Khadas Tone2 Pro

General Information

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.

Latest reviews

cash1489

New Head-Fier
Pros: Beautiful Design
Great Build Quality (Tons of Features!)
Great Balanced Sound
Cons: Sound lacks a little depth
Operation Isn't Intuitive
I’ve reviewed quite a few dongle style DAC/Headphone Amps over the last year or so, and I must say I dig them.

Their compact size coupled with their affordability makes them an ideal way to upgrade a smartphone or laptop's sound while on the go.

Recently, I was really wowed by the $99 HELM Audio Bolt DAC/AMP, which offers amazing THX Certified sound and MQA/DSD compatibility in a ridiculously small package.

However, these dongle or USB Stick (think AudioQuest Dragonfly) style DAC/Amps do have their limitations. For example, If you need a line output other than the 3.5mm jack, a digital input, or even physical controls in most cases, you’re out of luck.

If that’s something you’ve come up against, then the $199 Khadas Tone 2 Pro DAC/Headphone Amp may be just what the doctor ordered. It’s not that much bigger than an Audioquest Dragonfly, yet it has all the stuff mentioned above.

Not only that, it has two balanced outputs (both 4.4mm and Line Out), which is remarkable for its size.

We put the Tone2 Pro through its paces and found it to be a very competent performer. It plays all major music file formats (PCM, DSD, MQA full unfold!), plus the sound was balanced, layered, and clean. It’s also built well, utilizing a slick-looking aluminum frame and control knob.



The only issue I had with it was the confusing control scheme. It works, but it’s rather hard to follow and will take some time to get used to. If you can get past this, the Tone 2 Pro is a compelling DAC/Amp option for those who want a tiny yet flexible device.

Read on for the complete rundown of this fascinating piece of gear!




Key Features:

  • DAC + Headphone Amplifier - Uses top-of-the-line ESS ES9038Q2M Sabre DAC Chip with 4 super-quiet TI OPA1612 operational amplifiers.
  • Hi-Res Decoding - Up to 32bit 384KHz sample rate for PCM and bit-perfect DSD512.
  • Full Hardware MQA Decoding - XMOS XU216 processor for full MQA decoding.
  • Balanced RCA - Innovative "balanced RCA line-out" with 3-pin output
  • Linear Power Supply Compatible - Tone2 Pro has a second USB-C (I2S) port that supports 5V linear power supplies.
  • Coaxial Input - Solid connection for CD-Transports
  • Digital Filters- 7 digital filters to tweak the sound with.
Build/Features

If you’ve never heard of Khadas, don’t feel bad. Before this review, I didn’t know about them either. When I was offered the Tone2 Pro for review, the design and feature list piqued my interest.

However, I still like to do my due diligence regarding the manufacturer of a product. Thru research, I found out they’re a Chinese company that specializes in mini-computer boards for the DIY market (similar to the Raspberry Pi).

They appeared on the DIY audiophile radar a couple of years back with a compact DAC/audio Card called the Tone Board (now Tone 1). It’s a bare board audio card that incorporates an ESS DAC chip.

Despite being a bare board, which means it has no casing, the $99 Tone Board stirred up some buzz as a budget DAC option since it has a USB power connection and RCA outputs. Folks built cases for them and plugged them into headphone amps. The buzz grew so loud that it even made an appearance on the popular YouTube channel Z Reviews.



In an attempt to build upon that success, Khadas came out with the product we’re reviewing today, the $199 Tone2 Pro DAC/Headphone Amp. The Tone 2 Pro is for those who may like the Tone Board's sound quality but want a finished DAC design, and the 2 Pro delivers that along with a pretty powerful headphone amp section.

Like the Tone Board, the Tone 2 Pro is based around the much desired ESS ES9038Q2M DAC chip. That chip has been paired with four TI OPA1612 operational amplifiers (said to be some of the quietest on the market) and three buffer amplifiers.

According to Khadas, this 3-stage amplification pathway allows their newest DAC to drive a wide range of power-hungry headphones (up to 150 ohms impedance recommended).

