freddie85
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Post by freddie85 on May 13, 2005 16:55:06 GMT -5
Hi,
I was wondering if anyone could explain to me about grounding guitar circuits. I know it's necessary to stop you getting electrocuted if there's some kind of fault etc. What I would really like to know is:
a) What needs to be grounded b) How to do it
I've seen diagrams that say "grounded to bridge", but that always struck me as potentially risky, as might that just divert current through the bridge, into the strings, and, well, into me!
Is there another place to ground to? Somewhere on the input jack? Would that then make use of the ground connection of my amp?
This is something that I don't think I want to get wrong!
Thanks!
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Post by wolf on May 14, 2005 1:17:46 GMT -5
Hello again freddieYou ask many questions. Anyway, here is what John Atchley (founder of the original GuitarNuts website) says about grounding and avoiding electrical shock:
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freddie85
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Post by freddie85 on May 14, 2005 14:22:47 GMT -5
I read that link, but I don't think I understand it. I'm very confused.... all that I know about guitar electronics I've learnt during the past week. So, I still get confused. Firstly, can I make sure I have this right about the wires that come out of the pickups - the positive ones are "hot", and the negative ones are "ground"? So, the negative wires have to be connected to the ground connection? And the positive ones lead into an amp? As I understand it, all the various ground connections need to be routed to the same place - is that right? And then from there, lots of sources seem to suggest that this is then connected to the bridge of the guitar, but I don't know what the purpose of this is. Where does it go from there? Do you ground any shielding as well? And if so, to the same place as everything else? Reading about the risks of electrocution, it seems to suggest to me that when things are grounded to the bridge, all it serves to achieve is the possibility of routing power through the strings, then through the player to earth, which could of course be deadly. I have also read this: "On any good quality guitar, you will find a wire running from the bridge to the earth side of the guitar's wiring. This is the string earth, and is essential for cutting down string hum and noise, and you can add this item to replace it altogether.
Wire together in parallel, a 220k ohm resistor (red, red, yellow and silver or gold) and a .001 capacitor with a minimum voltage rating of 500 volts. Twist the wires and then solder them together on both ends.
Wire this unit inside the guitar between the bridge or tailpiece and the earth side of the circuit, replacing the string earth wire.
In the event of the chassis going live, it will only send about 40 volts through the strings, enough to give you a warning tingle without hurting you. It will allow enough leakage for the string earth to operate normally. "
(found at; www.harmony-central.com/Guitar/Faqs/faq/faq.grounding.txt)So would I be right in saying that doing this would conduct any current that happened to find its way to the strings to earth, bypassing the player? I'm also confused about what is meant by "the earth side of the circuit". Isn't this the part of the circuit that's connected to the bridge anyway? Also, I think I read somewhere about a ground connection at the jack socket (presumably this would have something to do with the amplifier's grounding?). Would this be a good place to connect the "negative wires" in order to ground them? Or is the bridge connected to this via the above string earth idea? I'm sorry for not understanding all this - I'm really trying! And also very sorry for the length of this post... I'm just scared that I'm going to wire up a guitar I've made and end up electrocuting myself. I've even pondered buying one of those rather expensieve wireless systems as this seems to be the safest thing to do. Thanks!
