Douk Audio U3 Headphone Amplifier measurements found on YouTube

[fws]

Hi, found a video review with measurements of Douk Audio U3 on YouTube, the video is in Italian, but the English subtitles seem ok'ish.

First off the original video by "HiFi Cheap".
If it is ok, I will post some screenshots for discussions sake.
My own experiences with the device at the end.

Douk Audio is supposedly a subbrand of Nobsound. Recently those amps also been sold rebranded as Cadisi X2-U301.
The official price is $41.99, the actual price online is around $22-30

Product page specs
Output power - >=1300mW @ 32Ohm
Headphones impedance - 18-600Ohm
Frequency response - 20Hz-30KHz
Signal to noise ratio - >=110dB
Max output amplitude voltage - 25Vpp
Input DC voltage - 5-20V

The description says the device takes anything between 5-20V and internally always work at 26V, uses socketed TI NE5532P OpAmp, and "using 1300mA large current output transistor working in class A"

Douk Audio U3 Mini Class A Headphone Amplifier HiFi Desktop Stereo Amp for HD650/K701/DT880/T70/RS1e

Warm tips: Not inlcude power adapter, recommend to use original high-quality power adapter above 5W. For example: the current should be above 1A if use DC 5V while need above 0.5A if use DC 12V power adapter. Features Adopting innovative circuit design, DC 5-20V wide input working voltage, the...

doukaudio.com

The DC input is a 2.5x5.5mm barrel plug, and the amp comes only with a short barrel plug to USB A cable.

Frequency response measurement

Distortion with switching power supply

Distortion with linear power supply

IMD

Power output

I've seen a comment on Amazon's product page where someone claimed to measure power, I have it written down, but unfortunately can't find the comment anymore
10Ohm - 420mW
33Ohm - 509mW
82Ohm - 396mW
240Ohm - 192mW
620Ohm - 84mW

So while not exactly the same, it is close enough, and shows the same behaviour whereas power at 32Ohm is far below (4-4.19Vrms) claimed 1300mW (6.45Vrms), however it gets more in line with higher impedance loads. That said the output voltage at 300Ohm load calculates to 7.08Vrms and 7.20Vrms at that 620Ohm, which is again a bit short from 25Vpp which is 8.9Vrms. Would still call it "decent", no idea why the brand feels like they need to lie.

The YouTube reviewer also mentions he had tried feeding U3 with higher voltages and found no changes. As for my experience I also haven't heard any audible difference when feeding U3 with higher voltages, actually it seemed like U3 was heating up more at higher input voltage so I returned to using it at 5V.

As such I'm powering U3 from 5V 2A mobile phone chargers branded Samsung and Xiaomi. There is no audible noise present when using those. Trying to power it from any USB host device results in considerable noise, be it desktop PC or mobile phone. Likewise I've tried a few 12V PSU's, mostly high powered laptop and camera ones, and most of them were noisy.

I own 2 units of U3. Bought one around 2021 as a cheap amp for also cheap Sennheiser HD430 (600Ohm, 94dB/mW). I've kept using it with current production (bought in 2022) HD600 (300Ohm, 97dB/V according to official specs), and also threw plenty of others at it like HD414X (2000Ohm, 94dB/mW), including less demanding headphones like SHP9500, HD598, Koss Porta Pro, Creative Aurvana Live, Samson SR850, and earphones like KZ ZVX, FAAEAL Snow-Lotus, BGVP DX6. At one time I also had Topping L30 II, but I've returned it, cause I didn't felt it was worth the money vs U3. For reason unknown to me L30 II seemed to improve soundstage accuracy in fps gaming, but in music I didn't felt I needed to spend $150 on it. If I was pressed hard maybe the treble on L30 II were a bit smoother, but also more prone to sibilance at the same time if that makes any sense. I was concerned if my unit of L30 II worked properly though, as it was constantly running hot/at full blast even without input signal present, the PSU was a bit warm when the amp was turned off, and I could not distort HD600 with power from it. My only qualm with U3 is a short sound when powered on/off, its kind of "shhh" as when you turned off an old black and white CRT ages ago, it is less audible on high impedance headphones, but I almost feel like a pressure effect (I felt a bit of it with L30 II as well).

This is my first post, so I'm sorry if I've missed some rules, feel free to point that or any annoyances with my post, out.

 

[solderdude]

Welcome to ASR and nice recap.

So while not exactly the same, it is close enough, and shows the same behaviour whereas power at 32Ohm is far below (4-4.19Vrms) claimed 1300mW (6.45Vrms), however it gets more in line with higher impedance loads. That said the output voltage at 300Ohm load calculates to 7.08Vrms and 7.20Vrms at that 620Ohm, which is again a bit short from 25Vpp which is 8.9Vrms. Would still call it "decent", no idea why the brand feels like they need to lie.

