The single most important development goal of the Radial J48 was increasing the headroom without compromising sound quality. To this end, every possible effort was made to deploy the limited energy resources of phantom power to the audio signal path.

To begin, phantom power is converted using a super-efficient digital switch-mode power supply that steps up the internal rail voltage to an impressive 10 volts. This allows one to hit the J48 with as much as 9-Volts without choking! To further increase available horsepower, all non-essential devices such a power-hungry LEDs are turned off when the J48 is in use. A typical LED requires almost as much current as does the complete audio circuit!

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Open up the Radial J48 and you will see huge, over-sized capacitors that provide ample current storage to assure clean, unobstructed power for the signal. With added headroom comes improved performance in all areas: Less than half the phase distortion of competing DIs, significantly lower harmonic distortion and single-digit inter-modulation distortion are all realized. Paying attention to these basic details has the net result of better sound.

But great sound is not the only innovation: The Radial J48 introduces several new functions that improve functionality and open the doors for greater creativity. The input panel features the usual ¼” instrument input and thru-put connections. An innovative Merge function converts the thru-put into a second input to sum stereo sources to mono such as stereo keyboards or CD players when mixer input channels may be of short supply. A -15dB pad may also be inserted when confronted with abnormally high signals.

To reduce low-end rumble and run-away acoustic resonance, an 80Hz high-pass roll-off filter is provided. As with any power system whether it is acoustic or electrical in nature, bass always contains significantly more ‘RMS power’ than high frequencies. This is why low-frequency drivers require anywhere from 10 to 20 times more power in PA system designs than high-frequency tweeters. By gently removing unnecessary lows, the J48’s dynamic handling is increased by a full 3dB or twice the power handling. This innovative feature both reduces mud and increases headroom at the same time!

The filter switch also performs a second function. Depressing the switch will momentarily illuminate the front panel LED to advise if 48V phantom power is present. The LED does not stay illuminated as it would draw energy away from the audio circuit and reduce headroom.

The output panel contains the balanced 3-pin XLR wired ‘pin-2 hot’ following the AES standard along with a polarity reverse switch that toggles pin-2 to pin-3 ‘hot’. This allows the engineer to match older equipment and ads a dimension of creative freedom. A ground lift switch disconnects the XLR pin-3 thus grounding the J48 to the input side.

Construction

As with all Radial direct boxes, the Radial J48 is designed for use in abusive environments such as on fast-paced stages of concert touring. An innovative book-end design provides a protective zone around the switches and connectors that makes it practically impossible to damage these components.

The inner skeletal frame features a unique 14-gauge welded I-beam construction that makes it impossible to torque the PC board. Stress on the printed circuit board can introduce intermittent solder joints, which by all accounts is the primary cause of direct box failure.

An innovative full-bottom no-slip rubberized pad works double duty by assuring the J48 won’t slip and slide around when placed on an amplifier. The protective pad also ads an element of electrical shock resistance by providing a mechanical shield from guitar amp handles that are often directly coupled to the amp chassis.

Using the J48

The Radial J48 is a pleasure to use. It is ‘plug & play’ easy and is perfectly adept for studio as well as live concert sound. Connect the instrument to the ¼” input, the instrument amplifier to the ¼” output and the mixer to the XLR. Lift the ground if you encounter hum or buzz in the system.

The polarity reverse can sometimes help when looking for a ‘sweat spot’ and is always worth trying. In the studio, when combining a mic’ed signal with a direct feed, reversing the polarity can be huge!

Using the 80Hz roll-off filter is generally recommended for acoustic guitars as this will reduce the boxy sound that is often associated. It will also lessen run-away resonant feedback that can creep-up, especially as systems are being run loud. Depressing the filter switch will momentarily provide ‘48V power status’ which of course is a good idea before turning up sound system volume levels.

Another innovative function on the J48 is the merge switch. This resistive mixer allows a stereo source such as a stereo keyboard to me merged or mixed mono at the XLR output. This handy feature makes life easy for the engineer when confronted with more instruments than available channels. For the keyboard player, reprogramming stereo-panned outputs is not required. Just plug the stereo source in, hit the merge and you are ready to go.

As an added bonus, the Radial J48 and the Radial JDI can be mounted into a 19” rack device called the J-rack. This ‘inventory management device’ allows the same DI inventory to be allocated to individual instruments or be rack-mounted for keyboard set-ups as needs arise. There’s nothing more frustrating than having to waste a rack-mount DI when a single unit is required and nothing more irritating and unprofessional than a pile of DIs messing up a stage.