Really Quick and Easy Boxes
Version 1.0, September 1999 Copyright 1999 R.G. Keen. All rights reserved. This article served from GEO -http://www.geofex.com
As effects experimenters and Do-It-Yourselfers, we're all interested in what magical delights await us inside the next circuit, whether that's a new MegaBlaster Belchfire box or an old standard from the Golden Age. We tend to spend a lot of our efforts on the electronics and at the end of the building frenzy look around and think "OK, now what kind of box can I put this thing in?" and then get fairly disappointed. In the Guitar Effects FAQ I tried to bring some focus on this point by listing both the economic and technical reasons to consider the enclosure that something goes into first, not last. I also emphasized the need for durability, for making boxes that absolutely will stand up to literally being stomped on. This leads down the path of industrial quality stomp switches and cast-aluminum boxes.
However, there is also a need for stomp boxes that will not be for touring, an enclosure will not need to withstand roadie-abuse, but will serve for experimentation and practice use.
One of the most common beginner effects questions is "Why can't I use plastic boxes to put effects into?" The standard answer is "they're not strong enough, and being non-conductive, they will not shield against hum." We've disposed of the strength question by deciding that maybe there are uses that don't demand strength, so maybe we can do something about the hum as well. The advantages of plastic boxes are very seductive - you can make a box with little more than the box and an X-Acto knife, no drilling or other metal working.
All you really need to do is to make the box conductive somehow. We can do this two ways - cover the box with either a metal foil, or a conductive paint. Conductive paints start with multiple strikes against them. They are both expensive, rare, hard to use, and potentially toxic. Putting a metal foil over the box somehow seems to be the best approach.
The only two metals that are even possibly available for this use are copper and aluminum. Aluminum foil is almost ubiquitous, but suffers from being non-solderable. Copper foil exists, but is hard to find in the thicknesses (thinnesses?) that are easy to work for our purposes. Both copper and aluminum come in sticky-backed tapes that can be used. The copper tape is sold explicitly for electronic shielding, and is available in widths from 1/2" to 3". The 3" copper tape is ideal for box shielding; I found a roll of it in a surplus store, and it works GREAT. However, a roll of 1" wide copper tape is over $42 if you have to buy it over the counter - not a good choice. Aluminum tape is available for very reasonable prices in auto parts stores and air conditioning supplies/repairs places, in 2" and 3" widths for about $10, and so this may be a good choice for really quick and dirty boxes.
Tape suffers from a couple of problems beyond availability as well. It comes in fixed widths, and so you have to cover a box in strips, and it looks ugly.
What we'd like to do is to find a way to use aluminum foil, which is everywhere and cheap. I think I've figured out a way. All we really need to do is get the foil to stick to the box semi-permanently. We'd like to have that look good as well.
Scotch brand "Super 77" spray adhesive takes care of the stickiness. This is a stable, transparent acrylic based spray adhesive that is intended to "permanently attach foils, carpeting, foams, paper, cloth, etc. to painted or unpainted metals, wood, hardboard, and other base materials." This gook sprays on, and will stick aluminum foil to plastic boxes very well indeed.
We can put the foil on the inside or the outside. Putting it inside allows us to be a bit messy, but does leave the outside looking nice, and it avoids the problem of any foul-ups in foil placement looking amateurish.
A good way to do this is to take a sheet of paper, and fit it to the inside of the box, carefully cutting it to fit when folded into corners and contours. When it fits well, take it out of the box and use it as an outline to cut a sheet of aluminum foil to the right size and shape to perfectly fit inside the box. Then place the flat aluminum foil on a spread out newspaper and spray it with spray adhesive. Be careful to spray the side that touches the box. Then carefully fit it into the box, pressing it into place. Be sure to leave the foil a bit big on the outer edges to allow it to contact the foil on the bottom. Do a similar process on the bottom. Trim off the excess foil with a sharp blade.
You can also put foil on the outside. In this case, take the top off the box and spray the top with adhesive, then fold aluminum foil over it, trimming it to fit on the corners. Any minor gaps on the corners can be ignored, in shielding terms at least. Be neat - remember that people will be looking at the outside.
Be sure to fold the foil around the edges so that the foil layers on both the top and bottom parts of the box will touch when the box is closed. Also remember to fold a tab of aluminum foil into the inside so it covers the area where the hole for the input jack will be in the box. This is critical - you have to have something that connects the metallic layer to signal/circuit ground, or you will get much less hum and RF shielding. If you glue an area of foil under the input jack mounting hole on the inside, the jack will still contact it even if you use insulating paint on the outside.
Once you have this thing in place and the glue has dried, you can protect the metallic look by spraying the foil covered box with clear lacquer, or get a really whizzy look by spraying it with tinted, not opaque lacquer. Several coats with drying in between should look nice. If you don't paint it, it will eventually get dull gray like other weathered aluminum surfaces.
Once you have your plastic box well and neatly covered, you can cut holes for controls and jacks right through the plastic and foil together, with the same X-Acto knife. This should really be done before any painting, I guess.
When using a foil covered box for shielding, you have to be careful about grounding on jacks, pots and switches. The portions of the jack or pot that would be grounded must touch the foil covering. This is especially true for input and output jacks. It's good practice to run ground wires to both jacks from the circuit board and not rely on the foil carrying ground current anyway, even in a metal box. This is especially good advice for a plastic-with-foil box.
I'll be adding some pictures of this technique in the near future.