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Review and Measurements of XDuoo TA-01 and Schiit Fulla V2 DAC and Headphone Amp

rebbiputzmaker

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#61
The problem with valve power amps isn't just the valves it is the output transformer. There are probably no transformers which perform well over the entire audible frequency bandwidth since what is required for good performance at low frequencies may compromise the performance at high frequencies and give early roll off. Having written that, even solid state stuff with inter stage transformers can sound "nice" so maybe the distortion/ addition/ removal of some of the signal by a transformer is something people like????
It isn't high fidelity though.
Transformers can be beautiful devices and they have their place in audio. Through the chain, microphone, mixing, recording and various other locations we may find transformers. They are high fidelity, in fact, can be very high fidelity, it just all depends on the quality and understanding of the application.

Transformer design is a combination of Art and Science, sadly mostly lost in this day and age modern engineering. Most haven't the foggiest idea how to design or even understand transformer design. The height of classic transformer design was probably the fifties into the early 60s. Amazing high quality superb sonic qualities were the norm. The Peerless company part of Altec basically a child of Bell Labs and with research from the Golden Age of audio created some of the best audio transformers ever made. High-quality materials, sophisticated multiple winding schemes and exotic laminations, were just some of the features of these transformers. Frequency response was not an issue with these high-quality devices
 
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#62
Through the chain, microphone, mixing, recording and various other locations we may find transformers. They are high fidelity, in fact, can be very high fidelity, it just all depends on the quality and understanding of the application.
Matching impedance between a mic and high impedance input circuitry, or simply floating the mic's ground, is a very different thing than trying to drive a multi-way speaker with 50 watts of power. With the mic, you don't have to worry about reactance or damping factor with the driven load.

Frequency response was not an issue with these high-quality devices
How did they keep the inductance and capacitance of those output transformers from reacting with speaker drivers and crossovers?
 

Frank Dernie

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#63
Transformers can be beautiful devices and they have their place in audio. Through the chain, microphone, mixing, recording and various other locations we may find transformers. They are high fidelity, in fact, can be very high fidelity, it just all depends on the quality and understanding of the application.

Transformer design is a combination of Art and Science, sadly mostly lost in this day and age modern engineering. Most haven't the foggiest idea how to design or even understand transformer design. The height of classic transformer design was probably the fifties into the early 60s. Amazing high quality superb sonic qualities were the norm. The Peerless company part of Altec basically a child of Bell Labs and with research from the Golden Age of audio created some of the best audio transformers ever made. High-quality materials, sophisticated multiple winding schemes and exotic laminations, were just some of the features of these transformers. Frequency response was not an issue with these high-quality devices
Yes considerable investment and effort was put into the design and manufacture of transformers when they were inevitable though better materials are perhaps available now.
Still not all that good at audio frequency extremes . Distortion at 1kHz can be pretty low though.
I rarely use my valve amps, they look nice on a shelf though and give a classic old fashioned sound through my horn speakers for a bit of fun now and again.
 

DonH56

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#64
I think I am missing some of the discussion but there are reactances with microphones too, though you do not have the power requirements that amplifiers driving speakers require. It is fairly trivial to show how a transformer-coupled output causes the frequency response to vary when presented with a reactive load, plus you have generally high output impedance (increasing load sensitivity) and things like transformer hysteresis and saturation to contend with in addition to the transformer's impedance itself. And transformers are big and bulky, and generally not required (nor desired) when the paradigm shifted to amplifiers as a voltage source and speakers were free to have wild(er) impedance excursions. Atmosphere, Audio Research, Bob Carver, and other tube amplifier vendors, plus Macintosh (though more of a balun than conventional transformer IIRC), probably a few others are still making their own output transformers and probably represent the state of the art, but can't get around fundamental issues (physics).

I loved my tube amps on Magnepans but the amps struggled a bit on deep bass and very high frequencies as the speaker's impedance varied (drops below 3 ohms at HF with the ribbon tweeter) or lower output impedance was needed (e.g. to better control panel modes in the bass frequencies). Most tube amps I felt got a bit harsh at HF extremes with ESLs where the impedance drops. And of course with very few exceptions most transformers struggle dipping deep into subwoofer territory. With a lot of speakers exhibiting pretty wide variations in impedance over frequency I've gotten away from any desire for output transformers in the past few years (OK, decades...)
 
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SokK

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#65
Hello !

Sorry to bother you, but I wasn't able to find an answer anywhere... and you guys seem to know what you're talking about !

I bought a Fulla 2 a few days ago, I intend to use it on a daily basis.
As there is no ON/OFF switch on it, should it stay ON 24/7 ?
Isn't it going to damage this little guy ?

It's so nice and cool and I don't want to break it !

Thanks a lot ! I hope you don't mind me bringing back up this topic !
 
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#68
This is a review and measurements of the XDuoo TA-01 tube DAC and headphone amplifier and comparison against Schiit Fulla (V2) solid-state DAC and headphone amplifier. Both are on loan to me from kind members although I had also purchased a Schiit Fulla V2. I may compare the two Schiit units later in light of some of the review outcome.

