The World’s Biggest Fuzz Box? Mama Mia!!!

With regard to the capacitor to "ground" the bridge: I still consider this a "band-aid" but I suppose if you never touch the output plug or amplifier chassis and only the strings you could be spared electrocution. In any case it will do no harm. Just be sure the capacitor you use is properly rated for this kind of protection - ordinary capacitors are not. Look for Type Y "Line-to-Ground" capacitors rated for 250 VAC. They're specifically intended for this kind of use (where failure can cause death or injury). Another point, while a voltmeter (VTVM or DVM) can indicate POSSIBLE hazards, it won't tell you which is innocent and which is lethal. Any device with a 2-prong plug has a small leakage current (enough to pass the tiny current drawn by a voltmeter) so you may be alarmed to find 50 to 100 VAC between the chassis of your CD or DVD player, for example, and ground. But, because the current is limited (UL requires it to be under 750 micro-amps) there is no hazard. However, a guitar amplifier (or any piece of equipment with a 2-prong AC connection) can be defective and show the same voltage. The difference is that the defective equipment can supply 10 milli-amps (enough that you can't let go) or 100 milli-amps (enough to kill you). With a 3-prong plug, that hasn't been defeated of course, you have no worries. I mis-typed my e-mail address in a previous post - it really is whitlock@jensen-transformers.com. Contact me if you want a copy of my paper on the true origin of ground voltage differences among AC outlets. There are many other tutorials at our website. - Bill Whitlock, president & chief engineer, Jensen Transformers, Inc., Life Fellow of the AES, Senior Member IEEE.

The purpose of the string ground capacitor to block 120/240 volts from the players hands is valid. It is not a cure for bad amplifier grounding or anything connected directly to the player. As Bill mentioned, other metal parts will still be at ground potential, like metal knobs, jack plates, 1/4" instrument cables. 1980's era Gibson Les Pauls had internal metal covers for the controls and switch, those guitars were not fitted with a string ground as the entire electrical system was encased in steel.

The purpose is to prevent lethal voltages from stage microphones. Many stage sound systems have poor or unsourced grounding. Many times I watched an opening act get nasty lip burns from poorly grounded sound systems. That would usually give me a good laugh as I knew my instruments would not cause that problem. A DVM is a good tool to bring to these 'gigs' just to test voltage potentials between the grounded case of a stage mic and your guitar. However, watching someone burn their lips was also a good test as long as I wasn't the DUT.

Screening cavities are not enough to prevent buzz, the P-90 plastic pickup covers on mine are lined on the insides with 3M adhesive copper foil tape. That is very effective to reduce buzz pickup in those. The humcancelling P-100 pickups also require this if you want to remove the buzz pickup. The Gibson mini humbuckers that also fit this cutout are entirely encased in metal and don't have that buzz problem. Outside of using either of those two pickup replacements, the only other option is to remove and reverse the magnets in one pickup and reverse wire the pickup coil wires. That will create an in phase hum cancelling effect when both pickups are on together.

No vintage amps are being used, i.e., the type that used to have polarity-reversing switches. Nearly all new guitar amps are polarized internally vis the ac cord's one-way-only plug. Also, everything is well grounded and shielded as pointed out in the article. We are essentially going for consistency of noise performance between a fairly large number of the same efects pedal. Yes, those P-90s are a challenge in this respect.

Regarding "on another note" - this is a serious safety issue that shouldn't be dealt with by the "band-aid" described! If the ground wire to the bridge is "lethal", it means all other guitar metal (output jack, etc.) is lethal, too. This indicates a fault in the amplifier or other device the guitar is plugged into. Most dangerous of these are "vintage" guitar amps that have 2-prong AC cords. They were designed long before modern safety standards existed and most had a rather large-value capacitor (often old paper-dielectric and wax dipped) connected from one side of the incoming AC power to chassis. If it happens to fail, the chassis of the guitar amp can become energized at 120 VAC. Even if it didn't fail, the capacitor allows several mA of 60 Hz current to flow (which can cause a nasty but non-lethal shock). New standards either limit this "leakage" current to 0.75 mA (which feels like a slight tingle) or less OR requires a 3rd prong on the power cord to ground the chassis (protecting you against electrocution, the ultimate shock!). NEVER EVER disconnect or defeat this third prong (I've seen them clipped or twisted off or, more commonly, defeated with a 3-to-2 prong adapter) - several guitar players have been killed this way, and with "vintage" amplifiers that suffered a simple part failure. I highly recommend replacing the 2-prong power cord set on any vintage guitar to 3-prong grounding (have it done by someone knowledgable if you're not) cord set. An ungrounded amplifier can kill, for example, if he touches a microphone that's properly grounded to its grounded amplifier and simultaneously touches a metal part on his guitar that's plugged into a defective ungrounded guitar amplifier. Another story: some of you may recall that a preacher was electrocuted in Waco, TX several years ago as he was standing in a baptismal tub when he was handed a microphone. It turned out that there was nothing wrong with the microphone or the amplifier it was plugged into - all were properly grounded. What killed him was the fact that whoever replaced the electric water heater for the baptismal didn't bother to connect the green (safety ground) wire to the heater. Because of a corroded heating element inside the heater, the water was energized at over 90 VAC ... and that's what killed him. Musicians in general are at high risk because so many are ignorant of what that grounding connection does. Disconnecting it is NOT the way to eliminate hum or buzz ... you'll be betting your life!!

