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Review and Measurements of Allo Katana and ApplePi Raspberry Pi DACs

amirm

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#1
This is a review, Measurements and comparison of "high-end" Allo Katana and ApplePi Raspberry Pi DACs. If you are not familiar with Raspberry Pi, it is an ultra-low cost small computer board that runs Linux operating system (primarily). For just $35 you get a full computer with networking, HDMI video output, multiple USB ports and expansion port that allows countless peripherals to be connected to it. These DACs are two examples of high-end audio solutions for "the Pi." The combination of the Pi and these DACs allows you to have a full networked, remote DAC that you can place next to your computer with the media server anywhere else you like. In contrast, few desktop DACs come with built-in networking and require close-in connection to your potentially noisy server connecting over USB.

The Allo Katana has been kindly loaned to me. A bit of background on this. Shortly after I created ASR Forum and started to measure audio equipment, Ioan from Allo contacted me and wanted me to test their Pi peripherals. I warned him that if sends me something and it doesn't measure well, I would be publishing it as such. To my pleasant surprise, Ioan responded with: "that is fine. If it doesn't measure well, we will work on it until it is fixed!" Alas, for a myriad of reasons despite them sending me equipment from time to time, I never got a chance to review them. I apologize to them for taking this long to do this.

The Katana is not cheap as Pi DACs go, retailing for $249. For that though, you get a pretty fancy sandwich of no less than three boards that stack up:

Allo Katana DAC Raspberry DAC Review and Measurement.jpg


On the left is a microcontroller which interfaces with the Pi and the ESS Ess9038q2m DAC located on the middle board. Instead of using an integrated op-amp IC, they had a discrete one designed by Sparkos Labs which you see on the right.

I must confess, I was worried about yet another "boutique" solution in the form of the discrete output stage, thinking it would generate sub-par performance compared to dedicated ICs. As you will see later, that did not turn out to be the case.

Allo was kind enough to send me a full stack in acrylic casing including the Raspberry Pi running Volumio OS. Volumio is a shrunk-wrap version of Linux with a nice web interface so you can remotely control and access it without knowing much about Linux. It essentially turns the Pi and the DAC into a networked DAC appliance. Alas, it is easy to screw things up as I did when attempting to shut off the wireless networking on the Pi. In doing so, somehow I changed the network settings and I could no longer connect to the unit. I had to hook up a monitor and keyboard to the Pi and manually configure the Ethernet settings to get it back online. I also found that sometimes Volumio would not play right requiring a reboot to get things going again. Overall it "works" but is a bit flaky and you need to be comfortable with messing with what is essentially a DIY solution.

I like to use Roon with my remote DACs but alas, Volumio does NOT support Roon's native RAAT protocol. Instead if speaks Apple's airplay which is fine for playing 16 bit content but anything above that, gets truncated down. Sample rate is likewise is limited to 44.1 and 48 kHz. They really need to step up and support RAAT seeing how Roon itself gives away a Pi solution.

For comparison purposes, I ordered the ApplePi DAC which started as a kickstarter by now Orchard Audio. I purchased it through Amazon at $200 plus $5 shipping. Alas, that is an incomplete solution to get this DAC going. If you look at this picture you see that it requires stand-offs and an extra long "stacking header" to mate with the Pi:

ApplePi DAC Review and Measurement.jpg


Otherwise the board interferes with the Pi's components. This is a $1 connector and 50 cents worth of stand-offs that is left off. The company sells these pieces through ebay for something like $4.99 but then charges another $8.45 for shipping! And you still don't get the stand-offs you need to mount it. So here I am sitting with a $200 DAC and no way of getting it even connected. I went on Amazon and found a seller that offered four of those connectors and another who sold the stand-offs. All in all I think I spent over $20 on parts and had to wait for them to arrive to plug this thing in.

And oh, there are no manuals or instructions of any kind with the unit. I had to go hunt around online to finally find a Youtube video that shows how to put the thing together. Yes, this is an enthusiast that has put this together but come on, not including essential connectors and stand-off to make a $200 DAC work is just wrong. As a minimum there should be a strong warning in the listing that you need to buy these extra parts.

The ApplePi uses Ti/BurBrown PCM1794 DAC chips. And uses integrated OP-amps for the output stage. So this makes for a interesting battle of different approaches to building a DAC.

