A little help explaining shielding with archtop guitars?

[chris32895]

OK so I took delivery of a Fender Player Telecaster which I proceeded to copper insulate the body, as I do with all my solid body guitars. The guitar is stupendously quiet, even with stock single coils in my small apartment room with computers and lamps and such. I only get 60 cycle hum if I crank the volume and tone of the guitar or amp practically all the way up. I play pretty quiet so this is no problem. I also have the same level of hum/background noise regardless of if my hands are touching metal on the guitar or not.

Now, if I plug in my Ibanez PM35 archtop into my amp it's pretty quiet unless I take my hands off the strings in which case I get a lot of hum. This is not a huge deal but it is annoying when playing my archtop. Obviously, I can't copper insulate the entire inside of my archtop guitar but is there some other thing I should look at ? Is the pickup bad? I have opened the pickup in it a bunch of times to mess around with different style Alnico magnets in there. I see sometimes that humbuckers have the grounding as a metal shield around the regular hot lead, is that something that would help?

Any help would be appreciated as I play in such a small space that any little glitches or hums really stand out.

[AllanAllen]

I’m in the camp of, Keep your hands on the strings and turn down the volume knob when you aren’t playing.

[sgosnell]

I would first make sure the strings are grounded. That's easy enough to do with a multimeter/ohmmeter. You can still get some noise even if the strings are grounded, but if they're not, there will be noise. I don't know of a practical way to shield the electronics in an archtop.

[Cunamara]

The strings are grounded, if the noise goes away when he touches them. So we already know that. It's remotely possible that the ground connection between the cover of the pickup and the wiring has been disrupted by opening the pickup up to swap magnets (although as long as the cover is soldered back to the base plate, that should not be an issue).

It's more likely that the noise is getting into the circuit through the wiring between the pickup and the controls, and between the controls and the jack. Using properly grounded shielded wiring (e.g., Mogami) might reduce that problem; I do want to emphasize "properly grounded" with this as otherwise the shielding becomes an extra antenna for noise. I discovered this in one of my own archtop guitars, in which the luthier used Mogami wire from the controls to the Switchcraft endpin jack, but did not ground the shield at the jack. Once I fix that, just a matter of stripping the outer insulator away from the shielding and clamping the shield down to the little grounding arm sticking out of the jack, about 80% of my noise problems went away.

[sgosnell]

The strings are grounded, if the noise goes away when he touches them.

That's not what I have experienced. I've played instruments with ungrounded strings (I know they were, because I built them) which were noisy when not being touched, but quiet when I touched the strings. Grounding the strings made them quiet all the time. The strings on the OP's guitar are probably grounded, but it's easy enough to make sure.

[chris32895]

I have used a multimeter checking ground. Doing a connectivity test I get sound when touching a metal tuning post and the grounding sleeve of the guitar cable. I'm fairly certain ground is accomplished throughout the instrument. Also, every time I've disassembled and reassembled my pickup I've ensured the outer pickup cover and pickup body have a solid connection with new solder.

It's worth mentioning that I am using quick disconnect wire ends for the pickup, the pot wiring harness, jack, and grounding wire (that goes to the bridge) for easier removal of the electronics when doing maintenance or swapping pickups or caps, things like that. These are what I used:
Amazon.com

It's been nice having them, but they aren't exactly "audio-grade" wires. I did the same thing in another Telecaster I had (that I sold), but again, that had grounded copper shielding all throughout the body cavity essentially creating a Faraday Cage around the pickups.

[sgosnell]

A Faraday cage in an archtop is probably possible, but not practical. You might try eliminating, or at least reducing, electromagnetic interference where you're playing. Computers, routers, phones, LED and fluorescent lights, Bluetooth devices, TVs, and many more all contribute to the interference. Sometimes moving them can help, but sometimes they just have to be removed entirely. Old wiring in the walls is another contributor to noise if it exists. The placement and orientation of the guitar in the room is also a factor. Sometimes just turning 90 degrees will be enough. In short, it's a complicated scenario, and one I've never been able to solve in every situation. Humbuckers can't completely eliminate hum, they just buck (reduce) it. There are pedals which purport to eliminate the noise, and some swear by them, but I've never used one so I have no opinion.

