Radial Engineering Firefly User manual

TruetotheMusic
www.radialeng.com
®
TruetotheMusic
®
User Guide
Firefly
Tube Direct Box
www.radialeng.com
Radial Engineering Ltd.
1588 Kebet Way, Port Coquitlam
British Columbia, Canada, V3C 5M5
tel: [phone] • fax: [phone]
email: [email protected]
™

Firey™ Tube Direct Box
TruetotheMusic ®
Radial Engineering Ltd.
Radial Firefly
Tube Direct Box
™
®
Table of Contents Page
Feature set ...................................................................................................................1
Overview.......................................................................................................................3
Making connections......................................................................................................4
Setting Up the Firefly for Various Instruments..............................................................8
Setting the output controls............................................................................................9
Remote switching and mute with JR•2.........................................................................10
Rackmounting kit..........................................................................................................11
Specifications ...............................................................................................................11
Block diagram...............................................................................................................12
Radial Limited Warranty................................................................................Back Cover
Congratulations and thank you for purchasing the Radial Firefly! You are now the proud
owner of what is arguably the most exacting direct box ever made. The Firefly combines state
of the art electronics with a tube drive and transformer coupled output to produce a clean
warm tone. And hidden inside are a ton of very cool features designed to enable the Firefly
to be used in all types of applications for all types of instruments.
Although you will find the Firefly to be super easy to use, we recommend you to take a few
minutes to read the manual to ensure you understand the various features and get the most
out of this amazing device. If after reading the manual you need further clarification, please
visitthe Firefly FAQpageon the Radialweb site.Thisis where wepost questions andanswers
from users along with the latest updates. Then, if you still do not find what you are looking
for, we invite you to send an email to [email protected] and we will do our very best to get
back to you promptly.
Now get ready to plug into one of the most enjoyable pieces of audio equipment ever!

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FRONT PANEL FEATURE SET
1
1 2 43 65
1. TRIM-A & B: Input level controls used to match the gain between the two instruments.
2. SELECT: Selects the active input for fast instrument changes. The illuminated LED
indicates the active input.
3. MUTE LED: Indicates when the mute function is active. Remote controlled via the
optional JR•2 footswitch.
4. DRAG: Used to retain the natural feel of the instrument by adjusting the load for
passive pickups.
5. LOW CUT: Variable high-pass filter rolls off low frequency resonance that can cause
feedback or muddy up the sound.
6. LEVEL: Level control for the balanced XLR output. Variable from mic to line-level.
7. PROTECTIVE FRONT LIP: The enclosure design create a protected zone around the
switches and knobs to prevent damage.
8. POWER: Locking 5-pin XLR power supply connection. The external supply helps
reduce noise and delivers +/-16 volts (1600mA) that is internally stepped up to 48V for
the tube.
9. OUTPUT: Balanced XLR output connects to the PAor recording system. Transformer
isolated to eliminate hum & buzz caused by ground loops.
7

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REAR PANEL FEATURE SET
2
10. 180º POLARITY: Inverts the signal polarity by flipping pins-2 and pin-3 on the XLR
output. Used to reduce resonant peaks that cause feedback.
11. GROUND LIFT: Disconnects pin-1 at the XLR out. Helps reduce noise caused by
ground loops.
12. AUX PRE/POST: Changes the signal path of the ¼” AUX OUT. When set to the
inward position (pre) the AUX OUT provides a direct clean buffered feed from your
instruments. When set to the outward position the AUX OUT is like the main XLR
output, post tube stage, filter section and insert loop.
13. TUNER OUT: Always-on, high-Z output used to connect an electronic tuner.
14. REMOTE: Used to connect the optional JR2 remote footswitch. When connected, this
lets you select the active input channel or mute the Firefly for tuning.
15. AUX OUT: High-Z thru-put for stage amp. Configurable ‘pre or post’ tube and insert.
16. INSERT: Buffered effects loop uses standard ¼” TRS send & receive cable to interface
guitar pedals and studio rack effects.
17. INPUTS A & B: High-Z inputs lets you switch between two instruments for quick on-
stage changes. The input level is set using the TRIM-A & B controls.
18. AUX THRU (side panel):Recessed switch engages transformer
isolation for ¼” AUX OUT to eliminate hum and buzz caused by
ground loops.
11 12 13 14 15 1716 18
98 10

