Does anyone know how I can engage an onboard effect when inserting my guitar's jack plug? I want to turn on some LEDs which are powered by watch batteries mounted in the control cavity, but I want this to happen when the jack is inserted instead of using a separate switch.
Easy as pie. The only catch is, you need a particular kind of jack, the ordinary, run-of-the-mill unit won't do the job. The usual name for this is a stereo jack. (Specifically, a 3 conductor ¼" phone jack.) Expect to shell out somewhere between 2 and 5 dollars, depending on where you go. (Even cheaper at some bargain-bin joints, but those are probably used, or of extremely low quality. Just be aware here.)
Essentially, you'll connect the battery's negative side to the "Ring" terminal on this new jack. When a standard guitar cord (mono!) is plugged in, the plug's metal sleeve will touch that terminal's contact arm, as well as the metal collar of the jack (called the bushing, it's where you tighten down the nut). The plug itself will now conduct current from the battery to the bushing, which is of course, connected to ground in some way. Most guitars use a wire to make that ground connection, but it could also be the shielding material on the back of the pickguard. Either way, the circuit is completed, and if your LED's are also properly grounded, they will now light up.
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warmstrat, if all you want is for the LED to come on when you're playing, maybe get brighter when you hit the strings harder, it's pretty easy.
Split the signal into a small amplifier with a couple leds on the output.
If it was me (and I'm frankly not the least bit interested in doing this), I'd build one of those distortion pedal circuits which use LEDs in the clipping stage. The TurboRat is one, I believe. Split the signal after the buffer section (might require a second buffer before the amp section?) and put a switch at the output to switch between the clean and distorted tones. The LEDs should light either way.
You would not want this little fuzz box to be true bypass, or else your LEDs would only light up when you're actually hearing the fuzz.
The TurboRat uses 2 x LEDs, one for the positive swings of the signal and one for the negative. You could just use one, and get an asymmetrical clipper similar to the the Harmonic Percolator. Should sound a little more "tubular".
You may to alter the feedback path in the amplifier to change the amount of available gain to get optimum the "sound to light" experience. And you might find that once you've got it tweaked to look good the overdriven signal won't actually sound the way you want (or need) it to.
Also, if you really want to get fancy, these multiple-LED style "VU-meters" that are ubiquitous in audio gear nowadays aren't really all that difficult to build. The hardest part is the fine tweaking that gets them to read consistently to some specified standard.
edit (because I got excited and pushed the post button early) - You've now got a buffer built into the guitar in order to safely split the pickup signal to the LED amp (whether you intend to ever hear the distorted signal or not) without loading problems. This means you won't get the effect of the cable capacitance rolling of the extreme high harmonics. This could make the thing sound overly harsh or brittle or bright. I think it's ChrisK that just recently told somebody on another thread how to choose a capacitor to simulate that cable. If it was somebody else, I'll happily modify this post to give credit where it's due.
Last Edit: Dec 17, 2007 14:19:49 GMT -5 by ashcatlt