The Universal Audio Astra Modulation Machine is a digital stereo modulation stompbox that gathers three emulations in one enclosure: a bucket-brigade chorus, a rackmount-style flanger/doubler, and a tube amp tremolo. Universal Audio, a company better known for studio equipment and plugins, entered the guitar pedal market for the first time in 2021 with the Astra alongside the Golden Reverberator and Starlight Echo Station1. The pedal is built on UA's UAFX dual-engine processing, which runs separate stereo instances of each modulation effect2.
The three main modes are Chorus Brigade, Flanger DBLR and Trem 65, with secondary modes for Vibrato, Doubling and more3. Universal Audio describes it as a flagship, no-compromise stompbox offering bucket-brigade and tube-driven tremolo effects2. Note that the pedal is currently in limited availability, while supplies last2.
What the Astra does: the three main modes
Each of the Astra's three foot-selected modes is a circuit emulation of a specific vintage piece of gear, and each has an A and B variation reached with a toggle switch53.
| Mode | What it emulates | Details |
|---|---|---|
| Chorus Brigade | A 1976 Japanese gray bucket-brigade chorus/vibrato stompbox, the unit known as the Boss CE-1 Chorus Ensemble | Full circuit emulation including the original's preamp section26 |
| Flanger DBLR | A late-'70s rackmount bucket-brigade studio flanger/doubler, MXR's rack unit | UA calls it the only end-to-end circuit emulation of this ultra-rare unit27 |
| Trem 65 | A '60s American amp optical tube-driven tremolo | Models the interactions between the light source photoresistor and 12AT7 driver tube, with variable sine and square wave settings2 |
The Brigade Chorus mode is the Astra's take on the chorus sound of the CE-1, the pedal Universal Audio says changed the sound of music in 1976 with its thick, luxurious analog chorus2. The Flanger DBLR covers flanger and doubling territory, based on a studio rack unit famous for its whoosh effects2. Trem 65 handles tremolo, down to the behavior of the photocell and driver tube in the original amp circuit2.
Controls and how you set it up
The control surface is the same layout across the UAFX line. The top row of knobs handles Speed, Depth and Intensity, and the bottom row handles Shade, Shape and Mode8. MusicRadar's review lists the full control set as Speed, Depth, Intensity, Shape and Shade knobs, toggle switches for effect type, preset store and A/B sound selection, a rotary mode switch, and manual/bypass and preset/bypass footswitches7.
Not every knob does something in every mode. Guitar.com's review notes that the Shape knob is only active with the flanger and the harmonic tremolo5. The three mini-switches choose the effect type, store the preset, and flip between the A and B variations8.
Power and connections
The Astra needs an isolated 9V DC, center-negative supply delivering at least 400mA, through a 2.1 x 5.5 mm barrel connector, the same size as standard Boss connectors2. The power supply is sold separately29. That 400mA draw is worth planning around: Guitar.com's reviewer pointed out that these units each demand 400mA of current5, so a typical daisy chain won't be enough.
The Astra requires an isolated 9V DC center-negative supply rated at 400mA minimum, and the supply is not included. There is no battery option. Full-sized UAFX pedals with two footswitches need 400mA; the compact single-footswitch UAFX pedals need 250mA2.
Connections are stereo-capable: two unbalanced TS inputs and two unbalanced TS outputs, with input 2 and output 2 for stereo operation2. Input impedance is 500 kilohms in mono and 1 megohm in stereo, output impedance is 500 ohms, maximum input level is 12.2 dBu, maximum output level is 12.1 dBu, and frequency response is 20 Hz to 20 kHz, ±1 dB2. The USB Type-C port handles registration and firmware updates via a computer2, and the pedal also has Bluetooth v52. Firmware updates are done by connecting the USB-C cable to a compatible computer and running the UA Connect application2.
For rig control, the Astra has no 5-pin MIDI ports but receives MIDI over USB: the rear panel USB-to-MIDI connection lets it fit into a programmable MIDI rig, receiving preset changes and BPM clock sync2.
Bonus effects and the UAFX Control app
Registering the pedal, either with the UA Connect desktop app or the UAFX Control mobile app, unlocks downloadable bonus effects2. MusicRadar's chorus pedal roundup describes the full picture: beyond the CE-1 chorus/vibrato mode and the MXR-based flanger/doubler, there's a Phase 90, a Fender amp tube-driven tremolo and UA's own Dharma Trem 61, some available to download after registration6.
Guitar.com's review details the two downloads:
- The first offers two flavors of MXR Phase 90 swirliness, script logo and block5.
- The second lets you flip between a phasey tremolo and something more like a Uni-Vibe, each with the option of setting the trem speed to respond to pick attack. The reviewer called it "arguably the pick of the whole bunch"5.
