The Electrical City Manifesto

"Manifesto" is a loaded word, conjuring images of Karl Marx, and the Unabomber. Like the Unabomber, i have a Ph.D. in mathematics, and i am fond of the sunglasses and orange hoodie look. Be that as it may, here are some quick thoughts on the "Electrical City" project, written to myself, to clarify goals, ethos etc.

Karl

Una

Another Marxist - Groucho

• the purpose of this project is to make music, not design/manufacture/sell modules
• build/sell modules from kits to finance your own projects
• design simple as possible but no simpler
• minimize turnaround times for parts orders and everything else in the process
• don't try to be an electrical engineer. Approach this project as what you are -- mathematician, software engineer, musician
• don't try to get into PCB design/manufacture -- stick to stripboard
• don't try to use high learning curve tools like KiCad (although it's an amazing tool)
• live on the edge - feel free to experiment
• leverage your coding skills to modify open source software tools (e.g. DIYLC) to own needs
• develop software, or modify OSS tools to speed up design checking/validation, e.g., comparing connections on stripboard to schematic

VCO - Square (and Saw and Triangle) Biz

 The VCO (Voltage Controlled Oscillator) is a component in an analog synthesizer that creates raw waveforms, usually under voltage control to control the pitch (1v/octave at least since the days of R. Moog). 

Robert"1v/octave" Moog 

These waveforms are basic shapes, like square (or pulse), sawtooth, and triangle, among others, which provide raw material for the rest of the system, such as filters, envelopes etc.

Some waveforms

There are some very nice VCO designs out there on the web, e.g., from Look Mum No Computer and Eddy Bergman.com built around the Curtis CEM3340 VCO chip, or its clone, the Alfa AS3340. The AS3340 data sheet itself has pretty detailed sample schematics.

The VCO i ended up building is deeply indebted to the above designs, with some aspects borrowed from one or the other, and some pieces that i don't care about omitted. I also tweaked some component values to get the pots to yield usable ranges. For example, the range of the pulse width pot didn't even get to 50% (i.e., a standard, plain old square wave) in my first attempt, so i increased the resistors to 5.1M, which allows the pot to cover the range from 0% to 100%.

Here's the stripboard layout (DIYLC file linked below)

I was able to calibrate this pretty accurately with the 10k trimpot. Here are photos of the (almost) finished product:

The front panel is ink-jet printed on adhesive backed vinyl, sprayed with a layer of clear coat (will do a separate post on cutting, drilling, and printing panels). 

RESOURCES

• DIYLC File
• Bill of Materials (.xls)
• Panel Design (.pdf, editable in Illustrator)
  

The Attenuverter

Greetings, Earth creatures! And welcome to "Electrical City", a new blog i have started to document some of the electronic music projects i have been working on.

Here is a video showing my usual process of building a Eurorack synthesizer module, starting with finding a schematic on the web, building the circuit on a breadboard, then on stripboard, based on a design created from the schematic, testing, and finally cutting and drilling a front panel, and assembling (the soundtrack is also all original music so hope you enjoy that ;-).

This particular module is an "Attenuverter", based on a schematic by skullandcircuits.com. An attenuverter is a utility module for attenuating or inverting signals, so it's a potentially handy signal management tool, where those signals could be audio, or voltage (haven't tested this one yet with voltage, but it would be interesting to see what happens).

The Skull and Circuits resource page is here. Here is the stripboard layout, designed with DIYLC (the jacks are on a separate board).

Resources:

• DIYLC file
• Front Panel design (.pdf)