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FiiO K9 Pro ESS Desktop Bluetooth DAC/Amp (Open box)

bluetooth supported


Product SKU: K9 Pro (US PLUG) (OB)


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Product Details

↓ Details provided by FiiO
(Specifications and appearance of this product are subject to change without notice)



High performance DAC ES9038PRO*2 | THX-AAA 788+ Tech | Dual femtosecond clocks Qualcomm QCC5124 | Supports LDAC/aptX adaptive/aptX HD | Truly balanced design Dual voltage linear transformer | Wide connector selection | App control

Moves your human “core”, and not just by a little!

Inside the K9 Pro ESS are 2 ES9038PRO DAC chips, specifically designed for maximum performance in desktop-grade equipment. One ES9038PRO chip, with all of its 8 parallel outputs, is used for each channel to achieve richly detailed sound with minimal distortion.

Pure clean sound, satisfying even demanding listeners

The THX AAA 788+ chips used in the K9 Pro ESS provide exemplary details and dynamics no matter if you are using low or high-impedance headphones. The K9 Pro ESS can produce an undistorted 1100mW* under a 300Ω load, and an undistorted 2100mW* under a 32Ω load, 50% higher than the original THX AAA 788 amplifier chips.

*As tested in FiiO Labs under balanced out.

Precise Design

Fully differential, fully balanced design
Fully differential signals go through the DAC, volume adjustment, and amp for a truly balanced design. Such a design ensures minimal interference between different components in order to fully maintain all details and large dynamic swings in music for unmatched sound quality.

Six-stage audio circuit, to reveal every last detail
Every audio signal goes through a mammoth 6-stage circuit to reproduce music as faithfully and as detailed as possible

Separated analog and digital sections, partitioned design
The PCB of the K9 Pro ESS uses a partitioned layout, wherein not only the power supply and signals are separated, but the analog signal loop is also put in an independent section, guaranteeing the integrity of the audio signal being processed.

Electricity is the mother of sound, so special attention was paid to optimizing the K9 Pro ESS’s power supply to ensure excellent sound. The K9 Pro ESS’s linear power supply, with its low-frequency transformer and 4 massive 4700uF capacitors, makes sure that the rest of the system gets abundant clean power.

Electricity is the mother of sound

Immensely robust, Linear power supply
Electricity is the mother of sound, so special attention was paid to optimizing the K9 Pro ESS’s power supply to ensure excellent sound. The K9 Pro ESS’s linear power supply, with its low-frequency transformer and 4 massive 4700uF capacitors, makes sure that the rest of the system gets abundant clean power.

Just pure sound, Isolated digital and analog power delivery
The digital portions of the K9 Pro ESS physically receive power separately from the analog portions, for effective shielding against audio interference between the two circuits. This ensures pure and faithful reproduction of your music.

* Due to the instability of the supply chain, some materials may be replaced due to shortage. The accompanying drawings are for reference only.

Quality and quantity, LDOs for each circuit stage
Besides the special high-performance linear power supply, the power stabilization and filtering within the audio circuit is also a big contributor to the K9 Pro ESS’s excellent sound. Specifically, in each stage of the audio circuit, ultra-low-noise LDOs are employed for voltage regulation.

Dual femtosecond clocks, Precise clock management

A dual-mode clock management design is utilized for the K9 Pro ESS. Under USB and Bluetooth decoding, dual asynchronous femtosecond clocks are used, while under optical and coaxial decoding, automatic PLL clocks are employed. A more precise clock management system makes it easier to handle any kind of source and maintain the maximum quality possible.

MQA Renderer, Lossless sound reproduction

The K9 Pro ESS supports the unfolding of MQA tracks, allowing you to listen to high-resolution audio files that are not only reasonably sized, but also retain master-level sound quality that bring you directly into the recording studio.

*With an appropriate music player supporting MQA, the K9 Pro ESS supports up to 8x unfolding

Fast and reliable Hi-Res Bluetooth

The K9 Pro ESS employs the Qualcomm QCC5124 to handle Bluetooth duties, with support for formats such as LDAC, aptX HD and aptX Adaptive. This chip ensures that Bluetooth connections are both reliable and quick, satisfying both the low latency needs for games/videos and the high bitrate necessary for high-resolution audio.

