Radial Engineering JDI Mk3 User manual
User Guide
Radial Engineering
1638 Kebet Way, Port Coquitlam BC V3C 5W9 tel: 604-942-1001 • fax: 604-942-1010
email: [email protected] • web: www.radialeng.com
Radial Engineering is a division of C•TEC (JP CableTek Electronics Ltd.)
JDI and
www.radialeng.com
DUPLEX
Mk3
RADIAL JDI & DUPLEX USER GUIDE
TABLE OF CONTENTS PAGE
1. Introduction .................................................................................1
2. JDI feature set ............................................................................2
3. JDI quick start ...........................................................................3
4. Direct box basics .........................................................................4
5. Features and functions ...............................................................7
6. Other cool uses for your JDI .................................................... 11
7. Frequently asked questions ......................................................12
8. Block diagram and specifications ..............................................15
Warranty ...................................................................... Back cover
Radial Engineering
1638 Kebet Way, Port Coquitlam BC V3C 5W9
tel: 604-942-1001 • fax: 604-942-1010
email: [email protected] • web: www.radialeng.com
Radial Engineering Ltd. is a division of C•T
EC
(JP CableTek Electronics Ltd.)
Features and specifications are subject to change without notice.
Part 1 - Introduction
Congratulations on your purchase of the world’s finest direct box! The
Radial JDI Mk3 is the latest version of the highly acclaimed JDI
and is without a doubt the finest passive direct box available
today. The JDI is very unique in that it does not color or alter
the sound in any way. This ensures the natural tone and
harmonic balance is retained, bringing out the very essence
of the instrument.
The JDI Duplex is a two-channel (stereo) version of
the JDI with two totally independent and isolated PC
boards. This allows the Duplex to be used with two
sources without causing ground contamination or
crosstalk. For simplicity, this manual will discuss
the JDI. All features and functions on the Duplex are
identical to those of the JDI.
Both direct boxes employ the Jensen JT-DBE
transformer for unmatched audio performance,
exceptional noise rejection and high signal handling.
This makes them ideal for acoustic guitar, bass and
keyboards. In fact, just about any audio signal is
transformed gracefully without artifact.
We advise that you read through this manual before using
the JDI so that you can maximize it’s potential. Please log
onto the Radial Engineering website at www.radialeng.com
for further details and updates. We invite you to forward any
comments, questions or suggestions to [email protected]
- we’d love to hear from you.
Enjoy!
True to the Music
Radial Engineering JDI User Guide
1
DUPLEX
JDI
Mk3
Radial Engineering JDI User Guide
2
Part 2 – The JDI Feature Set
(1) 15dB PAD switch - a -15dB pad can be introduced to
reduce the input voltage and ensure a clean, distortion-
free signal.
(2) MERGE switch - left-right merge function turns the
input and thru-put connectors into a pair of left-right inputs
with a mono output at the XLR.
(3) INPUT - 1/4" jack, 130kOhm instrument input.
(4) THRU - 1/4" jack, thru-put to send instrument signal
through to the instrument amplifier.
(5) Protective bookend cover overhangs the chassis
providing protection for switches and connectors.
(6) Welded I-beam construction for maximum strength
and durability and a baked enamel finish offer years of
trouble free performance.
(7) Full bottom no-slip pad - reduces slipping in use and
provides mechanical and electrical isolation.
(8) Double sided PC board - military grade circuit board
features a full ground plane for maximum protection
against stray magnetic fields and RF noise.
(9) XLR output connector - wired to the AES standard
with pin-1 ground and pin-2 hot, provides a balanced
150-Ohm mic level signal.
(10) POLARITY switch - 180º polarity reverse toggles the
XLR pin-2 and pin-3 to interface with older equipment.
Also used when combining two sources such as a mic
and a DI.
(11) GROUND switch - lifts the XLR pin-1 ground at the
output to eliminate hum and noise caused by ground
loops.
