I can confirm the same as
@krismusic. Basically I've found that any IEM or headphone that works well within the voltage and current delivery limits of the the Apple dongle sounds identical on the Mojo. Where the Mojo kicks in is with high impedance headphones requiring a lot of voltage, or very low impedance IEMs which require a lot of current. These can sound a tad dull and un-dynamic on the Apple dongle.
In fact in my tests with Beyer DT1990s with 250Ω impedance it was a case of Mojo = Fiio E17 = Dragonfly Red > iPhone dongle.
The only DAC that I have that was noticeably better was the ADI-2 DAC which provided a better scale and separation
making the others sound a touch congested by comparison, but you'd only really notice it doing direct A/B.
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I find this very interesting, and in direct contradiction to at least one reply given by another person
here over a year ago that the apple dongle
sounds "thin" compared with the Mojo and even
when compared with other phones and other reasonable priced players.
My opinion is that the dongle
looks thin (and also looks fragile)
but can
sound really good, at least at lower to medium volumes
and with some reasonably priced audiophile headphones - my Grado SR80e, SR225e and Shure SE535 all sounding fine through the dongle -
including the Apple USB C dongle through the new iPad Pro!
And although they look fragile, my original dongles are still working fine and for well over a year.
Of course with harder to drive 'phones, at higher volumes and with uber-detailed phones - e.g. SE846 - the Mojo's superiority over the dongle will likely be obvious.
I'd like to make another point - my Grado GS1000i are 32 ohms, same as my other Grado's but is the only phone I have that
doesn't sound assured and full-bodied out of my Mojo, instead my ALO Island, which has a simpler but good dac but is
able to drive the large driver's GS with its much higher current and the sound is much better as a result.
Even at low volumes the GS is under-powered by Mojo but sounds magnificent out of the lower cost Island.
So even though it looks good on spec be aware that the Mojo may be underpowered for higher performance 'phones (I'm sure this point has
been made on these forums before many times).
....one last point: I've resisted upgrading from Mojo - e.g. to Hugo 2. It seems like an endless upgrade ladder -
Hugo 2, then M-Scaler, etc. What I've gleaned is that the Hugo 2 really only comes into its own when
paired with certain headphones, and with others may not sound that much better than Mojo.
Regardless, I'm very happy both with the musical quality of the Apple dongles out of my devices
as well as that of my Chord Mojo, and although I have heard Hugo 2 and can hear and appreciate the difference
(much bigger soundstage, better layering, air, seperation, detail, more refined, etc.it just ain't worth the outlay to me.
...so far anyway.