The Original JD4 Rackmount DI

The original JD4 rackmount DI

Problem: Ground loop creates DC hum and buzz

Problem: Ground loop creates
DC hum and buzz.

Solved: transformer isolation eliminates DC noise

Solved: Transformer isolation disconnects the 'hard wire' electrical input from the output while allowing the audio signal to pass. Ground loops are eliminated.

JD6™ Development

The Radial JD6 circuit design stems from the original Radial JDI direct box which debuted in 1996. Over the following years, we received many requests from sound engineers for a rackmount high-density version of the JDI for keyboards and electronic drum machines. This resulted in our developing the Radial JD4™ which quickly gained prominence on stages with artists as diverse as Journey, Styx, Garbage, Nine Inch Nails, k.d. lang and Linkin Park.

The engine inside the JD6 is a high performance Jensen® audio transformer that isolates the input from the output to eliminate the hum and buzz caused by ground loops and problems introduced by stray DC offset voltages. The other advantage with the Radial JD6 is the way it handles the signal. Unlike active circuits that are 'dynamic range limited' depending on the rail voltage or available power, the transformers inside the JD6 saturate. In other words, high output devices like active basses and digital pianos can easily overload most active direct boxes causing harsh sounding distortion. The JD6 will not distort like an active circuit. This creates a warm sounding effect that is often referred to as having a vintage character. There is good reason for this: Most vintage audio devices are equipped with transformers!

Of course it must be noted that not all transformers are created equal. Just as a good dynamic microphone is only as good as the capsule, a passive direct box is only as good as the transformer inside. The JD6 employs the Jensen® audio transformers to ensure the transition from the unbalanced signal to the balanced output is both smooth and distortion free. Jensen® transformers have a warm sounding Bessel response curve and the ability to transfer all frequencies from 10Hz to 40kHz without introducing harmonic distortion.

When the JD4 was released, it heralded in several innovative features which had never been seen on a DI before:

  • A merge function passively sums a stereo source to mono by converting the input and thru-put to two left-right inputs.
  • A high frequency roll-off filter that eliminates bothersome hiss from older vintage keyboards and drum machines.
  • A 180° polarity reverse function that lets you correct the phase when combining two sources should one be reversed.
  • A series of switching jacks that allow the front panel inputs to override the rear panel for quick tracking in the studio or guest appearances on stage.
  • A series of radio frequency (RF) noise suppression filters on each channel to keep system noise down to a minimum.

The Radial JD6 further redefined what a rack direct box should be by adding two more channels, RCA connectors for interfacing Hi-Z sources such as CD players and computers – all the while improving the quality of the switches and connectors for greater durability when exposed to the harsh environment of professional touring.

The Radial JD6 sets the bar a step higher by introducing a series of internal ground switches that allow each channel to either float (factory default) or be grounded to the chassis. For system engineers who prefer to ground devices from a single point, a Channel-1 chassis ground switch is provided. This switch is recessed to prevent accidental use and is actuated using a 'tweaker'. We have even added a separate rear-panel ground lug should direct grounding to the rack or star grounding in the studio be preferred.

Best of all, in redesigning the JD6, we were able to significantly reduce the manufacturing assembly time and metal costs to the point where we could offer two extra channels at around the same price as the old JD4! And what could be better than six channels for the price of four, all in the same physical size!