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Post by StratLover on May 14, 2005 17:10:26 GMT -5
Hello freddie85, Your assumption is correct to a point. The Positive and Negative BOTH are connected to your amplifier via your volume comtrol, the 1/4"output, then your cord and finally to your amp. Nothing between your amplifier plug and you goes to EARTH unless the electrical circut you happen to be on is grounded to EARTH or equipped with a ground fault circut interrupt. Newer homes and newer clubs have to comply with the codes of electrical wiring for a particular year built and are required to also use particular electrical components as well. The reason for putting a large capacitor in between YOU and the amplifier is simple. The capacitor lessens the electrical shock you would recieve if you were otherwise un-shielded. Here are some other things for you to consider. If you are not currently gigging at local venues that have a sound system that is touched by WAY too many hands in the course of a week, or an electrical system that is most of the time overloaded and outdated, or using an older model vintage TUBE amplifier that has been fooled around with by an otherwise non-qualified person you have absolutely nothing to fear. This mod. is for the ones of us that indeed do use common stage equipment and older tube amplifiers. Should you really feel the need, there is a step-by-step construction of this mod. on the old "GN" site at: I do realize that there are a lot of sites out there that will show you how to do specific mod's and I will tell you this with some partiality, "GN" and it's founder "John Atchley" experimented through the YEARS to perfect the mod's contained on that site. I myself would not trust another mod. of shielding than the one contained in the above link. This post was from "wolf": Anyway, here is what John Atchley (founder of the original GuitarNuts website) says about grounding and avoiding electrical shock. Above all, take your time, and if you get frustrated, walk away and pick it up again later. Remember the old saying "Rome was not built in a day" and moreover your life is worth more than ANY guitar mod. if you yourself have ANY doubts at all.
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Post by JohnH on May 14, 2005 17:13:25 GMT -5
Freddie,
Long queation followed by long reply. (If anyone else reads this, I would be grateful for a tick or a cross depending if they agree)
I dont think you are too far off with your grounding, based on the diagrams you posted the other day. In fact, if you just build what you drew, it should basically work out fine. (see Will this work? post)
Heres a few more points on grounding:
There is never an intention to have any dangerous voltages at all in a guitar. The dangers only happen if your amp is faulty and if what should be the ground connection to the chassis goes to mains live.
Do you have an amp of reputable make that is in good condition? - If so, theres no problem.
Are you planning any 1960's style rock festivals in the middle of a field durring a thunderstorm? - Acoustic guitars sound nice too!
Theres two aspects to the grounding design, related to the 'sound' signal. and to noise.
For the 'sound', the amp and the guitar form a circuit in which very small currents generated by the pickups flow from the pickups, through the output wire to the amp and back through the ground to the pickups. Very often, one side of the pickups are directly connected to the ground wire but not always. Your circuits, with phasing and series/parallel etc do it via switches. Same result however.
With regard to noise, the wires in the system, pickup radiated interefernance from mains hum and radio frequencies. All stuff we dont want. If this is intercepted and conducted to ground it will go away and not affect the signal that we do want. Thats why it's advisable to screen the guitar cavities with a conductive material which is connected to ground, and why guitar leads are shielded.
With regard to the bridge ground: The bridge and strings form a large antenna sucking up interferance from all around and reradiating it, right into the pickups beneath. We ground the bridge to get rid of this. The thing about the resistor and capacitor (instead of a wire, to the bridge from ground) is that this RF interferance is very high frequency and low power and will pass easily through a capacitor/resistor to be cancelled out to ground. If however, the worst happens and your amp goes bad with a live ground, the much lower mains frequency is mostly blocked by the cap, giving you a 'jolt' rather than a 'zap', suggesting that it may then be a good time to unplug. I dont think that many commercial guitars have this cap/resitor feature, they mostly have the wire to the bridge, but it seems like a good idea.
Why take all grounds to one point? This is considered the best way to avoid ground loops. The fundamental thing is that all routes to ground (being, on the guitar, the outer jack connection) must have only a single possible path. This is easiest to check, if they all go to one point, then that point goes to the jack. I believe its also OK if other branches come in along the route as long as no electron, on its journey from a point being grounded to the jack, has more than one possible route.
What is a ground loop? - heres where I get wooly, someone else please correct if disaggreed. In an environment full of mains interferance, currents are induced in any conductive object where a closed circuit can be developed. If that circuit is also low resistance (such as a loop within a group of grounding wires as advised against above), those currents could be significant and cause signals in our output, Cut the loop however and they cant occur. (its something like that, actually I still cant really see why they'd be significant in a guitar, but Im prepared to believe. My guitar has a nice ground loop joining all the controls. I cut the loop and it made no difference!)
