Recently DIY Computer Build has Major EMI Issues, Remedies??

[OldAsMono]

I'll try to be brief. At 67, recently retired, I built my first own PC to replace my 13 year-old Dell. All is fine but son was first to say, "What is that constant sound?" I couldn't hear a thing. It seemed to get worse (I guess). Then I did hear it (one of those things you can never unhear it once heard). All by hi-fi equipment is in a hall closet and includes my computer as it drives ALL my music and recorded media like movies and TV shows. I was worrying it was my AVR or separate amps crapping out on me. Until I isolated it to my computer causing the noise. Turn off the computer and the sound is gone for regular Cable TV and Streaming through an Amazon Stick. I also noticed doing high computer processing like condensing a movie with HandBrake increases the noise. I'm thinking it is mostly the fans putting out EMI (Electromagnetic Interference). I read many,many solutions online BUT most did not actually solve the issue or very old.

Curious if my fellow QQ nerdies have a remedy they would suggest. I do have one side with glass on my case. Not by choice but all new cases seem to have one glass side now. I do not run any LEDs on my fans either.

Help Please,
OldAsMono

 

[DrKlahn]

I've experienced a hum with less expensive motherboards using the built in analog outs (it changes in pitch with load). Digital outs, such as Toslink or HDMI haven't had this issue for me.

If it's already connected digitally to the AVR, might be in the grounding. Might try an extension cord from an outlet on a different circuit/breaker.

 

[OldAsMono]

Great minds…. The computer is HDMI only to the AVR. There are analog connections from the AVR (acting as a preamp) to my amplifier. I recently went tie wrap crazy and made sure all power cables were separated from all others cables like audio, HMDI, internet, USB, etc.

Lastly, I did a 50 foot extension cord just for the PC to a far away outlet. I was a little surprised it made NO difference. We also completely redid all the house electrical and verified good grounding.

I know it maybe sounds silly but I’m going to try wrapping my computer case in aluminum foil while making sure no fan intake/outputs are covered. Hey, it’s cheap and easy.

Thank you for your suggestions!!!

 

[DrKlahn]

Does unhooking the HDMI from the PC to the AVR stop the noise?

 

[quadsearcher]

Try disconnecting TV cable from the cable box. Not likely the problem but a variable to eliminate. RF cable ground is/can be a wildcard.

 

[OldAsMono]

Does unhooking the HDMI from the PC to the AVR stop the noise?

YES, it certainly DOES stop the noise disconnecting the HDMI cable from the Computer!

Try disconnecting TV cable from the cable box. Not likely the problem but a variable to eliminate. RF cable ground is/can be a wildcard.

NO, it did not stop the noise disconnecting the HDMI out of the Cable box to the AVR and still noise. I also tried disconnecting all other HDMI cables (one at a time); AVR to TV, Firestick to AVR, etc.

As stated above the ONLY HDMI I disconnected that DID stop the noise was the HDMI out from the computer to the AVR.

Does this maybe mean I need some type of Ferrit Core on my HDMI cable ??? Or are we still working to isolate.

Thank you both for your replies! I am farther down the road on a possible remedy!

 

[jimfisheye]

That sounds positively like a ground loop. Digital circuit noise found a path down a ground wire and out the HDMI cable. A ferrite core would likely do absolutely nothing to help.

Best case:
Poorly made HDMI cable. (eg. Amazon purchase)
Faux HDMI cables (that might sometimes sort of still work for low def video) are plentiful these days. Monoprice is usually a decent place. Still be careful and read the fine print! Watch out for reduced spec. eg. When the more expensive one lists 4k compatable and the cheaper one doesn't... that cheapo one is not to spec.

Even better case:
Mains power related ground loop.
Make sure both devices are on the same circuit.

Shitty:
Design limitation in the logic board leading to this. You already have good cables and proper setup but the logic board has a ground fault. Worst Purchase computers...

Shitty:
Ground fault in the AVR. Same deal with no solution.

In the past (stereo only days) the impossible case could be solved with an optical cable. If your only choice is an HDMI connection, that's kind of that.

