Nobsound E6 Part I Douk Direct Heated Triode Preamp

Click pics to enlarge. From L: Reisong 1:1 Transformer; E6 (note the rear power supply plug is in 2 segments, 5*52.1 supply cord with adaptor to required 5.5*2.5); ETA Preamp; 6J4/6P3P Preamp.

Review: Nobsound (Douk) E6 Direct-Heated (Triode) Preamp, Part I
Letter from Shenzhen (23-10): Antagonistic or Complementary? vs Eastern Transmission Audio 6N3 Preamp

Part II, which details the Capacitor Mod, and feedback from my NYC friends, had been published.

Part III, which tells of Phase Reversal and more ways to combat Microphonics, also published.

Editor: 1) As detailed below, the Review Unit was a loaner; 2) Just before writing this article, I was able to confirm a few technical aspects from the company; 3) Before writing this article, I read the Amazon comments and there are misconceptions there that should be corrected.

How It Came About Not so long ago, I was on wechat with our own HK Author Shawn P, and he mentioned his interest in the Nobsound (Douk) E6. It just happened that I have also noticed this for a long time. It‘s a tiny preamp that nonetheless employs a Direct-Heated tube (DH)!!!! As a long-time purveyor of DH Triodes, of course it came under my radar! Just like our other HK author ELO’s interest in Aiyima T9 spurred me on to my Aiyima adventures, I decided to pursue this one.

I first contacted the TB Nobsound (Douk) Customer Service. Despite some delays, the fellow eventually through wechat referred me to Vivian of Administration. The lady was nice (but cautious, for good reason), and meticulously verified me as owner of this Blog. After a while, I was loaned the E6 for Review. Although I didn’t buy it through Taobao, I’m still providing the details for you.

https://m.tb.cn/h.UrSBNMH?tk=bKVCdQqfg4E

Shipping The package was a surprise. It came in a small plain cardboard box, no logo whatsoever. The unit had the tubes installed and bubble-wrapped, with a USB cable on top and not much else. I’d imagine it could suffer damage in some circumstances.

Ergonomics There’s not much to it. It’s not much bigger than a deck of cards. The back has only the Single RCA Input and DC Input. The RCA Output is at the front, together with the Volume Knob/On-Off Switch. Having the Output at the Front is a Form Factor that takes some getting used to for most audiophiles. No 5V Power Supply included (everyone has some USB chargers). At Turn On, there is no sound until the Relay clicks a few short seconds later. For those who use solid state amps I’d wait a little longer (say, 1 minute, for safety against DC offset, in general) before turning on the amp. Ah, it’s too bad its face and rear plates are in gold - I wish a black or grey version option is available. I ain’t no fan of gold, like the Jadis and Sonic Frontiers that sell to Asian markets.

Specifications and Technical Aspects
This VERY unusual Preamp employs an obscure 2J27 DH Pentode (stock is Chinese). Wow! Direct-Heated! IT TURNED OUT THE E6 IS CONNECTED AS A TRIODE! ALL of the DH Preamps that I know of are Triodes and quite expensive. My own Manley 300B is an example (much cheaper would be the interesting Transcendent 300B Preamp Kit). And, in the recent Shenzhen Audio Show I heard the excellent Line Magnetic Foshan 安歌 2A3 Preamp (around RMB 20k), and it was great! If I were to start over serious, that would be on the top of my list! I enthusiastically applaud Douk for designing this Preamp out of the blue! At this bargain price, people don’t know the efforts that went into it. DH tube and low filament voltage mean high variability and susceptibility to Microphonics, as you shall see.

The Unit employs a 5V DC power supply, and only comes with an USB to DC Plug (5.5*2.5; the most common type) that even the manual suggest you to use with your USB charger (one that delivers above 0.34A). That’s not what I used of course! I used my Wanptek SMPS. The display shows a constant draw of 0.4 mA, no more. As some 2.5 sockets will accept 2.1 (standard for DC power supply plug) I tried without the adaptor - no go. So you need to make sure it’s 5.5*2.5 (with an adaptor in my case).

