Direct Boxes Uses

A Direct Box or simply DI (Direct Inject) is an electronic device that connects a high impedance line level signal that has an unbalanced output to a low impedance mic level balanced input, usually via an XLR connector. DIs are frequently used to connect an electric guitar or electric bass to a mixing console's microphone input. The DI performs level matching, balancing, and either active buffering or passive impedance bridging to minimize noise, distortion, and ground loops. DIs do not perform impedance matching.

Passive DI Boxes

A passive DI unit typically consists of an audio transformer used as a balun. The turns ratio is typically chosen to match a nominal signal source (such as the magnetic pickup of an electric guitar) to the input of an audio mixer.

Some models have no settings, while others can have a ground lift switch (to avoid ground loop problems), a pad switch (to accommodate different source levels) and a filter switch for coloring the sound.

Active DI Boxes

An active DI unit contains a preamplifier. Active DI units can therefore provide gain, and are inherently more complex and versatile than passive units. Active DI units require a power source, which is normally provided by batteries or a standard AC outlet connection, and may contain the option for phantom power use.

Most active DI units provide switches to enhance their versatility. These may include gain or level adjustment, ground lift, power source selection, and mono or stereo mode. Ground lift switches often disconnect phantom power.

Passthrough Connector

A passthrough connector is a second output, sometimes simply connected to the input connector, that delivers the input signal unchanged, to allow the DI unit to be inserted into a signal path without interrupting it. This is essential in many applications. Passthrough is more common on active than passive DI units. Passthrough is also commonly referred to as a bypass.

True bypass occurs when the signal goes straight from the input jack to the output jack with no circuitry involved and no loading of the source impedance. False-bypass or simply 'bypass' occurs when the signal is routed through the device circuitry with no intentional change to the signal. However, due to the nature of electrical designs there is almost always some slight change in the signal. The extent of change and how noticeable it may be can vary widely from unit to unit.

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