GeMusic Posted April 21, 2002 Share Posted April 21, 2002 I recently bought a used Washburn Solid Body Nylon String guitar. Once I plugged it up (into an LR Baggs Para DI into console) I noticed a terrible hum. When I touched the volume and tone knobs (all of which are metal) the hum pretty much stopped. I then inspected the guitar and noticed a stray wire soldered across all three pots (volume, tone, tone). The end of this wire was taped (yes, taped not soldered to anything)to the shielded side of the electronics cavity back cover. When I touched the silver (shield), the hum stopped. I then removed the 'ground wire (I guess)' from the shield (the back cover) and touched the end of it....the hum stopped. So, when ever I touch any of the metal components that this 'stray ground wire' is attached to, including the wire itself...the hum stops. Other than that, it's the noisiest thing I've ever heard. I've plugged up other guitars and they're all silent. How can I fix this problem?? Is it a grounding issue or something else? I also noticed that the 9 volt battery wires (red and black) were cut in half and soldered to other wires--a black one and white one going into the electronics along with the piezo pickup wire..etc. I'd appreciate any advice. Thank you. Link to comment Share on other sites More sharing options...
Christopher Posted April 21, 2002 Share Posted April 21, 2002 Weird. To get rid of stray noise, the ground wire should be connected to the ground of the output jack, not the shielding. (Alternately, you can connect a second wire from the shielding to the ground of the output jack.) Some electric guitars have a ground wire connected to the bridge of the guitar, which stops the hum, provided that you're touching the strings. This obviously doesn't work for a nylon stringed instrument. Link to comment Share on other sites More sharing options...
Nollykin Posted April 21, 2002 Share Posted April 21, 2002 Originally posted by Christopher: Some electric guitars have a ground wire connected to the bridge of the guitar, which stops the hum, provided that you're touching the strings. This obviously doesn't work for a nylon stringed instrument.aahhhh... thats why my guitar hums a bit (when the amp is turned up) and stops when I touch the strings. Weird. Nolly "Money, Bitchez and Cheese!" http://www.playspoon.com/nollykin/files/voxline.gif "I never thought about it, and I never stopped to feel - But I didn't want you telling me just what to think was real. And as simple as it comes, I only wanted to express- ...But with expression comes regret - and I don't want you hating me." Link to comment Share on other sites More sharing options...
signal1000 Posted April 21, 2002 Share Posted April 21, 2002 You can also do "string grounds" on guitars that have a ground from the bridge but still hum unless you are touching the strings. This involves running a ground from the saddles. With regards to grounding, a star ground should always be used. A bus ground is where you join ground wires together and run one to a single ground. This is very susceptible to noise. A star ground means you run all your ground wires to one ground spot individually. Here is some useful wiring info that someone posted on the http://www.agi-lace.com user forum: =========================================================================== Tim Stanley's FAQ for rewiring/grounding questions Also see my shielding FAQ since shielding and grounding are related issues. =========================================================================== Single coils pickup noise. Period. Grounding problems can be subtle. If you a a beginner at wiring your pickups etc, you may have made some subtle mistakes. I have made wiring mistakes myself. Loud humming is certainly a wiring mistake, and likely to be related to grounding. Who knows? Here are a few hints: -------------------------------- Shielding -------------------------------- Shield your guitar with some of that paint you can get from (say) Stewart MacDonald. They also sell tape and foil for this application. It will almost certainly make a difference. Take your time, do a good job, they recommend at least 2 coats, go for 3. I did this to a stock Strat Squier and it cleaned things up quite a bit. IMHO - whenever someone goes to the trouble to open up their guitar for custom work - the first task (particularly with single coils) is to shield the cavity. Do it do it do it. -------------------------------- Hum -------------------------------- Are your pickups single coil or humbuckers? If you are getting noise