View attachment 12406

The XDuoo TA-01 retails for USD $160 on Amazon including Prime shipping. The Schiit Fulla is $99 from Schiit direct (not sold elsewhere) and you have to add shipping to it. So prices are not identical but close.

The XDuoo as you see in the above picture, resembles an aircraft instrument or something. It definitely has nice design cues. The volume is hefty and feels nice with that big knob. Toggle switch and power indicators are nicely in the front. It comes with an external switching power supply. It can act as both a DAC+headphone amp combo or with analog input, as just a headphone amp.

The Schiit Fulla design language is similar to other Schiit products. I find their style too plain and industrial but in this instance, I think there is some cuteness with that large knob. The knob itself feels plasticy and not as weight as XDuoo. But not too bad. What is bad though is all the awful little markings substituting for actual labels. Funny that a Chinese company puts nice labels on their product in English but an American company chooses to use symbols! Everyone in the world understands the few English words used in Audio so please use them Schiit. No reason for scratching one's head wondering what a 3.5 mm socket is output or input. With no less than three of them on the Schiit Fulla, it can and does make my grumpy!

On the plus side, the Schiit functionality and robust enclosure seems like good value at $99.

Both DACs were plug-and-play under Windows 10 Creators Edition which was nice. I used Roon media player for DAC/USB related tests, and the line in for pre-amp testing.

Let's get into measurements and see how they did. As usual, if you are not familiar with what these graphs are, refer to my tutorial on understanding audio measurements: https://www.audiosciencereview.com/forum/index.php?threads/understanding-audio-measurements.2351/

Measurements
Let's start with a simple test of frequency response. This is performed using the analog input. First up is the XDuoo TA-01:

View attachment 12407

Overall frequency response is fine. But oddly channel imbalance is bad at full volume but gets better at lower volumes! Since most of us will listen at lower than max volume anyway, this is a good thing I guess. But better would be full matching regardless of level.

This is how the Schiit Fulla V2 does:

View attachment 12408

Matching here is pretty good and only deviates at very low volumes.

Let's examine the DAC portion and see how they do on jitter and noise:

View attachment 12409

We see substantially higher noise floor than our reference Topping D30. I kind of expected this from the XDuoo but seeing how the Schiit Fulla V2 lose to it on noise is surprising. OK, maybe not surprising given how Schiit products have done on my bench but still, a solid-state device should do better than a tube on noise.

How is linearity? Let's look:

View attachment 12410

They are essentially neck and neck until about 15-16 bits. After that, the Schiit deviates more radically although neither is very good at the extreme.

Let's see how they do with a very low amplitude -90 dB sine wave:
View attachment 12411

We see that the XDuoo TA-01 is saddled with tons of noise as compared to Schiit Fulla V2 which does pretty well here.

Let's dig into distortion profile using a 1 kHz tone that itself is filtered:

View attachment 12412

We see the classically talked about distortion with tube amps of lots of second harmonic distortion relative to higher order ones. At -45 dB that is quite high though. With other test conditions, it was as high as -30 dB!

The Schiit again shows its higher noise floor which hides higher order harmonics.

While quite unfair, I have shown the RME ADI-2 DAC at the bottom in yellow. The second order harmonic there is almost 80 dB better than XDuoo TA-01! It is 40 dB better than Schiit Fulla 2 too.

Let's dig into the headphone output performance. First up is the output impedance:

View attachment 12413

Schiit Full V2 does well with 1.0 ohm output impedance. The XDuoo TA-01 though falls behind with 5.6 ohm.

Let's examine power output in the form of output voltage versus distortion (power = output voltage ^2/load impedance):

View attachment 12414

This remarkably consistent distortion profiles. Unfortunately levels are sky high, rising well into single digit THD+N percentages. Lowest level is around 0.06% which is not far off from published spec (these are both channels driven by the way).

Let's look at how Schiit Fulla V2 does:

View attachment 12415

What the heck??? Each channel produces entirely different distortion profile! One is far more distorted than the other as this single measurement shows at 33 ohm:

View attachment 12416

Look at how different red and yellow curves are. They were so different that I thought I test my setup with another yet unreviewed headphone amp: the Fiiio A3. As you see from its graphs, both channels produce identical distortion with the two lines falling on each other completely.

Come on Schiit. Can we not review any of your products without something so broken popping out? How can the two channels differ so much? Do they use the wrong parts in one channel? Not enough feedback to counter part variations?

Look, I don't get paid enough to sit there and annotate that power graph like I did with XDuoo TA-01. So if you want to know what power it puts out, you need to do the work yourself. I am too unhappy right now...

Listening Tests
I did fair amount of comparison listening tests with levels matched prior to making measurements. The results were very inconsistent. Depending on headphone in use, volume level and content, I would get different outcomes as to which was better. Not helping is the amount of noise generated by the XDu001 TA-1 which would bleed to Schiit's output once connected via my AB box.

Eventually I got one set of consistent results: using HifiMan HE400i with output levels matched around 0.350 volts. There, the Schiit had consistently better bass, and more resolution. Switching to XDuoo TA-1 the detail in between notes would collapse and bass would become weaker.

