@atmasphere
i got this off a Stereophile review:
In MC mode, the switch controls a "variable-load auto tranny" (more Manley lingo), which is the Steel-head transformer/autoformer that gives the preamp its name. The switch controls five taps on the proprietary "dual-primary, bifilar wound, high-bandwidth, low-resistance, and multiple-shielded nickel-core step-up autoformer," which allows you to choose among 25, 50, 100, 200, and 400 ohm settings.