How to reduce electromagnetic field?

[Monroy]

Hi,

Is possible to somehow reduce electromagnetic field in the room? Depend where I turn my guitar, hum is bigger or smaller. Probably computer is main unit which generate hums. Is possible to fix this?

[Philbo King]

Originally Posted by Monroy

Hi,

Is possible to somehow reduce electromagnetic field in the room? Depend where I turn my guitar, hum is bigger or smaller. Probably computer is main unit which generate hums. Is possible to fix this?

I bought a roll of copper tape, pulled off the pickups and electronics, and lined the cavity of the guitar body with the copper tape. I soldered all the tape seams and reinstalled everything. Noise was reduced a bunch, like 25 or 30 dB. This was on a Strat.

[Monroy]

Thanks. Of course I've got picups isolated, but not with copper tape. I have better solution - with steel box which close all electrical things in guitar, similar for this:



Also with isolation from ground loop in this box too.

[kstn]

Originally Posted by Monroy

Hi,

Is possible to somehow reduce electromagnetic field in the room? Depend where I turn my guitar, hum is bigger or smaller. Probably computer is main unit which generate hums. Is possible to fix this?

Do you have PC or notebook? If you have the last try to unplug AC adapter and work on batteries when you record guitar.

Do you record clean guitar or use some pedals before? If the last try to not use adapters for them but batteries.

Good cables also may help. When I make guitar cables from micropfone cable with separate shield I've got significant lowering of noise. Also guitar (unbalanced) cables should not be long (afair critical point is near 5 meters) but lesser is better.

You can also try to find place in your room where the noise is lesser. Even direction can change noise level.

At any case say more about your chain for better answer.

[Monroy]

So,
- I was tried notebook and is quiet with battery power. Suddenly my notebook is very weak to audio production and I must using desktop.
- I'm not using any pedals. Just guitar > interface (focusrite 2i4 with no power cable, just USB)
- I'm using Klotz AC106 which is very good guitar cable. Any noises coming from cable even if I take cable near electrical outlet.
- When i take guitar to other place than normally I'm playing, hum is bigger or smaller, it's depend. The best results are when guitar is at perpendicular line to computer.

I will try some UPS working on battery power. If problem stay the same, then I remove power supply from computer, and put them away from guitar recording area.

I didn't check yet ferrite oring with power cable. Maybe it helps.

[MrBongo]

what kind of guitar?
sounds like it´s the usual singlecoil pickup hum. More noise when facing a source of electromagnetics, less when angled in relation to that source

[kstn]

Originally Posted by Monroy

So,
I will try some UPS working on battery power.

I hear some tales that it may help but didn't test it by myself. Write about the results.

Originally Posted by Monroy

So,
If problem stay the same, then I remove power supply from computer, and put them away from guitar recording area.

Or move not pover supply but all pc as far as you can.

PS Mad idea - to shield pc case with diy shiled like foil. Or put it in a metal box.

[drumphil]

PC cases should be properly shielded, but often aren't.

Cases should be complete enclosed in metal, be it a metal box, or other material lined with a conductive film like foil lined plastic, with no holes bigger than what you commonly see on the fan outlets on the back of the box. This lets air through, but blocks radio waves. If you have larger holes, or as is quite common, gaping holes in the metal structure, with just plastic blocking them off, then a lot of RF is going to be getting out of the box. The holes have to be smaller than the wavelength of the signals you want to contain.

This happens for a few reasons. Incompetent design, where large holes are left when they shouldn't be.

Cases where you have to snap out a bit of metal to put a CD drive or whatever in the case, but you can't replace the metal bit if you remove the drive.

And business just plain not caring, or working around the rules by selling computer cases without a power supply. If you sell a case without a power supply, it isn't classed as an electronic system, and doesn't have to have any shielding at all built into it's design. That's why you can buy cases that are mostly plastic. And who's knows what people might build with a computer case.. Maybe they won't put a computer in it. Who's to say?

If the case is designed properly you shouldn't have to line it with something to make it sealed as far as RF is concerned.

If your case is mostly designed right, but has a hole behind the front plastic cover where a CD drive might go or something like that, you could solve the problem by just blocking that hole off with something metal, or even a bit of cardboard with aluminium foil glued to it.

[drumphil]

I'm surprised by the amount of noise rejection claimed for lining inside of the guitar electronics cavity. I thought most of the noise was getting in through the pickups, which can't be shielded because that would stop them working.

[vdubreeze]

Originally Posted by drumphil

I'm surprised by the amount of noise rejection claimed for lining inside of the guitar electronics cavity. I thought most of the noise was getting in through the pickups, which can't be shielded because that would stop them working.

If a single coil electric has poor pickups and bad or no shielding it can be helped by lining the cavity. Having done a few of these as an extra step precautionary measure for the hell of it, I can say fairly confidently that it doesn't do much for a decently made guitar with decent pickups. I can't recall a not-cheap guitar I've opened up in the last few years that wasn't shielded well enough, certainly never went from not usable to usable.

Inexpensive guitars are another story (hey, I love beaters!) but with the pickups most of them come with all eliminating the electrical noise will do is make the pickups own shitty noise ratio problem more obvious : )

[Flaneurette]

Try different cables.

They act like antenna's. I had good results with ProCab MC305. It's dead silent, even with metal jacks, whereas an expensive cable with gold jacks hums like crazy and even picks up a radio station.

ProCab MC305 cable is the best I found. Has excellent shielding. It's cheap too.

[jerome_oneil]

The Navy actually sent me to school to learn this waaaay back when. Tempest classified spaces were cool.

Short answer: "yes."

Long answer, "Yes, but you can't afford it."

