If you’re using multiple hardware tempo aware devices that need clocking or a hybrid computer and hardware set up you’ve likely heard of Circuit Happy. Makers of the ‘Missing Link’ clock device. I put our 20 Questions interview series to Ed & Matt and as with all the interviews its a pleasure to learn more about them and share this with you.
01 How would you introduce yourself to someone who has no idea who you are and no idea of the modular, synth, & music tech spaces?
We are Ed Guild and Matthew Campbell, co-owners of Circuit Happy. Circuit Happy is based just outside of Boston, Massachusetts. We make electronic music hardware to make it easier for musicians to record their synthesizers and drum machines into their computers. Ed founded Circuit Happy back in 2018. Matt joined in 2025 as a partner to help Ed see through some of his bigger ideas and help Circuit Happy grow so we could make more cool stuff. Ed focuses on designing the products, supporting the customers, and marketing/sales efforts. Matt heads up engineering of the hardware and firmware. He also handles our accounting. Basically, if it’s got numbers, Matt handles it!
02 How would you introduce yourself to someone who is aware of modular, synth & music tech worlds?
Circuit Happy makes a family of clock generators collectively called The Missing Link. The Missing Link makes it easier to sync up your modular synths, drum machines, and groove boxes to your DAW using WiFi and the Ableton Link protocol. It is also a great way to share sync with other musicians in a group jam. Ableton Link is a unique way to synchronize. Everyone in the Link session on the WiFi network shares a common tempo and timeline grid. Anyone can alter the tempo and all the other Link devices update instantly. No one is the master clock. We like to call it a communal clock where everyone has a say. The Missing Link was born out of a desire to bring Ableton Link to Eurorack and desktop hardware such as drum machines and samplers that do not have any way to communicate with Ableton Link. The Missing Link takes the Ableton Link protocol and translates it into CV clock or MIDI clock signals that these devices understand.
Currently there are two devices in The Missing Link family (with a third on the way): The Missing Link Junior and ML:2m. They both offer CV and MIDI clock outputs in two device formats.
The Missing Link Junior is a device that sits on your desktop and has a screen to display the tempo.
ML:2m is a Eurorack module that is only 2 HP wide.
Circuit Happy really is a story of collaboration, not just one person doing everything on their own. Although at times Circuit Happy has been just Ed on his own, he was never really alone thanks to a little help from his friends.
Ed: Long before Circuit Happy, I was in a band for ten years where I played a laptop doing audio and video sampling live alongside a drummer, bassist, and a synth player. In 2013 I changed careers from book publishing and found myself working at the award-winning music software company, iZotope. I was hired as a Quality Assurance engineer. I worked on some really cool products such as BreakTweaker, Iris 2, RX, and VocalSynth. In my early days at iZotope I got to wear many hats doing QA, sound design, preset making, building prototypes in Max/MSP, and designing and writing the user documentation. I met so many like-minded people with the same passion for sound and music.
While I was at iZotope we started a new department to build a hardware recording device called Spire Studio. I referred my friend Matt Campbell to an open position for a hardware engineer in that department.
Matt: I’m an electrical and firmware engineer by trade, but really I just love to create. My toolkit keeps growing: wood, stone, circuits, 3D printing, lasers, a home pick-and-place machine, and whatever comes next. I tend to follow a problem wherever it goes, which for me means the whole stack, from the circuit board and firmware up through Linux and into the cloud backend. I like understanding how the entire thing fits together. Across my career I’ve worked on hardware, firmware, and DSP for a range of products including the iZotope Spire Studio, medical devices, industrial 3D printers, and even radar systems. Outside of Circuit Happy, I run an independent consulting practice out of my home lab to keep the lights on.
I also play music casually, mostly guitar and piano, with synths as a current “work in progress”. Most days you’ll find me on this couch coding or designing my next build, with my dog Bongo parked at my feet.
Ed: Another co-worker at iZotope, Nick Donaldson, was also working on the Spire team developing a mobile app that paired with the hardware. Nick and I both left iZotope around the same time in 2016: Nick for a new job and I for a newborn son. I had hit a wall at iZotope. I was in Quality Assurance and was trying to make moves into Product Design but wasn’t getting any headway.
So when our first son was born I talked to my wife Christina about taking some time off to look after our son and figure out the next career move. A couple months after leaving iZotope I ran into Nick Donaldson at a friend’s barbecue and we hatched a plan to build a little prototype of an idea for an Ableton Link clock. Nick wrote the software to run on a Raspberry Pi and I designed an enclosure and a custom PCB for our user interface.
