Building your first Eurorack case: power, HP & planning

The most expensive mistakes in modular happen before a single note is played: a case too small to grow into, a power supply that browns out mid-set, a ribbon cable plugged in upside-down that kills a module on power-up. This module builds the whole task of planning a first system on paper — case, power, and module list — so that the money you spend lands on a rig that works, whether it lives in a techno-jam studio corner or travels to a live set.

The arc starts supported. First you learn the sizing grammar — HP widths and 3U rows — and the case-size heuristic that says buy bigger than your current plan suggests, with built-in power to skip PSU wiring entirely. Then you drill the accounting core: the three independent rails, and the procedure for planning module power draw in milliamps against PSU capacity — first on a given two-module example, then on modules you choose yourself. ModularGrid is your just-in-time workbench throughout, surfacing each candidate module’s HP, depth, and per-rail draw; the minimal-voice strategy (one oscillator, filter, envelope, VCA) keeps the shopping list honest.

The capstone strips the scaffolding: a full ModularGrid plan with a power/HP budget sheet showing per-rail headroom, plus a power-up checklist. Every required atom gates it — sizing facts make the case choice defensible, the rail and current-budget atoms make the budget sheet correct, and the unplug-first and stripe-down procedures are exactly what the safety checklist must encode. Supporting atoms enrich rather than gate: module depth and skiff clearance, portability trade-offs, the internal CV/gate bus, why polyphony is priced out of a first system, and how regulated supplies work under the hood.