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Nobsound E6 Preamp Uses Directly Heated Tubes

Haven't tried it yet. Was replacing resistors yesterday. Found a 230k resistor correctly color banded that read 2.5m! Same resistor on opposite channel read 270k. Maybe an error at Allen Bradley? Will get the e6 and plan my next move. Can't wait...weeee!
 
Acopian transformer came in yesterday and the pio caps are coming in today( according to usps email ?!). was looking over the 3rd phase mod and I do have 20uf poply caps. can't see from the photo what value the fg nichicon cap is...1000uf/ higher voltage?


Lenco803 said:
Finished. Better bass and tone.
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Okay, all assembled and warming her up. Probably will need some time for the unit to reach proper temp. Seller of pio' s was kind enough to gift me a similar 2uf pio.
 

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raycarr00 said:
Acopian transformer came in yesterday and the pio caps are coming in today( according to usps email ?!). was looking over the 3rd phase mod and I do have 20uf poply caps. can't see from the photo what value the fg nichicon cap is...1000uf/ higher voltage?
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Yeah, just a higher voltage that was already in my stash.
 
Tested five nichicon fg's and only one tested at 1000uf+. Others were at about 940's. Can't wait to try her out in the next few days with several different amps, speakers. Was going to work on an audible illusions modulus pre, but figured I'd have some fun,first. Thanks for the mod.
 

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Okay, on the third hour of listening to the new mod and it's definitely an improvement. Still leaves me wanting a bit more treble; crisper , loud cymbals. Plenty of bass, but not overwhelming. Otherwise, it's dead quiet and much more mellow sounding.
 
raycarr00 said:
Okay, on the third hour of listening to the new mod and it's definitely an improvement. Still leaves me wanting a bit more treble; crisper , loud cymbals. Plenty of bass, but not overwhelming. Otherwise, it's dead quiet and much more mellow sounding.
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Those Russian PIO’s can be a bit mellow for sure. Maybe try some CDE caps…
 
Is this another single stage pre where it reverses absolute phase?

These are single Triodes aren't they?
 
I’ve done plenty of cap listening over the past 40 year and coupling caps will effect the overall sound and I know for sure CDE caps will add a little treble lift not those little smd caps.
 
So, could one of you guys ( @Lenco803 , @raycarr00 )who have their E6s out of the case take a meter and make some resistance and voltage readings?

It shouldn’t be too hard to take a few basic readings. I’d be happy to walk you through the steps. It would be interesting to know what operating points are being used for these tubes.

My bench is occupied with a breadboarded preamp project so I can’t crack mine open.
 
Oasis8 said:
Is this another single stage pre where it reverses absolute phase?

These are single Triodes aren't they?
Click to expand...
The tube is a pentode but it’s wired in triode in an effort to reduce gain and lower the tube’s impedance.

Yeah, the E6 has a single gain stage. And each time the signal goes through a single tube section it inverts absolute phase. But it’s unlikely that you would notice it. There’s a website that allows you to listen to the same recording with different absolute phases but it turns out that almost no one can hear the difference.

The fact is that modern recordings are not recorded in a single absolute phase. Instruments on the same song are not even in phase with each other.

For example, two guitar players play through two different amps. If the amps have a different number of stages then their absolute phase is different. The recording engineer just puts a mic in front of each amp and records them. They don’t check to see how many gain stages each one has. So the two guitar tracks are not in absolute phase with each other.

Or consider how drums are recorded. The kick drum pedal / mallet hits one side of the drum head and the mic is placed on the other side. Yet, when a snare drum is recorded the mic is almost always placed on the same side of the head that the drummer hits with the sticks. So the kick and snare are not in absolute phase.

You can switch wires around and see if you prefer one to the other but you'd probably find that your preference, if you even have one, differs with each song.
 
i can do so tomorrow. sorry, up until 2am last night....
are the measurements based on the tube's diagram? pins 1, 3, 5 and 7
 

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Thanks to @raycarr00 for taking some measurements on his E6! This shows the basic operating point used for the 2J27L.

E6 Op Pt.jpg
The tube is actually a pentode but it’s wired in triode with the plate, G2 and G3 wired together so I’ve simplified the diagram by showing it as a triode. Also the 10k plate load is actually a pair of 20k resistors in parallel. I don’t know anything about the specs of smd parts but I assume they did this to increase the wattage rating, which doubles when two resistors are in parallel.

The literature on the E6 says something about it running on 105v. As I suspected, this is the supply voltage. The tube itself is actually running at ~65v. Current is calculated at .004A or 4mA. So the total dissipation is ~0.26w.
 
