Getting rid of noise, Line-Active UPS System or Isolation TransformerPosted by sb-woo on April 19, 2022 at 3:17 pm
I recently bought a new computer for my home theater. When I connected it I had a lot of noise. Seemed like it was directly corresponding to the GPU workload. At this point my TV, AVR, XBOX and Playstation were all connected to a power conditioner/sequencer from Monoprice from a single plug in the wall. Then on the opposite side of the room, my Crown amp and MiniDSP were plugged in to another wall outlet. All on the same breaker.
After doing a little research, I tried connecting all directly to the Monoprice on one outlet (so I added the Crown amp and DSP all to one plug) This made a difference and things got quieter. But the GPU of the computer was still very audible. All of the noise seemed to come from the subwoofers connected to the Crown amp.
I then ran an extension cord to another room and put the PC on that by itself, basically isolating it from the entirity of my home theater. This all but eliminated all noise issuses.
I cant have cords all over the place and dont want to run new power lines through the walls. So I did more research and what I came to was either a “Line-Active Uninterupted Power Supply” basically a battery back-up or an isolation transformer. The line active UPS system was the cheaper of the two so I ordered that for around $170 from amazon.
As usual. A few moments later I read on Audioholics Patreon community chat area that the UPS System wasnt that great of an option because you have to basically replace it every 3-5 years.
I also read somewhere else that the isolation transformer can introduce noise of its own. So I’m wondering if anyone is familiar with these, and what’s the best option? Is there a better option?
MemberApril 19, 2022 at 3:23 pm
Just to clarify, I have not received of connected the UPS system yet. Should be here on 4-20-22.
MemberApril 24, 2022 at 7:51 am
I believe this may be coil whine (how would you describe the sound?). If it is, it’s either the power supply, the GPU itself, or a combination of the two. Probably that the power supply isn’t filtering it out properly like they’re meant to.
ModeratorApril 24, 2022 at 9:39 am
I hate chasing noise in a system. There’s so many causes, and it’s usually the one you think is least likely or you’ve initially ruled out.
Just to clarify, with your previous computer you didn’t have this issue. You also state that you hear the noise from the subwoofers through the Crown amp.
What diagnostic equipment do you have? I’m sure at least Multimeter. Do you have an outlet tester? An Oscilloscope would be great, but not necessary, and if you aren’t up to using one properly with lines voltage (all the safety precautions for not only you, but the scope as well), better to not worry about it. Do you have any ground lift adapters, aka 2 prong to 3 prong plugs (extremely inexpensive for a 2-pack at just about any store)?
A video showing exactly how things are hooked up and a demonstration of the sound would help as well.
You have done one of the biggest troubleshooting steps already. You’ve isolated it to impressed noise on the common power line branch. One last thing on that particular line of reasoning would be to plug the computer back into the monoprice strip and then use the extension cord to plug into another (third) outlet on the same circuit. If the noise returns, then it’s hard confirmed to be an issue with all connected to the same circuit.
Next thing I would do is try using the ground lift adapters on the computer first, then the Crown second.
Another question is, how is the Crown ultimately connected to the AVR? The interference may be introduced there.
MemberApril 25, 2022 at 7:23 am
I think it is probably from the GPU. I dont know much about computers these days, but it’s my understanding that it has a high quality power supply. Thats not exactly proof of anything though.
I did not have a PC in the setup before this.
The noise I am hearing is a clicking that changes frequency as the computer does things. (Maybe that helps)
The noise is heard through the subwoofers which is powered by a Crown amp. The RCA wires running to the amp are 35′ each. (Potential source)
I have a simple analog multimeter. No oscilloscope, ground lift adapter or outlet tester.
My plan for today and tomorrow is to: run speaker wires in place of the 35′ RCA cables which would permanently place the Crown on the same plug as everything else and bring the RCA cables down to 4′ total. I will be testing more configurations with the isolation transformer. At the moment it is plugged into a different plug than everything else. I plan to clean up and consolidate all theater equipment onto the one plug. I also ordered a crap-ton of Ferrite sound suppressors. Or Ferrite Beads. $20 got me 40 of them on amazon. Im not 1000% sure the propper way to use them with different wires/sources etc so I will try to do a bit of research beforehand. I will also do my best to seperate steps and judge results as I go.
Very greatfull for the help!
- This reply was modified 3 months, 3 weeks ago by sb-woo.
