Review: Fidue A91 Sirius – Pure Black Wizard

But how do they sound?


Fidue wanted to make a reference TOTL earphone and it is exactly that as is simply produces a top level qualitative sound. The Fidue A91 has a perfectly black background like every flagship should have and the Dynamic and BA drivers work seamlessly fine together. The sound stage width and depth are good to very good and from bass to treble the layering is excellent, even though it’s a little less so in the treble region.

The mids and bass have really good and full body and bass even has a little more than average. Depending on source and tips used bass body/impact might even be too much if you’re not that much in to bass. From bass to treble though, the level of detail is very good and the A91 shows great resolution but it always keeps everything musical in the best kind of way. The Fidue A91 Sirius is clear and clean yet it has a darker touch to it. Because of this, and with the extra bass body, I myself wouldn’t call it a perfect neutral sound signature but it is one that has detail and musicality, making it very enjoyable and non-fatiguing/natural to listen to. Its separation and airiness/spaciousness is just right and I can’t say anything negative about it.

I like bass but I don’t like too much bass, bloated bass, uncontrolled bass or bass that runs in to the mids and ruins everything. Even though the Fidue A91’s bass presence might be a little over “neutral”, the bass – and especially the sub bass – is one of the very best I have ever heard in a universal IEM and that’s a big compliment. Like I said earlier it might sound a little thick for non-bass lover but everyone else will enjoy its depth, layering, richness and punch/presence. I love it.

The Fidue A91’s treble is good and lively but isn’t the furthest extended or most focused treble for a Flagship. Personally it doesn’t bother me as treble is detailed, clear and dynamic. The A91’s treble is energetic enough to contrast the excellent bass and mids and it won’t leave you with a feeling you’re missing out on something. But if I have to nitpick and compare to other flagship status monitors, this is an area where some improvement still can be made. It could be even better but it already is quite good, so don’t worry unless you’re a treble freak (and there’s nothing wrong with being one for that matter).


The mids, just like the bass section, are full bodied but it never feels too much here. Sirius’ mids are rich, layered, musical and slightly to the warmer side. The perfect marriage between detail, musicality and precision is again present here. The musical and rich mids are easy to listen to and The A91 Sirius is perfectly worth its flagship status, together with the Andromeda’s and Nobles of this world.

Combos (DAPs and Amps)

With an impedance of 20Ω and a sensitivity rating of 113Db, the A91 should be easy to drive and it is exactly that. There’s no real need for a dedicated headphone amplifier although that of course will be audible in the end result.

Straight out of the 2.5mm balanced output of the Luxury and Precision L3PRO, the Fidue sounds rich, very well layered and extremely musical. The L&P DAPs are known for their excellent sound quality and the L3PRO makes it sound smooth, musical, and spacious. Listening fatigue? Non-existent.

Out of the Astell&Kern AK380, the Fidue A91 sounds very clear and precise with a lot of detail and good speed. It’s always musical and natural sounding and voices are to die for. You don’t get the smoothness of the L&P brand but you get everything the AK380 is known for. The AK70 (2016 DAP of the year)and the Fidue sounds like the L3PRO but more refined with better separation and a wider sound stage. I absolutely love the bass, mids and vocals here (with a slightly smoother delivery). With the Cayin i5 you get a very powerful bass with awesome bass and great vocals. Here it’s musicality over precision but the level of detail, separation and layering can be better.

In combination with the Cypher Labs Duet (fully balanced mode) you get a full bodied and natural sound that is fast, precise and very balanced. Treble with the Duet/A91 is excellent as well. With the tube driven ALO Audio CV5 (non-balanced) there is audible background noise. The CV5 adds some tube smoothness to the overall sound signature and from top to bottom (with the Mullard tubes) the sound is very rich. It sounds more like the L3Pro but at lower volumes you have to be able to not pay attention to the noise or it will, like in my case, get on your nerves and you’ll stop listening right away.


From the Mojo, connected to the L3PRO by coax, the Fidue A91 sounds fast, precise, dynamic and very much in control of everything (bass). It’s maybe not as musical sounding but it’s dynamic and energetic. Precision above all. From RHA’s latest DacAmp L1 the A91 in single ended more has very good 3D- positioning and great balance. The L1 and A91 combo is very powerful, rich and deep sounding with great layering. And to me it’s one of my favorite combos when using my laptop as source.


The new Cypher Labs Austru is a 4-driver universal with one Dynamic 10mm aluminum driver and three transducer drivers per earpiece. The configuration is: single Low / Single Mid / Dual High. The sound signature couldn’t be any more different from the A91. It’s thin and gentle, light bodied and very neutral. Austru’s bass compared to the Sirius in non-existing and the mids are a lot thinner. It’s detailed and analytical while the A91 is detailed, natural and musical.

The Inear ProPhile 8 has eight drivers and also sounds more neutral like the Austru. It does have more body than that last one but not as much as the A91. It’s a more balanced, refined and reference (flat) tuning and the amount of body in bass and mids isn’t like in the Sirius, even with the switches turned on. Micro details in the PP8 are of a higher level as well.

The custom Vision Ears VE5’s sound signature is lighter and more neutral. It doesn’t have the same amount of body and it sounds more forward with a focus on the vocals. Treble is further extended and the overall presentation is more neutral. I prefer using the VE5 in a non-balanced configuration with a warmer and bass oriented amp or DAC, using a copper based cable. In a way the VE5 compares to the Jomo5 which also has forward vocals and the same amount of body. The VE5 does sound more spacious though. Both are more neutral and thinner body-wise. The Lime Ears Aether compared to the two previous customs has bigger bass and mid body but it’s still nowhere near the A91’s. Treble does seem further extended on the Aether which overall is natural to listen to, it just doesn’t have the thickness and light warmth of the Fidue.



The Fidue A91 is a top quality universal flagship monitor that scores big in all areas. Its performance is very good and I find the asking completely justified looking at what you get in return. If you want even better sound quality you will have to fork up quite some more money or go the custom route.

Sound wise, especially compared to other multi-drivers, it’s bass and mid body is bigger than any of the ones in my collection. The Fidue manages to be musical, detailed, layered and natural and I really am a fan of how the A91 was tuned. Some might find the bass a little too present or the treble to rolled of but the A91 Sirius has an excellent price-quality ratio. It’s a flagship that lets you hear everything a flagship is supposed to let you hear but it stays natural, engaging and non-fatiguing at all times. On top of that it is really easy to drive and it will sound good out of anything.

Excellent work Fidue, call me a fan.



Lieven is living in Europe and he's the leader of the gang. He's running Headfonia as a side project next to his full time day job in Digital Marketing & Consultancy. He's a big fan of tube amps and custom inear monitors and has published hundreds of product reviews over the years.


  • Reply January 12, 2017


    How would you compare the Fidue A91 with the Shure 846? Thanks

  • Reply August 15, 2017

    Desmond Wong

    How’s the sound quality comparing to aurisonics 2.5?

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