iFi iDSD Diablo DAC with iPhone and Focal headphones

The iFi Audio iDSD Diablo is a semi-portable digital to analogue converter and headphone amplifier. It promises super high performance and enough battery power to handle any headphones. Let’s check it out.

tl;dr

  • Built-in battery with up to 12 hours battery life
  • Works with computers and phones
  • Standard 6.35mm and balanced 4.4mm headphone outputs
  • Balanced 4.4mm line output
  • USB, S/PDIF and Toslink inputs
  • iPower Low Noise charger included
  • iPurifier3 USB cleaner included
  • Supports PCM up to 384kHz/768kHz (see text) and up to DSD512
  • Supports MQA encoding
  • Largely compatible with standard Windows 10 drivers
  • With solid sound performance, being luggable for travel, and wide digital audio signal support, the iFi iDSD Diablo is a fine choice for many. But it’s not a good fit if you also want standard (non-balanced) line output for your home audio system
  • Inclusions: optical to 3.5mm adaptor, 3.5mm to 6.35mm headphone adaptor, USB Type-A to USB Type-C adaptor cable, USB 3.0-rated USB extension cable, 4.4mm Pentaconn plug to 2 x 3-pin XLR plugs adaptor for balanced line output, carry case
  • Price: $1,399
  • Available: here

iFi iDSD Diablo front

The iFi Audio iDSD Diablo details

Well, you won’t confuse the iFi Audio iDSD Diablo with other DACs. I guess you’d call the colour of the finish diabolical red. It’s certainly bold. Slab-shaped, it’s body is 153mm deep, 70mm wide and 25mm tall, and it weighs 334 grams. It feels nicely solid.

On the front is a knob for the analogue volume control – it pokes out an additional 7 or 8mm – an indicator light, a three-position slide switch and two headphone outputs. One of the outputs is a standard single-ended 6.35mm socket, while the other is for a 4.4mm Pentaconn balanced headphone connector. The switch is for output mode, which is basically the gain setting. The lowest setting is intended for highly sensitive in-ear monitors. I found that it was fine for my regular headphones, although I did notice when I was doing some measurements that as the volume control got near the extreme maximum position, the output started clipping at considerably below what the unit is capable of producing. So it’s best to choose the gain setting that has the volume control near the middle.

At the other end are four more connections. One is a USB Type-C socket for powering and charging the unit. iFi has included its iPower Low Noise 5-volt power supply with the unit (available separately for $79.95). The battery is rated at a hefty 4,800mAh. iFi says this is good for around 12 hours of operation at the low gain/Eco setting, 9 hours at the Normal setting and 6 hours at the high gain/Turbo setting. Those figures are also going to depend on such things as actual output level, headphone impedance and sensitivity. A small LED indicates battery level by its colour.

iFi iDSD Diablo rear

The 3.5mm socket is a combined coaxial and optical digital audio input, while the 4.4mm Pentaconn connection is a balanced line output. Note, there is no single-ended line output. That would rule out using the iFi Audio iDSD Diablo as the system DAC in systems lacking balanced line inputs. I suppose you could cobble up an adaptor that would work, but it would be worth getting assurances that this would be safe. That is not always the case with balanced connections. But if your system does have balanced line inputs, it is nicely catered for by the iFi Audio iDSD Diablo because it comes with a 4.4mm to 2 x XLR plugs adaptor cable, ready to plug into a balanced preamplifier input. The line output is fixed in level.

Finally, the last connection is for most people the main input. This is a USB connection for use with a computer or phone. We’ll spend more time on that shortly.

iFi iDSD Diablo internals

I’m starting to lose count of the number of DACs I have used and measured which use the fine SABRE DAC chips from ESS. And those which don’t have mostly used the equally fine AKM chips. So it was interesting to see that the Diablo uses two Burr-Brown DAC chips. Go back a few years and Burr-Brown was the bee’s knees in DAC chips. Since then it has been bought by Texas Instruments, and seems to have gone a little out of fashion.

iFi iDSD Diablo with iPhone

But it encompasses a somewhat different decoding philosophy to those other chip designs. Most use Delta-Sigma decoding. I partially understand this, but even to that extent it is way to mathematical to get into here and is far from intuitive. By contrast, iFi labels its system “Burr-Brown MultiBit”. I don’t know if it’s full R2R old-school decoding, but it clearly eschews Delta-Sigma. Many swear by multibit. I’m a fan of results, rather than the technical means by which they’re achieved.