For anyone who'd like to measure and/or locate the source of 60 Hz magnetic fields, I'd recommend the AlphaLabs "Tri-Axial" meter. It has a very sensitive 0 to 3 milli-Gauss range that makes it very useful. Generally, the background field should read under 1 milli-Gauss. I was once called to a rehearsal studio whose complaint was that one end of a stage was unusable because of hum in electric guitars. The field measured over 70 milli-Gauss ... and was due to 13 A flowing in a cold water pipe under the stage. Even though there was no apparent problem with anything electrical, the problem was traced to a extra neutral-ground bond in a recently-installed sub-panel for an air-conditioning unit. Code allows only one such bond and it must be at the main service entrance panel. Once found, the problem was fixed in a few minutes by just removing a jumper in the sub-panel. Another common source of magnetic fields from premises wiring is the ubiquitous "3-way" light switch (where two switches control the same light). General advice for troubleshooting: turn electrical things off one-at-a-time to check the effect.

As Bill said, the source is magnetic fields entering the P-90 single coil pickups. That must be addressed at the source. I also use the P-90's as they have a unique tone quality. This can be done one of two ways: the use of a stacked-humcancelling pickup design like the Gibson P-100 or the use of a hum cancelling coil/circuit. Any use of mu-metal will require annealing of the metal after re-shaping and the thickness will interfere with some of the string harmonics.
I prefer the circuit as stacked single coil pickups do not have the same tonal characteristics due to doubling the windings and other changes.
I use a circuit utilizing low noise, low power opamps. I installed a dummy coil using a Japanese Fender Stratocaster coil with the pole pieces and magnets removed. That was shielded with copper foil tape (as the rest of the innards are done) and mounted. The circuit has two stages, one a buffer/preamp for the pickups and another for the dummy coil. With some filtration and phase reversal, I achieved a -80 db null of the hum pickup. Trimpots are provided to fine tune the null. The results are 1960's single coil electric guitars with no noise, hum or buzz. After that, any fuzz tone is quiet. I also have about 6 of them I use here. All are quiet.
On another note: electric guitars are fitted with a wire to the bridge to ground the strings preventing buzz pickup. This can be lethal. How OSHA misses this is strange. The cure is to install a .022 uf cap in series with that string ground. That will allow harmonics to pass but not the lethal 120/230 volts that can give a vocalist a nasty lip burn.

One would think that with today's DSP's, it would be able to very quickly 'learn' the significantly slower 60/120 HZ noise envelope, then track it as it seems to me to change more in amplitude (relative to stage movements) than it does in characteristics. This could then essentially subtracted.

About light dimmers, especially for "Jimelectr" (thanks for your very kind comment). Dimmers create ground voltage differences which then test signal interfaces for noise rejection. This is a "cause celeb" for me since I recently presented an AES paper on the exact mechanism of this coupling(request a copy by sending me an e-mail at whitlock@jensen-transformes.com). Everyone knows $10 light dimmers are trouble for sound systems but, for the first time I believe, this paper fully explains - and confirms with measurements - exactly WHY this is so. Briefly, premises wiring consisting of 3 conductors (line/hot, neutral, and ground) forms a long skinny transformer (line and neutral are the primary and ground is the secondary). As is well-known, the voltage induced in transformer secondary is proportional to the rate of change of current in the primary. A standard 600 W dimmer, set at 50% power (you've no doubt noticed this is the worst case), causes over 8 A of peak current with a risetime of about 5 micro-seconds. This induces a large peak voltage over the length of the ground wire (causing a voltage difference between AC outlets). This mechanism is, by far, the dominant source of hum and buzz when signal interfaces can't reject it (the paper has much more detail). Unbalanced interfaces inherently are unable to reject this noise ... and it's why balanced interfaces should be standard on anything that calls itself "professional"!

I think Droche is right - noise comes in off the raw pickups and you have to deal with it. Routing, I agree, is not an option. There are some good hum-canceling P90 pickups that are the same width, but still require a depth route. To cancel hum with no routing you would use a mini-humbucker - something that Gibson came up with in the late 60's to be able to put humbuckers into bodies that had been routed for soapbars (called it the Les Paul Deluxe). They sound like a cross between a soapbar and a full-size humbucker, making them very versatile.

In response to "Jimelectr", the issue here (or with any electric guitar) is NOT noise pickup in the cable - unless it's broken, of course. Balanced interfaces are used to make interfaces immune to external electric and magnetic fields impinging on the cable and, more importantly, to make the interface immune to ground voltage differences between the signal source (here the guitar) and signal destination (here the FX box or amplifier). Neither of these is a significant problem with guitars (since the guitar is not independently grounded and magnetic fields would affect the pickup long before they were strong enough to affect the cable). Since Jensen Transformers, my company, is widely recognized as the expert on ground loop and system noise issues, we often get calls from guitar players who think the hum is due to a ground loop issue and want to use our transformers to "balance" the guitar's output. I've never heard of a guitar hum/buzz problem solved this way ... see my earlier post.