AUNE B1 is an outlier in portable headphone amps. It has two characteristics that are rarely used to describe other portable amps. Class-A and discrete.
(You can skip this if you are familiar with the terms.) For your information, there are multiple types of amplification methods. Class-A, class-B, class-AB, and class-D. Class-C is not used for audio system. Class-A is simple and is considered to make the best sound (the least distortion). However, class-A requires constant currents running even though there is no incoming signal. It has disadvantages of wasting power (i.e., short battery life) and creating heat. That’s why class-A is a rare exception for a portable amp. Yet, B1 has a decent battery life of 10 hours (or 5 hours with high currents, which will be explained later).
For the term ‘discrete,’ you can find a long-time debate about ‘op-amp vs. discrete.’ It is actually ‘op-amp IC vs. discrete,’ because op-amps can be made using discrete circuits. Op-amps can save space and manufacturing cost, and usually require less power than discrete circuits doing the same thing. That’s why the most of portable amps use op-amp chips. But many people think discrete amp sounds better than op-amp chips. (Personally I don't agree.) B1 chose discrete circuit to make their amp and you can see it through the two windows of the front panel.
We know that discrete class-A amplifier doesn’t automatically mean that it sounds better. There are more factors than a circuit design. Choosing class-A and discrete can be a marketing strategy rather than a necessary. But the chose was a wise one and it works !!
For design, B1 looks great. You can tell that it is at least $200 worth. On the front panel, there are two windows showing the circuit, which is very nice. Volume and in/out ports are at the top side. The right side has a button and a small light with which you can check remaining battery life. The left side has a power switch, a gain switch, and a current switch. The gain switch toggles the output gain between 5 db and 15 db. For a high impedance phone, such as HD650, you will need the high gain. The current switch (labeled as class-a) toggles output current between 20 mA and 40 mA. Selecting the current to 40 mA reduces the battery life to half (5 hours), but it feeds power-hungry headphones better. I believe that B1 can run the most of (if not all) headphones. It had no problem to run HD650 (300 ohm) with the low current selection.
For the sound, it is hard to describe. I say B1 sounds very ‘pure.’ It doesn’t add or remove any flavor from the source. Someone says that B1 sounds warm, but I don’t hear it. For me, B1 just adds more power without changing a sound signature. Isn’t this what a good amplifier is supposed to do? ;) Please note that my main source is AK120. Improving sound of AK120 is not an impossible job, but a tough one. With line-out from AK120 to B1, I really enjoy music from B1. I hear crisp high and tight bass. I don't hear any boost with bass. The mid is fine too. I feel that the mid is a little bit forwarding, but it is early too tell. I will update my impression later.
Other than B1, I have MF V-CAN and FiiO E11k to compare with. Comparing with those amps, B1 sounds brighter. This is expected. V-CAN is known to be warm. E11k has a little bit of bass boosting, even though bass circuit is off.
I use HD650, DT1350, and SE425. SE425 doesn't need additional power. Still SE425 sounds fine with B1. It means that B1 would work fine with low impedance phones. DT1350 matches well, IMO. But someone may think that the combo is too bright, or even piercing. The best match for me is with HD650. Combination of B1 and HD650 sounds the best.
Update: I matched B1 with iPhone 5s. I can hear sound improvement. The first one I notice is wider sound stage. The sound is fuller with better control. I think I can live with B1+5s combination if I don't have AK120 ;)
I see two cons. First one is heat. Definitely it gets warm ;) During the winter, it is good. However, soon I will not want to keep it in the inside pocket of my jacket. Second one is the charging usb port. B1 uses micro usb for charging, which is kind of a standard now. But the unit I got has the usb port a little tilted. So putting a micro usb plug into the port needs a technique. Better quality management is desired.
Actually one more con. The size. The spec says the height is 110 mm. But it is actually 120 mm. So it is a little bit big to carry around. For size-wise I prefer E11k which is perfect size for AK120.
Overall, B1 is very unique. Someone may argue class-A and discrete are just for marketing. But for me, it shows how much AUNE, the company, is serious about the sound quality. And B1 delivers the result. It sounds very good in a pure way. I absolutely recommend this amp.
Reviewed by: Lewis Lee from Lexington, MA.