Finally, run a grounded wire as a single spur to all the bodies of your switches. This is not part of the signal path but may reduce noise when you touch them. Alternatively, if you shield te inside of the scratch plate, this will also ground the control bodies.
regards
John
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Post by JohnH on May 14, 2005 17:17:31 GMT -5
Hey Stratlover - you posted while I was writing!. I agree with all you say, do you agree with my reply. i dont want to underplay any risks
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freddie85
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Post by freddie85 on May 14, 2005 17:48:29 GMT -5
Thanks guys, I think that's cleared up most of my confusion! Have I been thinking of something backwards with respect to grounding to bridge? Is that connection for conducting noise from the strings, rather than conducting current from the pickups etc. to the bridge? John, just to clarify - you are suggesting that I need to connect the switch bodies to ground - is that literally just as simple as soldering a wire onto each that runs to ground? Actually, this may be slightly on a tangent, but is it possible to (and has anyone ever done it) put some kind of curcuit-breaker or fuse in the guitar circuitry? I know little about such things, but wouldn't that break the circuit if there was an amplifier problem etc that could cause a shock? Just a thought that popped into my head as I was reading. For the record, I don't use any vintage amplifiers etc. Nor do I gig at venues (I wish I was good enough!). I only have a little Marshall amplifier - one of those ones made for bedroom guitarists like me! I forget the wattage, I don't think it's much. I take it Marshall are reputable So I guess there's not a major chance I'll electrocute myself, but I just wanted to be sure there was a zero chance, rather than a million to one chance! Especially not having wired a guitar before. I don't, of course, want to face any risk if I get good enough to play with a band and use lots of equipment etc, and still use the guitar I'm planning. -Thanks
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Post by JohnH on May 14, 2005 18:02:11 GMT -5
My understanding is that the current required to blow even a small fuse is sufficient to blow you, particularly since thay take a little time to pop. So they are not used in this way in guitar circuits.
For the switches, I added a toggle to my guitar and i just soldered a wire to a washer which the shaft goes through- works for pots too. Actualy its hard to solder to a large object like a switch body, it sucks all the heat away.
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freddie85
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Post by freddie85 on May 14, 2005 18:09:29 GMT -5
John,
Thanks, that sounds simple enough to do.
I guessed the fuse idea probably wouldn't work, but I thought it might be an interesting possibility.
So, I was thinking about the nature of the bridge ground connection backwards then?
-Fred.
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Post by StratLover on May 14, 2005 19:09:20 GMT -5
Absolutely John I'm glad between you myself and ALL the rest of the "Nuts" we are able to help others out. I wish I had your short and subtle way of explaining things. Wait a minute! ;D I am an un-read struggling writer in my other job. Thanks for your input with this could have been a most serious matter.
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Post by GuyaGuy on May 15, 2005 3:46:29 GMT -5
hey, while we're discussing grounding basics, let me ask a question.
in the unlikely event that an electric current IS felt thru the strings, what is the best thing to do?
of course, the QTB should prevent this unlikely event and it's only happened to me once. (that was with a 60s ampeg amp in a practice space with some VERY dodgy wirings.) nonetheless, i think all of us would feel better knowing we could react properly. i simply stopped touching any metal on the guitar and swtiched off the amp.
what IS the thing to do? is touching the metal case of the cable dangerous?
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Post by JohnH on May 15, 2005 5:09:21 GMT -5
Thats a good question Guyaguy. If the ground has gone live, then the outer case of the jack is probably also live, and maybe the case of the amp too. My vote would go for pulling the amp mains plug out wthout touching anything metal.