Maybe try a thunderbolt port instead if you have one. Thunderbolt to HDMI cable instead of HDMI to HDMI. Should "just work" the very same way.

I've had a couple rogue USB interfaces do this to me before. Like trying to record off a Soundcraft MTK22 board! Cheap bastards! Meanwhile every M32, X32, and now Digico board was dead silent over USB. There was no solution for the MTK22.

 

[LuvMyQuad]

YES, it certainly DOES stop the noise disconnecting the HDMI cable from the Computer!

NO, it did not stop the noise disconnecting the HDMI out of the Cable box to the AVR and still noise. I also tried disconnecting all other HDMI cables (one at a time); AVR to TV, Firestick to AVR, etc.

As stated above the ONLY HDMI I disconnected that DID stop the noise was the HDMI out from the computer to the AVR.

Does this maybe mean I need some type of Ferrit Core on my HDMI cable ??? Or are we still working to isolate.

Thank you both for your replies! I am farther down the road on a possible remedy!

Did you try plugging the PC HDMI into a different port? That should definitely narrow it to the PC or the AVR.

 

[OldAsMono]

Thanks guys, I will trying these tomorrow. I buy from Monoprice all the time, in fact all my cables BUT, this specific HDMI cable is at least 10 years old. Thanks again.

 

[OldAsMono]

Devices are on the same circuit and run through a Furman Linear Power Conditioner. I'm pretty sure I did get a good motherboard as it's a Gigabyte Gaming Motherboard x670E Aorus Xtreme and I hope that is not the issue. I'll order a very good HDMI cable and maybe a Thunderbolt to HDMI cable as well.

I have an all day listening marathon with brother coming up Saturday. The sound isn't bad to me but if my brother's hearing is like my son's hearing I'm screwed.

 

[jimfisheye]

That all sounds really by the book! Hopefully a fluke with the cable that's easily solved. Otherwise maybe some star grounding. ie. All grounds to a single point in the case. Maybe some extra ground straps.

 

[quadsearcher]

YES, it certainly DOES stop the noise disconnecting the HDMI cable from the Computer!

NO, it did not stop the noise disconnecting the HDMI out of the Cable box to the AVR and still noise. I also tried disconnecting all other HDMI cables (one at a time); AVR to TV, Firestick to AVR, etc.

As stated above the ONLY HDMI I disconnected that DID stop the noise was the HDMI out from the computer to the AVR.

Does this maybe mean I need some type of Ferrit Core on my HDMI cable ??? Or are we still working to isolate.

Thank you both for your replies! I am farther down the road on a possible remedy!

Not the HDMI, but the coax coming out of the wall. Either should do the same thing interrupting a ground, but I mean specifically the RF coax that screws onto the RF input of the cable box, disconnect that to test. Seen it more than once, poor ground at cable entry to the house or at the pole causing a ground loop.

 

[MidiMagic]

I have done a lot of hum elimination in my life. Check for these:

- Enough ripple in the computer power supply to affect analog signals but not digital operation.
- An overloaded power supply unable to refill its main filter capacitors fast enough.
- A switching power supply with a bad filter capacitor in the oscillator circuit.
- A ground loop between the computer and the AVR (more than one ground path, including the 3-wire power cables).
- No ground connection between computer and AVR (bad cable).
- An audio cable is not shielded.
- Is a wire or device too close to a wall outlet power supply and picking up the magnetic field from its transformer?
- Is the hum other than 50Hz, 60Hz, 100Hz, or 120Hz? It could be a beat frequency between two different computer clock frequencies in different equipment.
- Note that DC computer fans do NOT produce any of the hum frequencies listed above. They make their own frequencies.
- Is an input on an audio board disconnected but turned all the way up (e.g. the original mic jack on the PC)? Is the original mic cable too close to a power cable?
- Check to see if feedback is occurring from some circuit in the AVR back into the computer audio board.
- Is a third device connected to both the computer and the AVR? Disconnect one connection and see if the hum goes away.
- Is some unrelated device producing an electromagnetic field near the computer or AVR? This could be a lamp, a clock, a fan, a fish tank pump, or some other device.

