A co-worker of mine gave me an old microphone he'd found while cleaning a relative's garage. It turned out to be a professional highly directional mic. I waned to build it into my operating position to hopefully reduce background noise. Part of reducing noise involved using its balanced output. Thus, the balanced-input preamp was born. Some quick research turned up this schematic: http://sound.whsites.net/project30a.htm . It met my needs perfectly except I needed a negative power rail. Since I only have a positive 13.8V supply, I needed to generate the negative rail from that positive supply. The TC7662B charge pump is ideally suited to this task. It can run at 100KHz, well outside typical audio range where it can more easily be filtered out. It uses only 1 external component, and can output more than enough current for this application.