J+4™ Development

The Radial J+4 is a product that audio engineers and system designers have been asking for. Why? Well it appears that although there are several consumer-to-pro interfaces in the market, they all seem to fall short on some key points. This in fact is why we developed the J+4 - not so much because the world needs one, but more so, it seems that the world is looking for one that has the right feature set and does the job as expected.

A line driver like the Radial J+4 is designed to take a consumer level -10dB signal and boost the output so that it can effectively drive a professional +4dB line input on a mixing console. Fundamentally, this appears to be a simple task. The difficulty comes when attempting to do it in a small package. The results are usually a trade off between size, signal handling and less than ideal audio performance and feature set. Or worse yet, the price is so high that it becomes unaffordable.

Our goals in developing the J+4 included:

  • It had to produce plenty of signal gain
  • We had to make sure it was quiet and noise free
  • A top quality audio signal path was a must
  • It had to be stereo to work with iPods and computers
  • All kinds of connector options needed to be on board
  • It needed a universal power supply for use anywhere
  • The construction had to be rugged for professional use
  • There had to be a way to have it permanently installed
  • We wanted it to be easy in any application
  • It had to be reasonably priced

In order to achieve good quality audio, you need dynamic range. This means providing enough current to the circuit to achieve acceptable headroom. Even though 48V phantom power has plenty of voltage, it is not an option due to the limited current (5mA). Therefore we chose to employ a 15V supply with 400mA.

Next, we chose to transformer isolate the inputs in effort to eliminate hum and buzz caused by ground loops. Transformers are also advantageous in that they saturate producing a pleasing 'limiting' effect. Look inside the J+4 and not only will you see the input transformers, but you will note that all of the parts are discrete for optimal signal transfer. Given the fact that the J+4 is stereo, there are actually two preamps built into this compact box! To eliminate noise we took the power supply out of the box. This old trick has been used for years with mixing consoles and although some may find external power supplies painful, they benefit by having universal safety standards and being easily replaced should a problem occur.

With so many possible sources, providing ample connectivity had to be considered. We chose to include ¼" jacks for keyboards and DJ mixers, RCAs to make it easy to connected CD players and other consumer electronics, and finally a 3.5mm (1/8") TRS to address computers and iPods. This, we felt would make it easy to use the J+4 in just about any situation. And keeping with 'easy' in mind, a simple level control was added to allow the user to set the signal level to suit.

Construction was easy... we simply employed the same proven design that we pioneered when we launched the J48 and JDI. This includes heavy duty 14 gauge steel, I beam construction, book end protective zones, and full bottom cushioning that provides both electrical insulation and mechanical isolation. This approach also enables the J+4 to be rack mounted in the J-Rak or bolted down using the J-Clamp.

The Radial J+4 is a solid, dependable line driver that will take just about any stereo feed and boost the signal to a +4dB professional balanced signal.