Brands like that often post incorrect specs.
Seems like 20Vpp would be a more proper spec.
Based on the fact that internal PS voltage is 26V and is a NE5532 followed by a buffer one can calculate the peak-peak voltage will be 26V -4V (5532 datasheet) and subtract 1.2V for buffer so 26V - 5.2V is 20.8V.

It isn't class-A either.... at least it isn't for headphones <600 ohm.

The YouTube reviewer also mentions he had tried feeding U3 with higher voltages and found no changes. As for my experience I also haven't heard any audible difference when feeding U3 with higher voltages, actually it seemed like U3 was heating up more at higher input voltage so I returned to using it at 5V.

Makes sense as the amp has a wide range DC-DC converter in it and depending on the used circuit it could be dissipating more heat at higher voltages.

Trying to power it from any USB host device results in considerable noise, be it desktop PC or mobile phone. Likewise I've tried a few 12V PSU's, mostly high powered laptop and camera ones, and most of them were noisy.

Yes, very likely as one creates a groundloop through the audio ground and the power supply ground which may well be connected internally.

I own 2 units of U3. Bought one around 2021 as a cheap amp for also cheap Sennheiser HD430 (600Ohm, 94dB/mW). I've kept using it with current production (bought in 2022) HD600 (300Ohm, 97dB/V according to official specs), and also threw plenty of others at it like HD414X (2000Ohm, 94dB/mW), including less demanding headphones like SHP9500, HD598, Koss Porta Pro, Creative Aurvana Live, Samson SR850, and earphones like KZ ZVX, FAAEAL Snow-Lotus, BGVP DX6. At one time I also had Topping L30 II, but I've returned it, cause I didn't felt it was worth the money vs U3. For reason unknown to me L30 II seemed to improve soundstage accuracy in fps gaming, but in music I didn't felt I needed to spend $150 on it. If I was pressed hard maybe the treble on L30 II were a bit smoother, but also more prone to sibilance at the same time if that makes any sense. I was concerned if my unit of L30 II worked properly though, as it was constantly running hot/at full blast even without input signal present, the PSU was a bit warm when the amp was turned off, and I could not distort HD600 with power from it. My only qualm with U3 is a short sound when powered on/off, its kind of "shhh" as when you turned off an old black and white CRT ages ago, it is less audible on high impedance headphones, but I almost feel like a pressure effect (I felt a bit of it with L30 II as well).

Yep, caused by an undefined state for the amp when powering down and the internal reservoir caps slowly draining. More expensive amps will mute the output signal before that undefined state occurs.
No need for DC protection as the output is AC coupled using output capacitors.

Fun amps for the money and perfectly able to drive most headphones and will be outperforming most 'headphone outputs' from many devices.

 

[kazuviking]

My measurement of a modified U3 with an OPA1656. This was done with the pcs sound card which is not the best but good enough. This is a modified U3, replaced the opamp, every capacitor with Taiyo Yuden aka ELNA, potentiometer and the stock bjts with BC327/337. Now the turn on sound is shhhhhhhHHH intead of shhhHUUUUUH and the turn of went from SHHHHHhhhhh--------LOUD POP to SHHHHhhh, left ear goes quiet , right ear shhhhh then goes quiet and the left ear goes shhhh then the unit is off. I feed it from the lowest noise phone charge on a site that i never found again. The charger is Nillkin 2A. That site compared a lot of usb chargers in safety, thermals and output ripple and that nillkin charger had leagues better ripple and load regualtion than others even beating apples offering by a good amount.

The 3KHz spike is from the soundcard.

 

[anthony 5]

Hi,I have a U3 volume pot has detents and first 4 notches does not do a thing, then 5 notch too loud sent back the unit got another one same problem now using a cheap passive pre amp for attenuating the loudness does someone have the same problem unit has decent sound thanks

 

[6Channel]

This post is sorta interesting. I bought 3 of these, since the first 2 had seriously mis-tracking pots: 3rd time's a charm. I primarily feed 300Ω & 600Ω cans, but also 30 & 60Ω's. The root of my Douk acquisition was to audition a relatively simple HP amp, noting the circuit was designed around a 5532, to which I've been partial for many years. Short story: SQ was certainly "promising", so I researched this amp & fed it with a beefy 6A power supply (keeping it at 5V, as many report higher voltages often result in sacrificed output & SQ); cycled many chips, finding NJM5532 sounding excellent, only recently supplanted by a very, very juicy LM4562. Far from the amp I initially received in the mail. I prefer the SQ to several 4 & 5-figure HP amps I've plugged into. YMMcertainlyV. [most will find HE6se's & 1266's a challenge].