MemberApril 26, 2022 at 7:46 pm
Only just seen @123toid tagged me in this, been busy with work recently
If im understanding your explanation correctly I have the exact same noise with my studio monitors and my RTX 3090 workstation although for me I can only hear it if I put my ear right up to the tweeter so I can mostly ignore it. My understanding is that @elliottdesigns is correct about it being coil whine however im dont think he is right about the power supply being part of the problem, its likely only coming from GPU. I have a very high end 1200W platinum rated PSU from EVGA and I have noise.
In electronic components such as graphics card you get coil whine when power runs through certain PCB components generating electro magntic forces. The strength of these forces are dependent on the quality of the PCB design and how much effort has been put in to mitigating them. These EM forces in turn cause the PCB component to vibrate at an audible frequency. However the generated EM forces dont just make anoying noises they can also introduce interference noise in electrical signals (EMI) , particulaly low voltage circuits e.g. a modern nvidia GPU core runs in the 0.9-1.1V range, hdmi signal pins are around 0.5V. As the GPU core frequency changes with PC load the ammount of power running through the card also fluctuates. This is why the noise changes as the PC does things. IIRC RTX 3080 and 3090 gpus can pull well over 300A across the core under max load and nvidias lazy design specs let the card have momentary spikes in the microsecond range at 1.5x or more their rated TDP, these large current draws can put out massive ammounts of EMI (fun fact thats why front panel audio IO on a PC case is bad to use, inside the case is a literal mine field of EMI)
These interference noises can travel out from the originating component along any conductive path. For me they seem to travel back through the motherboard and out down the USB cable that connects my audio interface to the PC. If you have your PC connected to the reciever via HDMI that is most probably how the noise is getting into your audio system. Even if the reciever is not set to your PC hdmi input or is even off simply being electrically conected is enough for the noise to make its way to the audio system
Unfortuntely, unlike ground hum, this type of noise is unlikely to be resolved by isolating the power to certain parts of your audio system as is trasmitted via an electricaly conductive signal connection not via the power lines. The one exception to this statement is if your building wiring is not properly earthed, In that scenario the EMI noise could be transmitted through power line. If that is the case you have a more urgent issue than noise in a speaker and should get an electrician to resolve it ASAP!
ModeratorApril 26, 2022 at 8:44 pm
@chedwin I wasn’t even thinking of the HDMI cable since the noise is ultimately emanating via the sub amp. It may be mostly mitigated in the AV section (digital), but the analog section is definitely having problems with it. Also makes me wonder if there’s enough EMI to pass through to the analog section, then what is the analog ground referenced to and why doesn’t it squelch the interference? Perhaps the best thing to do is to start measuring between different grounds to see if there are any potential differences (the reason I asked about diagnostic equipment). I would also check inside the PC for misaligned ground screws and check from the case to the ground wire on the power cable, since the case “should” be a good Faraday cage, unless it has a window on the side. Maybe check to see if the GPU heatsink is grounded.
The ferrite beads you ordered should be put on the signal wires close to the output connectors.
That’s enough for now.
MemberApril 27, 2022 at 8:23 am
I suspect the reson the EMI doesnt get pulled down to ground in the analog section is that it may have already been ‘encoded’ for lack of a better term into the audio signal by that point somewhere in the audio processing stage on the AVR, its no longer electrical interference but artifacts and noise in the audio signal itself.
I think you may be right about checking for a ground differential, partically between the PC and the AVR. @sb-woo I would start here in diagnosis and for now focus on the PC and the AVR in your diagnostics. I would guess the noise is already part of the audio signal before it passes through your RCA cables. Keep in mind during your troubleshooting ferrite rings can be used on the HDMI cable too, not just analog audio signals
ModeratorApril 27, 2022 at 9:18 am
@chedwin I don’t think it’s necessarily “encoded” (yes, there’s definitely other terms, but we’ll work with that for now 🙂 ), but more of a situation where the noise is coming over from the PC (obvious source since it’s the only new component in a previously quiet environment) and getting through to the analog stage, effectively getting around the digital buffer and packet inspection. When you think about it, it has to be a harmonic of the fundamental, and with video cards, that’s quite a few orders away to be in the audible range. If it’s that bad, just think how bad the fundamental must be. Would love to see a FFT on the noise.
@sb-woo If you unplug the PC and AVR from the outlet, but keep the HDMI or whatever patch cords you are using plugged in, can you measure the resistance/continuity between the computer and AVR cases? That may help deduce what’s going on.
MemberApril 26, 2022 at 10:25 pm
I was concerned about the clear plastic side, yes it has one to show off lights I guess.
