I just got my Fulltone earlier, and I've been running it on the 9volts it came with (I also run my pedal board with a 9volt daisy chain).

The manual says that it runs on 9-16volts, does using higher voltage change the sound, and if it does, how does it change?

Thanks in advance
It can go all the way up to 18V and anywhere in between 9 and 18. I asked one of the dudes and they said that it's basically for headroom purposes - comp cut mode can give a larger boosted signal and you should be able to turn up the gain and volume higher before it distorts. Yes, that equates to less distortion, but the result is higher headroom. If you're using the pedal to drive a tube preamp, I'd go 18V, but otherwise, leave it at 9.
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I was looking at a used Warwick Vampyre LTD 5'er for about $200. I went home to grab my wallet and came back and some jerk with an epic beard got it already..