News & Reviews

Field Guide - Telco and Codec
The JK Audio BluePack

Radio Guide Magazine - Jan / Feb 2009
by Eric Leonard

The BluePack is the latest must-have bit of radio reporter gadgetry from Joe Klinger’s JK Audio. Smaller than JK’s previous cellphone interfaces—and wireless—it has already proven itself invaluable in my field reporting in Southern California.


The BluePack combines a microphone preamp, audio mixer, and powerful headphone amplifier with the innovative cable-free Bluetooth interface that connects to virtually any cellphone.

The Bluetooth link eliminates the need to carry a dedicated headset-jack-to-interface cable. Guided by the manual’s well-described procedure, pairing the BluePack with a cellphone takes just a few seconds. Once paired, the BluePack memorizes the link to your cellphones, so it can make a call and connect quickly.

The front of the BluePack has only a few simple controls and indicators: three small, protected thumbwheels control microphone gain, line-in gain, and the headphone volume; a red LED shows power, another indicates peak audio level, and a single blue LED flashes with varying frequency to show Bluetooth status.

The case is formed from metal with a bomb-proof belt clip on the bottom and a 9-Volt battery tray on the side.

The back of the BluePack includes a single XLR microphone input, a pair of 3.5-mm jacks for line-level input and output, and a stereo 1/4-inch jack for headphones.


I pressed the BluePack into service the very day I picked it up. A Metrolink commuter train had collided head-on with a freight train in the San Fernando Valley, and our news team had to get to the scene – and on the air – as quickly as possible.

Police had closed the streets so reporter Aron Bender and I knew we would have to leave our RPU-equipped trucks behind and hike into the location. Additionally, rescue helicopters were landing and taking-off as firefighters used power tools to cut through the metal skin of the passenger cars.

Noisy situations like that make live-reports on a cellphone difficult; few handsets can deliver loud, clear audio – especially when the cell phone and cell-network’s echo-cancellation systems are at work. Nevertheless, the BluePack enabled me to bypass the cell phone’s auto-gain audio circuits and monitor a perfectly clear pre-delay feed from the radio station – despite the din of rescue workers around me.


In less chaotic situations, I have been using the BluePack to record incredibly clear telephone interviews in the field.

The stereo line-out jack includes the BluePack’s “send” microphone and line-in audio on the left channel and the “return” audio from the phone call on the right channel – with no crosstalk.

This can produce a perfect two-channel recording with my audio and the phone audio completely separated (just like a landline hybrid) and ready to edit.


Here are a few tips to help you get the best quality:

If possible, use a cell phone that allows the user to vary the Bluetooth audio output from the phone, because while the BluePack enables the user to adjust the overall headphone volume, it does not have a control for the incoming Bluetooth feed from the phone (my iPhone works great for this). Otherwise it may be difficult to find a good balance between the “local” and “return” program in your ears.

Secondly, pay close attention to the red “peak” LED on the front of the BluePack. While there is plenty of microphone gain available, it is easy to overdrive the audio sent to the cell phone over the Bluetooth link. I adjust the level so I can see the LED flash, then turn the gain down a bit so the LED does not illuminate, and the audio sounds great.

Finally, make sure your cell phone has “line of sight” to the BluePack while you are on the air. Although the Bluetooth link will stay connected at considerable range, I have found there are bits and pieces of audio garbled and dropped when the phone and the BluePack are separated by an object (or me).

KFI takes great care to use only the best quality audio in our news reports. When I need to do cell phone live shots, the BluePack delivers.

Eric Leonard has been a field reporter for KFI AM-640 in Los Angeles since 1995. He can be contacted at