I know I am late to this conversation but wanted to throw in my 2 cents. I have gotten Russian tubes for the 2J27L and 2p29L. My experience with the 2J27L was an immediate improvement over the 2p29L and the Chinese 2J27L. The sound was much fuller and detailed. The Russian 2J27L were fussier to get them seated right. Now I will let them burn in a bit. Then I will see about exploring the other mods you all are doing. Thanks for the advice. This is entertaining. This little unit is really very good.
 
FlaCharlie said:
I recently noticed this new preamp that uses directly heated tubes.

Many people prefer the sound of directly heated triode tubes, though they are typically used as output tubes in SE (single ended) amplifiers. The most commonly used DHT output tubes are the 2A3 and the 300B, both of which are currently produced by a variety of manufacturers.

But preamps that use DHTs (directly heated triodes) are, as far as I know, very rare. This is the first time I've seen a mass produced DHT preamp.

View attachment 2692028
The tube used in the Nobsound E6 is the 2J27L, which is not very well known. You may also see the tube number translated a bit differently into English. This is common with Chinese and Russian labels. The actual label is 2Ж27Л. It's a pentode but it's connected in triode, as pentodes often are when used as a preamp tube. The tubes used in the popular FX are also triode-strapped pentodes.

One of the key features of the 2J27L is that its 2.2v filament draws very little current - only 56mA. Such low filament current tubes are often called "battery tubes" because they were generally used in battery powered radios where their low current draw ensures adequate battery life.

When I was breadboarding a variety of tube types for a preamp project a while back, one of the tubes I tried was a close cousin of the 2J27L called the 2P29L. In all, I tried about a dozen different tube types and the 2P29L was (to my ears) one of the top 3. The others were the 6V7G and the 1626. In the end I built the preamp, which I dubbed the Boogie Factor, using the 1626.

But the 2P29L was impressive and, although I didn't build anything with it, I posted a thread over on DIY Audio about the circuit I breadboarded since a lot of European DIYers are into Russian tubes.

https://www.diyaudio.com/community/threads/2p29l-preamp.336620/

Seeing that this new preamp used a very similar tube, my interest was piqued and I decided to give one a try. I've been listening to it for a couple of weeks now and I'm glad that I did.

At the time I ordered it they were on sale on eBay ($50 shipped) but I decided to pay a bit more and get it from Amazon ($60 shipped) just in case I decided to return it. They offer free returns and it's a very simple process. No need, though. I'll be keeping it.

I don't mean for this to be a full review, I just wanted to give others a "heads up" on it since inexpensive Chinese tube preamps like the FX are so popular here. Perhaps someone will do a head to head comparison between the two.

I don't own an FX but some may recall that I did breadboard the tube it uses during my earlier experiment. I tried it at the abnormally low voltages used in the FX and also at higher voltages, closer to what the tube data sheet recommends. At lower voltages it sounded better than I expected. Running it at more "normal" voltages was a huge improvement. Still, it was near the bottom of my list compared to the other tubes I tried. YMMV, as always.

I'm not very good at describing what I hear but so far I'm liking the Nobsound E6 a lot in terms of overall sound. It does require some break-in. Audio memory has its limitations but it seems very similar overall to what I heard with the 2P29L on the breadboard. So that's a positive.

And, unlike the FX, they claim that the tube is being operated at a higher voltage, supposedly 105v on the plate. When I breadboarded its cousin, the 2P29L, I was running very similar voltage (112v on the plates) and many DIY builders run 2P29Ls in the same range, sometimes even a bit under 100v. So, if the tubes are operated at normal voltages, that's another positive.

There some negatives, however. I'm not too fond of the layout with the input jacks in the back and the output jacks in the front next to the volume pot. I'd much rather see all of them in the back.

To some that might be a deal breaker. That said, anyone who has pulled tube amps from old console stereos knows that they commonly have their inputs in the front. I even have one whose input jacks are right in the middle of the chassis, surrounded by tubes. Not ideal, but I guess I've learned to overlook such issues if the sound is good.

Those who are heavily into tube rolling might also be disappointed. It comes with the Chinese version of the 2J27L which, like most all vintage Chinese tubes, is simply a copy of the Russian version. As far as I know, those are the only choices. I ordered some of the Russian ones from a Ukrainian seller so I'll eventually see how they compare. Most people seem to find that Russian tubes sound better than the Chinese ones. We'll see when they arrive. But, at this point, I'm happy with what I'm hearing.