Also in there is a fully balanced amplifier. The decoded signal can drive balanced – plus and minus signals identically opposite to each other and quite separate from the earth/shielding/case/common rail of the system – or single-ended outputs. “Single-ended” is another word for the conventional 6.35mm stereo headphone socket.

iFi Audio says that the balanced output is good for over 600mW into 600 ohms, and nearly 5 watts into 32 ohms! For regular headphones, it says that you can expect 153 milliwatts into 600 ohms, and over 2.4 watts into 32 ohms.

Connecting via USB

Most portable DACs come with a Micro-B USB or USB Type-C socket for connecting to computer or phone. Most desktop DACs come with a full-sized USB Type-B socket for connecting to a computer. The iFi Audio iDSD Diablo comes with a USB Type-A plug, a bit like an ultra-portable DAC (eg, the AudioQuest DragonFly). Except that the plug is recessed all the way into the metal enclosure of the Diablo, albeit with a generous cut-out around it. So of course you can’t plug it directly into anything. A high quality USB 3.0-rated extension cable is included with the Diablo, so you use that to plug into a computer.

I also used this with a Lightning to USB converter (sometimes called a USB Camera Adaptor) to get sound from my iPhone. And with a USB Type-A to USB Type-C converter so that I could use it with my Android phone.

iFi iDSD Diablo

Also bundled with the Diablo is the iFi Audio iPurifier3 noise isolator (available separately for $169.95). In addition to cleaning noise out of the incoming USB signal, it acts an adaptor. Its input is a standard USB Type-B socket, while its output is a USB Type-A socket. It slips neatly into the hole in the case, although it looks a bit odd being white in colour.

Setting up the iFi Audio iDSD Diablo

We’ve covered setting up DACs for Windows here, but there were a couple of wrinkles with the Diablo.

First, there are two viable firmware installations. Firmware 5.30, which is pre-installed, gives you up to PCM384, DSD256 and MQA. You can install firmware 5.20 for PCM768, DSD512, but that does not support MQA. I stuck with the former since I have only one DSD512 track and zero PCM768 tracks. (Go on, try to find a PCM track with 768kHz encoding! I will applaud you if you are successful. I have not been.) But TIDAL has lots of MQA content. So MQA/PCM384 it is.

iFi iDSD Diablo front panel connections

And it turned out that my DSD512 track worked fine with firmware 5.30 anyway, making the front LED light up red, which is what it is supposed to do on receipt of DSD512.

Second, for some reason the in-box documentation didn’t make any driver-installation suggestions. That being the case, I initially ran the unit with the default drivers from Windows 10. It mostly worked okay with them … apart from some clicking in the right channel when I played DSD256 over DoP track via WASAPI. And there were lots of dropouts playing the MQA-encoded Rush album Permanent Waves from TIDAL. The LED indicator on the front panel kept switching between MQA (magenta) and USB Audio Class 1.0 resolution (green),

Since we’re mentioning MQA, I should note that the TIDAL app on the iPhone managed to invoke this mode, where appropriate, on the iFi iDSD Diablo.

Listening

Heh, there’s a whopping great battery in there, so why not go out and about with the iFi Audio iDSD Diablo? No, I don’t mean pocketing it. Too heavy for that. But I do mean taking it down to my local coffee shop – large flat white, please, with three shots, have here – and doing some work while listening. I had my typing computer rather than my media computer, and I didn’t want to install drivers on it so I figured I’d just rely on the Windows drivers. And because I’d be out in public, I took my old Oppo PM-3 Planar Magnetic closed back headphones. Flat folding for carrying, and boise isolation.

iPhone Camera Adaptor with iFi iDSD Diablo

I started with some TIDAL, and was soon reminded that high resolution MQA does not work with the iFi Audio iDSD Diablo when they’re relying on Windows drivers. That prompted me to check some variations. Beyonce’s Lemonade is MQA encoded, but only for authentication, not for a higher sampling rate than standard CD. It worked perfectly. So did a downloaded MQA track which I sent to the DAC via the WASAPI interface using JRiver Media Center. It also worked fine.

Anyway, I could play any TIDAL I wanted, including otherwise problematic tracks, just by switching from “Master” to “HiFi” quality.

During the experiments I lingered for a while on Lemonade and simply basked in the bass. The Oppo headphones are pretty much flat down to 20 hertz, but are also lowish in impedance – 26 ohms with almost no variation across the audible bandwidth. That low impedance and bass competence will expose any deficiencies in the driving amplifier. There were none. I might has well have been plugged into a mighty desktop headphone amplifier. That’s what the system sounded like.

iFi Audio Diablo with Rubik's Cube for scale

The results were similar with all the other headphones I threw at the iFi Audio iDSD Diablo. In addition to the Oppo headphones, I used Sennheiser HD 660S in balanced configuration, Focal Celestee (also closed back, but a little too bulky to carry around to a coffee shop), Focal Elear and even some IEMs. Do be cautious with high efficiency in-ear monitors. This unit can drive them – and you – to distraction.

