Cons — No (affordable) linear power supply offered as add-on; learning curve; awkward operation with 2 hands; bluetooth module not yet implemented.

EXECUTIVE SUMMARY

The Khadas Tone2 Pro is an innovative miniature desktop dac with integrated headphone amplifier that offers a ton of functionality qualifying it as a competent “Jack of All Trades”.

INTRODUCTION

Khadas is a Shenzen company run by a team of audio enthusiasts. Their first release was the infamous “Toneboard”, a $99 dac/amp that came “naked” without housing. Much of the company’s inventory caters to electronics junkies with soldering skills.

DISTINCTIVE FEATURES OF THE KHADAS TONE2 PRO

The Khadas Ton2 ProPro is a miniature integrated dac-amp that works with Window and Mac computers as well as with Android and iOS devices. It shares certain features with traditional dongles such as the EarMen Sparrow or DragonFly Cobalt in that it is connected to a phone or computer via USB. But a dongle relies entirely on the power of its source and only outputs into 2.5 mm/3.5 mm/4.4 mm audio. The Khadas Tone2 Pro can be powered by its audio source or independently, and has more output options/possibilities than a dongle. It shows, however, less flexibility when connected to a phone because it needs an external power supply in this setup.

The Khadas Tone2 Pro’s distinctive features are:

• Unique encoder knob
• Flexible power supply options (source device or linear power supply)
• Balanced RCA connectors (cable available from Khadas; backwards compatible for connecting a single-ended headphone amp)
• Reversible S/PDIF coaxial input/output (for connecting a CD player or use as USB to coax converter)
• 4.4 mm balanced headphone socket (plus single-ended 3.5 mm socket)
• Add-on bluetooth module (still being developed)

SPECIFICATIONS

Khadas lists the Tone2 Pro’s full specs in every detail; they can be downloaded here. The most important ones are:

DAC chipset: ESS ES9038Q2M 32-Bit Stereo Mobile Audio DAC
Amplifier chipsets: I/V Stage: TI OPA1612 x2, LPF Stage: TI OPA1612 x2, Buffer Stage: RT6863D x3
Output Impedance: <0.3 Ω
SNR: 119-121 dB (depending on output)
Up to 32bit 384KHz sample rate, bit-perfect DSD512, and -118dB THD+N (line-out).
MQA decoding
Compatibility: Windows/Mac, Android, iOS

Maximum output, single-ended circuit (3.5 mm socket):

• 35.3 mW @ 150 Ω (2.0 Vrms)
• 125 mW @ 32 Ω (2.3 Vrms)
• 114 mW @ 16 Ω (1.35 Vrms)

Maximum output, balanced circuit (4.4 mm socket):

• 83 mW @ 300 Ω (5.0 Vrms)
• 167 mW @ 150 Ω (5.0 Vrms)
• 211 mW @ 32 Ω (2.6 Vrms)
• 123 mW @ 16 Ω (1.4 Vrms)

Full Specifications: https://dl.khadas.com/products/tone2/specs/Khadas_Tone2_Pro_Specs.pdf
Product Page: https://www.khadas.com/tone2pro
Purchase Links: hifigo or amazon
Tested at $199.90

PHYSICAL THINGS AND FUNCTIONALITY

In the box are the actual device, a USB-C to USB-C cable, and the manual. The very small Khadas Tone2 Pro ‘s enclosure and the encoder knob are made of aircraft grade aluminium, with a polycarbonate bottom cover on a soft silicone pad – in order not to scratch the underlying surface.

The manual is pretty confusing when it comes to setup with a computer (Mac is not mentioned at all but it worked just upon plugin), firmware update, and operation, but there are excellent videos available that offer all necessary solutions.

User Manual: https://dl.khadas.com/products/tone2/manual/tone2pro_user_manual.pdf

Firmware Upgrade: https://www.youtube.com/watch?v=qRswdL1HPZU

Balanced RCA: https://www.khadas.com/balanced-rca

Khadas Discussion Forum: https://forum.khadas.com

Khadas Facebook Group: https://www.facebook.com/khadas.official

CONNECTIVITY: THE SKY’S YOUR LIMIT

The Khadas Tone2 Pro offers a variety of connections – and therefore a variety of usages.

Inputs: USB-C (computer/phone/raspberry-type single-board computer), I2S (linear power supply, bluetooth module), coaxial (CD-player).

Outputs: 3.5 mm and .4 mm “balanced” headphone sockets (can be used simultaneously), balanced RCA (backward compatible), and the coaxial can be reversed with a firmware change.

INTRODUCING BALANCED RCA

Khadas developed “balanced” RCA connectors which they implemented in their Tone2 Pro. You can connect balanced RCA cables and stream to a balanced amp. While this is a great idea, such cables do not exist yet, and other manufacturers have yet to embrace the balanced RCA technology (but Kadhas sell you a $40 balanced RCA to XLR adapter). No third-party amp with balanced RCA connectors exists presently. Good that these connectors are backward compatible – you can use your old RCA cables.

