DI Boxes and Isolators
DI boxes are important for any musician, band or recording studio, they help in making connections between instruments, line level devices, mixers, amplifiers and powered speakers. There are two main types, passive and active. Both do the same job, but the active type can add gain to the system.
The main purpose of a DI Box is to:
1) Match input and output impedance, so correct levels are achieved.
2) Allow for longer cable runs, by turning unbalanced signals to balanced ones, thus reducing interference.
3) Isolate pieces of equipment from each other to reduce noise and hum.
Passive DI boxes are handy as they do not need any form of power supply. So, for example, a guitar can be plugged straight into the box with an unbalanced jack lead and connected to a mixer microphone input, via a balanced XLR lead, with no other connections are required. The long part of the lead can be balanced, reducing noise and hum and matching the mixer input correctly.
Active DI Boxes need some form of power, whether it be an AC/DC power supply, battery or power from the mixers phantom power supply. Since they have power other features can be added into their design, so a pre-amplifier circuit could be added to boost very low-level signals for example.