Marcus Dunn aka lonesoulsurfer DIY Modules

video uploads by Marcus Dunn

Playlist:

1. 7 Channel Mixer For My Modular Synth.
2. Medusa - Sound Effects for Modular Synths
3. Buffered Multi for Modular Synths. Powered by Arduino
4. Digital Delay Module - Powered by Arduino
5. Bleep - Modular Drum Synth - powered by Arduino
6. Solar - A Modular Synth, Powered by Arduino
7. Groove Box Modular Synth - Arduino Nano
8. Freaq FM Synth. My Take on the Awesome MeeBleeps Synth
9. Mutant Generative Synth - Powered by Arduino

Additional details on each:

1. 7 Channel Mixer For My Modular Synth.

GitHub - https://github.com/lonesoulsurfer/7_C...
GitHub Page - https://github.com/lonesoulsurfer?tab...
Instructables - TBA

Quick vid of my 7 channel mixer in action. This is based on Syntherjacks awesome little 4sum mixer which you can find a link below to. My modular synth runs off 9/5V so this amp works perfectly for what I need. You could also power it via traditional Eurorack sty;e powering, you would just have to add a step down converter from the mixer to the 12V power source.

I have also included a Eurorack 4 channel version as well which will fit perfectly into any Eurorack.

https://syntherjack.net/portable-audi...

7 Channel Mixer - Circuit Explanation

This is a passive-input, op-amp buffered audio mixer built around an NE5532N dual op-amp.

Here's how it works from input to output:

Input Stage (7 Channels)
Each of the 7 channels (IN_1 through IN_7) follows the same structure. A 3-pin connector feeds into a 100K potentiometer (VOL_1 through VOL_7) which acts as the individual channel volume control. The wiper of each pot connects through a 47K resistor to a common summing node. The 47K resistors serve as summing/isolation resistors — they prevent channels from loading each other and set the gain relationship between channels.

Summing & First Op-Amp Stage (IC1A)
All 7 channel signals meet at the summing node, which connects through a 10µF coupling capacitor (blocking any DC offset) into the non-inverting (+) input of IC1A (the first half of the NE5532N). IC1A is configured as a unity-gain buffer with a 47K feedback resistor, providing a low-impedance version of the mixed signal. VREF is applied to bias the op-amp at the virtual mid-rail since this is a single-supply design.

Second Op-Amp Stage (IC1B) + Master Level
The output of IC1A feeds into IC1B (the second half of the NE5532N). A 100K master LEVEL potentiometer in the feedback path of IC1B controls the overall output gain/volume. This gives you master level control over the entire mix.

Output Stage
The output of IC1B passes through another 10µF coupling capacitor (again blocking DC) into an output volume pot and then to the OUT_1 connector.

Power Supply
The circuit runs off a single +9V supply (PWR_9V connector). A BAT43 Schottky diode provides reverse polarity protection. Two 100µF filter capacitors smooth the supply rail. A resistor divider made of two 47K resistors creates a VREF mid-rail reference (~4.5V), which biases the op-amp stages so they can handle AC audio signals on a single supply. A LED with current-limiting resistor provides a power indicator.

2. Medusa - Sound Effects for Modular Synths

This is my sound effects synth in a modular format.
It runs off a Raspberry Pi Pico and I used Arduino IDE and C++ to code everything up. I also used Claude AI to help finesse the code and get me out of binds!

GitHub
https://github.com/lonesoulsurfer/Med...

Instructables - Step by Step Guide
https://www.instructables.com/Medusa-...

Ok - so what does it do? Here is a rundown of what the synth is capable of. Note that I still have some additional features to add. and there are other features i didn't have the room to add!

Instruments:
DUB SIREN - Classic reggae/dub sounds with 6 modes
RAY GUN - Sci-fi laser effects with 4 sound modes
LEAD SYNTH - Generative sequencer with 4 pattern modes
DISCO - 6 classic disco sound effects (orchestra hits, string sweeps, etc.)

These can all be played via the hardware interface:
4 Potentiometers - pitch, speed, modulation, and echo. However, they will change depending on what instrument or function you are using!
8-Key Keyboard
Multiple Buttons - Mode switching, gate control, delay cycling, mutation
mutation allows you to play around with the generative sequencer and musical scales when a sync in is active. - very fun!
Sync Input - trigger input
Real-time waveform visualization

Functions - I have currently 5 functions included with 3 more to come
SEQUENCER MODE (Function + Key 1) - 8-step programmable sequencer with per-step pitch control and enable/disable
LOOP PATTERNS (Function + Key 2) - 7 rhythmic gate patterns (swing, staccato, ratchet, etc.)
RECORD MODE (Function + Key 3) - Record up to 5 seconds of audio with loop playback
REVERSE MODE (Function + Key 4) - Reverse delay with pitch shifting (-2 to +2 octaves)
INFINITE HOLD (Function + Key 5) - Infinite sustain via 100% feedback (this is delay on forever!)

3. Buffered Multi for Modular Synths. Powered by Arduino

You can download the GitHub files here to build your own
https://github.com/lonesoulsurfer/Syn...

