Is it possible to run The Fat Boostered on 18v's?
Most pedals can be run at 18V provided that the parts used can handle the voltage. The parts you need to check are the IC's and Transistors in the circuit, and very importantly the Capacitors. Capacitors that are run over their voltage limit can become dangerous - they explode! So what you need to do is crack open your pedal, and make sure of the voltage ratings of the caps, transistors and IC's. The Caps will say right on them (the ones you really need to worry about are the Electrolytic caps). The transistors and IC's you will need to look at the data sheets for.
There is one thing I'd like to note here - it's not always beneficial to run a pedal above the recommended voltage. Most pedals are happy with 9V, and adding more voltage doesn't do anything one way or another. Some pedals, like the OCD, function better with more volts. That's not always true, so if you do decide to try it, take some time and really listen carefully to see whether or not it's even worth the effort.
Jacob
In the case of the FB, it's pretty safe that 18v will not cause any problems. The mu-amp/SSRP gain stage is self biasing and the input is a simple buffer. I think it will probably give you some increased output, though.
Thanks for the help. I have a Fulltone Fulldrive that I run on 18v. I like the increased headroom I get by doing so. I'm hoping once I build the Fat Boostered I can run it at 18v to match the output of the Fulldrive for cleantone.
I also have been thinking about placing a Deadringer, Fat Boostered and a Road Rage(either for the deadringer only or for both) in one enclosure. I recently ordered a Road Rage and a Deadringer, each one for two of my friends who really like the Fulldrive at 18v.
That would be a great combo. You should be able to run both off one Road Rage.