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"Helping You Sound Your Best"

Jordan Audio Consultants
GOING DIRECT: The proper use of direct input boxes

Have you ever tried to patch a tape deck or a synthesizer from the platform, through a microphone line to the mixer? Did it buzz? Did it hum? Did it distort the input channel? If you only adapted the 1/4 inch jack to an xlr plug it probably did hum, buzz or distort. It is not you, it is the equipment. The reason it did is that electronics which are powered by different AC circuits do not always get along. A keyboard on stage plugged into a socket with the piano lamp will require a direct input (DI) box to isolate the keyboard from the mixing console.

A DI box contains either a transformer or a circuit to isolate one voltage from another. The most common DI boxes are passive devices that use transformers. They are available from music stores, sound contractors and mail order houses. The cost is quite modest from $35 to $100 dollars. Active DI boxes use a powered circuit to achieve the same results. These are less common and are mostly used in studios. They range in cost from $150 to $300 dollars.

You may have seen a transformer device that looks like a long XLR connector with a phone plug on one end. You may have seen these transformers used to connect a keyboard to a mic jack. If you have ever seen this type of interconnecting work, forget it, (or remove it) and wipe the image from your memory. It is an error. It is among the most common mistakes in audio today. Those cute, little, inexpensive transformers have one purpose: convert a low impedance microphone signal into a high impedance microphone signal (or vice versa). They simply do not have any other purpose.

The DI box has a specific purpose. It connects devices to the microphone inputs on a mixing console. It provides a balanced signal from an unbalanced line. It isolates electrical devices. A good DI box will allow you to lift the grounding connection from the signal to eliminate ground loops, some use a switch while others provide a separate input jack. More elaborate units provide for the different levels of signals from various sources. (i.e.: an acoustic guitar is a very low level signal, a digital piano is a vary high level signal.) Even the least expensive DI's will have two 1/4 inch jacks. One is to feed the signal into the device. The other is to provide an unaffected output to feed to a stage amp. This allows a guitar player to feed to his own amp while still feeding the PA system.

Simply, they allow tape decks, keyboards, guitar pickups, etc. to be connected to a mixing console by way of platform microphone lines. This is how it is done.

Insert a phone plug from the source device to the direct input box
Attach a microphone cable with XLR connections to a platform input.
The platform input should connect to the console as a microphone.
Set the input gain and go to it.

The next time you need to patch that instrument into the sound system make sure that you are going direct.

1998 Jordan Audio Consultants