How To Get Digital Audio Output From Your iPhone

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Update April 21st, 2017
I would personally suggest a DAC that officially supports iOS devices such as the Chord Mojo, Chord Hugo or the great ifi Audio iDSD (will do a review on this soon – waiting to get my hands on one) to stay out of connection troubles. However, I have tested the SMSL M8 and it works with an iPhone 5c…go figure.

Update November 21st, 2016
Since there have been numerous connection problems and compatibility issues with iOS versions, I’d currently treat this as an experiment. If you are using your iPhone at home, I personally recommend streaming using AirPlay. Or take a look at one of the Raspberry PI setups

Apple’s iPhone is pretty well known to offer excellent sound quality through its analog outputs that is head and shoulders above the competition. Apple has been using Wolfson chipsets from the very beginning but later moved to Cirrus Logic chipsets – pretty good choices for a mobile device. The sound quality as actually more than decent at full volume level. A simply 3.5mm to RCA cable is all it takes to hook up your iDevice to your stereo system.

My plan is to use my favorite apps including Spotify and Qobuz with the hope of the sound quality being good enough for my main rig. Of course being an audiophile, I kept wondering whether I could outperform Apple’s built-in DAC chip.

With the advent of iOS 7, Apple has officially announced support for streaming digital audio. That’s great news because it means you can practically take any iDevice running iOS 7 or later – this includes iPads, iPhones or iPod Touches – and connect an external DAC (digital-to-audio converter) with USB input. There’s a limitation of bitrate however so you are not going to be able to play high-resolution 24bit tracks directly.

Self-powered USB DAC with optional USB hub

A self-powered USB DAC is an ideal starting point. Self-powered means your DAC won’t draw additional power from the USB port. This is important because Apple intentionally limits the power consumption by software to about 5mA. If however your DAC does rely on USB power or if it declares itself as more power-hungry than Apple allows upon connecting, you are going to need a powered USB hub. Apple will alert you so don’t worry – you can’t break anything.

I personally use a cheap powered USB hub from SIGMA which unfortunately is no longer available. You can typically find USB hubs for less than $20 on Amazon.com. Of course this means you have to manage yet another device but it’s a minor pain compared to larger music server projects.

Next, you need an adapter for your iOS device that provides a USB output. Here’s where things differ slightly depending on your iOS device generation:

You are going to need Apple’s 30-pin Camera Connection Kit (CCK) adapter (part number MC531ZM/A) and take the USB output to your DAC. More on that below.

Newer generation iOS devices including the iPhone 6 require Apple’s Lightning to USB Camera Adapter (part number MD821ZM). Again, connect your DAC from the USB output of the adapter.

Just about any standard USB cable will do the job. Nothing fancy needed here. Use what you have or purchase on from Amazon.com

First, connect Apple’s dongle to your iDevice and plug the USB cable into the provided USB port. Hook up the other end of the USB cable to your powered USB hub’s input. Finally, take the USB connection from your DAC to one of the ports of your USB hub – I use the first port for simplicity. You should now be able to play back music from your iPhone through your external DAC.

I use my company’s iPhone 4S hooked up to a JDS Labs ODAC
for experimenting purposes. As you can see, Apple’s CCK output goes straight into my USB hub’s input port. My external DAC does not have its own power source so the wiring is a bit messy.

Figure 1: iPhone 4s using CCK hooked up to my external DAC (not shown in picture)

I can hear a small audible improvement with lossless tracks, maybe a bit more air around the instruments. It’s hard to say because the volume levels need to be matched precisely. At the end of the day audio is subjective anyway and while your external DAC may be technically superior to what Apple offers, you may or may not hear sonic improvements on your setup. But for music afficionados seeking the best possible performance, I definitely recommend going with an external DAC as above. At least give it a try.

A problem with USB audio however is the actual clock reconstruction method leading to higher levels of jitter. Taking a digital signal to an external DAC can also introduce all sorts of nasty noise problems that can interfere with the audio signal.

Is this for you? I haven’t played with the setup long enough to draw final conclusions but I’d recommend going the extra mile with an external DAC only if you are traveling and want to squeeze out a tiny bit of extra performance for your mobile listening enjoyment. For stationary listening, pick a network music player such as the excellent Pioneer N50 or a more recent Marantz player. These already come with built-in support for your iDevices. I would peronally rather use my iPhone or iPad as a remote control device than becoming the sole source of music.