 

[Ropeburn]

This post is sorta interesting. I bought 3 of these, since the first 2 had seriously mis-tracking pots: 3rd time's a charm. I primarily feed 300Ω & 600Ω cans, but also 30 & 60Ω's. The root of my Douk acquisition was to audition a relatively simple HP amp, noting the circuit was designed around a 5532, to which I've been partial for many years. Short story: SQ was certainly "promising", so I researched this amp & fed it with a beefy 6A power supply (keeping it at 5V, as many report higher voltages often result in sacrificed output & SQ); cycled many chips, finding NJM5532 sounding excellent, only recently supplanted by a very, very juicy LM4562. Far from the amp I initially received in the mail. I prefer the SQ to several 4 & 5-figure HP amps I've plugged into. YMMcertainlyV. [most will find HE6se's & 1266's a challenge].

"I researched this amp & fed it with a beefy 6A power supply (keeping it at 5V"

Yeah... 5V and 30W should certainly be more than enough for ANY headphones, and more often than not even enough for fairly efficient speakers driven to neighbour annoying levels including fat subbass? Not sure what you're trying to tell us here.

"Partial to NE5532" - again, not sure what's the point here. It's been an industry standard for decades, especially in music production.

"Better than 4 or 5 figure amps" - I can easily see how, because that kind of thing is all too common and pretty much standard procedure by now that gear for hundreds outperforms other options for thousands.

I seem to be missing something big here. Where's the surprise, or the big bafflement? So far it really looks like nothing but the "good old". Please do correct me if I'm wrong. I'd be delighted to find out there's even better performing options for very little money, than those I already knew of.

 

[kazuviking]

Hi,I have a U3 volume pot has detents and first 4 notches does not do a thing, then 5 notch too loud sent back the unit got another one same problem now using a cheap passive pre amp for attenuating the loudness does someone have the same problem unit has decent sound thanks

It is a common issue with the U3s. The gain is 10X which is a lot imo for a headphone amp but this amp was made for the 0.5V output dongles from the now deleted zerozone listing on ali.

 

[fws]

It is a common issue with the U3s. The gain is 10X which is a lot imo for a headphone amp but this amp was made for the 0.5V output dongles from the now deleted zerozone listing on ali.

Could you explain please? Do you have some more knowledge on the amp? The voltage gain seems to be Av=3.6 (4.45 in spec), and the input handles 2Vrms without clipping. A 0.5Vrms dongle used as source would get only 1.8Vrms out of U3. This is also not that much for headphone amp, Atom Amp+ actually has Av of 4.5, and Topping L30 II 6.5.

 

[kazuviking]

Could you explain please? Do you have some more knowledge on the amp? The voltage gain seems to be Av=3.6 (4.45 in spec), and the input handles 2Vrms without clipping. A 0.5Vrms dongle used as source would get only 1.8Vrms out of U3. This is also not that much for headphone amp, Atom Amp+ actually has Av of 4.5, and Topping L30 II 6.5.

My U3 came with a 10X voltage gain, with a proper 2VRMS input it clips before 2'o clock. I feed with mine with a -28dB as the loudest signal(100mV input) and gets uncomfortably loud at 10o clock. In my case that limits the output to 1.1V max(0.7VRMS) which then you add the pots attentuation and 600Ω beyers and i'm in the μW range of output power. Way way less than the output of modern hp amps.

 

[fws]

My U3 came with a 10X voltage gain, with a proper 2VRMS input it clips before 2'o clock. I feed with mine with a -28dB as the loudest signal(100mV input) and gets uncomfortably loud at 10o clock. In my case that limits the output to 1.1V max(0.7VRMS) which then you add the pots attentuation and 600Ω beyers and i'm in the μW range of output power. Way way less than the output of modern hp amps.

Weird, I have 2 units and neither of them clips when fed 2Vrms and the knob is clean all the way, except for if the headphone itself would distort. As such I've driven 2000Ohm and 600Ohm Sennheisers with lower sensitivity than Beyers from it no problem. Both measurements from the first post give around 7.2Vrms output.

I've been playing a bit recently with U10 and HA400, where the both amps are distorting, and lowering the input signal might have a point, but my experience with U3 which I run on a daily basis, been nothing like what you are describing. So either U3 changed at some point, and you have that pre-change one (mine's was bought in 2021, will check PCB and try to date it later) or perhaps your unit might be faulty. If you would post the pictures of the PCB we could compare if there were revisions.

 

[kazuviking]

Ordered mine in early 2020 and the listing no longer exists. Superaudiobestfriends measurement have the same 10X gain version.

 

[kazuviking]

Checked my PCB and its marked: HY-A-U301 REV:2.0