Douk Audio U3 Review: The Douk of Wishful Thinking

Discussion in 'Headphone Amplifiers and Combo (DAC/Amp) Units' started by purr1n, Nov 18, 2023.

  1. purr1n

    purr1n Desire for betterer is endless.

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    A friend in town handed this to me to check out, presumably on the condition that I write a review about it. Weeks go by - where's that review? OK OK, I'll get to it.

    First of all, don't listen to me. Check out the plethora of Douk Audio U3 reviews on YouTube: https://www.youtube.com/results?search_query=douk+audio+u3! I think one guy even said it got him to listen to music again! Wow, this $40 amp must be really amazing! A giant killer even! A new standard in HiFi? Crafted by the ancient elves!

    IMG_1495.jpg
    IMG_1493.jpg

    It's OK. In many ways, the Douk U3 exceeded expectations. It didn't sound flat and boring like that 123 SINAD amps based purely on opamps and the TPA6120 chip under nested feedback loops, with each loop running 125db+ of feedback. The U3's driver/gain stage is opamp, on a DIP so you can roll your own, the output is discrete transistors.

    The U3 didn't sound too grating either. Maybe a bit glare with extended listening sessions that I bet could be corrected with some warmer or darker sounding opamps. It's a classic solid-state class AB sound. Some grain, a bit of an edge, but not too much. The problem is that most solid-state, even cheap solid state has moved on. Put it this way, the Magni+ is more mellow in the highs. The Douk U3's presentation reminded me of slight headamp version of this, but with just a bit more glare.

    That's the good news. I have a lot of bad news later. But first, let's measurebate!
     
  2. purr1n

    purr1n Desire for betterer is endless.

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    Douk U3 Headphone Amplifier
    • 300-ohm load
    • 90kHz bandwidth
    • APx555 "cheat" HPSA mode on
    • Volume knob of headphone was set for unity gain
    • Input signal output set on the APx555

    Second Harmonic (H2) Distortion Product
    upload_2023-11-18_18-45-35.png
    90kHz bandwidth, APx555 "cheat" HPSA mode on.

    Third Harmonic (H3) Distortion Product
    upload_2023-11-18_18-47-34.png

    Fourth to Tenth Harmonic Sum (H4-H10) Distortion Product
    upload_2023-11-18_18-51-0.png

    Notes:
    H2, H3, and H4 above do not include noise
    H2 and H3 tend to be dominant over the higher orders
    H2 and H3 do sound different from each other, as to how, that's another discussion
    H4+, the higher order distortions can be considered to be "crap" factor
    There is thought that higher order distortion may have an outsized negative affect on sound quality
    THD+N does include the noise component as well as THD (sum of H2, H3, and H4 and above)
    Distortion is signal that is not supposed to be there
    H2 or second order at 100Hz means there is a signal at 200Hz that is not supposed to be there
    H3 or third order at 100Hz means there is a signal at 300Hz that is not supposed to be there
    This graphs tells us how loud the distortion is at that harmonic
    Distortion that lands in the ultrasonic region matters, if SOTA
    chip companies like TI care, then so should you.
    0dBu (0.775Vrms) output level on most headphones will cause hearing damage after a few minutes of exposure
    0dBu output level may burn out the voice coil on sensitive headphones with extended use

    T
    HD+N
    upload_2023-11-18_19-0-39.png

    Commentary

    We haven't done very many distortion surface graphs yet, so it's hard to say anything definitively without a good amount of comparative data. Generally the H2 to H4+ results look fantastic. The THD+N, which includes a noise component, shows us that the noise component is a bit higher than typical for this kind of design.
     
    Last edited: Nov 18, 2023
  3. purr1n

    purr1n Desire for betterer is endless.

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    Now here are the bad.

    First is the volume control. The volume control has detents. Here are the problems:
    1. A few of the detents near the bottom (and also at the near the top) don't do anything to the volume
    2. The effective usable range is only down to -50db
    3. One early detent changes the volume attenuation from -80db to almost -50db! I was using Grados and I could have lost my hearing. This is a lawsuit waiting to happen and it wouldn't be user error!
    4. Sometimes the detents do not "take", that is we need to move up two notches and then back one, grrrr!
    Douk U3 Volume Crawl
    upload_2023-11-18_19-27-45.png

    Here is the second problem: Massive x10 voltage gain! The volume control issues are bad enough. But x10 voltage gain is massive considering that there are no gain switches on the Douk. This is a headphone amp. We don't need x10 gain!
    upload_2023-11-18_19-33-48.png

    Don't worry, there's more bad...
     
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    Last edited: Nov 18, 2023
  4. purr1n

    purr1n Desire for betterer is endless.

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    The Douk comes with a power cable that we are supposed to plug into a USB power brick. I have a nice one from my Pyle Power Sequence Controller which appears to be decently filtered. But given the "transportability" of the U3, one would assume that plugging the USB power brick into a computer or laptop is a likely use case. Alas, the results are horrible when plugged into a PC USB port! We are talking about the same PC USB ports that I get almost perfect results from with Schiit Modi+, Topping E50, etc.

    Douk U3 plugged into Pyle Power Sequence Controller
    -30dBu output
    upload_2023-11-18_19-54-12.png

    Douk U3 plugged into PC
    -30dBu output
    upload_2023-11-18_19-53-35.png
    NOTE: I can hear noise with Grados sometimes. It comes and goes. I can't replicate it now right.
     
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  5. purr1n

    purr1n Desire for betterer is endless.

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    Here are the distortion surfaces into a 29-ohm load, this time using the PC USB.

