Universal Audio OX User manual

OX Operation Manual
www.uaudio.com
Manual Version 180220

OX Amp Top Box Letter From Bill Putnam Jr.2
A Letter from Bill Putnam Jr.
Thank you for choosing the OX Amp Top Box as part of your music making experience.
We know that any new piece of gear requires an investment of time and money — and
our goal is to make your investment pay off.
Universal Audio’s family of products represent the best examples of what UA has stood
for over its long history; from its original founding in the 1950s by my father, to our
current vision of delivering the best of both analog and digital audio technologies.
The OX Amp Top Box allows you to play and record your tube amp in its perfect tonal
sweet spot — anywhere, and at any volume. Featuring the world’s best all-analog reactive
load, OX also offers album-quality mic and speaker cabinet emulations, UA’s Dynamic
Speaker Modeling, onboard UAD effects, and much more.
At UA, we are dedicated to the idea that technology should serve the creative process
— not be a barrier. These are the very ideals my father embodied as he invented audio
equipment. We believe the OX Amp Top Box will earn its way into your creative workflow
by providing stunning guitar tones and rock-solid reliability for years to come.
Please feel free to reach out to us via our website www.uaudio.com, and via our social
media channels. We look forward to hearing from you, and thank you once again for
choosing Universal Audio.
Sincerely,
Bill Putnam Jr.

OX Amp Top Box Table Of Contents3
Table Of Contents
A Letter from Bill Putnam Jr. ................................................................. 2
Welcome to OX Amp Top Box! ................................................................ 5
About OX Documentation.................................................................................... 6
Critical Operation Notes ........................................................................ 7
Critical Notes — Avoid Equipment Damage.......................................................... 7
Important Notes — Reduce Equipment Wear........................................................ 8
Quick Start .......................................................................................... 9
Important Setup Steps ....................................................................................... 9
Amp & Speaker Connections............................................................................. 10
Output Connections ......................................................................................... 11
Control Knobs ................................................................................................. 12
Quick Operation Notes ..................................................................................... 12
Controls & Connectors......................................................................... 13
Front Panel ..................................................................................................... 13
Rear Panel ...................................................................................................... 16
OX Software App ................................................................................ 22
OX App Features.............................................................................................. 22
Essential App Concepts.................................................................................... 23
RIG View......................................................................................................... 25
Presets Management........................................................................................ 28
Loading Presets............................................................................................... 30
Saving Presets................................................................................................. 31
Effect Editors .................................................................................................. 33
ASSIGN View .................................................................................................. 34
Store Individual Rigs to OX’s RIG Knob.............................................................. 35
Store Rig Sets to OX’s RIG Knob........................................................................ 35
SETTINGS View............................................................................................... 36
Rig, Cabinet, & Mic Descriptions.......................................................... 37
Default RIG Control Cab & Mic Presets .............................................................. 37
Default Rig Sets .............................................................................................. 38
Speaker Cabinets............................................................................................. 39
Cabinet Microphones ...................................................................................... 42
Room Microphones .......................................................................................... 44
Tip: Click any section or page number
to jump directly to that page.

OX Amp Top Box Table Of Contents4
OX System Overview............................................................................ 45
OX Wi-Fi Networking ........................................................................... 49
OX Wi-Fi Hotspot ............................................................................................. 49
External Wi-Fi Networking................................................................................. 50
OX Registration .................................................................................. 51
OX Registration Overview.................................................................................. 51
OX Registration Procedure ................................................................................ 52
Troubleshooting .................................................................................. 54
Wi-Fi Reset ..................................................................................................... 54
Factory Reset .................................................................................................. 54
Specifications .................................................................................... 55
Block Diagram.................................................................................... 57
Notices.............................................................................................. 58
Warranty ......................................................................................................... 58
Repair Service................................................................................................. 58
Maintenance ................................................................................................... 58
Technical Support............................................................................... 63
Universal Audio Knowledge Base....................................................................... 63
YouTube Support Channel................................................................................. 63
Universal Audio Community Forums .................................................................. 63
Contact Universal Audio Support....................................................................... 63