Step by Step Guide
TBA

What is it?
It's a buffered multiple that takes one sync input signal and produces six individually configurable outputs

FEATURES
Shows current BPM on OLED display
Each output can be configured with:
Normal sync (1:1)
Clock division (1/2, 1/4, 1/8)
Three groove patterns:
GS: Swing (delays off-beats by fixed amount)
GF: Shuffle (creates triplet-based rhythm)
GH: Humanize (adds random timing variations)

Groove Implementation

Swing (GS) = consistent delayed off-beats
Delays off-beats by shifting timing up to 66% through beat
Very classic swing feel at 50-75% intensities
Clean implementation with consistent timing

Shuffle (GF) = polyrhythmic feel with specific timing ratios
Creates 2-against-3 feel using weighted offset timing
Distinct from swing - pushes toward triplet territory
At 75%, approaches dotted 8th feeling (funkier)

Humanize (GH) = unpredictable variations
Adds random timing variation around off-beats
Much stronger randomization (up to 40% of beat)
More chaotic/organic feel compared to others

Each mode serves a distinct musical purpose, and the intensity levels (50%/75%) allow meaningful adjustment.
The two intensity levels (50% and 75%) offer enough adjustability without overcomplicating the interface. This gives users six distinct groove feels to choose from (three types × two intensities), w

4. Digital Delay Module - Powered by Arduino

This little digital delay is a gem! It's a stripped back version of the EchoTrek digital delay (see link below to the original build).

The delay has 6 selectable delay times (63 to 300ms) and a reverse option. I had to make some changes to get it to work on my modular synth which included increasing some cap values. I also added a switch to make the delay more subtler.

It's a super simple build and will transform the sound of your synth!

Echotrek (original Build)
https://projecthub.arduino.cc/CesarSo...

Github (all the files you need to build your own)
https://github.com/lonesoulsurfer/Del...

Instructables Step by step guide
https://www.instructables.com/Echo-De...

5. Bleep - Modular Drum Synth - powered by Arduino

This is the latest modular synth that I have put together. The synth is a copy of Bleep Labs Bleep Drum. I've created a custom PCB and front panel in a Eurorack format. It can also be played as a stand alone synth.

The heart of the build is an Arduino Nano.

All of the files required to build y0ur own can be found in my GitHub page. I''ve also published a step by step guide on Instructables - see links below

GitHub Files
https://github.com/lonesoulsurfer/Ble...

Instructables
https://www.instructables.com/Bleep-D...

Bleep Labs - Bleep Drum
https://bleeplabs.com/product/bleep-d...

6. Solar - A Modular Synth, Powered by Arduino

This is the latest modular synth that I have put together. The synth is a copy of Bleep Labs awesome Nebluophone. I added a couple sync in's, more LED's (because there is never enough LED's!), added cherry MX keys and created a front panel in a Eurorack format. It can also be played as a stand alone synth.

The heart of the build is an Arduino Nano.

All of the files required to build y0ur own can be found in my GitHub page. I''ve also published a step by step guide on Instructables - see links below

GitHub Files
https://github.com/lonesoulsurfer/Sol...

Instructables
https://www.instructables.com/Solar-A...

Bleep Labs Nebluophone
https://bleeplabs.com/product/nebulop...

7. Groove Box Modular Synth - Arduino Nano

An Arduino Nano based drum machine based on the awesome DrumKid build (https://github.com/mattybrad/drumkid) by Matt Bradshaw. My version includes 3 X trigger outputs so you can sync with other synths. I've also designed it so it will fit into any Eurorack and can be powered by either a standard 16 pin Eurorack power input or a 9V JST connector.

All of the information need to build your own can be found on mu GitHub Page
https://github.com/lonesoulsurfer/Gro...

You can find a step by step guide on my Instructables page on how to build your own - TBA

The main goal with building this module is to create my own 'simple to build' modular synth. I wanted to keep everything as easy as possble with each module built with the following aims:

Can be powered by 9V (and 12V)
Easy to build with minimum components
Use Arduino to keep it simple (plus it helps to keep the components down and everything in tune)
Can fit into any modular synth Eurorck (include the ability to power the module via normal module power sources)
Has to sound great!
Lastly, it should be portable and run off batteries

If you have any ideas on what modules I shuld build next then let me know in the comments. Remember - 9 to 12V so no negative voltages

Instructables step by step guide
https://www.instructables.com/Groove-...

GitHub
https://github.com/lonesoulsurfer/Gro...

8. Freaq FM Synth. My Take on the Awesome MeeBleeps Synth

This is my take on the awesome MeeBleeps Freaq Synth. I've developed my own PCB and front panel which is in a Eurorack form factor.
You can find all the files to build your own in my Google Drive below.
It's a blast to play and I have plans to add this to my own eurorack with a few other modules that anyone can make and play. Stay tuned...

GitHub Files
https://github.com/lonesoulsurfer/Fre...

MeeBleeps original Github Files
https://github.com/Meebleeps/MeeBleep...

Instructable
https://www.instructables.com/Freaq-F...

9. Mutant Generative Synth - Powered by Arduino

This is my version of the awesome 'MeeBleeps' Mutant Generative Synth. You can find the original Github files below:
https://github.com/Meebleeps/MeeBleep...

I have created a custom PCB and front panel with a Eurorack form factor in case any wants to include it in their modular set-up.
The overall build is pretty simple as there are really only a handful of components. However, the current version of Mozzi causes issues when compiling the sketch to IDE. You have to use an order version (1.1.2) when uploading it.

All this is explained in my step by step guide on Instructable so if you want to build your own then check out the link below:

The gerber files, parts list, Eagle files (schematic and board design) can be found in my GitHub Page
https://github.com/lonesoulsurfer/Mut...

Any questions please don't hesitate to reach out.