Nobsound E6 Preamp Uses Directly Heated Tubes

[bridger2086]

Great input, this I think should help potential buyers understand it better, sort of a tube filter with gain.

Few more observations:

-the bass bump/bloat that was present when first hooking it up has somewhat diminished now with 50 or so hours on it. A bit of a shame really, as the full range speakers in blh enclosures have a rather lean and fast bass.

- doesnt really add as much value (to my ears) with an analog source (turntable). With digital, it sweetens in the right places. Maybe that was their primary goal with this device.

I have read positive reports about Douk Audio from a few sources, that had first person experience with the company and its people, most notably Cheaptubeaudio. According to them, Douk Audio has real designers that do try and care. Exactly how much is very hard to judge, given a completely different business model..

 

[M70AB2]

Yesterday, I replaced the input and output capacitors with WIMA MKS 1uF. I have MKPs, but they are too large.

Only listened for several minutes on my garage stereo. It’s been a while since I listened critically, so it’s difficult for me to come to any conclusions.

Maybe there is a tendency for sharper dynamics? Similarly, and it certainly may seem contradictory, there could be a softer or sweeter high end? Maybe there’s no difference?

Again, I can’t say for certain.

I am also giving serious thought to rehousing this unit. It’s just too darn small, too easy to knock about, the RCA jacks up front are a dumb idea and I would like to be able to use physically larger capacitors including a higher value for the output capacitors. I would also be able to include a status LED.

 

[brranimal]

Yesterday, I replaced the input and output capacitors with WIMA MKS 1uF. I have MKPs, but they are too large.

Only listened for several minutes on my garage stereo. It’s been a while since I listened critically, so it’s difficult for me to come to any conclusions.

Maybe there is a tendency for sharper dynamics? Similarly, and it certainly may seem contradictory, there could be a softer or sweeter high end? Maybe there’s no difference?

Again, I can’t say for certain.

I am also giving serious thought to rehousing this unit. It’s just too darn small, too easy to knock about, the RCA jacks up front are a dumb idea and I would like to be able to use physically larger capacitors including a higher value for the output capacitors. I would also be able to include a status LED.

Hello - a huge thanks to all for the info on this unit - and apologies if this has already been covered in this tread. I am looking to replace the caps on my e6 and have a safety question out of an overabundance of caution:

If this were a standard tube amp, I would have a healthy fear of stored energy and make/buy a tool to properly discharge the 250v caps. (Would need to buy the resistor, high voltage wire, clip - and not sure if I can find a suitable ground from my worktable)

Being that this is only a 5v input - what, if any, precautions should I take to make sure I don’t get a shock? Thanks!

 

[M70AB2]

I didn’t bother with any of that. I worked on it on an anti-static mat — that might be my only precaution, per se.

Caps are small. It might be difficult to clip the soldered and trimmed leads.

 

[drjohnnyfeva]

There is something on the underside that you'll want to stay away from - right in the center of the board, I think. I can't remember if I read that on this thread or not... The caps came out pretty easily once I got the hang of it. I did an ok job re-soldering the new ones, but had to go back and touch it up. I didn't really notice much of a difference in the sound initially. I think it sounds better now, but it was hard to tell right after doing it. Now that they have been in and under regular use for a few months, it's pretty nice.

 

[M70AB2]

Someone please explain how say, MKP or MKS capacitors could “break in” or “burn in.”

I see so much of this, but dare I say, no actual scientific evidence. Then again, maybe I just haven’t read it yet.

 

[brranimal]

There is something on the underside that you'll want to stay away from - right in the center of the board, I think. I can't remember if I read that on this thread or not... The caps came out pretty easily once I got the hang of it. I did an ok job re-soldering the new ones, but had to go back and touch it up. I didn't really notice much of a difference in the sound initially. I think it sounds better now, but it was hard to tell right after doing it. Now that they have been in and under regular use for a few months, it's pretty nice.

