The pedal is a spin-off from a larger unit: Universal Audio says it "evolved from our flagship Astra Modulation Machine"1, and Guitar.com's Josh Gardner describes it as "this one takes the tremolo from the Astra and makes it a standalone unit"2. For players who wanted the Astra's tremolo sounds without the rest of its modulation lineup, the Flow is that circuit on its own.
What it does: tremolo with an emulated '60s tube preamp
Tremolo, the rhythmic rise and fall of volume in your signal, was commonly found built into many '60s tube amps, such as Fender's Vibrolux and the Vox AC305. The Flow takes that idea and models it in a pedal, with a captured tube preamp that Universal Audio says delivers "fat, three-dimensional tremolo tones"1.
Each of the three modes is built on a different vintage circuit:
| Mode | Waveform | What it emulates |
|---|---|---|
| Dharma | Harmonic tremolo | The "chewy throb" of early '60s American "brown" amps, with volume fluctuation and phase shifting, for vintage soul, surf and Uni-Vibe textures1 |
| 65 | Round sine wave | An "exhaustive end-to-end emulation" of a classic 1965 American tube amp's optical tremolo circuit1 |
| Square | Choppier square wave | Square waveforms built from UA's own virtual optical photocell, aimed at modern pop and R&B through blues and indie rock1 |
Gearnews describes the same three flavors as "harmonic Dharma, smooth '65-style sine, and hard square-wave chop," each paired with an emulated preamp circuit and a volume boost3. Their news coverage of the launch characterizes the set as "early Fender harmonic tremolo, later '65 style round tremolo and square wave trem-tones"4.
The controls, modes and connections
The Flow's control set centers on three things Universal Audio lists directly: switchable true/trails bypass, tap tempo, and a "make up gain" Volume control1.
- Tap tempo: onboard tap tempo for syncing trem effects to the tempo of a song1
- Volume control: adds boost effects, with make-up gain so the tremolo effect can sit at the level you want1
- Bypass: switchable between true bypass and a trails mode that lets the effect ring out1
Gearnews highlights how these features work on a modern board: "Tap tempo and selectable true or buffered bypass make it easy to integrate into modern boards without sacrificing feel"3.
On the connection side, the pedal uses 1/4" unbalanced TS input and output, handles up to 12.2 dBu at the input and 12.1 dBu at the output, and has a frequency response of 20 Hz to 20 kHz, ±1 dB1.
The Flow needs an isolated 9V DC supply, center negative, with a 2.1 x 5.5 mm barrel connector, the same as standard Boss connectors, and the power supply is sold separately1. Compact UAFX pedals with a single footswitch require 250 mA of current, more than a typical small analog pedal, so a dedicated isolated output is the safe choice1.
Where it came from
Universal Audio launched the Flow on 24 October 2023 as a new addition to the UAFX compact pedal series2. The tremolo circuit itself came from the Astra, with the Flow taking that tremolo and making it a standalone unit12.
What reviewers said
Guitar.com reviewed the Flow in their 60 Seconds video series in December 2023, framing the question of its broad appeal: "Is this the most universally appealing UAFX compact yet?"21
On That Pedal Show, Mick and Dan looked at the Flow alongside the Jam Pedals Harmonious Monk in March 2024, calling it "an exceptional value tremolo that also has harmonic and two amplitude modes, super versatile and dead easy"6.
Gearnews included the Flow in their best tremolo pedals buying guide, writing that it "brings studio-grade modeling to the best tremolo pedals conversation"3.
Videos
Sweetwater
Guitar Center
Tri Pedal Reviews
Questions
Is the Universal Audio Flow Tremolo true bypass?
It offers switchable true or trails bypass, so you can choose true bypass or a buffered mode that lets the tremolo tail ring out when you disengage the pedal. Gearnews also describes it as having selectable true or buffered bypass, which makes it easy to fit into modern pedalboards.
Does the UAFX Flow have tap tempo?
Yes. Universal Audio lists onboard tap tempo for syncing trem effects, and the pedal lets you sync your trem rate by tapping. Gearnews highlights tap tempo as one of the features that makes it easy to integrate into modern boards.
What tremolo modes does the Flow Vintage Tremolo have?
It has three modes. Dharma is a harmonic tremolo modeled on early '60s American brown-face amps, 65 is a round sine-wave tremolo emulating a classic 1965 American tube amp's optical tremolo circuit, and Square is a choppier square-wave mode built on UA's own virtual optical photocell.
Is the Flow the same tremolo as the Astra Modulation Machine?
The Flow evolved from the Universal Audio Astra Modulation Machine. Guitar.com describes it as taking the tremolo from the Astra and making it a standalone unit, so the tremolo sounds are related, but the Flow is a dedicated compact tremolo pedal rather than a multi-effect modulation unit.
What power supply does the UAFX Flow need?
It needs an isolated 9V DC supply, center negative, with a 2.1 x 5.5 mm barrel connector, the same as standard Boss connectors. Compact UAFX pedals with a single footswitch, like the Flow, require 250 mA of current, and the power supply is sold separately.
Sources (6)
- Flow Vintage Tremolo Pedal, Universal Audio (www.uaudio.com)
- 60 Seconds S1E12: Universal Audio Flow Tremolo, Guitar.com, 2023-12-18
- The 9 Best Tremolo Pedals for Any Budget: Vintage Pulses and Modern Vibes, gearnews.com, 2025-12-22
- UAFX Brigade Flow LA2A: New additions to UAFX Compact Pedal series, gearnews.com, 2023-10-24
- Best tremolo pedals for guitar: Shake up your tone, MusicRadar, 2019-10-23
- UAFX Flow Vintage Tremolo & Jam Pedals Harmonious Monk Effector Du Jour, That Pedal Show, 2024-03-12
