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:
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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.
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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:
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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:
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Mains and power supply noise likely contributes to the lackluster signal to noise ratio:
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Crosstalk was not good:
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Frequency response was nice though:
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Before I forget, this thing has tons of gain. I think I measured about 22 dB. With that comes large rise with distortion:
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Power supply noise is the main frequency dependent distortion and noise:
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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:
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Reducing that to two tones, we get similar results to our THD test:
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Finally here is our channel matching test of the volume control:
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Il aurait été préférable d’avoir moins de gain ou un commutateur de gain afin de pouvoir actionner le contrôle du volume là où il est plus adapté entre les canaux.
Conclusions
Selon nos normes de transparence en ce qui concerne le bruit et la distorsion, le Douk 6N3 est de la camelote. Selon les normes des personnes qui veulent un « son à lampes », cette boîte tient au moins cette promesse avec une grande quantité de seconde harmonique. Comme l’a dit Forrest Gump dans le film, « c’est tout ce que j’ai à dire à ce sujet ! »
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