Why do ribbon drivers require a step-up transformer?

The ribbon itself is, electrically, almost a dead short. It is a single strip of thin aluminium with a DC resistance often well below one ohm, and its impedance is dominated by that resistance (plus a small inductive component). This is nothing like the 4–8 Ω load an amplifier is designed to drive.

Driving such a ribbon directly would demand enormous current and would effectively short the amplifier's output stage. A step-up transformer is therefore required to match the ribbon's sub-1-ohm impedance to a standard amplifier load.

How the matching works

The transformer multiplies voltage and divides current by its turns ratio N1 : N2. The impedance reflected back to the amplifier is:

Z_reflected = (N1 / N2)² × R_ribbon

By choosing the turns ratio appropriately, the transformer presents a comfortable 4–8 Ω load to the amplifier while still delivering the high current the low-resistance ribbon needs.

Where Clarisys uses them

In a Clarisys speaker the step-up transformers are used for the midrange and treble ribbon sections — each of those sections is fed through its own purpose-wound transformer, so the treble is never modulated by midrange excursions. The bass section is engineered separately and does not use a step-up transformer.

The amplifier sees the combined load

It is worth being precise: the amplifier never drives a single bare ribbon. It drives the crossover, which feeds the transformers, which feed the ribbons. Through its transformer, each sub-1-ohm ribbon is reflected up to a comfortable impedance, and the crossover combines the sections into a load that is designed to be benign across the band. The raw fraction-of-an-ohm impedance of a ribbon exists only on the secondary side of the transformer; the amplifier sees the reflected, filtered, combined load.

The quality of these transformers is critical: each sits directly in the signal path, so its bandwidth, core linearity, and leakage inductance all influence what you hear. This is why Clarisys uses purpose-wound transformers and, on the upper models, a dedicated transformer for each midrange and treble section.