The use of twisted pair for wiring is sometimes effective in reducing noise. Perhaps twisting the wiring you're using might help, but I certainly wouldn't make any promises. It shouldn't hurt, though, as long as it doesn't shorten the wiring too much. It doesn't have to be a really tight twist, just not straight wires side by side.

[deacon Mark]

All you can do is make sure a ground is done to the strings. This should be done at the tailpiece inside. Run the ground wire to tailpiece hole.

[GuyBoden]

I'd create a temporary ground cable by using some crocodile clips. Attached one clip end to the strings and the other clip to other end to a metal input jack plug. Then see if the noise is less.

These crocodile clips and cable below:

[Bobby Timmons]

Since the hum cuts when you touch the strings, that means the bridge is grounded.

Your only option for improving things is to use shielded (2 conductor) coaxial wire. This is the same principle as shielding the cavity in a solid body. Those clippy wires you posted that you're using aren't shielded and noise gets pickup up by the wiring inside the guitar.

Fwiw: The strings do not need to be 'grounded' in a guitar. If they weren't connected to the electrical circuit in the first place, how could they introduce electrical noise?

The principle of the bridge being grounded is that of a chassis ground. An additional ground in addition to the main ground out the jack, out the amp, out the plug in the wall, into the earth, that helps dissipate noise further.

[rpjazzguitar]

Aero Instruments makes a product which was reviewed in GP.

Basically one end of a wire attaches to ground and the other to something that looks like a penny that you place against your skin. It might be more complicated than that.

I don't fully understand it, but I think the explanation is that your body is an antenna picking some kind of interference and that, when you touch the strings, you're grounding your body. I guess the pickup can sense whatever your ungrounded body is picking up.

Sounds crazy maybe, but one quick test might be to get the hum happening and then walk away from the guitar.

[aquin43]

The player is usually the main source of hum and the purpose of grounding the strings is to ground the player.

Most guitars seem to be already wired with shielded wire. Unfortunately the jack socket and the pickup switch have large metal areas that are part of the live circuit and are usually left unshielded. Wrap those in electrical tape and then in copper foil and ground the copper foil.
Its fiddly to do it neatly and without interfering with the switch action. I have done this to a particularly noisy guitar and cured it completely.

[nevershouldhavesoldit]

Fwiw: The strings do not need to be 'grounded' in a guitar. If they weren't connected to the electrical circuit in the first place, how could they introduce electrical noise?

The principle of the bridge being grounded is that of a chassis ground. An additional ground in addition to the main ground out the jack, out the amp, out the plug in the wall, into the earth, that helps dissipate noise further.

As aquin43 says, this is not correct. Strings don’t introduce noise, but we do. Grounding strings grounds us, which reduces the EMF we introduce into pickups, wiring etc. Here’s the explanation from LindyFralin:

“Grounding your strings is essential for having a quieter guitar. If you’ve ever noticed your guitar’s noise gets quieter when you touch the strings, you might have thought your body grounds your guitar’s parts. You’d be wrong if you did. It turns out, a human being makes a pretty good EMI (Electromagnetic Interference) antennae! Your body is an antenna for all sorts of EMI, so when you touch your guitar strings, the guitar is grounding you! ”

Some pickups and harnesses are more sensitive than others to EMF, which is why some guitars (especially archtops with wooden tailpieces and nonconductive bridge saddles) get away without string grounding. But that’s because their pickup(s) are not highly sensitive to external EMF and they’re wired wisely.

Bridges and/or tailpieces are grounded because this is the only practical way to ground strings. You do not want an “additional ground” - there should only be one ground contact for the entire harness and all attached parts, to prevent loops. All grounded parts should be connected linearly, each to the next one in a chain. Only the last one in the chain should be connected to the ground lug on the jack. The tailpiece or bridge ground wire should be soldered to the back of a pot, not the jack ground. The Fralin website illustrates this too.

[sgosnell]

It's not possible to ground most archtop bridges. Wood is not a good conductor, and can't be soldered at all.