For the Tone2 Pro, Khadas placed their compact DAC board inside an angular aluminum enclosure (comes in red, blue, or black) about the size of a credit card. The slimline case has a knurled aluminum volume/control knob (which is very smooth) on top, surrounded by an RGB ring light for visual feedback. The whole package is pretty snazzy looking and sturdy to boot.

The bottom of the enclosure is an anti-slip rubber pad that helps keep the device in place, but don’t expect total stability since it’s rather lightweight. A heavy headphone cable will cause it to shift around a bit.



On the side of the Tone2 Pro is a 4.4mm balanced headphone jack, along with a 3.5mm single-end jack, and on the rear are two balanced RCA jacks (a Khadas standard), a coaxial digital input for CD Transports, plus two USB-C connections. The balanced RCA connectors are the first of their kind. So to use them, you have to purchase special cables from Khadas. I didn’t receive those cables, so I didn’t have an opportunity to test the balanced output.

As stated before, there are two USB ports. Each performs a different function. One port is for power/external modules (I2S), and the other is a digital input for laptops or smartphones. Khadas says the I2S USB port will support a future Bluetooth module compatible with premium BT codecs like aptX HD or LDAC.

When it comes to features, the Tone2 Pro has tons of them, which is a blessing and a curse. That’s because, to access many functions, you’re locked into a frustrating control scheme based around the volume knob and the LED ring surrounding it.

For example, if you want to change the gain from low to high, you have to press the knob down twice (not easy), then scroll to the mode you want to set. To know what mode you are selecting, you have to count red lights on the LED ring, which are not easy to see. By the way, good luck remembering how many lights signify what.



To access Gain mode, you must scroll the wheel to reveal three red lights, and then you have to press the knob again. At that point, you have to double press the wheel another time to go through yet more color codes on the LED ring. In this case, it’s two different combinations of green and red lights for high/low gain, which are still not easy to see or memorize.

There are several more color combos for the other modes like DAC Filters or Input, and I had to look at the instruction booklet every time to see what I was doing.

The DAC’s visual indicators for file format and volume level are also mapped to the LCD ring, which means you have to remember even more lighting combinations to check operational status.

That said, it’s nice to have so many options (Inputs, Filters, Gain) on such a compact unit, but I wish they were easier to access.

Listening to the Khadas Tone2 Pro DAC/Headphone Amp

For my sound tests, I primarily hooked up the Tone 2 Pro to my laptop and used Tidal as a source. Upon connecting the included USB-C to USB-C cable to my HP Envy X360’s USB-C port, the WASAPI driver was installed quickly. If you want to play DSD files or high sample rate PCM, you have to download a driver from the Khadas website.

I hooked up several different headphones to the Tone2 Pro, and it showed itself to be quite powerful for its size. It even did a decent job running the relatively hard-to-drive Mr. Speakers (now Dan Clark Audio) Aeon Flow Closed on high gain mode. I did have to crank the volume to about 60-75%, but the sound was full and rich.



It did even better with more sensitive headphones like the Focal Elear, Beyerdynamic T5 (3rd Gen), Hifiman Sundara, and Sennheiser/Drop HD 58X Jubilee. My favorite pairing was the Sundara, which had just the right amount of detail and warmth to bring out the best of the Tone2 Pro.

Like most ESS-based DACs, I have heard that the Tone 2 Pro had a clean, detailed sound that tended to come out on the cool side. While it definitely had that ESS “sparkle,” it wasn't quite as shimmery as some of the ESS implementations I have heard, which allowed the sound to breathe a little bit better.

That said, there was definitely some emphasis on the upper midrange, which can be edgy on certain songs, but overall the sound was very clean and balanced. There was no trace of the noisiness that plagues other budget DAC/Amps.

As far as the DAC section was concerned, the separation of elements in the mix was decent for the price. On the song “Teach You” from Emily King’s “Sides” album, voices and instruments were credibly reproduced, but the presentation didn’t quite have the depth and air you would get at a higher price point.

