An Engineer Built a Working Cassette Player From Mushrooms and Old CDs

Deep in a converted sauna in Tampere, Finland, an audio engineer named Sanna Mäkelä has constructed what she calls the "Fungus Fidelity" cassette player. The machine looks like something a forest spirit might leave on a curb: a lumpy, beige-colored block studded with exposed copper wiring, with two translucent reels slowly spinning inside a glass dome. When turned on, it plays old mixtapes with surprising warmth—though the manufacturer's warranty is technically a mycelium culture that can regenerate damaged parts if fed oat bran.

Mäkelä, 34, is part of a growing movement called bio-hacking, but her work stands out for its sheer audacity. While other hobbyists grow mushroom leather or bacterial dyes, Mäkelä decided to grow a functional analog audio device. "Computers are boring," she said, sitting in her workshop surrounded by petri dishes and soldering irons. "I wanted a cassette player that was alive. Not metaphorically alive. Actually alive."

The heart of the Fungus Fidelity is a circuit board made from Ganoderma lucidum, better known as reishi mushroom. Mäkelä grows the mycelium—the thread-like root network of the fungus—in a custom mold lined with copper tape. Over three weeks, the mycelium colonizes the mold, forming a dense, leathery mat. She then bakes the mat at low heat to kill the fungus (sadly, the final device is not alive) while preserving its structure. The resulting material is lightweight, non-conductive, and surprisingly durable—similar to cardboard but with the flexibility of thin plastic.

"The mycelium board replaces the phenolic resin board that normal electronics use," Mäkelä explained, pointing to a traditional cassette player she had gutted for parts. "Phenolic resin is petroleum-based, toxic to manufacture, and almost impossible to recycle. My mycelium board is grown from sawdust and coffee grounds. When the player finally dies, you can compost the board and plant a tomato in it."

The tape transport mechanism—the tricky part that pulls magnetic tape across the read head at a steady speed—came from a broken 1990s Sony Walkman. Mäkelä initially tried to grow the transport parts from mycelium as well, but the precision required (gears with millimeter tolerances) proved impossible. "Fungi are amazing, but they cannot do injection molding," she admitted. "I had to cheat on the gears."

But the most delightfully weird component is the tape reel itself. Instead of standard plastic reels, Mäkelä uses circular saw blades repurposed from old compact discs, which she coats with a magnetic emulsion made from iron oxide powder and casein (a milk protein). The resulting tape has about half the audio fidelity of a normal cassette—think AM radio in a thunderstorm—but it has a character that audiophiles have started calling "the crunch."

Local musician Jukka-Pekka Laaksonen recorded an entire album using only Fungus Fidelity players for both recording and playback. The album, titled "Mycelium Dreams," features haunting cello and field recordings of rain on a tin roof, filtered through the player's wobbly pitch stability and high noise floor. "Digital recording is perfect," Laaksonen said. "Perfect is boring. The fungus player breathes. It has a personality. Sometimes it eats the tape. Sometimes it adds a ghost echo. You never know what you will get. That is art."

Mäkelä has no plans to commercialize the device. The mycelium circuit boards take three weeks to grow, and she can only produce two at a time in her sauna lab. However, she has released detailed instructions on the open-source hardware platform Instructables, complete with time-lapse videos of the mycelium colonizing its copper mold. As of this week, seventeen other bio-hackers around the world have reported successful builds.

The Finnish government, which has been investing heavily in bio-economy initiatives, awarded Mäkelä a €50,000 grant to develop a mycelium-based headphone amplifier. "The goal is not to replace conventional electronics," she said. "The goal is to show that there is another path. We do not have to mine rare earth minerals and manufacture toxic circuit boards for every single gadget. Some gadgets—the ones we use for joy, not for necessity—could be grown."

When asked what the late Steve Jobs might have thought of a mushroom iPod, Mäkelä laughed. "He would hate it," she said. "It is not thin, it is not sealed, it has no retina display. But it plays music that sounds like a campfire. And when you are done with it, you can bury it in your garden. Try doing that with an iPhone."