After only a year my 789 is already getting bad volume pot scratch. I was thinking of upgrading my 789 to the Topping A90. I think the black color version will pair nicely with my RME adi-2dac all hooked up balanced. 
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A90 kind of has a similar shitty pot. Just unscrew the backplate of the 789 (it is already out of warranty anyways), push out the pcb to gain access to the 789âs volume pot, and work in some liquid deoxit there. Spending $10-20 is preferable to spending a couple hundred dollars. Measurements-wise, I donât know how much of an upgrade the A90 would be since any measurable performance gains is inaudible already.
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Noob question. Iâm thinking about upgrading to this from 789. Along with using this with my DAC (RME adi-2) I hear you can use the xlr output for studio monitors? Is this really true and what controls the volume for the speakerâs and can I seamlessly switch from headphones to the studio monitorâs? Is there any drawbacks ect. Thank you for your time.
The performance gains from a 789 to an a90 is not inaudible like @mbvjmc thinks. All around smoother on the a90 without coming across as âcoloringâ the sound whatsoever. Noticeably less grain and the power when you need it is actually really nice to have.
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It is not what I think, it is what the measurements show. Read my post again, I emphasized measurements since those metrics are what people tend to use when evaluating these two amps. These amps are supposed to be âwire-with-gain,â so any colorations between the two, according to ASR acolytes, should show up on the measurement rig as audible distortion. That isnât the case based on the published measurements from ASR.
Also, to parrot an oft-used retort from ASR to subjective impressions, did you adequately perform a volume-matched double-blind test with these two amps?
PS. I really donât care for either of these two amps. Use whatever makes you and your wallet happy. I was just mocking how discussions on ASR are typically conducted.
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Yeah but their graphs are smoothed a lot and grain would show if they werenât.
THX 789 has a hum that is audible and measurable. I think Joshua Valour mentioned that, too. ASR also stated that. Link: https://www.audiosciencereview.com/forum/index.php?threads/apparently-the-thx-789-is-a-noisy-amp-i-call-bs.13392/
The hum only comes if youâre using it unbalanced, though.
That Topping guy (JohnYang1997) is being ehm⌠the A90 uses a pair of these integrated AC-DC power supplies. The extremely wide supply range of those means Switch Mode Power Supply.
Also: The voltage ripple (lower is better):
That said, two things:
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Why are we talking about this in the A90 thread?
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100mV peak-to-peak ripple on the power is definitely not great, I would say. AFAIK there is nothing in terms of power filtering in any of the THX amps, so to some degree that ripple will definitely make its way to the output.
You couldâve read the previous posts. It was about A90 vs 789. The hum in 789 is audible. Hum is never desired and harmonic.
I didnât say anything about A90âs power supply or JohnYang1997.
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 donât 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 itâs 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 wonât work correctly with A90.
I would do some more digging around to confirm this, but from what Iâm 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 Iâll hook it up to my A90 and tell you what I find⌠
This is the silliest thing Iâve heard yet. People truly believe that the M400 wonât work with the A90? Really? Are you absolutely sure about that? 
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Hook it up via RCA , Chops, see if thereâs any difference.
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Thatâs how I first had it hooked up. Worked just fine.
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Isnât 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 wouldnât be able to output the max voltage to the amp, but thatâs about it.
JohnYang1997 himself said:
Hi guys! Somebody did the comparison between a90 and a30 pro? Interested in sound differencesâŚ
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