Just Audio’s mobile headphone amplifiers, the uHA-120 and AHA-120

3rd March 2015


Looking to improve your mobile audio experience? Paul Rigby presents Just Audio’s mobile headphone amplifiers, the uHA-120 and AHA-120

Headphones are one of the most popular accessories in Hi-Fi, at the moment but getting a decent sound from a mobile set-up is not easy. Just Audio has released two mobile, battery-based, headphone amplifiers that promise to give audiophiles the quality they demand.


“I created the headphone amps after working at Nokia and Motorola specialising in baseband (i.e. user interface, audio and displays),” said Just Audio proprietor, Justin Harris. “I used to listen to headphones regularly at work, specifically a selection of Sennheisers and Beyer Dynamics through basic interfaces. I played around with different projects and this is where the uHA-120 came about, which incorporated the Lithium-Ion battery that I was using in the mobile industry.

This model was created as a discrete design to run at low voltages, “Discrete meaning that I could choose all of my own capacitors, resistors and so on. It took a while because you have to work out your inputs and outputs, what headphones you’re going to be driving and more. I initially had three prototypes, offered them to beta-testers and they all zeroed into the design used for the final uHA-120. The only addition to that early beta mode is a set of jumpers that you can access inside the chassis that will enable you to use In Ear Monitor (IEM) designs. “
For the uHA-120, the front of the chassis offers an in-house modified volume pot, a 3.5mm headphone socket (an adaptor is available for full-sized plugs) and input socket. The rear offers a micro-USB charge port, an adjacent charge light, which changes from red to green when the charge has completed plus an APSS switch: a charging selector. Normal charging mode in APSS is Battery but you can change the switch to the USB setting when listening to vinyl, during a ripping process, for example, to cater for the greater dynamic range. This switch handles a larger current. Finally, the Charge switch normally stays at Fast charge but you can change to Norm for older charge connections offering lower power servers. Basically, if the charge light dims dramatically, you need to change the switch from Fast to Norm.


The uHA-120 utilises a Class A/B amplifier, “I tried to utilise Class A only but the battery was just too small to cope,” said Harris. “I considered Class D but didn’t feel that the quality was high enough.”

Other components include an Op-amp for the input stage while the battery has a 30 hour life in between charges.

The AHA-120 features the same basic external controls (including IEM jumpers) with the addition of a rotary selector to select the optimum amount of Class A bias for a given headphone impedance. In this case, from 32-600 Ohms, “No-one has made a portable, battery powered, Class A headphone amplifier with USB charging before, that I know of,” added Harris. “Distortion is kept low by optimising the discrete stages coupled with the input stage by knowing what each of the components do and how they interact with each other.”


The AHA-120 also features an improved power conversion capability to effectively double the voltage of the battery, improving overall sound, “In fact, both amps are quite conservatively specified. Both have more headroom available which helps to boost the sound quality still further.”

Despite the extra power drain, the unit still offers 20 hours of use in-between charges.


To begin, I first played the 24bit/96kHz FLAC of Gerald Finzi’s ‘Let Us Garlands Bring, Op.18’ from the album, ‘Come Away Death’ by Marianne Beate Kielland & Sergej Osadchuk via my SSD-powered MacBook, using an Epiphany EHP-02 headphone amplifier as an aural reference. Both were run off battery power, as were the Just Audio amps.


First up was the uHA-120 (pronounced Micro HA-120) starting from a low cost option and recognising the mobile nature of Just Audio product, I plugged in my Sennheiser PX-100 headphones. A mixture of a haunting vocal plus strong, yet melancholy piano accompaniment was well handled by the uHA-120. There was a strength and fortitude that under-pinned the entire track lending weight and gravitas to the music. A sense of focus prevented excess bass bloom on the piano’s low-end frequencies while the vocal exhibited a welcome clarity that, despite some diffuse frequencies appearing during crescendos, provided a keen sense of emotion during the delivery. Generally, however, the presentation offered a single-minded approach to deliver the message of the music to the ear.

