CPU "noise" amplified through speakers on AMD HTPC Builld

Discussion in 'Home Entertainment Computers' started by jkharmer, Jun 17, 2015.

  1. jkharmer

    jkharmer
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    Hi all,

    I am pulling my hair out on this one!

    I have built an AMD based system to run Plex and I am over the moon with how it has gone with one exception. My silent PC is in fact rather noisy! There is a sound from the CPU (a digital artefact sort of high pitched thing - ramps up and down depending on what the CPU is doing) which can be heard if you take the top off the HTPC and stick your ear next to it. You might wonder why on earth you would do that, well the problem I have is that this noise is then replicated by every one of my tweeters on my 5 speakers. Very annoying indeed when I have KK Quattros which have 4 each = 20 tweeters! It can be heard clearly from where I sit.

    I am using a Nakamichi amp and wonder whether the noise from the CPU is normal, and my system is just super sensitive for whatever reason? There are a number of things I guess I could do:

    1. Replace the motherboard
    2. Replace the CPU
    3. Both 1 and 2 (swap AMD for Intel, or keep AMD)
    4. Replace the Amp
    5. Replace the speakers

    No 5 is not an option, 4 is not really an option (last resort sort of thing) so left to 1, 2 or 3.

    Has anyone else come across this? I am running the HTPC into a Nakamichi Processor via an HDMI cable and then into a Nakamichi Power Amp.

    Thanks, James
     
  2. Rambles

    Rambles
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    I had something similar a few years back and I think it was a 'ground loop hum' from what I remember I was able to get a filter from ebay that connected into the system via an audio cable and solved the problem. Might be worth a google?

    Also, I would look at the connection between your PC and your amp. Can you try a different HDMI cable, or a different connection to try and eliminate it?
     
  3. jkharmer

    jkharmer
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    Thanks for the reply.

    I would not describe it as a hum to be honest it is most definitely coming from the cpu itself and then transferring itself into the rest of the system down the hdmi cable. I suppose I could try an optical cable but not sure what that would tell me.

    Any other ideas guys?

    James
     
  4. Rambles

    Rambles
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    You could try an optical cable, if you don't get the noise, then that tells you that using the optical connection instead of HDMI is one option.

    Have you tried a different HDMI input on the processor / amp, or a different HDMI cable?
     
  5. Qactuar

    Qactuar
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    I've had this so many times I wouldn't know where to start or finish.

    I get it with HDD activity on some builds, but usually, a good quality DAC sorts it out. Optical should also do the trick where possible.
     
  6. andy1249

    andy1249
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    HDMI just transmits the data down the line and it will not contain any electronic noise data, the only way for that to travel would be down the shield/ground lines.

    Even if that is happening , all HDMI receivers re clock the data, so regardless of whats happening upstream the nakamichi is almost certainly at fault here as for the problem to be happening, the nakamichi must be picking up noise and modulating it on to its analog outs, something caused only by poor circuit design or a fault!
     
  7. Qactuar

    Qactuar
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    For clarity, my issues were only ever RCA/3.5mm analogue out!
     
  8. jkharmer

    jkharmer
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    Thanks guys, am I right in saying an optical cable will not transmit HD audio, though? Thanks for the update Andy, I could really do with picking up an AV amp to try instead then just to see whether the noise is picked up through that. If that is fine, it points to the Nakamichi combo, whether it is the processor or power amp, who knows!
     
  9. andy1249

    andy1249
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    You are correct, optical wont carry HD audio.

    The best first step in troubleshooting this is to connect to another receiver if possible, that will rule out the HTPC if the noise disappears.

    Then its a question of checking the ground connections on the Nakamichi, for this to be happening there must be a poor or bad shield/ground connection somewhere.
     
  10. noiseboy72

    noiseboy72
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    Try a different PSU, as actually, this is the culprit. It is dumping noise onto the earth line and as your PC does not have an isolated audio ground path, you hear it as noise. I believe it is caller Functional Earth Noise. Corsair AX range get good reviews in this respect.

    In stereo analogue systems, a hum loop isolator is all you need, as it decouples the ground, but this is not the solution in your case.
     
  11. jkharmer

    jkharmer
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    Noiseboy72, I am currently using a Streacom PicoPSU, so for Corsair range is pretty overkill I think looking online. I still think that it is amp related and need to get my hands on another amp some how.

