers, two on one side, and one on the other, it's purpose being to provide connections between the inside and outside of case, for the distribution of Eurorack style power buses, or with CGS93 and CGS98 bus driver as a way to link them between cases.


 * CGS70 Dev-mod Mixer/Inverter block
 * A universal DC mixer and/or analog inverter for use in developing custom modules, or as a stand alone DC mixer.


 * CGS72 Dev-mod PCB joiner
 * Methods, and a small board for joining Dev-mod PCBs together.


 * CGS12 Display Adapter
 * This board was developed to go with the Wavetable project, allowing easy displaying of the bank and wave numbers.


 * CGS73 Eurorack power distribution board
 * Eurorack compatible power distribution bus board.


 * CGS69 Dev-mod Gate/Trigger block
 * A universal gate and/or trigger processor for use in developing custom modules, or as a stand alone gate to trigger converter.


 * CGS71 Dev-mod Generic Prototyping block
 * A small board for building your own designs.


 * CGSLD LED driver
 * This is a tiny ancillary board that contains a single transistorized LED driver for monitoring synthesizer module outputs.


 * CGS74 MOTM distribution board
 * MOTM compatible power distribution bus board.


 * CGS63 Power Supply Delay
 * Does your commercial PSU fail to start propperly? Does one power rail remain off? If so, this module will solve your problems.


 * CGS88 Serge Triple Bi-Directional Router
 * The Serge Triple Bi-Directional Router is a group of three switches each of which can route one input to either of two outputs, or either of two inputs to one output according to a pulse or control voltage level. It can also be assembled to sequentially route one input to one of four outputs, or one of four inputs to one output.


 * CGS60 v2 Stomp Box Adapter
 * This is an external input amplifier with extra provisions so that it can also be used as an effects pedal interface. There are three identical amplifiers on the board.
 * It replaces both the CGS60 v1 and the CGS46 stomp box adapters.


 * CGS60 v1 Stomp Box Adapter
 * It can be used as an external input amplifier, a way to use effects pedals with synthesizer signal levels, or a way to use synthesizer modules with instruments such as electric guitars. This is a smaller version of the CGS stomp box adapter and is basically for use in the reverse situation - namely to allow use of stomp-boxes (effects pedals) as part of a synthesizer setup. while the original will do the job, this one dispenses with the power supply and bypass switching, and handles a single channel.


 * CGS46 Stomp Box Adapter
 * The Stomp Box Adapter has been designed to allow some of the regular CGS modules to be used as guitar effects. It has an integral power supply and provides two channels of amplification to bring guitar signal levels up to those used by synthesizers, and two attenuators to drop them again, post effect. It also provides the essential bypass circuit.


 * CGS91 PCB Mounting Rail
 * These mounting rails are a convenient way of mounting CGS PCBs behind a Serge style panel.


 * CGS93 Trunk Lines/Multiples
 * These boards can be used as cascadable multiples, to create trunk lines between different cabinets, or assuming you have something else that uses the same termination, for expansion/breakout. It uses 16 way ribbon, like used in Eurorack power, every second wire connected to ground to form a shield between the signal wires. You can mount one of these in each cabinet of a large system, and hook them up from behind with the ribbon. If you hook just two in different cabinets together, you have 8 trunk lines between them, reducing the need for long patch cables. If you place one in each of several cabinets, and run a common ribbon between them, then you have an inter-cabinet bus. If you mount them side by side, and use a common ribbon between them, you have a multiple. As a bonus, the board is designed to work with banana jacks as well, so your bus/trunk lines can go between different types of synths (mini jacks and bananas).


 * CGS94 Pot Mounting Rail
 * This PCB is designed to help mounting and wiring pots or LEDs to panels. It uses the 1 inch horizontal spacing standard of Serge panels, and provides mounting for 16 pots or LEDs.


 * CGS120 Utility Mounting Rail
 * This is a 6 inch long universal mounting board. When snapped in two, lengthwise, it can be used to mount smaller PCBs to CGS91 rails on a standard Serge-style panel. It can also be used to mount 6 pots, LEDS, etc. at 1 inch spacing. Small matrix areas allow for "flying" panel components to be given a sturdy mounting place.


 * Adapter Banana to 3.5mm adapter plug
 * Are your Serge and your Eurorack modules not talking? Try this.

Digital synth

 * CGS11 D/A Converter
 * This board was really developed for Ken Stone's own use, to allow his 486 based sequencer to connect to various VCOs etc. It has twelve bit resolution.


 * CGS20 Digitally Controlled Oscillator
 * This board was really developed for Ken Stone's own use, to allow his 486 based sequencer to drive wavetables etc. It has sixteen bit resolution.


 * CGS25 Keyboard Scanner Sub-Module
 * This board was really developed for Ken Stone's own use, to allow his 486 based sequencer to connect to various keyboards.


 * Parallel port adapter for IBM PCs
 * The adapter that Ken Stone used to interface to his DCOs and keyboard.

Other original designs

 * CGS gated comparator
 * CGS gate sequencer
 * CGS organ interface
 * CGS V8 and diesel simulators

Modules from other sources

 * CGS Carlsbro flanger
 * CGS combo ETI 447 audio phaser and shifty phase adaptor
 * CGS dual ASM-1 and Modulus LFOs
 * CGS dual ETI 414 master mixer
 * CGS Metasonix TS-21 Hellfire Modulator
 * Metasonix TS-22 pentode filterbank
 * Metasonix TS-22 pentode filterbank
 * CGS mixer and ETI 4600 VCA
 * CGS MOTM 101 noise, S&H and vibrato
 * CGS Roland VP300 vocal filter
 * CGS Welson Festival 2000 drum simulator
 * CGS208 Serge Wilson analog delay

Tube modules

 * CGS beam modulator
 * CGS vintage sequencer/programmer
 * CGS tube bandpass VCF
 * CGS tube module power supply
 * CGS tube noise source
 * CGS tube VCO
 * René Schmitz VCF

PCBs, kits and ready made CGS modules

 * Elby-designs.com - Kits and PCBS, CGS in Eurorack format.
 * Metalbox.com - Frac rack format.
 * Modular Addict - Kits and PCBS, CGS in Eurorack format.
 * Synthcube.com - Stocks some CGS PCBS and kits, (has taken over Bridechamber).
 * Thonk.co.uk - Stocks some CGS PCBS and kits.