R. G. Keen’s MAX1044 circuit is the basis for this project. The project itself is Chris’s brainchild: a daughter board to get ±9V from a +9V power supply. The only differences are that we added a decoupling cap to the +9V supply line and hard-wired the oscillator frequency boost. It’s first application was to our Gristleizer PCB and it worked wonderfully: no hum and no whine.
An advantage over using two batteries is that the voltage division is very accurate: you get equal magnitude supply on the positive and negative rails. Two batteries may not be symmetrical.
Also, you can use this circuit to provide power to positive ground circuits from a negative ground supply.