Nick and I took early prototypes such as the one pictured below to local synth meetups and then to Knobcon in Chicago. We met lots of cool people along the way and got some good feedback.
Originally we were making it for personal use. Nick wanted it for his Eurorack system and I was going to use it as a portfolio piece to show in job interviews for some future employer. I was also curious to learn more about Eurorack modular synths. While I was making the original prototypes I asked Nick, “Why don’t we make like 20 or 30 of these and try to sell them?”
Nick thought it was a good idea, but his new job did not allow him any time to focus on a side hustle. He gave me the code he had written and blessed me as a C++ developer. I paid him for his work with an Intellijel Plonk module and Arturia Pigments synth plugin.
I finished the C++ application code with many messages to Nick asking for help to figure out why my code would not compile. My brother-in-law, Karl, is a Unix ninja. He helped me create some Bash scripts that ran on the Raspberry Pi OS to aid with WiFi management and Over-The-Air system updates. And on my own I managed to figure out how to build a web app for the user to configure the WiFi and run firmware updates.
A friend of mine, Mike Kessman, I met in the local music scene in Boston. He is a talented screen printer. Mike printed the original product boxes and the white ink on the faceplate.
He also printed our smiley t-shirts, seen here modeled by Ed:
In 2018 I took the original Missing Link Desktop to Knobcon for its debut.
In 2020 I reached out to my friend Matt Campbell to see if he could help me make a better PCB design for my second product, a Eurorack version of The Missing Link. He did some amazing work for free to help me out.
In 2022 my friend Nick Donaldson quit his job and started doing independent contract work. I hired him for a few months’ contract to help me rebuild the Missing Link firmware from the ground up for our next product, The Missing Link Junior.
The Missing Link Junior replaced The Missing Link Desktop as our smaller, sleeker desktop offering
In 2024 I met Matthew Hodson, aka MATTHS, at Machina Bristronica. He came by the booth to thank me for making ML:2 as he found it so useful for recording in his studio.
I was familiar with some of his videos he had produced and asked him if he might want to work on some videos for me. This past year he has been working hard for Circuit Happy a few days a month to help us build a better social media presence.
And finally, in 2025 Matt Campbell, now also out on his own as an independent contractor, joined Circuit Happy as a 50/50 joint owner. Together we are trying to build the company up and make this our main income source.
03 What were your early influences for getting into what you do now?
Ed: My dad put a soldering iron into my hands when I was 11 or 12 so I could repair my RC cars. He was an electrical engineer. That’s where my interest in electronics started. But by high school I fell in love with the graphic arts and my professional focus diverted to ink on paper for 20 years. In college I dabbled in playing bass guitar and making music mixes with SoundEdit 16 and a CD burner. My first job out of college in the year 2000 was a startup that lost its funding a year after I joined. My severance included my G4 Macintosh computer and the company’s video projector (a whopping 640×480 resolution!). I used the projector and computer in a band I had recently joined as a Video Jockey. I projected improvised video effects while the band played improvised electronic dance music. The band was called Psylab. We played shows around the USA for about ten years. There’s still some video evidence of us on Youtube.
My decade in Psylab was highly influential to my development as a product designer. I was given lots of leeway in the group to experiment and try things out. I developed a drum sampler in Max/MSP for our drummer to play through. I also met lots of creative people in the scene who encouraged me to to dabble in hardware with Arduino development boards and LEDs.
We also played some cool parties like this regional Burning Man party deep in the Vermont woods. One year someone approached us as we were setting up to play and said, “Hey, I have this MIDI-controlled flame thrower. Can you send us some MIDI from the drums to trigger the flames?” 10 minutes later I had modified the Max patch to route and map MIDI to the notes the flamethrower needed. A video we posted made the rounds on a few blogs and was one of our more popular videos.
My time at the music software company iZotope was also extremely influential. I met so many smart and talented people there. One of my coworkers started building Eurorack modules on the side. I designed his logo for his module company in an effort to be involved with what he was doing. Seeing him do this made me realize that I needed to make my own products one day.
