We’ve all heard the effect, and possibly seen it too: a cool guitarist reaches for the pickup selector on his Les Paul, and starts to wiggle it back & forth to create a stuttering on/off sound. Trouble is, this only works on Les Pauls (and other guitars equipped with separate volume controls for the pickups). Try it on a Strat, and… well, the result is rather disappointing. But how about adding a switch to your Strat/Tele/whatever, to do this job? Piece of cake – all you have to do is interrupt the signal going to the output jack, route it via an on/off switch, and you’re set, right?
Actually, no. I’ve seen that exact piece of advice about a gazillion times now, and it never ceases to amaze me how few people seem to know rule #1 about electric guitar wiring: never, ever, disconnect the signal to the amp and leave it hanging. If you want to shut the signal up, there are other ways to do it, ways that won’t give you the dreaded “accidentally unplugged the guitar” buzz…
Ok, so how’s it done then?
Remember the cool guitarist with his Les Paul? What he did was simply to turn down the volume from the neck pickup, and use the pickup selector to flick between the (now quiet) neck pickup and the bridge pickup. Every time the selector hits the neck pickup, the guitar goes dead quiet, and when it’s flicked over to the bridge setting the sound comes back. But it’s important to remember how a guitar’s volume control works (as that’s what the killswitch needs to replicate). When turned down, the neck pickup volume control is actually connecting the output “hot” straight to ground, causing a short-circuit. This short-circuit means the amp goes quiet too, yet, it’s still connected – so you won’t get that “unplugged cable” noise.
It can be as easy as simply adding a couple of wires and a momentary (normally open) SPST switch. Locate the signal “hot” going to the output jack – this is a wire that starts at the center lug of the volume control, and ends up at the “tip” lug on the output jack. Now add a wire to it, for instance at the volume control, and solder that wire to the switch (either of the two lugs you identified earlier). Then solder another wire to the remaining lug (of the two you want to use) on the switch, and solder the other end to ground. A pot casing will work beautifully for this purpose, but you could of course follow the other wire from the output jack, and see where it ends up (you’ll find that it ends up at the pot casing, actually…).
But… if you place the switch far away from the point where you connect the wires, you could end up with noise when the guitar is operating normally. This seems to be a problem especially with guitars that isn’t properly shielded – that extra “hot” wire can pick up noise. The “professional” way to do this is to actually break into the signal path (what I told you earlier not to do, but now in a safe way) and connect an SPDT on/on toggle switch between the main volume control and the output jack. Wire it like this:
By orienting the switch so it matches the above layout (when seen from the back of the guitar), the guitar will be quiet when you flick the toggle switch up, and you can then push it down to make noises. You can of course turn it the other way if you like, but I’d want the guitar quiet with the switch up, so I can push down for sound. If you use a momentary switch – usually designated as “(on)/on” – make sure you turn it so the resting position is with the toggle arm down towards the floor. Then it’ll match the above drawing (so you’ll have sound when you’re not messing with the killswitch). If you’d rather have the switch rest in the “up” position (push down to kill the sound), you need to flip the drawing before soldering.
Seymour Duncan has a nice drawing of how to wire a killswitch, in which they use a DPDT switch to do the same job as above. It works the same, so which one to use is up to you.
What kind of switch do I want?
Some go for pushbuttons, while others prefer toggle switches. Again, I’d want to be able to flick the sound “on” with the beat (rather than “off”), so I’d use a toggle switch that will flick up/down, with the down position being normal (sound on – killswitch circuit open). That way, I can have the guitar make noises at my command, rather than shut up. It’s mostly an attitude thing – this just seems more intuitive to me. A big red pushbutton might look cool, but trying to time the “sound stabs” by releasing the switch, rather than pushing it down, seems to complicated for me.