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Radial J48 Phantom Powered Active Direct Box


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Radial J48 Phantom Powered Active Direct Box

This is a great DI Box for many applications!

The Radial J48 has been designed from the ground up to deliver the most natural tone. As a direct box manufacturer, we do not believe it is our task to alter the sound of your prized '1962 Fender Jazz Bass', but retain and transfer the true character of the instrument to the mixing console without adding distortion or introducing artifact. This design philosophy has gained a tremendous following from many of the world's most demanding musicians.

Using only 48V phantom power, the Radial J48 is an active direct box that produces an exceptionally linear response that extends from 20Hz up to well above 40kHz. Low distortion of all types is achieved via a unique digital switching power supply that raises the internal operating rail voltage for added headroom and improved signal handling. The results are truly amazing. The J48 delivers an ideal even-order harmonic cascade and a sonic performance that outperforms DIs costing several hundreds more.

And like all Radial products, the J48 is both feature-rich for studio and made tough to handle the road. This includes a -15dB input pad to tame extra loud signals, 180º polarity reverse for feedback control on stage and a ground lift to help reduce hum & buzz caused by ground loops. Special features include a merge function that elegantly mixes left-right signals to mono without phase cancellation. To minimize resonant feedback with acoustic instruments, the J48 is also equipped with an 80Hz high-pass filter (low-cut). When engaged, this also increases headroom by eliminating unneeded bass frequencies.

Radial's innovative book-end design protects switches and connectors from abuse while the internal I-beam construction eliminates stress on the PC board. This serves to reduce solder joints from going 'cold' and delivers trouble-free performance for years. A full-bottom no-slip pad provides mechanical and electrical isolation while providing plenty of 'stay-put' for rockin' stages!

The Radial J48 is used by artists as diverse as acoustic guitarist Tommy Emmanuel; super-star engineer Joe Chiccarelli; and one of the most successful bands of all time Fleetwood Mac. The Radial J48… the world's finest 48V phantom powered active direct box.

J48 for Live Touring

A direct box is primarily used to get an instrument signal from the stage to the mixing desk and PA system. The Radial J48 delivers the natural tone exceptionally long distances without adding distortion or coloring the sound in any way.

J48 in the Studio
When recording direct, the quality of the direct box interface assures the purest signal going to the track. The Radial J48 is particularly well suited for recording bass or capturing a direct track from a guitar.
Reamping™ with the J48
Reamping means sending a dry track from the recorder back out to pedals and amps. This tricks has been used for years by top professionals. The Radial J48 is ideally suited to capture the sound of the instrument for later Reamping.


J48™ Specifications

The Radial J48 has gained a tremendous following through the professional audio community. With significantly more headroom, lower distortion and unmatched durability, it is no wonder that the J48 has become the most specified direct box on stages around the world. As you will note with the specifications below, the J48 is exceptionally linear when tested both under laboratory conditions and when placed under the extra stress of 100 meters (300 feet) of cable. In the lab, the high frequency response actually exceeds 40kHz! This makes the J48 a perfect candidate for the most demanding studio recording while being the obvious choice for the artist on stage.

Radial J48 Block Diagram
Radial J48 Block Diagram
Radial Blue Report
The Radial Blue Report
In effort to provide the more discerning audio engineer with all of the technical support materials to make a proper and informed decision, we have produced the Radial Blue Report. This provides in-depth distortion tests and analysis of four popular direct boxes....

Click here to view pdf
Specifications are subject to change without notice.
Audio circuit type: Proprietary analog circuit with low-noise op-amp
Frequency response: 20Hz ~ 20kHz
Dynamic range: 109dB
Noise floor: -99dB below 0dBu
Equivalent input noise: -103dBu
Maximum input: +10dBu
Phase deviation: +10º at 20Hz | 0º at 1kHz | -1º at 20kHz
Total harmonic distortion: 0.002% @ -5dBu
Inter-modulation distortion: 0.003% @ -3dBu
Input impedance: 220kΩ - ¼" input
Output impedance: 600Ω - XLR output
Merge function: IN and THRU jacks are summed to mono
Input pad: -15dB
Polarity: 180º signal polarity reverse switch
Low-cut filter: -3 dB @ 80Hz
Ground lift: Disconnects pin-1 at XLR output
XLR configuration: AES standard (pin-2 hot)
Power: 48V phantom - proprietary digital switching
Construction: 14 gauge steel chassis and outer shell
Finish: Durable powder coat
Size: 3.3" x 5.0" x 2" (84 x 127 x 48mm)
Weight: 1.55 lb (720 g)
FCC approval: Complies with section 15 of the FCC Rules
Conditions: For use in dry locations only between 5°C and 40°C
Warranty: Radial 3-year, transferable
Radial J48 Distortion vs Frequency
Radial J48 Distortion vs Output
Radial J48 Phase Response
Radial J48 Intermodulation vs Output
Radial J48 FFT
Radial J48 FFT
Click to view larger graphs


J48™ Using & Applications

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. The following describes the basic approach to using the J48. For full details, please view the full J48 user's guide.


