here's a passac ec-1 acoustic guitar preamp that looks unused in original box, manual, even warranty card---owner's manual dates to 1986 printing. these units were considered to be very good back in the day to use with your acoustic guitar with under bridge piezo pickup, etc. uses 2 9v batteries so i guess it maybe runs on 18v for power and headroom. has a very in depth manual explaining lots about acoustics. very heavy duty enclosure.