04 What was the first thing you created either as Circuit Happy or something for yourself?
Ed: I would say the first thing I created was “DrumLab.” This was the drum sampler software I created in Max for the drummer in our band. Our drummer, Steve, played a Roland V-Drum kit that had a drum brain with preset sounds. You couldn’t load in your own sounds. A friend encouraged me to check out Max so we could expand our sound palette. I built the first version of DrumLab in a late-night session but it took about 6 months for it to come together. Eventually we had a sampler that the drummer could load different kits via the program change buttons on his drum kit. So Steve could see them from far away, the drum kit name and the calculated BPM were displayed in large type. He liked seeing the BPM so he could know if he was drifting too far in tempo. He did not like playing to a click. The best moment was when I loaded up a new kit made up of slices of Led Zeppelin’s ‘When the Levee Breaks’ intro drum break. The smile on Steve’s face as he was playing the sounds from his favorite drummer, John Bonham was priceless.
DrumLab let me control the timbre of the drums as our drummer played the sounds. I could alter the pitch, low pass filter the drums, add delay and reverb, and send some of the drums to a Korg Kaoss Pad for more audio destruction. We could also repitch the drums to a sequence of notes so each hit of a drum pad could progress through a sequence of notes.
Here’s a screen capture video I made back in the day (sorry about that watermark on there!) to demonstrate the pitch sequencing:
Steve and I became a single unit performing the drums together. He and I could anticipate what we were going to do next and flow together as one.
Here’s a video of our first time using DrumLab live. Steve was playing a sliced up Amen Break and I’m the dude behind the laptop layering in some vocal samples and adding effects to the drums here and there.
Here’s Steve and I on stage with Psylab playing a rave
Here we are on a local cable access TV show:
And if that’s not enough noise for you, here’s an audio recording from a synth fest we played long before I was even thinking about making my own hardware: https://soundcloud.com/vizzie/drumlab-electro-music-2011
05 What was the first product you brought to market and how was that received?
Ed: The first product I brought to market was The Missing Link Desktop. I designed the look of the enclosure to amuse myself, housed in a mirror finish acrylic plastic box with lots of LEDs shining through etched portions of the mirror finish. A clock generator is usually in a mundane black box. I wanted to make mine look like it could be used as a sci-fi movie prop.
I was a bit of an outsider to the synth community when I first started Circuit Happy. I mostly had been in software with a bit of outboard gear. I did not know my way around a modular synth. I had to learn about clocking standards on the fly as I started demonstrating The Missing Link. On the inside, I was suffering from Imposter Syndrome, but I kept it together during my video interviews.
The Missing Link Desktop was met with a positive response. A lot of people were excited to see an Ableton Link clock so they could more easily sync up Ableton Live to their synths. It’s always great to see someone’s face light up when they realize what it does. At Knobcon I sold my first five units I had with me. SonicState was there covering Knobcon and they shot a video of my product demo.
That video really put me on the map along with a few other youtubers there. My Circuit Happy site went from 10 visitors to 900 visitors overnight. This led to some brisk sales for a few months and lots of feedback and feature requests.
A few months later in December I received an email from Schneidersladen asking if they could buy some to sell in their shop. That’s when I said to myself, “OK, I think I need to keep doing this.”
06 How did making that first product influence the next one? Any lessons learned to pass onto others?
In 2019 I took the Circuit Happy tradeshow booth to Superbooth in Berlin. At the show I kept getting requests for a Eurorack version of The Missing Link. So it was pretty clear what I needed to build next… I started working on a 2 HP Eurorack version. I chose 2 HP as both a design challenge, but also figured most people have a favorite clock in their case so I should make something that can squeeze in next to the main clock to sync that clock.
An early prototype of ML:2 in my little custom development rack. Pamela’s New Workout was a constant companion for testing as there is a handy message that lets you know if the clock is unstable.
Adapting my first product to Eurorack proved to be quite challenging. I had to move from the Raspberry Pi platform to an ESP32 embedded system that could boot faster and not use as much power. The circuit design pushed me further than my rudimentary skills in electrical engineering allowed. My friend Matt Cambpell lent a hand and took over the design of the Eurorack PCB design in his free time.
In April 2021 my second product was released, ML:2.
The biggest lesson I’ve learned in releasing products is to listen to customers with an open heart and mind. One of my best skills I’ve developed is being able to listen to people and gracefully receive their feedback, either positive or negative, and file it away in my brain. I then take notes of anything I think I should act on. You don’t have to do everything your customers ask for, but my products wouldn’t be as well-rounded if it wasn’t for the valuable feedback I’ve received.