The 5V DC Power Supply goes through a switching supply to up it to 105V Rail for the HV B+. This is common in digital amps (usually 12V). In my own experience there is precedence in the ancient (and excellent sounding) Japanese Elekit TU-875 Preamp (which our ELO uses right now), which employs a 7V DC Input, which then is internally raised to higher B+. Fascinating (Douk told me it’s not easy to implement because of the very low filament voltage).

I was told by Douk that the Amplification is ALL tube (and it sounds as such, see below). As you can see from the pics at the bottom, crowded around the tube sockets are Surface Mount Components (SMC) of resistors and capacitors, which offer no route for upgrade (neither are there cables inside). But, fortunately, the 4 Grey Coffin Capacitors turn out to be for Input and Output Coupling. They are unusually high in Value, at 1.0uF 250V. This is great news for those of us who want to modify! Warning: very little room inside! Most big boutique caps would NOT fit!

Shock Absorption and Microphonics At first, I was greeted with the ringing sound of Microphonics, which died down after some seconds. The unit is very sensitive to impact. Because of its tiny size and lightweight, it can easily get knocked around even if you just want to change the volume. I put it on a solid slab of rubber shock absorber (now is different from the 2 cubes used in the top pic. Once the unit stabilizes after turn-on, there is no microphonics. This is due to lack of reinforcement in the internal tube structure. Some Amazon users though had continuous high-pitched sound, which may be a different matter, like a faulty tube. Ringing upon some form of shaking is normal for the Chinese tube. I would advise against using this on the desktop where you work, especially if your loudspeakers are also on the tabletop. Your moves (and those of your loudspeakers) may shake the table and cause trouble. Now, why bother, you may ask? Because of the Sound, of course! Also, before you move on to below, in the tube rolling section I have a very useful surprise, so make sure you read it!

Sound This is a surprise, to say the least. I’m not the only one who harbors the opinion that the larger the tube (and structure), the better the sound (hence 6SN7 > 6CG7 > 12AU7; for some too Globe > ST > GT, thought I have my reservations about that). With its big envelope (like a 6SN7 in size but housing only one triode) and large structures (the plate is about 2/3 the size of the output tubes 6V6 and EL84) I expected a bigger and sweeter sound, but I was still floored! Prior to receiving this, I have been using the modified Eastern Transmission Audio (ETA) 6N3 SRPP Preamp (Review and Mods), which is similarly priced and a formidable rival. Swapping in the Douk, the sound was instantly bolder and sweeter. Images were larger and fleshier, and so sweet that not a trace of digititis was to be had. Gain is still on the high side but not quite as much as the ETA. The amp is also very quiet, no background noise.

Does the E6 trump the ETA? It gets fascinating. A quick answer is - No. With stock tubes, great as it is, compared to the ETA, the E6 does have its weaknesses. The first is its Control, which, though not bad, does become less firm in classical big moments. The second is its Dynamic Shadings are less sophisticated. Also, the E6 is more saturated in color, but this is likely a plus rather than a minus for most people. Or, put it another way, the ETA has superior neutrality, control, microdynamics and details (or integration of the latter two). On the other hand, the Enhanced Presence of the E6 is amply evident - it puts the soloist forward and is very emotive, not something that a cheap (or even very expensive) preamp can do! 

For musical examples of ETA vs E6, in my recent Classical Streaming article I actually provided some, duplicated in the shaded box below ((if you want to read it in context, just roll down, or click here):

Either/Or: 2 Preamps
Recently, I was loaned a Nobsound (Douk) E6 Preamp, which uses the unusual 2J27S Direct Heated Tube. The chassis is very small and the tubes sticking out are big (almost size of a shorter vintage 6SN7) but the sound is big. Review to come. Before this, I have been using the modified Eastern Transmission Audio (ETA). In a nutshell, the diminutive Nobsound/Douk has a bigger, bolder sound, bigger images, but less control. The ETA has somewhat smaller images but greater depth and better dynamic gradations.

I stream mostly on NML, which has a leaner sound sometimes. I also do Tidal, which seems fuller, but colored. With some recordings, neither seem perfect. Sometimes switching from one preamp to the other brings improvement, even change of view of the performance. Let me just cite 2 examples using albums covered above.

