Universal Audio’s Amp Top Box

Unsurpassed effects, intuitive operation, and a diverse set of speaker emulations elevate this top box to industry standard status.

The three devices reviewed here cover similar territory as Universal Audio's $1,299 OX Amp Top Box. In some cases, the OX influence isn't exactly subtle.


We reviewed the OX almost exactly two years ago. I purchased the review model and have used it regularly ever since. The OX proved to be a hit, acquiring a large pro user base. It remains a go-to solution for low-volume recording and related tasks. I stand by the original review, and the device hasn't changed much since it debuted. So this is a rare opportunity to revisit a piece of gear after years of use while comparing its features to those of newer arrivals.

IRs vs. Modeling

Universal Audio refers to its emulating process as speaker modeling, not impulse responses. Impulse responses are realistic but static snapshots, whereas the OX aspires to mimic speakers in varying states, with a front-panel speaker breakup knob that introduces the harmonic variations that occur when speakers are pushed to extremes.

The OX's speaker emulations are magnificent. You get 22 superb models based on Fender, Marshall, Vox, Mesa, and Hiwatt cabs. There are six "usual suspect" mic models, and six virtual room mics. The room sounds are lush and realistic, and you can adjust the amount of room ambience via a dedicated knob on the box's front panel. You can also assign two virtual microphones to each cabinet, position them in virtual space, and tweak their characteristics.

But there's a downside to UA's proprietary speaker emulation process: You can't load additional IRs. I've never failed to find appropriate tones within the OX sound library. But if you insist on a specific speaker sound not included here, the OX may not be your best option.

Elevated Editing

The OX's software editor is attractive, powerful, and intuitive. Photorealistic depictions of the modeled gear make it easy to visualize your edits. You can store six favorite speaker/mic/effect combinations ("rigs") within the OX box itself and access them without connecting to a computer. The editors are available for Mac and PC. There's a mobile version for Apple iPads, but not for iPhones or Android devices.

Universal Audio\u2019s Amp Top Box editor

The OX's software editor has the sophistication of a full-featured DAW.

You don't need a physical connection to edit the OX's sounds. The device includes its own WIFI network. Just connect your computer or iPad to the network, and tweak away. It's a great idea, but it is sometimes problematic in practice.

We must often go online while recording to access files, manage authorizations, and search for relevant data, which can mean constantly switching networks mid-session. Most pro users I know keep a dedicated iPad connected to the OX network, while the DAW's computer remains on its usual network. Even then, the iPad tends to drop its connection if it goes into sleep mode. I've always managed to get the job done via the OX's network, but this clever feature has never quite lived up to its promise.

Exemplary Effects

To my ears, Universal Audio's effects modeling is unsurpassed. The OX includes two dead-accurate models of classic recording gear: a Urei 1176 compressor and an EMT 140 plate reverb. There's also high-quality EQ and delay. All the devices covered here include excellent effects, and picking favorites is a subjective task. But to my ear, nothing else touches the OX's.

Universal Audio\u2019s Amp Top Box back

Other Noteworthy Details:

  • The OX's impedance switcher supports 4, 8, and 16 ohms.
  • The OX is an excellent direct recording preamp.
  • The OX outputs sound via balanced stereo analog outs, digital AES/EBU, and optical digital TOSLINK. The analog outs are 1/4" TRS. But I've always wished there were pro-quality XLR outs, especially considering the OX's pro-level price. (The three newer devices all have XLR outs.)
  • The attenuation level is continually variable, as opposed to using fixed steps.
  • You can use one-, two-, and three-button footswitches (not included) to toggle the OX's effects.
  • The OX has no MIDI control.
  • The OX comes with 125 unusually good factory-preset rigs.

Despite the minor frustrations mentioned above, OX has been a miracle worker for me. I use it incessantly (including on many PG gear reviews) and I'm always delighted by the results.

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