Nobsound E6 Preamp Uses Directly Heated Tubes

[drjohnnyfeva]

Houston, we have a problem...

So I took the aluminum case off of the unit. Not difficult, but tighter than the FX to slide out of the case.

To answer a couple questions first.

1- the aluminum cover on the Russian tube will not fit into the tube socket of the Nobsound without either cutting off the entire cover OR taking off the part of the centering pin.

2- the Russian tube with the centering pin aligns into the socket, but the centering pin is too long to allow the tube pins to seat into the socket.

3- the holes in the case of the Nobsound, designed for the Chinese tubes without the cover, are a couple millimeters too small in diameter to accommodate the Russian tube WITH the aluminum cover.

Decisions, decisions... I think what I am going to do is take the avenue of least resistance and cost. There are socket extenders on the bay. Some are $2, but they don't particularly seem to be extenders as much as savers. There are others that are extenders, but they either don't have the protrusion that the centering pin has and the center "post" is the same height as the Russian tube minus the extended "nipple" at the extreme base of the case. Those are $18 plus delivery.

Plan: I'm going to leave the cover on the Russian tube. I'm going to cut off the bottom "nipple" of the tube cover and use a Dremmel tool to grind it down further so it fits into the socket correctly. Next, I'm going to use the same grinder to shave a few mm off of the existing holes in the case.

Basis for adaptation decisions: I'm a bit concerned about damaging the tube by getting the cover off, the cost of my plan is low, and if any tube rolling occurs in the future, the unit is ready for it without having to do anything to arriving tubes other than cutting and grinding the bases. Low effort, quick turnaround.

I'd appreciate some feedback on the type of Dremmel grinder to use for aluminum. I'll have the tube in a vice, but I'm going to need to have good, steady control of the tool so it doesn't careen into the tube pins.

That's the plan. Pictures of the unit below.

 

[45rpmspinner]

Too bad, looks like the LEDs are mounted where the center pin goes....
Might've been easier to just drill a hole in the board at that point, as long as the center pin didn't touch the chassis?

 

[drjohnnyfeva]

Too bad, looks like the LEDs are mounted where the center pin goes....
Might've been easier to just drill a hole in the board at that point, as long as the center pin didn't touch the chassis?

Yeah, not sure if the clearance would be right. It's pretty tight in there. Also, I'd hate to screw up any of the electricals by doing something to the board accidently or unintentionally. I don't think it is going to be too big of a job to get the tube cover and unit case adapted. But like I say, I'm going to need to have a steady hand in getting the centering post cut and shortened. I probably won't get to it until the weekend.

 

[45rpmspinner]

You should be able to remove them by just pulling upward and rocking them slightly, just like any other tube, since the "locking" guide pin is no longer present. I haven't tried yet, though, so perhaps the sockets are tight.

I see that now. Didn't want to be yanking on tubes any which way if there was a trick to it.

This arrangement would also provide some damping so it's possible that microphonics would be reduced.

Interesting.
The reason I'm harping on this is that while the preamp does sound quite clear and clean, it also sounds "bright' with these tubes.
Bright enough that i have to turn down my tweeters.
This is making me wonder if I'm hearing either upper mid distortion or microphonics, or both.
In my experience, it's all too common that upper frequency distortion gets confused with "extension" in that range.

I'm going to need to have a steady hand in getting the centering post cut and shortened.

Got access to a drill press? If you drill out the pin to the correct depth, it'll be easier to grind away what's left.

 

[FlaCharlie]

Houston, we have a problem...

So I took the aluminum case off of the unit. Not difficult, but tighter than the FX to slide out of the case.

To answer a couple questions first.

1- the aluminum cover on the Russian tube will not fit into the tube socket of the Nobsound without either cutting off the entire cover OR taking off the part of the centering pin.

2- the Russian tube with the centering pin aligns into the socket, but the centering pin is too long to allow the tube pins to seat into the socket.

