Phantom power

Why not just use 48? I know that you can go lower, but I wouldn't even fuck around with nice gear.
 
It depends 100% on what you're plugging into it....but wouldn't you hate to buy a new mic and find out you guessed wrong? I strongly second that you just go for 48.
 
I just wanted to know for design purposes how much I can go lower on the voltage. Sounds like I will be buying a bigger transformer and voltage regulators. I'm building my own power supply rather than spending $500 for an API lunchbox when I only own one mic pre that will fit in it.