The Expanse: Behind the Back Plate

Step by step walkthrough of how The Expanse harmonic tremolo is built

Sep 19, 2022

This is a picture tour of what’s inside The Expanse and how it comes together. I had to cut out many pics due to size limits on these articles, so let me know in the comments or by replying if there’s anything I glossed over that you’d like to see in greater detail.

The Expanse has 3 PCBs (printed circuit boards):

Controller board - does the switching, “listens” for taps or long-presses on the foot switch and toggles the effect
Main board - does the audio effects
Jack board - input, output, and two expression jacks

Controller Board

The fabricator who creates these PCBs also does assembly for most of the parts, using pick-and-place machines. There are a few parts they don’t have on hand and with the relatively small quantities I produce, it makes more sense to simply source those parts and solder them on in house.

There has been an ongoing digital microcontroller shortage for a couple years now, and you basically have to take whatever you can find at any given time. So this board is a modular piece that can be easily redesigned to accommodate a variety of microcontrollers without impacting the rest of the pedal. If no microcontrollers are available at all, I even have a completely analog version we can swap in.

Main Board

The main board does all the audio processing. Like the controller board, I get much of it pre-assembled. A few things I’ll solder in house:

The FV-1 Digital Signal Processor (DSP) is a specialty chip for processing audio signals. It gives some killer delay and reverb capabilities

The internal switch allows you to choose which function the right-side Expression Jack controls. This BluTack putty is phenomenal for holding parts in place :)

All of the capacitors in the audio path are box film types. Surface mount capacitors, which is the cheaper and quicker alternative, can often negatively impact the sound. While it’s possible to find good ones, it’s simpler to use these high quality blue caps instead.

I don’t usually use that BluTack to hold components in place ;) Instead this PCB holder has a foam cover you secure on the other side to hold all the parts while you solder.

Next, solder some DC power wires and the VAST foot switch to the PCB. I made a last minute change to SunTsu foot switches and absolutely love these. They feel much smoother and more solid than the cheaper alternatives.

These long connector pins will interface this main board to the controller board

Install all the pots and toggle switches, then place and solder the main board.

Jack Board

Unfortunately I had to cut a lot of these pics for space savings, but you can guess how it came together.

You can also see here the addition of the DC power jack. Both the power jacks and the input/output/expression jacks are securely mounted on the panel. Many pedals these days use perpendicularly board-mounted jacks that subject the solder joints to considerable force every time you plug and unplug cables. Over time this leads to cracked solder joints and is by far the #1 source of broken pedals.

That’ll never happen with this pedal. It takes more time and costs a bit more, but it’s definitely worth it.

Solder jacks to the jack board and connect it to the ribbon cable

Putting it All Together

And place the controller board and bypass foot switch.

Wow that looks quick and easy when I paste a few pics like this… but it’s actually a VERY long build compared to most pedals. Arguably I have it priced way too low, but I’m going to hold it out as long as possible.

Anyhow, that’s all for now. Any more you’d like to see?

Behind the Scenes at MAS Effects