out of the humbucker - you have a real problem. Talk to an experienced friend. I would bet on a ground problem of some kind, or a bad soldering connection. -------------------------------- String ground -------------------------------- Also, read a book that discusses the use of a string ground. I have seen two types - an actual wire from the cavity/electronics ground to the bridge/strings. And sometimes I have seen a small capacitor between the cavity/electronics and the bridge strings which would provide you protection from getting inadvertently shocked. In any case - check out that, too. -------------------------------- Rewiring -------------------------------- Your wiring should be short and shielded. Short means no longer than necessary - but not even close to mechanically pulling. Shielded means any long run is shielded (especially pickups to switches/pots, and the wire to the output jack). At least one end of the shield braid must be grounded. If you ground both ends, be careful of ground loops. Be *SURE* that all your connections (especially ground) are solid. Sure Sure Sure. If this was you first project with a soldering iron - really double check things. -------------------------------- Ground loops -------------------------------- Are you a EE or do you have electronic tech experience? Do you know what a ground loop is? Ground loops are easy to get into, not too common inside of a control cavity but definitely possible. Craig Anderton's Electronic Projects For Musicians goes lightly over the practical ways one gets into these loops. Basically, there can be one and only one path to ground; and in spite of what you learn in school, all grounds are not equal. One practical matter to remember, even for a college educated EE. All grounds are not alike. Be *very* careful not to create a ground loop. Follow these simple rules: + All grounds should come together at one and only one point (usually the back of a pot case). + Don't use the shield as ground, rather, use it to conduct noise to ground. The sheet resistance of the paint is at least a few ohms - not a good ground conductor, but low enought to conduct the noise to ground. Do you see the difference? + Thusly, there will *never* be two paths to ground. Consider this ground loop (as an example of a loop - this specific case may or may not cause you problems - that is the nature of ground loops!): a) The potentiometer case of the tone control pickup is used as the ground lug of your system. +-------+ +-------+ +-------+ | Tone | | Vol-B | | Vol-N | | | | | | | | | | | | | +-------+ +-------+ +-------+ | | | | | | | | | 0 0 0 0 0 0 0 0 0 b) One leg of your *bridge* pickup volume must be attached to ground. So, you attach that leg of volume control to a wire which is also attached to the case of the ground lug pot. +-------+ +-------+ +-------+ | Tone | | Vol-B | | Vol-N | | | | | | | /----| | | | | | | +-------+ +-------+ +-------+ | | | | | | | | | | | 0 0 0 0 0 0 0 0 0 | | \ | ---------------------/ c) One leg of your *neck* pickup volume must be attached to ground. So, you attach that leg of volume control to a wire which is also attached to the case of the ground lug pot. +-------+ +-------+ +-------+ | Tone | | Vol-B | | Vol-N | /------| | | | | | | /----| | | | | | | | +-------+ +-------+ +-------+ | | | | | | | | | | | | | 0 0 0 0 0 0 0 0 0 | | | | | \ | | \ ---------------------/ / \ / ------------------------------------ d) For some reason, you decide to also attach a wire between the ground connections of these two volume controls. +-------+ +-------+ +-------+ | Tone | | Vol-B | | Vol-N | /------| | | | | | | /----| | | | | | | | +-------+ +-------+ +-------+ | | | | | | | | | | | | | 0 0 0 0 0 0 0 0 0 | | |\ /| | \ | \-----------/ | \ ---------------------/ / \ / ------------------------------------ Now, from the either volume pot's grounded lug - there are two paths to ground: 1: to the other volume control, to the pot case, to the shielded surface of the pickguard, through whatever connection(s) the pickguard has to the output jack. 2: directly to the pot case to the shielded surface of the pickguard, through whatever connection(s) the pickguard has to the output jack. All paths have some resistance, there are two paths here, this is known as a ground loop. Which of the paths is real ground? In fact, both are paths to ground and each has a different resistance. Using shielded wire, etc., it is not uncommon to inadvertently create this situation. The best way to deal with this as far as I know is called star-grounding. Have one point