Whoa, Ok. Let me Clear it out for everyone!
I hope i'm right, but i may be wrong.
And sorry if i am wrong, i have much more to learn.
But just sharing
A90 power supply designed with Earth connection utilised.
So a potential ground loop issue is expected if you use it with the WRONG DEVICE
Simple to say, it is not the A90 fault design, but to know what interconnect devices you should use with and what devices you should'nt use with.
TLDR, Summary,
If you want to use A90 with a Earth Utilised Device, Use XLR interconnect ONLY
If you want to use A90 with a Non-Earthed Device, Use Either will be Good.
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if one wish to use the A90 with a Earthed Device, Use the XLR input only,
and dont connect other Earthed Device to A90 RCA input while using XLR input
I was told that XLR connection can prevent ground loop issues,
thats why it is recommended XLR interconnection if you're using between two XLR capable grounded device
(Example of device like Topping DX7 Pro, D90)
Using RCA Interconnect between two Earth-ed device is definitely going to be suffer from potential ground loop issues.
And Off course if you still insist you want to use A90 RCA input with your Earthed Device,
only way to do it is to Earth-Lift your A90 or your Earthed Device!
But not sure if is safe, but is not recommended by
@JohnYang1997
But if is ok or safe enough to do so,
John will you think is a good idea to implement a Ground/ Earth Lift Flick Switch on A90?
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if one wish to use the A90 with a Non-Earth device, You can use both RCA or XLR input no issues
(Example of Device like Topping D50s, Dx3 Pro)
Because the A90 will act as the Earth-ed station for your non-Earth DAC thorugh any cable
Those who used A90 with -
- RCA out from Desktop PC motherboard or Soundcard,
Your Desktop PC is producing a lot of noise and Desktop PC is Earthed!
Now you're Connecting to A90 RCA input
A90 utilised the Earth, so ground loop issue is one thing
Another is your Desktop PC dirty power noise will also leaked into the A90 and Earth through it
And thats the noise you heard when using RCA input,
Just to let you all know is not the A90 issues.
And Off course if you still insist you want to use A90 with your desktop,
only way to do it is to Earth-Lift your A90!
But not sure if is safe, but is not recommended by
@JohnYang1997
But if is ok or safe enough to do so,
Again,
@JohnYang1997 , will you think is a good idea to implement a Ground/ Earth Lift Flick Switch on A90?
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- Another is some using DAC that is eithered USB Powered or Draw power from PC using USB CABLE
or COAXIAL signal to your DAC
If your DAC did not reject the noise or Ground loop from your PC,
the signal send to A90 may suspect to noise or Ground loop issues as well if you are using RCA interconnect between them,
The way to solve it is to either get a USB Ground Isolater like the iFi iDefender+ to break the gound between your DAC and PC
For USB Powered device you will also need to get the iFi iPower 5V as well to Power your USB Powered device
And you may get sound quality improvement from doing so with a clean power supply from the iFi iPower
and end of the day you may potentially achieves even better sound quality to your DAC to the A90.
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- For All other user that compare the A90 with device like THX 789, 887, JDS Atom
The reason those device doesn't have the RCA noise is because THX 789, 887, Atom doesn't utilise the Earth Pin!
So they are designed to be used with a Earthed DAC!
So they Earthed through another Earth Device through the RCA Interconnect!
Simple to say, it is not the A90 fault design, but to know what interconnect devices you should use with and what devices you should'nt use with.
Try using Topping D90 with SMSL SP200 and you may get the same issues as well, maybe..
Since i guess SP200 is Earthed and designed to use with their Non-Earth DAC M300 M200 as well.
While M400 with SP200 amp may have potential Ground Loop issues too.
Just my finding and sharings.
I may be wrong
I'm still learning.
But hope i gave you an idea for reading XD
Thanks.
*Sorry that i wrote so long