DIY Modular Synth Walkthrough

This is a brief overview of the current state of my completely DIY modular synth. This is pretty much the bare minimum needed to have one complete bass synth voice along with drum machine. If only there was a music genre to describe what it could be used for…

I’m often asked when it’ll be finished, but the truth is, it’s a never ending project. I think there will always be parts of it that I can improve on, and the best way to find what needs improving is to play it as often as I can. So here is the current setup as of May 2020:

VCO: Based on a CEM3340 chip, I designed this mainly on the datasheet (along with small parts from LMNC’s latest design. The 3 knobs in the middle form a wave-mixer so that you can adjust the wave form without re-patching. Top left is a 5-way octave select switch (helpful for switching between bass/melody lines). The button at the top right is an auto-tune feature that I’ve designed from scratch. This is powered by an arduino along with a digital potentiometer. The arduino checks the frequency of the CEM3340, then adjusts the digital potentiometer accordingly on a button press. It’s accurate within 0.5 cent & it hasn’t failed me yet! This also improves temperature drift as there aren’t any exposed mechanical parts that can be affected. I’ve also removed all features that I thought were unnecessary, like: adjustable pulse width (I’ve stuck a 2.5v voltage divider into the pulse width so it’s consistent), and kept it at just 1 x CV input as I never found myself to use frequency modulation.
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LPF: This is a replica of the Rene Schmitz MS-20 filter schematic (with added High-Pass switch). Inspired by Look Mum No Computer, I’ve re-designed my own stripboard layout for this so that I could properly understand how it works.

VCA: This is based upon LMNC’s latest VCA offering. It revolves around the AS3360 chip, and works as well as a VCA can.

ADSR: This is another Rene Schmitz design, and again I’ve made my own stripboard layout for this & more info can be found on my web
site.

Midi-CV: This is a midi-muso kit, all I’ve done is build it & stick it on a panel I made. Works well if you don’t have a keyboard with CV out!

Baby-8 Sequencer: The iconic 4017 step sequencer. I designed & built this one from the datasheet & added a 555 timer circuit for an adjustable internal clock. It also has a switch to receive external clock signals.

Drum Machine (with 8 step sequencer): The drum synth is powered by a Circuit Bender DR-55 PCB that I’ve build, and to trigger it, I’ve designed an 8-step, 5 channel sequencer. It works in a similar way to the 808 sequencer but with less of the confusing controls. I’ve tried to keep it as simple as possible to improve play-ability without the need for menu diving.

4 channel mixer: This is based on the CGS DC mixer, and is the first project I’ve designed PCBs for. Very happy with the look of these. I’ve added signal indication LEDs, purely because a synth can never have too many flashing lights.

As always, there are more photos & stuff over on my Instagram (@TheDuskwork) & you can find build guides and schematics for all these projects over on the projects page.

Duskwork Synth

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