Summit Audio TD-100 Instrument Preamplifier and D.I. - Manual (Page 7)

Model TD-100 Tube Direct Box 7
Applications
Applications
Live Sound
A direct box or “DI” (direct input) is used to take a high
impedance instrument signal and transform it into a
balanced, low impedance output. In the example below, the
Direct Output feeds the Bass Amp and the low impedance,
balanced microphone output is sent to the mixing console.
Direct Box Connection