FiiO K17 R2R svart

FiiO K17 R2R: resistor-ladder conversion and four watts per channel

Converting a digital stream with a network of matched resistors requires space, carefully selected components and a well-designed power supply. FiiO applies this recipe at the top of its desktop K series: the K17’s delta-sigma chip conversion section gives way to an in-house segmented 24 + 5-bit resistor network, while the rest of the unit remains identical or nearly so, including a four-watt discrete amplifier, network playback and 31-band equalizer.

A segmented 24 + 5-bit resistor network

The R2R principle consists of reconstructing the analog voltage by switching a resistor ladder, one per bit, without modulation or noise shaping. Its well-known weakness lies in the transitions of the most significant bits: even the slightest value drift in these resistors results in an error that accumulates precisely when the signal crosses zero. FiiO addresses the issue by splitting the network, called R2R PRO, into two parts. The 24 least significant bits remain in a conventional ladder, while the 5 most significant bits are thermometrically decoded across 31 resistors: each step is exactly equal to the previous one, distributing the error instead of concentrating it.

Two conversion modes are offered. In NOS, the signal is reproduced at its original frequency, without oversampling: filtering is gentler at the top of the spectrum, with the relaxed rendering sought by fans of resistor-based converters. In OS, an interpolated filter takes over and narrows the bandwidth. The difference is heard mainly with 44.1 kHz files and is a matter of taste rather than technical hierarchy. The signal path remains fully differential from the converter to the headphone output, including current-to-voltage conversion and low-pass filtering, with low-noise Texas Instruments operational amplifiers in sensitive stages.

Four watts per channel and five gain settings

The headphone stage is a discrete class AB circuit with current boosting, built around a pair of ON Semiconductor MJE243 and MJE253 transistors. It delivers 4000 mW per channel into 32 Ω balanced and 1850 mW unbalanced, respectively 950 mW and 240 mW into 300 Ω. These figures set the bar very high for a desktop device, and make it possible to get more than a barely sufficient level from low-sensitivity planar headphones.

This power requires a counterpart: it must be controlled. The five gain settings, from L to UH, exist precisely for this purpose. A multi-armature in-ear monitor should be connected in L, otherwise the usable volume range is reduced to just a few degrees of knob rotation. The low output impedance stated by FiiO avoids the other pitfall of sensitive earphones, namely bass coloration caused by interaction between the amplifier and an uneven load impedance. Three sockets coexist on the front panel: 6.35 mm jack, 4.4 mm balanced and 4-pin XLR, while the original K17 is limited to a 3.5 mm unbalanced connection.

Eight operating modes, one remote control

The source list is extensive: network playback, local playback from a USB stick or drive via USB-A, USB DAC, Bluetooth reception, optical, coaxial, balanced analog input via 4.4 mm and unbalanced RCA input. On the network side, the device is Roon Ready certified, supports AirPlay and QPlay, and directly plays NAS shares via both SMB and NFS, all through Gigabit Ethernet or dual-band Wi-Fi, up to 384 kHz / 32 bits and DSD256.

One point should be known before purchase: the Linux system inherited from the K17 does not include a Tidal, Qobuz or Spotify app, nor their Connect services. Playback from these platforms therefore goes through Roon, AirPlay or a source connected via USB. The XMOS XU316 USB interface reaches 768 kHz / 32 bits and native DSD256, with a USB-C port on the front for a portable player and another at the rear for a computer. Bluetooth 5.1 relies on a Qualcomm QCC5125 chip that supports LDAC and the aptX family. The S/PDIF inputs accept 192 kHz / 24 bits via coaxial but remain limited to 96 kHz / 24 bits via optical, a limitation of the format rather than the device.

The analog output selector on the front panel determines what is powered: headphones only, preamplifier only, both together, or fixed-level line output. The line outputs provide 2.5 Vrms via RCA and 5 Vrms via balanced XLR, enough to drive a power amplifier or a pair of active speakers. A 12 V trigger input and output, RS232 port and chassis ground terminal complete a rear panel clearly intended for integration into an installed system.

Thirty-one EQ bands, including analog inputs

Signal processing is handled by a dedicated M21586Q processor, with 64-bit floating point at 360 MHz. It manages a 31-band parametric equalizer, with adjustable gain from +12 to -24 dB and a Q factor down to 0.4, plus a limiter and dynamic compressor. FiiO states that processing is performed without resampling on PCM streams from 44.1 to 96 kHz, meaning the majority of music libraries. Profiles can be exported, imported and shared, and the AUTO EQ function directly applies a correction curve corresponding to the headphones in use.