 

[M-K]

Mostly a ground loop. Professional audio interfaces use balanced wiring. So called DI boxes (see DI unit - Wikipedia) have a ground lift to separate the shield from units. This breaks the ground loop. But you can't do this with single ended (chinch) audio connections.

If the ground loop can't be avoided then a good very low impedance ground connection (also in term of high frequencies) between source and sink has to be done. As example connect a thick copper wire (ground strap) from case to case in parallel and keep distance as short as possible between the devices. This can reduce potential difference on ground.

 

[OldAsMono]

Wow, I feel I came to the right place to ask this question. I'll stop trying to do a magic fix by tomorrow for my brother's visit and attack this step by step, one item test at a time. Lots of great things to try (I say great but obviously very time consuming). The goal of no additional noise in the audio is more then worth the effort. The best part is that 'usually' once it's identified and remedied, it shouldn't be an issue again for a long, long time.

Thank you folks for all your suggestions and I will update in a few days.

@quadsearcher - I did try disconnecting the RF Cable into my Cable Box and the noise remained. Thanks for helping eliminate another possible source.

 

[jimfisheye]

...

As stated above the ONLY HDMI I disconnected that DID stop the noise was the HDMI out from the computer to the AVR.
...

This sounds matter of fact. This is the ground loop path.
Try another cable real quick if you have one.
Try a thunderbolt to HDMI cable from the thunderbolt port instead. (Mac user here assuming there would just be one.)

You said DIY computer build? So if not the HDMI cable at fault... You might just need a couple ground straps in the case. You might experiment by taking a piece of wire and connecting ground points - just touching the wire to chassis points. See if you find it and the hum stops. Then put a ground strap there. It sounds like you have electrical knowledge where I don't have to step by step tell you not to poke a wire into a circuit or live power? But if not... CAREFUL please! Don't even think of doing this if you aren't sure!

 

[OldAsMono]

SUCCESS !!!!! - I appreciate @jimfisheye giving me more credit then I deserve on my "electrical knowledge" because I really didn't know where to get a good ground point to attach to the Computer chassis. Sufficiently concerned by his justifiable warnings, I decided to try using the turntable ground on the AVR. Maybe not at all what he was suggesting but I felt this was safe (enough). I then attached the other end to an unpainted screw on the computer chassis that holds the power supply in place. I also waited an additional hour before sending this message to verify success. I had first attached to a painted screw on the chassis and thought I had success until I listened again before even completing this message. The sound had come back.

The GREAT news is it seems to be noiseless with a copper wire from the AVR turntable ground to the computer power supply screw in the chassis!

I do still have a new HDMI getting delivered tomorrow but that is more then fine. You people were AMAZING and gave me great ideas as these things always have a zillion different possible remedies. I just got lucky by trying the easy fixes first. I didn't even have to disconnect the computer which is always scary with a guest coming over tomorrow specifically to listen to music all day. I usually put a freeze on any new software/hardware updates a few days in advance like a software patch release to be sure I don't screw anything up.

I do still have one additional test when my son comes back in town Tuesday. Did I fix it or just change the pitch to something outside my old ears hearing range?

Thank you ALL for all your suggestions and very wise words.

 

[jimfisheye]

That's awesome! Glad to be able to help!

Yeah, I was going for some kind of extra grounding inside the computer box that landed in just being to plug the cable in as designed. But what you did is certainly more direct even if not perfectly elegant! Still matter of fact correct in the end too. You gave the noise that drain path it needed and kept it from hitching a ride on the audio signal wires.

 

[mandrix]

That's incredible! I've built so many pc's I couldn't even tell you, and never had any ground loop hum. I would question the power supply.
But glad you got a fix!

 

[mandrix]

That's incredible! I've built so many pc's I couldn't even tell you, and never had any ground loop hum. I would question the power supply.
But glad you got a fix!

Or the power cord for the psu.