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.