Make: Electronics by Charles Platt (classic books to read TXT) 📗

Today’s guitarists can choose from a smorgasbord of effects, all of which can be home-built using plans available online. For reference, try these special-interest books:

Analog Man’s Guide to Vintage Effects by Tom Hughes (For Musicians Only Publishing, 2004). This is a guide to every vintage stomp box and pedal you can imagine.

How to Modify Effect Pedals for Guitar and Bass by Brian Wampler (Custom Books Publishing, 2007). This is an extremely detailed guide for beginners with little or no prior knowledge. Currently it is available only by download, from sites such as http://www.openlibrary.org, but you may be able to find the previous printed edition from secondhand sellers, if you search for the title and the author.

Of course, you can always take a shortcut by laying down a couple hundred dollars for an off-the-shelf item such as a Boss ME-20, which uses digital processing to emulate distortion, metal, fuzz, chorus, phaser, flanger, tremolo, delay, reverb, and several more, all in one convenient multi-pedal package. Purists, of course, will claim that it “doesn’t sound the same,” but maybe that’s not the point. Some of us simply can’t get no satisfaction until we build our own stomp box and then tweak it, in search of a sound that doesn’t come off-the-shelf and is wholly our own.

Experiment 31: One Radio, No Solder,

No Power

Time now to go back one more time to inductance and capacitance, and demonstrate an application which also makes use of the way that waveforms can be added to each other. I want to show you how a simple circuit with no power supply at all can receive AM radio signals and make them audible. This is often known as a crystal radio, because the circuit includes a germanium diode, which has a crystal inside it. The idea dates back to the dawn of radio, but if you’ve never tried it, you’ve missed an experience that is truly magical.

You will need:

Rigid cylindrical object, such as a vitamin bottle. Quantity: 1.

22-gauge hookup wire, solid-core. Quantity: 60 feet.

16-gauge wire, stranded. Quantity: 100 feet.

Polypropylene rope (“poly rope”) or nylon rope. Quantity: 10 feet.

Germanium diode. Quantity: 1.

High-impedance headphone. Quantity: 1.

The diode and headphone can be ordered from http://www.scitoyscatalog.com. You cannot use a modern headphone of the type you wear with an MP3 player.

Some of these items are shown in Figure 5-59.

Figure 5-59. Just add wire and a coil, and this is all you need to receive AM radio signals. The black disc becomes the tuning dial, after it is screwed onto the variable capacitor (right). This is actually an optional extra. A germanium diode (center) rectifies the radio signal. The high-impedance earphone (top) creates a barely audible sound.

First, you need to make a coil. It should be about 3 inches in diameter, and you can wind it around any empty glass or plastic container of that size, so long as it’s rigid. A soda bottle or water bottle isn’t suitable, because the cumulative squeezing force of the turns of wire can deform the bottle so that it isn’t circular anymore.

I chose a vitamin bottle that just happened to be exactly the right size. To remove the label, I softened its adhesive with a heat gun (lightly, to avoid melting the bottle) and then just peeled it off. The adhesive left a residue, which I removed with Xylol (also known as Xylene). This is a handy solvent to have around, as it can remove “permanent” marker stains as well as sticky residues, but you should always use latex or nitrile gloves to avoid getting it on your skin, and minimize your exposure the fumes. Because Xylol will dissolve some plastics, clearly it’s not good for your lungs.

After you prepare a clean, rigid bottle, drill two pairs of holes in it, as shown in Figure 5-60. You’ll use them to anchor the ends of the coil.

Figure 5-60. A large, 3-inch diameter empty vitamin bottle makes an ideal core for a crystal radio coil. The drilled holes will anchor wire wrapped around the bottle.

Now you need about 60 feet of 22-gauge solid-core wire. If you use magnet wire, its thin insulation will allow the turns of the coil to be more closely spaced, and the coil may be slightly more efficient. But everyday vinyl-insulated wire will do the job, and is much easier to work with.

Begin by stripping the first 6 inches of insulation from the end of the wire. Now measure 50 inches along the insulated remainder and apply your wire strippers at that point, just enough to cut the insulation without cutting the wire. Use your two thumb nails to pull the insulation apart, revealing about a half-inch of bare wire, as shown in Figure 5-61. Bend it at the center point and twist it into a loop, as shown in Figure 5-62.

Figure 5-61. Wire strippers expose the solid conductor at intervals along a 22-gauge wire.

You just made a “tap,” meaning a point where you will be able to tap into the coil after you wind it. You’ll need another 11 of these taps, all of them spaced 50 inches apart. (If the diameter of the bottle that you’ll be using as the core of your coil is not 3 inches, multiply its diameter by 16 to get the approximate desired spacing of taps.)

After you have made 12 taps, cut the wire and strip 6 inches off that end. Now bend the end into a U shape about a half-inch in diameter, so that you can hook it through the pair of holes that you drilled at one end of the bottle. Pull the wire through, then loop it around again to make a secure anchor point.

Now wind the rest of the wire around the bottle, pulling it tightly so that the coils stay close together. When you get to the end of the wire, thread it through the remaining pair of holes to anchor it as shown in Figure 5-63. The