[Bobby Timmons]

@nevershouldhavesoldit, I asked the bot and it said we're both right. Grounding the bridge both extends the chassis ground and grounds the player.

There's a debate on my forum about guitar circuitry. I'm telling people the reason why running a ground wire to the bridge, which also conducts to the strings, dissipates noise is that it's a chassis ground. They think it allows the player's body to be grounded because it's an antenna and the player's body introduces noise to the guitar circuitry. Which is correct?


ChatGPT

The reason for running a ground wire to the bridge of a guitar, which also connects to the strings, primarily revolves around reducing noise, but the technical explanation involves a combination of grounding principles and shielding.
Grounding and Noise Reduction

1. Chassis Grounding: Your explanation that it's a chassis ground is on the right track. The ground wire to the bridge ensures that the bridge, and consequently the strings, are at the same electrical potential as the rest of the guitar's circuitry. This helps in minimizing hum and noise by providing a common ground reference for the entire instrument.
2. Shielding: When you touch the strings (which are now connected to ground), your body becomes part of the shielding system. Instead of acting as an antenna that introduces noise, your body helps to shield the guitar's circuitry from external electromagnetic interference (EMI). This is because any noise your body picks up (which is usually quite a bit, as bodies do act like antennas) gets routed directly to ground through the strings and bridge, rather than into the signal path.

Addressing the Players' Arguments

1. Body as an Antenna: While it is true that the human body can act like an antenna and pick up noise, the grounded strings allow your body to dissipate this noise to ground rather than introducing it into the guitar’s circuitry. So, the act of grounding the strings actually uses the player's body to help dissipate unwanted noise rather than contribute to it.
2. Noise Introduction vs. Dissipation: If the player's body were not connected to ground through the strings, the noise picked up by the body could be coupled into the guitar's electronics through capacitive coupling, leading to increased noise. By grounding the strings, any noise picked up by the body is given a path to ground, effectively reducing the noise introduced into the system.

Practical Effects

When you ground the strings:

• The noise your body picks up is diverted to ground.
• The overall system is more immune to external electromagnetic interference because your body, the strings, and the bridge all form a shield that protects the sensitive electronics inside the guitar.

Conclusion

Your explanation about the ground wire being a chassis ground is indeed correct. The reason this works to reduce noise is not that the player's body inherently introduces noise, but rather that grounding the strings allows the body to act as a shield that helps dissipate noise to ground, improving the overall noise performance of the guitar circuitry.


So your body furthers the chassis ground when you touch the strings which are connected to ground?

ChatGPT

Yes, exactly. When you touch the strings, which are connected to ground, your body effectively becomes part of the grounding system, thereby enhancing the shielding effect and helping to dissipate noise. Here’s a more detailed explanation of how this works:
Enhanced Shielding with Your Body

1. Grounded Strings and Bridge: By running a ground wire to the bridge and connecting it to the strings, you ensure that the strings are at the same electrical potential as the ground. This setup helps in creating a reference point for the entire guitar circuitry, reducing potential differences that could lead to hum and noise.
2. Body Acting as a Shield: When you touch the grounded strings, your body, which naturally picks up electromagnetic interference (EMI) from the environment, becomes grounded as well. This grounding means that any noise your body picks up is routed directly to ground instead of being introduced into the signal path of the guitar's electronics.
3. Dissipation of Noise: Your body, connected to the ground through the strings, effectively dissipates noise. This reduces the overall noise floor of the guitar, as any external EMI picked up by your body is now safely diverted to ground.
4. Enhanced Chassis Ground: By touching the grounded strings, you essentially extend the chassis ground. Your body, which is now at the same electrical potential as the ground, helps to further stabilize the electrical environment around the guitar's circuitry, reducing susceptibility to noise.

Practical Example

• Without Grounded Strings: If the strings were not grounded, touching them would not help in reducing noise. Your body would remain a source of EMI, which could be coupled into the guitar’s circuitry, potentially increasing noise.
• With Grounded Strings: By grounding the strings, any noise your body picks up is shunted to ground. The guitar's electronics are less exposed to EMI, resulting in a quieter signal.

