Schertler Lydia Active EQ for Steelstring Guitar, to be mounted on the underside of the bridge, LYDIA pickup, active A-CLASS pre-amplifier, small volume pot, bass and treble control which can be mounted inside the soundhole, width of pickup: 2,3 mm, length 70 mm, pickup is situated in the middle of the transducer, 3-V-lithium batteries inc, should be fitted by a professional luthier