Topic: PCIe,PSU, Earth, common ground issue = noise!
I have been using RME products for maybe 15 years, from 9636/52 , 9632, Raydat and now an AIO and I love them allot.
However, I have been having trouble with system noise, such as mouse movement windows open, rendering files) mainly from the headphone out but also the unbalanced RCA (not so much with RCA as we can set hot levels) but with in-ear, low impedance headphones it is very bad, in fact!!
Test room is very quite, no fan noise, all fans were reduced to almost inaudible levels for the test , so we can hear well.
2 x AIO's
3 x PC's
3 x sets of various impedance headphones,
we were able to test various configurations and have found some interesting things.
we have gone as far as using 'insulation tape' wrapped around the AIO mounting bracket, so to isolate
the AIO from the chassis (As mains Earth is bolted to the Chassis of the internal PSU)
In the UK we have Earth in all our mains sockets/outlets, this is then connected to the chassis of the ATX PSU. (standard) and that PSU is then connected with 4 conductive bolts/screws to the chassis of the PC and the AIO is also bolted directly to the chassis of the PC. So, the AIO has two grounds connected, the Earth from mains and the ground from the output of the PSU.
All my ATX PSU's have these 4 screws.
The AIO is designed to be used inside an ATX chassis and use ATX PSU's yet, there seems to be an issue with (common) ground.
1. when I power up the PC with the AIO bolted to the PCIe slot ( as it should be) and with all 4 screws of the PSU tightly connected to the PC chassis( as it should be) the interference noise is quite loud with various windows open and rendering.
2.When I power up the PC with the AIO 'isolated' with 'insulation tape' all over ('not' as is should be), so it does not touch the PC chassis/earth at all, but still with all 4 bolts of the PSU connected to the PC chassis(as it should be), There is no noise. (if i wrap the AIO in tape = no noise)
3.When i power up the PC with the AIO correctly bolted to the chassis with no tape(as it should be) but with the PSU 'not' bolted, instead with the PSU loose inside the PC chassis and so with its own chassis isolated from the PC chassis in the same orientation, in the same place, just minus the bolts( 'not' as it should be) the noise is no longer there. it is quiet. ( so no bolts = no noise)
So there is a definite problem with these two grounding points and the AIO
1. The ground from the output of the PSU ( black wires)
2,. The ground/Earth that is bolted to the PSU chassis > AIO mounting bracket.
The AIO seems to only like the one ground from the output of the PSU ( the black wires) if one allows the PSU's chassis/mains Earth to connect to the AIO through the PC chassis the interference noise is again present.
I have tried 3 x PSU's and my friend also has an AIO and PC! So that is 4 x PSU's and 3 x AIO's all tested in the same way, they all fail whilst bolted up correctly inside ATX systems.
Has the AIO got an Earth lift switch? Maybe it has, i can't see it? Would it be good if it was able to electrically isolate itself from the ATX chasis? future revision, maybe?
Yet, the newer AIO PRO version has the same issue. we tested that too.
Even when we disconnect the mouse,keyboard, Monitor, every add on peripheral = disconnected, with only the headphone connected whilst standing on rubber, in rubber shoes, in a quiet room, this issue is still present.
The tests were done with low impedance headphones approx 32ohm (in-ear), but also 64ohm , with 64ohm the noise was, of course, not as loud, but still present in a quite room.
This is maybe one reason why some people hear noise and some do not. also most people output to a mixer or headphone amp or receiver and use that headphone port instead , also many people use spdif or balanced out which is not effected!
There are many reasons why many people do not hear this noise, especially if sitting near to more than one pc fan, whilst overclocking.
I notice some people say " turn off power saving c-states" that reduces the noise, But one should not have to do that. Because With the AIO disconnected from the mains Earth, I can have c-states on, power saving on, and there is next to 'no noise' ! Whisper quiet! Even as the CPU clocks up and down ( we see in CPU-z.)
As soon as we reconnect the Earth back up to the AIO , by bolting the PSU back on/ pulling off all the insulation tape from the AIO = All the noise comes back!!
This did not take an afternoon to figure out. it was very stressful.
Any info would be gratefully received.