The Substation Synth

The Substation Synth (aka Holy Hand Grenade Synth) is a Synthesizer created by SubStation6. It was made to be played as a descant instrument that can play along with any type of music.  Whatever accompaniment you have, the Substation Synth can play along with it and “Solo” over almost anything.

It began with a Jackson Model No. 657 Tube Tester  (circa 1942) purchased on ebay.  The unit was non-functioning and cheap (around $40) and the esthetic of these old tube testers –many designed in an art deco style was really beautiful.  Inspiration struck to create some kind of sound generating device that utilizes all of those lovely knobs and buttons.

I started by ripping out all of the old corroded electronics, salvaging what I could, and cleaning it up.

The first sound generating device assembled was an Atari Punk Console kit (3.0 Deluxe model).  The pots were broken out to either end of the tube tester along with 2 photoresistors and 2 toggles for switching between the knob or PRs.  This made it possible to use hand gestures to to tweak the sound instead of just twisting knobs.

Tube tester synth

The Atari Punk sound is pretty cheesy on it’s own and sounds like an 8-bit video game from the 80’s, but it really came alive when adding reverb to it.  In this case, a Strymon Blue Sky set on “plate” reverb with a long decay sounded amazing.

Building a New Synth

The Atari Punk was fun, but limited.  Wanting to build something more unique, I delved into the world of microcontrollers.  Having a degree in electronics, I was no stranger to the soldering iron or ohm’s law, but I had never used or programmed a microcontroller before. It was great to discover that the Arduino and IDE software uses C++ to program the chip –a programming language I was already familiar with. I also found a cool little tutorial on building the “Auduino” –A Lo-Fi granular synthesizer by Peter Knight at Several people have built this synth and a few even made videos teaching others how to build the synth. One of my favorites is Dave from

Tweaking the Synth

After I built the synth on a breadboard, I started playing around with the programming.  It was awesome that you could play a scale using a single knob, but it was only a Pentatonic scale. I imagined a synth that could play along to any piece of music based on the key and mode –I went to work programming. Unfortunately, I hit RAM limitations almost immediately. My code was too much for this little chip. I discovered how to make my code more efficient so it wouldn’t use up so much RAM, but I had to remove a few things.

  1. Remove one oscillator and one filter.
  2. Eliminate any global variables that can be specified directly (using less RAM).
  3. Delete any unused code (i.e. support for other devices, etc.)

Removing one of the oscillators wasn’t a tough decision as both oscillators sounded exactly the same and didn’t really add much to the overall sound, so I nixed it.

In short, I was very happy with the new and improved synth.  I had a lot of fun playing along to other pieces of music, but I kept wondering how it could be improved.

The Happy (and intentional) Mistake

One day, I decided to save a copy of the code and make this my new playground.  The intention was to see if I could really fuck it up.  So, I started adding more knobs and had those knobs effect other knobs in a mathematical way.  For example: the value of Knob A + 100 – value of Knob B divided by the value of Knob C.  This made for some unpredictable behavior, but the real epiphany happened when I started messing around with time.

I discovered that if I created a counter during the main loop of the program, I could pay different notes based on what count it is.  Once the count gets to a certain number, I can have it reset and repeat.  Voila!  I just created a sequencer.  I then created a delay (between each beat) that took it’s value from a another potentiometer.  Now I have a tempo knob.  And this was only the beginning of my discoveries and tweaks.

29 versions and 1250 lines of code later and I have a pretty remarkable little synth.  I installed the synth into the tube tester and then later into an old capacitance decade enclosure.  I called it the “Holy Hand Grenade Synth“.

The Substation Synth Enclosure

Mini CNCAfter a while, I thought about the next stage of the HHGS.  It definitely needed a nicer interface and a custom enclosure worthy of it’s glory.  The problem was that I needed some way to cut perfect squares/rectangles into the aluminum plate (for the .96″ oLED display).  I came up with a bunch of options, but settled on a small Chinese “mini CNC machine”.  I figured if I ever wanted to mass produce the plates I would use a manufacturer to do it for me, but for these small runs, the CNC machine would be a great tool for prototyping.  That and a 3D printer, but the cost for a 3D printer far outweighs it’s value in creating small plastic thingys.

Next, I needed a cool design for the faceplates.  I knew I could screen print something onto the surface or do a metal etch which would be super cool.  But, at least initially, I wanted something fairly easy to do.  I settled on doing a simple photo transfer using a technique I found online by the “Crafsman“.  Not only are his tutorials funny, but the technique actually works pretty well for a prototype without investing too much time or money.

At this point a decided to rename the project.  The Holy Hand Grenade Synth sounded cool, but I didn’t something shorter and more concise, so I opted for the “Substation Synth”.  It’s sort of a play on words with “SubStation Six”.

Behold the Substation Synth Faceplate

Faceplate Design Substation Synth

Faceplate Design Substation Synth


The Wooden Box

Wooden Box Enclosure

These boxes were designed by me, but built by my friend and master carpenter Andy (aka GHOST).  He did a fantastic job.  He built two small boxes and two larger boxes (for the next version of the synth).  The idea is that the front panel would be sloped for effortless, table-top knob tweaking. The photos were taken just before he cut the diagonal slope.

A Quick Mock-up

mock-up of substation synth

Assembling the Components

Assembling the Components - Substation Synth

I decided on a dark stain for the boxes, but still allowing the wood grain to show.  First the pots, rotary encoder and oled were installed.  Then the circuit board and microcontroller were installed on top (mounted using the two brackets on the sides).

Assembling the components - microcontroller

The Substation Synth Foot Pedal

DF2210 Wah Pedal Conversion

Knowing how a basic wah or volume pedal works, I thought it would be cool to control the pitch of the synth (“scale” knob) using my foot so that I could play another instrument for accompaniment. For example, I could be playing rhythm on guitar and soloing with my foot on the synth.  It took a while to figure out how to bypass the potentiometer in the synth with the pot in the foot pedal.  I finally discovered switchable input jacks!

The wah pedal itself is dead simple.  I removed all the electronics on the inside and replaced the pot with a matching value one from the synth (5k ohm linear).  I removed the two 1/4″ mono input jacks and added a single 1/4″ stereo input jack.  Wired the input jack directly to the pot using the ground wire for the external shield pin.  For the synth, I added a Switchcraft 114BX 1/4″ TRS-F Double Closed Circuit Connector.  This stereo 1/4″ input jack has two switches that activate when a plug is inserted/removed from the jack.  See schematic below for how it works within the synth and foot pedal.  Now, when I plug a stereo cable from the synth to the pedal, it bypasses the synth pot and uses the foot pedal pot instead.  Brilliant.

Wah Pedal Conversion

Expression Pedal Plug and Schematic - Substation Synth

Substation Synth - Rear Plate

Watch video of foot pedal