As simple as magnets and contacts, but without any magnets or contacts.
It’s simple, really. Diode systems work much like old-style gang switches - but they’ve no moving parts and use one single contact on every key. It’s why many builders worldwide still use little else. SSOS have built thousands since 1968, and still carry spares for every system ever made.
Each system has two parts. First, a series of low-current diodes switches inputs from keys and stops. And in turn, these trigger higher-rated transistors to directly drive the magnets. They’re both mounted on sturdy circuit boards, clad in hinged wooden frames for easy wiring access.