inside the cavity where *all* connections to ground are made. Each and every ground connection comes directly to this point: no side stops allowed, no shortcuts allowed, no other connections allowed. It is probably easy to use a large solder lug of some kind for all of the wires. The back of a potentiometer is typically used for this purpose. Any grounding method that prevents loops is good! Wires that are shielded (and the shield is not used to carry ground), get one and only one end soldered to this lug also. With shields, it may be handy to solder a wire to the shield (careful that you don't melt the insulation on the wires inside the shield), and run that wire directly to the common ground lug rather than trying to drag the shield to the lug, but leaving the shielded wire somewhere else across the cavity. Finally, connect the shielded cavity to this lug once and only once (use some sort of wire mechanically screwed down to the timber or pickguard surface or something). Run a single wire from this common lug to the ground lug on your output jack. You now have no ground loops. In other words, for every desired connection to ground, there is one and only one path to get to the ground point on the output jack. One and only on is the key. Also, IMHO, don't use the shielded cavity as a path to ground - it is not such a good conductor. It entire purpose it to conduct noise to ground. Use it as a shield *only*. Use real wires to connect directly to the ground lug for all cases. I put three coats of shielding paint down - it was nice and thick. I ohm-ed out some long paths on the pickguard and it is definitely a few ohms. This is fine for a shield, but distinctly un-fine for a connection to ground that you must count on. Remember, it is paint, not wire! -------------------------------- Environment -------------------------------- After all of these things are squared away, you axe is as good as possible. If your cables are all good, you are left with only environmental causes. Motors, refridgerators, AC, dimmers, televisions, computers, etc. Good luck, Tim Stanley --------------------------------------------------------------------------- String Grounds --------------------------------------------------------------------------- In my experience, a proper string ground, rather than shielding, will take care of noise that goes away when you touch the strings. It is independent of the shielding issue. Orthogonal issues, you might say. If you shield, but neglect the string ground, you will still get the touching-the-strings-noise-reduction situation. Both are important and if you are in there fixing one, you may as well fix the other, no doubt. =========================================================================== Digest of grounding articles =========================================================================== From: dambik@fnalo.fnal.gov (Ed Dambik) Newsgroups: alt.guitar,rec.music.makers.guitar Subject: Re: Hummmm and buzzzzz Date: 6 Oct 93 12:00:28 -0600 Organization: Fermi National Accelerator Lab In article , rg@futserv.austin.ibm.com (R.G. Keen) writes: > Something I picked up from Dan Erlewine's guitar repair column: > The hardwired connection to the strings puts you at risk of > electrocution if another piece of equipment, say the PA or mixer > has a leak to its ground. You're grounded through the strings > and bridge, and the leakage from the other piece of equipment > flows through *you* if you are holding strings and grab a mike. > It is less risky to connect the bridge to the signal ground > through a 100K-200k resistor in parallel with a .001 capacitor. > This establishes you at RF ground through the cap and spaces > you 200K ohms off 60 Hz ground so the leakage doesn't zap you. Very good advice. I had an old tube amp which, if plugged in the wrong way, zapped you when you touched the guitar strings. Turns out cement floors aren't the best insulators either. Used to be able to light up a neon bulb by holding one lead and touching the other to the strings. IN those days, I played an Electrified guitar. > While we're on grounding - if youever take the time and effort > to tinker in your amp, replace the two wire line cord with a > three wire cord and ground the chassis to safety ground. This > protects you from a fault in your equipment, and dramatically > reduces the hum and buzzing from your setup. It can cause > problems with ground loops in complicated racks, but that is > another problem. This was the solution I used. Worked great. Ed --------------------------------------------------------------------------- Newsgroups: