Electronics > Projects, Designs, and Technical Stuff
Silly tread
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tggzzz:

--- Quote from: 001 on November 25, 2018, 02:28:16 pm ---My sons friend has marvelous problem with his electric guitar
It is some "computer"  whistling and audible "noise" at about 1kHz in the amplifier. And he says what he play at datacenter basement  :palm:
How to eliminate EM problem?

--- End quote ---

Insufficient information to diagnose.

Start with the techniques in  https://centralindianaaes.files.wordpress.com/2012/09/indy-aes-2012-seminar-w-notes-v1-0.pdf
Buriedcode:
What guitar?  Single coils pickup pretty much everything, which is why humbuckers were invented - the clue is in the name :D  These use two coils wired out of phase, so common mode noise (that is noise that imparts on both coils) is cancelled out.  It isn't perfect but often much quieter - and that is the reason we have high gain rock/metal that simply isn't possible with single coils.   The "hum" is often mains (50/60Hz) but it doesn't' have to be, it can be any EMI of sufficiently low frequency.

There are other "noiseless" pickups that can be single coil size or use shielding to reduce interference (lace sensors) but none of them completely eliminate noise pickup.

Could also be the (lack of) shielding in the guitar itself - as mentioned, broken grounding of the hardware can cause.

Moving on to the next bit - the cable.  Cables break, most often at the connectors.  Although given guitar cables are pretty simple single ended connections, if there is a break - you probably won't get any guitar signal at all.  With that said I have had some pickup loud hum due to a dodgy connection at one end. 

Then there's the amp.  Again, ground faults, poor shielding, even broken pots can cause loud hum.

Even if you have a humbucker equipped guitar, a decent cable, and a quiet amp, you can still pickup noise from things like PC monitors.  Especially if your friends son plays with high gain.  Tell him to turn the gain down and volume up - even the heaviest guitar tone is often at a much lower gain than you think, just multitracked several times :)
001:

--- Quote from: Buriedcode on November 25, 2018, 09:48:36 pm --- --

--- End quote ---

Huh, I was  playing bass in early 70th so it is not silly pickups/wires problem
It is sort of some RF modulation or other process in the amp
But amp is ok at my shop! How to save it from evil computer scream?
Gyro:
RF demodulation in the b-e junction of the input stage?  Maybe try a 100pF cap across the input.
001:

--- Quote from: Gyro on November 25, 2018, 10:23:56 pm ---RF demodulation in the b-e junction of the input stage?  Maybe try a 100pF cap across the input.

--- End quote ---
No way
You can turn tone knob at guitar to add 0.047uF across the input
It is not simple problem
Really

Do anybody has experience with server EMC?
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