Step down transformers detrimental to SQ?

Its also possible to step down the AC voltage by doing an old DIYer trick which is to buck the AC line voltage.

This is done with a smaller transformer that has a secondary rated for the current you need (50% more than the fuse rating is good) and the difference in voltage. Since most homes are at 120Volts these days, that's a transformer with a 20Volt output at however many amps your amp needs.
The primary of the transformer runs off of regular wall voltage. The secondary is put in series with the AC line going to the amp. You have to try the secondary hookup both ways- one way will buck the voltage up 20 volts (adds to the line voltage) the other way will subtract 20 volts which is what you want.

The result is a much smaller and less expensive transformer can be used but you have to know more about how to use it. There are always tradeoffs...

interesting Georgehifi on the 1:1 that may be useful for DC blocking. DC on the line can cause transformer mechanical hum.

Yes also RF as well.

Cheers George

+1 atmasphere, I have used a bucking transformer and it's a very clean solution to the problem, but if I recall mine only dropped the voltage around 14V, not 20V.

What about the difference in cycles per second? 50 v 60 hz....

A web search turns up ONE country on Earth running 100v, Japan. The world being a big place rendered tiny by the internet, where anything and everything can be found (a German man looking for people willing to be killed and eaten had several applicants) and knowing how people love to prove others wrong even if it means missing the whole point, saying there aren't any was a bad idea. I stand corrected.

But, calibrated (what I said) and regulated (what I never said) are two completely different things. Seriously. You could look it up. The 5% regulatory variance allows the NOMINAL (means, you could look it up, in name only) 120v to vary as low as 114v. Whatever. The question was, do stepdown transformers affect SQ. The answer is yes. And do I even need one? To go from 120 to 100? To avoid damage? The answer is no.