#1
I've never seen this mod before so bear with me while I try to explain it. I've got a cheap Les Paul knockoff and I'd like to mount a small metal plate, about the size of a coin (US quarter dollar) on the pickguard, right where my fingers would rest if I was the type of player that anchors the pinky/ring fingers. Under the plate, a wire would be soldered to it, run through a hole in the pickguard, and under the pickup ring (I'd have to make a hole for it). It would be connected to either the output jack or the pickup selector output, whichever works best. When this plate is touched (by my fingers), it would ground the signal and effectively be a killswitch. I'd install a push-pull pot so i could toggle this feature.

Why would I do this? I play flamenco guitar which incorporates a lot of rhythmic tapping on the face of the guitar simultaneous with right-hand technique. This mod would allow me to continue playing while creating rhythmic variations with volume cut-outs.

Would this work?
Last edited by Sabicas at Jul 1, 2013,
#2
What you'd have to do is rig up a touch switch. They are super simple. You can use a darlington transistor but a cmos logic gate would probably be better. Anyway its not hard. The touch circuit will ground the signal when activated. The metal plate will actually have to be two metal plates about 1/16 inch apart-- not touching but close enough to bridge with your finger. I can get a couple diagrams later. Its after 4am here...
Last edited by Invader Jim at Jul 1, 2013,
#3
Quote by Invader Jim
What you'd have to do is rig up a touch switch. They are super simple. You can use a darlington transistor but a cmos logic gate would probably be better. Anyway its not hard. The touch circuit will ground the signal when activated. The metal plate will actually have to be two metal plates about 1/16 inch apart-- not touching but close enough to bridge with your finger. I can get a couple diagrams later. Its after 4am here...



So, I'm curious why my plan wouldn't work? Would contact with a human body not be sufficient to ground the signal? I don't know that much about this and am trying to learn. Either way, it sounds like you have an easy suggestion. I'm looking forward to your next post.

I get the part about two plates with my fingers bridging the gap, but part of the point of a plate was to have a large-ish area that my fingers can't miss. Hitting that 1/16" gap is going to be more difficult. Some sort of "cant' miss" design would be needed.

Thanks!
Last edited by Sabicas at Jul 1, 2013,
#5
OK, you seem to have the common misconception that the human body grounds stuff (so humming noise goes away when you touch strings) but actually the body is a noise source, and the noise goes away because we ground ourselves.

That is why your plan wouldn't work.

Listen to Jim, he knows what he's doing
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#6
Quote by GABarrie
OK, you seem to have the common misconception that the human body grounds stuff (so humming noise goes away when you touch strings) but actually the body is a noise source, and the noise goes away because we ground ourselves.

That is why your plan wouldn't work.

Listen to Jim, he knows what he's doing



Ok, I get it. Also, I wasn't doubting Jim. Like I said, I just want to know why and now I do. Thank you for correcting my misconception.

So, I think I what i need to do is to have two plates, one grounded and one with the "live" signal from the pickups and use my finger to bridge the gap between them. Correct?

Seems simple enough. I just have to find some plate design that creates a "can't miss" field with multiple bridging spots like a yin yang but not as cliche.
Last edited by Sabicas at Jul 1, 2013,
#7
This is a bit trickier than I thought but nevertheless I have this diagram. Be advised that I haven't built it.



It should work fine provided you tweak the resistor and capacitor values to turn the thing off immediately after your let go of the plates. This circuit was originally designed to stay on for a bit after you take your finger off the plates. Original component values were 2M2 and 47uF.

And about the plates, as long as a small part of your body contacts both of them the circuit will switch. They don't have to be right next to each other. For example you could put one plate in the spot where your arm rests then touch the other with your finger.
#8
I think I'm in over my head. Is there a guide i can use to read this schematic you've posted? Is that "9v" suggesting this is active vs passive? I thought this would be a little simpler than what that looks like. Just pulling a lead off a ground and another off the "hot" and bridge them.

What's the reasoning behind the complexity of the schematic? I've read about "popping" sounds when using a killswitch and playing clean. Does your method prevent that?
#9
It really isn't as complicated as you think it is, although it aint as easy as you hoped

The circuit is indeed active. It needs a battery, 3 resistors, a capacitor, an IC (CD4011) and a transistor (not sure which one though...) and ofcourse your metal plates.
I'm not sure if it will pop, because the transistor isn't as sudden as a switch, but if it does, it can be fixed with a single resistor.
If you like I can draw it up on a veroboard scematic (not sure what it's actually called), which you eventually can put in your guitar.

