Stone valve preamp, hand wired in the UK in the 70's I believe. The volume control can be switched in as a signal boost or to drive the front of your amp a bit harder, and the tone control can be varied to go from a deep dub tone (fully anticlockwise) to more bright and zingy (fully clockwise).
It's a cool unit, also sounds good with guitar!
It comes with the original box but no manual. The photo of the manual was sourced online.
£70 👍🏻