However, the Tone2 Pro did provide nice weight and presence, which made it engaging. That carried over to the RCA outputs, which played loudly and cleanly into my hi-fi rig.



Compared to the iFi Hip Dac

I chose the $149 iFi Hip Dac for a comparison unit, which has a similar feature list and costs just a little bit less than the Tone2 Pro. As far as power was concerned, I would give the Hip-Dac a slight edge as it could drive the Aeon Flow Closed headphones a little harder than the Tone2 Pro. It was also a whole lot easier to select high-gain mode on the Hip-Dac using the “power match” button on the front.

However, the Hip-Dac didn’t have the RCA connections of the Tone2 Pro nor the extra USB port for expandability. The Tone2 Pro was also more detailed on the top-end than the iFi DAC, providing a little more sparkle and separation. It also had a little bit more depth in the mids.

That said, some may like the warmer, more rounded-off sound of the Hip-Dac over the cold crispness of the Khadas product, especially if they have a brighter headphone. To me, the iFi DAC is a little more organic. On the other hand, the Tone2 Pro will probably match better with warmer, darker headphones as it will open them up a bit.

The Wrap Up

The Khadas Tone2 Pro is a very well-built and powerful DAC/Amp, which offers more connection options than other devices its size. It has a very clean and detailed sound which is sure to open up darker, warmer headphones. It also has a wealth of features, including full MQA decoding (remarkable at this price point!), DSD compatibility and seven different DAC filters.

The only issue I have with the Tone2 Pro is the confounding control setup. If you can master that, you will find this flexible device to have a lot going. Those looking for a space-saving DAC/Amp with good power, clean output, and a lot of connections should check out the Tone2 Pro.

This review was originally posted at hifitrends.com: http://hifitrends.com/2021/02/22/kh...onary-dac-amp-will-make-your-headphones-sing/
Last edited:
  • Like
Reactions: OceanPoet
O
OceanPoet
Great write-up.

Wiljen

Headphoneus Supremus
The Toneboard turns 2!
Pros: Tons of connection options, great sound, well built, well priced
Cons: Controls are not very intuitive, limited output power in single ended mode, proprietary connectors.
Khadas-T2P-kit-800x445.jpg


Khadas Tone2Pro​


disclaimer: The Khadas Tone2Pro was provided by Hifigo for review. I purchased the balanced RCA cables at retail price to be able to test the unit thoroughly. I have no financial interest in either Khadas or HiFiGo, nor did I receive any advice or remuneration for this review. If you need more information, see Khadas webpage or Facebook and to purchase a toneboard, see HiFiGo.

Packaging:
The Tone2 Pro arrived in a white lift top style box with a photo of the unit on front and a labeled diagram as well as specs showing on the reverse. Lifting the cover reveals the manuals with the unit hiding beneath in a plastic tray and the usb-C cable in small box next to it. The entire kit consists of the unit, cable, manual, and warranty card with balanced RCA cables being an additional cost add on if desired. It is clear from the lack of carry case that the unit is intended for desktop use, but with its diminutive size I think many will use it for travel purposes and some form of carry case would have been a nice touch here.




Build:
The first thing that strikes you about the Tone 2 pro (T2p) when you open the box is its size. Even having had a first generation tone board, I expected that the addition of all the new features in the T2p it would require a larger board and housing. In short it doesn’t the unit is not much larger than a standard credit card it height and width and is barely over a centimeter tall at the height of the rear of the unit. It feels solid in hand with its metal casing and all the jacks are well fitted with no slop and little room to wobble within the housing. Jacks consist of two USB type-C ports on the rear of the unit along with a coaxial input/output and a pair of RCA outputs (more on these later) and a 3.5mm and 4.4mm headphone jack on the right end of the unit. the volume knob sits top left and requires a little getting used to, but once learned is very simple to control and operate. Although not marked for it, the 2nd USB port (Marked I2S can be used to provide power to the unit so use of a linear power supply is possible if desired. I found myself wishing the unit had more heft as the RCA cables I purchased with it are heavy enough that they do pull the unit around on the desk when moved. That is easy to cure with a little non-slip for the bottom of the unit, but is something to address should you decide to purchase one.




