A beginner's guide to the components of a modular synthesizer


1 - THE VCO (immediately below this Table of Contents)

2 - THE VCF (Voltage Control Filter)

3 - THE VCA (Voltage Control Amplifier)


5 - VCLFO (Voltage Control Low Frequency Oscillator)






Others modules :

1 - THE VCO (Voltage Control Oscillator) :

The oscillator is the main element of the modular synthesizer.

It is it what produces the sound (a continuous tone). Often different wave shapes (waveforms) are available as outputs. The most important waveforms are sine, triangle, saw, and square. While the frequency of a tone determines its pitch, the waveform determines its timbre or character.

The VCO has a potentiometer (a knob) to adjust the frequency or pitch of the note. This knob is often labelled Frequency or also Tune.

Also one or more CV (control voltage) inputs (1V / octave or not) can adjust the pitch and other parameters with an electrical signal sent by another module, like an LFO (low frequency oscillator) to give a tremolo or vibrato effect.

Another use of the CV input is having a signal sent by a sequencer, allowing it to play a different note on each step of the sequencer.

Sync (synchronisation) allows two VCOs to be linked together (one master and the other slave).

FM (frequency modulation) a little another kind of CV IN to also modulate the frequency.

PW (pulse width) works only with the square wave and acts on the width of the wave.

like this :
pulse width

PWM (pulse width modulation) pot is an attenuator for the PWM input.
Send a voltage with another module into the Input jack PWM to control the PW pot without touching it with your hands (for exemple with a very slow LFO )


2- THE FILTER (VCF / Voltage Control Filter) :

As the name suggests, this module allows you to filter the sound by removing certain frequencies from the incoming sound.

FREQUENCY CUT OFF pot : cut some frequency of the incoming sound

RESONANCE pot : add some harmonics and a little saturation to your signal.

HP / LP (Hight Pass / Low Pass) : a switch to slect what sort of frequencies that you can cut.

INPUT : enter for the signal you want to filter (3 input on this one), a VCO for exemple.

LEVEL INPUT : potentiometer to adjust the input signal (Attenuator)

CV IN : (control voltage) you can control the CUT OFF pot without touch it with your hand with an electrical signal sent by another module, like an LFO (low frequency oscillator), an Envelope (AD/AR or ADSR)

CV ATTENUATOR : adjusts the incoming CV signal

OUT : the out of the module

Exemple of a simple Patch with this 2 modules (VCO + VCF) :

OUT of the VCO (triangle wave for exemple) into the INPUT of the VCF and the OUT of the VCF to your system.


3 - THE VCA (Voltage Control Amplifier) :

A module that allows you to let the incoming signal pass only when you want, using an external signal from another module (LFO, Envelope, Clock signal … for example).

IN : jack input for your incoming signal

CV : CV IN jack for the incoming external source (from another module) which will open the VCA (more or less and more or less long depending on the signal) to let the signal through.

CV ATTENUATOR : a pot to adjust the level of your CV in.

Exemple of a simple patch with this 3 modules (VCO + VCF + VCA) +1 for triggering the VCA :

OUT of the VCO to INPUT of the VCF, OUT of the VCF to INPUT of the VCA, OUT of the VCA to your system

  • one LFO or ENVELOPE or SQUARE WAVE … OUT to the CV IN of the VCA for triggering it, and now the VCO sound is no longer continuous

if you can multiply the trigger source (with a Multiple), or use another source different from the first (another LFO, Envelope …), you can also act on the CV of the filter.


Excellent! (random exclamation to see if that prevents discourse from yelling at you if you try to add more comments to this thead)


4 - ENVELOPE GENERATOR / ADSR (Attack, Decay, Sustain, Release)

This module when triggered by a Gate / Trigger signal (coming from a keyboard or another module) allows you to manage the curve of the signal produced : the way it attacks the note (Attack), its decay until ‘’ held (Decay), the duration of the note (Sustain) and finally the way the note will end when the signal is off (Release).

This module does not generate sound. The output of the Envelope Generator must be sent in the CV of a VCA, a VCF …

ATTACK pot : potentiometer for adjust the level of Attack

DECAY pot : potentiometer for adjust the level of Decay

SUTAIN pot : potentiometer for adjust the level of Sustain

RELEASE pot : potentiometer for adjust the level of Release

LOOP Switch : switch to select ADSR fonction with an external trigger, Loop (the module generates its own clock) or Gate Loop (an external clock triggers the loop)

TRIGGER Switch : switch to select external trigger or manual trigger position.

