A project fromJunkyard Jam Band: DIY Musical Instruments and Noisemakers

THE SLINKIPHONEMAKE & COLLABORATE:

1

The “walking spring” is well-known for its “slinkity” sound, but that metallic ring-ing is far from the only music it has to offer. The humble Slinky is a veritable wellspring of great sci-fi sound effects. In fact, when properly amplified, it can even serve as a rudimentary vocal echo unit.

This project is quick, and the results are impressive, making it a great one to do with a younger assistant—whose little hands will prove very helpful when working within the confines of a disposable plastic party cup. This is also a good project for a beginning solderer of any age.

If you choose to eschew the electronics, this is a five-minute project suitable for ele-mentary schoolers and scout troops on a

The

Slinkiphone

4 | Project 1

budget. Without amplification, you’ll lose the zappy undertones and have a much more subtle vocal reverb, but you’ll also cut the project’s price in half. If you are going to “go electric” with the Slinkiphone, then please heed my warnings (outlined in Step 4) when selecting your piezo.

The finished Slinkiphone is shown in Figure 1-1. Hear samples at http://www .nostarch.com/jamband/.

FIGURE 1-1: The finished Slinkiphone (with pickup installed)

PreparationBuild Time

� 5 to 20 minutes, not including drying time for glue

Tools

� A standard soldering kit (See page 340.)

� A pushpin

� A sewing needle (It should have an eye large enough to accommodate your fishing line.)

� Needle-nose pliers or very small hands

� A hobby knife, utility knife, or pocketknife with a small, sharp blade

Supplies

� A disposable 16-ounce plastic cup

� A full-sized metal Slinky (This is usually marketed as the “Original” Slinky; a “mini” or plastic Slinky won’t work for this purpose.)

The Slinkiphone | 5

� Electrical tape, duct tape, or heat-shrink tubing1

� Silicone-based household glue (This is also called room-temperature vulcanizing rubber, or RTV-1; the 1 means that it’s in a single tube, instead of two tubes that you have to mix together. Don’t use glues like Super Glue or Krazy Glue here, as some formulations of these cyanoacrylate-based adhesives melt polystyrene plastics. Double-sided foam tape is a suitable replacement.)

� Nylon fishing line (Anything you have handy will do. I used 4 lb. test mono-filament, which is strong but still easy to thread through a normal sewing needle. Even dental floss would likely work in a pinch.)

� A piezo element (I highly recommend using one that is 22 mm or smaller in diameter because it will be easier to install and work with. I used a 20 mm, 6.5 kHz piezo buzzer element, which is Digi-Key part #102-1126-ND.)

� 24-gauge insulated wire (Either stranded or solid core wire is fine, as is 22-gauge speaker wire.)

� A 1/4-inch mono phone jack, also called a guitar jack

FIGURE 1-2 : Tools and supplies

1. Bare wire-to-wire and wire-to-component solder joints have a tendency to short against each other when you’re rocking out, which sounds just awful. You can insulate them with electrical tape or duct tape, but tape tends to either get gummy as it ages or dry up and fall off. Heat-shrink tubing, on the other hand, stays put and doesn’t muck up your project’s innards. You can buy lengths of heat shrink in a variety of diameters—and even as multicolor precut sampler packs—at many hobby, electronics, or hardware stores.

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Building the SlinkiphoneStep 1 Use your pushpin to pop two holes, roughly 3 mm apart, through the middle of the

bottom of your plastic cup, as shown in Figure 1-3. We’re using a cheap 16-ounce “party cup” here for two reasons: (1) it’s easy to pop a hole through with a pin, and (2) the thin, rigid plastic vibrates readily, making a nice diaphragm. The Slinki-phone ultimately functions as both a rudimentary microphone and an amplifier, so a relatively rigid diaphragm with a large diameter is a plus.

FIGURE 1-3 : The pinholes in the bottom of the disposable plastic cup

Step 2 Thread your needle with about 18 inches of fishing line and just let it dangle with-out tying a knot. (You don’t actually need that much line, but you’d go insane trying to work in the cup’s confined space with anything much shorter than 10 inches.) Working from the outside of the cup, run the needle through one of your holes from Step 1. Then use pliers (or the tiny hand of a tiny helper) to pull the needle through and send it back out the other hole (as in the left image in Figure 1-4). Finally, while holding one end of your monofilament, pull the needle so that the other end snakes through both holes in the cup and off the needle. The result should be a long piece of monofilament threaded through the party cup with both of its ends hanging out-side the cup, as shown on the right in Figure 1-4.

The Slinkiphone | 7

FIGURE 1- 4: Threading the cup

Step 3 Tie the final coil of the Slinky to the bottom of the cup. Try to make this as tight as possible, but it’s perfectly acceptable if there are a few millimeters between the Slinky and the cup when you hold the cup aloft. Triple-knot the fishing line. Thicker fishing line doesn’t like to stay knotted, so if you’re having trouble, you can secure it with a bead of glue. (Cyanoacrylate-based superglue is okay here—it’s perfectly safe on nylon or metal, but keep it off the cup itself.) Once you have a satisfactory knot, snip off the excess fishing line.

