What has your experience been using Bluetooth? I've had some issues with dropouts and dropped connections using it with a Noble BTS.

I thought it was a bit bright too but if you're using UERM and not having issues I guess it can't be that bad. Thanks for the impressions. This looks like it might be the one.

Now that I've been living with the Jr daily for almost four months, I think it may be appropriate to post a review of it. Though this is my first review of any kind ever... Please be kind. Entirely subjective.

Note: I highly suspect my pair of UERM is an outlier: it's what I would regard as on the bassy side. The treble is not bright, but certainly revealing. 80% of listening is done with UERM, 10% with TH900, 10% with other stuff.

AK Jr firmware 1.02. updated.

Form factor, Hardware: I like it. It stays in my pocket nicely. Stack it with an ALO Rx and the whole bundle is still somehow not very bulky.

It does get a bit warm sometimes, but it's at most as warm as an iPhone 6 can get. Even in this abnormally hot Vancouver I don't feel this heat can be an issue.

UI, Software, Battery:

UI is similar to the AK100/120 II and pretty easy to get around with, albeit laggy - though I don't think the response of Sony ZX1 (that I previously owned) will best the Jr by a large margin if I don't disable all the Android functions and bloatware.

Battery can run on average four days given my usage is ~2 hours a day, at ~40 volume powering UERM directly. If I use the lineout to the Rx, the battery seems to last 2~3 days. Not bad at all.

Sound:

The Jr is better than everything I've heard, save the Calyx M which I recall as an entirely different approach of sound. I tried some cans than IEMs: Beo H6, AT M70x, and TH900; all were driven with enough volume and some sort of authority. I jokingly tried it with HE400S and certainly it's bad. My comfortable listening level with UERM is around 35~45 setting. No hissing at all is a good trait.

Overall sound signature is decently neutral if not a touch bright. Pretty balanced.

Plaknton performance in midrange is certainly above minimal expectations but still I can't say very satisfying. With UERM the very low bass and the very high treble are a bit unrefined. Bass can sound muddy and treble can sound cold and articifial/metallic/sterlie. I highly suspect this is because of the 2ohm output z of the Jr, since adding the Rx can mitigate a lot of the problems, making the Jr's sound satisfying refined and also bringning out a decent amount of low/high end information.

Now things get a bit complicated. The negatice things I will write below are not daily issues and does not affect my overall favor of the Jr, I nevertheless think it's necessarily to fully explain what I have encountered.

Here we go:

1. I highly recommend turning off the auto-refreshing library funtion. This function is completely unnecessary: it drains battery (at most one day), is extremely slow, and cannot be quitted. I don't even know how often it auto-refreshes, except I know if I left it on every time I wanted to use the Jr it was refreshing.

2. Funtioning as a USD DAC is no problem for PC and non-SSD Mac, but the dealer and I couldn't get the Jr work on our newer SSD MacBook Pro and Air. It was recognized, and the OS indeed was outputting through the Jr, yet no sound came out. We contacted AK to get the answer that it's because SSD Mac's USB 3.0 ports aren't compatible with Jr and the problem is not mitigatable. Pretty sad.

3. The physical buttons are occasionally irresponsive. I though this may be a hardware defect and my local dealer replaced it (and he confirmed the irresponsive problem); however the problem is reoccuring on my second (current) unit. I assume this is a firmware issue.

4. Also occasionally when first I turn on the line out function (not simply to max out the volume, but by selecting line ou t in the menu) to use the RX, then turn down the volume to listen directly, then turn off the Jr, the turned down volume will not be memorized. Once the Jr is turned on, the volume will be remembered as maxed out and my ear drums have suffered multiple times. Pirates be careful!

Verdict:
Given the current DAP market is hyper-inflating and every other manufacture has this and that kind of firmware/hardware/UI issues, the Jr is at least not outstandingly bad. With a comparatively outstanding sound and comparatively lower price, the Jr is a decent product.

Wow, thank you for the measurements! Would you mind if I include your results into my original post, credited to you?

If I recall correctly, my previous Sony ZX1 has an output z of ~3 and a S/N of 94, which means on UERM, ZX1 is fucking beaten to death by Jr. Jr clearly has more volume range and can drive some slightly inefficient portable cans (i.e. Beo H6) with far better authority than ZX1. Just looking at the specs posted, I was almost sure ZX1 stands no chance against Jr. Yet I strongly suspect the muddy low end I'm expereincing is a result of UERM's wonky z response and Jr's 2 output z. The low end problem is not very prominent on TH900 and N4.

I tend to agree with your comments: screen is crap (so the slow touch response), edges are too sharp, but these are quite minor issues for me. It's not like the sharp edges hurt me, so I'm good with that. Volume touch input is awesome to me tho.

OTOH, my expreience with the original AK120 was very bad (using SE535 at that time). The sound sig of AK100ii was somewhere in between Sony ZX1 and Calyx M, neither lean enough nor thick enough. A disappointment for the price. Even if the 120ii or 240 or 380 were good, I'm not carrying 1500 USD+ DAP and 1000 USD CIEMs around - that's more money than a car. If I have the extra $1000 (the difference between Jr and 120ii), I'd rather get some air tickets to visit my friends.