High pitched hiss from PC

Hi guys,

I have the following setup:

PC ---HDMI---> Denon 4311CI (as preamp) ----RCA---> W4S MC3x500 (amp) ----> speakers

(As well as some speakers being amplified by the receiver, but those aren't relevant here)

While the amp is on, I get a high pitched hiss from the speakers. The volume I put the preamp at is irrelevant--it can be turned off and the noise is still there.

I can unplug the preamp and the noise is still there.

If I unplug the HDMI cable from the PC, the noise goes away.

If I touch the front of the HDMI cable to the back of the preamp (just metal to metal, not near the HDMI socket), the noise returns.


The HDMI out on my PC is running from an Nvidia GTX 460.



Does anyone have any advice on what I could do to reduce or eliminate this noise?
I can (barely) hear it from my listening position, but it is still annoying.


Thanks!

Anyone? If no one here has any ideas, any suggestions on where else I should post?

Thanks!

Thanks for the suggestions, I'll give them a shot and see what happens.


Here is a more detailed layout of what is going on:


Circuit 1 (20A):
- the amp for the 3 front speakers

- a UPS powering the below (maybe run through a power strip, I forget... can check. If so the power strip may be handling the things I don't care about having on the UPS)
- PC
- 30" monitor
- printer
- FIOS router
- MoCA adapter for TIVO (cables in to the router via ethernet & coax)
- a set of speakers on the PC side of the room (logitech something or other, 5.1)

Circuit 2 (20A):
- HDTV
- Denon 4311CI
- 2 Rhythmik F15HP subwoofers
- PS3
- XBOX 360
- FIOS set top box


I tried plugging the Denon into circuit 1, but that didn't help. (I figured it wouldn't, since the noise came through even when the Denon was unplugged)

Also note that the noise comes through just from touching the PC cable to the receiver (in a spot that conducts)--it doesn't have to be plugged in to an HDMI slot.


Will try isolating the PC to see if its something external, or something in the PC itself.

Ok, I did some testing.

The high pitched whine is from when my printer's USB cable is in the PC, and the printer is on.

However, even with the printer disconnected, there is some variable noise/static that isn't there when the PC isn't connected. (When PC is disconnected, there is hiss/static still, but quieter and not variable)
Moving the PC power plug didn't help that I could tell.

I'll play around with it more later, but for now, I'm happy enough with the printer powered off.

Argh, nevermind, its still here.

The high pitched sound went away for a short time when I unplugged the printer, but is now back. I tried disconnecting everything from the PC, its still there.

With the PC unplugged, I still have a minorly annoying sound, but not nearly as bad as when the PC is in. And it changes when I open really intensive stuff on my PC--furmark (a GPU load testing tool) causes a very fast, relatively quiet (but certainly noticable) thumping noise (sort of... its relatively low pitch, like a rurring sound) to come from my speakers (either as the GPUs suck up more juice, or as their fans go nuts. I think the former.)

Loading the CPU also causes noise changes: it completely hushes the sounds down to as if the PC were unplugged. E.g., running intel burn test with all 4 cores active shuts off the noise.

And scrolling my bluetooth mouse's scrollwheel while viewing a webpage causes some sounds too (static), but only on certain webpages. Others I can't hear it, or I barely hear it. Sounds almost like when you are right next to a computer and you load the CPU--that kind of whirring static sound.

Its hard to swap things around in the circuits for more extensive tests because circuit 1 only has 1 outlet right by the PC, while circuit 2 is every other outlet in the basement.

I guess the next thing to try is having everything on the same circuit and seeing if the noise is different?

EDIT: Ok, moved PC & Amp to circuit 2 with the receiver. A couple differences:
- the high pitched whine is a little worse, I think. But only when the PC is actively being displayed via the receiver--otherwise its better than before. (This doesn't help me though, as the vast majority of my usage is via PC). With the PC & Amp on circuit 1, the noise was the same regardless of whether the PC was displayed via the receiver or not. (EDIT: turns out it was the TV--when the TV is actively displaying anything I got high pitched ringing)

- when I fire up the GPUs via furmark, the thumping/rurring noise is still there, but much quieter.

- .firing up the CPUs has no effect on the noise with everything on the same circuit

for now I'm back to the original setup, and just suffering through it... I don't know what to try next...
It seems odd to me that the pre-amp output volume has no effect on the sound. I mean if I crank the volume way way up, I'll get noticable hiss, but the normal hiss, not this annoying high pitched weird variable stuff.


