I love this amplifier, Looks great, the tubes sound good but if you want to upgrade I would recommend "Riverstone Audio - Tested/Matched Pair (2 Tubes) 7-Pin JAN 5654W". The power wire was short and hardly reached my power outlet, I had tension on the power wire from hardly reaching and after a year I started to get a buzzing sound. I thought it was the tubes originally and upgraded but still had the noise. Than I noticed the power wire near the box was loose and could be moved left and right. Ordered a new power wire, was belker universal one. No issues. The difference in sound quality using this amplifier is night and day. I love it. I use DT 990 Pro 250 ohm studio headphones, they are very popular, highly rated and affordable. I have an 80 ohm pair and this amplifier makes a big difference with those too

I am giving this amp 4 stars as out of the box it is just ok. Build quality for the price is really pretty good, with the volume control feeling nice and solid. The sound of it is not bad, especially at volume. However, with the supplied tubes it is a noisy little amp, with audible hum at low volume levels. I guessed that the hum was originating in the tube preamp section so I replaced the tubes with UE 6136 tubes ($10/per) and that did the trick. It became MUCH quieter, and the sound was nice and rich. I compared it with a Schiit Magni (solid state amp, $99) and with the new tubes the Nobsound could hold its own, and, depending on your preferences, I could see many people preferring the Nobsound. It was quite musical. (I came away pretty impressed with the 6136 tubes! I had originally selected them randomly as they were pretty inexpensive.)Because it offers such an easy upgrade path it gets a thumbs up.

After reading the reviews about the tubes that come with it I went ahead and ordered a matched pair of GE JAN 5654W tubes from Riverstone Audio (after a lot of searching around these seemed like they'd be a great option for this type and I personally do love what I'm hearing so far.) Well, it's pretty much normal that the tubes that come with a tube amp should be replaced I guess, though it would be nice if more could come with excellent performers right out of the box. Naturally we buy something with slots so we can roll our own, but it would be nice if an amp came with tubes that almost no one would want to swap out. Regardless, I counted on that as part of the cost of this purchase.So far I've really been enjoying the sound. I'm debating if maybe I might even like it better than my Vali 2 despite it having a really nice tube (lots of options for the Vali 2's tube type, maybe not as many for this.) This is with a Sennheiser HD650 with the so called "KISS mod" (eg just minimal padding so you don't overdo it.) I don't have golden ears though, so YMMV. This amp is smaller than my Vali 2 which is designed more for sitting on a desk than this is (though still not exactly a huge amp regardless) so it's a little easier to move it from one area to another. The cord is very short though, so this is a problem wherever I have it (the plug doesn't really reach on my desk and needs an extension.)I have not had any problems with the recessed audio ports. Though I suppose there is no particular benefit or reason that I can think of for them being recessed. Normal 3.5mm connectors and even some adapters should fit fine in there. I think you could probably widen the recession itself using a drill and a really large bit (in reverse so it doesn't catch and pull) if it really was a problem, but I really think most things should fit without a problem and any that don't are insanely wide so will have problems with other things anyway. The connectors are -- all of them -- insanely hard to actually plug things into though. It's enough to make me worry I could loosen the jacks on the board at times and I'll probably brush on a bit of a dielectric to act as a bit of a lubricant later on (really thin ones don't actually interfere with electrical connections -- especially really tight ones like these.) The tube connectors are insanely tight though. Vacuum tubes are actually a lot tougher than people think, which is a real life saver here, but I was legitimately afraid I could break them and cut myself terribly while trying to push in the tubes I had bought. I had to just slowly work them in, wiggling back and forth a bit as I went. This worries me because it may be dangerous if anyone ever does break a tube while putting it in, but I will admit it may have an advantage in that it probably scrapes any oxidation off of the pins (since, more likely than not, people will probably be using NOS tubes with varying degrees of oxidation on the pins after all) or even holds so tightly over such a relatively large area as to more or less negate the resistance that would add even if it doesn't scrape.The only thing I do have a problem with is the volume control uses a sort of almost clicky internally notched wheel that makes the volume change in relatively large amounts. That makes it a lot harder to get just the right volume. I don't know why they would do this really. Maybe this kind of volume control is less wear and tear on the pot or something, but in the end I'm not sure if it's worth it. I'd rather have more control I think. I will say that this thing definitely has plenty of power and voltage. My headphones are the 300 ohm variety, not the 600, so I can't speak for anything higher than this, but I have plenty of volume and even on the quietest devices I own I never got the volume control higher than about 75% or so. Most of the time it was between 33-50% depending on the music's mixing and which device I had it plugged into (some have intentionally lowered outputs.) It's definitely outputting sufficient voltage from the tubes. Since these are pretty efficient headphones I can't speak for current, but it sounds like the opamp is pretty powerful too. These sorts of hybrid designs are an excellent compromise. (Of note, most of the tube sound goes into the voltage rather than the current anyway. Current *does* affect the tubes somewhat so this does ever so slightly change the coloration, but not a huge amount. These hybrid designs really are an excellent compromise.)I checked power usage because I was thinking of running this from a battery pack to a DC-DC converter outputting 6V. I don't know if anyone else is interested in doing that, but I'll at least mention my results. It's approximately 463mA most of the time (the actual volume setting doesn't make a huge difference, but if I turned it up enough it kind of hurt I read 465mA.) I guess the heaters are probably 99% of the power usage with the rest barel...

I bought this back in 2016 and have been using it almost daily ever since. I run this as part of my work setup and it has made listening to music while I work so much more enjoyable. After a few years, I started to get some popping and distortion noises, so I upgraded the tubes to NOS Amperex 6688s and they made a subtle but noticable change in the sound tone. I recommend this little amp to a low of people.For a while now, i have been getting intermitten popping and squelching that seems to just keep getting worse. I tore into the amp itself, expecting to see a bad connection on the DC power port. Upon inspection the amp is actually really well put together and not issues were found. Upon putting a scope on the provided 110vac-6vdc power supply the problem was found. The little wall wart power supply has degraded and is absolute garbage, it is a non-regulated switching power supply. I am finding that to get a regulated linear 6vdc power supply is more costly than the amp itself. It does look like the amp is internally regulated to run at 5vdc so that may be useful for those that are also looking for a updgraded power supply.

I really like this product with the upgraded tubes. There's no feedback and moving or touching the amp does not cause any ringing. I was able to drive my Monoprice 50 mm headphones and the difference was very noticeable with the bass, mids and the highs. My Samsung Galaxy S10 phone could not drive the headphones on their own but with this amp it felt like I had subwoofers mounted to each side of my head. They had a kick and and nice rumble to them. Not just a boomy effect, but you could literally hear the speakers phasing as though it was a powered subwoofer or bass shaker. Not loud bass in your ears but you could feel the bass. The highs were extremely high and when listening to vocalists in high quality audio samples, I could literally hear them breathing in between the words. I did not notice much modulation in the sound itself but it is definitely a good amplifier. I tried it plugged into the 3.5 mm and I used a high quality USB-C DAC. The specific DACA used is a 32-bit decoder but not much of an amplifier. Sound was definitely better with the DAC in-line. Volume and bass was the same but with the digital audio converter the voices and higher pitched sounds just sounded more colorful. They didn't cut off, you could hear them fade off to infinity. For the price and quality I'm very happy with this tube amp. Nothing feels loose, everything is finished and the tubes are extremely snug. If anything to complain about... the cord on the wall adapter could be just a little bit longer.