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Post by firebottles on Dec 12, 2005 14:36:56 GMT -5
Ok... I've been thinking this through before I start my shielding project. Faraday Cages are ususally constructed of grounded wire screen. They filter out unwanted electromagnetic radiation. They are used to shield scientific or sensitive equipment from electrical fields. The idea is that wavelengths of interference that can be heard cannot pass through the mesh. A few stray x-rays or Gammas may pass through but that might sound kind of cool ! haha. Radio waves etc are many yards long.
Anyway I am thinking of "upholstering" the P'up and control cavities with copper mesh (currently $1.85 sq. foot from high end window suppliers) then using copper tubing for the wire trench. No need to worry about non-conductive adhesive, or soldering except where the tubing enters the mesh.
Thoughts? Anyone try this yet?
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Post by JohnH on Dec 12, 2005 15:01:31 GMT -5
Not tried that, but it sounds like a great idea. Foil is so awkward to work with. On one of my guitars, I shielded the cavity and was about to take the step of removing all the switches to do the guard, but noticed that there were lots of switches all grounded, and several grounded wires around and across the switches. This seems to make a grounded cage and a rough test wrapping the guiter externally in grounded foil showed me that there was no further benefit to more shielding.
I have a question about Faraday cages, which as you suggest, would seem to be the principle behind our screening:
Do you have to fundamentally create loops of connected cage around your cavity, so that induced currents can circulate? or can you have several seperate parts which are only connected at one point to each other. Assume in each case, the actual coverage area is the same, it is the connections between parts that are different.
It becomes relavent where, if you screen the cavity and the pickguard, do you then have to lip the cavity screen up over the edge of th body to seal continuously (or a close centers), or can you set the cavity screen say 1/8" down form the top of the cavity (which is neater and less vulnerable), and just connect one wire to the pickguard screen.
I know thee are a few science dudes out there. Somebody who was awake during electrical theory lectures please offer your best guess!
John
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Post by firebottles on Dec 12, 2005 15:09:10 GMT -5
If I am right that an improvised F.Cage around the interior of the guitar will work.. I am guessing that one needs to bring the mesh up out of the cavity to make an electrical connection with the foil on the back of the pickguard. To work though, it is my understanding that the cage would be grounded. Not sure about your other questions though... anyone?
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Post by Mini-Strat_Maine on Dec 12, 2005 15:17:07 GMT -5
Anyway I am thinking of "upholstering" the P'up and control cavities with copper mesh (currently $1.85 sq. foot from high end window suppliers) then using copper tubing for the wire trench. No need to worry about non-conductive adhesive, or soldering except where the tubing enters the mesh. Thoughts? Anyone try this yet? Hmm. I'm no engineer, but I do know that there's a big ol' radio spectrum out there. If the mesh will work against EMI and any RFI you might encounter, then it might be worth a try. I still remember a winter night some years back when a friend of mine was doing a gig at a local lounge. The radio transmissions of a DPW truck outside the restaurant came through his sound system as the truck went past. We had no idea where the stray signal got in, and Bob's a radio engineer at his "real job." I'm not going to do the math to figure out the wavelength of the frequency involved, but it was VHF-hi, anyway. I just remembered a phrase from my ham radio days: "DC to light." It's all out there, ricocheting around, looking for an antenna to worm into.
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Post by firebottles on Dec 12, 2005 18:09:31 GMT -5
Yep , here it is... EMI and RFI click the link "all you need to know about RFI" under the photo. www.twpinc.com/twp/jsp/product.jsp?type=11Actually .. after some thought, I think the screen would not need to come up over the edge of the cavity but meet the edge, then an electrical connection could be made with the foil backed pickguard by wire to a pickguard screw. That would certainly be easier too.
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Post by eljib on Dec 12, 2005 19:17:58 GMT -5
I have nothing electrical to add to your thread, but your idea could mean an improvement in tone quality from your wood. I have read quite a bit about the benefits of removing any paint and varnish from the inside of the pickup, control, and trem cavities to allow for better "breathing" of the wood. I haven't tried it yet because I need the smooth surface of the paint for my foil to stick down properly. (The same page also recommended you strip down to bare wood everything covered by the pickguard).
If the screen works well enough I think I'll carry out the above recomendations and report back with the tonal results.
Sorry for getting off topic a little.
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Post by firebottles on Dec 12, 2005 21:57:28 GMT -5
Interesting idea... I may take the opportunity to Dremel out the cavities.
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Post by bam on Dec 13, 2005 3:29:18 GMT -5
.. that idea also adds your guitar's susceptibility to humidity, the enemy of all (tone) woods.
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Post by firebottles on Dec 13, 2005 16:36:46 GMT -5
Yeah, left the paint alone...Started the screen shielding project...
1. rubbed pencil over paper over holes to get cavity floor shape templates.. then cut pieces to fit bottoms then cut strips to go around the sides.. tack soldered. 2. used single pieces of screen to line trenches.
all screen is cut flush with surface of guitar. My guitar is black so a black permanent marker made it easy to mark the side strips before cutting. An old pair of scissors cut the screen just fine.
took about an hour total.
decided to use some 1/2 inch copper tape from stained glass supplier (it is conductive through the adhesive) to come up out of cavities over to pickguard screw holes. Tack soldered to screen. I got to thinking that if the screen came up to the foil.. it could rub and rip the foil up and potentially lose contact.
