Since early 2013 my iMac has shepherded every last yenny into my business. And though I trust it almost implicitly in matters of heavy image processing, I don’t plug my headphones into it. Why? Two reasons:

It’s a computer, and I’m an audiophile. No matter how much of a skeptic I am, I’ve listened too much to audiophile claims, one of which is that on-board sound sucks.
The headphone jack is located out back. And I’m not one for the reach around.

Pish poo.

Well, in the last few days, I’ve been listening to my DT880/600, IzoPhones-30, and Ultrasone IQ, straight from my iMac’s headphone port. And to be honest, I’ve been surprised. Volume-matched to my Lynx Hilo, my DT880/600 and IzoPhones-30 render no notable differences, and it raises volume well past my personal discomfort level. Evidently the iMac’s headphone output supplies 1,4 VRMS (iMac external features, ports, and connectors), which is more than a number of dedicated amplifiers. It is, in fact, almost as powerful as the Hilo.

Where it fails is hiss. It hisses. I’ve heard worse, but not in a long while. That hiss is really amplified through sensitive earphones such as the Ultrasone IQ. It is a shame especially because otherwise, its output is very good. In fact, if its hiss were lower, and the jack easier to reach, I’d happily recommend iMac users skip the whole DAC/amp thing unless they absolutely need more than 1,4 VRMS.

Anyway, onto RMAA.

The following Rightmark Audio Analyzer tests were conducted through this equipment.

Source: iMac 2012 27”
ADC: Lynx Studio HILO LT-TB
Computer: 2012 27" iMac
Cables: 1,5m Hosa Pro 3,5mm stereo to dual 3-pin XLR (around 8$); bespoke y-split 2,5 TRRS to dual 3-pin XLR made by Musashi Sound Technology.

Loads:

NL - no load
SM2 - Earsonics SM2
ES7 - Audio Technica ES7
DT880 - Beyerdynamic DT880/600

24-bit all loads results @+6dBV - headphone output

24-bit @+6dBV - headphone output summary

End words

While the iMac sounds good with non-sensitive headphones, and spits decent very good quality signal to earphones, it hisses way too much to be a reliable all-in-one or a recommended source for earphone users. It surpasses 16-bit spec in almost all metrics, and is stabler than many dedicated amp/DACs out there.