Skip to main content


Showing posts from 2017

More VCO's and a Mixer

3 More TH-VCO1 Modules and a Mixer to Make Them All Sing Together! As already mentioned in the previous post, I got 11 PCB sets for the TH-VCO1. I decided to build 4 of them for my own rack. I also had to build a mixer module to utilize all the signal sources. Almost Mass Production! I had already built one TH-VCO1 so building the rest of them was pretty straightforward. I tried to avoid the issues I discovered with the first unit. Figuring out what to do next and where each component should go takes significant time so I decided to assemble all three at the same time. It did save time but was more frustrating because it took much longer to get anything ready. Mass Production. Assembling all three units in parallel. This time I left out the IC socket. Now THAT340 and Tempco resistor fit nicely under the potentiometer board. I added some thermal compound under the Tempo resistor. I don't know if it is necessary because the first unit seems to be stable also wit

Oscillators. More is More! TH-VCO1

The Very Beginning of the Signal Chain Voltage controller oscillators, or VCO's, are the root of everything in subtractive synthesis. That's the place where the sound is born and everything after that is just modifying it. VCO really creates the sound. It is also the component that defines pitch and thus makes melody and harmony possible. Rest of the signal path is mostly about timbre. (And rhythm of course.) I started my modular synth by building a Doeper DIY Synth so I only had one VCO. It really limited things so I had to get more. Things got a bit better when I added another Doepfer DIY Synth to the rack but 2 oscillators is still not that much. There's two reasons to add more oscillators. First one is to be able to play multiple notes at the same time to generate harmony. The second one is to configure multiple oscillators to play the same note to generate more complex sounds. Analog VCO's are always more or less out of tune so the sound will get thick

Waiter, there's an Arduino in my Eurorack!

I want to write code! Modular synths are traditionally all analog but nowadays there's plenty of digital modules available too. As I'm a software engineer I have been planning to add some home made digital signal processing to my modular synth. I already have an STM32f4 processor taking care of midi2cv and two digital outputs but additional modules that are open for custom software are always welcome. Cavisynth Ardurack PCB and panel I have been playing around with Arduino HW and got an idea to use it for eurorack module. Soon I stumbled upon  Cavisynth Ardurack Module  and realized others have got the same idea too! It's a simple eurorack module that uses the really popular Arduino embedded computing platform to do various things. It can be used for example as a square wave oscillator or a noise source. See Cavisynth website for full feature listing. The module is available as a cheap DIY pcb+panel kit and all software is open source so I had to order one immediat

Double Doepfer!

Getting Rid of the Empty Panel Half As already mentioned in my earlier post , I started my modular synth with a Doepfer DIY Synth kit. It happened to take exactly one half of the 3 unit rack panel. It was clear that sooner or later I would need to add something there because the half empty panel looked somewhat silly. "Must fill panel! Must fill panel!" You might have noticed that Doepfer gives a rather nice discount promise in the DIY synth webpage : If you build one and send some photos to be added to the page you will get 50% discount for another diy synth board! (Or possibly an extension board in the future). After I had documented my modular synth beginnings into this blog I sent a link and some photos to Doepfer. Pretty soon I got a reply from Dieter Doepfer himself! You can spot my synth in the page now. At this point it was pretty clear that I would build another DIY synth to fill the panel. I had already been missing another oscillator and ADSR and thi

Let There be Noise!

Let There be Noise! The blog has "noise" in it's name so it's about time to write a post about noise! After finishing the 4xLFO module I started looking for another simple but useful module to build. After studying the ASM-1 schematics  it was somewhat obvious that  the noise module  would be my next project. It's almost as simple as the LFO and significantly widens the sonic possibilities of my synth. I only have 8hp wide blank front panels so a noise circuit alone felt like waste of panel surface. Of course the obvious companion for a noise module is sample and hold. By feeding white noise to sample and hold you get randomly changing control voltage. Feed that into the CV input of your oscillator and you get the classic "computer speaking" sound from the past. White Noise White Noise? Pink Noise? Most common noise types in synthesizers are white noise and pink noise.  White noise  contains equal amount of all frequencies and sounds a

LFÖ x4 module

More Modulation, Please! After I got the Doepfer DIY synth up and running I immediately realized I needed more than one low frequency oscillator to modulate things. In the current setup I can modulate oscillator frequency, pulse width, filter frequency, filter resonance, another filter frequency, amplitude of the VCA etc... So one LFO simply isn't enough! The Schematic Because of my "quantity over quality" synth building philosophy I started looking for a really simple and cheap LFO circuit that I could easily multiply. I finally ended to the ASM-1 DIY synth page.  That's actually one of the pages I spent a lot of time in ten years ago when planning to build a modular synth for the first time. ASM-1 is a complete modular synth but not exactly compatible with the current Eurorack format as it uses -15V/+15V voltage. After studying the LFO schematics it turned out that the LFO is really simple. The circuit is pretty much as simple as it can get. A Schmitt tr