I just used the same copper tape to cover the back of pickguard.. we're out of tinfoil and I'm impatient.
I am up to the wiring.. but I need to finalize those plans. It's very easy to solder to screen. The one problem when working with screen... finger pokes.
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Post by firebottles on Dec 14, 2005 22:01:03 GMT -5
I should post a problem I am running into.. maybe so you can avoid this.
I am really into this screen idea at least as an experiement/alternative but here's the rub.. well the rub. The neck position HB fits so tightly that the extra space taken up by the screen all the way around it is making it very difficult to adjust the pickup height..I can make it fit. but it's tight. And I am concerned that the forces (should I later decide to adjust) may either cause a problem by cracking the pickguard or at least mess up my nice screen lined pickup cavity.
Another part of this equation is that my HB is pretty and chromed steel, so to avoid contacting the screen I had to cover the sides and bottom with electrical tape.. adding a small amount more to their girth.
HMM what to do? Abandon my Faraday Cage shielding and copper tape this pickup cavity? I may need to do that. But I am REALLY curious just to see if screen will shield properly.
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Post by UnklMickey on Dec 14, 2005 22:38:17 GMT -5
...HMM what to do? Abandon my Faraday Cage shielding and copper tape this pickup cavity? I may need to do that. But I am REALLY curious just to see if screen will shield properly. i think this will probably shield WAY better at radio frequencies than foil, because of the eddy currents induced into the wires of the screen. at low frequencies (60hz, 120hz) where the evil hum is, i expect it to perform about the same as foil. i don't really know for certain. i'm only guessing. anyway, good luck with the challenges this has been presenting to you. we're all rooting for you as navigate through this uncharted territory. unk
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Post by UnklMickey on Dec 16, 2005 19:13:16 GMT -5
firebottles,
i suspect you won't be dissuaded from continuing on with your faraday cage experiment by others opinions. and that's a GOOD thing!
i can tell from our previous conversations, that you are imaginative and inquisitive.
i was quite impressed with the fact that you have been reporting to us on the problems that you have incurred along the way. that shows an appropriate concern for others who may be paralleling your experiment. -- very responsible!
i have voiced my suspicion that the screen will not improve on the results of foil in the frequency range of the hum. nonetheless, i think i speak for most of the members here when i say: if my suspicions are wrong, and you do end up with a superior method of shielding, this WILL be a major find.
regardless of what it may look like, or the fact that it may bring it's own set of challenges to work with, IF this is effective, it WILL be worth considering.
other than the case of a lucite bodied guitar, a guitar with superior hum shielding beats one that looks prettier BEHIND the pickguard IMHO.
even if this proves to be a dead-end, you will have determined that it doesn't work by a real-world trial.
in any case, most of us here DO appreciate your efforts, and will be glad to hear your conclusions whatever they may be.
good luck!
unk
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Post by bam on Dec 17, 2005 6:15:54 GMT -5
actually, the original aluminium/copper foil shielding IS a faraday cage, too. the difference is only in the cage's material (which affects the shielding frequency band). if you find that electrical tape is too thick, try this; MASKING TAPE. find the thinnest one; they do great. one more thing : if that HB is pretty and chromed steel then I assume that it's a covered HB? if yes, then you should NOT shield it. the tone WILL be altered. My HB's are non-covered type, and thus I do this :
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Post by firebottles on Dec 17, 2005 14:28:11 GMT -5
Thanks for the encouragement! I now have two shielding projects underway. The Tele and a Rick 4001.
My cage idea experiment is going into the Rick.. more room and the wiring will be unchanged except the star grounding. It will be a better experiment as only the shield and grounding will be different from the stock bass.. and easier to put back to stock. My Tele on the other hand has got me into some deeper water. I decided to go back to the "tried and true" copper foiltape as I have a very unsure outcome with regard to wiring.. my desire to completely change the wiring to non-interactive with HB options.. and the disassembly/rebuild of the poorly crafted HB inorder to keep shield and signal grounds separate... not to mention the tighter cavities.
The HB was made so that pole screws were touching the outer cover. I took it apart and added rubber spacers to keep poles and cover apart. I was going to drill the holes out, which I may still do, but I think the chrome plating would start flaking off.. I am not too concerned about looks but I don't want it to rust. I can go without the top cover if I had to.. but the bottom was making contact with the poles as well.. so did the same fix.
The Tele seems quieter...but I've got a funny situation going on with the controls.. so I am trying to work that out. I've posted some questions regarding this under schematics. One change for the better is that I split the pickguard so I can keep it strung now as I fiddle with wiring changes.
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Post by bam on Dec 18, 2005 1:32:12 GMT -5
JA from the original GN told us that "trouble, in most guitars, are more often caused by the controls rather than the pups". good luck !
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