I saw somewhere that a ground shunt (I think it’s called) might help. Where i take a wire from receiver case to comp case may help with the hdmi noise.
It does make a big difference when I put the pc on a different “branch” or basically run extension to another room, so I dont want to return the isolation transformer just yet.
I did not get a chance to work on all this much yet. I was sidetracked with a brake job that took 3x too long. Hope to get to it ASAP.
ModeratorApril 27, 2022 at 8:52 am
Just a clarification – when you run the extension cord to the other branch, you keep the computer in the same room as before and still connect the same way to the AVR? If so and the noise goes away, then there’s the proof of the power connection being the issue. Makes me think of a bad grounding issue in the branch you are using or possibly a mis-wired outlet. In North America, the 3 wires are Black (hot, small blade), White (neutral, large blade), and Green (earth ground, D prong). Back at the breaker panel, Neutral and Ground are tied together, so should be at the same potential – 0. If you measure anything above a few to tens of millivolts AC, then you need to call and discuss your findings with an electrician, giving the backstory on why it is a problem (AV setup issues). A good honest electrician will help you discover further issues / root cause and help decide on a common sense cost effective remedy.
MemberApril 27, 2022 at 6:40 pm
When I run the PC power to another room and keep the hdmi plugged into avr the noise diminishes significantly, but does not go away.
I have finished running the wires and connecting everything with all HT components on same plug (including the PC which is plugged into an isolation transformer) and the result is very similar to what I had when running the PC on extension to another room.
There is still some noise but I think I can (will have to) live with it.
I greatly appreciate all the help, thank you
MemberApril 27, 2022 at 7:23 pm
Also, a couple of things to note. The noise is not volume dependent. It is there even when system is silent and it does not go up or down with the volume. Another thing i noticed.. I have two independent subwoofer outputs on my receiver, those go to a minidsp then they go to the amp if I have one channel of amp output going to one speaker I can hear the noise, even if i disconnect that speakers RCA connection. As long as there is an RCA connected the noise will come through but if I disconnect both the noise goes away.
ModeratorApril 27, 2022 at 7:26 pm
Glad to hear it’s greatly reduced.
Only 2 things I would be curious about:
1. If you again plug the PC directly to the power strip, does the noise increase?
2. If you were to take.a wire and connect the AVR case and PC case together, does that change the noise level?
Really, that’s about all that’s left that can easily be checked. Hope you are finally enjoying your system.
MemberApril 28, 2022 at 8:45 am
Ok so I was wrong. It seems that the isolation transformer isnt doing much of anything for me. One thing that may have helped is setting a low pass @150 on my minidsp, but ultimately getting everything on the same plug did the most. I have not tried the “ground shunt” yet. Im a little scared to do that. A lot of $ spent to watch it all go up in sparks.
ModeratorApril 28, 2022 at 12:27 pm
Instead of just connecting a wire, use your Multi-meter set to continuity and measure between the cases. Theoretically, it should be an extremely low resistance – somewhere between 0 and, say, a few 10’s of ohms. If you are reading a high resistance, then the cases (at least one of them) are not referenced to ground, or each other. At that point you can switch to volts – check both AC and DC – to see if there’s a potential charge between them.
If you are in the “good range“, you should be good to connect the wire between the cases to see if it helps.
MemberApril 29, 2022 at 6:27 am
You may also find there’s no continuity at all (no resistance reading at all, e.g. no number showing up), this would show that one or both of the cases aren’t grounded whatsoever. Though it might be worth adding that bit of information to Charlie’s answer for a point of clarification.
ModeratorApril 29, 2022 at 9:46 am
There is always that possibility, or that the point you are measuring from is not grounded. I’ve seen cases within cases where the inner one is grounded and the outer is not. You just never know what you’ll find.
MemberApril 29, 2022 at 8:18 am
Thanx guys. Hopefully I will get a chance to test that today. Im not familiar with how the word “continuity” is being used here. I will do some quick searching to get a better understanding but for now im going to assume that I need to check resistance (continuity) and voltage DC/AC. Those readings should all be very low but if resistance is zero there might be a problem with ground on one or both because there should be an electronic connection between them being that they are both on the same circuit and connected to each other through the hdmi.
MemberApril 29, 2022 at 12:45 pm
Resistance continuity is the one we meant. The one where the multimeter bleeps when there’s a connection between the two probes.
MemberApril 29, 2022 at 2:35 pm
I may have to buy a digital multimeter for that. Just have an analog at the moment.