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Modular Synthesizer

This project began as my first foray into analog electronics at the end of high school, and I have been working on it ever since. Inspired by musicians like Klaus Schulze, Tangerine Dream, and Vangelis, I wanted to practice composing and performing music with the synthesizer. And seeing some impressive DIY projects online by Look Mum No Computer and others, I decided to go ahead and build my own analog system. DIY was also attractive to me because I had wanted to learn more about circuit design, and I thought I would get more out of a system I built up over time rather than paid lots of money for up front.

The system went through multiple iterations, the first of which being made of cardboard and breadboards:

Eventually, I started making PCBs for the breadboarded circuits and built a larger case:

Here is what the system looked like after making some more modules and a separate drum machine unit:

Second Synthesizer Iteration (Complete, Front)

Second Synthesizer Iteration (Complete, Back)

This iteration of the system was rather noisy due to poor PCB routing on some of the boards, poor power distribution (tiny power cables all connected thin PCB busbars), and a MIDI interface whose Rasperry Pi computer injected significant digital noise on the supply. The modules also took up a large amount of space in the case, so I couldn't expand the system without building another case. Over time, I redesigned all of the modules to be more compact and use separate signal and chassis grounds (avoiding ground loops in the current-carrying signal ground). I also built a new power supply and distribution system using 16 awg cables and thick aluminum busbars. This is the synthesizer in its current form:

Third Synthesizer Iteration (Complete, Front)

Third Synthesizer Iteration (Complete, Patched)

Third Synthesizer Iteration (Complete, Back)

Below is a list of the modules currently used in the synth:

Sources
- 7 voltage-controlled oscillators made using the AS3340 IC for stable tuning. May be used as either an audio-rate or low-frequency oscillator.
- 3 noise sources (BJT in avalanche mode).

Voltage-Controlled Filters
- 3 transistor ladder low-pass filters based on the filters used in many Moog instruments.
- 1 diode ladder low-pass filter based on the filter used in the TB-303.
- 2 state variable filters (high-pass, low-pass, band-pass) based on the filter used in the Oberheim SEM.

Voltage-Controlled Amplifiers
- 5 dual voltage-controlled amplifiers, each capable of voltage-controlled stereo panning.

Envelope Generators
- 6 ADSR envelope generators made using the 555 timer.
- 4 decay-only envelope generators (short attack time).

Audio Effects
- 4 soft-clipping distortion modules, which work by saturating the BJTs in a differential pair configuration. May be tuned to provide approximate triangle-to-sine waveshaping.
- PT2399 delay.
- Spring reverb.

Utilities
- 5 4-to-1 mixers.
- 4 1-to-4 active mults.
- 2 balanced outputs.

USB MIDI Interface
- Supports up to 8 channels of pitch/gate/velocity/CC outputs and has a built-in tuner.