OX Amp Top Box Welcome to OX Amp Top Box!5
Welcome to OX Amp Top Box!
Get Legendary Studio Tones from your Tube Amp — Anywhere, at Any Volume.
OX is a premium reactive load box and guitar recording system, giving you perfectly
studio-miked amp sounds from your favorite tube amp. OX lets you play and record your
amp in its sweet spots — from huge clean tones and edge-of-breakup to fully cranked —
at any volume level, and with mic, room, and speaker cabinet emulations at the turn of a
knob.
Featuring Universal Audio’s breakthrough Dynamic Speaker Modeling, OX is the first
system to accurately emulate speaker drive, breakup, and cone cry — making it the
world’s finest speaker attenuator and guitar amp recording solution.
Now You Can:
• Play and record your tube amp in its tonal sweet spot — anywhere, at any volume,
with full dynamics
• Get stunning mic and guitar cabinet combinations at the turn of a RIG knob — no
miking required
• Audition, tweak, and save more than 100 jaw-dropping custom Rigs from
compatible iPad or Mac
• Get authentic “edge of destruction” sounds, complete with UA Dynamic Room
Modeling, speaker breakup, and cone cry
The World’s Best Reactive Load Box
With decades of analog hardware engineering expertise, Universal Audio’s dream team of
engineers set out to design a reactive load box that retains the tone, dynamics, and feel
of your tube amp — no matter how much it’s attenuated. The goal was for your tube amp
to “see” OX as an actual speaker — with continuously variable impedance and response
— so you don’t lose a drop of tone or playing dynamics.
A Complete Guitar Recording System
OX’s front-panel, six-position RIG control allows you to quickly choose from complete
setups — including emulated speaker cabinets, close mics, ambient room mics, and up
to four simultaneous studio effects. OX is also the only guitar recording system to offer a
complete selection of expertly placed room mics, giving you the authentic experience of
pushing air while recording your cranked amp in a world-class tracking room.

OX Amp Top Box Welcome to OX Amp Top Box!6
Dynamic Speaker Modeling
UA’s groundbreaking Dynamic Speaker Modeling faithfully emulates speaker breakup,
drive, and cone cry — an essential ingredient to authentic tube amp tones. Using
the Speaker Breakup knob in the OX app, you can control the harmonics and sonic
complexity that occurs only at certain frequencies and volume levels on various
speakers — far beyond a static Impulse Response system — giving you the same sonic
phenomenon that occurs with a real speaker cabinet.
A Beautiful Software App
Most guitar products do digital awkwardly. They’re ugly and hard to understand. The
OX software app, on the other hand, offers slick, intuitive control over all of OX’s RIG
settings via Wi-Fi — letting you tweak, store and recall hundreds of presets from your
iPad or Mac. You can then save your six favorite tones onto OX’s front-panel RIG knob for
instant recall in the studio or at a gig.
The Right Connections
Not only does OX Amp Top Box feature a front-panel headphone jack for silent practice
with your cranked tube amp, it also sports a bevy of connections for all kinds of recording
and live workflows. Stereo S/PDIF digital outputs via RCA and optical TOSLINK, as well
as balanced TRS stereo line outputs with front panel level control, give you the necessary
connections for studio monitors, DAW, or live mixing console inputs.
About OX Documentation
This manual is your primary resource for connecting and operating OX hardware and
software. See the Table Of Contents to find the information you’re looking for.
Links to other manual sections and web pages are highlighted in blue text. Click the link
to jump directly to the item.
Tip: Use the “back” button in the PDF reader application to return to the previous
page after clicking a link.
For additional resources such as videos and knowledge base articles, or to contact our
technical support team, see Technical Support.

