Get Connected Pt1 - Analogue Connections

Ever wondered why an XLR plug has three pins, or why it's called an XLR? Ever looked at a Jack plug and asked why some have two poles and some have three? Well, fear not dear reader, for today, your questions shall be answered!

In the first of a series of Blog posts, we'll be guiding you through the connections you'll find on your iConnectivity interfaces, and explain the differences and history behind them. In today's Blog, we'll take a look at the 'bread and butter' analogue audio connections, so commonplace in our industry.

The Jack Plug
The 1/4" Jack Plug is possibly the oldest audio connection still in commonplace usage. It dates back to the 19th century where it was originally developed for use in telephone switchboards. Its simple, rugged nature has led to it living on, over 100 years later.

In the music world, 1/4" Jack Plugs are most commonly found as an instrument connector; you'll find one on every electric guitar, and it's the de-facto standard for most synthesisers, sound modules etc.

Unbalanced, two-pole (bottom and centre) and balanced, three-pole (top) jack plugs

Unbalanced, two-pole (bottom and centre) and balanced, three-pole (top) jack plugs

Two main variants of the 1/4" jack plug exist: the regular, unbalanced (two-pole) jack plug, and the balanced (three-pole) jack plug. Typically, guitar plugs are two-pole connectors, pro-audio and some synthesiser modules are three-pole balanced. Headphones also use a three pole connector but that's because they're a stereo connection.

Whether it's an iCA4+, iCA2+ or a CA2/4, all our audio interfaces utilise 1/4" jack plugs. All our interfaces support balanced 1/4" inputs, with the iCA4+ offering two, additional, unbalanced Hi-Z inputs on inputs 1&2. The outputs on all our audio interfaces are on balanced 1/4" jacks to enable connection to professional equipment.  

The XLR Connector
The XLR connector, sometimes called a 'cannon' connector, is a professional connector which was introduced in the 1950s by the Cannon connector company; hence you'll sometimes hear some old-timers call it by its trade name.

Contrary to occasional myth, the XLR connector is so named because of Cannon's connector naming scheme (not some strange technical designation as is sometimes stated). X = X series connector, L= Latching, R = Resilient

With a few exceptions, all audio XLR connectors are of the three pin variety; this is because they're a balanced connector. They're most typically wired as: Pin 1 = earth, Pin 2 = Hot, Pin 3 = Cold

Male and Female XLR plugs with their connectors

Male and Female XLR plugs with their connectors

The XLR connector has been used for a few purposes over the years, but by far the most popular is for use with microphones. Almost without exception, every microphone made within the last 40 years has used an XLR connector.

All iConnectivity audio interfaces feature XLR connectors for the microphone inputs. We use highly convenient 'combi-jack' sockets which integrate the jack socket and XLR connection into one socket; saving space and helping to make our interfaces compact and portable. 

XLR connectors are also used on professional equipment for balanced line-level inputs and outputs - however, their large physical size means that balanced jack sockets are often used instead, to save space - as on iConnectivity audio interfaces.

Bob Malkowski