However, balance amps exist and in order to connete them with the Tone2 Pro, Khadas are selling RCA to XLR adapter. Problem solved…for now. But other manufacturers will have to embrace the balanced RCA technology for the technology to survive.

THE CRAZY VOLUME KNOB IS ALSO A JOYSTICK

Khadas introduce a hybrid digital/analog volume control knob that works like both a normal rotary knob and joystick.

You can turn it like a standard volume knob but also push it sideways…but you need to hold the light device with the other hand during operation…awkward when it is sitting on an amp. Typically each two lateral pushes cycle you through the different modes from volume through track forward/backward, gain, input selection, and digital filter. Here the overview of all modes (from the user manual):

In each mode, you rotate the knob to change the functions as indicated in this graphic. Any setting is visualized by a colour combination in the RGB ring light at the base of the knob. While it is painful to read is, you just watch these two videos to get the details:

PRACTICAL USE OF THE KHADAS TONE2 PRO

In real life, you can use the Khadas Tone2 Pro as follows, for example:

CD player/streamer/computer/tablet/phone –> Khadas Tone2 Pro –> headphone

CD player/streamer/computer/tablet/phone –> Khadas Tone2 Pro –> headphone amp –> headphone

CD player/streamer/computer/table/phone –> Khadas Tone2 Pro –> stereo amp –> loudspeakers

To give you some idea: I first connected the Khadas Tone2 Pro to my computer via USB-C and also used the computer as power source. This was just fine for listening to iems and even the 300 ohm Sennheiser HD 600. I then added power by connecting the Schiit Magni 2 Uber headphone amp via RCA cables. The Khadas Tone2 Pro now served as pre-amp.

I then moved to my stereo system and connected the Khadas Tone2 Pro to my CD player via coaxial RCA. I also connected my phone to the Khadas Tone2 Pro’s USB-C port…and had two music input sources to choose from. I switched between the sources using the rotary function of the dial after having it set to “Input” mode….and listened to CDs with my Sennheiser HD 600 connected to the Khadas Tone2 Pro 3.5 mm socket. I now had to option to use the RCA out to connect the Khadas Tone2 Pro either to a headphone amp or to the stereo’s power amp.

Streaming music from your phone to the Khadas Tone2 Pro via Bluetooth would be an interesting asset. This functionality has not been implemented yet – a add-on Bluetooth module is presently being developed.

SUPPLIED POWER VS POWER SUPPLY

The Khadas Tone2 Pro is driven from the USB-port of your computer without problems. I was told that a notebook is an electrical firestorm and that there is some electrical noise associated with Mains power at 20, 60, and 180 Hz on laptop USB.

The Khadas Tone2 Pro features a second USB-C port (labelled I2S), designed for input from a Linear [Voltage] Power Supply (“LPS”). An LPS supplies a constant current, which minimizes electrical noise and generates ultra-clean signal-to-noise ratios. But I was warned that the “wrong” LPS could make the Khadas Tone2 Pro (and similare devices) “dull and uninspiring” sounding. When in use, I2S prioritizes the LPS over the USB source. Separating data flow and power, and supplying power from a “clean” LPS serves the purpose of improving sound quality. This is particularly important when the Khadas Tone2 Pro is used as dac. Any distortion/impurity in the signal will be exaggerated by the attached power amplifier.

And while an LPS may feed the Khadas Tone2 Pro with “clean” power, this also opens a can or worms.

First, an LPS is expensive. At a minimum, you spend 40% of the Khadas Tone2 Pro’s purchasing price – when you live in North America. In Europe, a quality LPS sets you back 120 EUR. And even if you convert your old microwave into an LPS, it takes $50 in parts. This is cost prohibitive.

Second, these LPS are bulky and heavy, which is contradicting the idea of the Khadas Tone2 Pro’s lightweight and small dimensions. This is less of an issue when don’t locate the LPS on your desk but use it as a kick plate underneath.

Third, the music coming out of the computer’s USB port will still carry impurities.

Khadas failed to design an affordable LPS as an add-on, which I consider a flaw considering all the good ideas that went into the Tone2 Pro. After all, the buyer wants a perfectly functional device out of the box.

So, what are the alternatives? After all, any dac or amp comes with its own power supply – and you don’t have to worry about it – and therefore not pay extra through your nose. I tested a $15 powerbank (stable power supply), Apple stock 5 V chargers for iPhone and ipad (all switched-mode power supplies but of good quality), and two low-noise power supplies provided by ifi Audio (for a separate review). The potential issue with switching currents is electrical noise being introduced to the signal.

First of all, all of the above principally powered the Khadas Tone2 Pro. So the question is whether LPSs are overkill. We will answer this question below.

SOUND IN DIFFERENT APPLICATIONS

My tonal preference and testing practice

My test tracks explained

Equipment used: MacBook Air, iPhone SE (first generation), Marantz SACD8005; Khadas Tone2 Pro, Schiit Magni 2U; KBEAR TRI I3, Shozy Form 1.4, Sennheiser HD 25 and HD 600; ddHifi adapters DJ35AG/DJ44AG; diverse power supplies (ifi Audio iPower & iPower X, Apple iPad 12 W switching power supply, Tzumi 10,000 mAh power bank); Snake Oil Taipan and Radio Shack RCA interconnects; Amazon basics coaxial RCA cable.

