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www.LeonAudio.com.au
D.I. Boxes are constructed using one of two common techniques.
• The first type uses electronic circuitry and are known as active D.I.
Boxes. They require either Phantom Power or a battery supply.
• The second variety uses an audio transformer and are known as
either transformer or passive D.I. Boxes. They require no power supply.
A D.I. box is required to perform three separate basic tasks.
1. Impedance Conversion
2. Unbalanced to balanced conversion
3. Earth isolation
1. Impedance Conversion
The medium or high impedance of a signal source is converted to a low
impedance suitable for feeding down a long multicore to a mixing
desk’s microphone input. A low impedance enables long cable runs,
with very little quality loss, and also low susceptibility to external
electrical interference which can cause hum and buzzes. A D.I. box
should provide a high input impedance for connection to a signal
source, and a low output impedance for connection to the microphone
input of a mixing desk. The input impedance of many D.I. boxes is too
low, resulting in either the highs or lows being attenuated.
The very high input impedance of
2.
Unbalanced to balanced conversion
The unbalanced (2 conductor) wiring of a signal source is converted to
the balanced (3 conductor) wiring of a mixing desk’s microphone input.
A balanced cable provides good rejection of electrical interference,
while an unbalanced cable does not. Active D.I. Boxes are potentially
capable of providing excellent unbalanced to balanced conversion, but
due to cost restrictions, most are poor performers in this area.
a
transformer to provide
excellent unbalanced to balanced conversion.
The Leon Audio Active D.I. Box
preserves the full frequency response of the original signal.
The Leon Audio Active D.I. Box uses
quality
What’s in a D.I. Box?
3. Earth isolation
A D.I. Box provides isolation between the earth wiring of a signal source
(e.g. musical instrument) and the sound system to which it is being
connected. This prevents earth loops from occurring. An earth loop
occurs when a device such as a keyboard is connected to the mains
earth via more than one path. The first path is via the instrument’s own
power cable to the mains earth. The second path is via the
interconnecting audio cable to the sound system, then via the sound
system’s power cable to the main’s earth. Any resultant circulating
earth current is amplified and is heard as a hum or buzz. These
unwanted earth currents are usually induced from nearby power and
lighting cables. Active D.I. Boxes are usually very poor at providing good
earth isolation, because there is usually a direct electrical path
between the instrument and the sound system, even if its earth lift
switch is lifted.
The Leon Audio Active D.I. Box uses a quality transformer to provide
earth isolation.
Earth Lift Switches
D.I. boxes have an earth lift switch to allow the earth connection
between its input and output connectors to be broken to prevent earth
loops. Disconnecting the signal (audio) earth is not a safety issue, as the
Protective Earths in all the mains cables are still connected and fully
functional.
excellent
Pad Switches
Pad switches are often provided to allow D.I. boxes to handle higher
level signals which would otherwise overload the D.I.’s electronics.