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3
OVERVIEW
The Firefly is a direct box. What this means from a ‘technical’ standpoint is that the Firefly is
designed to deliver the sound of the instrument to the recording system or PA without intro-
ducing artefact. But the sheer fact that the Firefly employs a tube as part of the circuit means
that the tube will add warmth and natural even order harmonics to the signal. Technically,
DI boxes like the Radial JDV™ are much more accurate while the Firefly is designed to add
character. That being said, the Firefly remains a direct box and therefore, it must perform the
task... and do it well.
The primary task of a direct box is to convert the unbalanced high impedance signal from
an instrument to a balanced low impedance signal suitable for a PA system or for recording.
The output from a direct box is usually equivalent to a mic level signal. This enables the DI to
‘comfortably live’along side microphones, using the same mic splitters, mixing console inputs
and microphone preamps. Standardizing the signal makes it easy to switch around cables
on hectic stages when trouble shooting. And although the Firefly is able to produce a much
hotter output than a typical DI box, turning down the master volume is all that is required to
match things up.
Several extra features have been added to the Firefly to increase functionality on stage and
better adapt to the various instruments that may be connected. For instance; two inputs make
it easy to swap instruments. Drag Control lets you adjust the load on the pickup for optimum
signal transfer. The 4 meg-ohm input impedance lets you properly load piezo pickups so that
they sound right. You can also add options such as a remote control for input switching and
quiet tuning on stage. And of course you can rack mount the Firefly in a single space using
the optional 19” rack adaptors.
TYPICAL SETUP

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MAKING CONNECTIONS
Before making connections, always ensure all levels are turned down or equipment is turned
off. This will help you avoid turn-on transients that could harm more sensitive components
such as tweeters from being damaged.
Connect the power supply to the Firefly. This mid-cable supply is equipped with a 4-pin XLR
connector at one end and a universal IEC connector at the other end. The power supply will
acceptinputvoltagesfrom100Vto240VthusenablingtheFireflytobeusedincountriesaround
the world. It comes with the appropriate power cable to comply with local electrical systems.
Start by setting theTRIMA& B controls and the LOW-CUT filter fully counter-clockwise to the
7 o’clock position (minimum setting). Set the DRAG control about halfway to the 12 o’clock
position and ensure the ON button is set to the inward position. Set the master LEVELcontrol
to the 2 o’clock position.
MIN MAX MIN MAX
TRIM-A TRIM-B
MIN MAX
LOW CUT
DRAG
MIN MAX
LEVEL
Cable connections are made at the rear panel. Connect the instrument to INPUT-A using a
standard ¼” guitar cable. Connect the XLR output to your mixing desk or preamp using a
standard XLR cable. Make sure the three rear panel recessed switches are in the outward
position by checking with a tweaker or small screwdriver.
Test at low volume
You are now set to start testing audio.Always test at a low volume first before turning up. This
willhelpyouavoid loud transients fromdamagingmoresensitive components.Turnupthegain
onyourmixing desk or preamptoa low level.Setthe input SELECTbutton to input-A.TheLED
will illuminate to show you which input is active. Slowly increase the input TRIM-A until you
reach a comfortable listening volume. If you like, plug in your second instrument and adjust
the TRIM-B to match. Simply depress theAB selector switch to toggle between instruments.

