Tanchjim Fission VS Letshuoer S12 Ultra

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The Tanchjim Fission is an absolutely spectacular IEM that feels and performs far beyond its $129 price tag. It comes loaded with a ridiculous amount of customization, featuring three interchangeable nozzles (stainless steel, titanium, and brass) and a four-way tuning switch, creating a potential 12 different sound combinations. The entire package feels flagship-tier, boasting an excellent interchangeable cable system with 3.5mm, 4.4mm, and USB-C terminations, a waterproof bag, and even a keychain tool for adjustments.

After extensive testing, the definitive "cheat code" for the best sound is using the brass nozzles with the tuning switch set to Pop mode, which seemingly bypasses internal circuitry for a pure, direct sound. This configuration delivers exceptional clarity and a surprisingly wide soundstage, though they are not bass monsters. The fit is excellent, passing the "pinky test," and the build quality on everything from the IEMs themselves to the accessories is exceptional.

While not every combination of nozzles and switches is a winner, the sheer number of options ensures you can find a sound you love. For the price, the value is unmatched, feeling like a product that should cost $279. It comes as a full recommendation, offering a premium, highly tunable experience that is arguably one of the best deals in the IEM market, cementing Tanchjim's reputation for making no bad gear.

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The TANCHJIM FISSION comes as a single dynamic driver IEM in roughly the 100 to 130 dollar bracket, with a metal shell that feels robust yet lightweight and a very soft modular cable. The package includes multiple tips, three tuning nozzles, a dial for four sound modes and a USB C plug that unlocks the Tanchjim app, so there are a lot of tuning options even if the inclusion of only a pouch instead of a case and the familiar shell design feel a bit safe.

With the preferred combination of default dial position and silver nozzle the overall signature is basically neutral with a slightly vocal forward tilt. Bass quantity sits in a truly neutral zone with good punch and very solid bass dynamics, though the transition into the lower mids can sound a bit congested and separation could be cleaner. The midrange carries some warmth and note weight for male vocals while a steady rise into the upper mids around 3 kHz gives vocals and instruments clear presence without becoming shouty. Treble is tuned safely and naturally, with enough energy for cymbals and strings to cut through without harshness, plus just enough upper treble for a bit of air and shimmer and some welcome micro detail for a single dynamic driver.

Technical performance is generally good but more in the average range for this price. Detail retrieval and soundstage sit around class typical, with staging that leans a little intimate in depth but respectable left right stereo focus and imaging that makes it easy to place instruments. Compared with other recent sets in this bracket like the Yaksha, TRN Jaws or Juzear Defiant, this is a pretty decent neutral option but not the clear standout, especially with its more relaxed bass and others offering similar or better technical ability with more low end presence. Overall the FISSION feels like a versatile, neutral leaning daily driver that will appeal to listeners who value natural tonality, safe treble and EQ flexibility over big bass and showy technical fireworks.

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Tanchjim Fission comes in at $130 with a quirky onboard tuning dial that offers four bass positions—but every setting trends toward modest bass anyway, making the adjuster more novelty than necessity. The default “bass-max” profile presents that familiar single-DD contrastiness with a bit of dynamic punch, a slightly bright/forward tilt, and overall inoffensive treble. It never tips into harshness or sibilance, but the bass attack reads a touch pillowy and the whole presentation stops short of truly incisive.

In direct comparison, it’s more comfortable tonally than the spikier sets yet less engaging and less tight than the standouts, settling into a solid C-tier alongside other “fine but unremarkable” options. Resolution and imaging are serviceable, treble stays safe, and the included cable is surprisingly nice, but there’s not enough slam or bite to push it up the chart. Net result: a competent, easy-listen single-DD for those who value smoothness over excitement, with limited payoff from that bass dial.