I think if you’re going to use the 7660S you’d need to add a cap and 2 diodes to turn it into a voltage doubler as well as a voltage converter the same as the mule kicker combo circuit
Obviously you’d need to ensure everything is rated for 18v particularly electrolytics if it were me I’d leave the 7660S part of the circuit empty and build it on a piece of vero and connect it appropriately
It’s do-able but not without a fair bit of work
You could cut traces and add your extra components but to me the benefit wouldn’t be massive running it at 18v even with a 9v input you’re probably going to get closer to 16v with the voltage drop through components like the 2 diodes
It’s not simple because you need -9v for ground that part is already taken care of you just need to double the 7660S output voltage