Internals/Connectivity:
The TB2 uses the latest generation of XMOS the XU216 for its USB input which then feeds an Intel Altera CPLD that handles jitter filtering and pre-shaping. Here a CPLD makes sense as the operations it is being asked to handle are fairly simple and an FPGA (the other alternative to CPLD here) is best at handling more complex tasks. DACs are a pair of the ESS ES9038Q2M chips that are the 2 channel mobile (low power) version of the 9038. These then feed OPA1612 Op-amps in both the I/V and LPF stages. Volume control is handled by a NJU72315 digital control which keeps the unit size down as an analog volume control would take up much more space and finally the buffer stage amplification is handled by RT6863D buffer chips. A full schematic can be seen below for those interested in more detail. The T2p supports up to and including 32/768khz PCM, DSD512, and full MQA decoding when using USB input so pretty much all formats are covered (Coax is limited to 24/192 and PCM only at the time of this writing). Output power is listed as up to 114 mW at 16Ω for the 3.5mm connection but drops to 35mw at 150Ω which does mean the T2p is best paired with iems when using the 3.5mm connector. The 4.4mm balanced is a bit more potent and capable of delivering 211mW into 32Ω loads or 83mW into 300Ω so gives a bit wider usable range. I used it with the HD800 but would suggest that is about its realistic limit as the He6 and other harder to drive models simply didn’t have enough headroom to be usable.

The T2p allows for all types of connections other than optical but First up and probably most popular is the USB type-C ports on the rear of the unit. A single cable can be attached from the source device to the T2p USB labeled port and provide both power and data connectivity (The LED between the USB Ports will glow red when powered by the 1st port). If a power only cable is plugged into the i2s labeled port in addition to the data cable to the first port, one can provide data and power over different cables and the LED light between the USB ports should glow white. Alternatively, a Bluetooth adapter can be plugged into the I2S port as yet another input and power provided via USB1 with or withouut the use of USB1 for data. The Coaxial port also can be used as coaxial input or with a firmware change as a coaxial output allowing the T2p to be used as a USB to Coax converter. The RCA jacks will be covered in detail in the cable section, which leaves us with the standard 3.5mm single ended and 4.4mm balanced jacks on the right end of the unit. These are volume controlled by default but there are already rumblings about being able to set volume levels in firmware for dedicated line out from the balanced port if so desired.




Controls:
Controls are straight forward enough. The volume knob doubles as a button but the instructions to “push” the volume knob to control functions is a bit confusing to say the least. First off, placing a finger on the rear side of the volume knob and gently pulling it forward is a much more appropriate way to define the switch than “push”. Do not expect to feel the volume knob move, you won’t as it is a very slight movement. The light ring under the volume knob also takes a bit of getting used to as you have to know what mode the unit is in in order to understand the meaning of the indicators. I have included the pages of the manual below that apply as well as a video that helps show the use of the volume knob.




Cables:
Normally this would be a pretty short section but with the introduction of the balanced RCA a bit more needs to be said. The RCA jacks on the rear of the unit have the standard post/ring connectors of any RCA and can be used as a standard RCA with the sleeve operating as ground and the post as the positive terminal. There is a shelf around the base of the post though that establishes a third point of contact when a matching cable is used and operates as the negative connection so each jack now has positive, negative, and ground connections and operates as a differential (often called balanced) output. I’ve tried to do my best on the pictures below to show the 3rd connection point that differentiates this connector (pun intended) from a standard RCA. The sixth picture below probably does the best job of showing the 3rd connection point on the male connector while the 2nd shows the sleeve in the female connector that mates to it. I purchased a set of the RCA to XLR cables from Khadas directly as I was unable to find any other source of “Balanced RCA” cables at this time. They do indeed work as advertised and I was able to measure appropriate signals on each connection to show they are functional. I did my Testing with the Balanced RCA to XLR and a standard RCA to XLR cable run to the Little Dot MK3se to show the differences in the two outputs.




