Effects of voltage converters.

Does anyone have experience in using voltage converters to power products with various voltages? Any advice would be appreciated.
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.