Calibration

The Moduleur consists of Eurorack compatible modules that work independently. To get the most out of the system as a whole, you should go through a standard calibration procedure. This process makes sure the modules are tuned to work together well, everything is within appropriate voltage range to bring out the best possible sound.

Tools you’ll need

• Oscilloscope — use AC coupling
• Precision screwdrivers for trimmers — flathead and Philips
• Multimeter — a calibrated one is ideal but generally the more precise, the better
• ~5 patch cables
• Tuner
• Amp + speakers or audio interface for audio monitoring

Full calibration checklist

1. Brain

• Output 1 hardware gain
• Output 2 hardware gain
• Output 1 software calibration
• Output 2 software calibration

2. VCO 1

• Saw wave balance
• Triangle wave shape
• 1V/oct tuning

3. VCO 2

• Saw wave shape
• Triangle wave shape
• 1V/oct tuning

4. Mixer & sidechain compressor

• Mixer balance (0V reference)
• Mixer base level
• Side chain compressor attack
• Side chain compressor release

5. Filter

• Max resonance
• Balance / recovery

6. Envelope / VCA 1

• VCA balance (0V reference)
• VCA base gain
• Envelope gain

7. Envelope / VCA 2

• VCA balance (0V reference)
• VCA base gain
• Envelope gain

8. Bitcrusher / LFO / Output

• Line level

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1. Brain

We start with the Brain module because we’ll use it to calibrate some of the other modules. You’ll need the following firmwares so download them from the Brain firmware library:

• Brain Diagnostics
• CV Tuner
• Le Controlleur

Output hardware gain

1. Load up the Brain Diagnostics firmware on the Brain module
2. Follow the instructions of Test 14 to set the hardware-trimmer gain

Output software calibration

1. Load up the Brain CV tuner firmware
2. Follow the instructions to fine-tune the CV output of the Brain module so it tracks perfectly for 1V/oct

Make sure to calibrate both Audio/CV outputs of the Brain module. You don’t need to calibrate the Pulse OUT.

Prepare Brain for calibrating other modules

1. Load up Le Controlleur firmware (user guide)
2. Connect a MIDI keyboard to MIDI IN using a TRS-A MIDI adaptor
3. Make sure
   1. you’re in MIDI to CV converter mode
   2. your MIDI channel is set to the same as on your MIDI controller
   3. the Pitch CV Output channel is set to the output you’ll use later on in the calibration process

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2-3. VCO

Board

VCO core

Calibration setup

• Connect scope to VCO output

Saw wave balance

1. Switch VCO output to sawtooth
2. Use trimmer SAW BIAS to move the saw wave on the Y axis (amplitude) until it oscillates around 0V

Triangle wave shape

1. Switch VCO output to triangle
2. Use the TRI BIAS trimmer to move the triangle to oscillate around 0V
3. Use the SAW BIAS trimmer to fine tune the shape of the triangle (the triangle is built up of the saw output and an inverse of that, that’s why changing the saw balance defines the shape of the triangle wave)

Tuning

1. Connect the VCO OUT to a tuner
2. Turn the OCTAVE (main tune) knob all the way down and the FINE knob in the middle.
3. Connect a 1V/oct CV to the VCO PITCH input. If you have calibrated the Brain module, use Le Controlleur firmware in MIDI mode and a MIDI keyboard, and connect OUT 1 to the VCO PITCH input. (Make sure you set the Pitch CV Output channel to OUT 1.) Alternatively you can use a keyboard with 1V/oct CV output like an Arturia Keystep, Beatstep Pro, Korg SQ1 or similar.
4. Turn HI-FREQ pot all the way down: play a very high pitch note on the keyboard and turn the knob until the pitch stops going down.
5. Play C1 on keyboard. Use the BIAS trimmer to set the frequency to C1 (32.703Hz)
6. Play C4 and use the BIAS trimmer to set the frequency to C4 (261.63Hz)
7. Play C1 and use the WIDTH trimmer to tune it to 32.703Hz
8. Loop steps 3 + 4
9. When C1 and C4 are in tune, play C7 and use the HI-FREQ trimmer to make up the pitch for higher frequencies.
10. Go back to step 3 & 4 to adjust tuning for lower frequencies, then go to step 6 again, until you get to a reasonable end result.

Repeat for VCO 2.

