This is a review and detailed measurements of the JDS Labs EL AMP II Headphone Amplifier. It was kindly supplied to me by the company and is the companion to the EL DAC II I just reviewed. The EL AMP II costs US $249. JDS previously set a record with the Atom headphone amp which produced superlative performance for just US $99. Many people have asked for that performance but in a metal enclosure. Is the EL AMP II the answer? We will find out.The EL AMP II uses the sexy enclosure of previous generation product with its massive volume control:As you see, it stacks nicely on top of the EL DAC II.All controls are in the back:The power button plays double duty controlling whether the headphone or line out is active. I limited my testing to headphone out.The gain switch toggles between high and low.The same universal chunky 16 volt AC external transformer powers the EL AMP II. So you better have a dedicated power strip to accommodate the two.The volume control is the star of the show. It feels good to use. So much so that you may be tempted to just play with it.Anyway, I am sure you are hear to know how it performs so let's measure it.Setting our input level to 2 volts, and keeping the unit at max volume in low gain gets us unity gain:I like this gain setting so that you don't over power sensitive headphones.Performance is just a hair better than the Atom which may be due to sample to sample variation or slightly better implementation. You have audibly transparent distortion giving you what comes in, into lower impedance load and with more power. Just what an amplifier needs to do.Ranking is of course near top of the class:Signal to noise ratio at full output is exceptional (left):Reducing the output to just 50 millivolts to check how noisy it would be with sensitive IEMs, also shows excellent performance:Frequency response doesn't get better than this:Intermodulation (plus noise) versus level shows an exceptionally quiet amplifier in low gain mode:In high gain it goes past what our reference THX AAA 7890 amplifier produces (in single-ended mode).Let's expand on that power point by measuring THD+N using 300 ohm load:The low gain mode again shows it stuff with exceptionally low level of noise and distortion. High gain (red) bests the Atom (green) as well at lower volumes. And produces a tiny bit more power.The situation doesn't change a whole lot at the other extreme with 33 ohm load:The only regression was the one channel not being able to keep up as well (dashed in red).Channel matching showed variations early on:This is supply dependent so may be an concern for some very sensitive IEMs. With my Sennheiser HD-650 in high gain, it only happens when I just come out of mute. So definitely not a problem there. And the low gain mode should mitigate this as well.I hooked up the EL DAC II and EL AMP II together and drove them using Roon music player.I started testing using my MrSpeakers/Drop Ether CX closed back headphones. These are 25 ohms and very inefficient. But they were no match for the EL AMP II which pushed them to extreme levels of fidelity and loudness. At just 12:00 to 1:00 o'clock on the volume control, I had incredibly dynamic range with amazing impact and detail. Turning up the volume to max kept going with no hint of increasing distortion.Switching to Sennheiser HD-650s with their high impedance left me with the same outcome. The detail and impact of your recordings come to surface like nobody's business. I am tapping my toes listening to this setup as I type this.I wish there was no risk of hearing loss as I would push the volume higher and have the best time I could.There is no question who is the master in the equation of amp versus headphone: the amp rules.The JDS Labs EL Amp II takes the peformance of Atom and delivers it in their super attractive "Element" package. The matching DAC finally gives you a great pairing as far as looks, making you want to keep looking at them.Both tactical, subjective beauty and sound fidelity is delivered in this package.Of course, if matching looks is not important, you can use the amp by itself with other DACs in which case, I would hide the DAC and put the amp within reach.Needless to say,FYI, there is a comb package in the form of JDS Labs ELEMENT II which I will review later today or tomorrow.--------As always, questions, comments, corrections, etc. are welcome.I have to review no less than three products today so I demand overtime pay! Pleaselest you want me to go in strike using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/