Thank you both for the boost of confidence! I got the 4 caps out pretty easily and had enough room to stay clear of the "high voltage" marked areas whether or not that would have been an issue. Most importantly, was able to cram everything back into the case - just waiting for my expectational bias to settle while I get some more hours on them, but it was a fun tweak to make, thanks!

 

[drjohnnyfeva]

@M70AB2 I imagine to some degree it is mere acclimation or listening bias when people do "upgrades." I don't know if there is any reality to film capacitor break in. There definitely is with tubes, but not sure about caps. What I was remarking about is my resoldering. I don't really think the unit sounds any different than it had before I replaced them - and that's after some regular listening over the months since I did the exchange. I did, however, get a marked sound improvement when I put WIMA caps into a FX Audio Tube03 unit I had. I liked that so much I did the same with the other two units I had.

 

[M70AB2]

@M70AB2 I imagine to some degree it is mere acclimation or listening bias when people do "upgrades." I don't know if there is any reality to film capacitor break in. There definitely is with tubes, but not sure about caps. What I was remarking about is my resoldering. I don't really think the unit sounds any different than it had before I replaced them - and that's after some regular listening over the months since I did the exchange. I did, however, get a marked sound improvement when I put WIMA caps into a FX Audio Tube03 unit I had. I liked that so much I did the same with the other two units I had.

Definitely agreed on the 6J1 preamp capacitor replacements.

With this E6, I just am not sure.

 

[drjohnnyfeva]

@M70AB2 yeah, I just don't know. I think someone on this thread (or maybe the Tube01 REDUX thread) recently did it and the values of the caps he put in were different, so I was looking forward to hearing about that mod. As @FlaCharlie says, it's difficult to tell without having the circuit diagram. Sometimes you can spot something that might indicate a better value or there's something suspicious about a part when looking under the hood. I just don't know.

I did the WIMA improvement on the Tube 03 and had enough of those same WIMA caps leftover that I could do the E6, which had the same blue original caps as the Tube03 did. I just threw caution to the wind. I was nonplussed about the result. I didn't hear any difference, maybe even a bit of degradation, but I didn't do the best solder job on it AND I explained to myself the difference I wanted to hear by thinking it was the new caps not being "broken in." After several months and a resolder, it sounds good - as good as I think it did, originally - which probably had a degree of bias to that initial assessment too.

I think this unit has the potential to be modded, but there are not enough people playing with it, as there were with the Tube01, who can compare notes. The issues of microphonics have sort of scared people away, perhaps. Nevertheless, I just hope that as the first entrant into the directly heated tube class of cheap Chinese pre's that the experiment doesn't end here.

edit - - - I did the change on the Tube03, I changed it in the response. But I did it as many on that long 6J1 wonder thread had christened the 03 as the heir-apparent to the 01 and the caps were the same in both with much written about mods in both.

 

[M70AB2]

A problem is that we don’t have a schematic. And I just do not have enough time to trace a schematic out, unfortunately.

 

[FlaCharlie]

A problem is that we don’t have a schematic. And I just do not have enough time to trace a schematic out, unfortunately.

I suspect that trying to draw a schematic from something that uses circuit boards might be quite difficult. The board traces are not always easy to follow visually and some boards actually have different layers so there are traces that are not visible at all. Of course you would need to use your multimeter but in some cases there may be combinations of parts that prevent you from getting accurate readings, even basic continuity readings.

@M70AB2As @FlaCharlie says, it's difficult to tell without having the circuit diagram. Sometimes you can spot something that might indicate a better value or there's something suspicious about a part when looking under the hood. I just don't know.

Yes. The point I've tried to make is that if you're replacing parts it shouldn't be a random, "shot in the dark", exercise. You really need to know where the parts are in the circuit and understand their role and how different parts values affect the function of the circuit.

Most modders have little to no understanding about circuits. But when they spend the time and money to mod the device with "upgraded parts" they usually claim to hear improvements. In many - perhaps most - cases it's just "confirmation bias". In some situations it's technically impossible for the change to have an audible effect but of course they claim otherwise. Then they post a video on YouTube and the result is that you have "the blind leading the blind".