* Bluetooth format support: AAC/SBC/aptX/aptX LL/aptX HD/LDAC/aptx Adaptive

Essentiality of volume adjustment

Adjusting the volume may look like a simple concept, but a good execution of it is crucial to an excellent audio experience. The ADC curve reconstruction method of volume adjustment used in the K9 Pro ESS effectively minimizes any left-right channel volume imbalance and noise. It also results in a smooth change of volume across all levels. This attention paid to the simple process of volume adjustment is just another layer to making sure you truly savor your music with the K9 Pro ESS.

Lighting up the mood

The RGB indicator lights surrounding the volume knob can light up differently depending on the currently playing sampling rate.

Dial it in with three gain levels

Choose between high, medium, and low gain with a physical switch to fit exactly your needs when listening to your particular pair of headphones. Thanks to the pure hardware gain circuit, even when listening at low gain with high-sensitivity headphones both dynamic range and musical fidelity remain uncompromised.

Plentiful connectors to choose from

Front: XLR 4-pin, 4.4mm balanced, 6.35mm single-ended headphone outputs

Rear: 4.4mm balanced line in; coaxial, optical, Bluetooth, RCA, USB input; RCA SE out and XLR*2 balanced out

Side: USB Type-C port

Refreshingly modern, custom stand

The included custom stand not only reduces the amount of space the K9 Pro ESS takes on your desktop, it also allows for more efficient dissipation of heat through convection – making the stand a true example of both form and function.

A true Renaissance man

  • Drive power-hungry headphones (desktop USB audio + Headphones)
  • Connect to home audio setup (desktop USB audio + active speakers)
  • Side-mounted Type-C port for easy connection to mobile devices
  • RCA+XLR balanced line out (for active speakers, monitor speakers, external amplifiers)
  • Connect to mobile devices (players, computers)
  • App-controllable desktop amp Built-in Bluetooth Low Energy (BLE) technology allows you to use the FiiO Control App to control functions like filter selection, channel balance, etc. even when not in Bluetooth mode.

Packing list:

1. K9 Pro *1
2. Power cord*1
3. Square port USB data cable*1
4. Bluetooth antenna *1
5. 6.35mm male to 3.5mm female Headphone jack adapter*1
6. Quick start*1
7. Warranty card*1
8. Instruction card for voltage selection*1
9. Fuse*1
10. Voltage protection plug*1

General specifications

Name / Model No. K9 Pro ESS Hardware solution

DAC: ES9038PRO*2, USB: XMOS XUF208, Bluetooth: QCC5124, LPF: OPA1612 * 2,

volume IC: NJU72315 * 2, AMP: THX AAA 788+ * 2, linear transformer:THAILIN/BingZi

Color Black Volume Scroll Potentiometer+ADC Sampling
Weight ≈2750g Channel balance L12~R12 (0.5dB per level)
Gain L/M/H FiiO Control Surpported
Bluetooth format indication Surpported Sampling rate indication Surpported
Firmware upgrade System firmware and Bluetooth version can be upgraded via USB Deep standby Long press the multi-function button for about 3s
Low battery reminder / Dimensions ≈200x224.5x72mm (excluding feet)
Bluetooth transmission / Bluetooth receiver (5.0) AAC/SBC/aptX/aptX LL/aptX HD/LDAC/atpX Adaptive
Bluetooth format indicator SBC: blue, AAC: cyan, aptX HD: yellow, aptX: purple, aptX LL: purple, LDAC: white, atpX Adaptive: green Charging indicator /
Maximum supported sampling rate 384kHz-32bit/DSD256(USB DAC) Recommended headphone impedance 16~600 Ω
192kHz-24bit (coaxial)
96KHz-24bit (optical)
Buttons and interfaces
Button Physical key + toggle switch USB Type-C, USB B (data transmission)
Single-ended line input interface RCA socket Balanced line input interface 4.4mm balanced socket
Spdif in Optical fiber socket Digital coaxial input interface RCA socket
Balanced output interface 4.4mm socket, XLR4 balanced socket Headphone output interface Standard 6.35 mm socket
Balanced line output interface XLR3 balanced socket Single-ended line output interface RCA socket
Power parameters
Power supply AC 110-115V~/AC 220-230V~ (Recommended) Battery capacity /
Charging time / PO battery life /
Audio parameters
Single-ended line output performance parameters
THD+N <0.00042%(1kHz/10kΩ/dbA) SNR ≥123dB (dbA)
Crosstalk ≥115dB (1kHz/10kΩ) Noise floor <1.9μV(dbA)
Frequency response 20Hz~20kHz (-3dB) Line Level 2.5Vrms (1kHz/10kΩ)
Balanced line output performance parameters
THD+N <0.00025%(1kHz/10kΩ/dbA) SNR ≥128dB (dbA)
Crosstalk ≥125dB (1kHz/10kΩ) Noise floor <1.9μV(dbA)
Frequency response 20Hz~50kHz (-1.5dB) Line Level 5Vrms (1kHz/10kΩ)
Single-ended headphone output performance parameters(6.35mm)
Continuous undistorted output power 1 ≥1.1W(16Ω / THD+N<1%, AUX IN) Output impedance <1Ω(32Ω)
Continuous undistorted output power 2 ≥1.0W(16Ω/THD+N<1%,UAC/SPDIF/BT IN) Crosstalk ≥75dB (1 kHz/32Ω,AUX IN)
Continuous undistorted output power 3 ≥281mW(300Ω / THD+N<1%,AUX IN) THD+N <0.00033% (1 kHz/32Ω/dbA)
Noise floor