alt.guitar From: rg@futserv.austin.ibm.com (R.G. Keen) Subject: Re: Hummmm and buzzzzz Date: Thu, 7 Oct 1993 15:00:10 GMT Organization: IBM Coporation - Advanced Workstations and Systems. I looked up Erlewine's article, and he attributes it to Adrian Legg. The circuit values are 220K and .001 uF. Since this resistor never has any significant current flow in it (that is the point!) it does not need any significant power rating. Beyond being long lasting and not mechanically fragile, any 220K will do. I used 1/4 watt carbon film. The .001 cap should withstand at least the line voltage peak where you are. For USA, with 120VAC, a 250 volt cap is good enough. for UK, make it at least 500 V. I used a ceramic disk cap. If you want to use premium, high power and high reliability components, you should go ahead. I decided that since there is no significant electrical stress on them other than perhaps voltage, I would use parts that fit easily in the cavity of the Strat. Your mileage may vary. R.G. --------------------------------------------------------------------------- From: backstge@aol.com (Backstge) Newsgroups: alt.guitar Subject: Re: HELP - Guitar SHOCKS me! Date: 22 Oct 1994 03:04:11 -0400 Organization: America Online, Inc. (1-800-827-6364) In article <388ted$4qr@hermes.unt.edu>, sed0001@jove.acs.unt.edu (Scott Everett Douglas) writes: This excerpt from Adrian Legg's "Customizing Your Electric Guitar" may also help: "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. " -Richard --------------------------------------------------------------------------- From: gwatts@cv.hp.com (gary watts) Subject: Re: Grounding problem on a LesPaul Date: Fri, 3 Feb 1995 22:10:59 GMT Adam Gotheridge (adamg@xnet.com) wrote: : I have a hum problem with my 79 Les Paul. I f I am using a lot of gain it : is very noticeable. Anyway, I find when I touch the strings the hum gets : louder, but if I touch either of the pickups the virtually goes away. I : know on strats their is a ground wire attached to the bridge, is their : supposed to be one on a Les Paul also? It makes sense to me, but I don't : see where you can run a wire to the bridge. There is not always a string ground in Les Pauls. They rely on the metal covers to provide the shielding for the pickups. If you have replaced the pickups with an aftermarket pickup, you will almost certainly need a string ground. There has been some debate about string grounds on the net regarding safety. If you are grounded thru the amp and touch a object that is not grounded, you caould get quite a jolt. All this to say that there can be problems with having a string ground. I personally do use them as I want the guitar as quiet as possible. On Les Pauls, you can solder a wire onto a spring from a ball point pen and drill a hole from the control cavity diagonally to the large studs for the tailpiece. Unscrew the tail piece studs and feed the wire thru the hole. Reinstall the stud. The spring provides contact with the stud and is invisible. Solder the wire to any ground point like the back of a pot. Gary Watts Newsgroups: rec.music.makers.guitar Organization: Tandem Computers, Inc. From: COLLINS_JIM@tandem.com (Jim Collins) Subject: Re: Help! My Tele is buzzing! Date: Mon, 02 Dec 1996 10:56:58 -0700 In article <57ttad$id5@blackice.winternet.com>, jkodadek@winternet.com (J. Kodadek) wrote: > > It's starting to get obnoxious. If I don't touch it, it buzzes like crazy > (away from all CRTs, amp, etc). As soon as I touch the strings, bridge, > volume/tone knobs (etc) it stops. It also stops if I roll back the volume > all the way. I'm no electrical wiz, but is this a grounding problem or > what? BTW, I noticed it awhile ago, but it's getting worse. > > > P.S. It's not the cord, I've tried others. > > jess kodadek > jkodadek@winternet.com Jess, It sounds like a grounding problem. The metal bridgeplate of a Telecaster has to be grounded, in order to eliminate this buzz. If your guitar originally had a vintage style bridge pickup, no special grounding would be needed, because the vintage style bridge pickup has a copper-coated plate underneath the pickup, and this plate serves to ground the bridge. If your Tele has a newer style pickup, without this metal plate, then the bridge must be grounded. This is a very simple procedure. Remove the control plate and the bridge plate. Thread a wire through the channel between the bridge cavity and the control cavity. If you can find a wire that is not solid core, but stranded, this will work out better -- you'll see why in a