This D.I. unit incorporates a FET amplifier offering 4.7Mohm input impedance suitable for matching to acoustic guitars and an extremely high quality audio transformer for bass guitars (essential for re-amping).
Customer feedback dictated the inclusion of the transformer even when using the acoustic input, the FET amplifier feeds the transformer via an insert jack (centre jack) that is used for the direct input from a bass guitar. A monitor switch provides a PA amplifier feed from either the FET amplifier or the transformer input.
In practise sessions the D.I. box may be used as the interface between either type of guitar and the P.A. (providing there is a phantom power feed to the FET acoustic input)