My bench is currently occupied by a breadboarded, directly coupled SET, project which I've been working on sporadically, so it will be a while before I can open the E6 up and measure things. But one of the things I want to see is how they have the filaments wired and exactly what the operating points are.

Depending on the stoutness of the filament supply it's possible that the 2P29L can be rolled in safely since it uses the same pin arrangement. The 2P29L filaments run on the same voltage but they draw about 2x the current. Such a swap can be risky and this is not normally something I would try or recommend. On the other hand, the current draw of these "battery tubes" is quite low - a 2P29L draws less current than one of the tubes used in the FX, for example. And one of the FX tubes draws over 3x the heater current of the 2J27L.

So, if the filament supply is stout enough that it can be used safely, the 2P29L might provide another tube rolling option.

Another difference is that the 2P29L has a lower mu (amplification factor) of ~8 compared to ~16 for the 2J27L used in the E6. In comparison, I believe the tube used in the FX is somewhere in the 30 to 35 range, which is more than necessary in many cases. Some people complain that the volume control of the FX is too touchy - that it's difficult to make precise adjustments because it gets loud too quickly. This little Nobsound E6 doesn't seem to suffer from that problem. It's quiet too, no hiss or hum even with the volume at max.

Nobsound / Douk is also not totally forthcoming about another characteristic of the 2J27L. In stock form the tube is enclosed in an aluminum shell and has a plastic knob on the top to make it easier to insert and remove from its loctal type socket. Here's a pic:

View attachment 2692029
They obviously realized that a metal tube wouldn't fly in terms of marketing so they ditched the aluminum shell and removed the glass tube from it. It does look more familiar like that and I did the same thing with the 2P29L, which uses the same metal shell.

All the glow, however, comes from LEDs mounted under the tubes. None of the "battery tubes" I've tried had any noticeable glow due to their very low filament voltage and current. On the positive side, the LEDs used are orangeish and not ridiculously bright. Much better than green, blue or red, which just looks wrong to me.

While the description of the E6 suggests that you might want to try the Russian version of the 2J27L, what they don't tell you is that you will need to cut off the shell because, even if the looks don't bother you, the opening in the top of the preamp is too small to insert the tube unless you remove it from the aluminum shell. This holds true for both the Russian and the Chinese version of the 2J27L.

And removing it from the shell creates another issue that must be dealt with. These tubes use a loctal base which, just like the more familiar octal base, has a central locator pin that ensures that the tube is oriented correctly when you plug it in. When you remove the glass tube from the shell the locator pin is part of the aluminum base, which is discarded. So you need to mark the position of the locator pin on the glass before removing the tube from the base.

The description does mention that the stock tube is marked in this manner and that if you insert the tube wrong damage will occur but it doesn't give any background information.

Now if you forget to mark the position of the locator pin it is possible to identify the locator pin's position using a multimeter. That's because the pins on either side of the locator (pins 1 and 8) are the filament. So if you find two adjacent pins with continuity between them the locator pin would be between them. That said, it's probably safe to say that many who buy these little Chinese preamps don't own a multimeter.

I'd also note that while the tube type is marked on the aluminum shell, there are no markings at all on the glass tube itself since it was never intended to be removed from its shell.

So, while this preamp certainly has some quirks, you might consider giving it a try.

I'm not sure who developed it. Nobsound / Douk seems to be the distributor and their eBay listing shows it branded Cadisi, which I've never heard of. The one I purchased through Amazon is branded Nobsound. They are obviously the same, though.

As for the sound . . . I'm impressed but so far I've only listened to it for a limited time using a SE tube amp. I'll be trying it with my Aiyima A-07 Class D at some point I'm sure.

With the tube amp, mostly streaming jazz, I would say that it's very clear, open and detailed. This aligns with my previous experience with directly heated tubes. It has excellent imaging and the highs are very spacious and airy. It seems well balanced but, to be clear, I haven't been listening to any thumpy, bass heavy, material.

So only first impressions so far and YMMV, as always. Check it out if you're so inclined.
Click to expand...

Sorry for being late to this thread.
I've had the Douk E6 for some time now running it of a "beefed up" mobile charger - although still being "only" 5 Volts.
I'm to receive a variable SMPS with up to 35 volts 5A supply. Have you any experience with giving the E6 more than the recommended 5 Volts?
Have also bought the russian tubes from Ukraine. And next step will be replacing the 4 grey square coupling caps with something better. Said to bring this lil' marvel a lot closer to near high(er)-end. Well see...
 
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