Ta-da! You now have the five-minute version of this project, guaranteed to entertain and delight children of all ages along the inverse bell curve shown in Figure 1-5: a kindergartner will laser-blast this acoustic Slinkiphone all afternoon, middle-schoolers will shout into it for a half hour, teens will disdain it and then warm up once they see their kid sister belting “Party Rockin’” into it, and grown men will laser-blast it all afternoon. But if you want to push this into rock ’n’ roll territory, then it’s time to break out the soldering iron and add a pickup to your Slinkiphone.

24

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Pre-K MiddleSchool

Teen Stay-at-HomeParent

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Age of Slinkiphonist

FIGURE 1-5: Slinkiphone appeal correlated to age of player (confidence interval: 97%)

8 | Project 1

Finding Amplifiers

The majority of the projects in this book require amplification, and most of them

should be safe to use with any run-of-the-mill guitar amp or PA system. My

testing amps include an old Gorilla GG-10 bass practice amp, a Roland KC-100

keyboard amp, a Behringer Eurorack UB1204 mixer, and a slew of little DIY

amps. However, a modified or flubbed circuit might result in a noise toy that

could damage your amp (which is why I tend to test everything on my home-

brew amps and the beat-up old Gorilla first).

You might not want to chance your ’58 Fender Tweed Champ on the first

little synth you’ve ever built. Fortunately, there are plenty of low-budget options

for amplification:

� Old computer speakers: Most of us have a few sets of these kicking

around in a milk crate in the basement. If the speakers have a wall-wart

power supply, then they have a built-in amplifier. Many of these offer sur-

prisingly good bass and high-end response. Computer speakers are a

good item to watch for at garage sales and resale shops, as they go cheap.

� Cheap practice amps at garage sales: Lots of kids pick up guitars,

and 90 percent of them lose interest. There are plenty of dinged-up—but

perfectly serviceable—practice amps (smaller, usually less expensive,

amplifiers, around 10 watts) sitting around garages and attics. You could

probably snag one for $30 or less while eating an ice cream bar in some

empty nester’s driveway this summer.

� RadioShack Mini Audio Amplifier: This is part #277-1008, which

RadioShack has made for decades. It’s ugly and sort of tinny, but it’s

cheap (they currently sell for $15) and easy to get, and it doesn’t burn

through batteries. It weathers plenty of abuse and can output to external

speakers, making it a fairly serviceable preamplifier (a subject we’ll hit

again in Project 5, the Scratchbox).

� Old tape decks: Many old dual-cassette boomboxes (the ones designed

for copying tapes) will pump whatever is plugged into the mic input

through the speakers. If you want to get a little crafty, you can always

convert any old tape deck into a grimy little amplifier (see “Building a

Tape Deck Amp” on page 62).

� DIY: You can build a perfectly serviceable test amp using $5 in parts.

Plus, it’s great practice for soldering and reading schematics. You’ll find a

circuit diagram for my “Dirt-Cheap Amp” on page 363, and full step-

by-step build instructions in my first book, Snip, Burn, Solder, Shred.

This is a great amp for beginners to build, and it makes a wonderful test

amplifier for dicey projects. There are also tons of simple amp designs

floating around online.

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Step 4 If this is your first time soldering, then plug in your iron and, while it’s warming up, peruse the soldering primer in Appendix A (“Soldering” on page 346). When you’re ready, consider the piezo element shown in Figure 1-6.

FIGURE 1-6: The 22 mm piezo element, front (left) and back (right)

For our low-fi, high-abuse purposes, pretty much every piezo element is the same. Lots of folks who don’t like waiting for a mail-order delivery run out to the hobby store, purchase a “piezo buzzer,” crack it open, and pull out the element. I don’t approve of this (it’s a little pricey and a big pain), but grant that it’s an acceptable way to source a piezo if you’re in a hurry.

That said, for this project you really want to order something a touch smaller. Our piezo pickup needs to rest mostly on the cup’s flat, slightly raised bottom without blocking the pinholes or touching the edge of the cup. The piezo elements in most prefab buzzers tend to run close to 30 mm, which is too big. You’ll cover the pinholes, which will prove bothersome down the road when your kid finally breaks off the Slinky and you want to reattach it. Also, harvesting a piezo from the buzzer’s plastic housing risks breaking the already overpriced component (annoying!).

Step 5 To build the piezo pickup (also called a contact pickup or contact mic), start by cut-ting two 5-inch lengths of insulated hook-up wire. Strip 1/4 to 1/2 inch of insulation off each end and tin the ends of the wire. (All of this is covered—and illustrated—in the soldering primer in Appendix A.)

Step 6 You’ll note that your 1/4-inch “guitar” jack has two lugs. If you like, you can tin these lugs, too (although with thicker-gauge wire like this, it’s less necessary). When you’re ready, solder one wire to each lug. Finish by slipping a 3/4- to 1-inch snip of heat-shrink tubing over each wire (see Figure 1-7).