    Thanks, James
     
  12. noiseboy72

    noiseboy72
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    My money is still on the PSU. for that level of power requirement, you would be better off with a linear supply, not switched mode. I would imagine that the PSU is not coping terribly well and is modulating with higher periods of demand.
     
  13. jkharmer

    jkharmer
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    Could you recommend a different one then that you think would be more up to the job?
     
  14. noiseboy72

    noiseboy72
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    As I said, a high spec Corsair or a linear PSU like these: http://www.hd-plex.com/HDPLEX-Fanless-Linear-Power-Supply-for-PC-Audio-and-CE-device.html

    You could also try playing with the earthing, maybe taking an earth cable from the case of the PC to a radiator, to improve the ground path. Lifting the earth on the amp using one of those Chinese 1 size fits all socket adapters might also work, but PLEASE DO NOT DO THIS, as it could be very dangerous.
     
  15. andy1249

    andy1249
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    For the record, I'm using a streacom pico PSU with a streacom silent case, no fans anywhere, with an intel motherboard and using intel onboard HDMI graphics connected directly to an AV receiver.

    I have no noise problems and the Streacom PSU,s are more than adequate for the Job.
    Assuming the OP has no heavy current draw items such as standalone graphics cards or a high amount of hard drives, then changing the PSU is unlikely to make any difference to this issue.
     
  16. jkharmer

    jkharmer
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    Hi Andy,

    All I have in the FC8 Alpha case is a bluray drive, 120Gb SSD and a FLIRC adapter.

    Are you saying that if you stick your head into the case, you can't hear anything coming from the CPU at all? Or is there a bit of noise, but it is not being transferred through to your speakers?

    Noiseboy, I have sent an email to HDPlex to see what they say.

    James
     
  17. andy1249

    andy1249
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    @jkharmer
    I have no noise in my PC because there are no fans at all.
    Here is a picture of the chassis , note the cooler pipes that transfer the heat to the chassis.
    FC5 OD Fanless Chassis | Streacom
    My components , other than the motherboard , CPU and Memory , are an SSD and a BD drive. So not to different to yours.
    The unit is powered by the Streacom Pico PSU , specifically designed for their cases.

    Are you saying that your CPU makes an audible noise , even though there is no fan ?

    Either way , I doubt very much that the streacom psu is at fault here , these cases and their PSU's are pretty robust.
     
  18. andy1249

    andy1249
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  19. jkharmer

    jkharmer
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    I'll try that overspeed protection thing, but yes I am effectively saying that the CPU makes a noise despite no fans. When I load Plex up, it goes bonkers! and the sound from the CPU (only very quiet - you have to put your head into the case to hear it) transfers through the amp through to the tweeters on my speaker!
     
  20. Navvie

    Navvie
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    I had something similar with an old PC. Headphones/speakers would pick up "noise" from the CPU - honestly, a high pitch whine that would change tone depending on CPU load/frequency. Gigabyte X48 motherboard and Intel Q6600 CPU.

    Turned out I was running the case audio lead to the motherboard header near some noisy tracks on the motherboard. Rerouted one day during a clean out and never heard it again.
     
  21. andy1249

    andy1249
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    Im using an intel i5 cpu on a gigabyte motherboard, no noise whatsoever!
    I have checked.

    The issue your seeing seems to be well documented and is down to poor components on the motherboard, most replace under warranty for this issue it seems, but a lot report the replacements were no better!
    Nearly all report that the problem goes away once the overspeed feature is turned off, so the circuitry and regulators involved with this feature must be the source!
     
    Last edited: Jun 22, 2015
  22. jkharmer

    jkharmer
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    Thanks guys, Navvie there are no audio leads in my build from what I can see. I'll look at the over speed feature first, and then maybe see if I can return the motherboard for a new one. Can't see it being the CPU itself!
     
  23. Rock Danger

    Rock Danger
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    I'm just going to necro bump this as I have a similar problem and I know @andy1249 probably has a good idea what the issue could be.

    I have it mostly under control now but the noise is still there, I'll try and explain briefly what I've done.

    I added 3 Lyngdorf power amps recently and along with my Anthem A5 - this is a total of 11ch of amplification running back to an Anthem MRX720.

    There's always noise on a line to some degree, for most it's the dreaded 50hz hum from grond loops but mine is more of a high pitched whine that modulates as in it doesnt change pitch or volume but will go solid then stop and start etc.. like morse but nowhere near as bad.

    I tracked this down to the HDMI cable going from the HTPC to the AVR, the klinker is that this only kicks off when you play a movie, not when it's idle on the desktop.