bit. The end of the wire that is in the control cavity should be soldered to the casing of either the volume or tone control. It doesn't matter, since both of these are part of the ground circuit. The end of the wire that is remaining under the bridge should be stripped of insulation for about an inch. If the wire is stranded wire, spread the strands out. You are going to lay the wire on the body of the guitar, underneath the bridgeplate, so that when you bolt the bridgeplate down, it will make firm contact with the bare wire. If the wire is stranded, it is easier to bolt the bridge plate down -- if it is a solid core wire, you'll really have to crank the bridgeplate down, in order for the wire to dig a little trough into the body. Whatever the type of wire you are using, when you bend the wire over the edge of the bridge pickup cavity onto the top of the body, you'll want to bend the wire where there is no insulation. If you bend it where there is unsulation, the bridge plate won't bolt down properly, and it may not make contact with the ground wire. When you try it out, if there still is a lot of noise, there are two other things to check. The first is the neck pickup. If it has a chrome cover, the cover must be grounded. The chrome cover usually has three tabs -- two of the tabs are on the side of the pickup opposite the lead wires. These tabs are merely bent over, in order to clamp the top in place. The third tab is right where the lead wires are connected to the pickup. This tab is actually inserted into the base of the pickup, and it must be soldered to a ground lug that you'll see on the bottom of the pickup. The final thing to check is the control plate itself. The control plate is supposed to be conductive, and it is supposed to serve as the common ground to all the controls. It is possible that the connection isn't good. You can connect the volume pot casings to each other, and to the base of the selector switch by merely soldering a wire accros the sides of the pot cases, and to a part of the switch that does not come in contact with the wipers. There ought to be a little rivet hole down very close to the bridge plate. All this ought to handle the ground noise, but it won't help the normal RF noise that is part of the joy of single coil pickups. Nothing will kill that. Good luck. Jimmy Newsgroups: rec.music.makers.guitar From: ai585@lafn.org (Gil Ayan) Subject: Re: electricution Organization: The Los Angeles Free-Net Date: Thu, 12 Jan 1995 19:28:01 GMT In a previous article, rogers@sasuga.Hi.COM (Andrew Rogers) says: >In article edyk91@ursa.calvin.edu (Edward Dyk) writes: >>Recently I read a book dealing with guitar electronics and it made mention >>of the possibility of electricution due to a grounded bridge & not using >>shielded pots and jacks and switches and such when in the presence of >>a 'reverse ground loop'. Is this a REAL possibility or just like the >>possibility of being 'stuck by lightning.'? >Alternatively, there is an RC network - Stew-Mac suggests something like >a 220K resistor in parallel with a .001mfd (500V) capacitor - which you can >wire in series with the string grounding wire (wrap the whole thing in >electrical tape or, even better, heat-shrink tubing). It will effectively >still act as a virtual string ground at weird-noise frequencies, but at 60Hz >it will reduce a potentially lethal 220V shock to a merely uncomfortable >30-40 volts. The above claim should work. Before soldering the ground cable to the bridge, just put a small cap (0.001 - 0.022 Uf will do) in *series*. You actually don't need the resistor, but of course there's more than one way to skin the cat... The bottom line is that the cap will block out deadly DC that could fry you. If you wanna play it *real* safe, buy a wireless and go with that. Other than Mickey mouse induced currents, nothing will get into the guitar. You are guaranteed safety with a wireless...of course, it'll cost you and you need to watch the batteries (they go dead), etc. Above all, make sure your amp is properly grounded (you should never lift the ground of an amp), and watch out if you daisy chain things. If you do, you should make sure all the chassis of the amps have a common ground and smae with the negative terminals of their power supplies. -- ______ __ __ ______ __ __ / __ / / /_/ / / __ / / \/ / Gil Ayan / /_/ / \__ / / /_/ / / / / / email: ai585@lafn.org /_/ /_/ /_/ /_/ /_/ /_/\__/ Newsgroups: rec.music.makers.guitar From: jrg@hplb.hpl.hp.com (John Grinham) Subject: Re: electricution Date: Fri, 13 Jan 1995 14:01:04 GMT