I ran a Luxman Class A amp 100v with a step down and found it wonderful. You do need a step down as the extra 10-20v in NA can cause issues.
If you are concerned think of it this way there is a huge step down transformer out in front of your house or very close to it taking the 20'000ish VAC down to your house voltage so we all have a (many)transformer(s) in our circuit weather we want to admit it or not, well unless your running off batteries. Also there is always one inside your amp so another one really isn't a concern just make sure its big enough to handle turn on surge and power delivery.
Look on the back of your unit for power usage and triple it for a good measure. I ran a 1kw step down with my 50wpc Class A amp with no issues and room to spare.
interesting Georgehifi on the 1:1 that may be useful for DC blocking. DC on the line can cause transformer mechanical hum.