Conclusion

So, when you touch the grounded strings, your body effectively furthers the chassis ground, enhancing the noise-dissipating properties of the guitar’s grounding system. This setup is crucial for minimizing unwanted noise and hum in electric guitars

[teeps]

Just ranting.

On hollowbodies I think the common practice with humbuckers is to use shielded cable where possible and to ground the strings through the tail piece. In case of unshielded single wire routing as common practice on Fender singlecoil pickups then the two wires in any signal path should be routed close together - some twist the pair for even lesser sensibility to picking up field noise. As switching is generally on only the "hot" - i.e. not the "ground" - avoidance of ground loops is the third good practice to observe.

The area where most mess arise is where the signal path is most likely single wire so loops can form to pickup noise. It starts where the inner conductor is separated from the (probably) shielded wire from the pickup (probably the volume pot(s)) and ends at the it enters the shielded cabling again somewhere. This, the control block, would be the area to focus on.

This of course assumes that everything else in the signal path works. It is always good to start by checking if the problem disappears if you try another cable or another amp. Also look for loose assemblies. The grounding of the output jack dose not work optimally if the socket is loose. Even a quality - but worn out - jack cable may have a "loose tip" which does compromise signal transfer. Or if you (later in the chain) use XLRs you may have the possiblility to decouple the grounds (look for a switch labeled "Ground lift").

[nevershouldhavesoldit]

It's not possible to ground most archtop bridges. Wood is not a good conductor, and can't be soldered at all.

Duh……

There are metal bridges, tailpieces, and combos on solid body and semi-hollow guitars. It is these that one grounds to a pot. There are nonconductive saddles, eg nylon, Tusq, etc. As these will not ground the strings, you have to ground the tailpiece if your saddles are not conductive.

[nevershouldhavesoldit]

@nevershouldhavesoldit, I asked the bot and it said we're both right.

You asked “the bot”?!?!?!

Read the answer you got. It says that “[t]he ground wire to the bridge ensures that the bridge, and consequently the strings, are at the same electrical potential as the rest of the guitar's circuitry.” No it doesn’t. It ensures that the bridge and strings are at the same electrical potential as the chassis ground. If the signal path (which I hope you will agree is also part of the guitar’s circuitry) were also grounded, there would be no signal.

I suspect Lindy Fralin has a bit more practical knowledge than “the bot”. Do you know how they train those public AI bots? They feed them everything they can find on the internet, whether or not it’s validated. Algorithms are developed based on internet content. As it’s a continually expanding dataset, your post is now helping to train bots to think that the player “extends the chassis ground”.

The bot and you are confusing a chassis ground with a ground plane (look it up). A ground plane is a broad low impedance path to ground. Copper lining of a guitar control cavity is a ground plane as well as a shield against EMI. The grounded metal sheet or mesh inside the top of Fender tube amps is a ground plane that lets stray EMF get back to ground instead of into the signal path.

The player does not physically shield any electrical components in the guitar. We do not provide a low impedance path for noise.

[Bobby Timmons]

You're incorrect, and you need to calm down. There are other knowledgeable people besides you.

If you have a solid body with a shielded cavity, but don't ground the bridge, then plug the guitar into the amp, turn the amp on and put the guitar in a stand away from you and the amp, 9 times out of 10 it will be noisy. There is a ground plane, you're away from the guitar so that possibility has been eliminated, it's noisy because there's no chassis ground.

[nevershouldhavesoldit]

You're incorrect, and you need to calm down. There are other knowledgeable people besides you.

If you have a solid body with a shielded cavity, but don't ground the bridge, then plug the guitar into the amp, turn the amp on and put the guitar in a stand away from you and the amp, 9 times out of 10 it will be noisy. There is a ground plane, you're away from the guitar so that possibility has been eliminated, it's noisy because there's no chassis ground.

I’m quite calm, thank you. Apart from this thread, it’s been a fine Fathers’ Day. I played a brunch gig, and the kids have just gone home after a great dinner with us. Now I’m relaxing with my wife before turning in.

