Tone2 Pro

Your mini desktop Hi-Fi anytime, anywhere!


Tone Board, re - imagined.

Tone2 Pro is our second generation Tone Board from Khadas that incorporates a variety of user feedback from our first-gen product, the Tone1. ESS ES9038Q2M DAC has been paired with four powerful OPA1612 operational amplifiers, and three buffer amplifiers. This 3-stage amplification pathway enables Tone2 Pro to drive a wide-range of demanding audiophile-grade headphones with impedances of up to 150 ohms. 


Other additions to the Tone2 Pro include a 4.4mm balanced headphone jack in addition to the standard 3.5mm single-end jack. The Tone2 Pro's aluminum enclosure incorporates a hybrid digital/analog volume control knob, allowing you to rely entirely on analog signal attenuation for accurate sound reproduction. With not one, but two USB-C ports, you can connect a 5V linear power supply to the second USB-C port whilst having USB-C data on the first for excellent power-noise isolation. Finally we've added an industry-first balanced RCA line-out. These novel RCA ports have three signal-pins instead of two, yet retain the same size and form factor as regular RCA ports.


The latest addition to file format support is MQA decoding. The onboard XMOS XU216 processor enables bit-perfect, hardware-native, USB class II, asynchronous "unfolding" of MQA data for both web streaming and local high fidelity audio playback, enabling future-proof "original master quality" audio reproduction just as the artist intended, but at reasonable file sizes and streaming bandwidth requirements.



Tone2 Pro, water blue, onyx black and ruby red.
Tone2 Pro, water blue.
Tone2 Pro, ruby red.
Tone2 Pro, onyx black.
Tone2 Pro, water blue, onyx black and ruby red.
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Headphone Amplifier

Tone2 Pro incorporates a 3-stage amplification system between the DAC and your 3.5mm single-end or 4.4mm balanced headphones. The TI OPA1612 op-amp provides superior audio quality and excellent distortion characteristics.

  • Volume Knob: Hybrid Digital-to-Analog Volume Control

  • Independent Volume Path: Does not affect RCA line-out

  • Hardware analog volume for the best possible performance

​High Performance

Tone2 Pro continues with the time-tested ESS ES9038Q2M DAC chip that is also used in the Tone1. Our community is delighted to know that we've also eliminated the "ESS hump".

  • THD+N: 0.000126% (-118dB)

  • SNR: 121dB

  • Noise Level: 3.5uVrms

  • Crosstalk: >120dB @200K

Full MQA decoding

MQA (Master Quality Authenticated) is an award-winning British technology that delivers the sound of the original master recording. The master MQA file is fully authenticated and is small enough to stream or download.

  • XMOS XU216 for full hardware MQA decoding (tri-unfold)

  • Listen to hi-res streaming audio and local files

​Balanced RCA

Balanced RCA is a new standard pioneered by Khadas that gives you balanced stereo line-out in a standard RCA form-factor. This innovation is covered by a protective-patent.

  • Yellow: Ground (Zero)

  • Blue: Cold Line (Negative)

  • Pink: Hot Line (Positive)




Mechanical & Thermal

Tone2 Pro has a bespoke design that is unique to the DAC world. It's slim aluminum enclosure accommodates many features and requests from our community. For example, a silicone thermal conduction pad moves heat away from the XMOS XU216 processor into the aluminum enclosure, ensuring that bit-perfect audio transmission is unaffected by thermal noise. The hybrid digital-to-analog volume knob is damped with a silicone O-ring and high-viscosity gel, to give you a confident, potentiometer-like feeling every time you need to adjust the volume or change input modes.

