Radial engineering J48 1-channel Active 48v Direct Box User Guide
- June 3, 2024
- Radial engineering
Table of Contents
J48 1-channel Active 48v Direct Box
User Guide
J48 STEREO USER GUIDE
JENSEN TRANSFORMER EQUIPPED
ACTIVE 48V PHANTOM POWERED DIRECT BOX
Radial Engineering Ltd.
1845 Kingsway Ave., Port Coquitlam, BC V3C 1S9, Canada
Tel: 604-942-1001 • Fax:
604-942-1010 • Email:
[email protected]
J48 STEREO DIRECT BOX USER GUIDE
Introduction …………………………………………………………….. 1
J48 Stereo Features …………………………………………………. 2
Making Connections …………………………………………………. 3
Using the PAD …………………………………………………………. 4
Using the Ground Lift………………………………………………… 4
Using Various Instruments …………………………………………. 5
Examples ………………………………………………………………… 6
Using the High-pass Filter …………………………………………. 7
Using the Polarity Reverse ………………………………………… 7
Optional mounting accessories ………………………………….. 8
Specifications ………………………………………………………….. 9
Block diagram ………………………………………………………… 10
Radial Limited Warranty ………………………………Back Cover
Thank you for purchasing the Radial J48 Stereo. This wonderful active direct
box employs a unique internal switching supply that employs 48 volt phantom
power and steps it up to increase the signal handling while it lowers
distortion of all types. Part of the magic behind the design is that it
enables the user to lift the audio ground connection to eliminate noise
without disconnecting the 48V phantom power source. This means that you can
enjoy the benefits of an active direct box without having to resort to
batteries or some form of external power supply. This makes the J48 Stereo a
very effective DI box for all types of instruments in both live stage and
studio recording applications.
The J48 Stereo is in fact a very easy to use direct box that is purpose-made
to be compact and quick to deploy. You simply plug it in, turn on the phantom
power and it goes to work. There are however a number of features built in
that should be understood in order to get the most out of your J48. So please
take a few minutes to go through this user guide to ensure you get the most
out of it. If after you have read it, you find yourself asking questions;
please visit the FAQ section of the web page. This is where we post updates
and questions from users. If you still do not find the answer or need further
clarification, we invite you to send us an email at
[email protected] and we will do our very best
to reply in short order.
Now get ready to enjoy the world’s finest phantom powered active direct box!
FEATURES
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¼” THRU-PUTS: Left and right parallel outputs used to connect the hi-Z instrument signal to an amplifier, tuner or personal monitoring system.
-
¼” INPUTS: Left and right unbalanced, hi-Z inputs used to connect instruments.
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-15dB PAD: Reduces the input sensitivity to prevent overload.
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+48V: LED indicator will glow when the J48 Stereo is receiving phantom power.
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HPF: High-pass filter switch gently rolls off bass to remove rumble and resonant feedback (-3dB @ 80Hz).
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BOOKEND DESIGN: Creates a protective zone around the switches and connectors.
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180° POLARITY (side panel): Reverses the polarity of the RIGHT XLR output by toggling pins-2 and 3.
-
I-BEAM REINFORCED: 14-gauge steel enclosure with rigid
I-beam construction makes it impossible to torque the PC board. -
XLR OUT: Left and right balanced, low impedance mic level output. Wired to AES standard (pin-2 hot).
-
GROUND LIFT: Disconnects the ground from the audio signal path and helps eliminate hum and buzz caused by ground loops.
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NO SLIP PAD: Provides electrical and mechanical isolation and keeps the J48 Stereo from sliding around.
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POWDER COAT FINISH: Durable finish keeps your J48 Stereo looking great for years.
OVERVIEW
The Radial J48 Stereo is an active direct box that derives its power from the
48 volt phantom supply from the mixing console or mic preamp. You simply plug
in and it will quietly go to work.
MAKING CONNECTIONS
As with all audio gear, always ensure audio system levels are turned down or
equipment turned off before making connections. This will avoid plug-in or
turn-on transients from damaging more sensitive components such as tweeters.
There are two channels on the J48. These are identical and feature a ¼” INPUT,
a ¼” THRU-put and a balanced XLR out.
