Nonlinearcircuits (NLC) is an analog Eurorack module designer founded by Andrew Fitch, an Australian engineer based in Perth whose academic background includes a PhD on memristor-based chaotic circuits from the University of Western Australia. The brand sells PCBs, panels, and assembled modules for the DIY synth community, with a strict focus on analogue circuitry — no microprocessors or MIDI are used in any design.

The catalog is unusually broad and experimental, spanning oscillators, filters, sequencers, utility modules, phasers, and even a spring reverb. Many designs draw on chaos theory or obscure academic research papers, reflected in modules like the Triple Sloths and 1U Sloth Chaos (which generate slow chaotic voltages), Let's Splosh, Bi-Di Choppers, Ming Rod, and Let's Get Fenestrated. Other notable releases include the Suppository of all Wisdom, Encephalo Adjuster, and Poultry in Motion. While influenced by Serge synthesizer designs, Fitch's approach leans more whimsical and exploratory than purist.

NLC grew out of a long-running workshop series hosted by West Australian Modular and remains closely tied to the DIY scene. The Nonlinearcircuits Builders Guild on Facebook and an associated Discord channel function as the primary community hubs, where builders trade troubleshooting tips and share completed projects. The cellF system, a neural-network-driven analog synthesizer built around NLC modules, is one of the brand's better-known appearances outside the strictly modular world.

Nonlinearcircuits has 3 products cataloged on Equipboard, including Modular Synthesizers. Their gear is featured by 1 artist, with the strongest followings in Electronic and Pop. Notable users include Andrew Huang.