The Radial J48 is a professional direct box that is equally useful for studio as it is for performance. It serves the purpose by converting the high impedance output of an instrument to a low input impedance, microphone level signal that is compatible with mixing console inputs. It also balances the signal to allow long runs to upwards of 1000 feet (300 meters) without appreciable signal loss or noise.

Unlike typical direct boxes that simply use phantom power to drive an internal buffer, the J48 actually converts phantom power from DC to AC, then uses a unique internal switching power supply to increase the internal working voltage in order to achieve much greater headroom. Because of this process, the active amplifier (buffer) is not constantly red lining. This means we do not have to trade off frequency response for dynamic range. The result is a response curve that starts at 10Hz and extends well above 40kHz! This assures the natural tone of the instrument is retained without degradation or introducing artifact.

Making Connections

As with any electronic audio device, make sure all levels are turned down and/or power is off before making connections. This avoids power-on transients or capacitor discharge from harming speaker components.

J48 Standard Instrument Setup
Click to view large image.

Standard Instrument Setup

  1. Connect a ¼" cable from your instrument to the J48 input.
  2. Connect a ¼" cable from the thru connector to your instrument amplifier. This 'straight through' parallel connection is easily tested by turning up your amp. Always test at a low volume to make sure connections and cables are working properly.
  3. Connect an XLR cable from the J48 output to a mic-preamp input on your mixing console. Make sure you turn the 48V phantom power on. Today pretty much all mixers are equipped with 48V phantom powering. This ingenious system sends a DC signal back to the J48 that powers the internal amplifier and does not interfere with the AC audio signal path.
  4. Slowly turn the volume up on your mixer to a low level and test to make sure signal is present. If you encounter any buzz or hum, try lifting the ground. Begin playing. If you encounter any distortion, lower the source volume or hit the input pad.
  5. It's that easy! You are set to go!

Once connected, turn on your sound system. Make sure the 48V phantom power on the console is on before you turn up the system volume levels. To check for phantom power, depress the 80Hz high-pass filter on the J48 while looking at the LED. It should flash once to tell you that phantom power is present. The LED will not stay on. This is done on purpose to deploy all available current from phantom to the audio circuit. You are now ready for audio testing. Play your bass or acoustic guitar. You should be able to hear it in you stage amp if one is connected. Slowly increase the sound level. If you encounter any hum or buzz, try lifting the ground on the J48. This can often be used to eliminate the hum caused by ground loops.

Using the J48 with an Acoustic Guitar

Using the J48 with an Acoustic Guitar

One of the most common applications for the Radial J48 is with an acoustic guitar on stage. The J48 is designed to be used alone, with the PA and monitoring system, or in combination with the PA system and on-stage instrument amplifier.

On large professional concert stages, the monitors or sound on the stage is typically controlled by a monitor engineer or the front-of-house (FOH) engineer working double duty. In this case, the J48 is basically invisible whereby the guitar connects to the J48 and the rest is handled much in the same way as a microphone would be. An instrument amplifier is optional.


Fighting Feedback

The single biggest challenge with acoustic instruments is obtaining sufficient level on stage before feedback. To help eliminate feedback, the J48 is equipped with a low-cut (high pass filter) that gently rolls off bass below 80Hz. This greatly assists by eliminating low frequency resonance.

Once on stage, if you find that you get more feedback in some areas, and less in others, try flipping the polarity switch. This will change the way the PA system and wedge monitors interact which can improve the sound and eliminate resonant feedback hotspots.

Some players enjoy having their own instrument amp on stage. This lets them set up a sound that they may enjoy. This may however be counterproductive to good sound in the room. For instance, adding reverb on stage may sound good, but when playing in an echo filled arena, more reverb in the hall could completely loose the acoustic guitar. The same applies to EQ. Cutting mid range on stage may sound good to you, but when mixed through the PA, you will want to send a flat signal to FOH so that the engineer can mix the sound so that it can be heard above the drums and other instruments.