Essentially, it drew the best out of each set of headphone that they were capable of delivering, and you can’t ask more than that.

Measurements

When I measure headphone outputs, I start with virtually no load at all. Basically, that gives the same result as if I had plugged the headphone output into the line input on a high-fidelity system.  The method is simple: just turn up the level until the tops of the sine waves start to flatten on the oscilloscope, or there’s some other sign of distress. I’m figuring that the iFi Audio iDSD Diablo has some kind of protective circuitry built in because early in the piece, the unloaded output briefly got up to over 8 volts. Then the waveform started pulsating a little, I turned it down to get back to a stable waveform, then up a bit and clipping was coming in much earlier. After fiddling for a while, I could get a steady, held 2.5 volts. I’m confident that there’s a lot of headroom above that for momentary peaks.

Then, when I started putting headphone-like loads on the output, it stabilised and allowed me to consistently dial in higher output levels. The net effect was that into 300-ohm loads, the iFi Audio iDSD Diablo was able to deliver around 84mW, or 19dB above the sensitivity rating of the headphones in use. Into 16-ohm loads, the output was 960 milliwatts, or almost +30dB. I doubt you’ll find many headphones that the iFi Audio iDSD Diablo can’t drive effectively. All those measurements are for the regular 6.35mm headphone output – I’m not set up to measure the power of the balanced output – but you can expect those figures at the very least from the balanced output, and probably significantly higher.

The impedance of the unbalanced headphone output was a tiny 0.35 ohms by my measurement and calculation. If your headphones have a wildly varying impedance, you need not worry about this inducing frequency response variations in this unit.

Frequency response

You can’t fiddle with the filters in this DAC. I suspect that’s because the Burr-Brown multibit system doesn’t support such a function. While I generally like more options given to the end user, they really can become confusing, and I tend to find it impossible to audibly distinguish the various filter options.

iFi iDSD Diablo frequency response at balanced line output

That standard filter yields a frequency response with CD-standard signals which is dead flat from 10 hertz to 20,000 hertz (-0.2db at 5 hertz and 20,300 hertz – see graph immediately above). A lot of my measurements showed a channel mismatch of 0.5dB, especially with the volume control set to around 50%. I did not hear this. With 192kHz sampling, the output was down by 0.1dB at 20kHz – it must use a gentler filter for higher sampling frequencies than it does for 44.1kHz – -1dB at 46kHz and -3dB at 78kHz:

iFi iDSD Diablo - frequency response with 192kHz sampling

I won’t bother putting up the graph for the headphone output because it was identical to the balanced line output.

My measurement software simply did not like the iFi Audio iDSD Diablo when it came to measuring noise performance. Using the balanced line outputs it reported, with 24-bit signals – a signal to noise ratio of -116.5dBA, which is way, way beyond inaudible – but the graph showed a kind of weird rise around the test frequency. I spent at least half a day fiddling around trying to work out what was going on. Because, the fact is, that graph makes no sense. In listening, DAC-created noise was simply not a thing. One thing that was clear, however, was that there was no effective difference in noise levels regardless of whether the Surface Pro 2017 feeding the unit was running independently from its battery, or connected to both power and a very noisy Ethernet network. Lots of DACs don’t provide that kind of isolation. Mind you, that was without even using the iPurifier3 USB cleaner. I was impressed.

Here’s the signal produced on the line output when fed with a single 1kHz sine wave. Very clean, very low noise and only a few low-level harmonic distortion products:

iFi iDSD Diablo noise with 24-bit audio

The measurement software reported THD of 0.00099%.

iFi does boast in its promotional material about having a total harmonic distortion out of its headphone output of less than 0.002%. I measured well under than for 0.5 volts RMS output into both 300 ohms and 16 ohms. The noise was higher than I expected, though, at -89.6dBA and -86.9dBA respectively. Both still inaudible though.

Conclusion

Despite the slightly weird measurements, I found the iFi Audio iDSD Diablo to be a stunningly fine piece of audiophile-grade equipment. You can throw at it any digital audio standard that you like, and it will deliver the goods over the headphone output.

But, remember, it is not suitable for plugging into most regular home audio systems. Unless, of course, your system has balanced line inputs.

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