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Post by bam on May 15, 2005 7:50:04 GMT -5
If your strings are zapping you, it could probably be that your amp has a "ground leak". It is most common in unproperly grounded amp (no matter if it's SS/tube) since the current picked up from the amp's shielding cannot go to the ground; In tube amps, it can also happen when a tube breaks, and in that case, the voltage sent to your hand could reach hundreds of volts. JA's QTB™ capacitor (a.k.a. "The Big Cap") does not prevent string zapping 100%, but reduce it to a small "bite". In that case, I suggest re-checking your house's grounding or at least your amp's grounding. (of course your last resort is an amp technician,btw :lol: )
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Post by roadtonever on Aug 10, 2010 3:03:02 GMT -5
Sorry to bring up this old thread, I just want some clarification on application of the shock protection mod. I assume the lead wire coming from the bridge is correctly connected to common ground from the factory as touching the strings reduces hum. On my guitar the connection point is the neck pickup volume pot on my bass it's the tone pot.
Is soldering the bridge ground lead to one leg of the parallel cap/resistor combo and the other leg to the pot sufficient?
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Post by newey on Aug 10, 2010 6:04:39 GMT -5
RTN- You've resurrected one of the oldest threads on this board, 5+ years ago. That's a record! Not only sufficient, but that's the only way to do it. The connection must have one route only, through the cap. Over the past years, several people have made several points concerning this issue, and rather than link to all of them, I'll try to summarize the Board's "collective wisdom": - There are two possible hazards to protect against. First, with older tube amps, a fault can develop where DC + plate voltage can short to the ground, thus putting several hundred volts of DC to the player. Second, on any amp, a mains fault can put AC (110V or 220V, depending on where you live) onto the ground. The original QTB mod sought to alleviate the first risk, and was later amended to help with the second.
- In either event, the circuit breaker or fuse on the mains should pop- but this doesn't happen instantly, and the capacitor mod is designed to provide a moment of protection until this happens.
- Risks can also be minimized by using a GFCI (also called a "GFI"), which is a "ground fault circuit interruptor". If you play your guitar using primarily one outlet at home, use a GFI on that outlet, or get a power strip with its own circuit breaker, like the ones used for computers and such.
- The risk can be eliminated completely with a wireless setup. As pointed out, the real risk comes not at one's home, but from dodgy-wired House PAs in clubs, and that's what the capacitor is meant to address. But consider the use of a wireless system for gigging. Also buy and use a circuit tester to check the House wiring before you plug your amp in at a club.
- Putting the cap on the string ground protects the player from a voltage through the strings, which is after all where one's hands usually are. But this still leaves all the other metal components as a potential risk- pots, knobs, switches, etc. If you're going to open up the guitar to do this, better still is to collect all the grounds to one point ("star grounding"), and wire the capacitor between that point and the output jack negative lead. This will then protect all the metal parts of the guitar from the hazard except the output jack itself. One would still get a shock if the failure occurred just as one happened to be touching the metal of the jack, but that's a minimal risk.
- For a fuller explanation, read this:
The "Blocking" Capacitor
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Post by roadtonever on Aug 10, 2010 18:39:05 GMT -5
Mains power is 50Hz/230v where I live. I assume I should seek out a higher voltage rated capacitor?
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Post by newey on Aug 10, 2010 21:01:53 GMT -5
No, the 600V value recommended by ChrisK in the article I linked should still be sufficient. Remember the 2 separate failure scenarios I mentioned above? The 600V value was recommended by Chris because a DC plate voltage fault can put up to 600V DC (this is decidedly not a good thing) onto the operator. However, the cap blocks DC once it charges up, so any shock to the operator should be momentary only, as the cap charges up. In the case of the AC mains fault, the cap doesn't prevent a shock, it just lessens the blow, so to speak. In the article, he estimates it down to 25mA based on US mains current. Yours will be different at 230V, of course, and the difference could be calculated- but not by me, there's vectors and differential equations involved. But the voltage in an AC situation can't be more than your 230V, so a 600V cap is plenty big. As Chris also noted, in the AC case, while the cap can lessen the shock, 25mA can still kill under the right conditions- wet socks on a beer-soaked concrete basement floor is the usual description of those conditions around here. A history of cardiac problems is another determinant. IOW, using the cap doesn't provide "perfect safety". It may help reduce the risk in certain situations. So far as anyone knows, the cap has never been "tested under fire", in the sense that no one knows of any electric shock incidents on cap-equipped guitars. The benefits are purely theoretical at this point. Luckily, the risk is small- but real! Install the cap, but also use a GFCI, outlet tester, and preferably a wireless system as well. Only the wireless provides complete electrical safety short of the odd lightning strike.
