Guitar stops buzzing when i touch the strings electricity khan academy


I saw this at a trade show last year, but never played with one. Taylor makes a "string ground" fuse that’s supposed to "blow" before the musician is injured. See and the text below.

Hmmmmm….. The cost is $16 for a pair of 10 mA replacements fuses from Taylor. Seems a little pricey. An interesting idea, but I’m sure it would be inconvenient if a fuse blew and you had a humming/buzzing guitar for the rest of the set. I agree that the shunt capacitor could work if sized correctly, but I doubt that many guitar players would let you hack up their ax. There’s got to be a million guitars out there with all the metal strings and hardware "grounded" to the shield.

String Ground Replacement Fuses. The fused string ground for Taylor Expression System® electronics and electric guitars features a fuse that’s designed to blow in the event of improper electrical ground, in order to protect the player. If the fuse blows, the guitar’s electronics will continue to work, but the strings will no longer be grounded, and the guitar could be more susceptible to electrical hum, so a replacement should be installed. Replacement fuses are compatible with all Taylor fused string grounds, as well as the Taylor universal string ground, designed for other electric guitar brands. (10mA Replacement Ground Fuses, set of 2, #84925, $16.00)

Yup, the idea is to build a GFCI outlet strip with a few of the receptacles set up with a floated "SafeGround" for guitar players. I don’t think the NEC or UL will allow any kind of switches on the individual safety ground paths, even if there’s a GFCI involved. But I think they might allow a few receptacles on the end of the strip (or the entire strip) to be permanently ground lifted with a stinger cap and bleeder resistor, but only as long as there’s a GFCI in that circuit. The idea is to eliminate hard-grounding the meat puppets in the first place, but protecting them from a hot-chassis to earth-ground hand-to-hand fault. And yes, this circuit should protect the musician (puppet) from an RPBG outlet induced shock between the mic and the guitar, even if the mic OR the guitar was the source of the hot-ground voltage.

More to experiment with, but I think this simple grounding system would eliminate electrocution hazards for the guitar player from his amp, while stopping ground loop hum, high-freq buzz, and even providing shock/electrocution protection from a "hot" microphone. And there would even be protection from shock due to Reverse Polarity Bootleg Grounds. I might even have a better filter design than the stinger cap and bleed resistor, but if that works and envisioned I’m keeping it proprietary for a potential patent.

I’m heading out to Texas for 12 days to teach a bunch of seminars, but I’ll build one of these when I get back and test it for guitar-to-mic fault currents and buzz abatement. In the meantime, unless you’re qualified to work on live voltages and measure them safely, then PLEASE don’t go building one of these and wade into the kiddie pool holding your guitar. This is all still highly experimental.

Quote from: Mike Sokol on September 23, 2013, 10:54:15 am I have a diagram to post later, but according to my logic the answer is The Strings Are Grounding You. When you’re holding the guitar but not touching the strings (or anything else grounded) then your own body is ungrounded and picking up all sorts of noise from the environment. This is the same buzzing noise you’ll hear if you touch the tip of a 1/4" phone plug that’s connected to the input of your guitar amp. Since your belly is close to the back of the guitar, this noise voltage is coupled into the unshielded, high-impedance circuity of the guitar (including the pickups). The reason it’s a high-frequency "buzz" and not a low frequency "hum" is that there’s high-pass filter circuit formed by the capacitor formed by distance of your "belly" to the internal guitar wiring.

When you touch the guitar strings with your hand, that provides a low-impedance earth-ground path from your body, through the strings/bridge/tailpiece of your guitar, via the shield of your phone plug, to the chassis of the stage amp, then finally through the power cord to the (hopefully) grounded wall outlet. So any of the ambient electrical noise your body was picking up via a capacitive coupling to the wiring in the walls (and more) has now been shorted to ground, and the noise stops.

If you ask guitar players and sound engineers how this works, I would guess that 99% of them think the opposite, that your body is grounding the strings. But being that the strings are always grounded (should be), then that can’t be what’s happening.

However, I do like the discussion on decoupling caps and 10 mA fuses which could probably stop musicians from being electrocuted. But very few guitars have these features, with the vast majority being wired with strings and all metal pieces being "grounded" to the sleeve of the 1/4" phone jack. I’m sure it’s 99.999% that way in the guitar world unless someone knows something I don’t know.

There’s quite a few different types of buzzes you can hear during a sound check. The one referenced in this thread is caused internally by electric guitars with high-impedance electronics. It occurs when a human is standing very close to the back of the guitar (within a few inches) but not touching the guitar strings. The body acts like an antenna booster, collecting harmonics of the 60 Hz hum all around us, and coupling it into the guitar electronics as buzz. If you turn the volume knob(s) down on the guitar or move away from the back of the guitar, this type of buzz should stop. If it doesn’t stop, then there’s a different reason for the buzz. For instance, if the guitar player is using an unshielded speaker cable instead of a shielded instrument cable to plug into his amp, then the amp will probably be nearly quiet with the guitar volume turned down, but buzz like a swarm of angry bees with the guitar volume turned up, even if your body is far away from the guitar body. If the amp buzzes or hums even with it’s volume control turned down, then the amp itself likely has an open capacitor in its power supply. Also, I’ve been on stages with a lot of big electrical conduits and wiring underneath, and the guitar or bass would buzz/hum depending on where the musician stood or oriented the neck of the guitar.

During a sound check you can only do quick fixes, so if the guitar/amp is buzzing, get the musician to move around a bit and see if it changes. Have them try a different instrument cable and see if it changes. If the backline amp buzzes just sitting there with the volumes turned down, then tell them to get a backup amp.

Also, I found a Yamaha bass guitar a few months back during a sound check that had double pickups and a balance knob to set the relative volume. It hummed/buzzed when the bass player turned this balance knob all the way to the left or right, but was hum/buzz free in the middle. I’m guessing it was some sort of split humbucker pickup arrangement, but once we got his bass hum/buzz free during sound check, I was good to go for the gig and didn’t do more research.

The key to this sort of troubleshooting is to have a quick bag of tricks you can quickly try. If it’s really the instrument doing it, then all you can really do is put a gate on that channel. But I like being able to help a musician figure out what’s really wrong with their rig which helps the next sound guy to work with him or her. Pay it forward…