Q: Some effects pedals say that you can run them at either 9 volts or 18 volts DC. Most power supplies are 9 volts. What is the advantage to using 18 volts?
A: The higher power supply voltage provides additional clean headroom. Keep in mind that this is not something you should do without making sure that your stompbox can handle it. Damage may result!
But if — and we emphasize that “if” — your pedal supports 18-volt operation, try it both ways. If you hear an improvement or a change you like, use 18 volts. Otherwise, most pedals are designed to provide full capability and outstanding sound quality at 9 volts.