About this module

This 10HP Eurorack module has all the features a basic VCO needs. The module is based on the famous CEM3340/AS3340 chip. It outputs multiple waveforms, namely, square waves, triangle waves and sawtooth waves. The frequencies of all these waveforms can be voltage controlled using either the V/oct input or the vanilla frequency CV input. Next to that it has more advanced features like hard and soft sync, and also includes a knob and CV input for pulse width modulation. All in all, a great VCO to add to your Eurorack modular synthesizer.

Tuning the 3340 VCO

Video here!

Hey folks! Here are some steps to get your Cosmic Instruments 3340 VCO in tune. Note that if you don’t have a device that supports V/Oct, there is no need to tune it. You can then just adjust the knob and trimpot to you liking.

Setup:

1. Plug a device that supports Volt per Octave (e.g. Arturia Beatstep or Keystep) into the V/oct input.
2. Wire the triangle (or one of the other shapes) output to a speaker, so that you can hear it.
3. Install a tune app on your phone (e.g. Tuner T1 for iOS) and place your phone with the app open next to the speaker.
4. Adjust the trimpot on the back to the lowest frequency possible.

Tuning steps:

1. Play a C4 using your V/oct device.
2. Adjust the knob on the front of the VCO until your tuner indicates that you are playing a C4.
3. Play a C6 using your V/oct device.
4. Adjust the trimpot on the back of the VCO until your tuner indicates that you are playing a C6
5. Repeat step 1 to 4 until you don’t need to adjust the knobs and trimpot anymore. This can take quite some time, the first time you are tuning it.
6. Congratulations your VCO is in tune!

This approach basically only tunes 2 octaves, although the other ones should also be reasonably in tune. To get a more accurate tuning you can also tune over more octaves (e.g. use C3 and C7).

About Cosmic Instruments

Cosmic Instruments started off as a synth DIY hobby project and mostly consisted of hand-soldered protoboard modules and hand-drawn front panels. At some point my setup required more robust and reliable modules. I converted many of my modules to PCB designs and also started making professional designs for the front panels. Now, after many iterations of my designs, I feel that my modules are ready be used by other people around the world. Tindie seemed to be the right place to start...