I have the Luxman L-509Z direct from Japan. I use a step-down transformer, and I can usure you it DOES NOT affect the sound in any way!
I have 47 years in the electronics industry as a radio technician, and I have built and modified many amps and various other stereo components.
The Japanese voltage version of the Luxman works flawlessly in the USA with a transformer.
You can listen to people who think they know or someone who actually has the setup in the USA...your choice.
I enjoy my $14K amp for the $7K I paid...

