Safety

Some Thoughts on Safety

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At first glance, it might seem that there is little reason for a discussion of safety among those of us who set out to design, build, and modify effects pedals. After all, most pedals operate on 9 volts, which can make tinkering with them feel about as risky as using a flashlight or grabbing the TV remote. Safety considerations, we might reason, are best directed towards those who build mega-watt amplifiers and rig the PA system in the club.

In truth, of course, not all pedals operate on flashlight-level voltage, and the knowhow (as well as the interest) that the DIYer gains in modifying a pedal can lead naturally to a decision to tear into that amp in the corner that suddenly stopped working. Also, when the sound guy is running late at the club, asking the pedal DIYer to take a look at the way the mixing board is wired into the rest of the rack might not seem like such a stretch. Who else are you going to ask, the drummer?

Not only that, let's face it: except for the rare individual who builds or modifies pedals solely for the aesthetic benefit, it is safe to assume that most DIYers will at some point patch their pedals into a signal train that includes an amp (mega-watt or otherwise). At that point, the fact that such amps just happen to be connected to 120v (in the U.S.) is no trivial detail, especially when one considers that by touching the strings of the guitar, the player becomes part of the circuit. All of a sudden, grabbing the remote, even with wet hands, begins to look at lot less risky.

Fair enough, you might say, but what more can be shared about safety and electrocution risks that hasn't already been repeated on 1000s of webpages? Good question, but here's an even better one. Since many of those webpages do contain excellent and reliable information, why would so many people continue to be killed (or at least burned, scared, and left very apprehensive) by electrocution? Nobody seriously believes, outside of Hollywood, that being electrocuted will leave you with special powers, yet it is apparently true that many people each year take unnecessary risks, and not all of them can be dismissed away as being unfortunate victims of sticking a knife into the toaster while hung-over the morning after a party. At least some of those who are injured or killed did know better, and had considerable experience with electronics and audio gear.

Common Risks and Common Warnings

Capacitors One of the most common of warnings has to do with capacitors. The main thing to remember about capacitors, sorry, "caps," is that they can zap you by doing what they are supposed to do. In other words, a cap doesn't have to go bad or give into peer pressure in order to pose a significant danger to you. A cap is designed to store a charge and, given the right conditions, discharge it, usually very quickly. Things would be greatly simplified, and I for one would feel a lot less nervous if caps had the equivalent of a gas gauge, a way of indicating whether they were charged (i.e., "full" vs. "empty"). Unfortunately, the engineers haven't gotten that far with caps, and even if they do someday come out with "charge gauges" the wise DIYer wouldn't trust them anyway. It is much, much safer to simply assume that the cap is charged, and discharge it. Treat every rifle as though it's loaded, and treat every cap as though it's charged.

There are a number of sites on the web that are helpful in learning how to safely discharge the caps in your audio gear. As an illustration, the website below recommends the use of a large screwdriver, though technically any insulated-handle tool with a conductive (i.e., metal) end would work for discharging the caps. The general idea is simple enough, to short the cap to ground (almost always the chassis) with the metal tip.

http://www.netads.com/~meo/Guitar/Amps/Kalamazoo/Mods/safe.html#zap

While this method will discharge the cap as effectively as any other method, from a safety standpoint it is far from ideal. Not only is there the possibility of a large spark when contact is made, the sudden discharge can startle the user or damage the components that might be, in effect, arc-welded by the spark. The startle-effect might seem trivial, but reactions and "freak-out" thresholds vary from person to person. I once saw a technician toss a reasonably expensive meter into the air when one of the leads unexpectedly shorted across 120v. Everyone laughed, of course, except him; when you're not expecting it, even a static-electricity discharge from the carpet to the doorknob is, however brief, unpleasant.