But I am curious. It looks like the dude in the video indeed only has a single plate that he touches.. How does that work then?
#10
You better be careful. Have you ever been shocked in the lips by a microphone? Sucks!
You may be on your way to doing that on guitar. Some times a building may have bad wiring, and if you plug your gear that has mod's such as your guitars or amplifiers you could get a jolt.
Some older buildings don't have a neutral and a ground. Ground is used for safety reasons, its hooked directly to a pole that's dug deep into the dirt. The whole reason behind ground is that if a short occurs due to bad wiring or any other issue, that the ground pulls the current instead of you. I'm not saying this isn't cool, it's like having a three way selector switch with a dead position like Tom Morello. I like it. but I would definitely get your local guitar tech to check things out.
#11
It's difficult to understand why this needs to be active. The killswitches I've seen are a simple radio shack switch which introduces a ground to the "hot" when pressed. Wouldn't two plates bridged by a finger do the same thing?

Also, two plates might not be necessary if my fretting hand is touching the strings which are grounded to the bridge, correct?
Last edited by Sabicas at Jul 1, 2013,
#12
The transistor can be any N-channel JFET. As for popping, a single resistor won't work here. You'd need a resistor and cap to ground on the gate lead of the JFET to keep it from switching instantly, causing pops.

Sabicas: there is a resistance of several thousand or hundred-thousand ohms between the plates when your finger bridges them. This resistance lets enough current flow to activate the circuit but has basically no effect (other than adding lots of noise) without the active circuit. The circuit also buffers against this 'finger noise'.

As for the single plate, some touch switches use capacitance to ground (provided by your body touching the plate) or are operated by a noise spike provided by your body (you can hear it if you touch the tip of your guitar cable while it is plugged into your amp).

As for reading the diagram, there are plenty of tutorials on the web. I have to use my phone for internet so I can't really offer an in-depth primer like I usually would. The diagram just looks complicated because of those intimidating NAND-gate symbols.
Last edited by Invader Jim at Jul 1, 2013,
#13
Quote by Rocket-Man66666
I'm not sure if it will pop, because the transistor isn't as sudden as a switch, but if it does, it can be fixed with a single resistor.

a transistor should actually switch much faster than a mechanical switch. probably will still get a pop though.
Quote by Rockstarscat
You better be careful. Have you ever been shocked in the lips by a microphone? Sucks!

9V DC is not really considered a shock hazard though. if you've ever licked a 9V battery, that's about the worst you could do. and using your finger (much higher impedance) will reduce the current to next to nothing. if using an external power supply you will want to be careful, but with a simple battery you will be hard pressed to shock yourself.


Jim's diagram looks straight forward. other than the metal plates, its only got six parts. you could probably build the entire thing onto the back of the socket for the IC, except for the JFET.

Quote by Sabicas
It's difficult to understand why this needs to be active. The killswitches I've seen are a simple radio shack switch which introduces a ground to the "hot" when pressed. Wouldn't two plates bridged by a finger do the same thing?
this is actually doing something fairly different, so it has to be active. if you want passive, it may be easier to use an actual switch. you could probably find something with a very low travel distance that could work.
#15
Well, after looking at this stuff for a while, I decided to try something. I'm not even sure if I'll like this project when it's complete, so I set out to find a test system with my iPhone. Here's what I came up with. I found a MIDI controller app that can be used to control the JamUp modeling/fx app via Virtual Midi. I use GuitarJack 2 as an input.

I designed a big momentary killswitch button and added a "mode" button that toggles between a normal killswitch and a "resume" switch that only passes signal when pressed. While I was in there, I added some other controls for the fun of it. It all works very well. I'm going to find a way to attach it below the strings in place of my pick guard (again, cheap Les Paul copy). I'll probably use velcro.

This obviously affords a lot more options than a hardwired touch switch, but the biggest problem I see with this is that I'll be restricted to JamUp or some other app for my tones. While it's not bad, it's not fantastic either. In particular, the clean tones are weak.

If I find the effects musical and develop some usable techniques, I'll be revisiting this thread and try to decipher all the new (to me) information that's been contributed.
Attachments:
photo.PNG
Last edited by Sabicas at Jul 3, 2013,
#16
Okay, this got me thinking...

How about going back to mechanical and rigging up a mini momentary switch (wow, that one's expensive (edit: just noticed it's a 4 pack)) into the pickguard mounting bracket somehow, so that pressing the pickguard activates the switch.

The main drawbacks I can see with this are:
1. Not physically having enough room to fit it in.
2. Ideally you'd want the primary activation nearer the strings - this makes it pivot the wrong way.
3. The whole pickguard becomes the switch, not just a part of it.
4. It'll take more than a light touch to activate.

But it does save messing about with active circuits and electronics builds. Just a thought.
Last edited by von Layzonfon at Jul 3, 2013,