Radial Engineering J48 Stereo User's Guide

j48 stereo user guide
jensen transformer equipped
active 48v phantom powered direct box

Radial Engineering Ltd.
1588 Kebet Way, Port Coquitlam BC V3C 5M5

Tel: [phone] • Fax: [phone] • Email: [e-mail]

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

Specications .................................................................... 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 benets 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 nd 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 nd the answer or need further
clarication, we invite you to send us an email at [e-mail] and we will do our very best to reply in short order.

Now get ready to enjoy the world’s nest phantom powered active direct box!

Radial Engineering Ltd. J48 Stereo™ User Guide

1

FEATURES

1. ¼” THRU-PUTS: Left and right parallel outputs used to

connect the hi-Z instrument signal to an amplier, tuner or

personal monitoring system.

2. ¼” INPUTS: Left and right unbalanced, hi-Z inputs used to
connect instruments.

3. -15dB PAD: Reduces the input sensitivity to prevent overload.

4. +48V: LED indicator will glow when the J48 Stereo is
receiving phantom power.

5. HPF: High-pass lter switch gently rolls off bass to remove

rumble and resonant feedback (-3dB @ 80Hz).

6. BOOKEND DESIGN: Creates a protective zone around the
switches and connectors.

7. 180° POLARITY (side panel): Reverses the polarity of the
RIGHT XLR output by toggling pins-2 and 3.

8. I-BEAM REINFORCED: 14-gauge steel enclosure with rigid
I-beam construction makes it impossible to torque the PC
board and cause solder joints to go cold.

9. XLR OUT: Left and right balanced, low impedance mic level

output. Wired to AES standard (pin-2 hot).

10. GROUND LIFT: Disconnects the ground from the audio

signal path and helps eliminate hum and buzz caused by

ground loops.

11. NO SLIP PAD: Provides electrical and mechanical isolation
and keeps the J48 Stereo from sliding around.

12. POWDER COAT FINISH: Durable nish keeps your J48
Stereo looking great for years.

1

8 9 11 12107

2 3 4 5 6

Radial Engineering Ltd. J48 Stereo™ User Guide

2

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.

MonitorsSub-Mixer

ThruThru

InputsInputs

J48 Stereo with a keyboard, mixer and powered speaker.J48 Stereo with an acoustic guitar and stage amp.

Radial Engineering Ltd. J48 Stereo™ User Guide

3

Balanced OutsBalanced Out

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 amplier 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.

Radial Engineering Ltd. J48 Stereo™ User Guide

4

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
rst line of defence 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.

SOURCE

GROUND LOOP HUM

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.

Radial Engineering Ltd. J48 Stereo™ User Guide

EMI & RADIO NOISE

60Hz

Hum

ELECTRICAL GROUND PATH

5

TRANSFORMER

BREAKS THE LOOP

RECEIVE

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 benet

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:

1. Fender bass to DI to amp and PA

PA

2. Acoustic guitar with active electronics to DI to PA

PA

Tuner

Amp

3. Upright bass to dedicated preamp to DI to PA 4. Stereo keyboard to DI to PA

PRE
AMP

PA

PA

Monitors

Radial Engineering Ltd. J48 Stereo™ User Guide

6

USING THE HIGH-PASS FILTER

A very handy feature that is built into the J48 Stereo is the high-pass lter. When activated,
it gently rolls off low frequencies below 80Hz and helps eliminate resonance and feed-

back. This handy feature is particularly effective at cleaning up the low registers, making
it easier to mix.

The other benet 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:

1. 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.

2. 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.

3. 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.

Radial Engineering Ltd. J48 Stereo™ User Guide

7

As this switch is recessed, use a

small screwdriver to activate.

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.

J-Rak 8 J-Rak 4

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 ange and user-writable tabs.

Radial Engineering Ltd. J48 Stereo™ User Guide

8

SPECIFICATIONS

Audio circuit type: ..................................................................................... Proprietary analog circuit with low-noise op-amp

Frequency response: ..................................................................................................................................... 20Hz ~ 20KHz

Dynamic range: .......................................................................................................................................................... 109dB

Noise oor: .............................................................................................................................................. -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 lter: .................................................................................................................................................. -3 dB @ 80Hz

XLR conguration: ......................................................................................................................... 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

Radial Engineering Ltd. J48 Stereo™ User Guide

9

BLOCK DIAGRAM

J48 Stereo Block Diagram

PAD

INPUT

THRU

INPUT

THRU

SWITCH

PAD

SWITCH

Radial Engineering Ltd. J48 Stereo™ User Guide

HIGH-PASS

FILTER

SWITCH

BUFFER

HIGH-PASS

FILTER

SWITCH

BUFFER

10

PHASE

INVERTER

PHASE

INVERTER

IN+

ISOLATED

POWER
SUPPLY

IN-

180° POLARITY

REVERSE

SWITCH

CHASSIS
GROUND

VCC

TO

+

CIRCUIT

-

GROUND

LIFT

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 nish 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 [e-mail] 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 modication 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, INCI-

DENTAL 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.
1588 Kebet Way, Port Coquitlam BC V3C 5M5

Tel: [phone] • Fax: [phone] • Email: [e-mail]

Radial J48 Stereo™ User Guide - Part #: R870 1017 00 Copyright © 2015, all rights reserved. Appearance and specications 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.