Learning Electronics
September 16, 2004 2:48 PM   Subscribe

I've devised what I believe to be a simple project for myself to help me learn some basic electronics skills. however, being an absolute neophyte, I know not where to begin. [perhaps there is more inside?]

I'd like to add a button to my guitar that will mute all sound when it's pressed. my guitar is unique in that it is hollow with a top consisting almost entirely of pick guard (see what I mean?) so I imagine it would be easy to modify the wiring beneath and add switches and toggles and the like. but like I said, I've never built or modified an electronic device in my life so I don't know where to begin.

I'm not asking for a walkthrough (but if you are so inclined, by all means go ahead!) but maybe a list of tools and supplies and some sort of basic steps that I could go off and research on my own would be helpful? thanks in advance!
posted by mcsweetie to Education (13 answers total)
There's no guitar picture at your link, AFAICT. Be that as it may, if you're trying to put a "mute" button on an electric guitar, it's not as easy as all that. It's easy to put in a switch, and after you press the switch, the sounds stops, but you're very likely to get clicks & pops and other nastiness just as you press and release.
I don't know how to take care of that in any simple way (but I'm not a practicing audio EE). But if you just want to hack around on the wiring in your guitar, you should be good to go with a wire stripper, diagonal cutters, shielded cable scraps, heat shrink tubing, and a 10-15w soldering iron.
posted by spacewrench at 3:11 PM on September 16, 2004

Just a thought -- maybe if you haven't built any electronics in your life, perhaps you might want to start with building a mute-switch into a box that you can plug between your guitar and your amp...then that way you won't be knocking holes into your guitar until you're handy with the soldering iron.
posted by Vidiot at 3:22 PM on September 16, 2004

oops! the link should work now.

I think Vidiot has the right idea.
posted by mcsweetie at 3:42 PM on September 16, 2004

if they're passive pickups then a simple switch might work ok, in my uninformed opinion (passive means that b1tr0t's shift in voltage levels isn't a problem, i think).

you need a knife, some pliers for cutting things, a soldering iron (a simple one is fine), flux-cored solder, a stand for the soldering iron that includes a little sponge thing (you can probably by soldering iron, stand, solder, and maybe some other stuff in a "starter kit" from an electronice store), wire, a switch, and some insulating tape to wrap round things. you can also buy a funny looking contraption with crocodile clips on a stand that holds wires while you solder them - that's really useful.

is the idea that you hold the button down and it's silent until you release (ie a kind of performance related thing), or do you want something that switches on and off?

practice soldering stuff first. google for soldering advice.

this is a good choice of project, i think, because there's no high voltage involved.
posted by andrew cooke at 4:24 PM on September 16, 2004

mcsweetie: Effectronics seems to be a very good page for learning how to build electronic effects for guitar, including tips for beginners and a section on theory. i'm no engineer but from the looks of the theory page at least, a high-school-level grounding in physics/electronics should be enough to let you follow what's going on there.
posted by louigi at 4:34 PM on September 16, 2004

okay, here i am wasting time reading about guitar effects. this article seems to suggest that a good no-popping-sound guitar mute is a patent-worthy thing, which may discourage you from trying it as your first project.

but if you go for it, more power to you.
posted by louigi at 4:42 PM on September 16, 2004

Also, those "crystal radio"-type circuit-building kits aimed at kids (you can get 'em for about $10 at any Radio Shack, I think) are good for teaching you how a circuit works, reading a schematic, et cetera.

Also, "Getting Started in Electronics" by Forrest Mims is a good introductory book.
posted by Vidiot at 4:47 PM on September 16, 2004

I don't know about building a "mute" button (although I'd implement it as a switch between the volume knob and the output jack, easy-peasy), but I'm an electronic moron, and I managed to wire up an old Strat copy a few weeks ago with individual in phase/off/out of phase switches for each pickup. Easy as pie. There are plenty of diagrams on the web (check Guitar Nuts, for example) but really, there is nothing at all complicated about the wiring of most electric guitars (with a few exceptions).
posted by uncleozzy at 5:26 PM on September 16, 2004

Andrew, if they're passive pickups, the abrupt cutoff and bouncing both still matter. The abrupt voltage change will be amplified by the amplifier, leading to a pop. Bouncing will create many abrupt voltage changes, thus many amplified pops.

The simplest solution I can think of to both problems is to use a solid-state switch controlled by your physical switch, with a simple filter between the physical switch and the solid-state switch. The first problem there, though, is that it would need a power supply.

So if providing a power supply (5V DC from any standard AC adapter - you can buy one at RadioShack) is okay, something like the following could work:

The signal from the guitar just passes through a FET (field-effect transistor) on its way to the amp. The FET acts like a switch. It can be turned on or off (or something in between) depending on the voltage on its gate (one of the transistors connections/leads).