(12) SPEAKER switch - a pad circuit that allows you to tap
the signal from a speaker cabinet. Features a band-pass
filter to emulate a 12" driver. Note: Only use in parallel
with a speaker cabinet or load box.
True to the Music
Radial Engineering JDI User Guide
3
Part 3 – The JDI Quick Start
This section is for advanced users — it provides a quick set of instructions for those that are familiar with direct boxes and
gets right down to action! We suggest that you read through the entire manual for a better understanding of your JDI.
Caution! When connecting or disconnecting any audio device always ensure the power is off or all levels are set to
zero. This practice will reduce the opportunity for any noise such as a capacitor discharge from being sent through the
amplifier to the speakers, which could cause a big bang in your sound system or even cause a speaker to blow. This
is especially true with phantom powered equipment.
The Radial JDI Mk3 is a passive direct box and as such does not require any external power such as phantom or batteries
to make it work. Just plug-in and play!
To start, make sure all switches are in the ‘out’ position. Plug the instrument into the INPUT. Connect the THRU to the guitar
amplifier or keyboard mixer and the XLR OUTPUT to the PA or mixing console. Set the PAD to 0dB. Slowly turn up the input
level at the mixer and listen. See the Part 5 ‘Features and functions’ section about the ‘MERGE’ function.
The JDI’s Jensen audio transformer should be able to handle most instrument signal levels without distortion. At exceptionally
high signal levels, the –15dB pad should be used to reduce the input level to the transformer. If you hear distortion, simply
depress the –15dB pad button. If you intend to use the JDI in parallel with a speaker load, it is important that you read the
details on this application in the ‘Part 5 - Features and Functions’ section of this manual.
Since the Radial JDI employs an audio transformer, you are actually isolating the electrical connections between the input and
output. This will usually eliminate all buzz and hum caused by so called ground loops. The JDI is designed to be grounded
at either the input or the output side of the transformer. If you encounter 60-cycle hum or noise, lift the ground at the XLR
output. This will assume the JDI is deriving its ground at the input from the instrument or instrument amplifier.
The JDI also features a polarity reverse. This reverses pin-2 and pin-3 at the XLR. As the JDI is set following the AES
standard with pin-2 hot; reversing the polarity is generally not required unless the instrument is being both DI’d and mic’d.
The polarity reverse switch would allow both the mic and the JDI to be set ‘in phase’ should these be reversed.
You are ready to go! Now... close your eyes and listen. The JDI is without a doubt, one of the most musical DI boxes ever
manufactured.
True to the Music
Radial Engineering JDI User Guide
4
Part 4 – Direct Box Basics
What is a direct box anyway?
The name ‘direct box’ comes from ‘direct insertion box’. This is why these marvelous contraptions are also called DI’s. ‘Direct
Insertion’ means exactly that: To insert a signal directly or take an audio signal from the source and send it directly to a
mix point or recorder. We take this very seriously with all our direct boxes and as such, have designed them to reproduce
the most accurate ‘picture’ of the source no matter what the instrument.
Direct boxes perform the important function of impedance matching and signal balancing. This means that they take the high
impedance output from a guitar or keyboard and ‘transform’ it to the low impedance signal used in balanced sound systems.
Balanced signals inherently cancel noise and due to their lower impedance, can travel much further without degradation.
Balanced signals are the norm in professional recording, broadcast and live sound. By properly matching the impedance
you will enjoy better sound, less noise and an extended frequency response.
True to the Music
Radial Engineering JDI User Guide
5
Getting to know your Radial JDI Mk3
As a rule, all direct boxes follow the same basic procedures when connecting them to a sound system. The instrument plugs
into the INPUT, the musicians’ instrument amplifier connects to the THRU and the mixer or recorder is connected to the
XLR ‘OUTPUT’. Since the XLR output connection to the mixer taps the signal before it goes to the musician’s amplifier, this
allows the mixing engineer to ‘capture’ the signal before it is modified by the musician, thus resulting in the purest source
possible. It is important to note that what may sound good on stage may not necessarily sound good in the venue.
