Effects of voltage converters.

It will void your warranty from many manufacturers, and some will even refuse to repair an out of warranty unit that was powered by a voltage converter. If you are talking about a new product [buying in Japan, and shipping to the USA], this is called a grey market product, as you are buying it outside of the manufacturers authorized distribution chain.

If you have moved from one country to another, and it is a used product, call the manufacturer, explain the situation, and ask if they can covert to the voltage standard where you now live.

For pricey audio stuff a well built and slightly oversized outboard transformer is an option, this gives you some cleaning of the ac line as a bonus. Sola is a good brand if you want a regulated (somewhat immune to normal voltage swings in your ac line)transformer.