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Bridge Ground Capacitor


ihocky2
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I have read a bunch of places about including a capacitor on the bridge ground to work as a safety in the event that the wall outlet is wired poorly and you get high voltage traveling through your axe. I was just wondering why to use a capacitor instead of a very small resistor. I would think the resistor would blow out quicker, which seems like it would be better. Or will the resistor have some affect on the grounding of the strings where a capacitor doesn't?

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It has nothing to do with the component burning out. The idea is to limit the possible 60 Hz current in a fault situation to non-lethal values while normally providing a low impedance path for the higher harmonics that cause "buzz". I consider this a bad strategy because you cannot really be sure the current will be low enough to be safe, but if you think you are safe, you might not bother to test the grounds. You must make sure that everything is properly grounded.

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My understanding was that by using a low voltage cap in series, it would fry out soon as it saw the lethal voltages, and disconnect the circuit. Appears I was wrong. Electronics was never my strong suit, thanks for the information.

This is off the top of my head, but I believe when a capacitator dies it goes to a short? If so, this wouldn't help at all in blocking wall voltage.

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I've only seen this done 600V caps. I've had long discussions with my father about it, and we came to the conclusion that it may help, but probably not, so don't rely on it. But when talking about mains, you can never be too safe. As said above, when you feel safe, you may stop bothering to test grounds.

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From what I've read, the capacitor is very similar in its function to the couplings capacitors found in tube amps. In other words, they allow AC currents to pass but block DC currents.

I would suggest reading http://www.guitarnuts.com/technical/electr...afety/index.php also

I believe a capacitor's farads or microfarads determines its low-frequency cutoff. So (I think?) you could have a cap that will block DC as well as 60 hz AC but not higher AC frequencies. That's probably what the intention is with these things.

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From what I've read, the capacitor is very similar in its function to the couplings capacitors found in tube amps. In other words, they allow AC currents to pass but block DC currents.

I would suggest reading http://www.guitarnuts.com/technical/electr...afety/index.php also

I believe a capacitor's farads or microfarads determines its low-frequency cutoff. So (I think?) you could have a cap that will block DC as well as 60 hz AC but not higher AC frequencies. That's probably what the intention is with these things.

Where would the DC come from? And while you're busy 'splaining that one, move on to where would the 60Hz AC come from... And what higher AC frequencies would we be protecting ourself from? 120 hz? Even higher?

The use of a cap in grounding a guitar as explained on the guitarnuts site - is nothing more than a solution in search of a problem. Read the disclaimers carefully - and you're realize they claim nothing at all.

The cap idea is dangerous to your health because it leads you to believe you are doing something to protect yourself - when no protection AT ALL is provided.

Improper grounding won't give a dang if you ground your guitar through a cap or not - and come to think about it, proper grounding of AC equipment won't give a dang grounding your guitar though a cap either. In other words, grounding through a cap or not, you will still be just as dead if you don't pay attention to proper grounding.

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Where would the DC come from? And while you're busy 'splaining that one, move on to where would the 60Hz AC come from... And what higher AC frequencies would we be protecting ourself from? 120 hz? Even higher?

Dude, you're funny. :D

Of course blocking 60 Hz wouldn't be enough. But if there was wall voltage on your bridge, it would be 60hz AC. That's where it comes from. Hope it didn't shock you. :D

I can't for the life of me figure out why you would put a cap there. That's why I was listing some reasons that somebody who doesn't know what they're doing might try it.

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Where would the DC come from? And while you're busy 'splaining that one, move on to where would the 60Hz AC come from... And what higher AC frequencies would we be protecting ourself from? 120 hz? Even higher?

The use of a cap in grounding a guitar as explained on the guitarnuts site - is nothing more than a solution in search of a problem. Read the disclaimers carefully - and you're realize they claim nothing at all.

The cap idea is dangerous to your health because it leads you to believe you are doing something to protect yourself - when no protection AT ALL is provided.

Improper grounding won't give a dang if you ground your guitar through a cap or not - and come to think about it, proper grounding of AC equipment won't give a dang grounding your guitar though a cap either. In other words, grounding through a cap or not, you will still be just as dead if you don't pay attention to proper grounding.

That is pretty much why I asked this question. I couldn't figure out what a capacitor would really do in the circuit. I took a extremely basic electronics course for a few weeks, about 10 years ago and remember the instructor hooking a 1 watt rated resistor inline to a 110v lightbulb and turning the light on. It took a few seconds but the resistor burned up and broke the curcuit. That is why I wondered if a resistor would work as part of a ground bridge. I would think a 1/4 watt 10M ohm resistor would fry out pretty quick and break the circuit. You would probably get a pretty good shock, suffer some injuries, but hopefully the circuit would break quick enough that it wouldn't kill you. I know a lot of the higher voltages, tend grab the victim and not let them go. At least by breaking the circuit, the victim would be broken from the circuit.

I do agree though, that the best practice is still to test all outlets before plugging into them.

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Couldn’t you just wire an inline fusible link into the ground between the pot and the bridge? This way, if the current passes through the link at higher than lethal voltages it blows the fuse. Use an automotive fusible link. It would always blow before you got zapped. This would not help with limiting buzz but a properly shielded circuit should'nt have excessive buzzing anyway.

However, as said several times. A good outlet tester is the best way not to get zapped.

Edited by zyonsdream
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+1 use a fuse - that is what Taylor is doing on their new solidbodies.

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+1 use a fuse - that is what Taylor is doing on their new solidbodies.

Genius. I'm definitely doing that when I wire up my electronics for the new build, even just for peace of mind.

I just did some reading, Taylor uses a 5-milliamp fuse. Where in the chain would be the best to put it? I was thinking right after the output jack. As much as I myself don't want to suffer from horrible electric shock, I imagine it mustn't be good for the electronics of the guitar too, so putting it right after the jack might save the equipment as well.

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If I were going to install one I would install a short lead from the back of my pot and wire it in-line with the wire going to my bridge. I’d make sure it was inside the control cavity for easy replacement if necessary. I suppose you could put it at the end of the electronics chain. I’d have to experiment to make sure that it didn’t cause signal degradation since a wire fuse isn’t shielded.

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"It's the mills that kill, the volts that jolt"

That was the old saying at vo-tech. A capacitor will do nothing except maybe reduce some noise, only a fast-blowing fuse will protect you from the current. 100 mA will stop your heart, a 5 mA fuse like Taylor is using is good enough if it blows in time. Best practice is to carry an outlet tester with you to ensure that the house wiring is good.

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-1 on safety. Rely on yourself, your sense and safety procedure as opposed to dropping all that in favour of something you have no guarantee will work, even if it does in theory. Which this doesn't. Unless you get hit with some crazy amped up megahurtz.

Although +1 on the cap adding mojo somewhere, maybe.

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+1 use a fuse - that is what Taylor is doing on their new solidbodies.

Genius. I'm definitely doing that when I wire up my electronics for the new build, even just for peace of mind.

I just did some reading, Taylor uses a 5-milliamp fuse. Where in the chain would be the best to put it? I was thinking right after the output jack. As much as I myself don't want to suffer from horrible electric shock, I imagine it mustn't be good for the electronics of the guitar too, so putting it right after the jack might save the equipment as well.

You install in the same place as Taylor, the bridge ground. If you install it as part of the output and the fuse blows then you will no longer have output.

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