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Win or lose the video goes on YouTube and the story is published on this blog. The test would be administered by an independent third party (I won’t even be present). The challenging op amp’s measurements must at least meet the minimum criteria outlined in the O2 Design Principals. If you can’t tell them apart, you donate $500 to the charity of my choice. If you can tell them apart, I’ll give $500 to the charity of your choice. And if you’re still a skeptic, let’s schedule your YouTube video appearance with an ABX comparator, the op amp of your choice, and a $0.60 NE5532 using two O2 boards and the op amps in the gain stage. But I did test a couple parts from National and Analog Devices.īLIND TESTING CHALLENGE: For those of you who believe there’s more to op amp sound than just the measurements, please read the Op Amp Myths article if you haven’t already. So most of my evaluation was limited to what Mouser stocks. Mouser offers Ti, Burr Brown, JRC/NJR, On Semi and others, but they don’t offer National, Analog Devices or Linear Technology. MOUSER’s SELECTION: One of the design goals of the O2 was to purchase as many parts as possible from a single vendor and, for some good reasons, that turned out to be Mouser Electronics.

While I did adjust the compensation and feedback impedance with some op amps, ultimately, the measurements are all in the same circuit configuration unless otherwise noted. This rules out single devices, surface mount packages, and lower voltage op amps. It also requires op amps that can operate comfortably at +/- 12 volts (24 volts total). LIMITED SCOPE: The O2 headphone amp uses DIY-friendly DIP8 dual op amps.

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I’ve also referenced the work of Douglas Self who has run many op amps through an Audio Precision SYS-2700 series audio analyzer in various configurations.

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It’s a 436 page monumental effort in the form of a huge 35 MB PDF (which is why I’m not linking to it here).

For an example of a more ambitious effort, look up Samuel Groner’s “Operational Amplifier Distortion” published in 2009.

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A complete op amp survey is at least several full weeks worth of work. So please don’t expect a technical paper worthy of the Audio Engineering Society. It’s mostly a side story to my research and development of the O2 Headphone Amp. REALITY CHECK: This isn’t a comprehensive comparison. This article is all about measuring the results and putting some facts around the differences between op amps in a typical audio application. But when someone “upgrades” to an expensive op amp with high expectations many assume the different sound must be better sound. Some of the differences heard could be high frequency instability. Worse, these usually faster parts can easily be unstable in a circuit designed for a much slower part. A lot of op amps get “upgraded” to much more expensive parts usually with zero real world benefit. THIS STUFF MATTERS: A lot of people play around with “op amp rolling” but they mostly lack the ability to measure the results. This is the follow up with more technical information, a summary of many popular op amps, and some of the measurements I made.