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Post by roadtonever on Aug 12, 2010 16:00:53 GMT -5
A few more question before I pick up the parts from my electronics supplier. I have the choice between ceramic, multilayer ceramic and polypropylene capacitors. Is any suitable? Do voltage specs matter for the resistor?
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Post by D2o on Aug 13, 2010 11:52:59 GMT -5
Lots of folks use lots of different things with no ill effect, but I think we have more or less come to accept polypropylene metal foil caps as being a pretty good choice.
The little green chiclet-looking ones will be fine, or you can use orange drops, or whatever tickles you.
The voltage does not matter on tone caps nor on treble bleed resistors.
The voltage VERY MUCH matters on the DC blocking cap - seek out 400V to 600V (and lean towards the higher if you can).
Cheers, D2o
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Post by roadtonever on Aug 14, 2010 10:17:38 GMT -5
Wouldnt a paper-in-oil cap make the eventuall shock more pleasant? Seriously though thanks for the advice. I'm glad I found a 630VDC 1nf polyprop cap locally. As for the resistor I can get metal oxide type rated 4w/750V at 220k. Now my understanding of electronics is very limited but I suppose it's is better to avoid carbon types as behave more erratically to fast voltage changes. If nothing else may be the higher rated resistor would reduce the need to replace the circuit in case of shock?
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Post by roadtonever on Aug 17, 2010 6:12:35 GMT -5
Still don't know which 220k resistor to get.
Metal film 2W 500V Metal film 3W 750V Metal oxide 1W 500V Metal oxide 2W 500V Metal oxide 3W 750V Carbon film 0.25W 500V
I'm sure I'd play it safe with the highest rated metal film type. Though it would be nice to know if I use the cheaper components without adverse effects as I intend to add the curcuit to all my guitars as well as all my friends guitars and costs do add up.
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Post by newey on Aug 17, 2010 7:06:48 GMT -5
You should read this, from the original GNutz site: There isn't going to be any "cycling" of voltages in this application. Understand that the cap provides the voltage protection, the resistor acts to allow some of the noise to go to grond around the cap. As noted in the article above, with a 1nf cap, more noise can be expected than with the 33nf specified in the GNutz scheme. Not that the original GNutz scheme doesn't use a resistor, and is implemented on the jack ground, not just on the string/bridge ground.
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Post by roadtonever on Aug 17, 2010 11:04:46 GMT -5
Times like these I wish I had at least attended a primary electronics course. I've read The guitarnutz.com article which made me believe resistor+cap for extra protection at the expense of noise is the way to go. With known safe and tested power source and amp one could wind an old guitar string between a knob and the bridge. Do you mean that a robust resistor I'm aiming for defeats the purpose of the circuit? I can see an some advantage/disadvantages either way. The resistor is suposed to break down rather than robustly feed current during an electrical failure.... On the other hand after a the event of electrical failure the player (ie my friends) might remove the circuit and continue to play "unprotected" or some hack guitar tech (like me ) might use wrong values when replacing the circuit. So maybe maybe then the cap value needs to be changed If one intended a robust circuit to not be an pointless excersize. And with the revised robust circuit: Hello, more noise!... I hope my assertions are mostly correct as I need to wipe away the perspiration from my forehead now....
