Using 120V amp in a 100V area

I am currently looking for an amp. I have been looking at new and used amps at audiogon and one problem that I have been having is that the voltage (120) is different from Japan (100). While 120V electronic equipment does work here, I wonder how it would affect both an amp and the sound. One suggestion has been to use a voltage converter. I wonder whether this would make any difference to the sound since ideally your amp is plugged into an outlet. Advice would be appreciated.
I was letting someone else answer this, but...

One effect of running a 120v. amp on 100v. will be c. 1/6 lower maximum power. Another will be incorrect bias voltages/currents. A technician (or perhaps you) can adjust the biases.

At 100v. I THINK you'll get MOST of the power and quality that was designed into the amp but probably not the last and finest degree.
It all depends on whether the equipment has a regulated power supply or not. A piece that I just bought does have a regulated supply, and, according to the owner's manual, will function properly with ac voltage from 92 to 130 volts, 50 or 60 Hz.

As Jeffreybehr says, even without a regulated supply a power amp ought to be OK.