No idea. Lots of folks really hate the A90, calling it lifeless. But they can’t show any evidence, even when they have GRAS or equivalent equipment. I’m sure there’s some sort of measurement that’d illustrate the issue, but no one has put that forward. My Liquid Platinum measured nearly identical to the A90 with stock tubes (not so now that I “upgraded them,” whether it’s better… can’t really say). A90 sounded better than the SP200 it replaced. I’m not sure if folks are having an impedance issue (e.g. using it with low output impedance DACs, or listeners really liking the sound of high output impedance amps) or if it’s all in their heads (like premium cables giving you better sound). The only amp in my house that’s complete shit is my OG Schiit Valhalla (crazy amounts of noise and distortion, I hooked up my Clears to it exactly once…).
The placebo factor is large in our hobby, but then again, there are people paying kilodollars for a stamp that neither looks nor sounds good. So it’s hard to judge someone for thinking an amp with an alluring orange glow sounds better than one that doesn’t shine. In any case, a beautiful amp looks better than a rare stamp any day, in my eyes!
Anyway … thank you for your observation. One plus for A90, really, then, at least if we go by sound rather than rarity.
@Solan , you could create a new thread. The A90 is very popular, so I’m surprised a thread doesn’t exist.
If that’s permitted … Will do! 
That what you do you create the thread, then it get up-leveled to Offical Thread by a moderator. You see I started a few threads on different solutions Including one for the Topping DAC we are on. But to do it you have to write a review to open the thread. Also, put the background on the device in the opening of the thread similar to what you see above.
Ah … I have no review, as I have no Topping A90. It is on my “consider to buy” list, next to an Xi Audio Formula S. One of the two, depending on money and reviews.
Hi @Solan , I think placebo can be a real thing in any hobby to an extent. I also think there are some real audible differences between amplifiers however. Newer ears to the hobby may mot be able to pick up on them at first. I don’t think anyone is saying there is a right and wrong preference; at least not on this forum, we leave that up to other forums. We are open minded here to tubes, solid state, well measuring not so well measuring. There is no one way on this forum, just the way you enjoy your music and the way the next person enjoys theirs. I had the A90 as my reference amp for a very long time and I am very familiar with how well it measures and it’s sound signature. Do I think some amps that glow sound better than it? Absolutely. Do I think the A90 sounds better than some of the THX variants? Yes. This is based on the synergy of my complete audio chain including the DAC, the files, headphones and amp. If the A90 is your favorite amp nobody is going to judge you here, but we also shouldn’t judge others that love the sound of their tube amps. Hopefully that makes sense. Cheers and welcome!!
I have silver cables for my IEMs just because I think they look nice, so … no judging! (And they might sound better too. Maybe. I have not A/B tested. I just like silver.)
Well said. Kudos 
Certainly Placebos are real. Steve Martin proved that back on November 4, 1978. (SNL). But it’s true.
After owning the A90/D90, SMSL SU-9/SH-9, CAYIN IHA6, Little dot 1+ tube amp for sometime. I could not tell the difference while A/B Testing for weeks with different headphones and different music between amps.
I was starting to think my ears must be bad for noticing small details.
I think they all sound so similar it is very difficult to distinguish them apart.
But after testing them more and more I did notice a very very small difference in dynamics comparing the cayin iha-6 vs a90. I would say that with hard to drive planars there would probably be more of a difference with cayin iha6 being better( hardest headphones I currently have is arya and hd 600).
I received a rebelamp two weeks a go and I can say with massive confidence that the difference is much easier to notice.
The rebelamp is much more dynamic has a lot more punch/slam a lot more texture and detail in the notes. It makes the a90 in comparison sound dead and smeared.
I have custom made XLR cables for all of my headphones so I just got a xlr to single ended custom cable made and it works a treat.
I bought the a90 because Every YouTube video about the a90 claimed it was the best amp ever or giant killer.
My advise for anyone looking at buying the A90/D90 stack buy the D90 and rebelamp instead.
Another note that I am very confused about is the power the rebelamp has. It suggest its only 1watt @ 32ohm and a90 is 6.4watts @ 32ohm. I find this strange as the power of the rebelamp is so close to the a90 definitely does not seem like 5.4watts difference. 
Got my A90 going on eBay very soon.
There is a long, long, long history of Class A amps being perceived as louder, fuller, smoother, and richer than other solid state amps. This applies to both listening and music production. Furthermore, tubes have been also been considered essential for recording and stage performance. There was a big push toward digital recording and solid state equipment in the 1970s and 1980s – many people didn’t like the resulting harsh tone and pushed back toward vinyl records and tubes.
Some hardcore believers in measurements say that amp differences are an illusion, for all technologies put out the same energy as measured by watts and dBs. My response is that this may be true, but human perception need not correspond to these specific measurements. To my ears, Class A amps are more time coherent than other solid state technologies. As they are always on, they are capable of instantly delivering on their maximum potential – all rapid musical changes occur in coordination with each other (e.g., clean bass definition). Non-Class A amps aren’t as ready to deliver and thereby perceived to emphasize what they can do fastest (e.g., they excel at treble and exaggerating unpleasant transitions, aka thinness with “analytical” elements).
Tubes seem to have a related perceptual benefit, as they generate copious harmonics. This is classified as distortion (e.g., grass) in measurement charts, but harmonics may facilitate smooth transitions during rapid and complex musical changes. Tubes may better prepare or ease human listeners into the next note. Tubes often just “sound right.”
My THX 789 may also go to eBay, but not yet because I like it for some specific needs.
Hello, I’m about to buy one of e30, d30 pro, d90 for my a30 pro and have questions as I have never been using external dac before.
- Can I still control volume in Windows or have to use pilot or knob in dac?
- Do I a lot of quality and loudness pairing e30 with e30 pro amp instead of d30 pro or d90?
- Does length of cable between source and amp matter?
Thanks for help up front
Never thought I’d see AKUS mentioned in a headphone thread lol! Sorry for replying to an old comment, but I just couldn’t resist… I’m a banjo player as well as engineer, so I listen to bluegrass music almost 75% of the time. Anyway, thank you for the well-written review!
@jhsmastering - have you heard the New Appalachians binaural recordings on Chesky Records?
@tjg I haven’t yet! I’ll check it out! Thanks!
i have a d90 running between my cd player and my willsenton r8
tube amp driving Kef
REFERENCE series model threes
4 ohms
sounds BEAUTIFUL
open revealing tight base
my question is
If the d90 is also a pre amp w volumeccontrol
does it perform the same in pre amp setting as it does in pure Dac
mode ?
if so why the need for two modes?
i guess i would likevto use it as a preamp if im not giving up any dac features
thank you
isnt the D90 also a preamp?
the owners manual is vague about the preamp side
when in preamp default is it still decoding at the same levels as DAC MODE?
i too am using with willsenton r8
i guess i wonder whatvadvantage or disadvantages there are
to each variation
the willsenton remote is junk and buttons have fallen out
with LIMITED use
so d90 volume control might be superior?.
Yes it has preamp
This from there marketing materials on APOS TOPPING D90 DAC (Digital-to-Analog Converter) – Apos Audio
“It comes with a volume control function so it can be used both as a DAC and as a DAC/Pre-Amplifier. This volume control can be disabled to make the D90 function purely as a DAC that produces output levels of 4Vrms (XLR) and 2Vrms (RCA).”
One thing if I wanted to I could plug this directly to a set of Powered Near Field Speaker for example where I would need the pre-amp feature. But you can shut if off if your going to Amplifier with Pre-Amp and use it DAC mode only.
So
When in pre amp mode is it also
Working as a dac?
Thank you!!