    Douk U3 Headphone Amplifier
    • 29-ohm load
    • 90kHz bandwidth
    • APx555 "cheat" HPSA mode on
    • Volume knob of headphone was set for unity gain
    • Input signal output set on the APx555
    H2
    upload_2023-11-18_20-41-51.png

    H3
    upload_2023-11-18_20-42-30.png

    H4+
    upload_2023-11-18_20-42-53.png

    THD
    upload_2023-11-18_20-44-13.png

    With a more difficult load, the Douk U3 starts to become less perfect. Still, I wouldn't say that the distortion levels are high (well, the H4+ "crap factor" is a bit concerning). The noise, inferred from the THD+N graph, is highish, and reflective of my experience with low impedance Grados which are used at lower voltage output levels, like microvolts.

    In conclusion, I wish I could give the Douk U3 a half-assed recommendation - it sounds decent, good even for this type of sound, but I cannot. The volume pot could very well be defective; but every time this happens, I always have to wonder why YouTube reviewers or the likes of Audio Science Review never seem get any defective gear from Chinese manufacturers, whereas I seem to be a magnet for defective Chi-Fi gear?* Examples of such below**:
    Anyway, the volume pot is more or less defective, this is made worse by the massive x10 volume gain. I'm sure an argument can be made that I should be running a fancy 12VDC+ l power supply, but give me a break! The likes of SMSL, Topping, iFi, Schiit, they offer everything I need when I buy anything from them. It entry level audiophile stuff supposed to be tweakable because of the insistence of unemployable nerds? The product description on Amazon sure doesn't say: you need to buy an external power brick for maximum performance.

    * The reason is that we tend to buy the gear and not have manufacturers send us cherry picked units. Or maybe it's because my livelihood doesn't depend on me cranking out positive reviews of products.

    ** I swear, I can't make this up. With me, Chi-Fi gear has at least a 70%+ of being defective in some way or not measuring anywhere near the results at ASR. It's like I am the anti-Amir. Remember when Schiit gear measured at ASR would be broken, borked, etc.
     
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    Last edited: Nov 18, 2023
  6. Lyander

    Lyander Official SBAF Equitable Empathizer

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    It's either the trans-Pacific shipping or different barometric conditions damaging components; you're obviously unable to test them in fair circumstances! (sarcasm).

    With how much more lower-impedance loads stress this amp out, almost feels like it'd be worth keeping those 29R surfaces in your measurements pipeline, maybe redo some prior measurementst with em should you have the time? The differences esp in "crap factor" in the low end once you approach 0dBu output are massive.

    The upwards-incline of odd-order harmonics towards 20kHz is notable too. Partially-informed but largely uneducated guess: opamp in circuit getting really stressed out with the more difficult load, so it's well approaching the limits of what it can comfortably output, leading to the introduction of a bunch of thermal noise into the system?
     
  7. Hrodulf

    Hrodulf Prohibited from acting as an MOT until year 2050

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    Not bad for an n5532p Cmoy!
     
  8. purr1n

    purr1n Desire for betterer is endless.

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    LOL. It's got four transistors in the output. Basically opamp + current buffer design, like in the old days.
    [​IMG]

    The distortion pattern is nice, so I don't think it's a diamond buffer (which is odd order dominant).
    upload_2023-11-19_9-39-22.png

    No idea what that volume pot is, it's like a regular pot with steps. Obviously the QC guy wasn't paying attention. I guess that's what you get when your manufacturing crew is probably waiting for their organs to be harvested.
    qcpassed.jpg
     
    Last edited: Nov 19, 2023
  9. Hrodulf

    Hrodulf Prohibited from acting as an MOT until year 2050

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    Color me impressed! A BC550/560 buffer would be interesting. Pure opamps don't always like driving non-line level loads.
     
  10. Beefy

    Beefy Friend

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    Heh. People used to pay several hundreds of dollars for this sort of thing from Ray Samuel or Lehmann.
     
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  11. purr1n

    purr1n Desire for betterer is endless.

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    Well, Ray Samuel said he sorted through his pots. I would have to trust him. It's not like we can verify, or that it even matters now. The thing about Ray is that I actually liked the sound of his products (the exception being a chip based power amp designed for the HE-6 (it sounded terrible, boring).

    Ray definitely had ears and had a vision for what he wanted his stuff to sound like. There wasn't much competition back then. And let's face it, unless you built a factory or two, or used labor consisting of dissidents waiting for their organs to be harvested, it was harder back then for a small time operation to offer stuff at today's prices (taking into account inflation).

    In retrospect, the shade many of us threw at Ray, including from myself, was unfounded. Yup, I drank the Head-Case Kool Aid too. Personally, I think what it came down to was rivalry between Kevin Gilmore and Ray. (Or Kevin Gilmore -vs- everyone else). I'd give Gilmore more credence if he actually started a audio company. I admire Gilmore wanting to be "open source", communist, or whatever - but that's not how the world goes. People either don't want to DIY or can't DIY. And let me remind everyone that it would cost more than what Ray was charging to build a single CMOY+chip buffer with a battery in a nice solid case that wasn't a mints tin. Ray didn't become successful because his stuff sounded like shit or was broken like this Douk. It's the market that determines the prices.
     
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    Last edited: Nov 19, 2023
  12. Thad E Ginathom

    Thad E Ginathom Friend

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    Plainly, the graphics were done by someone on the liver-removal waiting list.

    Very peculiar. Trying to emulate something I can't place?

    "Hi-Fi" --- if it says it is, I tend not to believe it. And in that typeface, as if it is some sort of standard-approval mark.
     
    Last edited: Nov 20, 2023

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