This is a review and detailed measurement and comparison of Aune X7s and Arcam rHead headphone amplifiers. I purchased the Aune X7s from ebay for $250. I bought the Arcam rHead used from a member in UK who also bought it used. The total cost to me shipped was £98.55 or $127. The retail price is $599 but I see them advertized for half as much online.Note: John Dawson, the designer behind Arcam rHead is a long time professional friend and great designer. While I did not let that enter my review criteria, I thought I disclose that out of abundance of caution.Both of these units are substantial in weight. Quite a bit more than any audio produce in this price category. You can get an idea of their size here:Of the two, the Aune is much more attractive. They brag about getting the industrial design done in UK and it shows. It must be expensive to machine all those curves. Overall it is a very unique look in a sea of ordinary products.Feature wise these are pretty different products. The Aune X7s has three different gain switches (0, 12 and 20 dB). Instead of a selector, they give you three, very difficult to flip dip switches underneath. I thought I was going to break the little plastic on them as I put lots of pressure on them to toggle. After a few times they have become easier to flip but still, they need to get a different switch.There is only unbalanced RCA inputs but there is balanced headphone out.Power is provided by a rather larger, multi-voltage transformer.The Arcam rHead has a fixed gain of 16 dB (measured by me). It has both unbalanced and unbalanced inputs, but only unbalanced output. Got that?Arcam uses a switching wall-wart power supply that is less than half the size and weight of Aune's.Let's get into the measurements and see how they did.Testing headphone amplifiers is challenging given the differing gains and multiple settings for the same. Performance can even vary based on position of volume control. So there is really no 100% apples to apples comparison. To that end, I decided to show my dashboard measurements at the most optimal results I could get. That point at least is rather singular.First up is Aune X7s. Best performance was with unity (0 dB) gain:These are very good numbers if a bit shy of what Aune advertises (0.00013% distortion). Even with medium gain results were very good (108 dB SINAD).The Arcam rHead couldn't quite keep up:These are still pretty respectable results. As noted on the graph though there is mains leakage which is typical of devices fed by switching supplies. Distortion is otherwise much lower.Let's look at power output versus load starting at 300 ohm:We see the dashboard results reflected here with the Aune showing less noise in the downward part of that graph. The Aune also produces more power prior to clipping. The horizontal line is due to Arcam rHead going into protection and shutting off the output (a non-event given that we are way past clipping). So the nod goes to Aune here.Results at 150 ohm are similar:But the picture changes at 50 ohm and lower:Here there is a rise in the distortion of Aune X7s output prior to clipping which does not exist in Arcam. As a result, the Arcam rHead remains cleaner at higher power levels than X7s.Here is 33 ohm with similar outcome:So at lower load impedances/headphones, the Arcam rHead comes out ahead.Since the Aune X7s has balanced output, here is a comparison of that at 50 ohm against unbalanced:As noted on the graph, balanced produces higher noise, higher distortion and higher power. To the extent you don't need its extra power, I would stick with unbalanced output. This is in contrast to the prior two headphone amps I measured where balanced was both lower noise and distortion.Intermodulation distortion versus level shows what we already know:Note that the difference in noise is most likely not audible whereas the lower distortion in Arcam rHead will be (assuming you listen really loud).Looking at channel imbalance versus volume position, one shows as clear winner. First Aune X7s:For fairness I ran this in high-gain mode. Here we see +- 0.5 dB of channel imbalance (and more if you go really low volumes). In sharp contrast, the Arcam rHead delivers near ideal results:The rHead uses a resistor ladder rather than a potentiometer and hence its much better channel matching. With that unfortunately comes a rather steppy volume control that will not go below certain level. So extra sensitive headphones may be too loud to use with it.Last but certainly not least is the output impedance measurement:Ouch. The Aune X7s has an output impedance of 11 ohms! No wonder it is missing from their specs which even includes Audio Precision measurements.The Arcam rHead measures at 0.9 ohm which is inline with their advertised 0.5 ohm spec (my measurements usually show a bit high).I first level matched both units using my Audio Precision analyzer. I the used a Y cable to feed the same signal from a Topping DX7s to both units. From then on, I used the volume control on the DX7s to adjust the level of sound. The outputs of both units were fed to an AB switch which I randomized for testing. My youngest son was with me for this test which is good as his high frequency sensitivity is well above mine.I played my standard headphone test clips. My son could not find any difference across three headphones we tested: Sennheiser HD-650, Hifiman HE-400i and Sony MDR-V6. I thought I heard slightly better bass performance out of Arcam rHead but it was very slight and was not consistent.At no time was there any difference in soundstage, or any other mumbo jumbo you read in subjective reviews. Fidelity mimicked that of source content.To test for hum and noise, I plugged in my sensitive IEMs and both units were dead silent at all volume levels.Finding faults with these units was difficult. Both seem to be very competently designed. I love the look of the Aune X7s but its output impedance is too high to recommend it to everyone. If you have a headphone with flat impedance curve or very high impedance, then that should not be a problem and the X7s would make a good choice.The Arcam rHead had slightly less performance than state-of-the-art due to some mains leakage (which was NOT audible). Its low output impedance will make it a lot more of a general purpose headphone amplifier than the X7s. As such,That said, the Aune is an attractively designed and powerful amplifier. If the higher impedance is not an issue, it produces superlative measurements and lots of power and hence, gets a conditional recommendation from me (whatever that means).-----If you like this review,using Patreon ( https://www.patreon.com/audiosciencereview ), or upgrading your membership here though Paypal ( https://audiosciencereview.com/foru...eview-and-measurements.2164/page-3#post-59054 ).