ProDI

A passive mono DI for keyboards and guitars.  For a stereo version, check out the ProD2.

From the manufacturer

The ProDI is a passive direct box designed for use on stage or in home recording studios, with the ability to handle high output instruments without distortion, and a transformer-isolated output to eliminate noise from ground loops.

World class DI

The heart of the ProDI is a custom wound Radial transformer. It features an exceptionally high 140kΩ input impedance to reduce loading while enabling the ProDI to handle extreme signal levels at all frequencies without distortion. This is further improved upon with an internal MuMETAL® shield to protect against electromagnetic fields that can cause unshielded transformers to distort.