When I streamed the Van Kuijk recordings with the ETA, I frequently feel the sound to be a little on the white side. This is a consistent observation of the Alpha label. When I switched to the E6, the strings instantly became just a little fuller sounding. Just what it needs. On the other hand, when I streamed the Schubert Trios with the E6, things are just not as woven as I’d like. Switching to the ETA firms up the piano and knit things together.

You get the gist. Which one is more accurate? I don’t look at it that way. Truth, whether in audio or politics, has many facets. In audio, unlike in reality, we can search for truth as long as we want. Nothing is forced down our throats.

Click pic to enlarge. Note the Outer Perimeter of the Sleeve is folded inward on the top plate.

Tube Rolling There is not much choice. Aside from the stock Chinese tubes, there is only the progenitor Russian version of 2J27, or in transliterated Chinese notation 2米27, which is how it’s designated on TB (link below). And so I bought 2 from this fellow in Hebei. Cheap. Western readers shall find plenty (and cheap) on Ebay, most shipped from Ukraine, where else!

https://m.tb.cn/h.UJojzmO?tk=OiECdQq2gkb

Problem is, the Russian version is the original metal tube. They would not insert into the E6 as the diameter is just a little bigger than the holes. This is really silly - I guess Douk thinks the tube looks much better in glass form (it does) but to us old geeks, plugging in the metal tubes would make the E6 look like a Step Up Transformer (SUT), no problem. BUT, SO, you need to take off the outer armor. Douk takes them off the Chinese ones but they don’t offer the Russian (yet), so you have to DIY. In the pics at the bottom, I’ve provided what I hope are enough guidance. If you plan to do it, you MUST read everything carefully, particularly pin orientation.

There is little question that (as usual) the Russian version is superior. While just as bold and sweet, it firms up the mix and is more dynamically nuanced. It makes the E6 a more rounded preamp even in comparison with the ETA. It now wears its own attributes proudly, and there is no serious downside.

AND, importantly, a side-benefit! The Russian tubes also more sturdy, and certainly much less microphonic. Yes, a sudden jolt (or tap on the chassis) can still induce some ringing, but they are much shorter in duration and muted.

Conclusions

• Sonically, the E6 is a miraculous product for those who can use it. It offers a glimpse into the world of DHT output tube, at crazy low cost. It’s basically unique. Being a budget product (albeit one designed with love), it has limitations, but it’s a window into another world, far away from the usual humdrum of low-end products (so is the ETA, more conventional in design but good sounding). In fact, if you get both the ETA and E6, you shall have a good glimpse into the world of Preamps - they are like Yin and Yang in a way, challenging but supporting each other rather than having you say A is better than B, and B is better than C...ad nauseum. No better musical (audio) education at this price. These two should provide a reality testing for much pricier rivals. 

• Even after Tube Change, the differences remain: the E6 is "artistic", with great Presence, and paints in broader, "Live" strokes; the ETA is a more meticulous craftsman who arranges things in order, and minds every little detail.

• If you cannot provide better isolation for the E6, DON’T get it. If you use it on your desktop or have your loudspeakers on the desktop, and you type and vibrate the desk (not to mention when you pump your fist in frustration), it’s not for you.

• The Russian 2J27 is a definite PLUS for sonic as well as microphonic reasons. Order a couple more in case you mess up removing the shell (not likely). Believe me, It’s worth your while.

I now alternate between my ETA and Nobsound. I LOVE both for their different strengths. Now, those caps of the E6...As usual, watch this space...Obviously, I intend to purchase the Review Specimen.

Removing the Outer Metal Sleeve

Before doing anything else, The FIRST thing you do is to look at the bottom. The Center Guide Pin (which is part of the metal sleeve) has a Protruding Ridge. You MUST use a MARKER

and mark the two pins to the right and left, because after the glass tube

slides out, there is no orientation. 

After the tube is taken out, the 2 pins in question should be clearly marked.

Anatomy of the Tube. The Metal (Tin-like and soft) is folded on the top metal disc, 

beneath which are many cardboard rings（Khaki color; you can see many out-focused in the background) to adapt to the dome top of the glass tube.

First, remove the top black screw.

I use a sharp-nosed Wire-Cutter for the job. Nibble at the edge and create a defect,

 cut horizontally and roll back the metal. There's a lot of clearance

between the top metal plate and the tube, so don't be afraid.