Sound:
Using the USB input and the current Khadas driver from there website, I did my initial testing using the 3.5mm and 4.4mm output jack and operating the T2p as an all-in-one DAC/Amp. Once I completed this testing, I switched to using the RCA outputs and using the same headphones with an XLR cable instead of the 4.4mm (Same maker just different termination) in order to use the T2p as DAC only out to a couple other amplifiers.

Using the T2p as an all-in-one the sound is that of a well implemented ESS dac. Very clean, very detailed and with a good amount of energy throughout the audible range. I did find the sound to be a bit smoother and more fluid than a lot of lesser implementations of the 9038 and while not hiding a lot of detail in the process, it does seem a bit less aggressive than some other implementations of this same chip (Burson Swing). The 3.5mm output is somewhat power limited as I have grown to expect from any USB powered device and while it was able to power the HD800 it didn’t leave a lot of headroom and lost a bit of bass impact when run from the single-ended connection. The 4.4mm connection helps a good bit as dynamics were better, there was no loss of impact in the bass, and it gave enough headroom to be more usable with headphones requiring above average power. There is a nice musical quality to the sound of the headphone outputs not unlike the Chord Mojo or Earmen TR-amp with just enough warmth and weight to lose the analytical criticism so often leveled at ESS based dacs.

Using the RCA outputs to another amp highlights the fact that the warmth is being provided by the output section of the T2p as when coupled to just the DAC it presents a very clean, detailed signature with little if any coloration. I found it paired well with the Little dot Tube amp with its added warmth but also did well with solid state models like the Burson Fun and Topping A90. The balanced RCAs do offer a higher output power, but otherwise signature remains very much the same with good clean output, very little coloration, and good detail levels.


Conclusions:
I have owned a Toneboard since not long after its initial release and have long thought it was one of the best dacs on the market at the $100 price point (Still true today). The drawback was it is a DIY affair and requires the end user either build or buy a case for it as they do not come with one. Some time after initial release they started offering a case for sale through Khadas but even then it was not assembled so retains its DIY nature. The Tone 2 pro on the other hand is a stand-alone unit not designed to mate with Khadas micro-computers and incorporates a headphone amplifier not included in the original model. In doing so, it also doubles the price to $200 USD. Still, for what the user receives for that $200 spend the Tone 2 pro represents excellent value as it offers a dac that is in experience competitive with the Topping E30, Schiit Modi series, or SMSL Sanskrit. Adding the amp puts the T2p in direct competition with the likes of Mojo and the TR-amp both are which are more potent than the T2p but all share a similar musicality and neither the Mojo or TR-amp has the input/output options of the T2p despite costing significantly more. The balanced RCAs are interesting and functional but I would advise purchase of the cables with the unit as they are not currently available from other sources and until some other makers decide to adopt this connector it risks being orphaned with no way to get additional parts or cables later. I think for those looking for a high quality desktop unit that takes a minimum amount of room on the desk and offers a ton of functionality, the T2P makes a great choice, it can be used as a portable all-in one as well which only strengthens its market position, and then the specialty firmware options allow it to be used as a USB to coax or Bluetooth receiver as well. I was impressed with the original but reluctant to recommend it because of its DIY nature. I have no such reservations about the Tone 2 Pro, it is highly recommended and well worth an audition.
  • Like
Reactions: monsieurfromag3

Comments

searchingtom

New Head-Fier
This is so cool looking. Don't you wish there was a company that rented these types of items so that you could get a flavor of it ? initial $50 charge and then 10% per month or something like that ? Is any company doing this ?
 

Wiljen

Headphoneus Supremus
This is so cool looking. Don't you wish there was a company that rented these types of items so that you could get a flavor of it ? initial $50 charge and then 10% per month or something like that ? Is any company doing this ?
most people just do the 12 months same as cash offers at places like sweetwater and then return or resell items they don't fall in love with.
 
Top