My xDuoo TA-01 with Mullard 12AU7

I'm just going to say it - it's a brilliant HPA to be paired with my AKG K550.

There aren't too many reviews out there and it's not all positive. But I got it anyway because I just couldn't resist when I saw the spec. XMOS usb controller doing 24bit/192KHz and Wolfson WM8740 which is a personal favorite since I got my first Cambridge Audio CD player. A touch of tube flavor is also exactly what I'm after. These combination is not common in this price range.

Unboxing

There isn't much to say but nowadays everyone is photographing the unboxing process. So here it is, a white paper box and its content. The power cord is very short, it may not work for everyone. The power supply unit and usb cable are low end ones. I have no problem with that as they will be replaced anyway.

The HPA

It's well-constructed and well-finished. Again, everything I say here is relative to the price of product. The volume control is a bit soft and when I looked at the internal, it's not the best stuff. Albeit, volume control is very linear and silent. On the front, there is a golden headphone jack, a power switch, and a volume control knob. A the back, there is analog input, a USB port, and a power port.

When the USB port is connected, the link LED at the back lights up.

Changing tube

When I listened to it at the shop, I's only able to hook up my phone to it via the analog input. The shop keeper attempted to connect my phone to it with a special digital cable but Apple complains about XMOS being a high power device and refused to work with it. And with the stock tube, I wasn't too impressed. It sound clean and balanced but not much of a step-up to my existing MUSE HPA. There was no product name on that Muse amp and it's simply known as 'PCM2707+DIR9001+PCM1793 Mini USB DAC'. So I decided to give it an upgrade right away by replacing the tube with a Mullard from England.



To change the tube, I had to take the screws off in order to access the base of the tube. It's securely installed and there is no way to pull it out safely without opening the case.

The tubes

Last time I played with tube was years ago on a low-end, compact, analog tube amp. Honestly, I know nothing about tubes. I walked into a shop and asked what kind of 12AU7 they have - American, British, and German. I's sold the British unit because I had a Mullard before and yea I like British sound more than the others. As I's told, the American is not very good. The British has a warm tune and the German is more on the balanced side.

The internal of xDuoo TA-01

Since it's opened, I took a picture of it but the good stuff aren't shown on the photo. On the side, there is a PCB with the XMOS chip. I couldn't see the WM8740 and I suspect it may be at the bottom of the main board.

Time to hook it up

I use Linux and as soon as it's connected to my PC, kernel told me it has zero problem recognizing my new toy. It's running at USB 2.0. Then I go to KDE audio and video setting, switch the preferred output to "XMOS USB Audio 2.0 Analog Stereo". I'm not sure why it says analog since there is no analog connection I can imagine. Then I go to Deadbeef and changed the ALSA output to XMOS SPDIF.

At first, there was no sound at all. But wait, I think the circuit comes with some circuit is disconnected during the warm up phase. After ~30 seconds, there will be a small clicking sound through the headphone when the HPA is ready. So music started to pump through and then it stopped. I stopped and hit play again, this time it's golden. The XMOS controller has no problem receiving 24bit/192k audio stream. I wasn't quite sure what that glitch was about but it rarely happened again.

Tube amplifiers need time to warm up to deliver its true performance. This one is no exception. It takes about 10min to warm up and I can gradually hear bigger sound stage and deeper bass.

Here is some information about the USB controller. I's really glad that it's connected to the USB 2.0 bus. I tried to do a verbose listing of the device but there was no additional information revealed (such as version of the XMOS chip, etc).

[80679.288531] usb 8-1: new high-speed USB device number 4 using xhci_hcd [80679.305062] usb 8-1: New USB device found, idVendor=20b1, idProduct=0002 [80679.305074] usb 8-1: New USB device strings: Mfr=1, Product=2, SerialNumber=3 [80679.305081] usb 8-1: Product: XMOS USB Audio 2.0 [80679.305086] usb 8-1: Manufacturer: XMOS [80679.305091] usb 8-1: SerialNumber: 0000 # lsusb -s008: Bus 008 Device 004: ID 20b1:0002 XMOS Ltd Bus 008 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

Performance

Compared to when I listened at the shop, the difference is quite obvious. First, its DAC is working with the FLAC file compared to analog input. Second, it now has a better tube. The sound stage is wider and the bass goes deeper. Vocal sounds less harsh and there is a bit more detail. Strangely enough, I's satisfied at a lower volume. Here's my two cents on a few songs:

Adele - Skyfall (16/44.1 flac): it sounds open and powerful. yet it doesn't wear my ears out. near the end where there are lots of strings, it stressed out the amp and I'd welcome a bit more resolution

Alanis Morrissette - Perfect (16/44.1 flac): spacious and warm. her voice can be harsh at time but it's not the case here

玉置浩二 - 悲しみにさよなら (16/44.1 flac): overall very pleasing. the weak point is again the hi's which sounds a little dry

夏韶聲 - 結他低泣時 - (24/192 wav): very good dynamics with the guitar. I don't listen to this very often and I's just hoping to find a HD file to test 24/192 output.

Joanna Wang - I love you (16/44.1): this song pairs with this HPA well. vocal is solid and detail. bass is just right and smooth.

Sarah McLachian - Angel (16/44.1): such a pleasure to listen. warm and airy.

蔡健雅 - 十萬毫升淚水: Very sad song. I was particularly impressed when the cello kicked in. I can almost feel the French bow drawing on the strings.

Temperature

There is no heat problem. After 30min of enjoyment, it felt just a bit warmer than my finger. And the heat was well spread across the chassis. The tube isn't much hotter than the rest of the unit. The tube barely lights up. If that's helping with the temperature, I'd much prefer its subtleness.

$$$

The HPA costs HKD$1300 and the tube costs $500. There isn't a whole lot of choices in this price range and I'm very happy with what I got. Give it a week to run in and getting a better PSU may just bring about surprises!

Full spec

Working voltage: DC12V

Output Power: 2100mW (32Ω load)

Frequency response: AMP 10Hz ~ 100KHz (± 0.5dB), USB 20Hz ~ 20KHz (± 0.5dB)

USB sample rate support :16-24Bit, 44.1KHz, 48KHz, 88.2KHz, 96KHz, 176.4KHz, 192KHz

Distortion : 0.03% （1KHz）

Impedance: 16Ω ~ 600Ω

Gain: +6 / +17 Db

Crosstalk: 110dB

Size: 140 * 80 * 82mm

Weight: 410g

Link to product: http://www.xduoo.com/xduoo/ProductShow.asp?id=55

1 week later

I decided to give it a proper linear power supply. The difference is, however, not very notable. I made a mistake during the first order. I didn't check the input requirements and I bought a 1.25amp PSU. If you're planning on getting a replacement power supply, don't make the same mistake I made. Make sure the power supply can supply 2amp of current. Otherwise the xDuoo simply won't give you any sound even though the power LED will light up.

Couple months later

The xDuoo is a decent DAC+HPAMP. I's told that some other products have problems with occasionally pausing or rendering at incorrect clock. I haven't experienced all that, not even once. On the other hand, try connect it to a pair of speakers and it may surprise you!