Using the Radial J48 with a Bass Guitar


Using the Radial J48 with a Bass Guitar

As described above, just like an acoustic guitar, a bass guitar can either be used 'direct' or be used along with a bass amplifier. This applies to both recording in the studio and playing live. The advantage of a direct set-up is simplicity. No amps to carry around, no phase issues… just plug and play. For some, such as hired gun Ric Fierabracci, this approach can really work well.

"On the last Tom Jones Tour, I plugged my bass direct into the J48 and from there, had my in ear monitors set up to sound good for me and let the FOH engineer handle the sound up front. This is not about me or bass solos. This is the type of gig where all of the focus is on backing up the artist. I found this set up to be very effective. The Radial J48 quietly goes about doing its job so that I can concentrate on cues and making the artist sound great each and every night." Ric F.

Combining the direct feed from the Radial J48 with the sound of a mic'd amplifier is a more common approach, particularly in a live event. Here, the bass player can create the sound and feel he wants on stage which is extremely important when laying down grooves with the drummer. But the same applies when it comes to EQ… what may sound great on stage, may not necessarily sound good in the hall. This is why most players take a direct feed from the bass before it goes to the amp, thus allowing the FOH engineer to work with an unprocessed sound and optimize the EQ for the room. Reversing the polarity on the bas can sometimes help time-align the low frequencies to reduce resonance and make mixing easier.

Using the Radial J48 with keyboards

Because the Radial J48 is able to handle higher levels than other active DI's, it is well suited to handle keyboards and is particularly good with older vintage keyboards that have a limited output such a vintage Rhodes Piano. When using the J48 with highly dynamic instruments such as digital pianos, samplers and drum machines, it is advisable to introduce the -20dB pad into the circuit. This will reduce the opportunity for overload distortion.

Merge Function

A cool feature on the J48 is the merge function. This is specifically designed to help manage huge keyboard rigs when there are more left & right outputs from keyboards than available channels on the mixer. Depressing the merge switch changes the input and throughput to two inputs and allows you to passively mix the left & right signals to a mono output. This can save valuable time during setup and eliminate the need of reprogramming all of the sounds to mono.

Merge used mix a stereo keyboard to mono.
Merge used to mix a keyboard and sampler.

Using the Radial J48 in the studio

Do not be put-off by the J48's relative small size compared to large flashy studio direct boxes. We have tested most of these expensive devices and the J48 will usually outperform them when it comes to delivering great audio. This does not mean that some of these studio DIs are not valuable. It can be fun to add personality to an instrument by introducing effects such as tube distortion or radical EQ curves. The J48 was however not designed to do this. Its job is to send the most accurate signal possible to the recording system and then allow the engineer to make artistic decisions from that point.

With the advent of digital recording, 'extra tracks' open up the door to creative options like never before. As such, whether you are recording bass, acoustic or electric guitars, it is a good idea to always take a direct feed from the instrument and save it t a track. By doing this, you can capture a magical performance that may never be recreated and then fix it in the mix later.

The Radial J48 is perfectly suited for this. All you do is connect the instrument to the J48, and the thru-put to the instrument amplifier. The XLR out feeds your recorder where you ca quietly capture the takes and save them for future use.

Re-amping Using the Radial J48 and Radial X-Amp

Using the Radial J48 with a Bass Guitar
Reamping combo: J48 and X-AMP.

Re-amping or re-recording is a process that involves recording a clean track and then playing the clean track back through a re-recording device like the Radial X-Amp using effects pedals and amplifiers. This is most often used with electric guitars but is now finding more use with bass, keyboards, percussion and even vocals!

For guitar, you would start by setting up the guitar and amp as usual except you would connect the guitar to the Radial J48's input and the thru-put to the guitar amp as shown above. The J48's XLR output would then go to the mixing console and recording system. As the guitarist is playing, you would record his amp using a microphone and simultaneously capture the direct clean sound of the guitar through the J48. Once the track is recorded, you can then send the guitarist home and get to work!

Here's the deal: Once you captured the recording, fixing a botched note is easy when the signal is clean but trying to do so with a distorted guitar track is tough if not impossible. Also, having a guitarist play and play and then play more until you have moved the mics around his amp can often take hours. A tired guitarist does not perform as well as one that is fresh! Capture the performance, then worry about the sound later.

With the J48's dry track, you are now set to send the guitar signal into the Radial X-Amp. The X-Amp is basically a line level to guitar amp converter and distribution amplifier. It allows pre-recorded balanced line signal to drive guitar amps or effects pedals. Hit play on your recorder and then send the signal through the X-Amp back into effects, and various amplifiers. While you are playing back the track have your associate move the mic around the room until it sounds right. This is the magic behind re-amping.



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