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FIGURE 1-7: The prepared jack

Step 7 Strip another 1/4 inch of insulation off each lead on the piezo element and then solder one lead to each of the wires you connected to the jack in Step 6. Because this piezo element isn’t polarized, it doesn’t matter which lead goes to which lug (although technically the black lead is the ground and should go to the sleeve lug on the jack—phone jack anatomy is covered in “Quarter-Inch Phone Plugs and Jacks” on page 337). After the solder joints cool, slide the shrink tube up over the joint and snug it down to size by running the barrel of your soldering iron over it a few times, as described in the soldering primer. See the results in Figure 1-8.

FIGURE 1-8 : Our pickup. Note that only one piece of shrink tube is in place over its soldered joint.

Step 8 Now, let’s install the pickup. Squeeze a pea-sized dollop of silicone-based glue onto the brass front of the piezo element, and press it into the bottom of the cup. The edge of the piezo should be close to the pinholes from Step 1 without covering them, as shown in Figure 1-9. Set this aside. Most brands of silicone-based glue will set up in 30 minutes, although you want to allow a full 24 hours for it to dry com-pletely. If even 30 minutes is too long to wait, then it’s fine to use double-stick tape instead.

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FIGURE 1-9 : Gluing down the pickup’s piezo element. Note that the two pinholes have been left clear.

Step 9 The final step is installing the jack itself. Remove all the nuts and washers from your jack (most will have a single mounting nut and one or two washers). Use your hobby knife to cut a pickup hole in the cup, roughly 1 1/2 inches from the rim. Start small, with a hole not bigger than a 1/2 inch in diameter, and carefully enlarge it, periodically checking to see whether your jack will fit yet. Going a little big is okay because the cup will split if you force the jack through, but don’t make the hole too large. It’s easier to trim than backfill. Once you have a suitable hole, mount the jack from the inside. If it came with two washers, put one on the inside of the cup wall and the other on the outside. If you have only a single washer, put it on the outside. Finish by locking that nut down nice and tight (this will prevent the cup from split-ting). The guts of the finished Slinkiphone are shown in Figure 1-10.

FIGURE 1-10 : An interior view of the finished Slinkiphone

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Playing the SlinkiphoneOnce you tied that Slinky to the cup, this noise toy probably became pretty self-explanatory: shake the Slinky, and you’ll hear a reverberant “laser blast” rattle of booms and zaps. The cheap plastic party cup vastly magnifies the sound of the metal coils bumping against each other (working much like the belled horn on an old-timey gramophone). Plug the Slinkiphone into an amplifier (taking care to sup-port the jack as you do so—remember, this is a disposable plastic cup), and you’ll get a louder version of the same thing, with more undertones and stray zaps and twangs.

Pressing the Slinky’s connecting coil firmly against the cup’s bottom will muffle some of the booms, emphasizing the higher pitches (a trick that works in both acoustic and electric Slinkiphones). Your best laser blasts will come from holding the cup in one hand, resting the Slinky in the other, and then dropping the Slinky. When the free end hits the ground, it will send a compression wave traveling up the spring, which will rebound between floor and cup several times, making a terrific series of echoes of the initial metallic blast.

You can also use your Slinkiphone as a vocal echo effect, though the sound will be much more pronounced (and more impressive) if you’ve elected to build the full electric version. Plug in your Slinkiphone, press your mouth firmly into the cup, and hold the other end of the spring at arm’s length, letting it dangle slackly from the cup to your hand. Give a hoot. Shout some threats at He-Man. Cackle like a witch. Experiment with changing the tension in the spring: bring your arm in closer to add slack, or increase tension by gathering some coils into your hand. You could also loop the end of the spring to a doorknob and take a few steps back to give the Slinky some tension, or let it dangle directly from the cup with the end hanging in mid-air or resting on the floor (shorter Slinkiphonists may need to stand on a chair to keep the free end aloft).

Echoes and Amplifiers

A naturally occurring echo is the result of a sound (like your voice) reflecting

off a distant hard surface and coming back to your ear, somewhat delayed by

its travels. Something similar happens in the Slinkiphone: your voice vibrates

the bottom of the cup, and this vibrates the spring, setting it all a-jitter. These

jitters travel up and down the Slinky, resulting in an artificial echo. For years, a

contraption very similar to this was the only way to get an echo effect without

actually recording or performing in a grand hall or abandoned cave. Even

now, many guitar amps—especially those aimed at classic rock, blues, surf,

and rockabilly traditionalists—include a spring reverb effect that actually uses

springs to create a booming, sproingy ersatz echo.

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Tips, Tricks, and ModsIf you have a buddy to work with, you can use the Slinkiphone as a funky outer-space reverb pickup on an acoustic instrument like a guitar or hand drum. While one person plays, the other presses the Slinkiphone against various points on the instrument in either a “cup up” or “cup down” position, as shown in Figure 1-11. The “cup up” position—which puts the piezo pickup most directly in contact with the instrument—is especially effective where vibrations are most intense, like along the bridge of a guitar. The Slinkiphone handler should be encouraged to experiment with different spring tensions as well as cup orientations and placements.

FIGURE 1-11: Using the Slinkiphone as a reverb pickup in both “cup up” (top) and “cup down” (bottom) orientations