07 Would you say you make things for yourself? How much community influence comes into play with new ideas?
I originally approached making The Missing Link from a funny perspective. I wasn’t looking to solve sync issues for my own studio. My friend Nick wanted this device so he could sync up Bitwig Studio to his Eurorack. I just wanted to make a fun design that I could show in job interviews. But pretty quickly I got into modular synths and making music with more hardware. I especially love being able to easily sync up my setup with my music making friends. I just give them a Missing Link Junior to clock their setup and thanks to Ableton Link they are synced up with my setup that also has an ML:2m and Missing Link Junior. And if we want to record anything, it drops right on to the grid in Ableton Live.
Here I am at a gig with a DJ friend of mine adding in some synth squiggles to his tech house sounds. He DJs with Rekordbox, which has Ableton Link. I can drop in extra synth bits in time and on time with his beats.
My favorite part of doing this is talking to all our customers and people who are interested in our products. I depend on their feedback to make better products. I hear from people all around the world and get to learn their unique music-making setups. At the end of the day, what I hope you see from us are useful and simple-to-use, but funky-looking devices that help you get jamming quickly.
08 How do you decide on the value ranges for the controls or CV inputs on your modules?
So far my devices have only utilized buttons and endless encoders so I haven’t had to deal with setting many value ranges… until I made this creative clocking mode.
A conversation with Matt Hodson about making a broken clock mode inspired a new mode called Rhythm Explorer. You could purposely add dropped clocks and jitter to the clock output. The Jitter slider did take a lot of tuning to get it to go from subtle jitter to straight up chaos. I had to do a lot of under the hood range setting so the lower range of the slider was subtle movement of the clock pulses, the middle range was more jittery, but not too jittery, and then the last 10% of the slider took things to chaos. Getting this slider to work how I thought it should took a lot of listening and experimenting. I had to try clocking off various bits of gear to see how useful the jitter was at various settings. So it wasn’t a lot of scientific analysis and more just my ear and own musical taste.
09 Generally speaking, what do your products offer that others don’t?
The main thing that separates our clocks from other clock generators is the tight integration with Ableton Link. As far as I know we are the only clock generator with Ableton Link. Our products are also the only way to get my friendly technical support and Matt’s high quality technical designs 🙂
10 What are some of the challenges in manufacturing, any tips to share?
Ed: I hand assembled all the original Missing Link Desktops. My biggest challenge was keeping all the parts I needed in inventory so I could build them when I needed more. I had a spreadsheet for tracking all the parts but it was not a great system. I always forget to order something from Digikey or Mouser. Inventory tracking is so important if you build in-house as we do.
Now we build in-house with a Lumen Pick and Place from Opulo and a DIY reflow oven. We currently have two products with another on the way. It’s become even more important now to have good inventory tracking. We use Inventree for tracking our parts.
Now our biggest challenge is related to tracking inventory over the fiscal year so at the end of the year we can correctly deduct what has been used in sold goods versus what is still unused inventory versus what was used for prototypes. Taxes are so complicated. Thankfully Matt enjoys hacking together numbers and the challenge of figuring out how to make all these systems work for us.
11 How do classic instruments and designs influence your own work?
Ed: I’m more often referencing present-day designs from other companies. But I do love the future/retro design language of the 90s. Things like the Korg Electribe are so fun. I’m a big fan of the LED segmented display. I am holding out on using an OLED display until I deem it is absolutely necessary.
12 Do you find inspiration in areas outside of the one you work within?
Ed: Absolutely. I love sacred geometry and am fascinated by nature and the numbers that can define it. Both Matt and I love fractals.
The LED-lit rings around the knob of the original Missing Link Desktop is based on the Flower of Life symbol.
13 What would you do if you weren’t designing and making gear?
Ed: I love being on the water fishing in my free time. Perhaps I’d make my own line of fishing lures or rubber worms?
Matt: Honestly, pretty much what I’m already doing. About three years ago I left full-time employment for independent contract and consulting work, and I’ve never looked back. Getting to work with early startups and help bring genuinely new ideas into the world is a treat, and it leaves me enough room to chase an ever-growing stack of personal projects, Circuit Happy among them. So if I weren’t making gear, I’d probably just be making something else. It’s hard to imagine life getting much better than this, and I try to remember to be thankful for it every day.
