By Sam Holland, product design engineer and co-founder of the informal freelance collective

Why this crossed our desks: I’m obsessed by all things Teenage Engineering. I love their playful approach to making technical hardware, and their design aesthetic of Braun-meets-Lego makes me want to buy everything they make. It’s dangerous.

They got me again with the EP-40 Riddim Synthesizer and EP-2350 Ting microphone. I read this awesome article about how the product was designed using as many off-the-shelf components as possible during the pandemic supply chain shortages and thought it was a cool strategy. The end product is gorgeous.

So, yeah, I’m weak and ended up purchasing the Riddim and justified it as a fun way to teach my son how to make music, but it’s mostly for me to play with. If you’re interested in a full step-by-step overview, you can watch a video here. I learned a ton by tearing this down, and I’m very excited to show some really clever designs below.

Table of Contents

Overview

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The EP-40 Synthesizer is a slab of plastic with some colorful knobs and buttons and a display stretching across the entire width. It looks a bit like an oversized calculator or a sci-fi movie prop. I wanna touch all of the buttons. I love it.

The top edge of the device features a smattering of input and output ports (1) and a power switch (2).

A cover plate (3) is removable with the gentle pry of a fingernail and reveals the AAA battery compartment underneath. The speaker cover (4) can also be removed, but I’m not really sure why.

The display (5) spans the entire width of the unit and has a translucent plastic cover.

The bottom half(ish) of the device is full of knobs (6), small buttons (7), a fader (8), and larger buttons (9).

Pad printing is used to add logos and text to each button, meaning that they only needed to mold a few parts and choose different colors and prints to create this wide variety of button types.

The device is roughly 7 x 9.5 x 1” and feels super solid, despite being made of plastic.

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LEGO shoutouts

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I freaking love Lego — it’s literally the main reason I became a mechanical engineer. I immediately noticed a few features on the EP-40 while playing around with it that brought me back to my childhood.

1. The sides of the device feature a handful of holes that work with Lego Technic pins, allowing you to connect multiple devices together or to make custom attachments.
2. Removing the rubber foot from the rear housing leaves with you with a square that perfectly fits into a standard Lego 2x2 brick. Hell yes.
3. If you pull off the knobs from the device, you’re left with a Lego Technic standard plus-sign-shaped shaft, allowing you to connect gears and wheels and whatever else you can imagine. The knobs themselves are also Lego studs.
4. The removable battery and speaker covers are fully Lego-compatible and allow you to create custom covers. </aside>

Getting inside

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Flipping the EP-40 over reveals 4 rubber feet (1) and 8 Philips head screws, with an embossed callout on what screwdriver to use to open the device (2). It’s rare to see visible screws on a product, and a first for me to see actual encouragement and help marked on the device.

Some text is embossed (3) on the housing against a glossy ribbon of plastic, which helps it pop out on the otherwise matte texture. The remaining text is laser etched (4) and has certification and legalese.

Laser etching is a fast and high-resolution way to add text without committing to anything long-term. This allows them to change their certs, information, or tailor the text based on the region they’re selling their device. It also may be required for certain certification logos for visibility.

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A sh*t ton of screws

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After gently prying the rear housing up, I encountered some resistance form a few snap hooks. Pulling harder than I like worked, and the rear housing was free.

Inside is a single PCB that spans the entire size of the EP-40 device. I hope you don’t have carpel tunnel syndrome, or else you’re in for a world of hurt here. I counted 43 screws in total holding this board down. These screws are most likely installed using robotics or some other custom screw-installing machine.

Thread-forming screws are perfect here — they create their own threads as they’re screwed into plastic screw bosses molded into the top housing. These screws can be removed and reinstalled only a few times before you risk stripping them, so be careful!

I attribute the sturdy feeling of this device to the sheer quantity of fasteners used. It ensures that there’s little to no flex in the device when pressing hard on it. I also appreciate the Teenage Engineering logo added to the circuit board — a cute touch!

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Two super neat rubber parts

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Two rubber parts are doing the heavy lifting here.

One white rubber part (1) has five jobs:

1. Support backside of the speaker
2. Create an acoustic chamber to improve speaker range
3. Microphone gasket to improve sensitivity
4. Concentrate LED lights into square shapes
5. Add rigidity to the casing

The black rubber part (2) is fascinating. It seems to be compression-molded and has orange, white, green, black, and clear components all molded in one part — plus text added on some areas.

I’ve asked around, and the consensus is that this part is made by first molding the white, orange, green, and clear parts. The text on the colored parts is either added with a very crisp pad print or using mold decoration.

All of these parts are then placed in a larger mold, where the black rubber is molded around them to make a single part. It’s nuts.

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Cool ways to connect terminals and speakers

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I thought the way that the battery terminals and speaker connected to the PCBA were pretty interesting. Teenage Engineering designed two stamped metal parts (one for each battery terminal), which are pressed into plastic ribs in the housing (1).

A tiny PCB (2) is also press-fit onto plastic features on the housing. This PCB has two raised metal pins on it, and the speaker (3) is wired to this board.

I saw a few locations where the casing was marked with a Sharpie pen. My guess is that this is a quality control check prior to assembly. The assembly technician ensures that the speaker wire isn’t on top of the screw boss (4) and that the battery terminals are properly installed and in the right orientation (5).

On the PCBA, large copper pads make contact with the battery terminals (6). A neat semicircular feature makes contact with the speaker PCBA pins as well (7). My guess is the circular shape allows for some positional misalignment during assembly. I also noted 4 pads, which may be used for debugging or flashing the unit during assembly (8). They’re accessible even when the unit is assembled, but pretty discrete.

This is a very uncommon way to make electrical contact to a circuit board. It’s far more common to use spring pins, stamped metal spring fingers, or conductive foam parts to make these connections. I think the only reason this design works fine on the EP-40 is because of the sheer quantity of screws ensuring proper compression of these parts. I don’t recommend this for your product, but I’ll allow it on this one 🙂

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LED panel