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Years ago I bought a computer case because my other one was getting too small for the components. After moving all of the parts and booting up, one of the first things I noticed was that my guitar would very noticeably pick up interference (typical magnetic hard drive clicking sounds and so on), increasing in intensity and volume as I moved my guitar closer to the case. This never happened with the old case.

The interference is audible both through the speaker of the amp and through headphones connected to the amp. It occurs when the pickup is in the 1st, 3rd, and 5th position (cheapo knockoff fender electric guitar so 3x single coil pickups).

One noteworthy thing I suppose is that this new case material was labeled as "SECC" material, the old case simply listed "Steel", if that makes any difference.

The main issue is described above, below are just some more details.

This is a pretty big nuisance as I can't record anything without constant hissing unless I have my computer completely powered off.

I am looking to buy yet another case (I've been sitting on this one for a few years now) and want to understand whether it's a problem with the case material or if there is an alternative cause.

No new hardware was added initially when I switched cases so it could not have been a new component. In my unprofessional opinion I am leaning towards blaming the case material for the issue... honestly the material feels extremely flimsy, and bends easily compared to the rigidity of my old case.

I'm sorry if this is the wrong place to be asking such a question since it's a bit computer heavy however it involves concepts that aren't generally discussed on conventional computer boards. Thanks if you've read this far and I hope there's a concrete explanation behind the phenomena I'm facing.

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  • \$\begingroup\$ This just means that the electronics in your guitar and/or your computer are poorly designed. Some manufacturer somewhere cheated with their EMC approval. Quite common. The case just happened to help hiding the poor design of whatever part is causing this. Seems likely the guitar is the culprit but that's just speculation. \$\endgroup\$
    – Lundin
    Sep 5, 2016 at 6:47
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    \$\begingroup\$ Check the grounding of the case. Normally you would establish case grounding via the case PSU. Check whether the screws and the construction of the case allow for the whole case to be grounded by the PSU case. \$\endgroup\$
    – Jonas Schäfer
    Sep 5, 2016 at 7:40
  • \$\begingroup\$ Check to make sure that the case fits snugly together -- it sounds like some sort of gap is creating a slot antenna, oops! \$\endgroup\$
    – ThreePhaseEel
    Sep 5, 2016 at 11:52
  • \$\begingroup\$ @Lundin -- computer cases are part of the EMI-control equation for PCs (it wouldn't surprise me if a cheapo case can contribute to problems) \$\endgroup\$
    – ThreePhaseEel
    Sep 5, 2016 at 11:53
  • \$\begingroup\$ SECC = 'Steel, electrogalvanized, cold-rolled, coil' so it is also steel, probably just thinner than the old one. Thicker steel sheets come flat rather than coiled, but I don't know at what thickness a case manufacturer would change from one to the other. \$\endgroup\$
    – Pete Kirkham
    Sep 5, 2016 at 12:34

2 Answers 2

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Any type or thickness of steel will form a "Faraday Cage" shield to keep digital hash from escaping from the computer case.

HOWEVER. many cases have large holes in them for "windows" where you can look through and see the hardware (and the internal decorative lighting). I have no idea why this fascinates people, but who knows?

They also have large holes in the front for places where you can put extra floppy or optical drives, little panels with I/O connectors, etc. etc. The front panels are made of plastic which offers ZERO shielding.

You could experiment with some aluminum foil from the kitchen and just cover the entire front of the case to see if that might be the interference leakage path. Be sure to connect the foil to the case ground at some point. An ungrounded shield is worse than no shield at all because it becomes a re-radiating transmitting antenna for the interference!

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For all situations of ElectroMagnetic Compatibility (EMC) there are 3 paths to follow;

  • Conducted ( via ground path of power supply , MOBO, Case, Cable, which then can also radiate to guitar signal)
  • Radiated ( capacitive or inductive coupling of differential and common mode electric or magnetic fields into a differential mode signal.

Then come analysis to determine root cause and easiest solution; the noise source or over-sensitive destination

I understand in your situation you have 3 changed components;

  • CASE, PSU, MOBO,

Reported interference could be expanded on..

  • Computer noise increases in proximity of guitar to PC case.
  • hiss noise on guitar recorder external to PC until PC is powered off.

  • The video display contents may but should not affect noise content from video cable The HDD does not radiate or conduct significant noise. But cables might. Generic solutions;

    1. Grounding
      • check power ground to PC case and Video monitor
    2. Shielding
      • check case for loose contact on overlapped edges of side panel. Gap in PC side-panel should be bridged by design of mating contacts on case, edge slot overlap.
    3. Filtering
    4. Isolation
    5. Balancing

Guitars are often unbalanced with respect to impedance to stray CM noise and is improved with large balun choke clamped around cable or multiple turns in torroidal loop.

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