The clue is in the Name – Just Audio. Founded in the UK by Justin Harris in 2009 who has a first class Masters degree in Electronics and a background in the mobile communications sector he decided to switch in 2010 to portable amp development and not long after that out popped these two fine specimens – the uha-120 and the larger brother, the AHA-120 portable headphone amps.

Now I have gone through a ton of headphone amps in the last few years but when I took these two little guys to the big meets last month there was significant interest and I can understand why. These have been on the market for a while so those in the know will probably have read already a few of the things I want to draw your attention to but lets start with the more emotional responses that I got from the meet before we do the nerd fest.

Just Audio amp’s have filtered their way into Singapore resellers this year, in fact I saw one I think around Dec 2011 but never got a chance to play with it. This time bringing both amps with me the same people stepped up the plate with obvious sentimental attachment crying “Oh you have these? Let me try again!”. And off the two amps disappeared for the best part of the meet with nothing but positive comments on both of them. Hard nosed resellers grabbed them also and remarked on the build and design quality being way above what they are used to seeing shipping in from the East. It was fair to say the amps generated excitement and interest more than I expected and it made me stop and wonder if these amps were perhaps a tad unique or special to get that kind of level of distraction from hard nosed audiophile guys at the two meets.

Technical specs

AHA-120

60 mWrms/channel into 32 ohm @ nominal (3.6V) battery voltage
10 mWrms/channel into 300 ohm load @ nominal battery voltage
16 mWrms/channel into 300 ohm load @ fully charged (4.2V) battery voltage
28 mWrms/channel into 300 ohm load with 5.2V USB power supply
Distortion (THD): <0.002% @ 1KHz (11dBu output level, with both channels driven with 32 Ohm headphones) Dynamic range (dBA): >100dB
Bandwidth (-1dB): 10Hz-40kHz
Output impedance: < 3 ohm Output current limit: +/-250mA per channel Maximum Gain: 12dB Channel balance: <1.5dB (over entire electrical travel of volume setting) Battery recharge time (max): 9 hour fast charge; 21 hour normal charge Dimensions(approx): height: 26mm, width: 80mm, length: 126mm Weight: 332g +/-1g uHA-120

60 mWrms/channel into 32 ohm @ nominal (3.6V) battery voltage
10 mWrms/channel into 300 ohm load @ nominal battery voltage
16 mWrms/channel into 300 ohm load @ fully charged (4.2V) battery voltage
28 mWrms/channel into 300 ohm load with 5.2V USB power supply
Distortion (THD): <0.005% @ 1KHz (-20dBu to 5dBu output level, with both channels driven with 32 Ohm headphones) Dynamic range (dBA): >100dB
Bandwidth (-1dB): 12Hz-40kHz
Output impedance: < 1ohm Output current limit: +/-80mA per channel Maximum Gain:(REV B): 10dB/6dB (Jumper selectable) Battery recharge time (max): 2.5 hour fast charge; 6 hour normal charge Dimensions (approx): height: 23mm, width: 52mm, length: 85mm Weight: 125g +/-1g Both amps have roughly the same form factor but could be best described as the little and large show with the uHA-120 much smaller than the AHA-120. You would be dead wrong though if you thought one was just a miniature of the other. In fact both of them present sonic presentations that for me target two different audiences or two different needs. The AHA-120 would classed as more transportable than portable, in fact a miniature desktop system would have the AHA-120 right in there and nothing would be amiss. I have seen similar sized or bigger being carried around by our more hardcore members such as the Triad Lisa L3 or a dual stack ALO Audio combo so the AHA-120 shouldn't be seen as something rooted to the desktop.

In fact the AHA-120 carries a huge 4.2amp lithum battery in the housing to power the unique class A amplification circuit and hence the size which gives it oodles of playtime without resorting to a charge. Justin’s estimates runs it at around max 60 hours for 600ohms and 18 hours for 32 ohms which is really long to be honest, putting it in the much vaunted FiiO playback time for a far superior and weightier design which is fantastic. I have yet to really see a class a portable amp implemented like this, sure a few DIY interpretations from the hardcore but nothing this mature and market ready.

