Taken directly from BYOC.
Possibly the World’s cleanest, most transparent boost. It utilizes the
7660S charge pump’s ability to take a standard 9v power supply and
output both +18v and -9v. The op-amp based boost circuit takes advantage
of the whopping 27v differential to produce 20dB with an amazing amount
of headroom. It doesn’t matter if you’re using active pickups – you
will not get any clipping from this boost. Slam it with another boost,
it still won’t clip! The treble control allows you to cut/boost
frequencies above 3k3Hz by 6dB.
To be honest, it’s not as small neat as I would like it due to the three different power connections, but here she is.
On the site it says it uses a 7660s for the charge pump, but the schematic shows a MAX1044, remember the two are interchangeable.