Aune S17 Pro Headphones Amplifier

What if I told you the Aune S17 Pro is the most expensive part of this article going over four different products? This is a premium headphones amplifier that has taken the world of Head-fi by storm lately by offering an excellent feature set for the money. You also know this is not cheap in any way when you pick up the product box, which is large and heavy. It's a simple black throughout with the Aune logo on the front and a sticker on the back confirming this is the UK version compatible with 220 V AC input. Inside the box is a similar unboxing experience as the AR5000 headphones in that an accessory box is separately placed alongside the amplifier that comes covered and surrounded by thick foam for added protection. There's also a pamphlet containing paperwork in the form of a quick start guide and QC card, with the other accessories being a 3.5 mm to 6.35 mm adapter, a 2 m long AC power cable, and a low profile aluminium remote control that is super easy to use with clearly marked buttons, taking a user-replaceable CR1220 battery.


The Aune S17 Pro comes in black or white colors with the chassis made of anodized aluminium in both cases. It is 29 x 21 x 6.3 cm in size and weighs nearly 3.5 kg—this is larger than the photos might make it seem. Note also the gentle curves on the top, with Aune going for this arc shape on its desktop sources that looks cool but isn't very practical when you want to stack a DAC or network streamer on top. It still works given the larger surface area on offer, but I think you might be better off getting a rack stand for an all-Aune chain. I like how clean this looks though, with absolutely nothing but solid panels throughout—perhaps at the expense of cooling, as we will soon see. On the front are three outputs in the form of 4-pin XLR and 4.4 mm balanced, as well as 6.35 mm single-ended out. The remote controller receiver is alongside the 4.4 mm output before giving way to the large non-touch LCD screen in the middle. A power indicator light is to the right followed by a large multi-function knob with markings all around that are not really useful, given the knob can rotate infinitely and has no marking on itself to indicate the current position anyway. I would have much rather these markings not be there at all.


On the bottom we see screws that help secure the amplifier in place, along with more on the back. There are also four rubber feet that raise the amplifier off your desk, help prevent scratches to the aluminium chassis, and add some friction to prevent it from sliding around just in case the heavy mass was not enough. There's plenty going on in the back with everything neatly marked again for easier identification. The S17 Pro also works as a preamp, say for speakers, and thus we get not only analog inputs but outputs too in the form of dual 3-pin XLR and dual RCA connections. A substantial on/off switch is also nice to see, with the power connector all the way to the right to wrap up the I/O section.


Connecting the S17 Pro to your DAC or streamer is simple enough thus, you will have a minimum of three cables leading to the amplifier. I went with the dual 3-pin XLR inputs although, if you just care about output power, then RCA inputs will not change this metric. Turning the amplifier on also turns on the display that shows the input method (RCA or XLR) in the top left corner, the gain level (low or high) in the top right corner, the current volume level in the middle, the operating current mode (50 mA or 100 mA) in the bottom left corner, and the internal heat sink temperature in °C in the bottom right corner. The knob helps switch between the different parameters too, but I suspect most people will use the remote control. The screen changes color depending on the current level mode for easier identification, although I think Aune should have done this in a smarter manner.

Given this is not a review of the amplifier in itself, I'll point you to the product page if you were interested in knowing more about the S17 Pro's internals. As a general overview, this is a Class A amplifier so it takes up the maximum power draw from the wall all the time. The power is fed to a series of output transistors—two sets in parallel, 16 transistors in total—and each transistor gets fed 50 mA or 100 mA of quiescent current for a total of 100 mA or 200 mA per channel. The current level is dictated by the temperature of the heat sink placed over the various critical components inside, with a shift from 100 mA mode to 50 mA mode happening at >=69 °C. The issue is, in the absence of any ventilation or active cooling, that internal temperature is inevitably increasing over time in a normal use case. Even simply turning on the amplifier is enough to do this with the Class A architecture, and your eyes will naturally be drawn to this temperature readout on the display that slowly keeps increasing. You are naturally led to believe that 100 mA should sound better, be it placebo or otherwise, and will then be disappointed when the S17 Pro switches to 50 mA sooner than later. I honestly think Aune should just not have shown the temperature readout on the display at all, but I appreciate the transparency here. I also understand a newer amplifier is coming out soon with active cooling from an internal fan, so perhaps this will help address the complaints from those who think they have paid for something that is not delivering what was promised. To an extent yes, but also I would be shocked if anyone can really tell the difference between the two current modes when it comes to the outputs fed to headphones/speakers.

As it stands, the S17 Pro is a very good amplifier for the money. It's also an extremely powerful one, capable of providing up to 7.5 W per channel off the balanced outputs in high gain mode at 32 Ω, going down to 114 mW off the single-ended output at 600 Ω. If anything, even the low gain mode is too powerful for a lot of devices and the S17 Pro is certainly not an amplifier I'd recommend for IEMs or even easy-to-drive headphones such as the Aune AR5000 itself. But you can still use the two together, and helping this is the R-2R volume control that allows for no channel imbalance even at extremely low volumes. The end result was an extremely smooth and engaging sound compared to a more traditional Class D or Class A/B amplifier, and I will say the S17 Pro is the least expensive amplifier I have ever used that I felt was capable of driving the notorious HIFIMAN Susvara to its potential too.