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Old 28th June 2013, 01:08 AM   #31
diyAudio Member
 
Join Date: Nov 2012
Location: Melbourne
Quote:
Originally Posted by Kev06 View Post
Another update for anyone finding this thread: I got the chance to try a digital coaxial cable tonight - for me at least it works equally well as the optical one in avoiding the PC noises.

So as theres still a ground connection to the same place, in my case it seems a little less likely to have been ground loop issues to/with the power amp; combined with the amp having no ground connection either I'd be inclined to suspect something else.

It doesn't mean that there weren't electromagnetic effects on the cable, since although this one is also electrical it is (a) digital so better at rejecting subtle interference and (b) a different cable so may have better shielding. It probably doesn't dismiss electrical or electromagnetic interference affecting the sound card either, since by staying digital until later down the chain I've still bypassed the card's analogue output stage, which would have been more affected by such things in and around the PC.

Cheers
kev


Hi Kev06,

In my specific case, it turned out, that the culprit was the PC power supply (Thermaltake TT-450NLINH-1, PN W0276). The poor quality PSU has been replaced with Seasonic S12II-520W 80+Bronze PSU. Now, the noise level dropped by -15dB.

Looks like there are other major areas you need to look into.

PSU – compare for ripple and noise
Roundup: 12 Gaming Power Supplies Compared - New Tests: Ripple And Noise


BIOS.
Possibly disable C1E and E1ST ("speedstep"). Also Set PCI Latency Timer to
higher value.

Windows OS.
Enhanced Intel SpeedStep® Technology - How To Document

http://www.native-instruments.com/knowledge/questions/847/Windows+7+Tuning+Tips+\
for+audio+processing



Gain structure.
The sound level coming out of your sound card, should be set to maximum, therefore you will utilize the SNR of your sound card to the full range. This may overdrive your amplifier input, so if this is the case, you my need to insert a resistive attenuator between the sound cards output and amplifier input.

Ground loops.
You have already discarded those.


Best Regards,
Bohdan
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Old 28th June 2013, 07:45 AM   #32
Kev06 is offline Kev06  England
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Join Date: Oct 2006
Location: Derby, UK
Thanks for the thoughts, I'll certainly look at the BIOS and windows tweaks you suggested, much to learn!

TBH I'd feel cautious about swapping PC hardware out by this stage though, because it seems the cause of the PC noises has so many possibilities (PSU, graphics card, sound card etc) that it could get quite expensive trying to eliminate it. An external DAC would cost too, of course, but I now know that it absolutely solves the problem (in my case anyway), so would be a much more certain return for my money.

I've also got on surprisingly well with the borrowed dacmagic plus; I've been using it like a pre-amp and its got some other benefits (in addition to solving the PC noise), such as selecting different digital sources (like my TV) and offering a digital mute/volume control. Not sure how that would compare in sound quality with the Jriver's software volume control, but I'll be needing 'some' form of volume adjustment when I swap to active speakers.

Cheers
kev
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Old 28th June 2013, 08:48 AM   #33
phofman is offline phofman  Czech Republic
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Location: Pilsen
Quote:
Originally Posted by Kev06 View Post
a digital coaxial cable tonight - for me at least it works equally well as the optical one in avoiding the PC noises.
Looking at xonar pics I cannot locate the SPDIF isolation (pulse) transformer. Could it be integrated into the cinch female connector which is larger than the other two on the board? If it is the case, the SPDIF link is galvanically isolated just like the toslink one.
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Old 28th June 2013, 12:43 PM   #34
Kev06 is offline Kev06  England
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Join Date: Oct 2006
Location: Derby, UK
TBH I'm not sure; I bought the card more on reviews than any great understanding of its topography. Certainly the digital connector is one of those combined RCA/optical jobs and it would seem reasonable (to me) to isolate at or in the connector. The other two RCAa are for the analogue out.

Cheers
Kev
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Old 28th June 2013, 01:32 PM   #35
phofman is offline phofman  Czech Republic
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Join Date: Apr 2005
Location: Pilsen
Ok, I did not know the cinch is the combined coax-toslink type. That explains the extra size. IMO the cinch body contains no pulse transformer, just the toslink transmitter.
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Old 30th June 2013, 03:15 PM   #36
lsheng is offline lsheng  United States
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Join Date: Feb 2010
I got very obvious noise through computer earphone port before on a DIY computer. I can hear hard-drive activities or the computing process changes through earphone, so I figured that the noise related to the current computer consuming, it must be ground related inside the computer. I found the earphone port has two ground, one thought earphone cable, one through chassis, I cut the ground connection through chassis, it became much quieter. I can no longer hear any heard drive or process changing activities through earphone.
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Old 30th June 2013, 05:57 PM   #37
phofman is offline phofman  Czech Republic
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Good catch, thanks for sharing
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Old 1st July 2013, 09:42 AM   #38
marce is online now marce  United Kingdom
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Location: Blackburn, Lancs
Could you sketch out the earphones port gnd connections, please.
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Old 2nd July 2013, 07:22 PM   #39
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Join Date: Nov 2004
Location: Germany
Quote:
Originally Posted by lsheng View Post
I got very obvious noise through computer earphone port before on a DIY computer. I can hear hard-drive activities or the computing process changes through earphone, so I figured that the noise related to the current computer consuming, it must be ground related inside the computer. I found the earphone port has two ground, one thought earphone cable, one through chassis, I cut the ground connection through chassis, it became much quieter. I can no longer hear any heard drive or process changing activities through earphone.
Yeah, some front panels are messed up like that right from the factory, unfortunately. Gives a first-rate ground loop, as you found. Disconnect the extra grounding through the case so that only the audio ground from the ribbon cable remains connected to headphone jack ground, and the noises miraculously disappear the way they did here.

Note that there are some differences between AC97 and HDA front panels. HDA shares a single ground return for both headphone out and mic in, which must be kept separate from case ground at the front panel. With the front audio cable unplugged at the mo/bo there must not be any continuity from headphone ground to case - should be easy to check. If there is a connection, you have to look at the panel and devise a way of separating things. If there is a big ground plane or anything, it would be nice if most of it remained connected to case ground for EMI reasons.
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