Fidue Sirius (A91)

Sirius, the new shiny star from Fidue!

PROS: smooth detailed signature, harmonic coherency of 5 drivers, spacious sound, quality 8-core modular removable cable, beautiful design, accessories.

CONS: cable weight with adapters, price (in contrast to previous Fidue flagship), isolation, not for those with small ears.

Manufacturer website: Fidue. Available for Sale on Amazon, as well as from Penon and HiFiHeadphones.

The product was provided to me free of charge for the review purpose in exchange for my honest opinion.


I have been following Fidue and testing/reviewing their earphones for a few years now, and saw them grow and expand with a diversified portfolio of budget single driver releases, dual dynamic and 2-way hybrids, and 3-way hybrid flagship which I still hold in high regard. The curiosity of where Fidue would be heading next always crossed mind. Can a manufacturer top their current flagship performance and take it to the next level? We all have a wishful thinking without realizing how much risk is involved to push the design envelope further, to try to come up with something new and exciting, to make it stand out from the crowd. As it turned out, Fidue wasn’t resting on their laurels, and instead they were working hard on their next big release.

They left no stone unturned and went all the way with a new flagship release, aiming high and naming their new model “Sirius” which refers to a star system with the brightest star in the night sky. Call it a Star, call it a Rock Star, call it by its official A91 model number, but either way there is no denial this 5-way hybrid made a noticeable leap over their previous 3-way flagship design. This was not just another incremental release to keep up with a race by adding more drivers. It was definitely a risk because Fidue team spared no expenses which ended up raising the price. I’m sure many Fidue fans were not expecting such price gap between A83 and A91, and I also think many don’t realize that it’s not just 2 additional drivers but the entirely new design. So let me go into more details after spending the last month with Sirius, to share with you what I found and if it’s justifiable to go from A83 to A91 (Sirius).


Packaging of Sirius is the first indicator of how far Fidue has come to distinguish their product as a true flagship. You are still going to find a black and green outer sleeve, traditional with every Fidue product, and still can expect a detailed description and design highlights on the front and a complete spec list on the back. Removing the outer sleeve reveals a faux leather storage box, and that’s where all the “traditional” unboxing comparison stops. Right away you get a sense of a premium product, and lifting the cover reinforces that.

Like a jewelry box where the top cover is secured by side ribbons so it doesn’t flip all the way open, once the cover is up you’ll find two Sirius earpieces fitted inside of a precise cutout in the foam insert with a textured surface matching the box exterior. Below it, there is an area with silicone eartips resting on top of little stand-offs. Removing the top foam layer reveals a round cavity cutout inside of the next deep foam layer with a beautiful all metal storage container and the rest of the accessories inside.

I noticed that a number of manufacturers raised the bar of their product unboxing experience, so I can’t say that Sirius unboxing was the most rewarding one I have ever seen, but I can definitely say it’s up there at the top and definitely many steps above the unboxing experience with other Fidue products I reviewed in the past, including their previous A83 flagship.


While keeping up with premium packaging, you can be rest assured you also won’t be disappointed with accessories. I already mentioned about eartips, 4 sets of silicone single flange pairs in XS/S/M/L sizes, and also a medium size pair of genuine Comply tips. Personally, I would have loved to see more eartips included with this flagship pair of IEMs, especially since a number of people might benefit from a longer core/stem tips if you find nozzle fit to be on a shallow side. Moving on, you have a typical “filler” set with airplane adapter and 1/4“ headphone adapter. Although it’s a filler for me since I don’t have use for it, others might find it useful.

Now comes the good part! I absolutely love the metal round storage container. You can’t really call it a case since it’s not exactly pocket-able or portable, but its carved shape, rich finish, and etched company name on the cover look VERY premium. Regardless if you are planning to store your Sirius gems in there or keep other accessories or IEMs/CIEMs inside, it makes a nice conversation piece on top of your desk. At the same time, it would have been great to include an additional more practical storage case, maybe something like a soft drawstring pouch.