3- the holes in the case of the Nobsound, designed for the Chinese tubes without the cover, are a couple millimeters too small in diameter to accommodate the Russian tube WITH the aluminum cover.

Decisions, decisions... I think what I am going to do is take the avenue of least resistance and cost. There are socket extenders on the bay. Some are $2, but they don't particularly seem to be extenders as much as savers. There are others that are extenders, but they either don't have the protrusion that the centering pin has and the center "post" is the same height as the Russian tube minus the extended "nipple" at the extreme base of the case. Those are $18 plus delivery.

Plan: I'm going to leave the cover on the Russian tube. I'm going to cut off the bottom "nipple" of the tube cover and use a Dremmel tool to grind it down further so it fits into the socket correctly. Next, I'm going to use the same grinder to shave a few mm off of the existing holes in the case.

Basis for adaptation decisions: I'm a bit concerned about damaging the tube by getting the cover off, the cost of my plan is low, and if any tube rolling occurs in the future, the unit is ready for it without having to do anything to arriving tubes other than cutting and grinding the bases. Low effort, quick turnaround.

I'd appreciate some feedback on the type of Dremmel grinder to use for aluminum. I'll have the tube in a vice, but I'm going to need to have good, steady control of the tool so it doesn't careen into the tube pins.

That's the plan. Pictures of the unit below.
View attachment 2740537 View attachment 2740538 View attachment 2740539 View attachment 2740540

I can see what the issue is here from the pics. The sockets are mounted with very little space between the bottom of the socket and the board so the center locating pin hits the board and won't allow the tube pins to seat fully into the socket.

If you want to use the tube with the shell then, yeah, the only solution would be to shorten the locating pin. I'd probably use a cutting wheel rather than a grinder. It shouldn't be too hard to cut since it's aluminum and the locating pin is not solid, it's hollow. You might even be able to clip it off if you have some heavy duty tin snips but that's more likely to distort the round shape which might also make it difficult to insert.

I would still suggest just using a tubing cutter to remove the shell. They aren't that expensive and the shell comes off easily when you use the appropriate tool.

I was going to get this one from Harbor Freight since their smaller ones only cut up to 1 1/8" and the shell is 1 1/4".



https://www.harborfreight.com/no-2-pipe-cutter-62243.html

Instead, I found a very nice one made by Irwin Tools for a few bucks less at a place called Ollie's, which sells overstock merchandise, kind of like what Big Lot's used to be.

Then you won't have to enlarge the holes in the chassis cover, which might be difficult if you want them to look decent. You also wouldn't need to purchase socket savers / extenders.

I looked on eBay and didn't see any Loctal extenders or savers. Could you post a link? You may be looking at Octals, which will not fit because the pins are too large.

If the extender exists you may not want to use it anyway. It occurs to me that if it has the normal locking function it might put stress on the board when you remove a tube because it does take a bit more force than is typically needed for non-Loctal types. So shortening the locating pin might be a better option.

 

[FlaCharlie]

The reason I'm harping on this is that while the preamp does sound quite clear and clean, it also sounds "bright' with these tubes.
Bright enough that i have to turn down my tweeters.
This is making me wonder if I'm hearing either upper mid distortion or microphonics, or both.
In my experience, it's all too common that upper frequency distortion gets confused with "extension" in that range.

High frequency clarity and airiness are generally associated with directly heated tubes. If the sound is clear and clean, and not just "extended", then that doesn't suggest that there's distortion.

It's possible that you might need to turn down your tweeters if they were previously turned up when using indirectly heated tubes which don't have the same level of clarity and airiness.

After all, if your speakers have adjustable tweeter settings that's because the designers anticipated that they would benefit from being optimized when using a variety of equipment. Nothing wrong with using those controls if you've got them.

In my experience, if a tube is microphonic the ringing or other symptoms can be heard without any music playing, typically if you tap on the tube or the chassis. This may or may not be an issue with music playing. If it's a problem with music playing you'll be able to hear it if you pause the music. If the sound simply stops then it's not an issue.