The uHA-120 is an AB portable headphone amp which uses a push-pull circuit allowing the amp to switch between the “class A and the B” depending on the demands being put on the amp and is great for minimizing crossover distortion. Though less efficient than class B it is certainly more efficient than class A amps such as the AHA-120 hence the smaller size and smaller battery but great playback time of around 24 hours. Gain control in the u-HA-120 is adjustable with a quick opening of the casing and changing the gain jumpers on the pcb. The kit comes complete with a gain setting toolkit consisting of a hex key and battery tool and takes but a few mins to change to your desired setting with a max setting of 10db/6db possible on the jumper settings.

Both amps come with the ability to play portable or through usb through a feature called APSS which is controlled through a white selector on the rear of each amp. APSS stands for Amplified Power Source Select and in a nut shell it basically allows you to select USB or battery as your power source depending on your needs. Now interestingly this is not a benign feature designed to make the amps look sophisticated. The APSS does actively change how both the uHA-120 and AHA-120 sound by giving both amps a significant high voltage swing boost. Those using higher impedance headphones or demanding tracks might appreciate this over the standard battery selector allowing the necessary power to drive those demanding cans without risking distortion creep or loosing any dynamics in their playback.

The AHA-120 further differentiates itself with it’s smaller sibling with a front plate impedance selector dial allowing you to select impedance levels from 32ohms to 600ohms to get the most out of your headphone demands and of course depending on what genre of music your driving it with. The AHA-120 also comes complete with a really nice high end Vishay volume potentiometer which is a custom made high spec pot from France (hence Vishay right?) that specifies a tighter channel tracking over the standard volume control pot. The resistance and turn of the pot is very silky smooth indeed and very accurate. I have tried a fair few in my time and this one really exudes confidence in it’s level of control.

The uHA-120 front fascia is a bit more simple lacking in the impedance selector of the AHA-120 and the Vishay pot but the “white velvet” pot is the first resistance type based on and off pot I have used and I am quite impressed with it’s implementation. Rather than a clunky on and off you simply push through a small resistance barrier and its on. It wont turn on by accident due to the level of resistance but the functionality is very smooth indeed. It’s quiet, very quiet and you only really know its on with a combination of LED lights coming on and the resistance in the pot weakening.

Both amps have rear charge rate selectors through which you can choose between a fast and normal setting. In most cases the fast setting for USB should suffice but those with slower usb outlets might prefer the normal setting due to the reduced power of these settings.

How do they sound?

In short one is more musical and the other is more neutral but still both have a fairly thick audio signature that I am going to presume now is the house sound of Just Audio. Both convey a more analog feel to their playback but both with their own distinct signatures. They are though pretty balanced overall in their approach but the uHA-120 is the musical brother with a more pronounced tuning for bass impact than the more neutral AHA-120. That is not to say the uha-120 is in anyway muddied or attenuated. The mids on the uHA-120 are excellent, clear and detailed. The bass is tight, impactful rather than sloppy and work exceedingly well with beat centric genres and add a bit of extra oomph to some heavy rock that I am rather fond of.

Anyone who knows me knows my love of the K550 headphone this year. One of the most articulate and responsive closed back headphones and a marked improvement on the thin and incoherent K series. Well the u-HA-120 takes up the K550 enjoyment a big notch. AKG are famous for their frugal bass tuning in all but a few of their headphones and the K550 is no exception though certainly better than the K701/2. The uHA-120 adores the K550 bringing in a more pronounced bass emphasis and rounded more natural feel to the highs. The K550’s slightly sparky nature is somewhat tamed with the uHA-120’s balanced reproduction and the bass extension leaps up a notch or two also.

So I got a bit braver and threw the K501 into the mix also. A notoriously hard to drive headphone with glorious mids and below average bass extension if under powered. The results were almost as a good as the K550. Still slightly thinner the pot was up to about 1-2pm on the dial but the mids were just glorious as always. Slightly less bass oomph but honestly was not surprised as nothing short of a full desktop can get the absolute best out of the K550 but very impressive indeed. Everything was snappy, clean and very transparent and plenty of sound stage. A bit of a result there I think.