Next was a little surprise. In a small plastic bag there was a little poker which I figured right away to be a cleaning tool for air-vents in a Sirius shell. The surprise was a metal guitar pick with an etched Fidue logo. I really did mistake it for a pick, thinking to myself that now I can feel like a rock star. Not until I started to go through the pages of the included manual, which btw is very helpful, I learned this was a cable disassemble tool. Due to a unique cable connection which is not as easy to separate by hand, this pick works like a charm when you need to disconnect the cable from the shell by inserting it into the gap between the attached connectors while slightly twisting it to separate the cable. My only suggestion here would be to include a spare set of this tool, too keep one at home “locked” in a storage container, and another one on the go.

The cable.

If you think I was done with accessories, hold on to your hat, here comes the cable! A fully modular cable design with 2.5mm TRRS balanced headphone plug (A&K wiring adapted by many popular DAPs) and two additional adapters/converters with 3.5mm TRS single ended termination and 3.5mm TRRS balanced termination (HiFiMAN style balanced wiring). With an exception of PONO dual split connector, you are covered to take advantage of all the popular DAP headphone outputs. This means that you no longer need to invest extra money into replacement cable to go balanced. Also a small detail but I like how the cable adapter interconnects were neatly hidden inside of cutouts underneath of the top foam packaging layer, including a ribbon you pull on to remove these out.

The advantage of this cable is not just its modular design, but also a high quality material with 8-core (8 separate insulated braids) silver-plated cable inside of a fine braided cloth sheath jacket covering the cord. The housing of the connectors, both cable and adapters, is all metal with an easy to grip shape and a premium look with clear labeling, including a rubbery strain relief. The plug itself features a premium Rhodium plated alloy which has one of the highest oxidation resistance properties, unaffected by air and water up to 600degC.

The biggest surprise turned out to be the mmcx connector plug. Anybody familiar with A83 will know that Fidue tried to come up with something different in there by using a locking tab to prevent cable from rotating around the connector. Here they took it to another level, referring to it as 4th generation lock up design. First of all, the connector housing is a 90deg custom mold which naturally guides the pliable cable behind your ears, eliminating the need for a memory wire. The engagement of the connector is snappy and secure, to the point where you actually need to use disassemble tool. And on top of that, you have a color coded (red – right, blue – left) locking ring which screws on top of the joint to secure the connection. You don’t even have to tighten the ring all the way, leaving a little bit of room to adjust the cable connector angle relative to the shell for a more comfortable fit.

Do I think this cable brings up the best in sonic performance of Sirius? I will talk about it in the next section of the review, but can acknowledge that none of the replacements I tried showed a nigh’n’day difference in comparison. As an overall comment, this modular design is great and very flexible, but it does add to the weight and makes cable bulkier. The locking ring is cool but also overkill since mmcx connector joint is already secure, but at the same time some might prefer to be able to lock the cable rotation, especially due to 90deg connector housing. Disassemble tool is an accessory piece you might want to keep nearby, but at the same time how often do you need to disconnect the cable on the go? Also, I’m not a big fan of cloth sheath cable jacket, but it does a fantastic job in keeping microphonics away. In general, if you are not satisfied or have some issues down the road, you can always replace it with another mmcx cable.

Cable adapters.

Replacement cables.

I know that not everybody believes or hears the effect of the replacement cable, and I respect that. This section is not my way of trying to change anybody’s mind, but rather to share with you what I hear/feel which is obviously a subjective opinion.

Sirius (SPC) vs A83 SPC – I found sound to be nearly identical, maybe with a stock cable being a touch brighter, but it was hardly noticeable. Obviously, I couldn’t test the original A83 cable due to a locking tab, but instead used another mmcx cable (exactly the same wires as in A83) which Fidue sells as a separate replacement accessory.

Sirius (SPC) vs Pure copper (Pristine CX1 cable) – a similar performance, though I was able to hear with a pure copper a slight improvement in sub-bass rumble, making it deeper and more textured. Also, it adds a little bit of airiness to the sound, and makes treble a little crispier.

Sirius (SPC) vs Super BaX – has an interesting effect on low end performance, making bass tighter and more articulate, even a touch faster (tested many times, hopefully my mind is not playing tricks on me). Mids get a little more clarity and transparency, like a shade of veil was lifted off.

None of these changes introduced a night’n’day difference since Fidue already invested into a very capable 8-core SPC cable. I don’t have any plans to switch to another cable since I’m happy with a performance of a stock one, but if I did – I would probably be going to Super BaX cable. Also, Super BaX will be a good choice if you want something more lightweight with thinner wires.