EDIT: So frustrating... if I close all the open programs on my PC, the noise goes way down. If I have chrome or media monkey open, variable high pitched whine... I'm baffled
Edited by Morik - 1/14/13 at 10:30pm

Couple more things:

- when I am near my computer (its on the other side of the room), I can hear variable high pitched noises similar to what ends up coming through the speakers. It may be one of the fans, not sure. (Though that can't be the whole story, given that the noise goes away when no significant programs are open, comes when I open most programs, but goes away if I fully load the CPUs... unless its the CPU fan)

- I am currently connecting from my receiver to my amp via RCA cables. My receiver only has RCA outputs, but if I got an rca->xlr cable and used the XLR inputs on my amp, could that help? EDIT: I found a couple rca->xlr I had lying around that I had forgotten about. It helps a little, but can still hear the whine from my listening position. Loading my GPUs doesn't sound so crappy anymore though (need to get close to the speaker to hear the weird noise they make, instead of being clearly audible from the listening position). Still not what I'd like to get it to though.

- I could try a ground loop isolator for RCA, but I have read that they can noticeably degrade the sound
Edited by Morik - 1/14/13 at 11:50pm

And yet, there is a definitely noticeable difference... Not in normal use (where i think there is a diff., but could be in my head), but the loaded gpu sound is MUCH softer with the rca->xlr cables.

Maybe the higher input impedence on the balanced input path in my amp is responsible?

My PSU is a seasonic x-750
The MB is an Asus p6x58d-e


I am wondering about ground loop isolation again... If I cross my mains at 60 or 80, and run audyssey, would I have issues? I've read that its the low frequencies that suffer with a gli.

They don't seem expensive...

Would balanced connections fix this issue?

Of so, a more expensive option would be to move to a preamp with balanced outputs... I'd upgrade my amp to 7 channels (wyred 4 sound 3 channel right now, they offer upgrade to add more channels at whatever he price diff is between the units). I'd probably go with a pre with audyssey xt32 (e.g, integra 80.3).

Alternatively, if there is a good DAC with xt32, I could use that and connect to any preamp with balanced outs.


I'd rather stay away from trying to fix this on the PC end: I tend to replace my computer every 2-3 years, and if I have to go through purchasing and trying multiple MBs and PSUs, that would be annoying. I will look for a bios option to turn off any sort of "quiet" CPU mode when idle.

Hmm, I'll give that a shot.

Another note: I never had an issue when using speakers only powered by the denon. Don't know why...

Oops, I was thinking of another amp I had been considering. Turns out this one has the same impedance for both balanced & unbalanced.

I haven't convinced myself of anything... I just don't know much about eliminating noise.

I take it then that the possible solutions I listed in post 14 would only solve a ground loop issue, and not some other issue? (Such as noise from the PC PSU/MB/etc? Those aren't ground loop issues?)

I already stripped my PC down to:
- my 30" monitor (which I powered off, but could bother disconnecting if I do this test again)
- the power cord, which I had going into a power strip plugged into an outlet on circuit 2. (can't reach any outlet for circuit 2 without a strip)
- the mini-HDMI to HDMI cable from my video card to the receiver

As mentioned, the noise was still there. In fact, with the PC, preamp, and amp on the same circuit, the noise was much worse. (The HDTV on the same power strip as the amp was causing noise, but this goes away when the amp is on a different circuit... didn't try the amp in another outlet of the same circuit)


I don't see how this could be an external component issue (outside of the PC), given that the noise changes (significantly) as things inside the PC change--when I load the CPU, load the GPU, unload the CPU, mildly load the CPU, etc.


What I asked (perhaps my intent wasn't clear) is: are there any reasonable solutions that don't involve changing something about the PC? (E.g., would a balanced to balanced pre-amp -> amp connection eliminate this noise? What about a ground loop isolator between the pre & the amp? Etc)

As mentioned above, I'd rather avoid changing the PC--doing so would require:
- ordering a new MB, installing it (which is a PITA), and then seeing if it works...
- ordering a new PSU, installing it (which is a PITA, but not nearly as much as the motherboard), and then seeing if it works.
- if one of the above works, I'm good until my next PC... at which point I order the parts, put it together, and if things aren't ok, spend more money and time installing different parts to see if they work instead.


So, any thoughts on whether a GLI or a balanced->balanced connection (i.e., new preamp) would eliminate (well, massively reduce) this noise?
I suppose I could just give a GLI a shot, as they aren't expensive...
Edited by Morik - 1/15/13 at 1:12pm

Kapone--as mentioned earlier in the thread, if I disconnect the PC's HDMI cable from my receiver, the noise goes away (with the receiver on circuit 2, amp on circuit 1... there is still mild hiss, but none of the variable noise & high pitched whine that come through when the PC is plugged in to the receiver).

With amp & receiver on the same circuit (in same power strip with the HDTV), the HDTV causes noise even with the PC disconnected, but does not do so when the amp is on a separate circuit.

I have tried disconnecting everything from the amp (aside from the speaker wires and power cable, of course), and there is no hiss. (Well, very very faint)
Its no different when I put the preamp back into the amp.

I have various other things connected to the amp via the preamp, and its all fine without the PC connected.

I'm not at home right now, but I do know the MB standoffs & screws are metal, and though I haven't messed with my PSU in the ~3 years since I installed it, my recollection is that it is directly touching the chassis. I do know that metal screws passing through the back of the chassis help hold the PSU in place.