I did not consider 19 days old posts to be part of the conversation, my bad.
That is what I kinda of said:
Some people take what JohnYang says as gospel.
After L30 and all the destroyed headphones, I donāt think anyone would. But his NFCA at least sounds decent for being a measurement-focused amp.
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read again. He said measurable performance gains. Measurable. In regards to distortion, signal to noise ratio etc you CANNOT hear any gains. Sounding nicer cannot be measured
I heard that there is an issues with the A90 design, with itās really low input impedance. Apparently a topping designer confirmed that the A90 wont work with certain dacs.
-which wedding do you recommend?
-SMSL M400 MQA or Topping D90 MQA?-The much higher output impedance about 1.2kohm of M400 wonāt work correctly with A90.
I would do some more digging around to confirm this, but from what Iām seeing this is in reference specifically to an RCA connection. Please take it with a grain of salt, though.
Now if you want this tested feel free to ship me an M400 Iāll hook it up to my A90 and tell you what I findā¦ 
This is the silliest thing Iāve heard yet. People truly believe that the M400 wonāt work with the A90? Really? Are you absolutely sure about that? 
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Hook it up via RCA , Chops, see if thereās any difference.
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Thatās how I first had it hooked up. Worked just fine.
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Isnāt the impedance curve of amps flat? High output impedance of the dac means the voltage would be less than nominal, but nothing else would change. The dac wouldnāt be able to output the max voltage to the amp, but thatās about it.
JohnYang1997 himself said:
Hi guys! Somebody did the comparison between a90 and a30 pro? Interested in sound differencesā¦
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I really wish someone would do a tear down and post the pictureās. I donāt wanna do it to mine. 
Until then these are all I got to go on for my internal eye candy fix. 
Funny. I thought there would have been āMoreā going on inside. Iād love to see the underside of the pcb board.
All the measurement focused amps are the same in more than one way. In case of the A90, dual MeanWell SMPS, some filtering, some of ehmā¦? Regulators? Not sure:
And some Op-Amps or integrated Class AB amplifiers (like everyones favourite TPA6120A2.
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So I finally jumped. Got a stupid delivery man who got anxious when I said I did not know there are import duties because DHL did not let me pre-pay (remembered today that it only happens when a company files an import duty form, or at least I assume) and then told me he is coming back tomorrow. Reported him for not accepting my 40ā¬ of import duties oof. Got the wrong XLR cables, female ones because I did not look at the photos / naming but sure I will get a use for that soon with a DAC.
TLDR is simple: Everything said about it is true. It is not harsh, unaltered sound. Currently need to use a Anker battery bank to remove static from USB - Toslink - LineOut - to RCA instead of XLRā¦
Btw the FiiO Q5s has bad balanced audio. It is god awful. Q5s can not run NDH20 too. There was something missing even if it was just 10%
Hello guys:
I recently bought the A90 and iām going to paired it through the RCA input, from my schiit modi multibit (yeah i got no balance dac yet, but hopefully in a couple of months iāll get a balanced DAC). The problem is, i also have a valhalla 2 tube amp, and itās RCA too.
So my question is: Can i use the preamp function of the A90 to feed my valhalla 2 and avoid using a switcher? If itās possible, how do you recommend me setting the volumen and gain on the A90?
Thank you for your help 
I have a similar setup with my A90 and a Cavalli tube Hybrid. I set the tube amp at roughly 50% volume and then just use the preamp in the A90 to control the volume from there.
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So I just got the A90 today and am pretty happy so far. Other amps are Feliks Audio Echo MK2 and Asgard 3.
I have to agree with what most reviewers said. Its neutral and you will hear how your headphones and your source sounds. The amp itself has no distincitve character and that just what I was looking for.
I can really hear the differences in tuning far better then on my other amps and playing with eq is much easier as well. At the momen I am only using the 1/4" but I ordered some 4.4mm and XLR adapters from hart.
Next step is trying to get a second hand D90 non mqa to complete the stack and possibly selling off my Asgard 3ā¦
Topping A90 refresh with discrete circuit and volume display.
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Seems that they may be discontinuing the original A90 which is being replaced by the discrete version. This was my feeling after Apos said that they do not know if they will ever get it back in stock again. They do have the silver still available but absolutely no black.
Was originally thinking about buying the black version but happily ordered the singxer.
Also the internal components of the topping are inferior to the higher quality of the singxer.
Especially the potentiometer which always gave me headaches with my THX amps.