[phaedrus]

Oh, wait, that's the subject for my next "amp for sale" thread...

I'm considering using cherry to build the enclosure for my next amp trick -- handcut dovetails, danish oil, hand planed, a raised panel perhaps, etc. However, I recalled a few things from other posts about shielding, the need to get the PPA board into its enclosure, wood is not a good shielding material, etc.

I ran a quick search on shielding wooden cases and didn't see much that would be super helpful. Is there a material for coating the interior of a wooden case to provide shielding? I don't find foil to be a pleasing solution, given my experience using aluminum foil in and out of the kitchen. Am I better off looking at using a wooden case as sleeve for a metal enclosure? Would such an inner enclosure need to have six sides (top, bottom, right, left, back and front), or would an extruded piece similar to the hammonds suffice?

Is there a metal that is best to use in this type of situation?

Is there another solution?

 

[ppl]

how about that copper sheeting available in Hobby stores with sticky stuff on one side. you should shield all sides

 

[aeberbach]

You can get a can of shielding paint from stew-mac.com, it is used to coat the body cavities of solid-body guitars when hum and feedback is undesirable. Much easier than copper - if you use stick-on copper sheeting it will look nicer but might cost more, and don't forget to solder all the copper sheets to each other. You need a good electrical connection between each piece and overlapping sections are not good enough, they are separated by a layer of adhesive when applied and copper will oxidize anyway.

 

[Tomo]

Hi,

Shielding isn't necessarily important. One of my amp has a plastic chasis. I have no pick up unless it is placed in a metal detector.

Self-adhesive copper idea is really good one. You do not need to solder these copper layers together. Soldering them together will not improve the shielding. For the matter of shielding, the shield must be conductive, in other words, metal. The shield can be a mesh if the pitches are small. (I think 1-2 cm pitch would be sufficient.) The gaps of the copper layer should be as small, however, it is very easy to do.

Oxidation of copper layer will not change the effectiveness of shielding.

Note also, you might want to looking to pseudo-stealth technology. (Apparently Stealth Technology is classified.) This pseudo-stealth thing is pretty old idea not to mention easy. For the rumor goes, one has to stuff the chasis with sandpaper material. Some people stick sandpaper onto the inside of the chasis. However, I have not valified the effectiveness.

T

 

[jeffreyj]

Quote:

Originally posted by Tomo ... Self-adhesive copper idea is really good one. You do not need to solder these copper layers together. Soldering them together will not improve the shielding. T

Don't do much RF work, eh Tomo?

 

[Gariver]

A good place to buy copper sheets is Small Parts. Just click on "sheets" in the Copper Section. Take a look...

http://www.smallparts.com/materials/

Micro Mark sells the following...
--3 copper sheets (4" X 10") made of 0.025" copper.
--$12.00 (part# 60243).

http://www.micromark.com

Good luck with all this!

 

[ofb]

phaedrus, my lexan (acrylic?) cased meta42 didn't need sheilding. you might want to build a case without first to see if that works for you; just leave space to slip in shielding later if needed.

one source for shielding is old macs if you've got junkers handy. a plastic pizza box like the old 6100 series has a nice bit of tin that stretches across the whole machine. it's very easy to work with. you can cut it with scissors.

most plastic case machines probably have something similar inside. (funny, i just realized that my resin cased ibm PowerStation 320 has no shielding. i wonder if they added something to the resin mix?)

 

[Tomo]

Hello,

Soldering is necessary when conduction through the gap is necessary. So you must absolutely solder or weld all the walls of RF wave guides. But we are not guiding. We just wanna kill it. So all you have to do is to employ metals close enough that it will disrupt the waves.

I am sure there will be some high freq leaking through the gap, but all you have to do is to make sure that frequency is so high up, that amp pickup is no problem.

Tomo

 

[Steve Eddy]

Chalk me up as another who hasn't found shielding to necessarily give better sonic performance. Which isn't to say that shielding can't be effective for given circuits with given layouts in given environments.

Perhaps I'm just lucky. Or deaf.

se

 

[aeberbach]

Just to clarify, Tomo - what I meant was if you touch bare copper to bare copper the connection might be good initially but it will deteriorate as the surfaces oxidize. Twisting wires together tightly and wire-wrap technique avoids this problem by creating a gas-tight join. When connecting copper foil solder is the only way that lasts.

ofb, is the inside of your IBM case a dark color compared to the outside? I've never seen a computer case without some kind of shielding, it might be painted.

Shielding might help or it might not, depends on your environment.

 

[lini]

phaedrus: You could also create a Faraday cage with wire mesh inside the wooden enclosure.

Greetings from Munich!

Manfred / lini

 

[ofb]

Quote:

Originally posted by aeberbach ofb, is the inside of your IBM case a dark color compared to the outside? I've never seen a computer case without some kind of shielding, it might be painted.

good call. i'd thought that was the natural colour of the plastic and the tan was the paint, but it is indeed the other way around. a bit of scraping shows the shielding paint is actually rather thick, with a thin green primer under.

 

[Gariver]

I am architect. So I've got to know plastics.

Lexan is a polycarbonate, not an acrylic. Dupont makes its polycarbonate with the trade name Lexan. Other polycarbonate trade names are Hyzod and Tuffac. Great stuff, esp the scratch resistant polycarbonates.

 

[ofb]

whups. actually all i meant by that is i wasn't sure if the box was lexan or acrylic; not if lexan was acrylic.

it's nice shiny clear plastic is all i know. that, and memory serves that one goes yellow and the other blue with age? (or neither: probably they've been improved by now.)

to use proper names, do polycarbonates generally act like better quality acrylics? or is there a fair bit more to it than that?

 

[dokebi]

6 of my amps were in plastic enclosures and I never had interference problems. I tried using aluminum shielding material I scavenged from dead network equipment out of curiosity and there was no noticeable difference with or without. All of this was in a room with a lot of florescent lighting and computer equipment.