Active DI Units
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.
A pass-through connector is a second jack, sometimes simply paralleled 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. Pass-through 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 buffering and no other 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 from unit to unit.
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