Moving to ‘Big Bad Girl’ from Harry ‘Big Daddy’ Hypolite as a 24bit/96kHz FLAC and plugging in B&W’s more costly, yet equally portable, P5 headphones, this bass-influenced design was ideal when tackling the raw, passionate blues tones. The uHA-120 tracked the metallic analogue guitar very well. These upper mid frequencies were well timed with a crisp detail that added space and an extra dimension to the soundstage. Meanwhile, Hypolite boomed with an expansive delivery that provided both texture and power.

Skunk Anansie’s ‘Hedonism’, ripped via EAC as a WAV from a CD successfully reflected back onto the B&W, showing how, during heavy rock, the phones can be bass dominant. There was plenty of guts and bass heft here while lead vocalist, Skin’s, earnest delivery was packed with power and upper mid detail.

Moving to the jazz tones of ‘Blagutten’ via the Hoff Ensemble at 24bit/192kHz and plugging in my top-of-the-range Sennheiser HD800s, the Just Audios had no problems in driving these superlative transducers. The uHA-120 can be slightly dry in the upper midrange area and this showed itself here as the trumpet was tracked very well but didn’t fly, dynamically. What it did offer, however, was meticulous detail that was both considered and studied.

Moving to the AHA-120 and continuing with the same track, while moving the load switch to the HD800’s required 300 Ohms, the AHA provided a great deal of extra space and air around the soundstage. The latter, in fact, was now much larger, enabling all instruments time and space to better manoeuvre around the music. Piano was tonally accurate while percussion was nuanced and powerful. Trumpet had a sublime brassy smooth grain that was infused with a humanistic delivery.

Both ‘Hedonism’ and ‘Big Bad Girl’ lifted the B&W P5 headphones to new heights, opening up the midrange (a difficult job for any headphone amp), providing enhanced musicality. The sense of dynamic space was obvious on the AHA-120 as well as a distinct tonal correctness that gave the music a natural, relaxed presentation.

Moving to the classical tones of ‘Let Us Garlands Bring’ and the PX-100 headphones, the music now had a broad expanse from which to deliver its despondent dirge. Happily, there was no sense of any invasive bloom to spoil the delicate arrangement, just an open, rather epic soundstage plus an ambitious midrange transcript.

Turning to my iPod Classic 80GB as a musical source and playing a WAV of Mozart’s Symphony No 7 in D through the PX-100s, the AHA-120 made sense of, what can often be, a muddled and muddied musical output via the iPod. Despite the budget headphone choice, the strings sounded smooth and confident while the wind instruments had, at a times, an almost ethereal aspect about them. That said, in many respects, the mHA-120 sounded better than the AHA-120 with an iPod sound source, proving to be more sympathetic with the PX-100s.

So I took the higher resolution of the AHA-120 and plugged it into my Sony Walkman WM-D6C cassette deck, spinning a metal tape (recorded on a Nakamichi Dragon) of Madness’s selected hits.

On this analogue source, the AHA-120 truly soared, opening up the soundstage. Piano was vivacious in its presentation, bouncing and leaping with great effect while percussion offered heft and a certain snappy response that added momentum to the overall track. Allied to that, the treble-infused cymbals shimmered while the lead vocal was both persuasive and responsive.


Both the uHA-120 and its more expensive brethren, the AHA-120, provide a high standard of musical playback, especially for mobile devices. The uHA-120 is a true pocket-sized amp that will enhance the performance of any mobile device, whether that be MP3 player, phone or laptop. It provides much need control and detail retrieval that will prove a revelation when compared to the standard outputs fitted to these devices.

The AHA-120 is a true specialist device, aimed at the user who wants nothing but the best in the mobile field. With its loading tweakability to suit serious headphone fans and its open, subtle yet powerful presentation, this design will satisfy the most demanding of mobile audiophiles.

Price: £200
Email: [email protected]
Website: www.justaudio.co.uk


Price: £350
Email: [email protected]
Website: www.justaudio.co.uk


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Epiphany EHP-02
Sennheiser PX-100
B&W P5
Sennheiser HD800
Apple iPod Classic 80GB
Sony Walkman WM-6DC
Apple MacBook Pro with SSD