Real answer with stuff you can actually do: "Figure out where the interference is coming from, and eliminate that first. Then make sure all your equipment is on a common ground. Then used balanced cables/equipment everywhere."

[kstn]

Originally Posted by Flaneurette

Try different cables.

They act like antenna's. I had good results with ProCab MC305. It's dead silent, even with metal jacks, whereas an expensive cable with gold jacks hums like crazy and even picks up a radio station.

ProCab MC305 cable is the best I found. Has excellent shielding. It's cheap too.

Google said that ProCab is balanced (microphone) cable. Did you make cables by yourself or use finished? If the first - how did you solder it for unbalance (guitar) jack? red->tip, white->ring, shield->nothing, or any other way?

Price about 1.5$/m seems very interesting. I'll try it, thanks)

[Flaneurette]

Originally Posted by kstn

Google said that ProCab is balanced (microphone) cable. Did you make cables by yourself or use finished? If the first - how did you solder it for unbalance (guitar) jack? red->tip, white->ring, shield->nothing, or any other way?

Price about 1.5$/m seems very interesting. I'll try it, thanks)

Bought it as a finished guitar cable. ProCab uses MC305 on some of it's guitar cables. Not sure why though. Discovered it by accident when testing different cables. The best result I got from this exact model: MC305. I also have ProCab REF600 with gold jacks, which had more radio interference than the MC305. Plenty of other brands/non brands all picked up this radio beacon inside my home studio. The MC305 was the only one that didn't pick it up. Maybe because MC305 is also used for Mics, it's probably better shielded?

It seems excellent for studio use. How it holds on stage, I don't know. Something to keep in mind I guess.

Here's another thread specifically about using mic cable for guitar with more input/pros/cons:
https://forum.cockos.com/showthread.php?t=22422

I am thinking about buying a spindle of MC305 to make more cables, as I'm very pleased with it.



-

[Flaneurette]

Also a great video on studio cabling/wiring to prevent interference:

https://www.youtube.com/watch?v=G8XEjXN_Hyw

[Bri1]

PC cases should be properly shielded, but often aren't.


you could solve the problem by just blocking that hole off with something metal, or even a bit of cardboard with aluminium foil glued to it.

What! Now I know where I've been going wrong all these years-- instead of tinfoil on my head,it should be on the computer-- wow --need to just faceslap myself back into reality.
Them little computer mice are also noisey lickle critters-monitors too.

[DrKev]

If your case is mostly designed right, but has a hole behind the front plastic cover where a CD drive might go or something like that, you could solve the problem by just blocking that hole off with something metal, or even a bit of cardboard with aluminium foil glued to it.

The metal used MUST be grounded or nothing happens.

Originally Posted by drumphil

I'm surprised by the amount of noise rejection claimed for lining inside of the guitar electronics cavity. I thought most of the noise was getting in through the pickups, which can't be shielded because that would stop them working.

Sheiding the cavity help to eliminate noise pickup from the wiring but yes, the amount of noise reduction is often smaller than many people will expect.

If the noise changes when you turn the guitar, then yes the pickups are the biggest part of the problem. They do of course poke through a sheilded guitar cavity and so the sheild is of no use to them.

If you can't replace the source of the noise the cost-free solutions are to maximise your distance from the noise sources, move them (or the guitar) to a different room if possible) and and turn the guitar to minimise the noise when recording. Many a time I've recorded sitting on a swivel chair and making sure I'm the facing just the right direction before starting the take.

Otherwise I'd suggest noiseless pickups. There really are fantastic sounding options on the market that are as quiet as full-sized humbuckers.

[drumphil]

Yes, you'd have to make sure that the metal made contact with the metal in the case, but that isn't hard. And the whole case is (well, should be) connected to earth ground through the screws connecting it to the PSU casing.

[Monroy]

Originally Posted by Flaneurette

Try different cables.

They act like antenna's. I had good results with ProCab MC305. It's dead silent, even with metal jacks, whereas an expensive cable with gold jacks hums like crazy and even picks up a radio station.

ProCab MC305 cable is the best I found. Has excellent shielding. It's cheap too.

Thanks! I will try this MC305. But... now I'm using AC106 from Klotz which I think is very good cable with Neutrik plugs (silent version). Generally, if I want to know that cable is good or not, I hit him couple times on the floor. If I hear some crackling it means, that cable is weak. AC106 in this test is quiet.

[Philbo King]

Originally Posted by Monroy

So,
- I'm not using any pedals. Just guitar > interface (focusrite 2i4 with no power cable, just USB)
.

You have a signal-to-noise ratio problem. So you must either increase signal or decrease noise.

This sounds like you are running into a line level input. You might consider to try putting a preamp between the guitar and the focusrite.

[Monroy]

Originally Posted by Philbo King

You have a signal-to-noise ratio problem. So you must either increase signal or decrease noise.

This sounds like you are running into a line level input. You might consider to try putting a preamp between the guitar and the focusrite.

Switch is on "instrument" level in Scarlett. Gain knob is at 10 o'clock about to have guitar input signal between -12 dB to -6 dB.

[kstn]

Originally Posted by Monroy

Generally, if I want to know that cable is good or not, I hit him couple times on the floor. If I hear some crackling it means, that cable is weak.

It seems to me that this test doesn't checking shielding quality but only mechanical damage (tears in cable, falled off solgering, etc)

[Monroy]

Originally Posted by kstn

It seems to me that this test doesn't checking shielding quality but only mechanical damage (tears in cable, falled off solgering, etc)

Well, of course cable need to be plug into amp and then hit them on the floor or even gently knock by hand. Good cable is quiet when you knocking or hit him. Other test is put cable nearly electric wires - if hum is bigger, cable is worst. In this test also good cable is quiet.