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

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 using an external 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.


The top post is wiki editable, so you can edit it with a table of contents if you desire. :slight_smile:


I know, but I’ll let @Dud decide if he likes the idea.


yes I had thought about it too, it would actually be more practical, that’s also why I made a wiki.

Someone can plz completed the explication on ADSR for Time/Duration pot, i have not this module ready and don’t know exactely what it’s this fonction :slight_smile:

1 Like


It is a 6 channel sequencer that allows you to send a signal to trigger other modules.
Important : It needs to receive a clock signal to operate.

  • CLOCK INPUT : with an external clock you set the speed of the sequencer

  • CHANNEL SELECT : there are 6 channels, select for example channel 1 and the trigger signal will come out from the OUTPUT 1 when you press the Big Button or the Fill button.

  • 6 TRIGGER OUTPUTS : are the 6 outputs that will be connected to the modules that we want to trigger

  • SHUFFLE : “random mix”

  • STEP SELECT : with this pot you can choose the number of steps in the sequence (1/2/4/8/16 or 32)

  • BANK SELECT : 2 banks, you can record 2 sequences for the same channel, and switch from one to the other using this button.

  • CLEAR PATTERN : allows to erase the pattern of the selected channel entirely

  • DELETE ONE SHOT : unlike CLEAR, you can delete the “notes” one by one.

  • FILL : Pressing this button causes a rapid succession of triggers on the selected channel, to create an effect similar to a drum roll.

  • RESET : an impulse on this switch and the sequence restarts at the beginning

  • BIG BUTTON SWITCH : used to record sequences manually.

This sequencer can trigger a kick, snare … and a whole bunch of drum modules, but it can also be interesting to use it in an Envelope, a VCA, the SYNC IN of VCLFO …


If someone would like the details of one module ?
ask and i will try


Adding the description of a note sequencer such as the Keyboard Sequencer or the Baby 8 could be good as you mention the use of a sequencer in the VCO description, but the Big Button sequencer is not of the appropriate type to drive the VCO.
The mixer is the next missing essential modules.
And then passive attenuator, multiple, atennuverter, and the elusive final output module.


I thought that my proposal was for beginners who would have a problem with a module that does not really understand :wink:
but yes the sequencer is a good idea, for the others you propose I might take photos of my modules to illustrate because Sam has not yet done them on his site (multiple, mixer …), although they are quite simple to understand even by a beginner, but as soon as I have a little time I put it there

and thanks to all for your add and corrections !

1 Like


A sequencer allows to send a CV signal of different values ​​on each step to a VCO CV IN for example (but not only), to have a different note at each step.

Without an external clock you can still use the keyboard manually to send CV, but for it to scroll by itself from step to step you will need an external clock.

INDICATOR LED : allows to view the scrolling sequence

PITCH POT (1) : 8 pitch potentiometers (all the line), one for each step, to adjust the strength of the signal sent on the corresponding CV OUT for each step

PITCH POT (2) : the same thing like the PITCH POT (1) but for the second line

GATE OUT : each step can send a gate signal to another module

MANUAL KEYBOARD : you can play with it during a sequence , but also without clock in, when you press one of these buttons, the corresponding voltages are output on the CV OUT.

MANUAL STEP : without external clock you can move forward or backward step by step manually with this switch (to adjust the tune for each step before starting a sequence for example )

CLOCK IN (B) : clock in Backward, with an external clock in this jack the sequence goes backward

CLOCK IN (F) : clock in Forward, with an external clock in this jack the sequence goes forward

RESET INPUT : to restart the sequence at the start with an external trigger

RESET SWITCH : to restart manually the sequence at the start

KEYBOARD GATE OUT : send a gate signal to another module with the keyboard button

CV OUT (1) : it’s the OUTPUT CV for line 1

CV OUT (2) : it’s the OUTPUT CV for line 2

Example of simple patch with this module, a VCO and a LFO :

  • LFO OUTPUT (square wave) to trigger the sequencer (in CLOCK IN Forward), CV OUT (1) of sequencer in CV IN of the VCO : and play with all the PITCH POT (1) to change the tune of each step.

  • You can also take a GATE OUT of one step to trigger a VCA, ADSR, VCF …
    Or also the CV OUT (2) to tune another VCO to make some 2 notes “chords”

  • Also you can connect the GATE OUT of one step to the RESET IN to make a shorter sequence



In fact it is a mixture of 2 modules: a VCA (Voltage Control Amplifier) ​​and a MIXER (to mix different signals to only one output.

INPUT : this is the signal input

CV INPUT : controls the gain of the VCA, typically comes from an envelope generator, or an LFO

INVERT SWITCH : When activated, an offset equivalent to +5.6V is added to the input CV, this is typically used with inverted envelopes that are at 0V at rest and go negative when active, that way, the audio signal passes continuously and when an inverted envelope arrives the audio signal is reduced or even completely cutoff.

INDICATOR LED VCA : to signal what voltages are affecting the VCA

VOLUME POT : potentiometer to adjust the output level of the VCA

OUT : OUTPUT individual output for each VCA channel. When a jack is plugged into one of these outputs, the corresponding signal no longer goes to the mixer.

ON/OFF OUT SWITCH : to select to open or not each channel out.

INDICATOR LED ON/OFF OUT : to indicate which channel is open (not muted)

GENERAL OUTPUT : or Master OUTPUT it’s the output jack if you want to mix all the input together

GENERAL VOLUME OUT pot : potentiometer for adjust the level of the MASTER OUTPUT.

It’s a QUAD VCA MIXER module so it’s the same things 4 times (for the other pots, switches and jacks)

Example of a simple patch with this module :

A VCO OUT in the INPUT 1 of the VCA MIXER + a LFO OUTPUT to drive the CV INPUT of the VCA MIXER
Another VCO OUT (or the same but the first OUT of Triangle wave and the second OUT of the Saw wave) into the INPUT 2 of the VCA mixer, the same LFO (the VCLFO has several outputs) to drive the CV INPUT 2 of the VCA MIXER and test this channel with the INVERT SWITCH (the 2 VCOs will respond)
take the MASTER OUTPUT of the VCA MIXER in your system.

if you have seen the other small simple patches of the other modules, you can therefore as well before the VCA MIXER pass the VCO through a VCF, also the LFO first by the ADSR …


Yes, that was my point in wanting to take just the information about Sam’s modules and pin it as a read only. This way comments are not possible and one or a couple of people would have access to edit it / add new modules as Sam releases them. This way it is kept clean and clutter free. I think we should have two separate threads. One that just has Sam’s modules in it and one that has information about non-Sam created modules, components and how they work (which I saw someone did…Dud I think?) and terminology, etc… I realize some information would be duplicated on both, but it would allow users to find information on just Sam’s modules right away. I figure that since we are all on his forum that most of the people are coming to find information about his modules. If it were a site like Muffwiggler then I could see lumping everything together.

I’m a UI/UX website designer. (User Interface / User Experience) so I can’t help but have my work hat on. :slight_smile:

I’m sitting here at work right now conducting user research and watching videos of users click through sites to complete tasks and it is painstaking watching people click on 100 things in order to find the one thing they were looking for. :scream_cat:


I think the table of contents implemented in the first post solves most of the issue, have you taken a look?
And the topic is now pinned.