Math Module

FUSION CORE (synthesizer)

Goal

• Get to know delicious circuits (experimenting a lot)

• Use them in crude ways to generate sounds

• Learn how to design circuits & professionally manufacture them with KiCad

• Learn whats possible with analog circuits and what's not

• Have a lot of fun without the need of programming

• Get an overview of electronic parts out there

• Manage a big project

• Make ambient dub techno at the end lol

Sound samples

• Can be found under ./Sounds

Resources

• Books
  • Make: Analog Synthesizers (from Music from outer space)
  • The Art of Electronics
  • Make: Electronics & Make: More Electronics
  • Encyclopedia of Electronic Components (Vol. 1, Vol. 2, Vol. 3)
  • Engineers Mini-Notebooks
• Internet
  • https://www.lookmumnocomputer.com/
  • https://www.eddybergman.com/
  • https://www.birthofasynth.com/Thomas_Henry/TH_main.html
  • https://musicfromouterspace.com/
  • https://www.schmitzbits.de/index.html
  • https://www.ericasynths.lv/
  • and a lot more!
• University for background theory
  • Electronics I & II
  • Signals & Systems, Control Systems
  • Communications Engineering
  • Computer Engineering

Nice shots from June 17th 2024 onwards

Obviously go to Look Mum no Computer concert!

Test circuits with chaotic wiring

Gather lab devices (frequency generator & oscilloscope are from student research center)

Design some PCBs

Draw some fancy ideas

Meet with friends to build a fancy case

Having fun with nice dark & cozy athmosphere

What is this repo for?

• Contains my development files
• Contains some notes, but definitely not a tutorial to rebuild this on your own
• Contains some insights on what I did (this is still no complete log)
• The chapters in the following may not be in chronological order

Module Specifications

see https://sdiy.info/wiki/Kosmo for more info

Front Plate Dimensions

• 20cm height, variable width (KOSMO Format)
• aluminium front plates with ~1.5mm thickness (no 3D-Printing, it takes too long, is no fun and is not that stable)
• spray front panels black and use white edding and white sharp fineliner from the art shop to draw the ui

Power

• ±12V, +5V
• using official Eurorack 16Pin Plugs & Sockets with same pinout (CV & Gate pins are not used)

Signals

• Input impedance: 100k (0.1mA @ 10V)

• Output impedance: 1k (10mA @ 10V)

• Max. ±10V (~ ±5V for audio signals)

• 0V-10V for envelopes

• -10V-0V for inverted envelopes

• 1V/oct for Pitch/Freq. Control

• 0V or ~5V for Gate signals

Chapter 1: Buy buy buy

• E-Books from Make
• The Art of Electronics
• A lot of different parts from
  • Mouser, Reichelt
  • Aliexpress
  • Thomann
  • ElectricDruid (for old analog chips)

-> The first order cost me around 700 euros in sum, I felt reallly excited, but also under pressure, whether my plan goes well

Chapter 2: Build a prototype of a bipolar ±12V power supply

• used a lot of sources for designing the circuitry, especially the Make: Analog Synthesizers Book from Music from outer space
• Didn't want to use two 9V block batteries

How does it work?

1. A 14V AC voltage is fed into this power supply from an exteral transformer (from Roland, bought from Thomann)
2. A half bridge rectifier + 6x 4700uF capacitors are used to generate a bipolar, but unstable voltages (If I remember around 20V)
3. For +12V and +5V, step down converters are used (LM2596S) to avoid linear voltage regulators that heat up
4. For -12V, the L7912 linear voltage regulator is used, as I did not saw another easy way

Chapter 3: Play with circuits from Look Mum No Computer

• Built a simple VCO
• Built a simple VCF (voltage controlled filter)
• Made a lot of plans
  • chose Cosmo standard for dimensions and electronic properties of signals etc.
  • could not decide on whether the module height of 16cm or 20cm is better. 16cm seemed more handy, but 20cm are definitely a good decision! You have so much space and the synth takes in the room it deserves!