If it is, one commonly used strategy is to put rubber O-rings on the tube to dampen it. You can find them at Harbor Freight too, or spend big bucks on some that are "audiophile approved", I'm sure. Mine are silent when the music stops, but these "battery tubes" don't get hot at all so you could wrap them with pretty much whatever you'd like if you have a problem.

 

[FlaCharlie]

Did you prefer them to 6AK5’s?

Yes. See my comments in the first post of this thread and in the FX thread. I wasn't all that impressed with the 6AK5 when I compared them to other tubes. YMMV, of course.

 

[drjohnnyfeva]

I can see what the issue is here from the pics. The sockets are mounted with very little space between the bottom of the socket and the board so the center locating pin hits the board and won't allow the tube pins to seat fully into the socket.

If you want to use the tube with the shell then, yeah, the only solution would be to shorten the locating pin. I'd probably use a cutting wheel rather than a grinder. It shouldn't be too hard to cut since it's aluminum and the locating pin is not solid, it's hollow. You might even be able to clip it off if you have some heavy duty tin snips but that's more likely to distort the round shape which might also make it difficult to insert.

I would still suggest just using a tubing cutter to remove the shell. They aren't that expensive and the shell comes off easily when you use the appropriate tool.
View attachment 2740636
I was going to get this one from Harbor Freight since their smaller ones only cut up to 1 1/8" and the shell is 1 1/4".

View attachment 2740638

https://www.harborfreight.com/no-2-pipe-cutter-62243.html

Instead, I found a very nice one made by Irwin Tools for a few bucks less at a place called Ollie's, which sells overstock merchandise, kind of like what Big Lot's used to be.

Then you won't have to enlarge the holes in the chassis cover, which might be difficult if you want them to look decent. You also wouldn't need to purchase socket savers / extenders.

I looked on eBay and didn't see any Loctal extenders or savers. Could you post a link? You may be looking at Octals, which will not fit because the pins are too large.

If the extender exists you may not want to use it anyway. It occurs to me that if it has the normal locking function it might put stress on the board when you remove a tube because it does take a bit more force than is typically needed for non-Loctal types. So shortening the locating pin might be a better option.

FlaCharlie, you're the greatest! I envisioned having to use tin snips and was worried about breaking the tube. I was also keen to keep the tube shield because of the design and potential function aspect of it but I think given how easy it looks to cut from the pic you supplied, that I might be able to reuse the shield. If not, use the rubber dampers instead. As for the path of least resistance and cost, you've just improved on my model. I think I'll stop by Harbor Freight later today. I might actually have a pipe cutter, come to think of it.

What is the actual diameter of the Russian tube without the shield? Do you know off the top of your head?

Regarding the extenders, they were for Octals, not Loctals.

 

[FlaCharlie]

As for the path of least resistance and cost, you've just improved on my model. I think I'll stop by Harbor Freight later today. I might actually have a pipe cutter, come to think of it.

What is the actual diameter of the Russian tube without the shield? Do you know off the top of your head?

Regarding the extenders, they were for Octals, not Loctals.

Yeah, using the right tool for the job always makes it easier. The diameter of the Russian tube is the same as the Chinese one. Just make sure it gets inserted correctly as outlined earlier.

 

[StepheK]

This looks like a cool pre-amp and I plan to add this to my pre-amp shootout for the next round.

 

[drjohnnyfeva]

Pins marked, tube cases stripped, tubes labelled, and inserted without issue. They are now in the unit and playing very sweetly. I mentioned earlier in the thread that everything seems very natural. This is still the case with the Russian tubes in, but they have that little something that the Russian tubes had over the stock Chinese ones in the FX too. The bass is better with these just from the initial listen. The bass was natural with the stock tubes, but with the Russian ones, they seem a little more clear. Vocals are very clear and the treble is crisp. I can't wait for these to burn in a little. Tom Petty's, You Got Lucky and You Wreck Me sound awesome and Bo Diddley's, Hit of Miss is fantastic too. The funky bass line with all the horns and the lead sax is terrific. These are my standard test songs. The acoustic sections of Wildflowers were great too.