    So swapping the HDMI cable killed off most of it, it would only be audible a 2ft now it comes out of all the speakers (of which I have many)

    The first thing I did was put the HTPC on it's own socket on the same ring, then checked the house switching various things off and on with no joy. Then I got the laptop out and connected it to the AVR via the same cable and everything was fine, I then connected the laptop via it's psu and still no issues.

    Annoying right?

    The only thing i had to do was move my Anthem power amp closer to the pc tower and put the Lyngdorf amps on the other side due to speaker cable stretchage. I imagine that If I used the HTPC as a server and plugged something like an Nvida shield in as a streamer it would, like the laptop be silent.

    That would be a £150 fix but I'm happy to listen to suggestions. The house mains is pretty damn good considering the tangled mess behind everything.

    I'm certainly no newb to this having had to deal with many guitar amps, guitars, PA systems, wireless radio packs etc - but this is a different interference and I'm just not as up on it as some of you guys.

    Hopefully maybe a ferrite core on something here and there will shut it up?...

    Cheers.

    R
     
  24. andy1249

    andy1249
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    What motherboard do you have in the HTPC.?
    Is the HDMI port on the motherboard?
    Is the processor an intel and does it have intel integrated graphics?
     
  25. Rock Danger

    Rock Danger
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    It's a gigabyte board rocking an i3 from about 5 years ago, the onboard is disabled and it's using a radeon 6 series fan-less for gpu duites. I was just doing some room correction and noticed it started kicking off again as i was wirelessly transferring data from the laptop to the desktop.

    It might be a hard drive.. pretty sure i turned off the router and modem - maybe I didn't unplug them, the laptops only drive is also solid state.

    I've never noticed the HTPC cause problems before. The power amp which is now close to it runs the atmos channels and not the bed layer, tho that probaly is irrelevant.

    The virgin hub is behind the htpc and the router is on top of it (I know, I'm getting a shelf cut to move this) so with the pulse code noise it might be wireless / hdd related.

    Incidentally I had a screaming noise once before that was actually coming out of the superhub itself every time the led blinked, no speakers connected or anything, noise coming out of the superhub! had it swapped out.
     
  26. andy1249

    andy1249
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    Im basing this on you saying it kicks in when playing a movie, i.e. Processor under some load.

    Go into the Bios menu, look for " Advanced CPU core features" , look for " Intel Turbo Boost technology"
    If your board has this then it will be on auto by default.
    Disable this.

    Re boot.
    Play a movie.

    Does the noise change , specifically , does it stop or does it become constant?

    If so, its the usual problem, the caps/ circuitry controlling this feature are failing and pumping noise onto the line from the PWM control loop.
     
  27. Rock Danger

    Rock Danger
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    I don't think it's that advanced of a bios but I'll have a look. I know the noise will travel across all the AVR's input's so you'll hear it on SKY as well. It's certainly and under load issue as it only kicks in when the movie fires up and when transferring data across the network.

    The noise stops and starts but it'll be a long dash before a dot (to use a morse code analogy) which is why I went straight for the router / modem and active switch since they are blinky data transmitters. It doesn't change in pitch or volume and is a separate noise from what we all get if we jam our head up to the tweeters.

    Thanks for your thoughts Andy, keep em coming. I'll check the bios.
     
  28. andy1249

    andy1249
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    Yup, this is typical of the PWM bursts used to control the processor and ramp the fan speed on turboboost.
    Its not supposed to leak out obviously, but failing, underspecced caps cause it too.

    If you can give me the motherboard model number I can be more specific, Im going by the menus on my own gigabyte motherboard which is 2013, also 3 years old apprx.
     
  29. Rock Danger

    Rock Danger
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    Yeah lemme go stick my head in the case.. it's a good bit older than yours, but surprisingly well featured.. didn't see an obvious turbo boost on / off.

    H55M-S2H

    GIGABYTE - Motherboard - Socket 1156 - GA-H55M-S2H (rev. 1.0)
     
  30. andy1249

    andy1249
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    Your board doesnt have turbo boost.
    It does have a variable fan control based on temps though, which can be the source of the same PWM noise.

    Its under PC Health Status.

    CPU smart fan control. Enabled by default.
    Set this to disabled.
    The CPU fan will then run at full speed all the time.

    Try this.

    If the problem is PWM noise, it will either stop , or become constant.
    If nothing changes, I,m on the wrong track here.
     

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