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Connect an amplifier
You can now connect to your stage amplifier if you are using one.Astan-
dard¼” guitar cableconnects from theAUX OUTto the inputof your amp.
This output may be transformer isolated by depressing the side-mounted
recessed switch. This helps prevent ground loops that can cause hum
and buzz in your system. Using the isolated setting is recommended
when connecting to guitar or bass amplifiers and effects pedals. Taking the transformer out
of the circuit will deliver a slightly different sound. Try toggling the switch in and out to see
how it works with your setup.
Pre/post aux switch setting
The bufferedAUX OUT output can be toggled between
PRE or POST settings by depressing the set & forget
recessed AUX OUT PRE/POST switch on the rear panel.
When set to PRE (inward position) the instrument signal is
sent directly to the stage amp before it is processed by the
tube, effect loop and low cut filter.
AUX OUT
¼” OUTPUT
(PRE)
CLASS-A
BUFFER
DRAG
CONTROL
INPUTS
& DRAG
CONTROL
Simplified Block Diagram of PRE signal path
However, when set to POST (outward position) the AUX OUT output is identical to the main
XLR output. Most musicians will likely opt for the POST setting to send the tube processed
soundto their amp in orderto gain theadded warmth of the tube.Simply leave the PRE/POST
switch in the outward position if this is your preference.
Simplified Block Diagram of POST signal path
TUBE
AMPLIFICATION
STAGE
AUX OUT
¼” OUTPUT
(POST)
INSERT
SEND &
RETURN
CLASS-A
BUFFER
HIGH
PASS
FILTER
INPUTS
& DRAG
CONTROL

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Connect an electronic tuner
The Firefly is equipped with an ‘always-on’ TUNER output that is designed to hook up an
electronic tuner to provide constant visual feedback while performing. The TUNER output is
buffered and electronically isolated to prevent noisy digital tuners from bleeding clock noise
into your instrument sound. The TUNER output is tapped before the tube gain stage provid-
ing a clean instrument output that can be used to split the signal to another preamp when a
tuner is not connected.
JR•2 remote footswitch
Forevenmore control overtheFirefly,youcan add the optional
JR2 footswitch. This two button footswitch can activate the
MUTE function for silent on-stage tuning via the always-on
TUNER output and toggle between instrument inputs A & B.
For convenience the JR•2 can be connected with either a ¼”
TRS cable or a locking Female XLR ~to~ ¼” TRS cable. Both
connections are offered on the rear panel but only one should
be used at a time.
¼” TRS to TRS XLR to TRS

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Adding effects
As with any preamp or direct box, you can connect effects in line between your instrument
and the Firefly the same way you would when connecting pedals in front of your amp. With
this set up, each instrument can have its own set of effects.
The Firefly is also equipped with a ¼” TRS INSERT jack that enables you to share effects
between both instruments. This rear mounted jack requires a standard studio insert cable
whereby one end is equipped with a ¼” TRS and the other equipped with two ¼” plugs des-
ignated as send and receive. Simply connect the send to the input of the first pedal in the
chain and the output to the receive plug. With this setup, when you change instruments the
signal will automatically be routed to the pedals.

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SETTING UP THE FIREFLY FOR VARIOUS INSTRUMENTS
The Firefly is designed to adapt to just about any instrument whether it employs a magnetic
pickup, piezo or combination with an active buffer.
Magnetic pickups and Drag control
One of the more subtle yet indispensable functions is Drag Control™. Drag is designed to be
used with magnetic pickups such as the ones found on most electric guitars, basses and the
type that can be placed in the sound hole of an
acousticguitar.Magnetic pickups are verysimi-
lar to transformers in that they react differently
depending on the load that is presented. So
when connected to a tube amp, they become
part of the circuit and sound a particular way.
When presented with a high impedance buffer,
the sound changes. Guitarists often complain
that they hate wireless systems or pedals,
preferring true bypass devices. Drag Control
lets you reintroduce the load on the pickup
to replicate the tone and feel as if connected
directly to a tube amplifier.
Start with Drag Control set to the 12 o’clock position. Turning the Drag Control clockwise will
brighten the tone (less Drag) while turning the dial counter-clockwise with darken it (more
Drag). Turn the Drag Control on by pushing in the switch and use a small screwdriver or guitar
pick to adjust. Listen to find the tone that best suits your preference. 12 o’clock simulates the
tone of a Stratocaster connected to a Fender Twin.
Active instruments
Foractive instruments such as akeyboard, ac-
tivebassoranactiveacousticguitarwithbuilt-in
preamp, the Drag control will have very little or
no effect as the signal is already buffered. The
advantageto using the Fireflyis to warmupthe
tonebypassingthe signal throughthetubeand
audio transformer. This will produce a ‘vintage’
effect that is pleasing to the ear.
Piezo transducers
The Firefly is equipped with a special high
input impedance that is ideally suited for piezo
equipped instruments. Piezos are finicky
devices that tend to squawk or sound peaky
unlesstreatedproperly.WhentheDrag Control
is turned off, (switch in out position), the input
impedancejumpsto4meg-ohms.Thisprovides
the piezo with the right type of impedance to
properly load the pickup and smooth out the
sound.
Magnetic pickup in acoustic guitar sound hole.
Acoustic guitar with active preamp.
Passive piezo transducer on acoustic guitar.

