Radial Engineering Ltd.
JDI • Duplex User Guide
True to the Music
®
Overview
The Radial Duplex has often been dubbed the ‘swiss
army Knife’ of direct boxes. and there is good reason for
that. a real swiss-made knife combines tons of useful
tools into a small, yet very functional package and if
handled correctly, will provide a lifetime of service! The
Duplex is exactly the same.
From the outside, one immediately notices a ton of
connectors and switches (23 to be exact) that surround
the Duplex and bestow the incredible flexibility. a series
of ¼” connectors make for easy interacting with musical
instruments, such as a keyboards or bass guitars
and amplifiers. RCa connectors enable the Duplex
to be used with consumer electronic devices such as
CD or video players. a 3.5mm mini TRs connector
enables you to connect a cell phone, personal music
player, laptop or tablet via a headphone output. This is
augmented with a pair of XLRs that enable the Duplex
to be used to bridge and isolate two balanced line level
devices together.
once the signal is inside, the Duplex elegantly balances
the signal via high performance audio transformers and
produces a mic-level output that is perfectly suited to
run along microphones in a low-Z balanced audio
environment. This makes connecting to mixing consoles
or studio preamps easy and worry-free. You merely
turn up the volume and the Duplex springs to life. The
simplicity is augmented with a number of functions that
provide solutions to various challenges that may pop up
during a concert, aV show or recording session.
1
Passive Di basics
a direct box has the primary role of converting an
unbalanced high-impedance signal to a balanced low
impedance signal. Unbalanced signals typically ‘max
out’ at around 8 meters (25’) before noise begins to be
audible. Balancing the signal allows distances of 100
meters (300’) or more without noise. Balanced lines
employ twisted pair cable that naturally rejects hum and
buzz and lowering the impedance reduces the capacitive
effect of the cable to retain high frequencies that would
otherwise be attenuated.
DI boxes are typically equipped with an input connector
for the instrument, a thru connector to feed the stage
amp and a balanced XLR output for the Pa or recording
system. The engine inside the Duplex is a pair of high-
performance Jensen audio transformers. These are
carefully designed to reduce loading while maintaining
both a broad frequency response and minimal phase
shift. The transformer is surrounded by carefully designed
filters that bleed off RF (radio frequency noise) and a mu-
metal outer can further reduces noise by protecting the
sensitive coils from outside magnetic fields.
Transformers are particularly effective at managing
high level signals that will often overload the electronic
input stage of a mixing console. a transformer acts like
a natural limiter that rounds-out transients producing a
smooth tone that is often compared to the finest vintage
gear. There is good reason for this because vintage audio
gear uses transformers! Transformers have another
advantage; they employ a magnetic bridge that isolates
the input from the output, blocking stray DC voltages
which are often the root cause of noise in audio systems.
