I've been happily using the Xotic voltage doubler on 18V with my Fulltone OCD version 3 for few months now. It plays nice with it. It's a bit on the expensive side and doesn't feel extremely sturdy.
I own two Fulltone pedals, a PlimSoul and an OCD version 3. I had read on the internet that many people prefer running either or both of these pedals at 18V rather than the usual 9V. People had reported that it gives a more 'open' sound. I decided to find a voltage doubler to try it out for myself. I chose the Xotic because it requires only one 9V outlet from a power supply. Many (cheaper) voltage doublers require two 9V outlets. The only requirement is that the pedal cannot use more than 80mA, but this is not a problem with neither of the Fulltone pedals I have.
The result? They both sound more open than they do at 9V. There's more dynamic range and the transition from clean to clipping is smoother. Because the OCD is already more transparent than the PlimSoul, I decided to use the voltage doubler with the OCD. Setting the preamp to clip slightly makes it an even greater experience.
The only gripe I have with it is its price and build quality. I find it relatively expensive and the build quality doesn't seem as sturdy as I expected it to be. However, this should not be a problem if you secure it onto your pedal board.