<2μV(dbA,AUX IN)


SNR ≥129dB (dbA)
Frequency response 20 Hz~50kHz (-1.5dB) MAX Output Voltage >26Vp-p
Balanced headphone output performance parameters(4.4mm/XLR4)
Continuous undistorted output power 1 ≥1.1W(16Ω / THD+N<1%) Output impedance <1Ω(32Ω)
Continuous undistorted output power 2 ≥2.1W(32Ω /THD+N<1%) Crosstalk ≥114dB (1 kHz,AUX IN)
Continuous undistorted output power 3 ≥1.1W(300Ω / THD+N<1%) THD+N <0.0003% (1 kHz/32Ω/dbA)
Noise floor

<3μV(dbA, AUX IN)


SNR ≥123dB (dbA)
Frequency response 20Hz~50kHz (-3dB) MAX Output Voltage >52Vp-p


Model K9 Pro K9 Pro ESS


200*224.5*76mm (height including feet) 200*224.5 * 72mm (height excluding feet)

About 2750g

About 2700g

Volume knob

Stainless steel PVD silver

Aluminum alloy PVD gold

Heat emission hole


On both sides

Material&color All aluminum alloy, black All aluminum alloy, black
Interfaces power supply AC + built-in Linear Power Supply AC + built-in Linear Power Supply
Digital input interface USB; Optical; Coaxial; Bluetooth USB; Optical; Coaxial; Bluetooth
Analog input interface RCA;4.4mm balanced input RCA;4.4mm balanced input
USB interface USB B ;Type C USB B ;Type C
Headphone output Balance: XLR-4;4.4mm; Single-ended:6.35mm/3.5mm

Balance: XLR-4;4.4mm;


Line out RCA/Balanced XLR * 2 RCA/Balanced XLR * 2


Power supply unique design Digital and Analog Isolation Design Digital and Analog Isolation Design
Audio processing layers 6 layers 6 layers
Clock design dual mode dual crystal oscillator dual mode dual crystal oscillator

6 kinds

MQA Renderer Renderer
Bluetooth QCC5124 QCC5124
Audio clock High precision PLL + dual crystal oscillator High precision PLL + dual crystal oscillator
Audio DAC AK4499EQ*1 ES9038Pro*2
Output mode HP/LO/DAC HP/LO/DAC
Gain Three gears Three gears
Amp chip Dual THX AAA 788+ Dual THX AAA 788+
Output performance

Output power (PO)

2000mW(32 Ω), 278mW(300 Ω)

2100mW(32 Ω),281mW(300 Ω)

Balance: 2100mW(32 Ω),1100mW(300 Ω)

Output power (BAL)

2000mW(32 Ω),1100mW(300 Ω)

2100mW (32Ω)

1100mW (300Ω)

Peak output voltage 51Vpp 52Vpp


≤ 0.0003% ≤ 0.00025%


≥ 123dB ≥ 129dB

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