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Eurorack synth modules

Hardware synthesizers, in Eurorack format.

Technologies

  • Electronics

  • Circuit design

  • KiCad

  • JUCE

  • Raspberry Pi

About this project

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Wooden case and PSU

The case is made in pinewood and painted, four 84 HP Eurorack rails are mounted in the case, which makes it a 6U 84hp rack. The PSU PCB have a +- 12V rails as well as a 5V rail for digital modules. The PSU schematic and PCB is designed in KiCad.

A picture of the case before it was painted.

A 3D model of the PSU.

Eurorack bus to connect modules to the PSU.

Low Pass Gate

A classic module, the Buchla 292. Later it was cloned by Peter Grenader and released as a part of on Ken Stone's CGS project. I based it on the schematics found on Ken Stone's website but tweaked it a little bit and made a new PCB design in KiCad. The faceplate is made in aluminium, ahnd drilled and hand painted

CEM3340 VCO

Dual VCO based on the classic CEM3340 IC used in vintage synths like Roland SH-101, Moog Memorymoog, Sequental Circuits Prophet 5 and many more. Each VCO has saw and triangle outputs and 1V/oct and frequency CV inputs. There is a switch for turning on soft sync or hard sync between the two oscillators. If you feed the VCO with a negative voltage it is possible to use it as an LFO. The circuit and PCB was designed in KiCad, the faceplate is painted aluminium.

Drum Machine

A digital drum module with analog interface, based on Raspbery Pi Zero. You can find the project on this github repository. The circuit is soldered on a perf board with headers to mount the Raspbery Pi Zero. There are interfaces tp trigger a bd, sn, cp, ch, oh and cy drum sounds. The actual sounds can be replaced by logging in to the Raspberry Pi Zero via SSH and replace the files. I am using the JUCE C++ framework to trigger the sounds, and i cross compile the project using a gcc tool-chain for raspberry pi. For some reason i am having latency issues when the sounds are played, I've tried with different programming languages and libraries and i found JUCE having the lowest latency, but it's still pretty bad. It is on my to-do list to fix this issue.

Also, i drew R2D2 on the faceplate, because robots are cool!

Mixer modules

Two different mixer modules, one with knob for each input and input 1 is normalized to 12V to act as an offset knob if needed. The other one have a smaller footprint and a higher gain to boost signals if needed. Both mixers are based on the same circuit, an opamp coupled as a summing inverting amplifier followed by an inverter. The larger mixer also have an output before the second stage to get an inverted output

Picture of the other mixer module with more gain and smaller footprint.