DAC / AmpOverreview

THX Onyx

The dongle that measures like a desktop amp — and still split the critics on how it sounds and what it was worth.

23 sourcesUpdated
$200Typical US price

Score aggregates reviewer opinions across topics.

THX Onyx

The short version

What to know.

A bus-powered USB-C dongle DAC and headphone amplifier with a single 3.5 mm output, launched at $199.99 in 2021 and now out of stock at THX and Razer. Sources agree that it is very quiet, with no audible hiss on sensitive in-ear monitors, and that it is unusually powerful for a single-ended dongle: three independent benches measured about 130 mW into 32 ohms. A minority found its 2-volt ceiling short with 300-ohm Sennheisers and the hardest planars. They split on three things. Sound: two benches measured about 108 dB SINAD and most reviewers heard it as clean and neutral, while What Hi-Fi? found it crude next to the DragonFly Red and a few listeners called it flat or veiled. Build: reviewers praised the machined metal body, while one lab called the finish ordinary and a handful of owners had units die. Value: launch reviewers mostly called it worth $200, while forum regulars pointed to cheaper dongles that measure nearly as well.

About this product

THX's own USB-C dongle DAC and headphone amp from 2021, sold through Razer. Not the THX AAA desktop amps sold under Drop, Monoprice or Benchmark names, and not the cheaper THX-certified dongles from other makers.

The THX Onyx was the first consumer product THX ever sold under its own name: a slim black metal stick at the end of a soft rubber USB-C cable, with a 3.5 mm headphone jack at the far end and a magnet in each end so the cable can fold back on itself. Inside, an ESS ES9281PRO converter feeds a THX AAA-78 amplifier, the portable version of the feed-forward design used in Drop's and Benchmark's desktop amps. It renders MQA, accepts headset microphones and came with a USB-A adapter.

It launched in April 2021 at $199.99, well above most rival dongles, and later sold for around $150 before going out of stock at THX and Razer. Audio Science Review put it on its recommended list, and most launch reviews were enthusiastic. What Hi-Fi? gave it three stars for sound, and forum regulars kept asking why it cost so much more than cheaper dongles that measured nearly as well.

A good fit for

  • Listeners with sensitive in-ear monitors who want a silent background
  • One single-ended dongle for IEMs and moderately demanding over-ears, including many planars
  • PC and Android gamers who need a headset microphone through the same jack

Think twice if

  • You own 300-ohm Sennheisers or balanced cables and want more headroom
  • You want volume, filter or EQ controls on the device itself
  • The only new units you can find are priced well above its old $150–$200 range

The reviewer consensus

Agreement &
disagreement.

3 / 7topics divide opinion
noiseergonomicspowerfeaturestransparencybuildvalue
2 Strong agreement2 Mostly agree3 Divided opinions

Common ground3

  • Very quiet: no audible hiss even with sensitive in-ear monitors
  • Powerful for a single-ended dongle — about 130 mW into 32 ohms on three independent benches
  • Plug-and-play on Mac, Windows and Android, but it runs warm and costs more phone battery than low-power dongles

Points of contention3

  • Sound: clean and neutral to most reviewers and every bench, crude or veiled to What Hi-Fi? and a few listeners
  • Build: praised by reviewers, called ordinary by one lab, with a handful of owner units failing
  • Value: worth $200 to most launch reviewers, overpriced to forum regulars comparing cheaper dongles

A closer listen.

7 topics · 3 divided
Left: criticalRight: positiveTighter lines: more agreement

Power

PositiveMostly agree
Reviewer sentiment17 supporting sources
CriticalNeutralPositive

Band: opinion spread · Dot: weighted average

Mostly praised, with a clear limit. Reviewers and owners drove Audeze LCD-3s, Oppo PM-3s, Dan Clark Aeon Flow Closed and Diana v2s to loud levels, and three independent benches found about 130 mW into 32 ohms with no clipping — a lot for a dongle without a balanced output. The complaints come from the extremes. Owners of 300-ohm Sennheiser HD 600s and HD 650s found the volume merely adequate or the sound a little flat, and one hit clipping with a Dan Clark Aeon RT. The HiFiMan HE6se needed full volume. Below 22 ohms its current limiter can step in.

“Switching to 32 ohm load though, allows the Onyx to shine more with its high current delivery”

Amir · Audio Science Review

“While the Onyx felt slightly underpowered to do justice to the HD650 with the HD660s it was a totally different experience”

Ichos Reviews

“it's a great little dongle but it's not any more powerful than the dragonflys.”

roach7 · Head-Fi (with a HiFiMan HE6se)

Measured

ASR: 2.07 V maximum; 132 mW into 33 ohms and 14 mW into 300 ohms without clipping; protection engages only at 12 and 16 ohms. L7Audio Lab: 133 mW into 32 ohms at full scale. An SMZDM owner's bench: 2.067 V into 32 ohms below 0.1% distortion (134 mW). THX rates it at 180 mW into 22 ohms below 1% distortion, with a 22–1000-ohm headphone range.

vs. listeners — The ceiling is voltage, not current: at about 2 volts it has plenty for low-impedance planars but only around 14 mW into 300 ohms, which is why HD 600 and HD 650 owners were the ones asking for more. Balanced dongles with 4 volts double the voltage, which is the 'lack of balanced output' ASR counted as a miss.

Link to this topic

The hardware

Specifications.

Checked

Design

Form factor
Dongle
DAC
ESS ES9281PRO · Delta-sigma
PCM
384 kHz / 32-bit
MQA
Yes
Amplifier
Solid-state · THX AAA-78

Output

Output power
Single-ended: 180 mW @ 22 Ω
Output impedance
0.25 Ω SE

Connection

Digital inputs
USB-C
Headphone outputs
3.5 mm
Microphone input
Yes
Power
USB bus powercommunity-sourced

Physical

Dimensions
14 × 210 × 7.2 mm
Released
2021-04

DSD plays as DoP64/DoP128; the headset mic works on Mac, PC and Android but not iPhone or iPad. Manufacturer-published figures, not measurements · from thx.com, thx.com, razer.com. Power not published by the maker — community-sourced from hands-on reviews: audioxpress.com, hifichoice.com.

Follow the evidence

Sources 23

1–6 of 23 sources

Read with context

Limitations & method.

As of

What to keep in mind 5

  1. A read of where the reviews land as of October 2026. The Onyx is now out of stock at THX and Razer, and most of these reviews date from 2021–22, before newer dongles moved the field on.

  2. Many of the most enthusiastic launch reviews were written on units THX supplied, while the sharpest price criticism came from forum members comparing cheaper dongles — worth keeping in mind where the two groups disagree.