TIME (Duration) pot : This controls everything above it (Attack, Decay, Sustain and Release) by changing the overall time/duration.

OUT : output of the module for sending the gate signal to another module.

INVERTED OUT : output of the module for sending an inverted signal to another module.

Exemple of a simple patch with this 4 modules (VCO + VCF + VCA + ADSR) +1 for triggering :

OUT of the VCO to INPUT of the VCF, OUT of the VCF to INPUT of the VCA, OUT of the VCA to your system
also one LFO for exemple to trigger the ENVELOPE GENERATOR (EG)
the OUT of your EG into the VCA CV (also in the VCF CV if you can multipling the signal with a multiple)


great idea this new discussion !!!
It is true that I started in modular a few months ago and I admit that I was a bit lost to build my first module :sweat_smile:.


@Dud… THANK YOU!! This is what I needed was for Sam’s modules specifically to be explained so that I know what each module does and what each button/switch does. The example patch you give is extremely helpful!! I know Sam said he was working on a couple of videos starting with the VCA so maybe once he finishes a video we can add it to each module listing? This way myself and others can hear what each input is supposed to sound like / do so that we know ow they work and if we have built them correctly.

@fredrik @lookmumnocomputer
Would anyone be opposed to pinning this to the top of the Kosmo module category for easy reference since this is specific to Kosmo modules? Maybe we could go through and delete mine and other people’s comments so it is easier to read and only contains the module posts. Maybe make it a read only thread? I don’t know if that is possible but it would make this thread a great reference tool as opposed to a discussion thread.

Just a thought…


thanks Dud for starting this thread . it should prove useful . I know that I have a few gaps in my basic knowledge for sure .


No objection, but it isn’t really Information specific to Kosmo format though-These are module conventions that go back to the early days of Moog.

Would anyone object if I added some “west coast” style modules descriptions?


no it all applies to " how stuff works "


I learned that the 3rd cv on the filter is a 3rd cv lolol


A complex oscillator differs slightly from a VCO in that it contains at least two oscillators, one of which is intended as a “wave-shaper” to the other.

There are a variety of configurations, brands and models, but in general a Dual Complex Oscillator will have 2 oscillators, some kind of bus to allow the cross modulation and some form of waveshaper on the output of one of the oscillators. 1V/Oct is standard voltage to pitch, though often in this type of oscillator (particularly Buchla and Serge) will be tuned at 1.2v/Oct. On the DPO (pictured) you also have voltage control over Linear and Exponential response, shape of the modulation wave, Follow (for hard sync,) and a separate FM bus leaving the modulation bus open for other wave shapes to “fold” the signal.


Random Voltage Source
A random voltage source is useful for creating “surprises” within a patch, even surprises to the patcher. Don Buchla is often credited with the idea, and his 165/265/266 “Source(s) of Uncertainty” and “Dual Random Voltage Generator” are generally the basis for descendent models like the Wiard Richter Wogglebug.

Units such as this will often have a noise source included and to some extent will act as a noise coupled with a sample-and-hold to generate random voltages at a triggered interval, but also there will be quantized random voltages to keep the output at semitone intervals. There is usually some kind of voltage control over the range of voltages (degree, here,) the number of stored voltages that can be output if quantized (states) and various controls over the probability of the occurrence of change in voltages or gate-levels.


Function generators offer a way of controlling the slope of a voltage curve, usually including an option for repetitive execution of the curve. By far the most popular function generator (as well as the most popular Eurorack module in the world) is the Make Noise Maths:

Maths has inputs to trigger a cycle, voltage controls over the rise and fall rates and a “both” voltage control to create a stable waveform, and outputs for the generated waveform (“Cycle”.) In addition, Maths has a logic section that allows for summing, inverting or “or” gating waveforms, with inputs for 4 busses of logic manipulation.

Function generators are similar to envelope generators, and sometimes are used to generate AD/AR envelopes for the same uses as ADSRs. They’re also often used with their repetition (“Cycle”) functions as LFO and VLFOs.


“No objection, but it isn’t really Information specific to Kosmo format though-These are module conventions that go back to the early days of Moog.”

I think you misunderstood what I was asking for or perhaps I wasn’t clear enough. I realize module conventions go back decades. Sam didn’t invent PWM or 1v/oct, but what Sam has done is put each one of these options into his own design and that design is specific to Kosmo. Dud’s posts are referencing each of Sam’s modules with an image and providing descriptions for what each of the switches and knobs do, much like a manual would. So I guess I should say it that way…I’m looking for a manual for Sam’s modules that eventually includes a video that shows how a correctly built module should work and what that should sound like as a way for people to be able to test their modules. What Dud has done is perfect and if Sam creates a video we can add that to the post. I think having something that is pinned at the top of the Kosmo category that was read only and displays only Kosmo modules and information about each of the modules would be helpful to people, myself included.


i hope it’s not a mistake of me, some one can confirm plz ?


