iFi iDSD Diablo II Review

The Diablo II is the latest portable DAC and headphone amplifiers in the long-running iDSD series from UK audio designers, iFi. The Diablo II continues with the diablo red colorway of the original and comes in an even more industrial, and utilitarian design. 

The iFi Diablo II has an MRSP of $1299 and can be purchased at various online merchants. This review unit was provided to me by iFi directly.

The Diablo II features Burr-Brown DAC chipsets, similar to many of their other products in their history, and custom op-amps. The product also has both 4.4mm and 3.5mm outputs for both balanced and unbalanced jacks. In addition, the rear has a line in/line out 4.4mm port, a 3.5mm SP/DIF input, and a separate USB-C charging and USB-C data port. There is also a bluetooth connection button on the rear side. 

The unit also comes with 2 different sets of feet that can slide into the tracks on the chassis. The two sets let you have a lower profile or a more raised stand, making it both easier to use the volume knob, as well as allow for better cooling and airflow. The Diablo II also comes with a very nice iFi-branded carrying case that fits the stands and the unit as well as has plenty of room for accessories and a small set of IEMs or two.


The Diablo II advertises with a 5 Watt output, and one that can drive your hardest to drive headphones in a portable solution. Now this sounds much better in writing than in practice. In reality, it seems that the unit just has its amp gain turned up at every step of the way, and that inadvertently gives the impression of it being more powerful than it is. Case in point, GoldenSound measured a Diablo 2 review unit he received and it did not get to the advertised 5 Watt marketing material claims at a typical impedance load of a headphone, at least not using industry standard testing protocol. Instead, it reaches about 1.6 Watts, which is still, a very large amount of power in a small transportable DAC.

With that said, there is still the initial reaction of, "wow! this thing is powerful!" That's because it seems that iFi set the gain level to 0 at their lowest gain setting, a switch that is on the front panel. Most headphone amps typically have a -6 to -15dB gain at low settings to allow better volume control tuning on more sensitive headphones and in-ears, and that's very important for portable use headphone gear, since most are quite sensitive. Instead, when I use this with any of my in-ears, I barely turn the knob and its LOUD. Even the Subtonic Storm, which has sensitivity ratings lower than most headphones, is already loud with very little movement on the dial, at the lowest gain setting. 

When I put on any one of my Hifiman Planars - the HE400SE, there's also very little need to turn the dial on low. I'm actually not sure what the point of having medium and high gain settings are, as all you're doing is adding more distortion possibility to the signal, and its already way too loud at the lowest setting.

Of course, to combat this, iFi added their signature "IEMatch" attenuators to the circuit. On the very bottom of the device, there is a flip for 4.4mm and 6.35mm, as well as off. I'm actually not really sure what the point of the 4.4mm and 6.35mm flip is as they both get attenuated regardless, and that's probably because this is not a true balanced and unique setup. In addition to lowering the volume, this switch also adds additional output impedance to the amplifier line. This can have negative effects on some sensitive IEMs and headphones. In many cases, adding impedance will increase bass and lower treble, although it could also be the opposite and normally this isn't a good thing.

 So, to recap:

iFi chose to add a ton of gain to their amplifier instead of industry standard. This makes it very hard to control volume to practically all my headphones and makes it pretty much useless with most of my IEMs. To fix this, they added output impedance to the outputs, and that causes even more problems to some of my IEMs and if it doesnt change the IEM tonality, it affects the overall dynamics of the signal. Great design. Next time, just reduce the gain in the system and it'll be quite more useful because, the sound of this product is actually pretty good.

Sound Impressions

Before I get too far into the sound impressions, I do want to add that I did not have any hissing amp noise with the IEMs I tried -- this was primarily the Subtonic Storm, Unique Melody MEST and Hidition Viento.  One of the problems with some of the other iFi portable amps is their noisy nature, and I don't hear any of that with this specific model. That said, neither of these are inherently ultra-sensitive, so I can't comment on something like a Campfire Andromeda or a set of Vision Ears in-ears which are typically very, very sensitive to both volume noise, and impedance tonality changes.

The iFi Diablo II has a fairly neutral sound, that leans a tad bright on the upper treble end, but stays very focused in the linear sound, but does not come across as sterile. It has a good amount of dynamics, although, may not be the most dynamic amplifier I've heard. It also has good stereo width and resolution is good. In the past, I've found the old iFi products to have a good warm-ish sound, and more recently in the past few years, iFi has gone a bit too sharp in the upper treble with their filtering. This specific unit hits a very good middle ground of neutrality with a small amount of body. 

If I'd change anything, I'd probably try to reduce the upper sharp attack slightly, as I do find it has a small bit of ringing artifact in the headphones I used with this amplifier -- mainly the aforementioned IEMs and the Hifiman HE400SE and Sennheiser HD600. 

I did try the TOTL Hifiman Susvara with this, and while I got plenty loud, the synergy was very poor -- too bright, lacking dynamics, and just missing warmth and body overall. I just don't think the Diablo does a good enough job here with this headphone in particular. 

For the most part, I really enjoyed listening to the Diablo II with the Subtonic Storm. It does showcase the Storm's dynamics fairly well, and its very clean resolution. The upper mid-range does come across a little bright, but luckily with the Storm it doesn't become a big problem with its semi-relaxed presentation, at least compared to my other gear.

The HE400SE can sound bright with this -- as it is already a brightly-tuned headphone. What it does give to this headphone is a punch dynamic sound on the low end. Generally speaking, while this pairing works, I don't particularly like it.

The Diablo II does sound great with the HD600 though. This pairing is great as the HD600 is dark and relaxed enough to not get caught in the iFi brightness up top, and this actually provides a little more energy and punch to the timbre-king.

Final Thoughts

The Diablo II has a lot of potential. With the right pairing -- i.e. a relatively insensitive headphone or IEM that is warmer in nature -- I found the Diablo II to really sound solid with good clarity and air. I didn't particularly like it with brighter headphones, and the power gain levels are just too high to use with sensitive headphones and in-ear monitors without the use of their IEMatch switches, which also cause impedance shifts in some transducers.

I do feel like I have the same general "complaints" about most iFi devices: gain set too high, forced to use IEMatch, impedance mismatching, etc. At least this device does not have amp noise as far as I can tell on my IEMs. 

If iFi would just lower gain levels, it would fix a lot of my reluctances with giving iFi products a better review, but until then, there's a large caveat with using this product with IEMs in general. You may not be able to control volume easily for a lot of portable gear. If you're using this with headphones that require more power, then it's quite a suitable pairing for warmer and darker headphones.

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