Far more sensible is to rely on a technique that bleeds the stored charge, usually by way of a large resistor. The resistor can be connected to the cap in various ways, but the key is to make sure that its wire leads are not connected to you. Some excellent suggestions for how one might do this are contained in this recent thread:

http://www.diystompboxes.com/smfforum/index.php?topic=49434.0

One final thought on the cap-discharge issue. It is tempting to think that as long as one avoids contact with the cap, the risk of electrocution will be eliminated. Assuming that the equipment is disconnected from the wall outlet, this is in some respects true. Note, however, that caps are always connected to other components, and in many cases those components will have relatively large, exposed metal leads. Thus, while you might avoid the caps themselves, say, when changing a tube, if you touch a component that is soldered or in some way connected to the cap, you will still be vulnerable. The lugs on the back of the On/Off switch are a good example. Even with the amp (or other device) unplugged, simply brushing against these lugs can be enough to complete a circuit, and whatever charge the caps had been holding onto, they will gladly transfer to the surface of your skin. Some gifts just aren't worth getting.

One caveat: it is common for a discussion of cap-safety to arise in the context of tube amps. Those amps, we hear, operate on as high as 450volts, and this can add to the concern over any caps that might be in such a circuit. The rule of thumb, then, is to discharge any caps you find inside a tube amp, BEFORE touching anything else. But solid-state amps often have large caps in their power sections, and while they may operate on what seems wimpy voltage compared to tube amps, they should be taken just as seriously. With both types of amps (or any other audio gear), always (1) unplug the amp, and (2) discharge the caps before poking around inside.

Shake Hands with Mr Electron

Another common warning goes something like this: when working on electrical equipment, always keep one hand in your pocket, or behind your back, strapped to your chairleg, and so on. The warning is usually presented as though it is part of the lore of electronics, dating back perhaps to Ben Franklin (it is uncertain whether he actually flew that kite, and less certain that he did so one-handed). Others will say things like, "I remember, as a boy, watching my papa repair those huge television sets, and he ALWAYS kept one hand in his pocket. It kept him from being shocked."

Here's the rationale behind the warning: if you only reach into the back of the amp with one hand, and you happen to make contact with exposed wiring, or in some other way place your hand into the electrical path, you will "only" get a zap on your hand. This is supposed to be qualitatively different from what could happen if you reach in with both mitts. Do it one-handed, the thinking goes, and the electricity will stop at your hand (or wrist, finger, it's never clear where) and be done with it, without going all the way up your arm, across your chest, stopping to zap your heart, and then exiting through your other hand. At this point, the person giving the advice will usually add some analogies, e.g., look at those birds on the electrical wire, and notice how they aren't zapped, look at the rat that crawls along the subway 3rd rail without getting zapped.

I can't say why your father kept one hand in his pocket, but if he wanted to avoid unnecessary risks, there were better ways to go about it. And as far as modelling your behavior on birds and rodents, you can do better. Yes, the fact that birds don't get zapped does illustrate an important point about grounding and the completing of a circuit path. But here's the real point: your ability to do precise electronic work on the inside of your amp is going to be greatly reduced, to put it mildly, if you force yourself to pretend that you lost an arm in combat. From the pessimist's vantage point, that means that you will spend more, not less, time around potentially lethal charges. So if you want to try to solder one-handed, I suppose you have the right. But it makes more sense to ensure that nothing inside of the circuit can zap you in the first place.

Furthermore, the underlying idea, that the current will never get near your heart if you only have one hand on that charged cap, simply doesn't have physics or physiology on its side. At most, you will make the electricity work a little harder to kill you, and it can cause serious damage without short-circuiting your heart in any case. So, in the end, the one-hand rule is sort of like recommending that someone wear a leather jacket to for protection when confronting a grizzly bear. The jacket will slow the bear down, but there are much better ways to improve your odds of surviving.

An exception to this would be those rare occasions when you need to poke around in an amp while it is on. If you're unsure, you really should think about paying a pro to do this, since even pros don't do it that often or that casually. There are, admittedly, some times when you can troubleshoot a live circuit by gently nudging a wire this way or that (to see what effect this has on hum, for instance). But why take risks when you don't have to? Don't just keep one of your hands out of the way, keep them both out of the way by using a long wooden stick to do the prodding. This, once more, applies only if you're absolutely sure that prodding is the best way. Even with a long stick, you're still inches away from a serious health risk.