Review: Hands-on with Just Audio’s AHA-120 headphone amp

ImageAfter my wife reviewed some of the Final Audio Design headphones recently for Hi-Fi Widow, UK distributor HiFiHeadphones  was keen for me to review one of the headphone amplifiers it sells.

It’s an interesting reverse, for while the Final Audio Design headphones come from Japan, and are just being introduced into the UK, HiFiHeadphones’ Robin London-Willis explained that the Just Audio headphone amplifiers, made near Cambridge, England, are attracting a following from enthusiasts in Japan.

Founded in 2009 by Justin Harris, who has a first class Masters degree in Electronics and a background and telecommunications, Just Audio specialises in portable amplifiers for headphone enthusiasts, and rather than go for the budget end of the market, which is already well-served with inexpensive chip-based amplifiers, Just Audio is all about quality of both build and sound.

The AHA-120 is the larger and more expensive of the two models in the current Just Audio line-up, selling for just under £350 through HiFiHeadphones in the UK, and ¥44,700 from Guter Preis in Japan.

It’s a compact box, at 12.6cm long, 8cm wide and 2.6cm tall, and weighs a solid-feeling 332g, thanks to the inclusion of an internal lithium-polymer battery said to be good for 60 hours’ use – so you won’t run out of power even on very long flights.


Battery or USB power
The battery can be charged, or the amplifier powered, via a USB input, with the AHA-120 offering an Amplifier Power Source Selection (APSS) switch on the rear to select between battery and USB power. Usually battery power is best, but when using headphones presenting a difficult load to the amplifier, or playing very dynamic music, the extra power available from USB – 5.25V instead of the internal battery’s 4.2V – will increase the dynamic headroom available.


Also provided is a front-panel selector switch to adjust the amplifier for different headphone impedances, with positions for 32ohms through to 600ohms: this Headphone A-Class Alignment Control (HAAC) adjusts the bias of the Class A amplification to best suit the requirements of different headphones.

Connection is simple, the AHA-120 having a front-panel 3.5mm stereo line input and a headphone output of the same kind, located between that HAAC selector and the high-quality custom-made volume control, which also acts as an on/off switch.

I used the AHA-120 both with my MacBook computer, connecting power via USB and signal using a short 3.5mm-to-3.5mm cable, and also with my iPhone, with headphones including very affordable SoundMagic E10s and the excellent Phonak Audeo PFE111, some Monster iSport in-ears and B&W’s P3 on-ear headphones – I even tried the amplifier with a pair of stock Apple earbuds, just to see whether decent amplification could make them sound any better.

The news is that yes, it can – though given the poor sound of the earbuds, don’t expect miracles!

Even with inexpensive earphones the Just Audio amplifier sounds so much better than the output of either computer or portable player, just as modestly priced speakers of reasonable quality will sound better when driven by a good amplifier.

There’s weight, power and real bass attack on offer here: not loose and boomy stuff, but solid, confident low frequencies giving the music a sense of scale and substance not usually heard even through very good headphones. And as you improve the headphones with which the Just Audio is used, it simply goes on getting better.

The sound here is smooth without becoming soft, beautifully detailed and involving, and of course has that bass richness and control most of us want, but which many spend years changing and testing different headphones to achieve.

Yes, the Just Audio amplifier is perhaps a bit big for the daily commute – but then there are lots of smaller amplifiers, not least Just Audio’s Class AB u-HA120, to suit those needs – but for long-distance travel where only the best sound is good enough, or for listening at home, this is a remarkable product, handmade in the best tradition of British Audio.

Just Audio AHA-120
Headphone amplifier
Price £350/¥44,700
Maximum output 60mW rms into 32ohms
Maximum gain 12dB (0dB or 6dB available via internal adjustment)
Dynamic range >100dB
Bandwidth (-1dB) 10Hz-40kHz
Output impedance < 3 ohm
Output current limit +/-250mA per channel


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