Tone2 Pro is the 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. 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.

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, with eliminated the “ESS hump”.

THD+N: 0.000126% (-118dB)

SNR: 121dB

Noise Level: 3.5uVrms

Crosstalk: >120dB @200K

FULL MQA DECODING

The XMOS XU216 processor embedded within Tone2 Pro, enables full hardware decoding of MQA files (3 unfolds), so you can listen to hi-res streaming audio or local files, just as the artist intended at “Master Quality”.

XMOS XU216 processor for full hardware MQA decoding

Compatible with hi-res streaming & local playback

Tone2 Pro is approved by the MQA Company

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. Its slim aluminum enclosure accommodates many features. 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

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

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)

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.

Hybrid digital-to-analog encoder for volume control

Tone2 Pro can drive up to 150-ohm headphones

Separate amplifiers for each headphone jack

Purchase Link 

Update for specs :

Tone2 Pro – Spec Update, S/PDIF Out & More!

Updated Specifications
  • Headphone output impedance is now better suited for lower impedance headphones.

  • PCM bit-rate has been pushed to the maximum of 768KHz 32bit.

These are the latest THD+N specs based upon the average measured value of 100 devices:
Input – Auto Mode:

Thanks to a suggestion from our forum user Mike, the default firmware installed in your Tone2 Pro will automatically switch input modes when it detects a song playing. By default, the input is set to “Auto”, and you can still manually select the input mode using the volume knob.

Input Priority: I2S > USB > S/PDIF

When the input is set to “Auto” and a song is playing on Bluetooth (I2S), the Tone2 Pro will automatically switch from S/PDIF or USB to I2S input. Once your song on I2S stops playing, Tone2 Pro will switch back to either USB or S/PDIF.

Software Volume:

Our original plan was to have the pre-installed firmware include XMOS software volume support, but some users could be confused by both Software Volume and Hardware Analog Volume. Therefore the pre-installed firmware only supports Hardware Analog Volume.

Special “Dual Volume” firmware (XMOS Software and Hardware Analog) will be released separately at https://dl.khadas.com/products/tone2/firmware for the users who wish to use both volume controls in their Tone2 Pro.

S/PDIF Out:

Tone2 Pro will support S/PDIF Out when loaded with a special version of our firmware.

The Balanced RCA connector(J4) carries both SPDIF_OUT and SPDIF_IN signals via it’s PIN3 and PIN1.

  • Turn your Tone2 Pro into a USB to S/PDIF Converter

  • Direct digital-signal from USB to S/PDIF Out

  • Sample Rate: S/PDIF Coaxial Out can support up to 192KHz 24bit

With regards to firmware support, the pre-installed firmware does not support S/PDIF Coaxial Out; MQA decoding requires too many XU216 processor cores and the “S/PDIF Out” firmware will not be able to support MQA decoding. As with the “Dual Volume” firmware, the “S/PDIF Out” firmware will be released separately on our file server at https://dl.khadas.com/products/tone2/firmware for interested users. You will require a “Balanced RCA to Single-End RCA Adapter” to use S/PDIF Out, as Tone2 Pro uses the standard (single-end) RCA cable for S/PDIF Coaxial Input.