Setup 1: Khadas Tone2 Pro with MacBook Air and TRI3 and Shozy Form 1.4 earphones with DJ35AG/DJ44AG adapters

This test served the purpose of comparing the single-ended and balanced circuits using 2.5 mm balanced cables and the DJ35AG/DJ44AG adapters. I used the easily driven Shozy Form 1.4 and the harder-to-drive planar magnetic TRI3 earphones, both on low gain.

The balanced circuit was much superior over the single-ended one in that the sonic experience was much more three dimensional and atmospheric, with a much better spatial cues, more note weight…and it was simply louder. The technicalities were all quite good with one downside: the timbre was rather digital and a bit edgy for the cello sonatas I had started my test off with…and the sound was lively and crisp with rock music, though the bass could have been a bit meatier.

I mentioned it above: both outputs work simultaneously…two can listen.

Setup 2: MacBookAir with Khadas Tone2 Pro and Sennheiser HD 600 headphones

I could only test the “weaker” 3.5 mm single-ended output with the 300 Ω Sennheiser HD 600 headphones…and I was pushing the Khadas Tone2 PRO’s limits (on high gain). I achieved an astounding headroom considering this small device, although the dynamics stayed on the “polite” side. This combination principally worked, but it had reached its limit. I would not push any harder-to-drive headphones.

Setup 3: Marantz SACD8005 with Khadas Tone2 Pro and Sennheiser HD 600 headphone

This experiment served testing the coaxial input from the CD player with uncompressed music. I used a $12 CAD amazon basics coaxial cable that is surprisingly well made. The SACD has its own integrated headphone amplifier so I could A/B from the same source.

This combination sounded quite impressive with lots of headroom and transparency. In comparison, the integrated Marantz headphone amplifier (with unknown but probably high output impedance) sounded somewhat muffled with less extension.

Setup 4: MacBook Air with Khadas Pro into Schiit Magni 2 Uber and Sennheiser HD 600/HD25 headphones

In this setup, the Khadas Tone2 Pro was only used as a dac, with the Schiit as the amp. And it literally rocked. The punch returned to the Senns and so did naturalness. Yes, this combination sounded more natural than the Khadas’s integrated amplifier. Switching from the 300 Ω HD 600 to the 70 Ω HD 25 added some lightness and ease…but this probably has to do with the Schiit’s limited output rather than the T2 Pro.

I also played with cables and compared the sturdy Snake Oil Taipan interconnects (with their German Sommer wire) with some 20-year-old Radio Shack ones. And, compared to the Radio Shack ones, the Snake Oil added…no, not snake oil, but bass, as if a subwoofer had been added. Which one is better comes down to personal taste.

I then replaced the Khadas Tone2 Pro with the Dragonfly Cobalt as dac, which also sounded great but slightly less substantial. This probably lies in the quality of Khadas’s dedicated RCA outputs.

And what did the different power supplies contribute?

I tested the Khadas Pro with the different power supplies (ifi Audio iPower/iPower X, Apple iPad 12W switching supply, Tzumi power bank, Macbook’s USB power), musically sourced by the MacBook. Since the Khadas prioritizes the I2P port (it switches automatically when an external power source is connected), A/B-ing was easy.

What did I expect between Mac power and external power? From discussions and company advertisements/claims, the electric noises should should have been decreased – and the sonic impact should have increased with an external low-noise supply.

What differences did I hear? Absolutely none, zero, zilch. This relates to the Mac as the music source while using the Khadas as amp and as dac in combination with the Schiit amp. I would have expected this for integrated amp, but additionally amplifying the signal with the Schiit should also have further amplified the noise.

I also alternated the external power supplies when playing music from the Marantz SACD player…and could also not hear any differences between them. But I noticed an excellent clarity and headroom, which probably reflected the uncompressed nature of the music compared to the compressed formats on the Mac.

In the end, there were too many unknowns to allow for a conclusive answer on the LPS question other than that an external power supply likely does not make the world or a difference. The cheap compromise would be the power bank.

Talking to audio engineer Amir from Audio Science Reviews (who had also reviewed the Khadas Tone2 Pro), he told me that different power supplies can make a small measurable difference, which are not significant enough to justify their purchase. The Khadas Tone2 Pro’s performance is superb without.

I don’t object.

CONCLUDING REMARKS

The Khadas Tone2 Pro is not only a “Jack of all trades”, it is also a master of many. It incorporates a lot interesting concepts and innovations – and it works by itself or in combination with essentially anything. It has come a long way from the original “naked” Toneboard for the DIY person to this turnkey device that will provide users with lots of fun…after an initial learning curve. A unique product that is uniquely good.

Recommended.

Until next time…keep on listening!

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DISCLAIMER

The Khadas Tone2 Pro was kindly provided by hifigo for my review. Thank you very much.

You can get the Khadas Tone2 Pro from hifigo or amazon.

Our generic standard disclaimer.

You find an INDEX of our most relevant technical articles HERE.

GALLERY

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