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Power amp is picking up electrical noise from the PC via sound card ... it's a ground loop!

post #1 of 6
Thread Starter 

Hi there,

 

Well, this is driving me absolutely crazy. I would try to explain in relatively concise manner.

 

I'm aware that sound card (PC) and power amp can share only one electrical ground (either via RCA connectors or power sockets).  If you have two electrical grounds in parallel, ground noise from the PC can be picked up by the amp. I believe that's what happening in my case. Interestingly enough, it's happening even when external DAC is in place! It's at worst when doing some intensive GPU tasks or GPU stress test (I have Radeon 290X), so I believe that GPU card is the culprit actually as it's badly designed. Anyhow, I didn't experiment with ground loop or USB isolators. Simply put, not enough experience and there are rumors that isolators are damaging the sound path.

 

I know that when using optical connection to the external DAC you are effectively isolating DAC/AMP from the PC pollution noise, but in my case I want to use sound card explicitly. So, how can one have only one ground plane when using PC sound card? I know that you can disconnect the ground wire from the power amp plug, let's say, but that's safety concern.

 

Is there any other work around? I have very good internal sound card and simply put want to avoid external DAC route at the moment.


Edited by Incognito73 - 6/3/14 at 5:22am
post #2 of 6

What is the make and model of the sound card and the amplifier?

post #3 of 6
Thread Starter 
Quote:
Originally Posted by PurpleAngel View Post
 

What is the make and model of the sound card and the amplifier?

 

I was just about to shutdown when your msg arrived. Thanks for the follow up! Sound card is Cantatis Overture 192 (installed in very high end PC with excellent PSU) and amp is Rega Brio-R.

 

I just realised something! Rega Brio-R does have grounding (chasis) screw underneath, when used with devices without ground pin (like turntables as phono stage is present on this amp) I was thinking ...if I disconnect the ground wire from the PC power plug and connect Rega grounding screw (I just found metal spaded ground cable from previous uses btw) to the PC chasis (PSU screw let's say)... effectively they will share one (same) ground plane as PC will "borrow" the ground plane from the Rega itself! and that will brake the ground loops. So, for example ... should a fault develop within the equipment (PC in this case) that causes the active (live) conductor to come into contact with the chassis, instead of the current staying in the chassis and travelling through the body of the poor bustard who touch it ... it will travel via grounding wire to the Rega chasis and from there to the mains earth pole and eventually to the earth itself or braking circuit. I guess that other way around is possible too, so that Rega via grounding screw is using ground plane from the PC (if ground wire is disconnected from the Rega power plug).

 

Does this makes sense? Hopefully with the technique above hum/buzz/noise free operation can peacefully co-exist with safety measures.

post #4 of 6
Quote:
Originally Posted by Incognito73 View Post
 

 

I was just about to shutdown when your msg arrived. Thanks for the follow up! Sound card is Cantatis Overture 192 (installed in very high end PC with excellent PSU) and amp is Rega Brio-R.

 

I just realised something! Rega Brio-R does have grounding (chasis) screw underneath, when used with devices without ground pin (like turntables as phono stage is present on this amp) I was thinking ...if I disconnect the ground wire from the PC power plug and connect Rega grounding screw (I just found metal spaded ground cable from previous uses btw) to the PC chasis (PSU screw let's say)... effectively they will share one (same) ground plane as PC will "borrow" the ground plane from the Rega itself! and that will brake the ground loops. So, for example ... should a fault develop within the equipment (PC in this case) that causes the active (live) conductor to come into contact with the chassis, instead of the current staying in the chassis and travelling through the body of the poor bustard who touch it ... it will travel via grounding wire to the Rega chasis and from there to the mains earth pole and eventually to the earth itself or braking circuit. I guess that other way around is possible too, so that Rega via grounding screw is using ground plane from the PC (if ground wire is disconnected from the Rega power plug).

 

Does this makes sense? Hopefully with the technique above hum/buzz/noise free operation can peacefully co-exist with safety measures.

 

So this setup is for a speaker setup, not headphones.

(that is a nice looking sound card)

Unless you state otherwise, people (like me) will default at thinking your asking about a headphone setup.

 

Have you disabled your motherboard's on-board audio? in the BIOS.

 

I really know zero about grounding,

I'm sure there are others on Head-Fi who might be able to offer good advice on your issue.

 

Might consider to also post questions about speaker setups on the websites AVSforum and AVforum.

post #5 of 6
Thread Starter 

Well ... setup is for a headphones too :D as my Meier Audio Jazz headphone amp is connected to the rec out of the Rega Brio-R amp and ground loop is transferred to the headphone amp too! so I have ground loop noise when using headphones too.

 

Yes, sound card is pretty much amazing. It's dual mono BB PCB1794 design with heavily filtered three stage linear power supplies (it does have impressive black background). This is mine version, with heatsinks installed to cool the card and they act as nice EMI shield too:

 

 

 

Anyhow ... I have quite good feeling that I figured it out!  It's a bit late here in the UK, so tomorrow I will hopefully brake the ground loop, test and report back.

post #6 of 6
Thread Starter 

OK ... quick update. Ground loop is tackled now! Everything is dead quiet, even with headphones, with no single trace of buzzing/humming/interference even when doing GPU burn-in tests. Some people say that PC case itself is noisy environment, but honestly I don't understand what's all that fuss about. If you use good quality PSU, nicely shielded cables, take care of the grounding planes ... one shouldn't worry I would say.

 

Anyhow, I lifted the ground from the PC and headphone amp power cables. I've made a custom T type grounding wire going straight from the power amp grounding screw to the casing of each component. Additionally, I completely forgot about the monitor!  It was causing the ground loop too ... as it's already grounded via DVI cable to the PC itself (and it's case is made of plastic anyway so no particular need for secondary ground). So, now all components are using  the same primary ground plane - from the power amp itself.

 

Finally, perfect black background.

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