Electronics > Beginners
Unwanted digital noise (Not the standard noise floor) from studio monitors
Vildhjarta:
--- Quote from: madires on November 26, 2019, 06:59:02 pm ---Another possible source of the buzzing is a SMPSU powering audio stuff. In that case proper filtering of the audio gear's DC power input helps (common and differential mode noise).
--- End quote ---
https://www.corsair.com/corsairmedia/sys_master/productcontent/corsair-psu-spec-table.pdf
If you search for CX600M. Can you get any clue from the specs?
It seems to me as well that the issue comes from the PSU.
--- Quote from: Bud on November 26, 2019, 07:07:55 pm ---USB power bus is full if crap. Connect an oscilloscope and see it for yourself. If you power your audio from USB you should change to a standalone power supply as the first step. Eliminate that noise source before doing anything else.
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The sound card i use now has its own power supply, and uses a firewire connection to the PC.
magic:
--- Quote from: Vildhjarta on November 26, 2019, 06:32:15 pm ---I tried once more to disconnect my SHDD which is running at 7200rpm, but still the same. :/
--- End quote ---
I presume the mic picked this noise straight from the air, not through the speakers. No point testing such things ;)
--- Quote from: madires on November 26, 2019, 06:59:02 pm ---Another possible source of the buzzing is a SMPSU powering audio stuff. In that case proper filtering of the audio gear's DC power input helps (common and differential mode noise).
--- End quote ---
That audio stuff is powered by a normal transformer. And, tangentially, it is indeed earthed to mains.
https://www.head-fi.org/threads/yamaha-hs7-internals.745768/
By the way, you could do the headphone trick I described. Maybe use some cheap headphones, though nothing bad should happen unless something is terribly wrong with the computer. If you hear the exact same noise that comes from the speakers, we can be quite reasonably sure that it truly is ground bounce that gets into the speakers. I think.
And looking at those internal pictures really makes me curious what would happen if the ground of those speakers is connected to the PC's USB ground but there are no signal connections. You know what, it seems there are 1/4" jacks there in addition to XLR. So plug a jack cable in and plug any sort of USB cable into the PC. Take the USB plug at the other end and touch its metal part to the ground (sleeve) terminal on the audio jack. See if there is noise. BTW, if you touch any other terminal, there will surely be noise, and perhaps somewhat loud.
Vildhjarta:
I tried doing the jack vs USB cable experiment.
And indeed, the noise was there, even worse.
In this audio clip i first only have the tips touching, then i move the mouse, and lastly i drag windows around on my computer.
magic:
Hmm, I expected it to be exactly the same, not louder. Perhaps it's a matter of different resistance of the phono cable vs XLR. You are sure that you touched the ground part rather than some signal input?
https://connector.pinoutguide.com/3_pin_stereo_plug/
If that's confirmed then it seems that your monitors simply don't like ground currents flowing through them, simple as that, and the soundcards have nothing to do with it this time.
And I suspected that this may be the case because it looks like the monitors have plenty of ground loops inside, between the various boards connected with cables and screwed to the metal chassis.
That's :-- for Yahama.
Well, since this is balanced connection, you can disconnect ground in the analog cable, as others suggested. To protect equipment in the unlikely event that one side loses earth connection, a pair of diodes (one in each direction) could be wired between the two grounds where they are cut from each other. Diodes allow the two grounds to differ by a few mV, so the noise will almost certainly be stopped, but if one end becomes floating, they will ensure that this difference stays less than 1V. Maybe it's paranoia, but diodes cost peanuts so why not.
And there is another possible solution, which may also reduce noise pickup by unbalanced soundcard inputs. That is to modify the USB cable such that it takes its ground from the PC's chassis rather than the motherboard. You would cut open the external isolation of the cable, cut the shielding braid, cut the black wire inside the cable and tie its end to some screw on the chassis. USB will probably tolerate this hack, and the soundcard will have undisturbed connection to earth, coming straight from mains through the PC chassis.
EEVblog:
--- Quote from: magic on November 26, 2019, 09:41:27 pm ---If that's confirmed then it seems that your monitors simply don't like ground currents flowing through them, simple as that, and the soundcards have nothing to do with it this time.
And I suspected that this may be the case because it looks like the monitors have plenty of ground loops inside, between the various boards connected with cables and screwed to the metal chassis.
That's :-- for Yahama.
--- End quote ---
Googling shows similar reports from others, so yeah, maybe unforgiving Yamaha's.
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