It has been a while since I sat down to write some impressions her at Head Fi,  however the opportunity presented itself and herein are my thoughts. Thanks for reading.
 
 
I have had the Slimline UHA-4 unit in my possession for about two months. It has been used as both a USB DAC/Amp combo and a portable amp. In summary I like how this unit sounds and that it is such a compact performer.
 
The USB was recognized right away by computers running MAC OS 10.6.6, Windows XP, and Windows 7. This unit is charged via the included USB cable which also functions to “feed” the digital files. With the advent of home/car chargers that allow charging using the USB plug format the charging of the UHA-4 should provided added versatility.
 
The one feature I wish was incorporated is a line out, this would allow the user to feed the decoded digital files to an external amp of the users choice. I realize this feature is of minimal use to most users since the intended market is for those looking for an DAC/Amp unit with a reduced footprint to be used on the go.
 
Barring this small issue the UHA-4 sports some cool features, the main one being its small size. This is followed by low/high gain switch, x-feed, and an Alps digital volume control. The width of the UHA-4 allows it to sit below an iPod Classic or an iPhone perfectly, thus adding to its usability.
 
The unit sports two LED’s, the front is the power indicator and it is green if the battery has at least 1 hour of remaining running time. This turns red when the remaining running time is less than 1 hour. There is a 2nd LED on the back by the USB port, this turns orange while charging. A nice feature is the use of a 500 mAh iPod battery, thus it would be an easy task to find a suitable replacement.
 
Your can read more about this unit at: http://www.leckertonaudio.com/products/uha-4/ For those interested the technical specifications are:
 
• Dynamic range: 108 dB A-weighted with analog input (100 Ω load), 93 dB A-weighted with USB input

1. Up to 40mW into 32Ω,<1.0%TH
2. Up to 50mW into 100Ω,<1.0%TH
3. Up to 15 mW into 300Ω,<1.0%THD
4. THD, A-wtd: <0.025%, 1 mW into 32 Ω
5. 10 dBV max output level into high-impedance load (>600 Ohms)
6. Frequency response: 13 Hz to 22.5 kHz, +/- 1dB
7. Dimensions: 3.3" x 2.75" x 0.47"
8. 24 hours typical runtime on full battery • 32kHz, 44.1kHz, and 48kHz sample rates supported for USB audio streaming (16-bit)
9. Enclosure: extruded aluminum, anodized

 
Below is a list of the cans I used with the UHA-4, all four were driven effortlessly and IMO the sound was engaging, detailed, and with very good extension. Actually the clarity was the most distinctive feature.
 

1. Audio Technica ATH-ESW9
2. Yuin OK-1
3. Ultimate Ears TF10
4. Westone 2

 
In closing I would like to thank Nick of Leckerton Audio for the opportunity to try the UHA-4.
 

$169 + shipping is a very neat price for a DAC + AMP.
 
Any comparisons with other similarly priced amps like the Ibasso T3 ?

Thanks for the writeup, mrarroyo. I've been happy with the UHA-6 for a few months now, and it's a great little amp. I don't think Leckerton products get the attention here they deserve; Nick is producing some wonderful equipment.

^ Glad to hear you are enjoying the unit.
 
^^ I do not have the T3 anymore, gave it to a friend. Sorry.

@mrarroyo
How would you compare this with the minibox es?  These are the 2 amps I'm trying to decide upon.  Skylab had some really nice things to say about it's predecessor UHA-3 and it's bass presentation.  Also I understand the UHA-4 shares the same output amp as the pricier UHA-6.
 
The dac could come in useful as well on my acer timeline, which has a very weak soundcard.

The UHA-4 uses the same opamp as the UHA-6, but the rest of the amplifier section is probably different, since there are different advertised output ratings (the UHA-6 being more powerful). Probably not a significant difference unless you're prone to loud listening or wearing inefficient/high impedance phones.

I'll be using mostly IEMs and occassionaly Sennheiser HD497's, so nothing hard to drive.  The main purpose to amp is to enjoy the dynamic range of the phones at a lower volume level when compared to the HO of my apple products; and hopefully add a little body to the bass.

I have been a fan of the MiniBox E since it first came out, and I have own the E+ and the ES. I truly think they are a top tier portable amp. However the ES has three buffers per channel stacked which reduces the battery usage to about 11-12 hours and IMO it has way too much gain if you plan on using it with IEM. Perhaps you could ask Fang of Head Direct to scale back the buffers to just one per channel like the E and E+ had.
 
The UHA-4 is IMO a really nice sounding combo which allows the user dual use by incorporating a USB DAC. Personally I find it more useful than the ES and if I had to purchase one it would be my choice. However if Fang cut the number of buffers to one then ...

 

Looks good! Reminds me of the Headstage Arrow. 

So, how is the SQ??

This is a really good amp and probably the best value out there of all the offerings discussed here!  It easily competes with the TTVJ slim at 1/3 price and RSA as well.  Fantastic amp AND DAC and way underrated or unrated at a fantastic price!  Best value - have not encountered a better value out there yet.

Would love to know where this sits vis a vis a total bit head or TTVJ slim dac.    Id like to step up from the TBH and the TTVJ is my first choice....

The Leckerton UHA-4 is easily a better deal than the TTVJ slim with DAC, which is also a great amp and an ok dac.  UHA-4 is only $169+shipping (amp/dac), TTVJ with DAC is $450!  Or a whooping almost $300 more...  The SQ of the UHA-4 is quite on par, if not better (from memory as I do not have the TTVJ any longer) - UHA-4 pretty much lacks NOTHING.  Really an amazing amp at a price that beats ALL competition at the moment in SQ and features.

I just received mine, about 20 minutes ago.  So far, it works.  It is sort of an odd shape, wider than my touch 4g, slightly wider than my iphone 3gs, and an inch and a half give or take shorter.  I'm looking forward to actually giving it a test drive.  It will be AB'd against my Arrow.  I listen quietly, and the Arrow has a bit too much gain for me, even in a modified, lower gain configuration.  I think I'm in the minority on the Arrow being a bit too loud though.  I'm hoping the digital volume control and low gain on the Leckerton will solve my issue.