FiiO K9 PRO Desktop Headphone Amplifier & DAC (ESS Edition)

The FiiO K9 Pro ESS is a fully balanced desktop DAC and headphone amplifier built around two flagship ESS ES9038PRO DACs, one per channel, and THX AAA 788+ amplification that delivers 2,100mW into 32Ω. A linear power supply, dual femtosecond clocks, full MQA decoding and Qualcomm Bluetooth with LDAC and aptX Adaptive make it the centre of a high-end desk system, with 6.35mm, 4.4mm and 4-pin XLR headphone outputs, RCA and XLR line outputs and inputs for almost any source. Its awards include a VGP 2022 Summer award, a CIHE EHA 2023 Gold Award and an MMORPG Editors’ Choice.

Two ES9038PRO DACs, one per channel

The ES9038PRO is ESS’s eight-channel flagship DAC for desktop equipment. The K9 Pro ESS uses two, with all eight outputs of each chip in parallel for a single channel, for richly detailed sound with minimal distortion: THD+N below 0.0003% and a signal-to-noise ratio of up to 129dB. Where the original K9 Pro had a single AKM AK4499, the ESS edition’s dual DACs bring crisp resolution, seven digital filters and slightly more power.

THX AAA 788+: power for anything

The THX AAA 788+ amplifiers bring out detail and dynamics whatever the impedance. From the balanced outputs they deliver an undistorted 2,100mW into 32Ω and 1,100mW into 300Ω (FiiO Labs figures), 50% more than the original THX AAA 788. A hardware switch selects low, medium or high gain, and because the gain circuit is pure hardware, dynamic range and fidelity stay intact even at low gain with sensitive earphones.

“Electricity is the mother of sound”

FiiO paid particular attention to power. A linear supply with a low-frequency, dual-voltage transformer and four massive 4,700µF capacitors gives the rest of the system abundant clean power. The digital and analogue sections are powered separately to stop interference between them, and every stage of the audio circuit has its own ultra-low-noise LDO regulator.

Truly balanced, from end to end

Fully differential signals pass through the DAC, volume control and amplifier for a truly balanced design that keeps detail and large dynamic swings intact. The circuit board is partitioned, separating power from signal and giving the analogue signal its own section, and every signal passes through a six-stage audio circuit. Volume is set using ADC curve reconstruction, which minimises channel imbalance and noise and changes smoothly at every level.

Precise clocks, MQA and hi-res Bluetooth

Dual-mode clock management uses two asynchronous femtosecond clocks for USB and Bluetooth, and automatic PLL clocking for optical and coaxial. The K9 Pro ESS is an MQA renderer, unfolding MQA files up to 8× with a suitable player. Bluetooth is handled by a Qualcomm QCC5124, reliable and quick with low latency for games and video and high bitrates for music: AAC, SBC, aptX, aptX LL, aptX HD, LDAC and aptX Adaptive.

Every connection you need

The front has 4-pin XLR, 4.4mm balanced and 6.35mm headphone outputs. Round the back are a 4.4mm balanced line input, coaxial, optical, Bluetooth, RCA and USB inputs, and RCA and two XLR balanced outputs for active speakers, studio monitors or a power amplifier. A side-mounted USB-C port makes it easy to connect a phone or player. Drive power-hungry headphones from your computer, run a home audio system, or both.

App control, lights and a custom stand

Bluetooth Low Energy lets the FiiO Control app adjust settings such as the digital filter and channel balance even when you aren’t using Bluetooth playback. In Bluetooth mode the app also offers seven preset sound styles and three custom PEQ settings. The RGB ring around the volume knob shows what is playing: blue for 48kHz and below, yellow above 48kHz, purple for MQA and green for DSD. The aluminium volume knob has PVD gold-plated edges, and the included stand saves desk space and improves cooling by convection.

Good to know

• Power comes from the internal linear supply: just plug in the mains cable.
• Looking for something more compact with the same THX amplifiers? See the FiiO K7.
• In the box: power cable, Bluetooth antenna, USB Type-B cable, 6.35mm to 3.5mm adapter, sticky feet, vertical stand tray and quick start guide.