I recently started building my first Eurorack modular synth by purchasing some bread and butter modules. Today I will show you how to wire up a basic monophonic, single voice synth with a separate envelope for the amplitude and filter and a bit of modulation via some LFOs. Nothing too fancy here, just some basics to get you started.
We’ll be wiring up a VCO, a VCF, a VCA, a couple ADSRs and some LFOs. I’ll also be using an iPad to send MIDI data to the synth via a MIDI to CV module. Though I am using hardware that may be different from yours (you may even be building you modular in software), the basic building blocks should be the same.
Apologies for the low quality photos, my camera has decided to stop letting me transfer photos so I had to use my iPad’s camera.
To start lets make sure the VCO is working. I will patch the sawtooth output from the VCO to a mixer module I have that I can plug my headphones into. This will give me control over the level I am monitoring at which my ears will thank me for. If you don’t have a mixer module you could use an 1/8″ to 1/4″ jack and plug into an external mixer into which you could plug headphones or listen through your monitors. Now with the power on you should hear a constant signal out of the VCO outputs. At this point you could try the different outputs to hear the sound of the different waveforms, adjust the pitch and adjust the pulse width for the square wave output
Now that we know our sound source is working we want to create a way so that we only hear sound when we send a note from our keyboard or sequencer. To do this we will need to feed some MIDI into the MIDI to CV module. I am using an iPad running the StepPolyArp app and a Line 6 MIDI Mobilizer, but you could just as easily use the MIDI output from a computer audio interface or from a MIDI keyboard.
Plug a cable between the MIDI output device (iPad, computer, keyboard etc) into the MIDI input of the MIDI to CV module. Make sure you are outputting MIDI on the correct channel. Most MIDI modules should have a gate LED. With the input device connected make sure that when you play a note that the gate LED lights up. If you need to, consult the documentation for the module for how to set the MIDI input channel.
Next, connect the the sawtooth output from your VCO to the input on the VCA and connect the output of the VCA to your mixer. If you have the option use an exponential VCA rather than a linear one. Now connect the gate output of the MIDI module to the CV input of the VCA. This will allow the VCA to pass audio from its input to its output whenever the gate signal is received at the CV input. Depending on the VCA you have you may have a knob to adjust the amount of CV or the level of the VCA. If you have a CV input control knob turn it all the way up. If you have a VCA level control, turn it all the way down because we don’t want the VCA outputting any audio when there is no CV input (ie no gate).
We could stop there but it doesn’t really sound that great because even though we can play different pitches the sound just turns on and off without any interesting motion. The next thing we will do is add an amplitude envelope to control the amplitude (volume) of the sound over time when we play a note (open the gate).
To do this, unplug the gate form the VCA CV input and patch the gate to the gate input of an ADSR. Then patch the ADSR output to the VCA CV input. Now when you send notes to the MIDI module the gate will trigger the ADSR which will send a control voltage envelope to the VCA. You can adjust the attack, decay, sustain and release of the ADSR to change the amplitude of your sound over time. Attack is how long it takes to get to full amplitude, decay is how long after reaching full amplitude it takes to get to the sustain level set by the sustain knob, and release is how long it takes for the amplitude to go to zero once the gate has closed (key has been released). Set the ADSR to something pleasing to you.