Universal Audio OX Amp Top Box User manual

OX Operation Manual

Manual Version 180130

www.uaudio.com

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 Letter From Bill Putnam Jr.2

Table Of Contents

Tip: Click any section or page number

to jump directly to that page.

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

OX Amp Top Box Table Of Contents3

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 Table Of Contents4

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! 5

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 Welcome to OX Amp Top Box! 6

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 Notes 7

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 Critical Operation Notes 8

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 Start 9

Amp & Speaker Connections

Caution: Always POWER OFF the tube amp before connecting or disconnecting

its speaker output!

Power Supply

OX OUTPUT

“TO SPEAKER”

Amp Speaker Output

(to OX input)

OX INPUT

“FROM AMPLIFIER”

Tube Amplifier

Guitar Speaker

Cabinet

OX speaker wire connections to amp and speaker cabinet

Speaker Cab Input

(from OX output)

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 Amp Top Box Quick Start 10

Output Connections

Tip: All of OX's output connections are optional. You only need to connect the outputs you want to use.

LINE / MON

HEADPHONE (front panel)

DON'T connect OX

outputs to the amp!

OX "TO SPEAKER"

DIGITAL

Guitar Speaker Cabinet

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 Start 11

Control Knobs

RIG

Choose from six complete guitar cabinet+mic+room+effect presets.

ROOM

Instant access to mic’d studio ambience and air.

Quick Operation Notes

SPEAKER VOLUME

Adjusts the volume of the guitar speaker cabinet connected to OX. Set to 0 for silent operation.

LINE OUT

Adjusts the level at OX's stereo LINE/MON outputs.

HEADPHONE

Adjusts the volume of stereo headphones connected here.

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 builtin 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

OX Amp Top Box Quick Start 12

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.

3 4 5 6 8

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.

OX Amp Top Box Controls & Connectors 13

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

Green (solid) RIG not modiﬁed

Amber (solid) RIG modiﬁed

Amber (blinking) Firmware update Firmware update is in process

Green (blinking)

Red (blinking)

Wi-Fi reset initiated and

awaiting user conﬁrmation

Factory reset initiated and

awaiting user conﬁrmation

Rear panel POWER switch is in down position and/ or AC adapter is not properly connected

Active RIG has been loaded via RIG knob or OX app and is unchanged from stored version

Active RIG has been edited via ROOM knob or OX app and is not stored

Press reset switch again within 10 seconds to conﬁrm Wi-Fi reset

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 & Connectors 14

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 & Connectors 15

POWER Lamp (8)

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

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.

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.

OX Amp Top Box Controls & Connectors 16

10 13

20 21

OX’s rear panel elements

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

Off No network connection

Blue (solid) Hotspot connection Device is paired with OX’s internal Wi-Fi hotspot

Green (solid)

Green (blinking)

Indication Notes

No device is paired with OX’s internal Wi-Fi hotspot and OX is not paired with external Wi-Fi network

External network

connection

Attempting external network connection

OX is paired with external Wi-Fi network

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 & Connectors 17

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 & Connectors 18

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 & Connectors 19

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.

OX Amp Top Box Controls & Connectors 20

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