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Post by newey on Aug 18, 2010 0:22:33 GMT -5
Better start wiping! In other words, let's go back to basics here. No. This circuit is not a fuse that burns out. In the unlikely event of an electrical "event", it shouldn't need replacing. There are 2 separate schemes being floated here, and I think you're confusing the 2. 1) a cap and resistor, wired in parallel, across the bridge/string ground. This scheme provides protection only to the strings/bridge, and the resistor is used to allow some of the noise to find ground; the cap is what blocks the voltage in the event of a short. This scheme does not provide any protection in the event of a DC plate fault in a tube amp; it only helps minimize AC current in a mains fault situation. 2) A 400V .33µf cap, without a resistor, wired between the "star ground" (a point where the string ground and all other grounds are collected) and the output jack negative lead. This protects all metal parts of the guitar except the output jack (and plate) itself, and provides some protection against both AC and DC fault scenarios. It should not add noise, making the use of a parallel resistor unnecessary. My advice is to use scheme #2, forget the resistor, and live happily ever after. Follow the original Guitarnuts instructions for shielding, star grounding, and the cap.
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Post by roadtonever on Aug 18, 2010 4:57:07 GMT -5
Alright newvey, I'll get the .33 cap. I'll just add it to string ground for now as I have festival gigs coming up and I wouldnt want to rush a first-time shielding job.
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Post by roadtonever on May 18, 2011 19:37:04 GMT -5
Been 9 months already! The festival gigs never materialized and the band is no more. I have the .33uf 400v caps at hand however. I'm still unsure if I can simply add it between string ground and common ground. Avoiding ground loops was a premise for this mod to work, right? I'm not sure If I have ground loops of not. I suppose it will be easiest to get definite help on this if I show you guys my diagram. Here it is: i222.photobucket.com/albums/dd187/theworkoffire/SeriesParallelRotary3x4.gifi.imgur.com/t1KVa.pngimg153.imageshack.us/img153/8679/hoof.png On volume push-pull What I have in my cavity is a mashup of all three diagrams with a push-pull for phasing. I have made sure to connect as many (-) leads and pot/switch case leads(chassis ground?)to common ground unless it would brake a switching function I needed. I'm thinking one such case could be the a push-pull I'm using for phasing. Or maybe not, I really have no idea :/ I also have a brass sheet glued to the cavity plate (backrouted, unshielded stock) connected to common ground. I'm thinking about adding some more brass sheets to the pickup cavities in the same fashion. I may have digressed a little by now, sorry. One last thing I'm unclear about is the .1uf cap is mentioned as an alternative with pots an switches not being protected, what are the contitions that would require it?
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Post by newey on May 18, 2011 21:41:56 GMT -5
RTN-
No, avoiding ground loops is a good wiring practice to follow but has nothing to do with whether the project works or not (at least, not as far as anyone knows).
You can do so, this will provide some protection when one is touching the strings or the bridge but will not protect any other metal bits (like a Jazz Bass control plate, for example) that you might happen to be touching when you have an "event". Touching the strings is clearly the most likely scenario, though.
On the string ground, you may want to use the cap and resistor option as discussed above.
If you use a star-grounding scheme as shown in the original G-nutz description, the cap goes between the star grounding point and the output jack negative. This covers you on all metal parts you might be touching except the jack plate and jack (on a Strat-type git, anyway).
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Post by roadtonever on May 19, 2011 10:34:37 GMT -5
If you use a star-grounding scheme as shown in the original G-nutz description, the cap goes between the star grounding point and the output jack negative. This covers you on all metal parts you might be touching except the jack plate and jack (on a Strat-type git, anyway). Okay, that's what I want to do. Could you tell me about the requirements of a star grounding scheme or look at the diagrams I linked to and see if they can be compatible?
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Post by newey on May 19, 2011 21:30:43 GMT -5
Your diagrams are certainly compatible with star grounding. Star grounding isn't tied to a particular wiring scheme, it's a general principle for a means to collect the various wires that need to be grounded.
Review the original G-nutz diagram, linked to above. It's a better explanation than any that I could give you.
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Post by Yew on May 22, 2011 13:56:53 GMT -5
I have to do a question on that for my degree, as soon as i start revising for my exam on wednesday ill work it out (we are doing a circuit with an inductor, capacitor and resistor, I know that will be on, so ill work out what a cap would to for 230v ac)
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