This thing is really cool. I bought it and the knob was a little tilted didn't love that. With the existing opamps it's got plenty of power and sounds fine but wasn't what I really wanted. So I set up a return - then I decided to opamp roll before doing that. I got the burson v5i (2). Installed them and plugged in my Mangird teas and was blown away. I just bought some $700 iems that don't compete with this pairing. On their own the teas are good but not better than $700 ones. However with this amp with the burson opamps it's the best thing I've heard. I've got it strapped up with the hiby r3 and this is killer. Crazy 3d holographic presentation and excellent imaging. Couldn't be happier. I was about to sell the teas and return the little bear - so glad I didn't. You'd be hard pressed to find a tube amp that's portable for anywhere near this money

If you want flat, linear, detailed and accurate sound the Little Bear B4-X is NOT for you. Stop reading this and buy a Schiit Magni Heresey for $99 with lots of clean, accurate power. That's what you should look for in your first headphone amplier.

Unless you're 'tube curious'. This, then, is a very strong example of 'tube sound', though really it's not hi-fi tubieness and most tube-ophiles will say this is a gimmick.

I like the sound, the bass is SOLID and the treble is reduced audibly. Distortion is greater than you get with a Schiit or Topping 'tube amp' and is not "audiophile" but is a pleasant way to add tubes for a bit to see if you are interested in spending more on a tube amplifier (Schiit Vali 2 is the cheapest hi quality tube amp you can buy at $149 ... sound on that compares well to solid state but has the 'tube character'). Amplification is very good through the 3.5 mm outputs as is soundstage, imaging etc. Again not audiophile but 'fun'.

I love my Little Dot tube headphone amp. The problem is that I often need a portable setup. I've eyed this little amp for years, but never pulled the trigger. Glad I did.

Is this better than my Little Dot single-ended? No. Does it have that characteristic "tube sound?" Yes, definitely! Paired with a cheap portable DAC and my Sennheiser 6xx headphones, pushing 320 kbps from IDAGIO with my iPhone is simply gorgeous. So much ore character than a solid state amp.

I'm no audiophile. I've been blown up too many times. But, I am a classical musician, and have been around a lot of high quality live music. So, your ears my be pickier than mine. But, I do know what things are supposed to sound like, and this little amp delivers that sound.

I bought this amp 4 months ago more because It was a unique idea. Portable tube headphone amps are something that I didn't think existed and if they did they would be at least much more monetarily.
I have not upgraded the opamp yet to the Burson Audio which was suggested by another buyer but it really stands by itself as it is as a great audio product.
The fit of the audio cable is important from the source to the amp but they provided a pretty nice beefy short cable with the amp.
So far using a Pioneer Hires player, Sony AW55, and even my LG V40 thinq in Airplane mode with its 4 DACS and very good audio section the B4-X was solid amp quiet and works well with offboard DACS as well.
Having been a musician for many years and also a Progressive Trance DJ I have put it through its paces with my BeyerDynamic Dt1350s, Tesla T1, Focals, and IEMS from my Westone 4Rs to 5 Driver IEMs. It provides solid power to drive up to 300 ohm over the ears without an issue. Pair it with a good outboard DAC and it is really a great unit.
For 99$ it punches WAY ABOVE its class. It was so good I bought a second one and sent it to my Brother so he could use it with his Audeze and Hifiman Planers.
I look forward to swapping out the OPAMP to see the levels that I can drive it to.
In a world of expensive electronics that don't deliver the Little Bear B4-X is really a steal.
What started out as a "OKAY was looking at a Schitt Valhalla to listen at home but a Portable tube headphone amp!!!????? I gotta give it a whirl" turned into a great little tubeamp which is much better than the price or printing on the case shows.

Great product! I got this one because of the balanced output. Which worked great with my HiFiman h-440i, it made them shine! Battery life is great and the product is well built. Only thing I would have loved on it, that is why is 4 stars, to be able to charge and use it at the same time. Then it can be uninterrupted my desk and mobile tube amp. I am looking forward to upgrade the op amps for even better sound quality. Will do it when my hearing get tuned to actual op amps.