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4. Mixer & sidechain compressor

Board

Mixer & Sidechain core

Calibration setup

• Connect VCO 1 out to IN 1
• Connect VCO 2 out to IN 2
• Connect VCO 1 sub to IN 3
• Connect an external sound source (ideally a drum machine) to IN 4
• Connect Mixer out to an oscilloscope

Mixer base gain

The mixer goes through a VCA which is used for the side chain compressor. This step sets the base gain for the VCA so that there’s no bleed

1. Turn IN 1, IN 2, IN3 all the way up
2. Turn output level all the way up
3. Use the BIAS trimmer to set the output so that the maximum amplitude is not more than 10Vpp (+/- 5V) — from experience, this is pretty good for side chain compression

Mixer balance

1. Turn all input levels all the way down
2. Turn output level all the way up → The output is a fix DC voltage (no inputs waves should appear on the output)
3. Use the COMP trimmer to set the output (a DC signal) to 0V — this makes sure the mixer output will oscillate around 0V

Sidechain attack and release times

1. Turn IN 4 GAIN all the way down
2. Turn IN 4 THRESHOLD all the way up
3. Turn Mixer OUT all the way down — IMPORTANT: the output of the Mixer is now at 10Vpp. Connecting it to a speaker system that expects line level may damage it so be careful with the output level knob.
4. Connect Mixer output to a speaker or audio interface
5. VERY SLOWLY turn up the OUT LEVEL of the Mixer to a point where the input of your is not overdriven on your speaker/interface
6. Press play on your external sound source (drum machine) — a good old 4 on the floor with a punchy kick would do it
7. Turn IN 4 all the way up → you should hear the drum machine on the mixer output
8. You can turn up the GAIN to add more gain to IN 4
9. Turn the THRESHOLD pot down (setting the side chain compressor threshold level)
10. Use trimmer ATTACK to set the attack time of the side chain compressor
11. Use trimmer RELEASE to set the release time of the side chain compressor
12. If you want more compression then you can turn the overall Mixer base gain down a little, which will give more space for compression (but less overall mixer output)

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5. Filter

Board

VCF core

Calibration setup

1. Connect a saw output to LP IN of the filter
2. Connect the filter output to an oscilloscope

Max resonance

The resonance of the diode filter in the Moduleur is quite sensitive in the higher ranges. It can easily choke, so we added a trimmer to keep it usable.

1. Turn RESO to minimum
2. Turn CUTOFF to a position where you can see the low pass take effect (smoothens the spikes of the sawtooth wave)
3. Turn RESO to maximum — it’s likely that it’s going to go to self oscillation, that’s fine
4. Use the MAX RESO trimmer to set the maximum resonance to your liking. Turn it to a point so it does not choke (when it does, there’s a supersonic wave on the output with maximum amplitude). It’s better to listen to the output on a speaker / audio interface to calibrate to how it sounds, instead of how it looks on the oscilloscope.

Filter balance and recovery

1. Turn the cutoff pot up and down fast and look at the oscilloscope. Watch for how much time it takes the waveform to settle to oscillate around 0V (recovery time).
2. Use the BALANCE trimmer to set the recovery time to the minimum — ideally you shouldn’t see the whole wave move up and down in amplitude, just a steady sawtooth.

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6-7. Envelope / VCA

Board

ADSR-VCA core

Calibration setup

• Connect your MIDI keyboard to the Brain
• Use Brain’s Le Controlleur firmware in MIDI to CV mode
• Connect the Brain / PULSE OUT output to the Envelope’s GATE input
• Connect one of the VCO’s triangle wave from one of your oscillators to VCA IN
• Connect an oscilloscope to VCA OUT

VCA balance

1. Use the VCA COMP trimmer to set the VCA OUT to 0V (check it on scope)

VCA base gain

1. Use the VCA BIAS trimmer to set the VCA gain so that on the VCA OUTPUT you just don’t see the input signal appear. This sets the 0V baseline for the VCA.

Envelope gain

1. Connect Envelope ENVELOPE output to VCA CONTROL input
2. Hold a note on the MIDI keyboard so a gate triggers the Envelope
3. Set ATTACK, DECAY and RELEASE to minimum
4. Set SUSTAIN to maximum
5. Hold a note on the MIDI keyboard. You should see the VCO triangle appear on the scope
6. Use the ENV GAIN trimmer to set the VCA OUT to 10Vpp (+/- 5V) — same level as the VCO triangle signal. This makes sure that the Envelope is calibrated so that at max level the signal passes through with uniform level.

Repeat for VCA/Envelope 2.

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8. Bitcrusher / LFO / Output

Board

Utils-output core

Calibration setup

• Connect the VCO’s triangle output to MAIN IN of the output module
• Connect scope to the HEADPHONES of the output module

Output level

• Use the LINE LEVEL trimmer to set the output to about ~3Vpp (About: line level)