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Douk Pre-amp Tube Rolling (Russian 6N3P-E)

amirm

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I recently reviewed the Nobsound Douk 6N3 tube preamp. Owner was kind enough to also send me a pair of matched 6N3P-E matched vintage NOS Russian tubes bought from Amazon which cost US $47.50.
Nobsound Douk Audio Preamp Hifi Review rolling Audio 6N3P-E Tube Preamp.jpg


Let's roll them in and see if they make a difference.

6N3P-E Tube Measurements
I let the tubes warm up and was pleasantly surprised how fast they did so:

Nobsound Douk Audio Preamp Hifi Measurements Warm up Riverstone Audio 6N3P-E Tube Preamp.png


I then ran our desktop measurement:

Nobsound Douk Audio Preamp Hifi Measurements  Audio 6N3P-E Tube Preamp.png


Note that I could not perfectly match the volume as it is very sensitive in this range. And there are variability in this type of device that is unavoidable. With those disclaimers aside, mains hum was sharply reduced. To make sure this was not run to run variation, I quickly put the old tubes back in and noise floor went way up as in the original review.

On the other hand, distortion is worse in one channel with the new tubes. With the original both channels clocked at SINAD of 53 dB and we are down to 50 dB now.

In the last tube rolling test people kept asking for frequency response measurements. I explained that I did not expect the frequency response to change in the audible band. There are likely differences in capacitance and such but that affects much higher frequencies. I ran the test this time:

Nobsound Douk Audio Preamp Hifi Measurements  Frequency Response  Audio 6N3P-E Tube Preamp.png


I have left the gain slightly different so the two curves weren't on top of each other. As you see, over the audio band there is no difference at all. Above 50 kHz, the 6N3P-E slopes down a hair faster. That is not consequential in any manner.

I also ran the IMD distortion test which also confirmed what we already know about lower noise floor but slightly higher distortion in one channel:

Nobsound Douk Audio Preamp Hifi Measurements IMD Audio 6N3P-E Tube Preamp.png


Conclusions
Within the vagaries of products in this class and tube designs in general, it does seem like the replacement 6N3P-E tubes provide much lower mains hum. If hum is an audible concern, then replacing tubes can get you there assuming you have measurements such as this. Without it, we don't have enough data to know if there is a reliable conclusion regarding any specific brand or type of tubes.

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

Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
 

fordiebianco

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Confirms my experience that some tubes appear to be noisier than others.
 

BoredErica

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Every time I see that panther and the spilled egg I feel bad for the panther.
The devices that get such a rating, not as much. :)
 

SIY

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Confirms my experience that some tubes appear to be noisier than others.
There's quite a bit of data on that, See, for example, Merlin Blencoe's excellent paper. Note that there's enormous variations from tube to tube (or section to section in multisection tubes) even from the same brand or manufacturer, it's the nature of the beast. Selecting for low noise isn't crazy, but it's not a matter of "Oh, you gotta use the Flemish Amperex 1958 with the H-shaped getter" or whatever.
 

Lambda

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I don't see any value in swapping part without having the schematics of the amp reverse engineered to at lest some basic level.
we don't even know the topology of this amp?!
 
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restorer-john

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I don't see any value in swamping part without having the schematics of the amp reverse engineered to at lest some basic level.

I haven't tried 'swamping' tubes.

Is that a new tweak, perhaps better than cryo? How long do you leave the tubes in the swamp? What about alligators?

;)
 

fordiebianco

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There's quite a bit of data on that, See, for example, Merlin Blencoe's excellent paper. Note that there's enormous variations from tube to tube (or section to section in multisection tubes) even from the same brand or manufacturer, it's the nature of the beast. Selecting for low noise isn't crazy, but it's not a matter of "Oh, you gotta use the Flemish Amperex 1958 with the H-shaped getter" or whatever.
Dear SIY,

Thank you for this, very helpful signpost. Will have a look now.
 

ah-ra

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Without a doubt another great review job. Nevertheless I can't stop wondering why one would really want to know the performance of such a "thing" or is even thinking about buying it (same goes e.g. for the cheap JBL speakers and this "plastic" center speaker from KEF). Considering the time you @amirm have to spend to perform a thorough review like this including testing, documentation and shipping the components I think you should consider focusing on other components. Don't get me wrong. This is just my opinion, but why test these pieces, when there are many more Hegels, Marantz, Denons out there...?
 

