Overview

The SMSL D400EX is a flagship desktop DAC using dual AK4499EX in true dual-mono with an AK4191 modulator front-end. USB input is XMOS XU-316. It supports PCM up to 32-bit/768 kHz, native DSD512, and MQA/MQA-CD decoding. Inputs include USB, Optical, Coaxial, Bluetooth, I2S, and AES/EBU; outputs are balanced XLR and single-ended RCA[2][3].
Street price at writing: 959.99 USD (official shop)[7]. We also confirmed availability on Amazon Japan[8].

Scientific Validity

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• Published specs: THD+N 0.00006% (-124 dB, A-wtd), Dynamic Range 133 dB (XLR) / 128 dB (RCA), SNR 133 dB[3]—well within transparent territory.
• Independent data: L7Audiolab measured ~120 dB SINAD (SE/RCA), confirming transparency[4].
• Additional notes: ASR observed perfect USB jitter, a tiny Toslink jitter spur, and a small mid-level IMD hump[1], with overall excellent linearity and top-tier performance[1].

Technology Level

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Modern flagship AKM stack (AK4499EX×2 + AK4191, XU-316 USB), nine high-grade dual op-amps, CK-03 clocking, and two-stage SPDIF PLL—solid, best-practice engineering rather than a novel architecture[2][3].

Cost-Performance

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The cheapest equivalent rival is SMSL SU-10 (dual ES9038PRO, AES and MQA/MQA-CD feature parity) at 899.99 USD[5][6].
Computation: 899.99 ÷ 959.99 = 0.94 → cost-performance 0.9.
If you don’t specifically prefer the AKM implementation, the SU-10 is the value pick.

Reliability & Support

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• Warranty: Typically 1-year manufacturer warranty. Some retailers add an extra year (Apos One-Year Transferable Warranty)[9], while others have their own policies (Shenzhenaudio; SMSL.shop)[10][11]. Verify with your seller.
• Usability: ASR notes the front rotary control is stiff/hard to push; using the included remote is preferable[1].
• Firmware/Functions: Rich feature set including DSD Direct / “FIXED DSD BYPASS”[3].

Rationality of Design Philosophy

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A pragmatic design focused on transparent measurements and comprehensive connectivity: dual-mono AKM path plus jitter-reduction (CK-03, dual-stage SPDIF PLL)[2][3]. Minor quirks (tiny Toslink jitter, IMD hump) don’t affect its core value when used via USB[1]. For AKM-centric systems or AES/MQA use-cases, pricing is sensible.

Advice

• Pick D400EX if you want AKM voicing, AES, and MQA/MQA-CD support[2][3].
• Pick SU-10 (899.99 USD) for the cheapest unit with equal features and measurement class[5][6].
• Compare warranty terms across retailers[9][10][11].

References

[1] ASR review (mirrored on SMSL): https://www.smsl-audio.com/portal/news/detail/id/816.html
[2] D400EX official product page: https://www.smsl-audio.com/portal/product/detail/id/806.html
[3] D400EX manual (PDF): https://www.smsl-audio.com/upload/portal/download/D400EXManual.pdf
[4] L7Audiolab measurements (D400EX): https://www.l7audiolab.com/f/smsl-d400ex/
[5] SU-10 official page: https://www.smsl-audio.com/portal/product/detail/id/800.html
[6] SU-10 price (Apos): https://apos.audio/products/smsl-su-10
[7] D400EX price (official shop): https://smsl.shop/products/d400ex
[8] Amazon.co.jp listing (D400EX): https://www.amazon.co.jp/dp/B0BKWBWRGD
[9] Apos warranty: https://help.apos.audio/en-US/do-products-purchased-on-apos-audio-have-a-warranty-29454
[10] Shenzhenaudio warranty/returns: https://shenzhenaudio.com/pages/guarantees-return-policy
[11] SMSL.shop warranty & returns: https://smsl.shop/pages/warranty-returns

(2025.8.14)