@M70AB2I just hope that as the first entrant into the directly heated tube class of cheap Chinese pre's that the experiment doesn't end here.

There are probably very few directly heated types that are available in large quantities at very low prices. When I say large quantities I'm talking about tens of thousands or even hundreds of thousands. That's the key factor when it comes to commercial production.

Most all the of the really cheap Chinese preamps use tubes that are not currently produced. They're all old production, surplus tubes that sat in warehouses for years until someone figured out that they could be used in audio.

As always, if you DIY there are plenty of options.

 

[Supercool!]

OK, Because of this thread I tried one...with the Russian tubes. Cost $70 w/tax on Amazon (thank goodness I used them.) and $55 for a matched quartet of tubes...shipping in that was $35...no joke)... So I'm in for $125....for unusable crap. Howling and feedback from the word go...uncontrollable in occurrence and volume...better with the Russian tubes but still unusable.....not worth a shread more bother.

I should add mine says Nobsound not Cadisi.. on it's way back to Amazon...now I just have to sell the tubes... I really have to say this wasn't even fun...just annoying and disappointing.

 

[StepheK]

OK, Because of this thread I tried one...with the Russian tubes. Cost $70 w/tax on Amazon (thank goodness I used them.) and $55 for a matched quartet of tubes...shipping in that was $35...no joke)... So I'm in for $125....for unusable crap. Howling and feedback from the word go...uncontrollable in occurrence and volume...better with the Russian tubes but still unusable.....not worth a shread more bother.

I should add mine says Nobsound not Cadisi.. on it's way back to Amazon...now I just have to sell the tubes... I really have to say this wasn't even fun...just annoying and disappointing.

That was 100% my experience, junk.

 

[FlaCharlie]

OK, Because of this thread I tried one...with the Russian tubes. Cost $70 w/tax on Amazon (thank goodness I used them.) and $55 for a matched quartet of tubes...shipping in that was $35...no joke)... So I'm in for $125....for unusable crap. Howling and feedback from the word go...uncontrollable in occurrence and volume...better with the Russian tubes but still unusable.....not worth a shread more bother.

I should add mine says Nobsound not Cadisi.. on it's way back to Amazon...now I just have to sell the tubes... I really have to say this wasn't even fun...just annoying and disappointing.

If you had posted some details about your setup before returning it perhaps your issues could have been solved. Or maybe the one you got had some quality control issues. That's entirely possible. This is a cheap Chinese product, after all.

People's experiences with the E6 seem to be extremely variable. Some obviously enjoy it and use it without any major issues and others say it's unusable junk.

In my experience its performance is highly dependent on the amp you're using it with and, specifically, the input sensitivity of the amp.

When I first got mine I used it with two amps. The first is a tube amp that has low input sensitivity. It was designed to be used with an external preamp so it does not have a volume control. The E6 works fine with that amp.

The other amp I used it with was a little Aiyima A-07 Class D amp which has its own volume control. This seems to be how most people who buy tube preamps use them. They want to add some "tube flavor" to their Class D or SS amp.

As I mentioned on the first page of the thread, in that setup I was running the preamp volume between 11:00 and 1:00 with the volume on the Aiyima A-07 set very low, maybe ~8:00 at most. The E6 works fine like that too.

Since then I did try it with another tube amp which has much higher input sensitivity. It's an amp that was pulled from a Magnavox console stereo. The circuit is heavily modded (totally different from stock) but I set it up for use as a stand alone power amp so I didn't add a volume control. I normally use it with my DIY Boogie Factor preamp and the combo sounds fantastic.

1626 Preamp Build

Thought I'd post about my recent preamp build using the 1626. First, some background . . . I've been breadboarding a basic preamp circuit with a variety of tubes. This has gone on, somewhat sporadically, for the past couple of years. In all I think I tried at least 8 different tube types...

www.audiokarma.org

Recently I had that amp on the bench for a minor mod. At first I did some casual testing - streaming jazz using a little bluetooth module and controlling the volume from a tablet. But I wanted to hear it with some of the CDs I normally use for voicing so I needed to add a volume control.