OX Amp Top Box Critical Operation Notes7
Critical Operation Notes
Caution: Connecting and/or operating OX incorrectly can cause permanent
damage to your amplifier, OX, and/or other equipment connected to OX.
Universal Audio is not responsible for equipment damage resulting from
improper OX connections and/or operations. Review the important information
in this chapter before connecting or using OX!
Critical Notes — Avoid Equipment Damage
Amp Output Load
DON’T operate any tube amp without an output load such as a guitar speaker or OX. Using a
tube amp without an output load can permanently damage the tube amp.
Caution: Always POWER OFF the tube amp before connecting or disconnecting its
speaker output to guitar speakers or OX.
OX’s Red FROM AMPLIFIER Input Jack
DON’T connect the tube amp’s high-power speaker output to ANYTHING other than OX’s FROM
AMPLIFIER input jack. The nut on this jack is RED to indicate this input is ONLY for the tube
amp’s speaker output.
OX’s TO SPEAKER Output Jack
DON’T connect OX’s high-power TO SPEAKER output jack to ANYTHING other than a guitar
speaker cabinet to avoid equipment damage to other gear.
Amp Power Rating
DON’T use OX with amplifiers exceeding 150 Watts RMS output power. Any tube amp with an
output power rating of 150 Watts RMS or less can be safely used with OX.
Speaker Cable Insertions
DON’T partially insert ¼” speaker cable plugs halfway into the jack or only to the first click. The
cable from the amp’s speaker output must be fully inserted into OX’s red FROM AMPLIFIER
jack to connect the ground return for proper amp loading.
Speaker Cables
Use only high-quality 12 to 16 gauge unshielded ¼” mono TS (tip-sleeve) speaker cables for
OX’s high-power FROM AMPLIFIER and TO SPEAKER connections. “Speaker” is usually printed
on these cables.
Tip: As a general guideline, the longer a speaker cable is, the smaller its cable gauge
needs to be (smaller gauge = bigger wires).

OX Amp Top Box Critical Operation Notes8
Rated Speaker Power
DON’T connect OX’s TO SPEAKER output to any speaker that is rated for a power level that is
significantly less than the connected amplifier’s output power to avoid speaker damage.
Moisture and Liquids
DON’T expose OX to moisture or liquids. Make a habit of never putting beverages on your OX. If
liquid is spilled into the unit, immediately unplug the power cord from the AC socket.
Cooling Airflow
DON’T cover OX’s air vents or otherwise restrict airflow around OX. The amp’s output power is
converted to heat by OX’s fanless attenuation circuit, and the air vents must be unrestricted to
dissipate this heat.
Solid State Amplifiers
Using OX with solid state amplifiers (amps without vacuum tubes) is not recommended and not
supported. OX is designed and optimized for use with tube amplifiers only.
Important Notes — Reduce Equipment Wear
Circuit Wear with Power Attenuation
Circuitry within an attenuated amp is subject to the same wear and tear that would occur if
its output power was not attenuated. If an amp is constantly run at higher power levels, the
lifespan of an amp’s components is reduced accordingly.
Increased circuit wear applies especially to the amp’s vacuum tubes, capacitors, and
transformers due to the increased heat and current generated at higher power levels.
Tip: A tube amp’s sweet spot might not be at full output power — a “dimed” amp
doesn’t always sound better. Less power and soak might deliver better tone AND better
tube life.
Impedance
Set OX’s IMPEDANCE knob to match the impedance of the tube amp’s speaker output.
Similarly, the total impedance of speaker(s) connected to OX’s TO SPEAKER jack should match
OX’s IMPEDANCE knob setting.
Many tube amps have multiple speaker output jacks with different impedance labels (4Ω, 8Ω,
etc.) for each output jack. If the amp’s speaker output impedance cannot be determined, set
OX’s IMPEDANCE knob to 8 ohms.
Note that when multiple speakers are combined (such as in a multi-speaker cabinet), the total
impedance depends on how the speakers are wired together. For example, two 8 ohm speakers
wired in series has a total combined impedance of 16 ohms, but if they are wired in parallel,
the total combined impedance is 4 ohms.