The biggest surprise of all was how it handled the LCD-2 rev 2. Very impressive is the short answer. The uHA-120’s power should not be underestimated for it’s size. The LCD-2 is not the hardest planer to drive on the market but it does need some power to shine and reproduce that slam it is so famous for. To it’s credit the uha-120 did a fantastic job of ensuring the slam strayed right on cue without loosing that wonderful mid-section of the LCD-2 either. If there is one thing though the uHA-120 can’t quite achieve which it’s bigger brother has and that is sound stage. Just loosing out to the AHA-120 in terms of expansive sound stage. If you want an amp with a dirty club feel, aggressive bass tuning and a wonderfully transparent and lush mid section then the uHA-120 is the ticket. Honestly the gain on this is ridiculous for it’s size and capability.

So onto the AHA-120 and just because it is bigger I did say don’t expect a bigger bass monster or musical version x 2 of the uHA-120. The AHA-120 takes us in a different direction. That Class A amp is something special and the upgrade in resolution and detail and sound stage is immediately noticeable with the LCD-2 Rev 2. Working that Vishay pot to around 12 noon is sufficient for all but the most tone deaf to be honest so no question it has the power also for the LCD-2 rev 2.

It does not have the aggressive bass punch of the uHA-120 but it has a more detailed flowing reproduction with a much more expansive sound stage. Compared with the Ibasso Pb2 which is a 26v swing and very powerful amp I found the AHA-120 to offer a richer and fuller sound that was much more enjoyable and musical than the colder thinner Ibasso signature. It lacks the coloration of the ALO Audio range such as the National or Continental so it is not going to leap out at you but what you do get is a very competitive transparent and versatile amp that works wonderfully well with a ton of genres.

Concluding thoughts

These are special amps.

Understated as they look they punch hugely above their portable or transportable weight. If you are veering to bass and want a very portable setup grab the uHA-120 and if you want something a bit more detailed and resolving then the AHA-120 is going to cover a lot of genres very well indeed for the demanding audiophile. The balanced setup of both amps make them very likable indeed. The playback time is way above industry average. A lot of thought has been been put into these amps by Just Audio and a lot of high grade materials used in the process of manufacturing them also. I like it when a manufacturer doesn’t compromise on the build and quality of materials used and the price is well worth it. Both can driver planers with ease – there was a time when that was out of the question, and still is for most portable amps to be honest.

More info on these can be found at : www.justaudio.co.uk

If you fancy grabbing one on the Xmas rush or with your post-Xmas stash of loot then you can find them at Hifi Headphones here also: AHA-120 and the uHA-120

That’s it, I am done for Xmas, outta here and have a great one guys! See you in the new year!!

About The Author

Editor

Founder & Owner of headfonics.com. I first started reviewing in the late 80s (ouch!). Back then it was albums, rock concerts and interviews with a typewriter for the local rag. Now its desktop/portable and digital 2.1 audio on a rather nice laptop. How time flies.

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  • Justin

    Hi sir! Did you get the uHA120 velvet pot upgrade? Any idea what it does? thanks!

    • headfonics

      Better than 1dB Tracking plus White Velvet Modification – Your name is Justin? πŸ™‚

      • Justin

        Oh I see. Thank you for that. πŸ™‚ Yes sir! But not the one from just audio. :p

        • headfonics

          Maybe a new law should come out that all people called Justin should have 10% discount on Just Audio products hehe

          • Justin

            Hehe. I sure hope that will really apply to Just Audio. Hehe

  • Tin

    will this pair well with the hd25?

    • headfonics

      The uHa-120 should be a nice mobile pairing.

      • Tin

        Can you elaborate on that sir? Also, with the same headphone, HD25, this or the National? Thanks!

        • headfonics

          The amp is small to match the portability of the HD25 – it is also a warm amp where the HD25 can be a bit hot and should tame the highs on the HD25 a bit. I would get this over the national simply due to size considerations.

          • Tin

            Great to here that sir. Almost convinced now that I should buy the uHA-120. I just hope I could try one soon. Thanks again sir. πŸ™‚