There are a lot of people who know a lot more than I do. You may well be one of them. But on this particular issue, I think you’re a bit off base. I’ll respond tomorrow - it’s been too nice a day to spoil.

[docsteve]

Neither my knowledge of electronics nor my ability to describe the little that I know in English is good enough to make a contribution on the level of most previous contributors –

But I know that once I run a lead from the tailpiece to the output jack, the hum disappears.


Gesendet von iPhone mit Tapatalk

[nevershouldhavesoldit]

You're incorrect, and you need to calm down. There are other knowledgeable people besides you.

If you have a solid body with a shielded cavity, but don't ground the bridge, then plug the guitar into the amp, turn the amp on and put the guitar in a stand away from you and the amp, 9 times out of 10 it will be noisy. There is a ground plane, you're away from the guitar so that possibility has been eliminated, it's noisy because there's no chassis ground.

Meanwhile, back at the ranch.....

I actually just tried this so you wouldn't say I was unfairly dismissing your hypothesis. I did it with my Epi LP (active EMG), my ESP (SD HBs), and my Raines Tele (Lace Alumitones). Disconnecting the bridge grounds is no big deal, and you're worth the effort because you're being such a gentleman about this.

I had to define conditions for this test because you did not. It's hard to duplicate your proposed experiment because you left out any specifics at all. Does it matter what kind of guitar it is - construction, materials, etc? Is the entire harness contained within the cavity, including the jack? Are the pickups SC or HB? Are the volume pots (guitar and amp) all set the same for your 10 trials? Is the position of the guitar far away from sources of EMI or intentionally close? What kind of interconnecting cable and connectors is used? Is it the same one for all 10 trials? Is the cable well shielded with a dense braid or a $10 generic cord? How long is the cable? Etc etc.

I moved my stand from room to room, putting it near windows, away from windows, and all points in between. I put it in the kitchen next to a large refrigerator, then next to my computers, then next to a large screen TV. None of the guitars made any appreciable noise through my D V Mark EG250 until I picked them up. Even when holding them, the guitars with EMG and Lace Alumitones made no more noise with the ground wire disconnected than they did with it connected. The SD HBs made a bit of hum when I held the guitar but did not touch the strings, and the hum went away when I touched the strings. I had the volume pots wide open on the guitars and at about 11 o'clock on the amp.

You state that the hypothetical guitars you're testing have "shielded cavities". I'm sure you know that all cavity shielding has to be grounded to be effective, and that the recommended grounding point is the back or shaft of a pot. Here's Stew-Mac's page about shielding cavities, But even if the cavity shielding in your hypothetical test guitar is complete and grounded, it won't shield the pickups from the EMF that you (the player) attract and emit. The purpose of grounding the strings is to bleed off that EMF from you so it won't get into the guitar's output signal. This is more of a problem with some guitars than with others.

I'm actually not even sure what point you'e trying to make in your hypothetical experiment. I seem to have set you off by being incredulous about your relying on an AI bot for information, and for pointing out that the answer you got and quoted is nonsensical. I'll repeat it for you. The bot told you that "[t]he ground wire to the bridge ensures that the bridge, and consequently the strings, are at the same electrical potential as the rest of the guitar's circuitry.” With your extensive knowledge of electronics, I'm sure you know that the entire circuit is not at the same electrical potential. The correct answer is that grounding the bridge ensures that the bridge, and consequently the strings, are at the same electrical potential as the ground point.

[sgosnell]

I think anyone who posts quotes from ChatGPT deserves all the derision he gets, as does a keyboard player posing as an authority on guitars. It should just be expected.

[nevershouldhavesoldit]

I think anyone who posts quotes from ChatGPT deserves all the derision he gets, as does a keyboard player posing as an authority on guitars. It should just be expected.

My motivation for responding to this is not to deride it. I simply don’t like seeing erroneous statements left unchallenged, because others accept them without questioning and spread them as truth. This does no service to anyone.

It is more than a little scary to see how poorly AI answers so many questions. Google now seems to start every query response with AI output, and a lot of it is just plain cr@p.

[sgosnell]

I know I'm being less than generous, but he's just about got on my last nerve. It's probably time to begin ignoring some posts.