Cover plates....worth it?

[Structo]

If aluminum doesn't shield well then why did Fender shield their pickguards with sheet aluminum for years?

I thought that anything that can conduct would work since your are in a sense extending the chassis by physical contact to the shield.

I ended up using some copper shielding tape I use on my guitars.
It's from Stew Mac and has conductive adhesive on the back.

[scotto]

Interesting article supporting Funk's point (at least for low frequency magnetic interference):

http://findarticles.com/p/articles/mi_q ... _n21284353

[heisthl]

In the '80's I was involved with a designer to come up with the cheapest "Tempest" solution for a small computer installation at the pentagon. The cheapest solution was to lead line the whole room!
I have not researched the use of aluminum as a shield, I think it does seem to help against RF interference and light dimmer proximity noises. (although a lot of light dimmer noise is AC line related). If anyone knows what benifits aluminum does provide as a shield, I would be very interested, also interested in a better alternative. I'm not crazy about the use of copper because of the oxidation issues over time.

[glasman]

I remember Andy Fuchs telling me one time that he used the aluminum tape that you can get a Home depot in his amps. 3" wide and cheap....

Maybe Andy will chime in

[heisthl]

I remember Andy Fuchs telling me one time that he used the aluminum tape that you can get a Home depot in his amps. 3" wide and cheap....

Maybe Andy will chime in

If it's not a trade secret - what does GlasWerks use?

[butwhatif]

Aluminum and copper will produce some electrostatic shielding, with varying results. Steel screen like the stuff Leo used to use will help with electrostatic, and electromagnetic interference, because it's got magnetic permeability. Mu-metal foil is great for audio shielding, but i have not had
much success in gtr amps, as it's so permeable that it seems to 'pick up' stray magnetism from the pwr xformer. The shielding paint actually works well for hi impedance stuff, but i don't know how well it would work for an amp cab.

[fullerplast]

It's all about the type of fields and the frequencies. Neither aluminum or copper will be effective in shielding the magnetic fields created by the current in a 60Hz power source. The permeability of al or cu at those frequencies is about the same as air. OTOH, they both become very effective in shielding electric fields as frequencies increase to IF and RF ranges; also for static electricity. For example, if you were building a new room using steel conduit for your power lines, it would reduce the fields considerably while aluminum conduit would do nothing.

Essentially when you shield the amp you are creating what is called a Faraday's cage, which can be very effective for shielding both higher frequency magnetic and electric fields, but still doesn't do much for low freq magnetic fields.

Despite the limitations, aluminum is a cheap and easy way to gain some degree of shielding in an amp. Even a shielded guitar cable is basically a Faraday's cage and to hear what it does all you have to do is try a cable without shielding. As for aluminum tape vs sheet vs plate....the thicker the better from a theoretical POV, although it's going to be a case of diminishing returns.

[heisthl]

I'm going to make one of these to go along with my tin foil hat:


http://howto.wired.com/wiki/Make_a_Faraday_Cage_Wallet

Actually the testing could be done on your amp if you can cram your cell phone in there to see if it rings.

[fullerplast]

I'm going to make one of these to go along with my tin foil hat:


http://howto.wired.com/wiki/Make_a_Faraday_Cage_Wallet

Actually the testing could be done on your amp if you can cram your cell phone in there to see if it rings.

Very true...

[M Fowler]

All I can say is that with out my aluminum cover plate my amps are noiser than with, so I use them. Can't argue with my simple logic. Unless someone comes up with a better plan the aluminum wins for me.

Mark

[scotto]

I spent several days in one of Bell Labs anechoic chambers back in the mid nineties trying to sort out the shielding for a portable (laptop) pacemaker programmer that we designed. Wound up with copper plated plastic case with copper spring fingers at the opening cracks. I had a EMI/RFI consultant guiding me (I'm a mechanical engineer) and he said you don't actually shield as much as you provide a pathway to ground(faraday cage) to direct the interference. I didn't understand it very well then and I still don't. I had some mu metal from back then and subsequently tried to shield a noisy Quadraverb wall wart with it to no avail. I'll stick to mechanical engineering where all you need to know isF=MA and you can't push on a rope.

[Structo]

That was my understanding that even if the shield is non ferrous, it shields the components by providing a path to ground.
I suppose it depends on the frequency of the EMI whether or not it makes it past.

[BobW]

Cu and Al screens works against electrostatic interference when grounded to the chassis.

Any ferrous metal screen such as steel works against electromagnetic interference by providing a magnetic path to ground, as long as the holes are smaller than a 1/4 size of the wavelength of the noise sources fundamental frequency. This is why you can watch popcorn cook in the microwave w/o cooking yourself.

As mentioned before, both the AL and steel provide a Faraday Cage (shielding) around the amp.

Since noise sources can (and usually do) consist of BOTH static and magnetic properties, this is why AL alone seems to reduce the electromagnetic noise, when it fact it is reducing static noise.

There is a wealth of info on electrostatic and electromagnetic shielding on the web, but I usually use Al screen folded over on the edges to minimize fraying, then staple it to the cab. It provides sufficent shielding.

[M Fowler]

So if I use my usual method of an aluminum bottom plate along with a ferrous metal screen attached to the head cab that should help even more, right. I will try this.

I am not having any problems at this time as far as hiss or noise but when I get close to the amp with my guitar about 2 feet or maybe less, there is some interference. Backing away it goes away.

Mark

[Structo]

When close to the amp with the guitar is it a 60Hz type noise?

I get that on my amps too. Figured it was more of a problem with the guitars shielding than the amp.

I have some copper foil type stuff on the top of my head. I ground off the powder coating where the four screws go so it can make contact with the copper.
Didn't notice any change really.