Truthear KeyX

The keychain DAC that replaced my Apple dongle

Truthear built their reputation on value IEMs — the Zero series, the Hexa, Hype 4 — products with serious measurements at honest prices. The KeyX applies that same logic to source gear: a Cirrus Logic CS43131, a chip that typically anchors products in the $50–100 range, housed in a $30 keychain dongle that puts the usual “Apple dongle or bust” argument to rest.

I’ve been running the KeyX for a few weeks across a range of everyday listening, most notably on a recent holiday where it served as my primary mobile source paired to an iPhone and a pair of FiiO JT7 Planar headphones — a thirty-dollar dongle driving a planar, which turned out to be rather more capable than expected. The measurements go a long way toward explaining why. But first, let’s take a look at what’s in the box.

Unboxing and Build Quality

The packaging is clean and minimal — appropriate for the price, with nothing wasted. The box opens to reveal the KeyX nestled in a foam insert, with a short USB-C to USB-A adapter and the standard paperwork alongside it.

In the box: Truthear KeyX, USB-C to USB-A adapter, documentation.

The KeyX itself is a compact, fixed right-angle design — USB-C input on one end, 3.5mm TRRS jack on the other, with a small rectangular housing in between that feels solid for the price. The right-angle form factor is practical for desktop and laptop use, keeping the cable clear of the port and the dongle lying flat. For phone-in-pocket use, a cabled dongle would arguably be more comfortable, and that is a minor but real trade-off worth weighing depending on your primary use case.

The signature feature is the small keyring loop built into the housing, which allows the KeyX to live on a set of keys or a lanyard — a genuinely smart idea for a source you want permanently at hand without having to remember to pack it.

My only build quality concern is the connector point at the keyring loop itself, which feels like it could be a fatigue point under the daily stress of a key ring.

It is a minor concern and one that is easy to mitigate — the loop is a standard ring that could be swapped without difficulty if it ever showed wear — but worth knowing if you plan to rely heavily on the keychain functionality day to day.

Features and PEQ Support

The KeyX supports parametric EQ through an online DSP interface. Truthear’s recommended tool is their new EQTOOL.COM platform, though the device also works with graph.hangout.audio — and it fully supports my own DevicePEQ tool, which allows PEQ filter sets to be pushed directly to compatible devices from web pages with no desktop software required. Being able to apply an EQ preset from a review page or measurement database in a single click is genuinely useful, and the KeyX handles it cleanly.

Microphone input is supported via the TRRS jack, keeping the KeyX viable for voice calls and remote work without needing a separate adapter. Decoding capability runs to PCM 384kHz/32-bit and DSD256 — comfortably beyond anything most streaming services require.

Sound Impressions

The CS43131 is a well-characterised chip: neutral, transparent, and composed. The KeyX is a faithful implementation of it. I ran the KeyX from an iPhone and from a laptop, primarily with the FiiO JT7 Planar and a range of IEMs, and the consistent impression was one of effortless cleanliness — no grain, no obvious coloration, just the recording presented accurately. Source chain for these impressions was iPhone → KeyX → FiiO JT7 Planar and a selection of single-dynamic IEMs.

Bass

Sub-bass extension is accurate and neutral, with no added weight or bloom. The KeyX does not editorialize low frequencies — what the recording contains is what arrives. Kick drum texture on Steely Dan’s “Aja” comes through with genuine articulation: tight, defined, and uncolored. If your headphone has a tuned bass shelf, the KeyX will faithfully reproduce it; if it doesn’t, the KeyX won’t add one.

Midrange

The midrange is clean and transparent, with good note weight and no upper-mid hardness. Vocal presence on Dire Straits’ “Brothers in Arms” sits naturally — intimate without being forward, with clear instrumental separation behind the main melody. The CS43131’s neutrality means your transducer’s character comes through without interference, which is exactly what you want from a reference-grade source.

Treble

Treble extension is confident and free from glassiness. Hi-hat sheen on Michael Jackson’s “Billie Jean” has proper shimmer without etch or sibilance, and upper-harmonic resolution is genuinely present rather than merely implied. Whether your headphone takes advantage of it is its own business, but the KeyX is not the limiting factor.

Soundstage and Imaging

Staging characteristics reflect the headphone rather than the source, which is precisely the right behaviour from a neutral DAC. Channel matching is precise, background blackness is strong, and imaging holds its position cleanly within whatever space the recording presents. On Radiohead’s “How to Disappear Completely,” ambient tails float in their own layer rather than collapsing into the mix — a good indicator of a clean noise floor.

Comparisons

The most obvious comparison is the Apple USB-C dongle — the default mobile source for most iPhone users. The KeyX outputs at least 50mW into 32Ω, roughly double the Apple dongle’s rated output, and the measured noise floor and dynamic range are in an entirely different class. The Apple dongle remains a fine emergency backup, but the KeyX renders it redundant as a considered primary source. On the recent holiday trip, it replaced the Apple dongle entirely without a second thought — and drove the FiiO JT7 Planar with enough headroom that I never found myself hunting for volume.

Specifications and Measurements

The measurement results are the headline here. Tested on an Audio Precision APX555 — the reference bench for professional audio measurement — the KeyX achieves a SINAD of 112dB.

That result puts the KeyX well above the audibility threshold for distortion artifacts and ahead of many products at two to three times the price. Dynamic range of 122dB means the noise floor is effectively inaudible on sensitive IEMs — background silence is genuinely black, not merely quiet. The 50mW output into 32Ω provides real driving headroom, enough to handle a planar headphone from a phone without running into the top of the volume range.

Rating Explanation

A five across the pragmatic, features, and measurements ratings reflects what the KeyX actually is: an excellent implementation of a chip that usually costs far more, in a form factor that makes practical sense, with measurement results that hold their own against gear at multiples of the price. The built-in PEQ support — working across multiple platforms including DevicePEQ — is not a checkbox feature; it is genuinely usable and adds real flexibility for those who want to personalise their sound or apply a device-specific compensation profile.

The price rating sits at four rather than five not because thirty dollars is not outstanding value — it is — but because the fixed right-angle design does narrow the audience compared to a cabled equivalent, and there is a rung of ultra-budget competition that undercuts it for purely passive use. These are small points against a product that earns its scores decisively.

The KeyX is aimed squarely at mobile listeners who want a proper source rather than an afterthought, and at anyone who has been reaching for the Apple dongle out of habit rather than preference. If you fall into either camp, the upgrade case here is unusually easy to make.

Conclusion

The Truthear KeyX does what it promises with very little drama: a Cirrus Logic CS43131, honest measurements, built-in parametric EQ, and a clever keychain form factor for thirty dollars. It replaced the Apple dongle in my travel kit without ceremony, drove a planar headphone on a holiday without breaking a sweat, and delivered measurement results that most desktop DACs at this price cannot approach. Small, neutral, light, and now permanently on my keys — the KeyX is the upgrade that makes you wonder why you waited.