Chapter 4: Design first revision of VCO (and do first PCB designing experience)

1. Build and validate the circuitry found on the internet

2. Design first revision & meet with friend to solder it

• had some faults and wrong footprints, I wasn't happy
• also, the holes at the corners were a lot too small to mount it anywhere

3. Design & 3D-print the front panel (with a height of 16cm)

Chapter 5: Meet with friend to build the case

• Wooden box sprayed black
• 1m wide from the inside, 20cm deep, 20cm height from the inside
• materials bought from Bauhaus Germany, for around 55€
• used 2x Adam Hall 6161 as cheap rails

Chapter 6: Design proper PSU without the anxiety of shorts because of bad soldering

• similar circuitry like the prototype power supply
• but it has a lot of proper 16pin eurorack connectors
• and it has fuses, a prototype area and debug headers
• contains very ugly mistake: The main power PCB traces are a little thin

• Why not choose the RT65W? It got plenty of power! Because I heard it is noisy and the voltage rails have not equal power

• Why not choose prefabricated linear regulator power supply? (e.g. https://frequencycentral.co.uk/product/microbus/?attribute_pa_purchasing=pcbs-only) Because its a little expensive and I want the challenge

• Why not choose all in one power supply with easy DC wall wart? (e.g. https://www.mouser.de/ProductDetail/TDK-Lambda/CCG30-24-12D?qs=Cb2nCFKsA8qvzo4xGj%252BciQ%3D%3D) ...it is expensive

Next challenges:

• Make PCB trace width bigger
• Connect all Gate / CV Eurorack ports

Chapter 7: Build a CLI to search in my part inventory

• I ordered too many parts and unfortunately cannot remember all the component IDs! TL072 for my OpAmps is easy, but MCP3008 for an 8 channel ADC is not!
• you find it here: https://github.com/NEOZEO64/InventoryTool
• basically, it is only a json parser with some array filtering mechanics

Chapter 7: Build decoration module

• It really was necessary to put my nametag on the synth
• But with RGB leds!
• Used a Raspberry Pi Pico, powered by the 5V line on the eurorack plug
• Used WS2812B RGB leds
• Soldered a simple PCB and wrote a small MicroPython firmware for the Pico to control the LEDs (found at ./NEOZEO module/main.py)

Chapter 8: Hack AAAPPPCCC from Look Mum No Computer into my synth

(easy one-day project)

• measured dimensions
• designed some laser cutter guide
• laser cutted at the student research center
• sprayed black and drew fancy UI
• soldered on adapter connectors (fortunately the AAAPPPCCC module needs 12VDC for power that can be easily provided from the eurorack plugs, also the audio signal levels are fine)
• done

Chapter 9: Design proper working, functional VCO

Chapter 10: Design audio output module

• buffers synth audio signals and attenuates them significantly to line level and use NE5532 opamps for headphone output
• can switch between mono & stereo!

Chapter 11: Design some util modules

simple mixer (without voltage control of the volume)

• 4 sound inputs with potentiometers volume control
• 1 sound output
• not yet manufactured & built

simple math module

• Functions
• Invert sound
• remove offset voltage
• add offset
• attenuate / amplify (using potentiometer as control)
• not yet manufactured

Chapter 4: VCF (state variable)

• in heavy development
• First design on breadboard works, based on LM13700 Operational Transconductance Amplifier, but I want to make sure it workes in every situation and the output is in voltage bounds
• current challenge: Linear to exponential converter
  • if understood, the VCA module is also unlocked for design!
• automated the SPICE simulation with python to find variation of cutoff frequency due to input voltage changes

• trying to understand state variable filter from music from outer space:

Future chapters

• VCA
• Mixer
• Teensy 4.1 as digital signal processor for reverb / echo / delay / distortion / flanger / choir effects
• Splitter
• Clock & Clock divider (using 74HC Chips)
• ADSR!
• Sample & Hold
• Quantizer & Transposer
• Noise source & Random signal generator
• switch multiplex / MUX
• EQ
• Random
• Sample Player
• Sample Recorder
• Midi to CV