  • XMOS XU216: Thermally-coupled with the aluminum enclosure

  • Volume Knob: Damped with a silicone o-ring and high-viscosity gel

Parallel Lines
XMOS XU216 thermal contact with exterior aluminum enclosure
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Hybrid digital-to-analog volume encoder w/ silicone O-ring damping
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Audio Architecture

  • XMOS XU216: Bit-perfect USB Class 2 audio and full hardware-based MQA decoding

  • Intel Altera CPLD: for jitter filtering & pre-shaping

  • ESS ES9038Q2M: ESS digital to analog converter chip

  • Texas Instruments OPA1612: I/V and LPF stage amplification

  • NJU72315: Volume control chip

  • RT6863D: Buffer stage amplification

Abstract Architecture

PCB Layout

The motherboard is no larger than a typical credit card, yet contains everything you need from a mini desktop Hi-Fi device.

  • 6 layers stack-up

  • ​Low dielectric PCB board for smoother audio

  • 82.0 x 56.0 mm (compatible with VIM series SBCs)

Tone2 Pro - Motherboard (Top)
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Tone2 Pro - Motherboard (Bottom)
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Rotate - Push Encoder

Control your Tone2 Pro's headphone volume and mode selection with the ALPS rotate-push encoder. The RGB ring-light displays real-time visual feedback.

  • Rotation: Volume Control, Next, Previous

  • Double-Push: Mode Selection

  • Long Push: Power ON / OFF

Linearpower Supply

You can attach a 5V USB-C linear power supply to the second USB-C port, labelled I2S. Some users require clean signal-to-noise ratios when using high-gain amplifiers.

  • Connector: USB-C

  • Voltage: 5V

  • Tone2 Pro will prioritize power from LPS over USB

Hi-Res Bluetooth

Attach a Khadas-designed external Bluetooth module to your Tone2 Pro, and stream music wirelessly from your mobile devices. Our module is still in development.

  • USB-C (I2S) port with custom pin-layout

  • Khadas-designed external hi-res Bluetooth module

  • Compatible codecs: aptX HD, LDAC (Qualcomm QCC5125)

Converters & Cables

Connect your Tone2 Pro to existing balanced XLR-3 equipment, with our converters and cables.

  • Balanced RCA to XLR-3 Male Cable (1m)

  • Balanced RCA to XLR-3 Male Adapter (0.2m)

  • Use standard RCA cables for single-end applications

Couple Listening

Up to two people can listen at once with Tone2 Pro. There are two headphone jacks on the right-side, a 3.5mm single-end and 4.4mm balanced. Listen with those we love.

  • Hybrid digital-to-analog encoder for volume control

  • Tone2 Pro can drive up to 150 ohm headphones

  • Separate amplifiers for each headphone jack


[1] Performance testing based on USB input, coaxial input will have slight performance differences.        

[2] iPhone support requires the USB-C to Lightning (Apple C78-USBH) cable, normal Lightning charging cables will not work.


Crystal Oscillator

Accusilicon AS318-B Series Professional Crystal Oscillator.

Linear Power Supply

Attach a 5V linear power supply via the I2S USB-C port.

Film Capacitors

High accuracy film capacitors with a tolerance of +/- 5%.

Aluminium Shell

Every detail meticulously crafted out of tough 6063 aluminium.

Digital Filter

Switch between 7 digital filters to suit your listening tastes.

Relay Muting

Power-up and mode changes are free of pops and buzzes.

RGB Light Ring

Responsive RGB LED light ring encircles the volume control knob.

6 Layer PCB

6-layer printed circuit board composed of EM-damping materials.

DSD Playback

Playback hi-res DSD files from 64 to 512 Mbps rates.


Pre-sharping and source-sync eliminates analog jitter.

USB Audio Class 2

UAC2 (USB Audio Class 2) for high-res, bit-perfect, low loopback latency

Film Resistors

High accuracy film resistors with a tolerance of +/- 0.1%.

Firmware Upgrading

Upgradeable XMOS firmware ensures Tone 2 is future-proofed.

PCM Decoding

Decode 32-bit PCM at 768KHz.


Customised USB ASIO driver with Khadas PID from Thesyscon.

What's In The Box

  • x1 Tone2 Pro (DAC + HPA).

  • x1 USB-C Cable. 

  • x1 Quickstart Guide and Warranty Card.