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Douk HiFi 6N3 Vacuum Tube Preamp Review

Rate this product:

  • 1. Poor (headless panther)

    Votes: 113 66.5%
  • 2. Not terrible (postman panther)

    Votes: 41 24.1%
  • 3. Fine (happy panther)

    Votes: 11 6.5%
  • 4. Great (golfing panther)

    Votes: 5 2.9%

  • Total voters
    170

amirm

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This is a review and detailed measurements of the Nobsound Douk Hifi 6N3 Tube Preamplifier. It is on kind loan and is on sale on Aliexpress for US $110.

This is a two box package:

Nobsound Douk Audio Preamp Hifi 6N3 Review Tube Preamp.jpg


Large volume control is nice to have. The amplifier is based on a pair of 6N3 tubes as indicated in the name. There is also a 6Z4 rectifier tube to really make the heart of tube lovers glow. I can't tell the branding on either tube.

In a nod to make this a "high-end" amplifier, an external power supply box is provided as you see on the right. Shame it doesn't look anything like the amplifier itself.

Nobsound Douk Audio Preamp Hifi 6N3 Review back panel power supply Tube Preamp.jpg


Nobsound Douk Hifi 6N3 Measurements
Given the unbalanced input, we follow my standard protocol of feeding the unit 2 volts, and adjusting the volume until we get the same voltage out ("unity gain"). This is what we get:
Nobsound Douk Audio Preamp Hifi 6N3 Measurements Tube Preamp.png


Sadly this lands the potentiometer in the region where it loses fair bit of channel matching so the output is different in one versus the other (2 volts vs 1.7). I could not do much about the mains hum which you would hope would be better taken care of in an external box. That doesn't impact SINAD though as it is dominated by the 2nd harmonic to the tune of -55 dB. While by our standards this is horrid, folks buying tube amps kind of expect this and it is good that we essentially have that one component of distortion (third harmonic is down to -95 dB).

Unit warmed up fast enough:
Nobsound Douk Audio Preamp Hifi 6N3 Measurements Warm up Tube Preamp.png


Mains and power supply noise likely contributes to the lackluster signal to noise ratio:

Nobsound Douk Audio Preamp Hifi 6N3 Measurements SNR Tube Preamp.png


Crosstalk was not good:
Nobsound Douk Audio Preamp Hifi 6N3 Measurements Crosstalk Tube Preamp.png


Frequency response was nice though:
Nobsound Douk Audio Preamp Hifi 6N3 Measurements Frequency Response Tube Preamp.png


Before I forget, this thing has tons of gain. I think I measured about 22 dB. With that comes large rise with distortion:

Nobsound Douk Audio Preamp Hifi 6N3 Measurements THD+N vs level Tube Preamp.png


Power supply noise is the main frequency dependent distortion and noise:


Nobsound Douk Audio Preamp Hifi 6N3 Measurements THD+N vs Frequency Tube Preamp.png


Multitone test shows that if you are perceiving "resolution," it is not because of the amplifier is any good with that:


Nobsound Douk Audio Preamp Hifi 6N3 Measurements Multitone Tube Preamp.png


Reducing that to two tones, we get similar results to our THD test:
Nobsound Douk Audio Preamp Hifi 6N3 Measurements IMD Tube Preamp.png


Finally here is our channel matching test of the volume control:
Nobsound Douk Audio Preamp Hifi 6N3 Measurements Channel matching Tube Preamp.png


It would have been better to have less gain or a gain switch so that you could operate the volume control where it is more matched between channels.

Conclusions
By our standards of transparency with respect to noise and distortion the Douk 6N3 is junk. By standards of people who want "tube sound," this box at least delivers on that promise with copious amount of second harmonic. As Forrest Gump said in the movie, "that is all I've got to say about that!"

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

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Walter

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Unlike most tube gear Amir has tested, this at least does a proper job of only emphasizing the 2nd harmonic, which is what supposedly gives tube gear its appeal. Too bad it fails on every other respect.
 