I am sure you all are anxious to see the measurements. Per above note on Volumio, I could not use Roon to play my test tracks. Instead, I ran them from a USB thumb drive. Seeing how my analyzer cannot control the output signal, the number of measurements I can run is highly limited. It is even less than what I could run on my older Audio Precision analyzer (where I had after many hours of work, created some asynchronous tests for such things as linearity). Over time, I should be able to augment these results. I think we can get a good picture of them regardless though.

Another note is about power. Katana DAC can be powered using one, two or three power supplies! Jumper settings determine this. They recommend two or three supplies. For my testing, I used a switching supply Allo sent me for the Pi and an Sbooster Linear Power supply for the DAC portion. For ApplePi DAC, I just used the Sbooster linear supply. FYI in limited testing, switching power supplies generate similar results but required more attention to grounding. Otherwise mains leakage caused some degradation of SNR.

Measurements
Let's start with out dashboard view as usual. First, Allo Katana:
Allo Katana DAC Raspberry Pi Dashobard Measurement.png


Wow, this is pretty good performance! We have a bit more output than our 2.0 volt nominal requirement for unbalanced/RCA output. SINAD is 109 dB which is quite respectable.

Here are the results from ApplePi DAC:
ApplePi DAC Dashboard Measurement.png


So another respectable performance with SINAD of 107 or so.

Allo advertises an a-weighted THD+N (Sinad) of 112 dB which I had no trouble replicating (above measurements as always have no weighting).

ApplePi's rated SINAD is 106 dB and per above, it nicely matches or slightly exceeds that number.

This is how they stack against recently reviewed products:

1534896207754.png


Not bad at all!

Here is the frequency response:
Allo Katana DAC Raspberry Pi Frequency Response Measurement.png


The Katana DAC starts its roll off a bit early at 18 kHz. The ApplePi is flat to our 22 kHz limit.

Here is what they do when we feed them white noise which has much larger bandwidth than our sampling rate allows, enabling us to see how the DAC filters behave:

Allo Katana DAC Raspberry Pi vs ApplePi Filter Response Measurement.png


So first we see the wider bandwidth of ApplePi. But strangely, one channel is much less attenuation than the other (ideal case requires infinite attenuation).

Katana doesn't have this problem but then has an ultrasonic idle tone at 88 kHz or so. I understand Allo is working on better filtering of ultrasonics in the current revision of the DAC. Hopefully they will be addressing this even though it is inaudible and your system likely can't reproduce it anyway.

Switching to dynamic range, we get this for Katana:
Dynamic Range.PNG


Interestingly ApplePi does a bit better:
ApplePi DAC Dynamic Range SNR Measurement.png


That is well shy of advertised 128 dB however.

Let's look at jitter and noise (at 48 kHz):
Allo Katana DAC Raspberry Pi compared ApplePi DAC Noise and Jitter Measurement.png


Here, Katana (in red) is textbook perfect other than a tiny 4 kHz jitter component below -140 dB.

ApplePi on the other hand (in blue) has a lot of spurious noise and jitter sources. Broadening of the "skirt" around our main 12 kHz tone indicates low frequency random jitter (could be a clock issue or noise from the Pi). The higher frequency peaks are likely different timers and clocks running around in the Pi, bleeding into the DAC. Fortunately all of this is either very low in amplitude or masked so not an audible concern. But when you pay $200 for a DAC, you like to see such mistakes avoided.

An interesting chart is THD, harmonic distortion WITHOUT noise:

Allo Katana DAC Raspberry Pi THD+N vs Frequency Measurement.png


We see that the Katana pulls ahead as frequencies increase. With noise (not shown) the two are neck and neck as the noise is dominant in this measurement.

Conclusions
I must say, I am pleased with the performance of both of these DACs. They rival good desktop DACs. Especially interesting is the inclusion of a discrete output stage in Katana and still managing to keep up with integrated solutions. This is no doubt to hand trimming of the pots in the factory (those blue boxes on the board).

I am a bit biased given my virtual relationship with Allo folks but if I had to give the nod to one, Katana would be the one I would pick. It has far cleaner jitter and noise and doesn't have the channel imbalance in ultrasonics that ApplePi had. As a bonus, the Allo folks are very active in forums and that means they would be listening to comments and suggestions.

That said, the ApplePi is also a very good DAC too. So if you go that route and get the necessary bits to go with it, you can have another good solution.

The combination of the Pi allows you to have an under $300 networked DAC. Alas, as with all things DIY and networking, reliability is a bit compromised so this is not for everyone.

As always, questions, comments, corrections, etc. are welcome.