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Adjusting the high pass filter
One of the most effective features built into the Firefly is the high-pass filter. This variable
controllets you eliminatelow frequency resonancefrom the instrument and producea cleaner
more defined sound. This is beneficial for both studio recording and on a live stage.
20 20k50 100 200 500 1k 2k 5k 10k
Hz
0dBu
Freq Response Graph For High Pass Filter
In the studio, low frequencies can often blend together causing modulation and beating as
they compete in the same frequency bands. By rolling off unneeded bottom end, you can
more easily combine instruments and create a less congested recording. This ‘Nashville’
trick is often used to size various acoustic instruments such as contra bass, acoustic guitar,
banjo and fiddle to create a more uniform and pleasing mix. Start with the high-pass filter set
completely counter-clockwise.This essentially dialsthe filteroutof the circuit.Slowly increase
the cut-off frequency by rotating the control clockwise. You will hear it as it takes effect. Try
experimenting with various cut-off points to get a feel as to what sound best to you.
In live situations, the high –pass filter is particularly effective at eliminating low frequency
resonant feedback. By cutting out excessive lows, you will also gain more control over the
mix. Cutting lows reduces the demands on the PA system which in turn reduces distortion.
And if you have ever played electric guitar you know that feedback occurs much more readily
with a distorted sound... so yes, the same applies with acoustic instruments: less distortion
equals less feedback.
SETTING THE OUTPUT CONTROLS
The Firefly XLR output is equipped with two switches: a
180° polarity reverse and a ground lift. Start by setting both
of these to the outward position.
180° polarity reverse
The 180° polarity reverse can perform various functions. When pushed in, this toggles the
electrical phase at the balanced XLR output by swapping pin-2 and pin-3. If you so happen
to be using some older equipment that does not follow theAES standard (pin-2 hot), this can
be used to reverse the polarity and bring the Firefly into proper electrical phase.
More often than not, the polarity reverse will be used for other uses. For instance, in the
studio, you may be combining the direct feed from the Firefly with a microphone. Depending
on where the microphone is positioned in the room, you may find that reversing the polarity
can help fatten the tone.

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On stage, reversing the polarity is sometimes used by the front of house engineer to better
phase-alignthebass amp with thePAsystem.Thiscanbeveryeffectiveinsmallerclubswhere
today’s high powered bass rigs can compete with the PA. With acoustic guitars, sometimes
the sound from the PA can cause huge peaks on stage known as hot spots or room modes.
Thesecausetheinstrument to prematurely resonatewhichinturn causes feedback. Reversing
the polarity will electronically ‘move’ the peak and often solve the problem.
Lifting the ground
Pushing in the ground lift switch lifts the ground connection on pin-1 at the XLR output. When
you do so, this assumes that the instrument and Firefly are being grounded by another de-
vice such as a stage amplifier. Lifting the ground lifts the audio ground which in turn will often
eliminate hum and buzz caused by ground loops.After you have connected the system, if you
hear hum or buzz, try pushing in the switch to lift the ground.
REMOTE SWITCHING AND MUTING
TheFireflyisequippedwitharemotecontroljackfortheoptional
Radial JR2 remote control footswitch. This compact switcher
featurestwofootswitches and three LEDs.Poweris supplied by
the Firefly thus eliminating the need for batteries or secondary
power supply. Connection between the two devices is done
with a balanced cable with ¼” TRS connector at one end and
choice between a ¼” TRS or XLR at the other. The XLR has
the added benefit of being able to be locked.
Withthe JR2 connected, you canremotely select between inputsAandB to select the desired
instrument. The second switch is used to mute the Firefly for quiet on stage tuning via the
always-on TUNER output. Depressing the footswitch illuminates the LED indicators to let you
know which function is active.
JR•2 Connected with a ¼” TRS cable JR•2 Connected with locking XLR ~ TRS cable
12
TIP
RING
SLEEVE
TIP
RING
SLEEVE
TIP
RING
SLEEVE SHIELD SHIELD
3SHIELD
SHIELD
Wiring diagram for JR•2 connection cable.