I was always a big fan of the original A83 design with a faceplate that reminded me of open wings. Just like I was happy to see Fidue scaling down exterior shell design of 3way A83 to 2way A73, I was also pleased to see them scaling it up to 5way A91 (Sirius). Except this time we are looking at all metal shell with a rounded inner part facing your ear and a familiar layered “wings” stamped out on the faceplate with a company name across it. To scale it up also means that the size of the shell becomes bigger to accommodate more drivers, filling up both Concha Cymba and Concha Cavum areas of my ears. I didn’t feel any discomfort thanks to a smooth rounded edge of the inner shell, and it worked quite well with my average medium size ears. But I do have concerns where those with small ears might have a bit of a problem with this new universal shell. For sure, if you had issues with A83 fit, Sirius might not be for you.

The faceplate design of the outer shell does have a few sharp edges, but they never come in a contact with my ears, so I was OK with it. Inner side of the shell has 2 separate vents where I believe a smaller pinhole one is located right in the area across from the dynamic driver, and two other longer vents are there to assist with soundstage expansion and low end control. I was worried at first about the location of these vents facing in, thus getting blocked, but I didn’t experience any sound variation as I had Sirius in my ears and moved around. I did settle on another eartip pair with a longer stem/core, and that created a bit of an extra space, preventing vents from being blocked. Keep it mind, with Sirius you will need to consider a proper eartip selection not just for an improved seal and fit comfort, but also to prevent shells from being jammed right into your Concha area.

From eartips selection to a nozzle, I actually found it a bit on a short side. Also, the tip of the nozzle was smooth without any lip, something I wish Fidue would have implemented to make sure eartips won’t slide off easily. Through the metal mesh (earwax guard) of the nozzle tip you can clearly see 3 individual bores, assuming one for the low end (dynamic driver) and other two split between mids and treble covered by BA drivers. Last, but not least, you can also find a clearly printed L and R marking inside of the shell. Even so shell design is asymmetrical and easy to identify left/right sides with a color locking ring, I was still pleased that everything was clearly labeled to eliminate the confusion when replacing stock or after-market cables.

Overall, I didn’t find any show stoppers with a design or a fit, but do want to bring up a few things as a feedback to potential buyers as well as Fidue. The most important point, there are plenty of universal fit IEMs that have a generic and uninspiring design. Here, Fidue created quite an eye candy with an original shape that will definitely get you noticed. I know it’s probably shallow to talk about the appearance, but many people go for CIEM not only because of a custom fit but also to personalize the look of your monitors. Here, with a right selection of eartips to ensure a proper seal and fit, wearing Sirius feels like I have a pair of CIEMs in my ears, and I got nothing but compliments from everyone. Just don’t expect the high level of isolation with Sirius like you would get with CIEMs. Due to shell venting, even facing inward, sound isolation wasn’t its strongest point.

The fit.


Page 2: Sound analysis, Comparison, Pair-up, and Conclusion.

4 thoughts on “Fidue Sirius (A91)

  1. Great review as always, thank u for taking the time and sharing your findings. I have to say I think u r the best reviewer out there!
    Question how does the Sirius compare to the U12? And have u found an IEM that is better than the U12? I just got the X5 gen 3 and like it , what is your favorite pairing with it?
    Thank u again


    1. U12 will vary with modules, I no longer have ADEL shell, switched to APEX, but either way U12 has more mid-bass impact, the bass hits harder in comparison to A91, but then Sirius has more detailed and revealing upper mids, U12 is smoother in comparison. There are different IEMs with different sigs, some can’t be compared as “better” since they have a different sound. For example, I really enjoying AAW W900 hybrid now, but using it with 1960 cable, so that’s an added cost… For X5iii, it’s on my review list, only had a little bit of time with it, and I prefer more neutral and brighter IEMs with it.


    1. Sorry, haven’t touched it in over a year. Going by memory because it could take awhile before I dig through the boxes to find it. Sirius signature is more neutral, natural tonality, while Xelento and Vega both have more emphasis on bass and more v-shaped tuning where Xelento is smoother in higher frequencies, closer to Sirius, while Vega is more v-shaped with a peak in lower treble which can get sibilant/bright with poorly recorded music. Also, with a fit, Xelento could be a hit or a miss due to shorter nozzle. Sirius is definitely more all-round tuned IEM.


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