-----
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Sythrix

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#2
The Allo Katana has been kindly loaned to me. A bit of background on this. Shortly after I created ASR Forum and started to measure audio equipment, Ioan from Allo contacted me and wanted me to test their Pi peripherals.
Oh wow Amir. You mean you've been waiting on this for over 2 years? I think I speak for everyone when I say that if you need to take the time to get something like this done, go ahead and do it. We can wait. Those Allo people must have a ton of patience.

Anyways, Since I love DIY and may need a networked DAC someday, I'll definitely keep this review in mind.
 

Guermantes

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#3
Great review! I've been waiting for this one, thanks Amir.

Two things:
1. Am I seeing more power supply noise on one channel than the other in both DACs?

2. I have recently been looking at ultrasonic noise in DACs connected to the RPi, specifically Topping D30, D10 and HifiBerry DAC+ Pro. I found a lot of "chatter" above 35 kHz in all the DACs which was caused by a nearby laptop computer (see pic). When I switched the laptop off the noise disappeared but it made me wonder how prone the RPi and some of these DACs are to this type of interference.

MoOde 4.1 Topping D10 spectragram 20-48k sweep.jpg

RPi and Topping D10 - spectragram of 20 Hz to 48 kHz sweep
 

Ron Texas

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#4
Wow. I can't give this the hairy eyeball right now, but those s/n numbers are great. This is the stuff we need to see around here.
 

amirm

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#5
Two things:
1. Am I seeing more power supply noise on one channel than the other in both DACs?
Yes but the amount and which channel it is more in depended on how I powered them, and grounded my analyzer.
 
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#6
Wow!

I see this on the Allo site:

The Katana is a complex DAC that offers multiple filtering and powering options.The pursuit of the best sound quality is what drives our design team and the reason behind our recent decision to halt manufacturing of the late KATANA.

A new version, the 1.2, is in the works and will only have a few components changed resulting in a subtle, yet necessary SQ improvement.


I wonder what they are changing?
 

derp1n

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#7
How many versions of the Katana did Allo send before the version that was tested?
 

bennetng

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#8
Seeing how my analyzer cannot control the output signal, the number of measurements I can run is highly limited. It is even less than what I could run on my older Audio Precision analyzer (where I had after many hours of work, created some asynchronous tests for such things as linearity).
So it seems that an automated IMD vs level test is impossible, but how about a single shot IMD test at -30dB? Since it is where the "Sabre hump" happens.

Also, the Sabre has built-in ASRC so maybe that's why it excels in J-Test.
 
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#9
I think we should start shipping you more Pi streaming boxes and Pi DAC hats to test. :)

I really enjoy the UGeek Aiode Pi DAC hat I have. It sounds really good in my living room.
 

amirm

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#11
So it seems that an automated IMD vs level test is impossible, but how about a single shot IMD test at -30dB?
Could do. Need to create the test file though....
 

amirm

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#12
Also, the Sabre has built-in ASRC so maybe that's why it excels in J-Test.
Since these are internal DACs, much of what we are testing is interference into the DAC and not as a result of the source jitter (which ASRC would help with).
 

mi-fu

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#13
Allo makes something called Digione player too, which seems to have good reviews.

@amirm Did they send that one for you to test as well?
 

amirm

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#14
Allo makes something called Digione player too, which seems to have good reviews.

@amirm Did they send that one for you to test as well?
That may be in the pile of stuff they sent me in the past. :)
 

Wombat

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#18
Remember that Amir is not testing ICs but rather the products that use them. "Many slips twixt the cup and the lips". ;)
 
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#19
Hello everyone

first a big thx to Amir . I am a fan since he tested the uRendu and seen the extent that some manufacturers go to shade clear test results.

We decided to be diffrent , instead of hiding and arguing , we want the test to speak for themselves. We want to embrace the comunity and be open.

This is our Katana. Above are Amir test results (and we have the same readings)

Now some of you ask about our changes to Katana (Katana 1.2). Look at the above results , roll off is a bit higher than normal and the 88Khz noise...it was audible in one of our test setup.So we changed the filtering...and now roll off is much deeper and the 88Khz is gone. (we removed the R in front of the RC low pass filter)

Please note that jitter (for us) is one of the most important qualities in a DAC

Since we had some time in our hands we also looked at power rails and we decreased the noise on the dual rails feeding the opamp (from 2.7mV to 900uV). One thing we are observing is that THD+N decreased further (Katana 1.2) to (unweighted) from -111 varying to -112.2 (still more testing is required before we make this claim)

So please be patient but we think that our DAC can compete with the best of the best.
 
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