Before the advent of fancy digital and wireless matrix intercoms, productions the world over used the classic analog ‘partyline’. These systems typically connect via a 3-pin XLR, with one pin for voltage, one pin for line-level audio, and another as a common pin.
These party line systems have been produced by Creative Audio (a former division of Australia’s The PA People), Jands, and Clear-Com.
Due to their analog design, party line comms systems can be easily daisy-chained, split, and extended. The main system limit is the amperage of the power supply, and the noise floor (which will slowly get unbearable as you add more and more components).
For a recent church event (The Salvation Army’s Youth Councils 2019), I decided to experiment with wiring up a wireless extension of my analog party line. Our stage manager really needed to be un-tethered from cabling, but we didn’t have the budget to purchase a fancy wireless system.
My wireless system utilised a Sennheiser In Ear Transmitter system, a Shure Lapel system, and some custom wiring.
Wiring for Production Intercoms
Before we get stuck into the mechanics of a wireless intercom, let’s look at the wiring standard for these comms systems.
3-pin XLR Comms Pinout
The most common way to transport your intercom around the building is via 3-pin XLR. Almost all systems use the following pinout. You can verify this by measuring the voltage over pins 1 & 2 with a multi-meter.
- Pin 1: Shield/Common
- Pin 2: Power
- Pin 3: Audio
5-pin XLR Dual-Ring Comms Pinout
The classic Creative Audio system allows you to run two separate rings via a 5-pin XLR.
- Pin 1: Shield/Common
- Pin 2: Ring A Power
- Pin 3: Ring A Audio
- Pin 4: Ring B Audio
- Pin 5: Ring B Power
3-pin XLR Comms to 3-pin XLR Line-Level Audio Only
You can very simply wire up an adapter to take line-level audio out of your comms system, or inject line-level audio back into the intercom ring.
| 3-pin XLR Comms | 3-pin XLR Line-Level Audio Only |
| Pin 1 (Common) | Pin 2 |
| Pin 2 (Audio) | N/C |
| Pin 3 (Audio) | Pin 3 |
When wiring up such an adapter, it’s very important you don’t connect anything to the voltage pin. Verify it with a multi-meter, and then put some heat shrink over the pin so it doesn’t touch any other wires.
This wiring scheme can be used for both audio input, and audio output. It’s just line-level audio, so as long as you match the level you should be fine.
Connecting a Wireless System to your Wired Intercom
Now, let’s get back to the good part � freeing our stage manager of the wired belt pack!
This diagram shows the basic signal flow. You can see I am using standard off-the-shelf lapel & in-ears systems, along with some simple adapters.
4-pin XLR Headset Connector Pinout
Most comms headsets have a standard 4-pin XLR connector, carrying both Headset & Mic audio. This is the standard pinout for headsets:
- Pin 1: Mic Ground
- Pin 2: Mic Signal
- Pin 3: Headphones Ground
- Pin 4: Headphones Signal
4-pin XLR Headset to TA4F & 3.5mm TRS
The following table shows you how to wire up a headset to a standard Shure TA4F, and 3.5mm headphone jack.
| 4-pin Headset | TA4F | 3.5mm TRS |
| Pin 1 | Pin 1 | |
| Pin 2 | Pin 3 | |
| Pin 3 | Shield | |
| Pin 4 | Tip & Ring |
Your mileage may very with this, as some lapel belt packs are a bit fussy about the impedance.
You can save yourself the hassle of soldering up a TA4F, by purchasing a pre-made cable such as the Shure WA310. Cut the existing XLR end off this cable, and solder it to the 4-pin XLR.
End Result
The end result was faster, more efficient and seamless communication with our Stage Manager. This make periods such as sound check, and transitions, much easier. It’s also fun to try and make someone crack up while they’re walking across stage 🙂
Next event, I’m going to make a 2nd wireless system so I can wander around too.