Because nowhere in the specifications/manual Yamaha writes about AC voltages, I think the built in power supply works at voltages between 110 and 240 VAC.

Modern equipment have switching-powersuppl.

The mean sounding buzz probably comes from the step-down converter. Mostly the power that comes from it ís 'dirty' (no perfect sinusoide) If you use the SDC ánd the T2 switching one..... this will give trouble.