A useful feature: equalization remains active on all inputs, including analog ones. This requires digitizing the incoming signal with an ES9821Q analog-to-digital converter, then routing it back to the R2R network. Correcting the response of demanding headphones from an analog source thus becomes possible, provided this round trip is acceptable. Those who want an untouched analog path will leave the equalizer inactive on these inputs.

Linear power supply and physically separated boards

The power supply is linear, with a custom-made 35 W transformer and five 4700 µF filtering capacitors in reserve. The analog and digital branches are separated, regulation is performed in several stages with low-noise regulators, and the digital, analog and power supply sections occupy separate printed circuit boards to limit interactions. Three femtosecond oscillators clock the entire system, including two ACCUSILICON AS318-L units at 45.1584 and 49.1520 MHz, one for each sampling-frequency family.

The component selection follows the same logic: Nichicon, ELNA, Rubycon and WIMA capacitors in the analog section, silver-plated oxygen-free copper internal wiring, gold-plated Neutrik connectors. Protection circuits monitor amplifier and transformer temperature, output overload, DC component and power supply.

Machined aluminum and solid wood side panels

The enclosure retains the K series’ square design with rounded corners, with two North American solid wood side panels that visually distinguish this model from the K17: white ash on the silver finish, black walnut on the black finish. As the grain is natural, no two units are ever identical. The top grille serves for heat dissipation, something to keep in mind before installing the device in an enclosed cabinet, since a class AB power stage generates heat continuously.

Control is handled by a 3.93-inch touchscreen, five rotary controls on the front panel, including two clickable controls for volume and menu, and an aluminum infrared remote control. The FiiO Control app completes the package for NAS management and equalizer profiles. At 245 × 223 × 69 mm and 2.9 kg, the unit remains a desktop device, somewhat deeper and heavier than the K17 due to the wooden side panels.

Tekniska specifikationer

Presentation

• Digital-analog-omvandlare, nätverksspelare, förförstärkare och hörlursförstärkare
• Helt differentiell R2R-DAC utvecklad av FiiO
• Balanserad dubbel mono-arkitektur

Digital-analog-omvandling

• Egenutvecklat R2R PRO-resistornätverk, segmenterat i 24 + 5 bitar
• Termometeravkodning av de 5 mest signifikanta bitarna över 31 resistorer
• Två omkopplingsbara omvandlingslägen
  • NOS utan översampling
  • OS med interpolerat filter
• Helt differentiell signalväg från omvandlaren till hörlursutgången, inklusive ström-spänningsomvandling och lågpassfiltrering
• Brusfattiga operationsförstärkare från Texas Instruments i signalvägen
• Digital-, analog- och strömförsörjningskort fysiskt separerade
• Tre femtosekundoscillatorer, varav två ACCUSILICON AS318-L
• Naturlig och detaljerad återgivning av ljudsignalen
• Optimerad för högupplösta ljudfiler

Hörlursförstärkning

• Diskret klass AB-krets med strömförstärkning
• Utgångstransistorer ON Semiconductor MJE243 och MJE253
• Uteffekt
  • 4000 mW + 4000 mW vid 32 Ω balanserat
  • 1850 mW + 1850 mW vid 32 Ω obalanserat
  • 950 mW + 950 mW vid 300 Ω balanserat
  • 240 mW + 240 mW vid 300 Ω obalanserat
• Fem gainlägen: L, M, H, SH, UH
• Låg utgångsimpedans, kompatibel från känsliga in-ear-hörlurar till krävande planarhörlurar
• Utformad för att driva audiofila hörlurar, högimpedanshörlurar och högklassiga in-ear-hörlurar

Driftlägen

• Nätverksuppspelning
• Lokal uppspelning från USB-lagringsmedia
• USB-omvandlare
• Bluetooth-mottagning
• Optisk ingång
• Koaxial ingång
• Balanserad analog ingång
• Obalanserad analog ingång
• Väljare för analog utgång: endast hörlurar, endast förförstärkare, båda eller linje med fast nivå

