I feel as though the sectioned layout is best, so I will apply that here.
I tested this using a pair of Beyetdynamic T90s.
Introduction
These can be purchased for $75 + $10 shipping from eBay, $85 from Penon Audio, or around $97 from Shenzenaudio via Amazon on their website. I personally chose Penon and they were good, the processing took a little bit of time but it got here relatively quickly. The brand isn't well known, you'll find one other review of these on Aliexpress.com and that doesn't go much into detail, so this was pretty much an impulse buy for me. All I was really looking for is bass boost and high-ish output power for a good price. As far as the brand goes, they are definitely comparable to FiiO...while they aren't on the same level yet, Xduoo can definitely catch up if they try hard enough. As far as the product goes, this is a very compact device that fits in the palm of my hand yet is pretty powerful. It has a built in DAC that is 24 bit and has a sampling rate of 96KHz which is ample for most.
Ergonomics
This is a little weird, I will say. At first when I opened it I thought I might have gotten a faulty product (but remembered I bought it from a store that has a small yet good reputation around here) as I tapped the device and it sounded hallow. The board is so small it takes up little room in the case, which makes me think they should have made it thinner and longer rather than fatter and shorter. Regardless, this is a small device, the pictures do not do the size justice as I thought it would be bigger, but it's very small. The body, excluding the knob, is shorter than my index finger...it's ultra compact. Other than that, the I/O is ergonomically pleasing in the way it is oriented. 9/10
Build Quality
Bringing up the hallow case issue, this brings up a concern in regards to build quality, but it's nothing major. As previously stated, this is made of aluminum and it is a thicker sturdier aluminum than FiiO has on their E12 which is nice. The unit is held together with he screws, and has a face plate and back plate that can be removed to service or perhaps even replace the OPAMP...this is unclear if you can or not. 9/10
Input/Output
This is where it gets questionable and potentially problematic. First off, the only input you have is through USB...which is fine, but you also have no charging input so that means the USB is also used to draw power and that you might not be able to use this with a phone, and if you can it means you're going to drain your phone's battery pretty quickly...thus it has limited/no portability yet it is designed for that. This isn't a problem for me as I don't plan on bringing my open T90s anywhere and I'm just using this on a laptop, but this might not be a good choice for others. There is an RCA output, which should have been an input in my opinion, but oh well. There is also a standard 3.5mm output. As far as the knob goes, it turns very easily and if you touch it while music is playing then there will be some static. This might not be pocket friendly because of the sensitivity. 6/10
Sound
In general, it is quite neutral unless you turn on the bass boost which offers +3dB boost for low gain and +6dB for high gain. The gain options are +4dB and +9dB. Nothing really much more to add that won't be covered in other sections, so I'll continue there.
Treble
I don't pay much attention to this, but the T90s are a hot pair of cans...these do actually tame that a bit which is nice. There isn't much to add at all other than it tries for neutrality, so this won't add or remove treble unless there is too much, then it will remove a bit. 10/10
Mids
The mids with these are enhanced, but they're not boosted since this aims for neutrality, so not much to add here either. 10/10
Bass
This is where it adds things...but only if you want it, and does it give you the option to add bass. While this is no Cayin C5, this will give a slight bump depending on the gain setting (see sound for details) but it doesn't do just that. These have no special drivers, so Microsoft will give it generic sound card drivers which means it has a secondary bass boost option of up to +24dB which can means a total of +30dB can be reached. That is a massive boost, and that's all I should need to say about that. If you're a basshead, this might be for you. Personally, I got the +30dB going on without an EQ and love it. It gives a nice boom to my T90s yet preserves the mids. 10/10
Soundstage & Imaging
The T90s have less soundstage than the DT990s in my opinion, so I was hoping this would do something for them...and it did. While it wasn't a massive increase, it did widen the soundstage a little bit. This might be due to the fact that I would listen to these directly with my laptop's sound card and it needed more power, but it sounds better regardless. It doesn't increase imaging at all, but the neutral sound signature does help the T90s to do it's job better in regards to imaging. 10/10
Drivability/Impedance
These can pump out 330mW @ 32 ohms, which is a good amount. Addressing the generic Microsoft drivers again, it does benefit from loudness equalization so that gives a nice bump. I find that putting the Windows slider at 100% and putting the amplifier at 30% or so provides ample volume. It is capable of producing ear bleeding volume, but not unless it's on high settings. As for impedance, it can drive T90s just fine which are 250 ohms. However, the T90s are efficient, so they are easy to drive regardless. 9/10
Final Thoughts
I am probably forgetting something, but I can and probably will come back to update. Overall, this was well worth the $85 I spent on it. It does what I want, and it offers more features. If it wasn't for the weird I/O configuration it would be even better. There are better options, but this is a great affordable bass boosting amp, and I recommend people take a look at it and give the brand a chance. I will be enjoying this amp until I decide to fork the cash out for a tube amplifier. This, no EQ, +30dB bass boost, and my T90s = heaven.
Overall rating: 9/10