I don't hear any noise in the line at all. Even with the volume on the Nobsound turned to max no hiss, nothing. Haven't had any microphonic ringing either, but I was careful to place it where I wanted it and haven't moved or bumped it which is what happened when I had the ring initially.

I had a two hour delay this morning because of weather here in MD. Started goofing around with it not expecting to get the new Russian tubes in today. A quick stop at Harbor Freight on the way home and voila' the tubes are in, working, and sounding great.

Thanks for the guidance, FlaCharlie! And the heads up on these and your knowledge about the heated tubes and proper operating temps. So cool. Cheers! It's IPA time!

 

[45rpmspinner]

This looks like a cool pre-amp and I plan to add this to my pre-amp shootout for the next round.

It's a really interesting piece. No doubt about that.
FlaCharlie is right to bring to our collective attention.

 

[PCA]

Thank you FlaCharlie and drjohnnyfeva!

Is the Nobsound E6 a 'tube preamp' as opposed to a 'tube buffer'? Are any OP Amps used in the E6?

 

[FlaCharlie]

Thank you FlaCharlie and drjohnnyfeva!

Is the Nobsound E6 a 'tube preamp' as opposed to a 'tube buffer'? Are any OP Amps used in the E6?

Welcome to AK!

The E6 is a preamp, not a buffer, so it does have gain. I haven't opened mine up I don't think there are op amps. Perhaps @drjohnnyfeva can tell us for sure. I'm not sure what their function would be.

 

[45rpmspinner]

I opened mine yesterday.
No op amps.
If I recall correctly, something like 15dbs of gain.

 

[45rpmspinner]

It does require some break-in.

Can't say what happened, but the exaggerated upper mids I was hearing have mellowed.
Consequently, my tweeters have been turned back up to usual levels with no noticeable problem/annoyance.

Sounds good at this point.
Haven't tried it with a turntable yet.
If I have time tomorrow I'll swap back to one of my 12au7 based preamps for comparison.

 

[PCA]

Welcome to AK!

The E6 is a preamp, not a buffer, so it does have gain. I haven't opened mine up I don't think there are op amps. Perhaps @drjohnnyfeva can tell us for sure. I'm not sure what their function would be.

Thank you for the warm welcome! This discussion initiated by you on E6 is what prompted me to join AK. Based on your discussions, I gambled and ordered an E6 and got it delivered last month to a relative in the US [I am based in India and this product is not available here]. Unfortunately, have to wait a couple of months more before the device reaches me I look forward to the E6 replacing my FX-Audio Tube 03, in my audio chain. And also to StepheK's shootout video

 

[drjohnnyfeva]

Thank you FlaCharlie and drjohnnyfeva!

Is the Nobsound E6 a 'tube preamp' as opposed to a 'tube buffer'? Are any OP Amps used in the E6?

No opamps that I'm aware of. I know there are different types, but there's nothing in there like what I was accustomed to seeing in my FX Audio Tube03's. Take a look at the pics I posted above. I guess this unit, like any electronic, could be DIY'd, but that's beyond my ability level. I don't see anything in there that is "plug-n-play" like the opamps in the Tube03.

 

[FlaCharlie]

No opamps that I'm aware of. I know there are different types, but there's nothing in there like what I was accustomed to seeing in my FX Audio Tube03's. Take a look at the pics I posted above. I guess this unit, like any electronic, could be DIY'd, but that's beyond my ability level. I don't see anything in there that is "plug-n-play" like the opamps in the Tube03.

Did you take any pics of the other (bottom) side of the board?

I'm sure I'll eventually open mine up and investigate further but right now my workbench is occupied by my latest DIY amp project, so it will likely be quite a while.

 

[PCA]

If there are no OP Amps and the gain is attributable to the tubes, at 59 USD, could this possibly be the cheapest mass market tube preamp ever?