For those who still don't know: As with the Hugo, you have to use the
headphone output to feed external amps – hence with a signal considered not good enough on its own. That doesn't make sense, particularly when the Mojo's headphone output is more than strong enough for the headphones used – which it is in most cases except for the few with extremely low sensitivity. Underlined by extremely low harmonic-distortion figures according to the specs and the developer, Rob Watts, whose opinion about external amps for the Hugo can be read
here and
here. And since Hugo and Mojo share virtually the same design...
A systematic comparision with all my amps and the direct connection to the Hugo (and lately the «best», most accurate and neutral amp I know – the Corda Symphony – with the Mojo) showed that Hugo and Mojo sound best without additional amplification: more accurate, more transparent, faster, more detailed. I've paid special attention to very low bass notes – and there both DACs/amps are every bit as powerful as the external amp, moreover they show better control. One thing that also struck me is the more forgiving nature of the amps: all of them sound a bit rounder and smoother – less focussed –, which goes hand in hand with a sense of greater space and an illusion of increased «clarity». Tested with HiFiMan HE1000, Sennheiser HD 800 and Shure SE846, among others.
Like many tube amps also solid-state amps produce harmonic distortion that sounds pleasing to the ears. It's easy to mix that up with higher sound quality, the more so as this trait contributes to an icreased forgivingness toward tonal imbalances and resonances. So if you prefer a more puristic approach and are too lazy to carry an extra amp with you, there's a convenient tool for getting your sound where you want it to be if it's not quite there yet: an equalizer – like the one that's possibly built into your audio player. That way you're indepenent of the sonic synergy an amp may create between the Mojo and your head-/earphone after all, with above-mentioned disadvantages from a technical perspective.