Connect your source instrument to the input and the balanced XLR out to the PA
system or recorder. The THRU connector output provides the means for
connecting the signal to a stage amp or personal monitor system. Simply
connect the THRU to your amp or monitor. Unbalanced cables are much more
susceptible to noise than their balanced counterparts.
Keeping unbalanced cables under 8 meters (25′) in length is good practice
while balanced cables can easily extend 100 meters (300′). The balanced output
of the J48 Stereo is mic level, meaning that it should be connected to the
mic input of a mixing console or mic preamp. Once connected, make sure phantom
power is activated. The green LED on the J48 Stereo will illuminate to let
you know phantom power is present. 
USING THE -15dB PAD
Inside the J48 Stereo is a unique switching power supply that is designed to
provide plenty of headroom even when pushed very hard. There are however,
instances when the output from an instrument can be extreme. To prevent
distortion, the J48 Stereo has a -15dB input pad that reduces the input
sensitivity. Examples could be a very high output digital piano, active bass
guitar or maybe the overly aggressive output from a DJ mixer. If you hear
distortion, simply depress the PAD.
USING THE GROUND LIFT
An active direct box is in essence a unity gain amplifier that requires power
to work. In the early days, active direct boxes typically employed a battery
for power. Today, phantom power from the console has become the most common
power source.
This 48 volt supply uses the pin-1 (ground) and pin-2 (hot) on the XLR cable
to provide DC power to the direct box while audio is sent in the opposite
direction over the same cable.
GROUND LOOPS
A common problem occurs when connecting a stage amp to the direct box whereby
a so called ground loop can present itself. This is often caused by DC offsets
or voltage differentials that can introduce hum and buzz in the sound system.
The first line of defense is to lift the audio ground – pin-1 on the XLR. With
most direct boxes, when you lift the ground you also disconnect phantom
power. This then requires using a battery or external supply to provide the
power – options that are not desirable. With the J48’s unique circuit design,
instead of lifting the ground at the XLR, it is done in the power supply
section of the circuit board. This eliminates the noise problem without losing
power. If you hear noise, simply depress the ground lift switch.
The image above shows an audio source and a destination with a common electrical ground. As the audio also has a ground, these combine to create a ground loop. The transformer and ground lift work together to eliminate the ground loop and potential noise.
USING VARIOUS INSTRUMENTS
The J48 Stereo is active. This means that it has a built-in preamp or buffer
circuit that drives the signal. This is the benefit of an active direct box
over a passive counterpart. In other words, if you have a passive source such
as an old Fender bass, the J48 Stereo presents a very effective interface.
Many sound engineers also prefer the added gain of an active direct box on
active instruments such as with acoustic guitars and vintage keyboards that
may not have the optimal output.
In some instances the J48 Stereo can also improve signal to noise.
EXAMPLES OF INSTRUMENTS:
USING THE HIGH-PASS FILTER
A very handy feature that is built into the J48 Stereo is the high-pass
filter. When activated, it gently rolls off low frequencies below 80Hz and
helps eliminate resonance and feedback.
This feature is particularly effective at cleaning up the low registers,
making it easier to mix.
The other benefit with eliminating bass is that you actually increase the
available dynamics. Low frequencies and their huge waves require more power
than their high frequency counterparts. Reducing low frequency content in the
music program results in more available headroom and less distortion.
USING THE POLARITY REVERSE SWITCH
The RIGHT channel on the J48 Stereo is equipped with a polarity reverse switch
that toggles pin-2 and pin-3 on the XLR. This handy feature can be used in
several ways:
-
Stereo Imaging
In some instances, particularly when recording – changing the relative phase between the left and right channels can produce very pleasing results. Similarly, when using two sources such as combining a magnetic pickup with a piezo on an acoustic guitar, changing the relative phase between them can sometimes produce a more natural sound. -
Eliminating Feedback
Resonant feedback on a live stage is often produced when sound sources such as the PA and stage amp combine to create a hot-spot at certain frequencies. This can cause an acoustic instrument to vibrate, resulting in low frequency feedback. This can often be minimized by reversing the polarity at the XLR, electronically moving the problem out of the way, without having to resort to excessive (tone altering) equalization. -
Adapting to non-AES standards
When interfacing with older vintage audio equipment, the polarity may be reversed whereby pin-3 may be hot. Depressing the polarity switch lets you match the phase if needed.