OX Amp Top Box Quick Start9
Quick Start
Caution: To avoid equipment damage, read the Critical Operation Notes before
connecting or using OX!
This chapter provides brief instructions to help you get started with OX. For complete
details about every knob, switch, and jack, see Controls & Connectors.
Important Setup Steps
Follow these steps to properly connect and power OX and your tube amp. For visual
references, see the Amp & Speaker Connections and Output Connections diagrams on
the following pages.
Caution: Always POWER OFF the tube amp before connecting or
disconnecting its speaker output!
1. POWER OFF the tube amplifier.
2. Connect OX’s included power supply to an AC outlet and the power input jack on
OX’s rear panel.
3. Set OX's rear panel IMPEDANCE knob to match the tube amp’s speaker output
impedance. If the amp’s speaker output impedance cannot be determined, set
this knob to 8 ohms.
4. Connect a 1⁄4” speaker cable between the tube amp’s speaker output and the red
FROM AMPLIFIER input jack on OX’s rear panel.
5. Set OX’s SPEAKER VOLUME, LINE OUT, and HEADPHONE knobs to position 0.
6. Connect OX's outputs as desired (see Output Connections).
7. Power on OX with its rear panel POWER switch, then power on the tube amp.
After following the important setup steps, OX is ready for use. Adjust the tube amp and
OX controls as desired.
Important: If your amp doesn't seem loud enough or the SPEAKER VOLUME knob
behaves unexpectedly (for example, it changes line/mon output levels or OX app
signal levels, or speaker volume levels are not smoothly stepped), confirm the tube
amp's speaker output is connected to OX's red FROM AMPLIFIER input jack, not
OX's TO SPEAKER output jack.
Setup Notes
• To download the full-color Quick Start Guide and Rig Control Cab & Mic Presets
reference sheets included in the OX retail package, click here.
• Remember to connect OX to AC power. OX requires the included external power
supply to be operated.

OX Amp Top Box Quick Start10
Amp & Speaker Connections
Caution: Always POWER OFF the tube amp before connecting or disconnecting
its speaker output!
OX speaker wire connections to amp and speaker cabinet
Amp & Speaker Connection Notes
Caution: To avoid equipment and/or hearing damage, be careful to connect
and power the amp and OX in the proper sequence. See the Important Setup
Steps for specific instructions.
• Use only high-quality 12 to 16 gauge unshielded ¼” mono TS (tip-sleeve) speaker
cables for OX’s high-power FROM AMPLIFIER and TO SPEAKER connections.
“Speaker” is usually printed on these cables.
Tip: As a general guideline, the longer a speaker cable is, the smaller its cable
gauge needs to be (smaller gauge = bigger wires).
• If connecting a tube combo amp (speaker and amp in the same cabinet), you
might need a male-to-female speaker extension cable with (not included) to reach
between OX's TO SPEAKER output jack and the guitar speaker.
OX INPUT
“FROM AMPLIFIER”
Amp Speaker Output
(to OX input)
OX OUTPUT
“TO SPEAKER”
Speaker Cab Input
(from OX output)
Tube Amplifier
Power Supply
Guitar Speaker
Cabinet

OX Amp Top Box Quick Start11
Output Connections
Tip: All of OX's output connections are optional. You only need to connect the
outputs you want to use.
DIGITAL
LINE / MON
OX "TO SPEAKER"
Guitar Speaker Cabinet
DON'T connect OX
outputs to the amp!
HEADPHONE
(front panel)
Typical OX output connections
Guitar Speaker Cabinet
Connect a 1⁄4" speaker cable between OX’s rear panel TO SPEAKER jack and the guitar
speaker cabinet.
Line / Monitor Outputs
Connect OX’s rear panel LINE / MON OUT jacks to the line-level inputs of a stereo
monitor system, computer audio interface, or other audio gear. Use shielded 1⁄4"
balanced TRS or unbalanced TS line / instrument cables (not speaker cables).
Headphones
Connect stereo headphones to the 1⁄4" jack on OX’s front panel.
S/PDIF Digital Outputs
Connect OX’s rear panel S/PDIF digital output(s) to the digital input(s) of a computer
audio interface or other digital audio gear. The optical TOSLINK and coaxial RCA outputs
can both be used at the same time.

OX Amp Top Box Quick Start12
Control Knobs
Quick Operation Notes
Tip: See Controls & Connectors for complete details about OX's knobs and jacks.
• RIG and ROOM knobs don’t affect OX's guitar speaker output. Rig preset sounds
are heard in OX’s Headphone, Line/Mon, and Digital outputs only. OX’s guitar
speaker output is pure analog amp tone.
• Changing RIG presets and/or settings can cause sudden level jumps in OX's
headphone, line/mon, and digital outputs. Be careful when adjusting the RIG
knob, and settings in the OX software app, when volumes are at higher levels.
• Digital output levels can be adjusted with the OX software app.
Tweak and Save Your Rigs with Free OX Software
OX includes free software for Mac and iPad (OX registration required). With the OX
software app, RIG presets can be wirelessly accessed, edited and stored over OX’s built-
in Wi-Fi network. For complete details, see OX Software App.
Get the OX Software App
• From your Mac, visit www.uaudio.com/ox/app
• From your iPad, search “OX Amp Top Box” in the iOS App Store
RIG
Choose from six complete guitar
cabinet+mic+room+effect presets.
SPEAKER VOLUME
Adjusts the volume of the guitar speaker cabinet
connected to OX. Set to 0 for silent operation.
ROOM
Instant access to mic’d
studio ambience and air.
LINE OUT
Adjusts the level at OX's
stereo LINE/MON outputs.
HEADPHONE
Adjusts the volume of stereo
headphones connected here.

