Welcome again everyone to our weekly look into the Astra Sound microphone cupboard. Along with our collection of microphones we also have plenty of DI boxes which we store there. Over the years many people have asked what a DI box does so we will try and explain whilst highlighting some of our own.


DI stands for direct injection because it is inserted directly into the signal chain. The main function of a DI box is to turn an unbalanced signal into a balanced signal. Line level outputs from intruments with pickups can be plugged into the mic inputs on a desk. An unbalanced signal is carried by two connectors, a positive and negative with the ground connected to the negative. A balanced signal seperates the ground cable and makes for a signal that is more resistant to noise


There are also two types of DI boxes, passive and active. Active DI boxes use an external power source such as a battery or phantom power but a passive box does not. The general rule is that if the source is active then you need a passive box and vice versa. The reason is to do with the differing impedances. An active DI box outputs a higher signal and greater impedance that passive sources are incapable of producing.


DI boxes have a variety of other features. One of the most important features is the pad. This drops the input signal by a fixed number of decibels. A DI box will distort when an active source with a high output is plugged into an active DI box. Another feature is the ground lift switch. When there is a link between differing grounds a hum is induced. This is then transferred to the signal and is outputted as a square wave hum. By lifting the ground you break that loop and eliminate that noise.

The Collection

At Astra we have a large variety of DI boxes. It will be dull to give each one its own post as they all do the same job and have very similar functions. Our collection includes single and dual channel boxes both active and passive. This means we are well able to cater to any and all instruments that we encounter.