Your physical switch will control the voltage at the gate, to turn the FET switch on and off. To prevent the abrupt change and the bouncing, a very simple resistor-capacitor filter can be used. The filter will smooth out the transition, so the voltage that controls the FET will ramp up (relatively) slowly from the off to the on voltage (and back down when the switch is flipped/released). This Java applet might help you understand how a resistor and a capacitor can smooth out the abrupt change from a switch.

So overall, you would need four parts: 1 switch, 1 FET, 1 resistor, and 1 capacitor. And a bunch of wire.

That's a really inadequate description, but I think the basic idea should work. Hopefully it can help lead you in the right direction.

But then there are things to learn about like voltage polarity (your signal will be bipolar, meaning it will alternate between positive and negative), ground (simple enough concept in theory, pain in the ass in practice), avoiding interference (shielding is important - make it a metal box, but don't be surprised if you somehow add buzzing to your signal), and so on.

Hm, now that I think of it, you might need more than I described above. The FET might need both a positive and a negative voltage relative to the signal's ground... Not impossible, but yeah, half-baked idea.

Well, have fun! It is a good project, and you'll learn about all sorts of different things while doing it. Go a step at a time, though. First try to make a box that you can pass the signal through. Use a breadboard inside to let you easily change around your circuit. So first just make the circuit a wire you can disconnect just by pulling one end out of the breadboard. See how that works, how it sounds. Then move on to adding a physical switch or button. From there, add the FET (if that's what you use), then the filter. I think this is a good project to go step by step towards more and more complex things in an understandable way, at your own pace.
posted by whatnotever at 6:07 PM on September 16, 2004

i have a bass with passive pickups plugged into a cabinet here by my side. it's on - if i play a note, i can hear it. if i pull out the cord it goes silent. no pop. passive pickups mean no dc offset. switching ac is not hard.

i have a hi-fi in my living room. i have speakers in the kitchen and office. i switch the output between them using - gasp - commercial light switches (like on the wall). again, no pops (although i admit i'm switching the amplified signal here, which is much les sensitive).

reading the article, the only reference i can find to pops is switching the output from op-amps. they're going to have a dc offset, aren't they?

i agree that you can get *some* noise from bounce. if i thought i was giving advice to a sound engineer i would be less confident. but i honestly don't think (and, more importantly, don't hear in the two examples above) that the noise will be significant here.
posted by andrew cooke at 6:49 PM on September 16, 2004

whatnotever has a pretty good idea, but I believe a more standard solution is to use an "analog switch" IC. You can get models specifically designed for audio, and some can do fancy things like ramp the voltage up or down over a few millisec to get rid of the popping issue. You might try poking around in sci.electronics for suggestions on manufacturers and model numbers.
posted by Galvatron at 8:18 PM on September 16, 2004

i meant that switching the amplified signal is less likely to cause an audible pop. if you switch the signal earlier (before amplification) then any change in dc levels is amplified and you're more likely to get a pop (in either case the final signal level switched is the same, but noise in the switching is amplified if the switch comes before amplification)

a little googling turns up this. their third case reads:

finally, for true-blue mechanical switches, if the signal itself is not at exactly zero volts when the mechanical contacts touch (and bounce a few times!) this makes an instantaneous change of signal level just because the **signal** is suddenly connected. This tends to be smaller, but some people hear this as a pop. If the switch bounces a bunch, there is a whole train of these on-again, off-again signal bounces, so there's a "crackle/pop" sound if it's really bad..

that is quite reasonable. as they note, this is less significant than most "popping" which is caused by changing dc levels. note that in this case, you're going to get an instantaneous non-zero level only if the guitar is playing. in that case it will be even harder to hear any pop, since you'll also get the surprise of the sound being cut.

do you really think electric guitars have analogue switch ics in their bodies to do their switching (say to change pickup selection)? have you ever looked at the electronics in a typical electric guitar?

finally, can anyone explain how a switching that is not audible is going to damage speakers? serious question - they're expensive and i don't want to blow them. the only dangers i can see is if they had different efficiencies and the amp was higher rated than the speakers (so you run the risk of switching from low efficiency to high and getting horrendous volume levels), or high frequency spikes damaging the tweeters. the latter case seems more worrying, but would be audible, as far as i can see. remember that this is passive switching after amplification, so it's hard to see what would drive the spikes.
posted by andrew cooke at 5:10 AM on September 17, 2004

We call this a 'kill switch' over on guitargeek.com. If you're interested in learning about simple guitar mods, the folks over there are a great peer group.

You'll need a soldering iron (40 watt or so, cone tip), a screwdriver, a brace-and-bit, some 22 gauge wire, some narrow-diameter rosin core solder, a tin of rosin flux, and if you're getting older like me, a good light source for your tired eyes. I also find a pair of large tweezers helpful, and if you're really into it, you can get some alligator clips mounted on stands to hold everything in place.

I love tweaking with guitars - it's one of my favorite things. So relaxing!
posted by ikkyu2 at 5:57 AM on September 17, 2004

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