OX Amp Top Box Controls & Connectors13
Controls & Connectors
Note: See Quick Start for important power sequence and setup instructions.
Front Panel
Refer to the illustration below for descriptions in this section.
OX’s front panel elements
RIG (1)
Each of the six available RIG knob positions recalls a complete cabinet/mic/room/effects
preset. RIG tones are heard in the HEADPHONE, LINE / MON, and S/PDIF outputs, but
not in the TO SPEAKER output.
For a table of the six factory RIG knob assignments and the cabinet/mic/room/effect
settings used in each RIG knob position, see Default RIG Control Cab & Mic Presets.
Tip: RIG settings can be modified and stored with the OX software app.
1
2
3 4 5 6 8
7

OX Amp Top Box Controls & Connectors14
RIG LED (2)
The LED beneath the RIG knob illuminates to indicate certain operating conditions. The
LED states encountered during normal operation are listed in the table below.
Note: If RIG LED states not listed below are encountered, please contact UA
Technical Support.
RIG LED State Indication Notes
Off OX not powered Rear panel POWER switch is in down position and/
or AC adapter is not properly connected
Green (solid) RIG not modified Active RIG has been loaded via RIG knob or OX app
and is unchanged from stored version
Amber (solid) RIG modified Active RIG has been edited via ROOM knob or OX
app and is not stored
Amber (blinking) Firmware update Firmware update is in process
Green (blinking) Wi-Fi reset initiated and
awaiting user confirmation
Press reset switch again within 10 seconds to
confirm Wi-Fi reset
Red (blinking) Factory reset initiated and
awaiting user confirmation
Press reset switch again within 10 seconds to
confirm factory reset
ROOM (3)
The ROOM knob adjusts the amount of mic’d studio ambience and air. Increase this
knob for more room ambience, or decrease for a drier close-mic tone.
When ROOM is adjusted, the RIG LED illuminates in amber, indicating the ROOM
amount is different than the value stored in the active RIG preset.
ROOM sounds are heard in the LINE / MON, HEADPHONE, and S/PDIF outputs, but not
in the TO SPEAKER output.
Tip: ROOM settings can be edited and stored with the OX software app.

OX Amp Top Box Controls & Connectors15
SPEAKER VOLUME (4)
This knob adjusts the loudness of the guitar speaker(s) connected at OX’s rear panel TO
SPEAKER output jack. Six knob positions and five carefully crafted attenuation levels are
available.
Position 1 is the quietest available setting. Position 5 is the loudest available setting. At
position 0, the speaker is OFF for silent operation.
SPEAKER VOLUME does not change the signal level being routed into the digital
section, which receives signal before this loudness control. This feature allows you
to change the guitar speaker volume without changing levels at the LINE / MON,
HEADPHONE, and S/PDIF outputs.
Note: The guitar speaker volume is determined by the overall combination of
amplifier power and output impedance, guitar speaker impedance, and OX’s rear
panel IMPEDANCE knob.
LINE OUT (5)
The signal level at OX’s rear panel stereo LINE / MON outputs is adjusted with this
knob. LINE OUT does not change the level at OX’s SPEAKER, HEADPHONE, or S/PDIF
outputs.
Rotating this knob fully counter-clockwise to the “0” position shuts off the LINE / MON
outputs.
HEADPHONE Knob (6)
The volume of OX’s front panel stereo HEADPHONE output is adjusted with this knob.
HEADPHONE does not change the level at OX’s SPEAKER, LINE / MON, or S/PDIF
outputs.
Rotating this knob fully counter-clockwise to the “0” position shuts off the HEADPHONE
output.
HEADPHONE Output (7)
This TRS stereo unbalanced output jack accepts standard ¼” stereo headphones.
Headphone volume is adjusted with the HEADPHONE knob above the jack.
Important: Changing RIG settings and/or presets can cause a sudden jump in
headphone output levels. Exercise caution when adjusting Rigs (via RIG knob or
OX software app) when HEADPHONE output is at higher levels.