Out of curiosity I grabbed the E6 and I experienced some of the same issues others have complained about. Even with the volume down it was noisy so I didn't leave it in for long but when I briefly turned it up a bit I could tell that microphonics would be an issue. Definitely unusable.

So I grabbed a DIY "passive preamp" that I threw together a while back. It's just a volume control (stepped attenuator) in a little wooden box. I was going to substitute it for the E6 but I decided to try it between the E6 and the amp first. One of the main features of my Boogie Factor preamp is that it has volume controls on both the input and output. This allows me to control the signal drive into the tube while controlling the output independently.

I set the E6 volume at 12:00 then slowly turned the passive up. Doing it like this there was no problem at all. No noise and no issues with microphonics. I ended up running the passive's control at ~10:00 to 11:00 with the E6 between 11:00 and 1:00. Volume is as loud as I'd ever use and it is dead silent with ear to speaker. Even tapping the tubes did not cause any ringing, much less any howling.

Normally, if I was going to use an integrated amp (like a Class D with a volume control) as a power amp I would just turn the volume control up all the way because this, in effect, removes the volume control from the signal path as much as possible. Then I would expect to use the external preamp to control the volume. That approach clearly will not work with the E6 unless your amp has very low input sensitivity. But most all commercially available amps have relatively high sensitivity. They don't actually need any gain from a preamp to be driven to full power output.

What amp were you using? If it has a volume control, how did you have it set?

If you were having issues with noise and microphonics with the input control on your amp turned low then I would say your E6 was defective. That would be disappointing but at least you get free returns with Amazon.

As for your comments about the cost of the Russian tubes . . . prices and shipping costs vary so much on eBay that it's really important to shop around. I hadn't looked at 2J27Ls in a long time. Prices are still really cheap, it just seems you decided to buy from the seller with the highest shipping price. I noticed another seller who has quads for under $25 shipped with free returns.

 

[bridger2086]

Thats all lovely, but at the very least, one would expect to be able to use a preamp as a preamp. Have a power amp, put a pre to control volume. That kind of thing.

I fail to see the point in having this sort of minimalist/purist topology, but have to use an additional pre stage.

I have kept it to control volume on the Pass ACA poweramp into fostex blh-s, mostly because I have nothing else for my analogue sources. Comparing on analog, raw iphono2 into ACA vs E6 inbetween, i hear just added noise and smearing. For digital (streaming) though, it did get me thinking.. more noise yes, horrible UX handling the thing, still, but the sound was kind of sweeter and meatier than DAC direct to poweramp.

This might be a sensible use case, question is only if there is a fix for the hiss and microphonics.

FlaCharlie, you mentioned poweramps with high-sensitivity are problematic and bring out hiss and microphonics. What do you mean by high sensitivity? High input impendance?

Nelson Pass did design one powerqmp in the firstwatt line, that was essentially a powerbuffer with unity gain. It would be intresting to see how that worked out woth something like the E6.

 

[raycarr00]

Many who have tried the e6 have mentioned the sound/ amp factor on amazon reviews. my one and only issue was that there wasn't enough treble and too much bass, regardless of tube or transistorized amp, or speaker type. jacked-up the capacitance on specific points and it settled the issue. Certainly, the types of amps I'm currently rotating are a factor. I've only had microphonics on moving and bumping it. Sound is clear and dead quiet at no volume. I'm looking forward to future improvements like treble and bass control.

 

[FlaCharlie]

FlaCharlie, you mentioned poweramps with high-sensitivity are problematic and bring out hiss and microphonics. What do you mean by high sensitivity? High input impendance?

Input sensitivity is not the same as impedance. It's the amount of signal voltage that's needed to drive the amp to its full power rating. A "line level" signal is nominally 2v. That's the typical output of a CD player, a DAC or a streamer. Most modern amps will produce full power with an input of far less, sometimes even less than 1v. The lower the voltage needed to produce full power, the more sensitive the amp is.