By sending an unaltered signal to the front of house mix position (FOH), the engineer is able to get the sound he is looking
for with minimal phase and harmonic distortion. This is likely the main reason why Radial direct boxes are so popular with
sound engineers — Radial DI’s do not alter the sound in any way before it gets to the mixing desk.
High to low impedance conversion and balancing
The Radial JDI features a high 140k Ohm input impedance for the instrument. As the signal passes through the JDI to the
XLR output, it is converted to a balanced 150-Ohm low impedance signal. This allows long cable runs without introducing
noise into the audio signal path. It is important to note that the output of the Radial JDI is a mic level signal. This allows the
JDI to be used alongside other microphone signals without introducing cross-talk or causing transformer saturation when
driving the signal through the mic bridging transformers of a splitter.
The magic of a great transformer
The Radial JDI is a passive direct box – this means that it employs a transformer to convert the impedance and balance
the signal. At Radial, we believe quality should always be the most important deciding factor in any product design and the
best way to make great products is to use the very best parts. Many Radial products incorporate Jensen® audio transformers
which are expensive, but to an audiophile, these transfrmers are worth their weight in gold. A good transformer must be
able to pass every frequency between 20Hz and 20,000Hz flawlessly. The transformer must also ensure that all of these
frequencies retain their time-base relationship or ‘absolute phase’. In other words, whatever you send in should come out
at the same time. If the bass and mid range are not synchronized in perfect phase, it simply will not sound as good.
A transformer is a simple device. It is basically made up of three components: (1) the primary or input coil, (2) the core
material and (3) the output coil. The audio signal enters the primary coil and, taking full advantage of Faraday’s law of
electromagnetism, the coil converts the electron impulse (current) into a magnetic field. The core acts like a conduit to
contain the magnetic field and drives it into the secondary coil. A magnetic field, when driven into a coil, generates electron
True to the Music
Radial Engineering JDI User Guide
6
flow. Varying the number of windings on the input and the output allows us to control the input and output impedance ratio.
This is where the specification ‘10k : 150-Ohms’ comes from.
The beauty of a transformer is that there is no electrical connection between the primary and the secondary. The signal is
‘transformed’ from electrical energy to magnetic, then back to electrical; in effect, a ‘magnetic bridge’. This provides two
huge benefits: with no electrical path, ground loops are eliminated and when properly designed, a tremendous reduction in
common-mode noise is possible. In the ‘real world’ (not the test bench) signals are never truly balanced, leaving the door
open for noise to pollute the audio signal. Electronically balanced circuits (active circuits) are ill equipped to manage this
common mode noise, whereas the JDI provides exceptional noise rejection at 60Hz – the crest of hum and buzz.
An audio laboratory test called ‘The Green Report’ (visit www.radialeng.com for details) pitted the JDI against three other
direct boxes commonly used in professional audio. The tests showed that the JDI could handle more gain before distortion,
was more linear throughout the audio frequency range and showed significantly less phase distortion. All boxes tested
well at 1kHz, but as the frequency dropped, the ‘ugly truth’ started to appear. One popularly used DI was almost 20º out of
phase at 20Hz while another was almost 40º out of phase! The JDI tested at less than 4º off the mark, making it the most
phase accurate DI on the planet.
With its high signal level handling, dynamic response and unmatched phase accuracy, the JDI is a significantly better
choice for bass, keyboard and acoustic guitars with built-in pre-amps and this can be directly attributed to the quality of the
Jensen transformer we use.
The Problem:
Ground loop between
conneced equipment.
The Cure:
Equipment isolated with
an audio transformer.
Equipment is
connected
through A/C
ground.
Equipment is
connected
through audio
cable.
