Jumbo Sunshade - Ezine

What's the difference between a passive DI and an active DI?

Passive DI
In a passive (non-powered) DI box, a transformer does the impedance conversion and ground isolation.

With a passive DI, the input and output impedances can vary greatly based upon the impedances of the devices that are being connected through the DI's transformer.  I personally have mainly dealt with guitars and mixers, but there's also:
keyboards, amplifier preamp outputs, outboard gear such as modelers and preamps, A/D D/A converters, computer interfaces and other I/O...
...just tons of other balanced and unbalanced gear that might need to be used with a DI.

So, a major limitation with a passive DI in some of those situations would be an inconsistency of the input and output impedances dependant upon the gear itself (not the DI).

Active DI
In an active DI the non-powered transformer is replaced with a powered electronic circuit.  Almost all active DI's can be powered by either a 9v battery or phantom power from the mixer.  Many active DI's can also take power from a wall-wart-type power supply.

Unlike passive DI's, active DI's have a very consistent I/O impedance on both the hi-Z/unbalanced and lo-Z/balanced sides.

When using the Ground Lift function with many active DI's, the phantom power return is also cut.  With units like this, make sure a fresh battery is there or you could be stuck trying to figure out why your signal suddenly cut out part-way through a gig!


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