The FIIO S15 combines AK4499EX conversion with network streaming

The FIIO S15 is a desktop network streamer, local media player, DAC, and preamplifier built around AKM’s AK4191 digital processing stage and AK4499EX DAC. Its digital architecture combines FIIO’s DAPS audio system with dual ACCUSILICON AS318-B femtosecond oscillators, while the analog section uses a fully balanced signal path with OPA1612 op-amps and separate linear power regulation. Android 12, a 7.84-inch color touchscreen, HDMI ARC, Bluetooth, network storage support, and extensive digital I/O allow the S15 to operate as the central source and control component in a full-size two-channel system.

AK4191 and AK4499EX conversion architecture

The S15 separates digital processing and analog conversion between an AK4191 and AK4499EX. The AK4191 handles digital signal processing before conversion is passed to the AK4499EX, an arrangement designed to reduce interaction between the digital and analog sections of the DAC. AKM’s DWA Routing Technology is also used within the conversion architecture to manage element selection and reduce noise generated during digital-to-analog conversion.

The resulting analog stage is specified for a signal-to-noise ratio of at least 131dB A-weighted, with a line-output noise floor below 1.8μV A-weighted. THD+N remains below 0.00023% at 1kHz and 0dB into a 10kΩ load. Frequency response extends from 20Hz to 70kHz with less than 2.8dB attenuation.

Dedicated clocking and bit-perfect Android playback

Two screened ACCUSILICON AS318-B series femtosecond oscillators provide separate 45.1584MHz and 49.1520MHz clock references for audio based on the 44.1kHz and 48kHz sampling-rate families. Using dedicated low-phase-noise oscillators for the two clock families allows the S15 to generate the appropriate reference directly rather than deriving every sample rate from a single clock.

FIIO’s DAPS digital audio purification system combines this clock architecture with a customized Android audio core and low-jitter clock coprocessor. System-level and third-party application playback can operate without Android’s usual forced sample-rate conversion, allowing PCM and DSD material to retain their native sampling characteristics through the supported playback path.

Fully balanced analog signal path

The analog section remains fully balanced from DAC conversion through the preamplifier circuitry. FIIO uses OPA1612 low-noise precision op-amps in the current-to-voltage conversion and low-pass-filter stages, with both RCA and XLR connections available as fixed line outputs or variable preamplifier outputs.

Fixed RCA output is specified at 2.4Vrms per channel into 10kΩ, while the balanced XLR output reaches 4.8Vrms per channel. In preamplifier mode, maximum output rises to 4.5Vrms per channel through RCA and 8.9Vrms per channel through XLR into the same load, providing separate output ranges for downstream amplifiers with different input requirements.

35W linear power supply

A 35W linear supply powers the S15 through a custom low-noise transformer and four 4700μF ELNA audio capacitors. Digital and analog circuits receive separate power supplies to reduce electrical interaction between high-speed processing circuitry and the analog audio path.

Multiple precision LDO regulators provide additional local regulation throughout the analog section. This distributed approach gives individual circuit stages cleaner local supply rails while helping prevent fluctuations generated elsewhere in the unit from propagating through the analog path.

Android 12 streaming and local library playback

A Qualcomm Snapdragon 660 processor with 4GB of RAM runs FIIO’s customized landscape implementation of Android 12. The S15 includes 64GB of internal storage, approximately 46GB of which is available to the user, and supports third-party Android applications alongside a version of FiiO Music designed for its widescreen interface.

Network playback includes AirPlay, DLNA, and access to NAS, LAN, and cloud storage through protocols including UPnP, SMB, and WebDAV. Local libraries can be stored internally or accessed from microSD cards, USB storage, portable drives, and an M.2 SSD installed using the supplied drive cage. Roon Ready certification was listed as in progress in FIIO's supplied product information.

7.84-inch touchscreen and desktop interface

The front panel uses a 7.84-inch (19.9 cm) automotive-grade color touchscreen with a landscape interface developed around the S15’s desktop orientation. Playback controls, applications, system functions, customizable home-screen elements, and visual VU meters can all be accessed directly from the display.

The chassis measures approximately 16.93 × 10.81 × 3.52 inches (430 × 274.5 × 89.5 mm), placing it at the standard width of many full-size home audio components. Its all-metal enclosure weighs approximately 12.45 lb (5.65 kg) and is supported by non-slip feet.

USB, HDMI, I2S, AES, coaxial, and optical connectivity

An XMOS 16-core XU316 USB controller handles USB DAC operation at up to 768kHz/32-bit PCM and native DSD512. Native playback through the S15 itself supports up to 384kHz/32-bit PCM and native DSD256.

Digital inputs include USB Audio, coaxial, optical, AES, and HDMI. Coaxial and AES inputs support up to 192kHz/24-bit PCM, optical accepts up to 96kHz/24-bit, and HDMI input supports up to 192kHz/24-bit. HDMI ARC can receive 44.1kHz and 48kHz audio from compatible televisions and displays, allowing the S15's DAC and preamplifier stages to be shared with a video system.

The S15 can also function as a digital transport. USB Audio output supports up to 768kHz/32-bit PCM and DSD512 using DoP, D2P, or native transmission. Coaxial and AES outputs reach 384kHz/24-bit and DSD128 using D2P or DoP, while optical output supports up to 192kHz/24-bit and HDMI output supports up to 192kHz/24-bit. The configurable I2S output provides four selectable pin arrangements for compatibility with different downstream DAC implementations. Isolation transformers on the coaxial and AES outputs provide galvanic separation that can help limit ground-loop currents between connected components.

Bluetooth reception and transmission

Bluetooth reception uses Bluetooth 5.1 and supports SBC, AAC, aptX, aptX LL, aptX HD, aptX Adaptive, and LDAC. Bluetooth transmission operates over Bluetooth 5.0 with AAC, SBC, aptX, aptX HD, LDAC, and LHDC support, allowing the S15 to work either as a wireless source or as a receiver for phones, tablets, and other compatible devices.

A Bluetooth remote is included for playback, volume adjustment, favorites, and gesture-based interface navigation, providing control without requiring direct access to the front-panel touchscreen.

10-band parametric equalization

A 10-band parametric equalizer is available across the S15’s supported operating modes. Individual filters provide adjustment of frequency, gain, bandwidth, and Q value, allowing measured room-response corrections, loudspeaker compensation, or other targeted frequency-response changes to be applied within the player rather than requiring a separate external processor.

Availability

The FIIO S15 is available now on Apos.