14 Whose equipment besides your own inspires you and why?
If I’m stuck on a design decision I will often refer to the other manufacturers out there to see what they did in their products. Sometimes I even reach out and ask them questions directly. Everyone is so friendly in this business and generally happy to share their knowledge. I love 1010 Music, Future Sound Systems, ALM Busy Circuits, Erica Synths, Shakmat, Noise Engineering, Elektron, Korg, and Roland… the list goes on and on from there.
15 What was the last product you created?
Well, we are in the process of creating a new product right now, arriving this Fall. But the last product we released was ML:2m in September of 2024. The original version of our 2 HP eurorack module, ML:2, had a fragile connection between the two PCBs that made up the module. We originally planned on just doing a quiet fix to make a more robust connection between the two PCBs.
The new PCB interconnect is far more robust with two tongues that slot into the UI PCB from the CPU PCB. There are pads that have to be hand-soldered, but this connection is solid. You can throw it across a room (I did it so you don’t have to).
During this time I happened to get a customer email requesting a way to output MIDI from ML:2’s output jacks. Unfortunately there was no way to do that with ML:2. I asked Matt if he thought we could switch to 3.5 mm TRS ports instead of the usual TS ports used in Eurorack. Then we could add some software switching to turn one of the ports into a MIDI out port. This request from a customer turned into a revised module that had so much more functionality. We had to give it a new name to celebrate its new MIDI capabilities: ML:2m
16 Rather than ask “what’s next?” Where is your current inspiration and thinking for your future?
Ed: Our work with The Missing Link is not quite finished. There’s still a number of things our customers want that I wish to integrate into our products. I have a vision for a larger Missing Link device for the studio that will be more of a central hub of all things sync. I want to move beyond just being an Ableton Link clock. I’d like to add more sync sources that can be intertwined.
After that I really want to build some more creative devices. There’s a sequencer inside me that needs to get out. Naturally, the sequencer will be supporting Ableton Link 🙂
17 What’s a piece of music you’d like us to check out?
Ed: Geez, that’s a tough one. I love any album that flows together and takes you into a sonic realm, like Boards of Canada’s albums. One album that I discovered about ten years after it was released was Darkside ‘Psychic’. I have listened to this album countless times to make for the missed decade it wasn’t in my life. Another one that came out more recently is Djrum ‘Under Tangled Silence’. Talk about a sonic journey! A good set of headphones or speakers and some mindful listening really lets this album shine. Another group that I’ve been enjoying lately is Two Shell. They make some weirdo club music that is both retro and futuristic. It feels like music that would be played at the clubs in the world of the video game ‘Portal’.
You could also check out the EP I made with a friend a few years ago: https://thetransparency.bandcamp.com/album/it-might-get-dark
18 What is something unrelated you’d like to mention for people to check out or be aware of?
Ed: I am currently on holiday on the island of Sicily, Italy, while answering these questions, so Sicily is top of mind. There are many amazing beaches hidden around the island. And the layers and depth of archeological history here is astounding. You can snorkel next to ancient Greek ruins. Hit me up if you need any recommendations for places to get granita, gelato, or other treats.
19 What’s a question you wish I had asked?
What rituals or activities are important to the operation of your company?
Our answer: During the warmer months we make it a requirement to have some meetings on the water in either Matt’s canoe or rented kayaks. Fishing poles are generally present, too.
20 To end the questions here’s one from the previous guest –
Ale from Bartola Instruments asks – “Has a module ever done something you didn’t design it to do — and did you fight it or follow it?”
Ed: When developing ML:2 the clock output had some bugs that caused random clock drops or unexpected clock behavior.
Why is that clock pulse missing?
Some of the clock glitches were cool, but I needed to make a stable clock! We worked hard to have a super-stable clock, even if you change the clock from 60 BPM to 190 BPM, it does not drop a clock.
Later on, I had a conversation with Matt Hodson about ways to purposely make unstable clock output for creative purposes. Those observations from ML:2’s development came back and helped inform the features of the Rhythm Explorer mode.
So to answer your question, Ale, I both fought it and later followed it 🙂
and what’s a question you’d like me to ask the next guest?
In the early days of demonstrating The Missing Link I had bouts of “Imposter Syndrome.” It took me a few years really to get over it. Have you ever had this feeling during your time running your business? What has helped you remedy the feeling?
Thanks to Ed and Matt for taking the time to answer our 20 Questions interview. It’s a pleasure to learn more about the people behind the gear and share these stories. Who would you like to see in a future interview? Let us know!