Nätverksuppspelning och källor

• Gigabit Ethernet och dubbelbands-Wi-Fi
• Roon Ready, AirPlay, QPlay
• Direktuppspelning från NAS-delningar via SMB och NFS
• Nätverksuppspelning upp till 384 kHz / 32 bitar och DSD256 i DoP
• Lokal uppspelning upp till 384 kHz / 32 bitar och DSD256
• USB-gränssnitt XMOS XU316: PCM upp till 768 kHz / 32 bitar, DSD256 nativt
• Koaxial ingång: 192 kHz / 24 bitar, DSD64
• Optisk ingång: 96 kHz / 24 bitar
• Bluetooth 5.1 med Qualcomm QCC5125-chip
  • Codec-stöd: LDAC, aptX Adaptive, aptX HD, aptX LL, aptX, SBC

Signalbehandling

• Dedikerad M21586Q-signalprocessor med 64-bitars flyttal vid 360 MHz
• 31-bands parametrisk equalizer utan förlust eller omsampling
• Aktiv equalizing i alla driftlägen, inklusive analoga ingångar
• Justering av gain, Q-faktor, dynamikbehandling, limiter och kompressor
• Equalizerprofiler kan importeras, exporteras och delas
• AUTO EQ-funktion som applicerar en korrigeringskurva per hörlur
• Lyssningsförinställningar i minnet

Strömförsörjning

• 35 W linjär strömförsörjning med specialtillverkad transformator
• Fem filtreringskondensatorer på 4700 µF
• Separata analoga och digitala grenar
• Flerstegsreglering, brusfattiga LDO-regulatorer
• Nätanslutning med säkringshållare och huvudströmbrytare

Anslutningar på frontpanelen

• USB-C-port
• Hörlursutgång 6,35 mm-jack
• Balanserad 4,4 mm-hörlursutgång
• 4-polig XLR-hörlursutgång
• Strömbrytare med indikator
• Väljare för analog utgång
• Gainväljare
• Menyratt och volymratt, båda klickbara

Anslutningar på baksidan

• Optisk Toslink-ingång
• Optisk Toslink-utgång: 192 kHz / 24 bitar
• Koaxial RCA-ingång
• Koaxial RCA-utgång: 192 kHz / 24 bitar, DSD64
• Obalanserad RCA-linjeingång
• Balanserad 4,4 mm-linjeingång
• RCA-linjeutgång: 2,5 Vrms
• Balanserad XLR-linjeutgång: 5 Vrms
• USB-C-port
• USB-A-port för lagringsmedia
• RJ45 Ethernet-port
• 12 V Trigger in- och utgång
• RS232-port
• Jordningsomkopplare och chassijordanslutning
• Wi-Fi- och Bluetooth-antenner
• Återställningshål

Reglage och display

• 3,93-tums LCD-pekskärm (cirka 9,98 cm)
• Fem vridreglage på frontpanelen
• Intuitivt användargränssnitt
• Kompletterande styrning via appen FiiO Control
• Ingenic X2000-processor assisterad av en ESP32-S3-styrenhet
• Skydd för temperatur i förstärkaren och transformatorn, utgångsöverbelastning, likspänningskomponent och strömförsörjning

Angivna mätvärden

• Frekvensomfång: 20 Hz till 80 kHz, dämpning mindre än 3 dB
• Signal/brusförhållande: större än eller lika med 125 dB, A-vägt
• Brusgolv: mindre än 2,6 µV, A-vägt
• Total harmonisk distorsion plus brus: mindre än 0,0052 % vid 1 kHz, -8 dB vid 32 Ω

Konstruktion och mått

• Bearbetat aluminiumchassi med sidor i massivt nordamerikanskt trä
  • Vit ask i silverutförandet
  • Svart valnöt i svart utförande
  • Unik ådring på varje exemplar
• Nichicon-, ELNA-, Rubycon-, Panasonic- och WIMA-kondensatorer i den analoga delen
• Silverpläterad syrefri kopparkabel, förgyllda Neutrik-kontakter
• Optimerad värmeavledning
• Mått: 245 × 223 × 69 mm
• Vikt: 2,9 kg

Förpackningens innehåll

• K17 R2R
• Nätkabel
• Infraröd fjärrkontroll i aluminium
• 4-polig XLR-kontakt
• Säkring
• Två USB-kablar
• Hörlursjackadapter
• Garantikort
• Snabbstartsguide