What is DI box?

DI box its full name is Direct Box, but we call it DI box. Musician is familiar with DI box, the general device in stage performance. As music player known, guitar, bass, keyboard etc instruments are all high impedance unbalance signal output.

DI box converts high impedance unbalanced instrument signal into low impedance balanced signal. It avoids low frequency loss and long cable causing noise problem. It ensures console always getting low noise and dynamic signal quality.

✦ What is impedance output?✦

Output impedance depends on output electronic circuit. Lower output impedance features excellent signal transmission ability, even with heavy loading the signal can be transmitted clearly. In other side, with high impedance, transmit the signal will be difficult.

The relationship between input impedance and output impedance just like water and water valve. If water valve is smaller, some water will rejected by water valve. The same as impedance. If output impedance is lower than input impedance, you can not capture all signal.

General speaking, console mic amp input major used to connect to mic, mic's lower impedance matches console mic amp requirements. But as guitar, bass instruments with higher impedance, there is no way to connect to console, mic amp directly.

What's the result if connect these instruments to console directly?

It will cause signal overload, sound distortion and especially loss signal high frequency.

Under this you will need DI box to convert high impedance unbalanced signal into low impedance balanced signal. Matched input and output impedance is the reality sound. So DI box is necessary device for you to output original and purity sound.

✦ DI box theory ✦

The basic component of DI box is step-down transformer. This transformer is composed of two or more cables and a metal iron core. A section will be left at the end of each coil, one pair as input and the other pair as output. The input coil is called the primary coil and the output coil is called the secondary coil.

When the electrical signal passes through the primary coil, it will generate a magnetic field around the coil. Then, the magnetic field induces a similar signal in the secondary coil, and this signal will be transmitted to the output cable. If the number of windings of the primary coil is more than the secondary coil, it is called a step-down transformer because the signal level and impedance at the output is lower than the input.

Passive DI box, plug and play without power supply, with affordable price is used for direct signal conversion, such as electric guitar. Although passive DI box can achieve impedance conversion through transformer, it cannot achieve buffer amplifier function. The way to achieve balanced transmission is to reverse the phase through [transformer], rather than the phase reversal circuit formed by reverse amplifier circuit and non-reverse amplifier circuit, like active DI box. Passive DI boxes have poor anti-interference ability in transmitting signals and are more vulnerable to noise. The configurability of passive DI box is also lower than that of active DI box. However, the passive DI box does not need batteries and is simple to use. The high-quality passive DI box is quite reliable.

Some DI box without any button but some features ground button to avoids ground back problem and pad used to match different input source level. Some passive DI box also features filter button for coloration.

The active DI box has a built-in preamplifier, which can provide gain, and is more complex than the passive DI box, so the function is also more complex. Active DI box performance need power supply such as AC socket, battery or phantom power. Functionality comes from gain adjustment, ground lift, power, mono-stereo mode even EQ control. They also features pass-through connector.

The pass-through connector is another output that can be connected with the input to transmit the unprocessed input signal, and can insert the DI box into the signal path without interrupting the signal. DI box as the conversion device of instrument signal, the internal circuit design and component selection directly affect the effect of instrument. Generally, high-quality products features less coloration.

Conclusion:

1、If signal is active please use passive DI box.

2、If signal is passive please use active DI box.

✦ DI box application✦

DI box used in instruments and sound collector which without XLR balanced output. For example, keyboard, direct or via audio cable connects to console; another one is guitar or bass with sound collector audio signal through mix controller to mix as major mixing or monitor mixing.

If keyboard built-in balanced output(general high level keyboard has it), then there is no need to DI box. But it only has one line output, you can choose to use passive DI box. If monitor amplifier run needs keyboard then DI box must with pass-through connector.

DI box a hero in stage, it transmission the outstanding sound to console so we have excellent sound source to mixing. So we must pay attention to DI box.