As with most clever products, necessity is the mother of invention — The Radial JPC is no exception. In this case it was the demand from recording engineers out there for a useful and simple solution to allow them to take full advantage of the power of new technologies like computers, media players and recorders, integrating them into their productions. With this integration comes the many challenges of physically connecting disparate consumer grade devices to the world of professional audio. This obvious need spawned the development of the Radial JPC.

The challenge of a Computer interface

For the audio engineer, interfacing computers and video equipment to a professional audio system involves dealing with connectors, signal levels and integrity: For the most part, consumer level products are outfitted with less than ideal connectors, are generally unbalanced and are notorious for causing system noise.

For instance the audio output connection from a computer sound card or Laptop is typically a 1/8” mini TRS (3.5mm) connector while audio from a DVD/CD player is generally an RCA connector. These high impedance sources must be converted to a balanced mic level in order to work along side microphones in snake systems, mic splitting transformers and consoles. The Radial JPC is outfitted with 1/8” TRS stereo input, twin RCA jacks and sports a stereo 1/4” TRS jack to make this easy. To help address the various output levels, a –10dB input pad ads flexibility while reducing opportunity for overload which of course will cause distortion.

To further enhance functionality, all of the input connectors are designed to act as thru-puts allowing the signal from a given source to not only pass through the JPC to the XLR balanced output, but allows the system engineer to drive a secondary mixer or recorder at the same time. This would typically be used for personal monitoring, for recording a performance, to drive a second speaker system or possibly an assistive listening system.

The JPC's 'active hybrid' design

Probably the single most troublesome aspect to system design is eliminating noise caused by so-called ground loops. Most consumer electronic products are designed to work on their own and as such, do not incorporate extra ‘problem solvers’ in their circuit design. You connect the computer to the sound card, the sound card to some battery operated speakers and voila; it all works fine! The trouble of course starts when you connect the computer to the sound system and all of a sudden, you get that dreaded 60-cycle hum. This ‘noise’ is caused by stray voltage and the resulting common mode noise as the two devices are connected together. The solution: Transformer isolation.

Although the Radial JPC is an active direct box, the input connections are 100% transformer isolated giving rise to its ‘hybrid’ designation. These isolated inputs reduce noise while the active drive circuit performs the impedance conversion and balancing allowing long cable runs. This ‘best of both worlds’ solution makes hook-up noise-free, reduces input circuit loading and gives you great sound!

Why balancing in the first place?

Balanced circuits first appeared with the proliferation of the telephone some 100 years ago. It was found that when a signal is transmitted over a balanced low-impedance twisted pair of wire, noise was significantly reduced when driving long distances. This basic phase-canceling technology has remained unchanged and is the foundation for all balanced professional audio-interconnect equipment today.

There are many reasons for converting hi-impedance signals to low-impedance balanced circuits: First and foremost, it allows long cable runs without appreciable noise. Proper impedance and level matching not only improves sound quality, it also is critical when interfacing with snake systems that are outfitted with splitters. Splitters employ mic bridging transformers. These are designed to work with 600-Ohm microphone levels, which would otherwise be saturated with higher signal levels. Furthermore, since signals from microphones are usually running along side the output from direct boxes, excessive levels can cause crosstalk or induced noise from the higher output device. The Radial JPC automatically converts these signals to balanced mic levels, solving the problem.

The 48V Phantom Power advantage

The Radial JPC is 48-Volt phantom powered. This means that it derives its power source from a DC voltage supplied from the mixing console through the XLR cable as opposed to using batteries or a local power supply. Phantom powering makes hook-up easy and worry free. Simply connect, turn the phantom power on at the console* and you are ready to go!

* Always ensure that the volume levels are turn down to zero before turning on phantom power. This will ensure the turn on transient does not harm your speakers or sound system.

Getting down to size!

Another major concern for the field technician is keeping size to a minimum. What is the point of using a laptop computer only to have the interface double its size! As a tool, the JPC is compact enough to fit in a toolbox making it easy to carry anywhere and quick to deploy. The compact size also makes it easy to place adjacent to laptop computers and can be stored in computer bags for easy transport. Because of the JPC’s exceptional I-beam construction and protective bookend design, worry-free transportation means the JPC will not let you down and the show will go on!

The JPC can also be mounted in Radial's J-Rak, which can hold up to eight JPC, JDI, J48 or other Radial DI and splitter products.