NiagaraPete

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I never drank the grape koolaid for tubes but I do wonder how some of the better manufactures stuff measures. Anyone have a newish Luxman or McIntosh that can be tested?
 

ZolaIII

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I never drank the grape koolaid for tubes but I do wonder how some of the better manufactures stuff measures. Anyone have a newish Luxman or McIntosh that can be tested?
No need for the expensive ones and of course this is becoming ridiculous.
But this one mesure to good for the sakes of testing (along with some other things that don't really fit the purpose), we need a mid ground with approximately 75 dB SINAD at 1W and THD of about 1% (if such can be obtained) and how it performs all the way to the 1 mW so that it can be set in the mid grounds that SINAD doesn't fall to much but we still can hear second order harmonic impact and that it retains characteristics of typical tube progressive distortion gain increase (meaning not just as pass trough stage buffer). Then you can start testing impact of different values and be able to verify them both ways (meassuring and listening). It will still need more methodic work of course.
For the gaid line purpose only:
Also it would be good to see impulse response comparation (from all amp classes and on old school speakers and more stiff newer ones) if we ever hope to get closer to solving the paradigm of why do people realy prefer tubes.
Just my 10¢ on topic.
 

brandonhall

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Without a doubt another great review job. Nevertheless I can't stop wondering why one would really want to know the performance of such a "thing" or is even thinking about buying it (same goes e.g. for the cheap JBL speakers and this "plastic" center speaker from KEF). Considering the time you @amirm have to spend to perform a thorough review like this including testing, documentation and shipping the components I think you should consider focusing on other components. Don't get me wrong. This is just my opinion, but why test these pieces, when there are many more Hegels, Marantz, Denons out there...?
Amir is limited by what folks send him. Some companies send in stuff but it's usually members who send stuff. Many owners of big, high-end equipment aren't willing to part with it for the review process. You'd think an established manufacturer would immediately send new gear to Amir for review and exposure. I'm looking at you Emotiva. But, alas, they rarely do (Topping and SMSL are exceptions) so the question is "why"
 
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pseudoid

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Thank you @amirm for the follow-on.
I am wondering if you can put yourself in our [collective] shoes and possibly change the sequence of the magic that you perform.
Subjective listening first, followed by the objective measurements, and then another listening session to confirm the first session results.
Would you have been able to hear the 15dB 60Hz hum reduction or the increase in THD?
Like us, mere mortals, that only have our ears to make such evaluations?
 

NiagaraPete

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Like I said I have no tubes but I do have some Linn gear. I've already sent a DAC in maybe I'll see of Amir wants to test some Scottish tech.
 

H-713

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Tubes with the same number (but from different manufacturers or different eras) often had significant differences in internal construction. Differences in linearity and noise between different makes / eras of the same tube are well known and documented.

And if you think it's only tubes that suffer from this, compare a TI 5532 to an original Signetics or JRC 5532. Fun stuff.

@amirm , any thoughts on doing a comparison between different op-amps? Doug Self's measurements are pretty old and there's quite a bit of neat stuff released recently.
 

doug2761

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I used futz around with tube gear. I liked the visual glow of the tubes and the nostalgia. Kinda like spinning LP record. I can’t say there was a particular tube sound I got. Ultimately I switched to solid state gear to improve reliability and remove these very same tube to tube variations. Good listening experiences with both technologies. Measurement wise the solid state gear is far superior with much lower energy demand.

Archimago did some surveys with test tracks on audibility of different levels of distortion. It’s surprising how high some of those measures need to be in order to be audible. You can still listen to those test tracks to hear for yourself and gauge your own tolerances. I still get emotional for tube gear but don’t think I’ll ever go back.
 
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amirm

amirm

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@amirm , any thoughts on doing a comparison between different op-amps?
I have done a number of those as well with no difference seen. I did it for Topping DAC and at least once for Hypex based power amp builds.
 
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