I didn’t purchase this amp, someone gifted it to me as a Secret Santa present. But you can buy it at linsouls website. Little Bear B4-X

Disclaimer: Let’s clarify that this is my first amplifier review and also my first hybrid tube amp, so I am no expert at all, but I will give it a shot. I will be a little technical too.

In the box

The little bear comes in a brown box, very simple (my favorite type of packaging) with the following accessories:

1 interconnect cable. 3.5mm trs to 3.5mm trs, branded Huanzu.
1 12v charger.
2 rubber bands.

The new version comes with JAN5784 tubes

Fit and finish

The little bear is a regular size portable amplifier. It is 71 mm wide, 114 mm long (without the volume knob), and 25 mm thick. The volume knob is 13.12mm in diameter and is proud 12.35mm from the front faceplate. I can velcro it easily to my Fiio M11. The finish is brushed black aluminum. It feels smooth and has some good weight to it, very solid. The front plate is machined aluminum with a good finish and no sharp edges. From left to right it has a 2.5 mm trrs output, a 3.5mm trs output, a volume knob, a 3.5mm trs input and 4 2 mm screws. Everything labeled properly. The backplate is die-cut aluminum and has some sharp unfinished edges. You will find the on-off switch and a 3.5mm x 1.35mm dc jack and 4 Phillips screws. Everything labeled properly with no misspellings, but in my unit, the labels are slanted.

Topology

Contrary to what people think, the b4-x is not a balanced/differential amplifier. It has an independent circuit for each channel with its own power supply and they label it correctly as “Dual Mono”. Little bear never advertised the b4-x as balanced, but I understand people can get confused when they see a 2.5mm or 4.4mm jacks and think of balanced, I assume is mostly because of the lack of understanding of what a truly balanced amplifier is.
The circuit has some good components and some that could be better. There was no cold solders in mine and the board was spot clean.
The Little bear is tube hybrid amplifier. The tube is in the gain stage of the circuit, and the op amp is in the output stage. The op amps can be replaced, but I don’t think it is a must. Replacing the op amps them with audiophile ones like the muses or bursons can easily double the cost of the amplifier since it requires one dual op amp per channel. For example, a pair of sparkos SS3602 Dual Discrete Op-Amp can cost you up to 80 dollars each, thats a total of 160 dollars!.
One benefit of having amps in parallel is that you can get double the output, half the impedance, and get a cleaner amplification* Source Paralleling amplifers

Little bear is simple designed hybrid, dual mono, not balanced.

Sound

A little story before I can describe the sound...

The key feature of this amplifier is the tube amplification, and I was very excited to try it to get an idea of how tubes can change the sound. I read tons of reviews, but of course, nothing will give you a better idea than trying for yourself.

Right out of the box, there was a massive imbalance in the sound, I could barely hear the left channel, (there are some trim pots beside the tubes to compensate for imbalances). Instead of adjusting the pots, I balanced the source. I ended up having a whopping 15 points in my m11 adjusted to the left!. I knew I had to open this unit at some point to make the change. I noticed that one tube was glowing brighter than the other.

Once balanced on the source, I couldn’t hear anything that resembled the description of other reviewers. It confused me. The bass sounded thin; the mids lacked body. The only decent thing I heard was the treble, it became very energetic and homogenous, but grainy. The soundstage appeared to widen, and the imaging went up a notch. I tried different headphones, and I was getting a lot of unpleasant distortion past the 10 o'clock in the volume pot.

Most of the reviewers I watched on YouTube replaced the op amps with some” audiophile op amps”, but after studying the topology, I realized that since the op amps in the b4-x are in the output stage, replacing them with audiophile op amps could mask the sound of the tubes, so I got a super low distortion, high current op amp (OPA1622) to get the distortion fixed and maximize transparency.

OPA 1622, super low distortion operational amplifiers

With op-amps ready on hand, I opened the little bear for it first mods and I found a couple of things I wasn’t expecting:

The 12-12 voltage regulators were not matched; the right channel is the advertised mornsun, but the left channel is another brand named GodSend. I don’t really care about this because I had planned to upgrade the power supply side of the little bear so I will replace them. I don’t notice any difference in sound between channels. However, it was disappointing to see this.
The tubes are not JAN5899, they are JAN5784. After researching on the internet it seems this is a new revision since the JAN5899 are scarce and hard to find now. I assume they made some changes in resistors values to accommodate the new tubes.
The left channel adjustment trim pot is broken and won’t adjust the volume. I ended up decreasing the right adjustment pot all the way down, and now it sounds perfectly balanced. I think the right channel was being driven way too much, and this was the reason for the distortion. I will replace both pots with some high-quality variable resistors.

One thing I did like:
They added a relay in the output jacks. In the previous revision, the 2.5mm trs and the 3.5mm trs were connected, now the relay isolates the outputs, so it it is 100% dual mono.

Here you can see the different brand of regulators

After I installed the new op-amps and adjusting the trim pots, the first thing I noticed was that the tubes now glow at the the same brightness. ( I can’t explain why but they glow the same now )

Ready to have a listen

Now finally the sound.
Well, the sound depends a lot on the headphone you are using and if they can reveal the differences. But overall, this is what I heard: The bass became wider, now it sounds creamy, yet still clean. It is full of energy and it adds a pleasant warmth to the music. The mids became thicker, fuller, with more presence and body, and the treble remained crisp and lush, full of details. I find often my foot tapping to the music. It will give you a more engaging experience. Fed from the line out of my DAP it has enough juice to power big planars with good slam and no distortion. Let the tubes warm up for maximum effect, I find 5 to 7 minutes is enough. I can say now that I am more than happy after the adjustments, and I am excited to see how much it will improve with further tweaks. An excellent resource to see what people are doing with the little bear b4-x is head-fi.

The battery life.

I will get 5 to 6 hours of listening time with them, more than the time I have available for listening. So I am content with that. You can’t charge it while in operation, so bear that in mind.

New op amps looking good

Before I get into a conclusion, I will try explain why I considered the little bear. I believe that after the headphones; the amplifier is the second thing that has more impact on your listening experience; they have the benefit that they are relatively cheap and won’t age as fast as daps or dac/amps. If you mostly do your critical listening sitting in a quiet place, there is nothing wrong in having a portable amp strapped to your DAC/amp, DAP or phone if that’s beneficial to your listening experience. Desktop amplification is great, but then you have to deal with power supplies, power conditioners, ground loops, and a myriad of power-related issues. If you go all battery-powered, then all that is out of the table and you will get more time to enjoy your music and avoid extra expenses. The problem arises when you want to experience tube sound in a portable format, then you have limited options and most often they are very expensive. So, according to your budget, the little bear might be your only option if you want to experience tube sound.

Conclusion:

If you don’t mind dealing and fixing the qc issues some units can have like mine, or you know someone that can help you, then the little bear b4-x is a 100% rec. This unit is quite cheap, and sending it back for replacement for something you can fix yourself could be costly and time consuming, so keep that in mind. If you only want to have the tube experience without having to deal with all this issue, I suggest you go find a better unit. I am not saying you will have the same experience as me and YMMV, who knows, you might get a perfect unit. However, for me the sound I get from it is worth all these inconveniences.

That tube goodness. 😍

I consider the b4-x is a blank canvas, a modders dream. Avid diyers can really take this to the next level in performance and enjoy the changes in sound with every little modifications. If you have a true understanding of what each component does to the sound, you can really tweak it to your taste and have a unique product tailored to you.

I love it.!

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