With this charge pump (DC pump, volt pump, power pump...) you can have -9V and +18V from a +9V voltage source. Use the -9V output to get a dual power supply or power up effects with positive ground (Fuzz Face, Tone Bender...). Use the +18V output to give headroom to an overdrive. POWER SUPPLY CHAIN WITH POSITIVE GROUND PEDAL A positive ground pedal cannot be directly connected to the power supply in chain with your other negative ground pedals. You can use this PCB to build a voltage inverter and power your positive ground pedal in chain with the rest of your pedals.   PCB