5 - THE VCLFO (Voltage Control Low Frequency Oscillator) :

The VCLFO is an LFO that we can control in voltage.

As you might expect, it’s an oscillator which oscillates at very low pitch (usually so low that our brains no longer perceive it as a tone.)

RATE pot (frequency) : this potentiometer adjusts the speed of the LFO.

CV IN (for Rate) : is a CV input to be able to modify the speed (Rate) with an external voltage (another LFO for example)

ATTENUATOR for CV (Rate) : allows you to manage the signal entering the CV (CV in for Rate).

SAMPLE AND HOLD pot : generates random pulses

WAVE DISTORTION pot : allows to distort the outgoing waveform

SYNC ON/OFF switch : to select external or internal synchonisation.

LEVEL pot : to control the level of the LFO out

WAVE FORM BANK switch : to select Bank 1 or Bank 2 for differents wave forms

OUT : 2 output of the module + 2 others inverted out

CV IN for Level : to manage the LEVEL pot with an external signal

ATTENUATOR for CV (Level) : to adjust the level of the CV incoming

WAVE FORM pot : potentiometer to choose in a differents selection of wave form (square, triangle …)

SYNCHONISATION INPUT : to control the rate of the LFO with an external clock signal

MULTIPLICATION RANGE pot : to multiply the LFO rate

Example of a simple patch with this 5 modules (VCO + VCF + VCA + ADSR + LFO)

OUT of the VCO to INPUT of the VCF, OUT of the VCF to INPUT of the VCA, OUT of the VCA to your system

OUT 1 of the LFO to trigg the ADSR, OUT of the ADSR to CV IN of the VCA, OUT 2 of the LFO in CV IN of the VCF, maybe try INVERTED OUT of the LFO in the CV IN of VCO …

now there are starting to be multiple possibilities :slight_smile:


Wave shapers are a class of module that take an incoming oscillator signal and modify it while leaving its initial form recognizable. These may take the form of wave folders, wave clippers, wave multipliers and even sometimes distortion units. The classic example is a Serge wave multiplier:

Wave shapers will have signal inputs and voltage controls over the various factors that can be modified. Folders and clippers will have a control for the amplitude level at which the signal is clipped or inverted, multipliers will have controls for the frequency modulation to apply to the incoming wave, and distortion can have settings like clip, starve, choke, etc.

Low pass gates are the “west-coast” answer to both VCAs and to an extent, filters, both of which are sometimes missing from complex waveform synthesis. These are low pass filters with a cutoff frequency that goes below the range of human hearing as its control voltage approaches 0 volts, so that the input signal is functionally silenced. In a way this is the opposite of a VCA, which actively amplifies a signal based on a control voltage. The response of a LPG is usually a little slower and softer than that of a VCA, but the two can be modulated using the same input controls.

Many modern low-pass gates incorporate VCAs and filters into them, as in this example, the Pittsburgh Modular LPG. Here you see inputs for the signal being gated, as well as a control voltage input for the cutoff of the filter when used in filter mode, as well as a “ping” which is a gate/trigger input to flash the vactrol level and percussively modulate the frequency of the unit.



Surely the first thing to do when you start a modular synthesizer :

  • THE CASE :
    For Kosmo format: it must be made to accommodate 20 cm high modules.



A modular synthesizer generally works with either ±12V (Kosmo, Eurorack) or ±15V (Moog, Yusynth).

For Kosmo you absolutely need to have a power supply who will give you +12V / Ground / -12V.
A good easy cheap solution is this product from Frequency Central

You need also a wallwart 12V AC/AC (2 or 3 ampere it’s good)

The wallwart 12 V AC go into the power supply and your power supply transforms and regulates to a +12V DC / - 12V DC and Ground to supply several modules.

You can put 2 power supplies with one wallwart in parallel, like this

All information in this video


Because this thread is a mix of discussion and actual module descriptions, and because it is quite lively, it is quickly becoming harder to use as a reference.

I suggest we add a table of contents at the top of the first post with pointers to the various module descriptions.
Something like this:

Table of Contents
2- THE FILTER (VCF / Voltage Control Filter)

Since the VCO is in the first post, it might be a bit tricky to make a pointer to it within the same post.
If that is not possible, it could be moved to a new entry and pointed to there.