True to the Music
Radial Engineering JDI User Guide
7
Part 5 – Features and Functions
The ¼” INPUT and THRU connectors
The JDI features two ¼” jacks on the input panel. These are designed to accept normal instrument input levels from basses,
guitars, keyboards, drum machines, etc. The left-most ¼” input is normally connected to the source instrument.
The ¼” connector to the right of the input is normally used as a ‘thru’ connector
and feeds the instrument signal to the musician’s amplifier.
Using the JDI with a bass guitar with this setup allows both the musician
and the engineer to work with the original signal direct from the
bass. This way, the musician can set up his sound on stage
with his own EQ while the engineer can EQ the bass to work
better in the hall.
On live stages, it is common for instruments such as
acoustic guitar to be connected to the DI and then to the
snake system using the Lo-Z XLR output, splitting the
signal to feed the stage monitor mixer for foldback, just
as microphones are. In this case, the thru jack would
not be used.
The MERGE switch
The JDI features an innovative ‘merge’ function that turns the input
and the thru-put into a ‘left-right to mono’ mix. Depressing the merge switch introduces a resistive mixer circuit that sums
the two channels at the XLR output. This function allows two sources such as a stereo keyboard or CD player to merge to
‘mono’, saving valuable channels on the snake and the mixer when you have more sources than available inputs.
To ‘merge’ simply connect two instruments with similar output levels into the IN and THRU jacks, depress the MERGE switch
to the ON position and you are set to go. The internal resistive mixer is set up to do this without introducing any problems
such as phase cancellation.
True to the Music
Radial Engineering JDI User Guide
8
Understanding input distortion and using the –15dB PAD switch
Today, many acoustic guitars and basses have battery powered active pre-amplifiers that boost their pickup output signal.
These high gain pre-amps often generate between 2-volts and 7-volts at their outputs. This high voltage can saturate the
input of most direct boxes causing a harsh square wave distortion. This is most prevalent with active phantom powered
direct boxes that simply do not have sufficient headroom or rail voltage to handle these transients.
The JDI is designed to handle these signal levels without fear of overloading and is one of the main advantages you will
enjoy with your JDI. However, you may occasionally encounter devices with extremely high output levels such as from CD
players, a mixer output or even a headphone out that can overdrive the circuit or saturate the transformer. For these rare
occasions, the Radial JDI is equipped with a -15dB pad to ensure a clean and distortion-free signal is obtained.
The balanced XLR output
The JDI features a mic level, balanced output jack that uses a standard XLR male connector. This jack is wired to the
AES (Audio Engineering Society) standard with pin-1 ground, pin-2 hot and pin-3 cold. Today, pretty much all equipment
is manufactured using this standard. Connection is made to the mic-level input of the mixing console or to a standard mic
pre-amplifier. The JDI is ideally suited for interface with concert snake systems and splitters where mic and direct box
signals are directed to several destinations at the same time such as recording, monitor, broadcast and front-of-house mix
positions.
The POLARITY switch
A polarity reverse toggles the XLR pin-2 and pin-3 as the ‘hot’ or positive signal. This provides several operational benefits:
interfacing with older mixing consoles that have pin-3 hot is simply a matter of depressing the polarity reverse and when
mic’ing and using a ‘direct’ signal from the same instrument, one sometimes encounters ‘phase’ problems when these are
combined. Reversing one of the source polarities often alleviates this. This same process, while recording, provides the
engineer with another ‘tonal pallet’ and experimenting with different settings can lead to some very pleasing results.
The GROUND switch
It is common practice to ground all electrical devices in a sound system. Proper grounding assures safe use and generally
helps reduce system noise. As the Radial JDI is an interface, it is often placed between two grounded AC powered devices
such as a keyboard and a mixer. Often these two devices will be connected to different AC outlets or may have very different
ground reference potentials. When connected together, these can sometimes cause 60-cycle hum or a loud system buzz.
This noise is often referred to as a ground loop.
True to the Music
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