I don't think you can easily. Inside the newer Krell units is a voltage/frequency sensing chip (I believe Martin Logan and other high end vendors also do this, to protect their high priced markets in Europe etc.). If you try to use a 120V/60Hz unit on a 230V/50Hz power supply stepped down to 120V, the unit will sense a frequency error and not work. This is the problem I had when I took my Krell HTS from the USA to France (I tried to run it with a 220V-110V step down transformer). In the end, I had to have Krells agent in France modify the unit to work at 220V/50Hz.