OPTIONAL RACK MOUNTING KITS
The J-Rak 8 and J-Rak 4 are an innovative rack mount chassis. The J-Rak 8 has eight vertical slots for Radial J48 Stereo direct boxes or the other Radial J-Class products. The J-Rak 4 has four horizontal slots.
Each direct box can be front or rear mounted allowing the system designer to
have the XLR’s on the front of the rack or rear, depending on the
application.
J-CLAMP
The J-Clamp is a mounting adapter that allows any of the Radial J-Class
products to be permanently mounted in locations such as in podiums, under
board room tables and inside amplifier and effect racks. Features a heavy-duty
steel shell with built in mounting flange and user-writable tabs.
SPECIFICATIONS
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
Input pad:………………………………………………………………………… -15dB
Polarity:……………………………………………………………………….180º signal polarity reverse – right
channel only
Low-cut filter: ………………………………………………………………-3 dB @ 80Hz
XLR configuration: ……………………………………………………… AES standard (pin-2 hot)
Power: …………………………………………………………………. 48V phantom – internal switching supply
Construction: ……………………………………………………………..14 gauge steel chassis and outer shell
Finish: ……………………………………………………………………..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
BLOCK DIAGRAM
RADIAL ENGINEERING 3 YEAR TRANSFERABLE WARRANTY
RADIAL ENGINEERING LTD. (“Radial”) warrants this product to be free from defects in material and workmanship and will remedy any such defects free of charge according to the terms of this warranty. Radial will repair or replace (at its option) any defective component(s) of this product (excluding finish and wear and tear on components under normal use) for a period of three (3) years from the original date of purchase. In the event that a particular product is no longer available, Radial reserves the right to replace the product with a similar product of equal or greater value. In the unlikely event that a defect is uncovered, please call 604-942-1001 or email [email protected] to obtain a RA number (Return Authorization number) before the 3 year warranty period expires. The product must be returned prepaid in the original shipping container (or equivalent) to Radial or to an authorized Radial repair center and you must assume the risk of loss or damage. A copy of the original invoice showing date of purchase and the dealer name must accompany any request for work to be performed under this limited and transferable warranty. This warranty shall not apply if the product has been damaged due to abuse, misuse, misapplication, accident or as a result of service or modification by any other than an authorized Radial repair center.
THERE ARE NO EXPRESSED WARRANTIES OTHER THAN THOSE ON THE FACE HEREOF AND DESCRIBED ABOVE. NO WARRANTIES WHETHER EXPRESSED OR IMPLIED, INCLUDING BUT NOT LIMITED TO, ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE SHALL EXTEND BEYOND THE RESPECTIVE WARRANTY PERIOD DESCRIBED ABOVE OF THREE YEARS. RADIAL SHALL NOT BE RESPONSIBLE OR LIABLE FOR ANY SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES OR LOSS ARISING FROM THE USE OF THIS PRODUCT. THIS WARRANTY GIVES YOU SPECIFIC LEGAL RIGHTS, AND YOU MAY ALSO HAVE OTHER RIGHTS, WHICH MAY VARY DEPENDING ON WHERE YOU LIVE AND WHERE THE PRODUCT WAS PURCHASED.
To meet the requirements of California Proposition 65, it is our
responsibility to inform you of the following:
WARNING: This product contains chemicals known to the State of California
to cause cancer, birth defects or other reproductive harm.
Please take proper care when handling and consult local government regulations
before discarding.
Radial Engineering Ltd.
1845 Kingsway Ave., Port Coquitlam, BC V3C 1S9, Canada
Tel: 604-942-1001
Fax: 604-942-1010
Email: [email protected]
Radial J48 Stereo™ User Guide – Part #: R870 1017 00 / 09-2021. Copyright ©
2015, all rights reserved.
Appearance and specifications subject to change without notice.
This device complies with section 15 of the FCC Rules. Operation is subject to
the following two conditions: (1) this device may not cause harmful
interference, and (2) this device must accept any interference received,
including interference that may cause undesired operation.