Organization: Hewlett-Packard Laboratories, Bristol, England Andrew Rogers (rogers@sasuga.Hi.COM) wrote: > In article edyk91@ursa.calvin.edu (Edward Dyk) writes: > >Recently I read a book dealing with guitar electronics and it made mention > There are a couple variants on the Shielding FAQ which I'm sure others will > be happy to post. Basically, though, you want to cover every potential In addition to this use an RCD (Residual Current Detector - sometimes called an earth leakage detector) on the mains supply to your gear. It'll automatically trip the supply if the buzz you're getting is no longer just the music.... John. From: Dr.Distortion@bbs.mhv.net (Dr Distortion) Newsgroups: rec.music.makers.guitar Subject: Re: electricution Date: 14 Jan 1995 17:39:46 GMT Organization: MHVNet, the Mid Hudson Valley's Internet connection Mel Waldorf (Mel_Waldorf@brown.edu) wrote: > Seriously, you can be hurt badly by the right combination of > circumstances. Ground the electronics either to the bridge, or if the > guitar has a floating bridge, ground to the tailpiece, or any way to get > the strings (and you) grounded. Sorry Mel, but this is exactly what you DON'T wanna do. The reason you get the shock in the first place is because your body happens to provide a path to ground when your bridge or tailpiece is grounded. The best thing to do is DISCONNECT this deadly "string ground" and shield the inside of the guitar with carefully-applied copper tape or shielding paint. I did this to my Strat; and even though it has single-coils, it doesn't hum or buzz. If electric guitars were sent to UL (or CSA, for our Canadian friends) for safety approval, most would fail because of the string ground. This is just the manufacturers' cheap way of getting around proper shielding and is, IMO, inexcusable. --Dr.Distortion at STAUDCO, New York Newsgroups: rec.music.makers.guitar From: till@netcom17.netcom.com (Don Tillman) Subject: Re: electricution Reply-To: don@till.com Organization: NETCOM On-line services Date: Sun, 15 Jan 1995 04:26:57 GMT From: Dr.Distortion@bbs.mhv.net (Dr Distortion) Date: 14 Jan 1995 17:39:46 GMT Mel Waldorf (Mel_Waldorf@brown.edu) wrote: > Seriously, you can be hurt badly by the right combination of > circumstances. Ground the electronics either to the bridge, or if the > guitar has a floating bridge, ground to the tailpiece, or any way to get > the strings (and you) grounded. Sorry Mel, but this is exactly what you DON'T wanna do. The reason you get the shock in the first place is because your body happens to provide a path to ground when your bridge or tailpiece is grounded. If I might respectively disagree with my esteemed collegue Dr. Distortion... The path to ground is not the problem here, it's the source of 120/220 volts coming in contact with one's body that's the problem. Sure, that voltage wouldn't have much of an effect if one wasn't grounded, but that's no reason to take it out on the guitar. The best thing to do is DISCONNECT this deadly "string ground" and shield the inside of the guitar with carefully-applied copper tape or shielding paint. I did this to my Strat; and even though it has single-coils, it doesn't hum or buzz. If electric guitars were sent to UL (or CSA, for our Canadian friends) for safety approval, most would fail because of the string ground. This is just the manufacturers' cheap way of getting around proper shielding and is, IMO, inexcusable. Not true. There are oodles of industrial and consumer products with grounded metal chassis on the market passing UL/CSA/whatever approval left and right. It's a very reasonable and common practice. Jim Patrick (jpatrick@ralvm29.vnet.ibm.com) wrote: > I have an early 70's Super Reverb that in addition to the 2 prong > cord, has a ground-lift(?) switch (that in many cases still > doesn't keep you from taking a 10,000 volt arc from microphone to > upper lip). Anyone know if this amp requires more than just > adding a green wire ground to the chasis to make it safe? Yes: disable that "ground" switch. Rather than "lifting" the ground, that switch actually connects a capacitor between one side of the AC line and the chassis. This was originally done as a cheap and dirty way of filtering the AC coming in to the amp, but it doesn't really work all that well and it also causes quite a shock hazard to boot. Depending on the position of the switch, your amp chassis (and thus your guitar) can be "live" by as much as 120 volts! (220V in the UK). Link to comment Share on other sites More sharing options...
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