The term "preamp" is widely used but it is often used incorrectly. An actual preamp has the ability to add gain, meaning that it can boost the incoming signal voltage higher. So it's not just a volume control. That doesn't mean it IS adding gain in practice, but it has the ability to.

A so called "passive preamp" is nothing but a volume control. It does the same thing as the volume control that's built into an integrated amp. It does not have the ability to boost the signal voltage. If you're not running it wide open then it is attenuating (reducing) the strength of the input signal by shunting some of it to ground.

In most all cases both a preamp and a "passive preamp" are shunting some portion of the incoming signal to ground. The more gain the preamp has the more is being shunted to ground. Different tube types create different amounts of gain. And a preamp with a lot of gain can create issues from a practical standpoint because the gain kicks in at a lower setting on the volume control. This can severely limit the usable range of the control and make it difficult to make fine adjustments to the volume level. A preamp that uses lower gain tubes will have a wider usable range so it will be easier to make fine adjustments.

But, beyond the ability to add gain, tubes influence the sound in other ways. Mostly by adding a bit of 2nd order distortion, which many people find pleasing.

It seems that the popularity of tube preamps, especially inexpensive ones, is mostly due to owners of SS and Class D amps who want to use tubes to "warm up" or alter the sound of their amps in some way that they find pleasing. Sometimes it works, other times not. As with any combination of equipment the results will vary and, of course, it mostly comes down to personal preference.

Thats all lovely, but at the very least, one would expect to be able to use a preamp as a preamp. Have a power amp, put a pre to control volume. That kind of thing.

I fail to see the point in having this sort of minimalist/purist topology, but have to use an additional pre stage.

The purist approach is to minimize the number of elements in the signal path, so a minimalist would most likely prefer to control the volume in the digital realm with their DAC or streamer or with a "passive preamp" if they're using a source with a fixed output voltage like most CD players. A tube preamp (with gain) is not necessary at all and if you're using one because you like the sound better then some folks would say you're not really a purist.

Bottom line, people should use whatever sounds best to them in their system.

Personally, I greatly prefer tube amps over SS or Class D, even though I use both. If I really want to listen, I use tube amps. For more casual listening I sometimes use Class D or SS. I prefer my Boogie Factor preamp to the E6 but they each have their own character and both seem to improve the sound of my A-07. And I encourage everyone who finds that they like their Class D or SS better with a tube preamp to take the next step and try a tube amp.

 

[FlaCharlie]

my one and only issue was that there wasn't enough treble and too much bass

Funny.

There's a short thread over on the Tube forum which just popped up again after being dormant for a year after Supercool! complained about his recent experience. The OP was actually asking if tubes (in general, not necessarily these tubes) went through some sort of "break-in" and improved over time. Of course, that generated a few comments about the E6 itself, but not about the actual question.

The OP commented that he found it "nicely extended bass and treble .. but it sounds a bit canned in the midrange". He was hoping that the lower mids would eventually improve as the tubes got more hours on them.

Another person complained about "severely limited bass response".

And your comment is that it has too much bass and not enough treble!

So, not surprisingly, there is no consensus. Are the different views due to synergy, or lack thereof? Differences in personal preference? or even perception? I'm guessing we wouldn't agree on the causes anymore than the results.

 

[cipriano]

For over a year I have run the E6 with my Allo Volt+D. I set it on laundry machine pads and have never had a problem. See page 10 for that set-up.

But now I'm waiting for RSL to get some more of their budget 10E subwoofers (which might deserve it's own thread) so I purchased a new amp that has a pre-out. It is the Dayton DTA-100ST (which ALSO might deserve its own thread). Its main selling point is its variable high pass filter. I set up the new Dayton with the E6 and it sounded great, then I thought "Hey you know what would look cool?" - I set the E6 on top of the Dayton (anti-vibration pads in place) and within 10 seconds I was having problems. I moved the E6 off the amp with several inches of space separating the two. The E6 is back to sounding fabulous without any microphonics or distortion!

So, from my experience, having the E6 up on pads and giving it several inches of distance from another power supply is a must. Your mileage may vary. Here is a pic of the problematic set-up.