A DI box (Direct Input,Direct Injection depending on who you ask) is a box designed for connecting audio equipment to a sound desk's mic in that was not designed for the purpose. They're very useful when you have an unbalanced output and want to send it over a long cable to a sound desk.
Typical Uses of a DI Box
- Connecting an electric guitar (esp. bass) to a sound desk directly
- Connecting a laptop to a sound desk without interferance
- Connecting a guitar amp (output!) to a sound desk
- Sending unbalanced signals over a long cable to a sound desk
- Connecting keyboards to a sound desk
Types of DI Box
DI boxes come in two types: active and passive. YSTV has both types, where possible, use active.
Active DI boxes are balancing transformers with very high input impedance. Active boxes are far more useful because their response is not dependant on the impedance presented from the source, but they do require power; Either phantom or pp3 battery. Our active DI boxes are Behringer DI100. They can handle the output of a 3000W guitar amp on their input with both pad switches and ground lift on (see below in switches section)
Passive DI boxes are balancing transformers with some attenuation. They work well for high impedance input, low impedance output, however their output impedance and frequency response changes depending on the input impedance.
Using a DI box
Input is by a 6.35mm jack (Our active boxes have XLR input as well)
Output is via XLR. This is the side you connect to the sound desk, and is Mic Level (it's also where you feed phantom power to an active box)
The passive DI boxes YSTV has have two rocker switches: INST/SPKR and GND LIFT.
- INST/SPKR is fairly self explanatory and tells it whether it has a guitar or something connected, or the output of an amp. Use INST most of the time, unless you are tapping the output of an amp.
- GND LIFT separates the ground on both sides and prevents ground loops. Use it.
The Active DI boxes have basically the same controls, but in a slightly different form.
- Pad - There are two pad buttons, each applies 20dB attenuation. As a general rule of thumb, none for mic or instrument level, one for line level, and both if you're hooking it to the output of an amp. You might not need any for line level, in which case, not using any will increase the signal to noise ratio. They're next to the input connector.
- Ground Lift - Exactly as for passive, except it's a push button.
- On/Off - Not quite what it first seems: When it's in the off position, it will work off of phantom power only. When it's in the On position it will use battery power, or phantom power if available, switching between them automatically. The LED is solid on for phantom, and flashing for battery.
The manual for the DI-100 is available here in PDF form if you're interested. It has some nice usage example diagrams in.