GWolfman

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Multitone test shows that if you are perceiving "resolution," it is not because of the amplifier is any good with that:


Nobsound Douk Audio Preamp Hifi 6N3 Measurements Multitone Tube Preamp.png

Weird, it almost looks Iike someone drew a line with a ruler at ~68dB. Ok, it's not a hard limit, but odd that it's fairly consistent.

On another note, why would anyone ever need that much gain for a pre?
 

GWolfman

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Out of curiosity, anyone know the VOUT of the power supply? With 4 pins I'm guessing there's either two +voltages or +/- rails.
 

pseudoid

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Is the Headless PinkPanther taking some time off? Or is this your way of saying that even the PinkPanther only needs one arm to operate retro thingy?
Nobsound does manufacture (design? peddle?) some Linear PS that look attractive from both performance and price perspectives but I am not aware of any that are "2 way" (Chinese for dual output). There is much 60Hz powerline harmonics in the FFT results (2nd plot); so it maybe safe to say this is not a linear power supply w/o opening the can. << that one is a hint to @amirm, if it's not too late!:rolleyes:
 
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amirm

amirm

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There is much 60Hz powerline harmonics in the FFT results (2nd plot); so it maybe safe to say this is not a linear power supply w/o opening the can.
There is some verbiage about it being a switching supply which is confirmed by the universal input voltage.
 
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amirm

amirm

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Is the Headless PinkPanther taking some time off?
No, he is always a sucker for more work/food. But is demanding overtime pay so I pulled in his back up....
 

pseudoid

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There is some verbiage about it being a switching supply which is confirmed by the universal input voltage.
I think I am mistaken as the 6Z4 is possibly being used as the rectifier circuit and the "power supply" maybe just providing it some transformer taps.
Snag_396cae06.png
 

respice finem

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As a "normal" preamp it would be clearly headless panther territory, but considering its desired target, I gave it a postman panther too.
 
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solderdude

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Only 2nd harm at -55db may well be hard to hear at full power (when used as a pre-amp into a power amp).

As this is a pre-amp the output voltage, in normal listening conditions, will probably not go much beyond 0.5V (peak in music) where distortion will be even lower (guessing -70dB or so) but that hum may be its downfall.

Sometimes moving exposed tubes and open frame designs a bit away helps a bit.

It is an SMPS Douk describes it as:
With Hi-end switching power supply: Input: AC85-265V Output: DC12V / 2A
Indeed weird they did not go through the trouble of using a similar enclosure.

Chances are inside the amp there is an oscillator generating the HV which is then rectified by the tube just for the sake of having a tube rectifier (as some tube guys swear by it).

I wonder how they measured the following spec:
Distortion: <0.003%
As this would mean distortion would be -90 dB which, even ignoring the hum and noise, probably cannot be reached.
Then again, specs given by certain vendors can not be trusted anyway.
 
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nyxnyxnyx

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Unlike most tube gear Amir has tested, this at least does a proper job of only emphasizing the 2nd harmonic, which is what supposedly gives tube gear its appeal. Too bad it fails on every other respect.
This product is definitely more truthful to the value that tube amps are supposed to have so it's fine with me.
Lotta other tube amps have splendid marketing and honeyed words but when Amir measures it it wasn't even close to having the characteristic of a tube amp (dominant 2nd harmonic), while they are more expensive than this model and measure inadequate in other aspects as well.
 

F1308

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Are we to vote based just on sound performance or the good lookings are a must-have to be considered ?

Planning to ditch it next to a never opened encyclopedia...? Top notch.

You said yes, but wished it worked flawlessly...? Imagine placing a Topping PA5 inside that beauty.

Not enough room ? Time for case makers to resize. See: PA5 is 129mm x 166mm x 41mm.

Hurry !!!!

While we wait, PA5 could be placed close to but a little behind, not necessarily seen, just heard. Any discount when bought as a set, please ?
 
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F1308

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RCA !
Look, no need for new cables !
They even might come in the pack, although nothing is being said.
 

Mnyb

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Voted poor for shoddy design with the missmatched ps .

The things that wrong with harmonic distorsion is the word "harmonic" it's just a math thing where things reocur in a serie in this case multiples of the source frequency.

But harmonic as a word radiate bliss harmony and peace ( cue in pan flutes and pictures of laughing children...)
 
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