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RACK MOUNTING THE FIREFLY
For touring the Firefly may be mounted into a standard 19” rack using the optional rack mount
kit. This three piece kit (part number: R800 2020 02) enables one or two Fireflies to be rack
mounted in a 1RU rack space.
Single unit mounting:
Double unit mounting:
SPECIFICATIONS
Frequency response.................................................................20Hz ~ 20kHz
Maximum Gain - 1/4” input to XLR out.....................................+22dB
Noise........................................................................................-98dBu
Dynamic range.........................................................................100dB
Equivalent input noise..............................................................-100 dBu
Input impedance (drag control off)............................................4Meg-Ohms
Input impedance (drag control on)............................................Variable from 22k ~ 500k Ohms
Output impedance at XLR........................................................200 Ohms (nominal)
Low-cut filter:............................................................................Variable from 25Hz ~ 500Hz (-3dB point)
Size (W, D, H) & weight............................................................5.75” x 8.25” x 1.75” (2.75” with handle)
146mm x 210mm x 45mm (70mm with handle)
Weight......................................................................................3.95lbs. (1.80kg)
Power supply............................................................................+/-16v (1600mA) 5-pin XLR power supply
All specifications average – depending on tube or termination. Please see web page for further details.

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BLOCK DIAGRAM
TUNER
SELECT
LEVEL
Pre-Tube
Post
DRAG
CONTROL
COMMON
CATHODE
CLASS A
INPUT A INPUT B
A/B SELECT
TRIM A TRIM B
VOLTAGE
AMPLIFIER
CATHODE
FOLLOWER
CLASS A
HIGH
VOLTAGE
FET
BUFFER
GAIN
UNITY
BUFFER
RELAY
INSERT
CLASS A
FET
BUFFER
INSERT
DRIVER
INSERT
CLASS A
VARIABLE
HIGH
PASS
FILTER
CLASS A
HIGH
VOLTAGE
FET
BUFFER
MUTE PHASE
INVERT
OUTPUT
LIFT
INSERT
RETURN
BUFFER
CONTROL
LOGIC
MUTE
A/B SELECT
AUX OUT
CW CW C
NO
NC
CW
C
NO
NC
C
NO
NC
Direct
Isolate

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THREE YEAR TRANSFERABLE LIMITED WARRANTY
RADIAL ENGINEERING LTD. (“Radial”) warrants this product to be free
from defects in material and workmanship and will remedy any such de-
fects 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 an RA number (Return Autho-
rization 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 HEREOFAND DESCRIBED ABOVE. NO WARRANTIES
WHETHER EXPRESSED OR IMPLIED, INCLUDING BUT NOT LIMIT-
ED TO, ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FIT-
NESS FOR A PARTICULAR PURPOSE SHALLEXTEND BEYOND THE
RESPECTIVE WARRANTY PERIOD DESCRIBED ABOVE OF THREE
YEARS. RADIALSHALL NOT BE RESPONSIBLE OR LIABLE FORANY
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.
Radial®Firefly™User Guide - Part #R870-1175-00 • rev.2
Specifications and appearance are subject to change without notice.
Radial Engineering Ltd.
1588 Kebet Way, Port Coquitlam BC V3C 5M5
tel: [phone] • fax: [phone]
[email protected] • www.radialeng.com