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Khadas Tone2 Pro Review (DAC & Amp)

amirm

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#1
This is a review and detailed measurements of the Khadas Tone2 Pro portable USB DAC and balanced headphone amplifier. It was sent to me by the company for testing. As configured, it sells for $199 from the company website direct.

From the pictures, the unit didn't look all that nice but in person, it looks pretty good:

Khadas Tone2 Pro review DAC and Headphone amplifier balanced.jpg


I thought the rotary control is just for volume. It does that but if you push it forward different ways, it engages various configuration mode. They are incredibly hard to decipher. The manual is of no help but there is a video that walks you through it. After watching it, I could sort of change things but this is by far the most overloaded functionality I have seen in an audio device, next to horrible Chord interface. The fact that the light is below the rotary control makes it doubly hard to figure out what is going on. I rather not have all the functions than having to cycle through them this way. It is truly maddening.

Anyway, there is innovation on the back side as we have discussed before in the form of an RCA jack that can be used with an adapter cable to get balanced out as well:
Khadas Tone2 Pro review DAC and Headphone amplifier balanced I2S.jpg


Hopefully you can see the inner ring inside which gives you the third pin. Connector has a qualify look to it. I don't think you could have both balanced and unbalanced in this size package with any other option.

Dual USB-C connectors are provided. I tested with the primary one on the right. The other is marked I2S but can also provide auxiliary power which takes priority over the USB-C data connector.

Like the original Khadas Tone Board, there is a bare board option available:

Khadas Tone2 Pro review DAC and Headphone amplifier balanced bare board.jpg


I could not however find the price for it or even the listing.

Khadas Tone2 Pro Measurements
Let's start with the dashboard view using the balanced "RCA" output:

Khadas Tone2 Pro Measurements Line Out Balanced.png


Wow, I must stay, I didn't expect it to be this good. This is just a couple of dBs short of state-of-the-art.

I expected unbalanced out to be a bit worse but it is actually worse than that:
Khadas Tone2 Pro Measurements Line Out Unbalanced.png


Here are our two rankings then:
Best portable USB DAC Headphone Amp Review.png


Unbalanced has more high frequency noise as we see in dynamic range test:

Khadas Tone2 Pro Measurements Line Out Dynamic Range Unbalanced vs Balanced.png


From here on, tests are with balanced RCA out.

IMD vs level was excellent:
Khadas Tone2 Pro Measurements Line Out IMD distortion Balanced.png


Linearity was perfect:
Khadas Tone2 Pro Measurements Line Out Linearity Balanced.png


Multitone test showed how low the distortion products are:
Khadas Tone2 Pro Measurements Line Out Multitone Balanced.png


Jitter test showed problems though:
Khadas Tone2 Pro Measurements Line Out Jitter Balanced.png


There is some kind of clock selection but frankly, I got so lost in the settings I could not get to change it. Maybe that fixes it, maybe not. If it does fix it, it should be the default. Fortunately these are not audible distortions so practical implication is not there.

Filters were a nightmare to cycle though but I think I got them right:
Khadas Tone2 Pro Measurements Line Out DAC Filter Balanced.png


I don't understand why there is such high noise floor for out of band response. Something is not right there. This naturally screws up the THD+N response using its default (low) sample rate of 48 kHz:
Khadas Tone2 Pro Measurements Line Out THD+N vs Frequency Balanced.png


Switching to high sample rate (brown/green) removes the effect of the reconstruction filter and shows extremely nice performance.

Headphone Amplifier Measurements
The default mode is low gain so you have to suffer through the menus to switch on high gain. Without it, you have "phone dongle" level of power. There are both balanced and unbalanced modes. I tested both in low gain but only balanced in high gain:
Khadas Tone2 Pro Measurements Headphone Out Power.png


Khadas Tone2 Pro Measurements Headphone Out Power 32 ohm.png


These are respectable power levels for a USB powered, portable device.

Khadas Tone2 Pro Headphone Listening Tests
I used balanced out to drive my Drop Ether CX low impedance headphone. There was good level of power here for satisfying listen. Turn it way up though and distortion sets in so that clipping point is real.

I then switched to Sennheiser HD-650 using unbalanced output. There is not enough power here to do this headphone justice. Sound was Ok but for any type of real use, I would upgrade to balanced cables for it.

Conclusions
As a plain balanced DAC, the basic performance of the Tone2 Pro is superb with one notable miss: the reconstruction filter. I hope this is something they can fix in firmware. I am usually not harsh on performance of this subsystem but this is just not good. I don't know how you can fix the user interface given the mechanism and feedback LEDs available but hopefully they can figure something out. What is there, is not usable.

The Tone2 Pro has the potential to get my highest recommendation but I can't go there due to usability issues and filter problem above. Still, as a plain DAC that you plug in and use, its performance cannot be denied. So I am going to put it on my recommended list.

Edit: here is a video review of the product:

------------
As always, questions, comments, recommendations, etc. are welcome.

Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
 
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Nango

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#2
Can't really see the advantage of this one over 'premium dongles' with similar power like the Sparrow or the Lotoon S1. Creative Xfi Amp delivers also 370mW at 32Ohm and 55mW at 300 Ohm and has volume control buttons at half the cost.
 
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restorer-john

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#4
As a plain balanced DAC, the basic performance of the Tone2 Pro is superb with one notable miss: the reconstruction filter.
The filter curves all seem typical, but that bounce back up to -60dB down out of band (@24kHz) is strange for sure.
 

GWolfman

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#5
Interesting little piece of gear.

...an RCA jack that can be used with an adapter cable to get balanced out as well:
What does the male end look like? I've never seen this before. Or even both ends of the balanced headphone adapter?

@amirm I've never really looked before, but in the balanced (first) FFT, seems odd that there is no 6th and 8th harmonics, but all the other multiples appear to be there? Or is this just an artifact of it being a "snapshot-in-time"?
 

JSmith

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#7
@amirm what happened to the comparison chart with other DAC's etc.? ;)

It's a shame this unit has these physical quirks, otherwise would be great... however not bad for sub $200.

Keep these excellent measurement based reviews coming, it's a great resource for the community. :)



JSmith
 

Nango

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#9
Interesting little piece of gear.


What does the male end look like? I've never seen this before. Or even both ends of the balanced headphone adapter?

@amirm I've never really looked before, but in the balanced (first) FFT, seems odd that there is no 6th and 8th harmonics, but all the other multiples appear to be there? Or is this just an artifact of it being a "snapshot-in-time"?
Adapters charges like 30-40$ extra.

https://hifigo.com/products/khadas-bal-rca-to-xlr-3-adapter-cable?_pos=7&_sid=1bf6fa93f&_ss=r
 
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capslock

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#10
What is the DAC used?

Edit: apparently "ESS ES9038Q2M +xmos+ x4 amp OPA1612 amp" - can anyone confirm?
 

buz

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#16
Thanks for the review, been waiting for this.

Bit disappointed by the amp - power increase with external PSU? OTOH, in balanced it seems alright.
 

Harmonie

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#19
If the company has sent it, it proves that they wish to perfection it and surely they will thanks to Amir's review.
Such a device with HP amp, volume control measuring well below 200$ has certainly a good place in the over 100 below 400$ segment.

And it.... it's Red ;)
 
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