The UAFX Control app is also where you choose between true bypass and buffered bypass2, and where you manage the store-and-recall preset system with its Live and Preset modes2.
What reviewers said
The Astra reviewed well across the press. Guitar.com scored it 9/10, and its verdict praised "an irresistible array of top-class modulation effects all stuffed into one tidy little box"5. The same review found the pedal less smooth to operate, reporting that "navigating the pedals is not entirely intuitive and the non-latching model switch feels a little awkward and compromised"5.
"An irresistible array of top-class modulation effects all stuffed into one tidy little box"
The same reviewer found the sounds "phenomenal" and wrote that "you'll struggle to make a less-than-lovely noise with any of them"5. On specifics, the verdict on chorus was strong: "If you're after rich stereo chorus with impeccable clarity and absolutely minimal operating noise, you won't find better"5. Of the tremolo, the review said "the valve-y tremolo throbs away sweetly, with a choppy square-wave variant broadening your options in mode B"5. The criticism was about usability: navigating the pedals is not entirely intuitive, and the non-latching model switch felt a little awkward and compromised5.
MusicRadar's review of the three UAFX pedals called it "benchmark modelling in a pedal" for quality of sounds7. Gearnews praised the effects quality, and Guitar World's modulation pedal guide wrote that "the quality of the effects, as you'd expect from UA, is simply stunning," with special praise for the chorus mode89. Guitar.com also named the UAFX line among the best premium effects pedals of 20211.
On Universal Audio's own reviews page, the Astra carries a rating of 4.3 out of 5 stars from 15 reviews, with 80% of reviewers saying they would recommend it10.
Where it came from
Universal Audio announced the UAFX line in January 2021, with the Astra putting three emulated modulation sounds at your feet3. The pedals shipped that March at a list price of $3994. The company was an established name in studio gear moving into the pedal market for the first time, which Guitar.com said piqued its interest1. The Astra is made in Malaysia5.
The Brigade Chorus concept later got its own compact pedal: in 2023 Universal Audio released the UAFX Brigade Chorus, a digital recreation of the same CE-1 circuit the Astra's chorus mode is built on.
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Questions
Is the UAFX Astra true bypass?
Yes. The Astra offers true bypass via mechanical relays, or buffered bypass, and you choose between the two in the UAFX Control app. It also switches silently and can store and recall a preset, with Live and Preset footswitch modes.
Does the Astra have MIDI?
It has no dedicated 5-pin MIDI ports, but it receives MIDI over USB. A rear panel USB-to-MIDI connection lets the Astra fit into a programmable MIDI rig, receiving preset changes and BPM clock sync.
Is the Astra Brigade chorus the same as the UAFX Brigade pedal?
Both are Universal Audio emulations of the same 1976 Japanese bucket-brigade chorus/vibrato stompbox, the unit widely known as the Boss CE-1 Chorus Ensemble. The Astra's Brigade Chorus mode is a full circuit emulation that includes the original's preamp section. The compact Brigade pedal arrived later, in 2023.
Can the Astra do a phaser or Uni-Vibe?
Not from the factory, but two bonus effect downloads add them after you register the pedal. The first gives two flavors of MXR Phase 90, script logo and block. The second offers a phasey tremolo and something more like a Uni-Vibe, with an option to set trem speed to respond to pick attack.
Where is the Universal Audio Astra made?
The Astra is made in Malaysia, according to Guitar.com's review of the pedal. Universal Audio itself is an established audio company that moved into the guitar pedal market for the first time with the UAFX line in 2021.
Sources (10)
- Gear Of The Year: Best Premium Effects Pedal of 2021, Guitar.com, 2021-12-09
- Astra Modulation Machine Pedal, Universal Audio (www.uaudio.com)
- Universal Audio Announces UAFX Effects Pedals, Premier Guitar, 2021-01-27
- Universal Audio Ships UAFX Pedals, MusicPlayers.com, 2021-03-31
- The Big Review: Will Universal Audio’s entry into the guitar pedal market send boutique brands scurrying for cover?, Guitar.com, 2021-05-13
- Best chorus pedals 2026: Top-rated chorus pedals, MusicRadar, 2022-05-24
- Universal Audio UAFX Golden Reverberator, Starlight Echo Station and Astra Modulation Machine review, MusicRadar, 2021-12-26
- Review: UAFX Golden Reverberator, Starlight Echo Station and Astra Modulation Machine, gearnews.com, 2021-04-04
- Best modulation pedals: our pick of the best mod effects, Guitar World, 2023-06-02
- Astra Modulation Machine Reviews, Universal Audio