In less consistent tests I noticed that high frequencies were less in XDuoo TA-01 or put inversely, more in Schiit Fulla V2.

Further results were the effect of background hiss. This had an interesting effect at times of making one thing there was more sense of space between instruments. Hard to explain this. I hope to capture this and upload at some point for you all to listen.

I often hear people talk at length about change in soundstage when evaluating headphone amps. I heard no such thing despite focusing on it across many, many listening tests. There was no expansion or contraction of soundstage. What was there was always a function of content. Note that this was with levels matched. let them vary and you would come up with any outcome you wanted!

Conclusions
I struggled to figure out how to compare the XDuoo to other products. I thought by picking a solid-state product like Schiit Fulla V2, the difference would be clear in that the Schiit would produce better measured results across the board. This was not universally the case. A solid-state product lost out to a tube product from China no less in some of the tests.

At the end, this turned out to be a mixed results both in measurements and listening tests. If I had to pick one to listen between the two, it would be the Schiit Fulla V2. Otherwise, I would personally avoid both. The XDuoo brought no tube "magic" to the table. So I can't see dealing with a tube just for the sake of it.

Anyway, I may do additional comparisons of Schiit Fulla V2 to other products that compete with it.
As the Magni 3 also has the APx555 measurements from Shiit listed so does the Fulla 2, can check it out here...

http://www.schiit.com/public/upload/PDF/Schiit DAC APx555 Standard Test Suite_ Fulla 2.pdf

No other APx555 measurements were listed beside those from the Modi 3, Modi Multibit, Magni 3 and Fulla 2 at the time being. Was really hoping to see the Yggdrasil being the most perfect 21 bit resolution DAC ever made and measured by them, as it's making no guessing anywhere as they put it haha. :)
 

FireLion

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#71
Must be so cheap to get your own brand on capacitors in China!
It also has a transformer concealed in the top. One of the nicest sounding DAC amps out there. It's much superior to the 01 and well known reviewer has one right now. I loaned him some tubes, apparently he really likes it.
 

doomixy

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#72
I'm looking for the best AMP/DAC (in your opinion) that I should purchase for my beyerdynamic DT 770 PRO 250 Ohm. I've read a couple of threads here, but I'm still not sure what to buy. Each has its pros and cons...
I know that a seperate AMP and a separate DAC will always be better, but I need something that is also portable and will be plugged into my laptop most of the time. The price point should be somewhere from 100-150$.

I'm seriously thinking about buying a Schiit Fulla 2. Should I just go ahead or is there something better in my use case in your opinion?
 
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Veri

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#73
I'm looking for the best AMP/DAC (in your opinion) that I should purchase for my beyerdynamic DT 770 PRO 250 Ohm. I've read a couple of threads here, but I'm still not sure what to buy. Each has its pros and cons...
I know that a seperate AMP and a separate DAC will always be better, but I need something that is also portable. The price point should be somewhere from 100-150$.

I'm seriously thinking about buying a Schiit Fulla 2. Should I just go ahead or is there something better in my use case in your opinion?
Topping Nx4 is superb for portable needs. Really quite powerful, too. Skip the fulla.... (imo)
 

doomixy

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#74
Topping Nx4 is superb for portable needs. Really quite powerful, too. Skip the fulla.... (imo)
It's great for portability, yeah. But I don't actually need for it to have an internal battery. I read about it and apparently it cannot be used while it's empty. Would be great if you could bypass the battery. Anything else, tho? What about the DX3 Pro instead of NX4?
 

Veri

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#75
It's great for portability, yeah. But I don't actually need for it to have an internal battery. I read about it and apparently it cannot be used while it's empty. Would be great if you could bypass the battery. Anything else, tho? What about the DX3 Pro instead of NX4?
The Topping DX3 is probably the go-to recommended all in one here, it's really great.
But you said portable, DX3 is rather... trans-portable ;) needs wall wart power.
 

doomixy

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#76
The Topping DX3 is probably the go-to recommended all in one here, it's really great.
But you said portable, DX3 is rather... trans-portable ;) needs wall wart power.
Didn't know that it requires wall ward power. xD
Oh well, point is that I can't go wrong with either of them. All I need now is to decide what do I really need.

I've read so many things about the DX3 and its issues. I feel like you had a 50% chance to get an defected unit. I hope the V2 fixed those issues...
 

BDWoody

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#77
Didn't know that it requires wall ward power. xD
Oh well, point is that I can't go wrong with either of them. All I need now is to decide what do I really need.

I've read so many things about the DX3 and its issues. I feel like you had a 50% chance to get an defected unit. I hope the V2 fixed those issues...
For what It's worth, I have a dx3 pro, a d50s, and a d70, and have had zero issues with any of them. Lots of happy Topping users.
 

peng

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#78
I happened to have this thing but I used is as a SS DAC using the USB input and analog outputs without external power to it. It sounds great, but too bad Amir didn't measure it this way, or I missed something? It seems that he only measured it as a DAC/tube headphone amp.

If anyone has not tried it as a USB DAC yet, try it and you may be pleasantly surprised, or not..
 
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