So I am back here much later having acquired the D90SE stack and will post my impressions.
I set up A90 discrete to do a long listening session using D90SE as a DAC (set to 00 Db output, BT=off, output V =5, filter= fast roll off minimum - the defaulty) connected to A90D via Mogami Studio Gold XLR 3’ cables. HPs were HIFIMAN Arya via 4.4 mm A90D output, gain is M). I used Aryas because my goal is to comment on how A90D projects those HPs’ famous soundstage. I used stock power and USB cables and no power conditioning, listening on a dedicated power line.
Tracks were Fruhlingsgefuhle by Melokind, Magnetar by Mark Lettieri, Beldiya by Triplego, Twice by Ludovici Einaudi (Reimagined by Mercan Dede) Lifted by Love by KD Lang, Drover by Bill Callahan.
I also have the IFI micro iDSD Signature also (an integrated portable DAC/amp). I will comment on that briefly below, as I am mostly a DAP man (and the iDSD signature is after all more portable than most DAC/Amps). For DAPs I mostly use Cayin N6ii and Hiby R8, and it was compared to them I made the bulk of this A/B comparison. Sorry if this seems a bit strange but it may be useful to DAP users. I will add a comparison of my 64 Audio U12Ts at the end
WRT the Aryas, I was immediately struck by the difference between my DAPs and the stack in the overall smoothness and detail retrieval especially in the treble region. There are details not readily discernible on my DAPs that can I can hear, way high on the A90D, ie snare brush strokes but also breathy vocalizations or wind-like sounds that are elevated by the D90SE-A90D combo. Some softer instruments that had been hidden in the mix before were now more distinguishable on the Topping stack. Treble was also more forward placed in the mix, I was noticing a lot more snappy, crispy, sparkly details up top, especially on percussion instruments- transients were perfectly timed. OTOH as noted treble is smooth, I heard no harshness or sibilance, nor is it shouty or shrill - lower treble in the vocal range is clear, breathy, consonants are forward but really just right.
This all continued down into the mids, which were very real and present. On these tracks, voices are forward- intimate even, but not ‘in the head’ and when soft it’s like they are whispering in my ear or just behind it- more about this under imaging, below. No issues here of concern
Bass- on my DAPs bass quantity was always strong (especially EE Legend X and U12T), but with The Stack I am hearing a lot more bass detail, as well as loads of rumble and slam (read: lots), I think sub-bass rumble is in fact more - but with an important caveat. Roon DSP allows me to dial up a bass shelf and the Topping Stack scales up on this impressively- I encourage you to try it. The bass control I had wanted, hoped for in my DAPs is -THERE- . This is really noticeable on Bill Callahan’s Drover- kind of a test track for physical drums. With the Roon bass shelf ( below 60 Hz m, + 4 DB) those drums are right in the room with me. Mid-bass (especially bass guitar) vibration is palpable. Bass remains forward but there is zero bleed or suppression of lower mids. Micro-dynamics (max bass to max blackness in between bass drops) is excellent, decay seems a bit faster than with my DAPs. This is particularly impressive given that the Aryas are not a particularly bass-y set.
In terms of staging and separation overall, as I’ve already I think made clear, the Stack has imaging in spades- instrument separation and space between instruments across the FR is crystal clear. Stage width was a BIT narrower for the Stack vs my DAPs, OTOH. —about as deep as it is wide- literally like a small performance stage, and I am sitting in the front row. The preciseness of instrument or vocals location on that stage was crystal clear, with greater instrument distinctness than I noticed with my DAPs. Having said that, instrument separation was still great with R8 and N6ii- the Stack just dials it up a notch- again the most notable difference to me is in the details I can hear coming from A90D across the frequencies. If what you are looking for is massive deep/wide/tall soundstage, however, you probably should look elsewhere. Having said all that, the smoothness, musicality, and coherence I have always loved from the best of my DAPs (Hiby R8) is at least as good (better?)on A90D.
As an aside, while on the subject of soundstage, I did try different filters on D90SE to see if I could hear the difference. Difference between slow roll off linear and brick wall is noticeable. The former, however, seems to create some ringing between adjacent notes that I didn’t appreciate, so I have stuck with the fast roll off filters. I like the anodizing one best as it gets rid of any ringing or ‘reverb’ before the note strike, which seems more natural to me. The slow roll off filter does produce a more “tubey” sound and the impression of a wider soundstage, but overall I didn’t like what it did to the transients so gave it up and went back to the fast roll off filters.
Comparisons with ifi micro iDSD signature:
- Aryas - the Signature is an integrated portable DAC/Amp that uses a BurrBrown DAC chip and has the advantage of the 3D and XBass analogue switches (the latter is marvelous with the Aryas, and constitute an analogue bass shelf). In comparison to A90D, the mids are a bit warmer, smoother and more melodious but note definition is less crisp/detailed. Bass is essentially the same (especially with the XBass = ON). With 3D on, Signature does gain a bit on A90D in terms of stage size. Imaging is not as distinct though.
- U12T- on Signature without XBass or 3D, U12T has quite good slam and bass texture. Mids are quite forward in space, treble details are not so distinctly audible in the highest frequency (a bit rolled off, but note I have hearing loss above 10K so not hearing that upper shimmer the U12Ts are so famous for). Other elements of SQ about the same. Stage is intimate though imaging remains very clear and distinct. On A90D, bass texture and impact are clearer and stronger. Mids are closer in space to the listener, more crisp. Treble shines here- very clear, more details appreciable, at a higher frequency all the way up as far as I can hear, some that were not appreciated on the Signature at all, others that were barely discernable on Signature are much clearer… Stage is not as wide as the iFi Signature with 3D =on, but about the same depth- and height-wise, Imaging is clearer and more distinct, with more accurate instrument placement on the stage. This is a W shaped FR, not V shaped.
One important thing - this Stack is so smooth that is tempting to listen to it very loud- as there is no distortion or pain when doing so. I was getting up to over 80 on the Volume dial and it sounded = great! Be careful out there.
Conclusion- the A90D pairs wonderfully with D90SE across the FR, and can transmit detail and (with a bit of EQ) impressive impact and dynamism, and serve it up smooth as silk. Soundstage size is the one ‘fly in the ointment’ and (for my money) worth sacrificing for the rest of what I hearing, especially (as others have said) in terms of impactful bass, overall detail retrieval and clarity, and pinpoint imaging. Definitely good ‘bang for the buck’, and a keeper
Is it my “end game” amp? Not yet sure. I am curious how it will pair with Denafrips Pontus II, which I’m planning on ordering next month. I will need a Pre-amp between the 2 if I want to use my IEMs because DPII is a pure DAC so there is no volume control; but also because the balanced output impedance for DPII is 1250 ohms, and balanced input impedance on A90D is only 2000 ohms (the ideal ratio DAC:AMP is > 1/8) - so will probably pick up a Gustard P26 pre-amp which has input impedance 47K ohms (so plenty good ratio). OTOH I’m also considering picking up a Burson 3XP to use as a PowerAmp, which could do double duty as a pre-amp between the Pontus and A90D for speaker use, as it’s input impedance is 35K.
Finally there are a LOT more user impressions on HEAD-FI re: the A90D, which I won’t link here, you can Google it