OX Amp Top Box Controls & Connectors16
POWER Lamp (8)
The power lamp illuminates when OX is properly connected to AC power and the rear
panel POWER switch is in the UP position. When power is OFF, the lamp is unlit.
During system startup, OX’s outputs are inactive.
Important: OX outputs are active only when OX is powered on and system startup
is complete.
Rear Panel
Refer to the illustration below for descriptions in this section.
OX’s rear panel elements
POWER Switch (9)
Use this toggle switch to apply power to OX. The included external power supply must be
properly connected (10) to apply power to OX.
Important: Power must be ON to enable OX outputs.
In the up position, power is ON and the front panel POWER lamp (8) illuminates. In the
down position, OX power is OFF and the POWER lamp (8) is unlit.
System startup begins when OX is powered ON. While the system is starting, OX outputs
remain inactive. After startup is complete, the POWER lamp remains lit and OX outputs
are enabled.
Note: When power is OFF, OX presents a 16 ohm load at the FROM AMPLIFIER
input to prevent tube amp damage that could occur with an unloaded amp output.
POWER S/PDIF
OUT
FOOT
SWITCH
TO SPEAKER
IMPEDANCE
FROM AMPLIFIER
LINE / MON OUT
USB
1/L 2/R
SERIAL NUMBER
8Ω
4Ω16Ω
USB POWERS/PDIF
OUT
FOOT
SWITCH
TO SPEAKERFROM AMPLIFIER
1/L2/R
LINE / MON OUT
150W
RMS
MAX
!
+12VDC 1.5A
9
10 13
14
15
16
17
18
19
20 21
11
12
22

OX Amp Top Box Controls & Connectors17
POWER Input (10)
Caution: Connect only the included external power supply to the POWER
input. Using a different power supply could damage OX and void the
warranty.
This 4-pin locking XLR jack accepts the DC output plug from OX’s included external
power supply. OX requires 12 volts DC power and its power supply draws approximately
18 Watts.
Connect the included IEC power cable to the inlet of the included external power supply
and an AC power outlet.
Note: The following statement is provided for electrical compliance conformity:
“The POWER input is the primary disconnect device.”
Wi-Fi Status LED (11)
This LED indicates activity on OX’s built-in WI-Fi network. The LED states encountered
during normal operation are listed in the table below. For instructions on how to use OX’s
Wi-Fi networking, see OX Software.
Note: If Wi-Fi LED states not listed below are encountered, please contact UA
Technical Support.
Wi-FI LED
State Indication Notes
Off No network connection No device is paired with OX’s internal Wi-Fi hotspot
and OX is not paired with external Wi-Fi network
Blue (solid) Hotspot connection Device is paired with OX’s internal Wi-Fi hotspot
Green (solid) External network
connection OX is paired with external Wi-Fi network
Green (blinking) Attempting external
network connection
OX is attempting to pair with external Wi-Fi network
that was selected in OX app
Reset Switch (12)
This small pushbutton switch is used to reset OX’s Wi-Fi settings and reset OX to factory
defaults. For more information, see Troubleshooting.
Note: Reset is not necessary during normal operation.

