why do I hear my computer through my Crack (but nothing else)

[vafan13]

Trying to figure out why this is.  Not sure if it's bad grounding on the crack or the Crack (w/Speedball and DT880/600s) just being more sensitive. 

With my Crack connected to my phone or something otherwise not my computer, it is dead silent with nothing playing, even at full volume.   So I know the crack sans computer is fine.  Likewise, my headphones being connected directly to the sound card or being connected to my old Millet Hybrid and then to the sound card is dead silent, again, even at full volume. .  However, with the crack connected to my computer, I can hear the cpu/gfx card/hdd/mouse through it.  It was quite noticeable, but I've been able to reduce it significantly by moving some plugs around and introducing a couple power conditioners.  It's still there, though, and it's quite clear at max volume.


Why does my Crack have such an issue with picking up computer "noise" but either direct to soundcard or sound card -> millet hybrid is completely silent, and is there anything more I can do about it?

If it matters, there is a hum in the crack with no inputs connected, but it requires high volume to notice.  And I have the ground from terminal 4 attached to 22L instead of 14U, because I was tired when I did that part and didn't notice the revision. I did check the ground path and everything looked good.

Finally, if anyone wants to hear exactly what I'm hearing, I can email (or give a link to an upload) of a short recording.

[Paul Joppa]

The computer's audio ground is noisy relative to the power line safety ground. When you connect it to something that is safety grounded (the Crack) that noise current runs through the interconnect ground to safety ground, adding the noise to the audio signal. Direct to headphones is no problem because the headphones are not grounded separately.

This is called a "ground loop" although technically the noise is usually induced by a power supply, rather than being picked up by magnetic induction.

Of course, I may be wrong - noises are often very difficult to track down. But the above is consistent with your observations, and quite common, so I think it's a good guess.

[grausch]

I had a similar issue as you described - Crack was dead quiet using the headphone out of my iPhone, but the Crack always had the hard drive noise on it. In my case it was resolved by using a USB 3.0 port rather than USB 2.0. A powered USB hub made no difference, but the USB 3.0 port did the trick.

Based on your posts, I assume you have a PCI sound card. Can't recall where I read this, and do not know if it solved the problem, but I had seen people recommend using different PCI slots to try and reduce this type of noise. Although, if it is power-supply induced as PJ stated, then I am not sure if it can be solved by using different PCI slots.

[Paul Birkeland]

Acquiring a soundcard with a toslink output, then a DAC that will accept a toslink connection will completely remove this noise.  SPDIF might also accomplish this, but you need a transformer isolated SPDIF input on the DAC (which isn't an inexpensive feature).

-PB