OX Amp Top Box Controls & Connectors18
USB Type-B Port (13)
This port is not functional.
USB Type-A Ports (14)
These ports are not functional.
S/PDIF Digital Outputs
The S/PDIF digital output ports are for connecting OX’s left/right stereo output signals to
the digital input(s) of a computer audio interface or other digital audio equipment.
The stereo signal at the digital outputs is same stereo signal as the signal at the MON /
LINE and HEADPHONE outputs. Both digital outputs carry the same stereo signal, and
both digital outputs can be used at the same time.
Digital signal levels can be adjusted with the master fader in the OX software app. Digital
levels cannot be changed with OX’s hardware controls.
Note: The sample rate of the digital outputs is fixed at 44.1 kHz.
Tip: If connecting OX to the S/PDIF input of an Apollo audio interface, activate the
realtime S/PDIF sample rate conversion feature (SR CONVERT) in Apollo Console’s
S/PDIF channel input strip to enable compatibility with all Apollo sample rates.
Coaxial S/PDIF Digital Output (15)
This stereo S/PDIF digital output jack accepts a 75-ohm coaxial RCA (phono) digital
audio cable.
Tip: Use this port to digitally connect OX’s stereo output signal to the S/PDIF
input port on Universal Audio’s Apollo FireWire and Apollo 8 audio interfaces.
Note: For optimum results, use a 75-Ohm RCA cable that is specifically designed
for digital audio.
Optical S/PDIF Digital Output (16)
This stereo S/PDIF digital output port accepts a TOSLINK optical cable.
Tip: Use this port to digitally connect OX’s stereo output signal to the S/PDIF
optical input port on Universal Audio’s Apollo Twin, Apollo Twin MkII, and Apollo
8p audio interfaces.
Important: Although TOSLINK optical cables are also used for digital connections
in ADAT format, this port outputs S/PDIF format only and is incompatible with
ADAT optical inputs.

OX Amp Top Box Controls & Connectors19
FOOT SWITCH Input (17)
This input is not functional.
TO SPEAKER Output (18)
Caution: This is a high power output! DO NOT connect this output
to the input of studio monitors, audio mixers, PA speakers, audio
interfaces, computers, or similar inputs. Connect this output to a
guitar speaker cabinet ONLY.
Caution: DO NOT connect this output to a guitar speaker cabinet
that is rated for a power level that is significantly less than the
connected amplifier’s output power.
Important: Use only a high-quality 12 to 16 gauge unshielded ¼” mono TS
(tip-sleeve) speaker cable for the high power TO SPEAKER connection. “Speaker”
is usually printed on these cables.
The guitar amp’s attenuated (power soaked) speaker signal with OX’s reactive load is
output here. Connect a high quality ¼” speaker cable between this jack and a guitar
speaker cabinet.
OX’s front panel SPEAKER VOLUME knob controls the loudness at this output. At the
knob’s minimum position (0), the speaker connected here is OFF for silent operation.
The signal path between OX’s FROM AMPLIFIER and TO SPEAKER jacks is pure analog.
Because this output is dry without cabinet/mic/room/effects processing, OX’s RIG and
ROOM knobs do not change the sound of the guitar speaker connected here.
SPEAKER Output Notes
• To avoid sudden loud speaker volume, reduce the amp’s volume knob and/or OX’s
SPEAKER knob to before connecting a guitar speaker cabinet.
• This output is designed specifically for guitar speakers. Full-range flat-response
speakers are not recommended for this output connection.
IMPEDANCE Knob (19)
This three-position knob sets the reactive load impedance that is present at OX’s FROM
AMPLIFIER input (and the tube amp’s speaker output). Settings of 4, 8, and 16 ohms
are available.
Note: Set the IMPEDANCE knob to match your tube amp’s speaker output
impedance. If the amp’s speaker output impedance cannot be determined, set
this knob to 8 ohms.

OX Amp Top Box Controls & Connectors20
FROM AMPLIFIER Input (20)
Caution: To avoid permanent damage to the amplifier and/or OX:
• POWER OFF the tube amp before connecting or disconnecting its speaker
output.
• DON’T power or operate any tube amp without an output load such as a
guitar speaker or OX.
• DON’T partially insert ¼” speaker cable plugs halfway or only to the first
click. DO fully insert all speaker cable plugs to ensure proper ground returns.
• DON’T use OX with amplifiers exceeding 150 Watts RMS output power.
This jack is OX’s reactive load input. Connect a ¼” speaker cable between the tube
amp’s speaker output and this RED input jack. The signal received here is attenuated
(soaked) by the reactive load then passed to OX’s SPEAKER OUT jack.
Important: Use only a high-quality 12 to 16 gauge unshielded ¼” mono TS
(tip-sleeve) speaker cable for the high power FROM AMPLIFIER connection.
“Speaker” is usually printed on these cables.
Note: When OX power is OFF, OX presents a 16 ohm load at the FROM
AMPLIFIER input to prevent tube amp damage that could occur with an unloaded
amp output.