Why do you need a string ground ?

[David Schwab]

Thus your single coils are always going to have hum. The metal parts and strings are an antenna, but it will also transmit. Grounding to the bridge/strings will transmit some noise straight into the air, but much more noise will be grounded through your body when you touch the strings.

What are they transmitting, and how are they going to transmit at ground potential?

You touching the strings grounds you, and thus shunts what ever noise you are attracting to ground.

Also, the resistance of your body is pretty high... several megohms. The resistance of any grounded part in the guitar is close to zero. Electricity flowing through a circuit will always take the path of least resistance.

While every available path has some current flowing through it, the amount of current through each path is inversely proportional to its electrical resistance.

[Sir Cuitous]

What path does it take when I'm not touching the strings? It sure sounds less noisy when there's a ground to the bridge even when I'm not touching. I always compared guitars to boats or airplanes. Airplanes are designed to take a bolt of lightning. If it strikes the top of the fuselage it takes the path of least resistance by encirling the fuselage and exiting through the belly. The fuselage is the ground. I always thought a guitar sounded quieter by grounding to the metal parts.

[frank.clarke]

You don't have to have a string ground if everything else is super shielded. But a bridge ground is cheap, and much better than nothing. Your body is probably causing most of the noise, walk away from the guitar and listen, then push it against your tummy without touching metal. Ungrounded bridges extend your body across the strings, grounded strings ground your body. If you suck your fingers .

[David Schwab]

What path does it take when I'm not touching the strings?

The strings are grounded to the output jack, and then to the amp's ground, that's the path.

It sure sounds less noisy when there's a ground to the bridge even when I'm not touching.

Yes, because the strings act as an antenna, and that noise gets picked up by the pickups.

I always thought a guitar sounded quieter by grounding to the metal parts.

Yes, the metal parts should be grounded. But your body is not ground. Ground is established at the amplifier.

[Sir Cuitous]

You don't have to have a string ground if everything else is super shielded. But a bridge ground is cheap, and much better than nothing. Your body is probably causing most of the noise, walk away from the guitar and listen, then push it against your tummy without touching metal. Ungrounded bridges extend your body across the strings, grounded strings ground your body. If you suck your fingers .

I must have mistakenly been thinking of the current flow in reverse. Your observations and David's (..ground to amp...) make sense.

[tubeswell]

Reading all the above, I was wondering where the 'best' place to connect a 'string' ground would be on my noisome strat. After resorting to google just now I found this article

http://www.guitarnuts.com/wiring/shielding/shield3.php

[fernando]

Hi all. I have a question to David Schwab:

To avoid noise what is a better practice,

that the input jack is in contact with the pickguard shield and then the signal star ground connected to that shield? (no ground cable connected to jack)
OR
that the jack is isolated first from the shield, cable from jack to star ground and from star ground to pickguard shield (through the safety cap)?

Many thanks in advance. Best,

Fernando


(I'm trying to avoid ground loops on a Gibson S-1 and getting nuts)

[David Schwab]

My own personal opinion is that you can't get a ground loop in a guitar. I've never had it happen, and everything I've read about it has been anecdotal. You see more people taking about avoiding ground loops, than anyone one who said they had one!

Ground loops occur when the ground potential of one electronic circuit is higher than another, and you connect the two. Current will then flow through the ground connection.

Here's something from a Wikipedia article.

http://en.wikipedia.org/wiki/Ground_loop_(electricity)

Low current wiring is particularly susceptible to ground loops. If two pieces of audio equipment are plugged into different power outlets, there will often be a difference in their respective ground potentials. If a signal is passed from one to the other via an audio connection with the ground wire intact, this potential difference causes a spurious current to flow through the cables, eg: creating an audible buzz at the AC mains base frequency (50 or 60 Hz) and the harmonics thereof (120 Hz, 240 Hz, and so on), called mains hum.

The problem is always with something plugged into a grounded AC outlet. This is why we have ground lift switches on DI outputs... it keeps the grounds of your amp and the PA separate. Nothing inside a guitar is at any higher ground potential than the amp it's plugged into. A guitar in this aspect is like a microphone plugged into a PA. If the guitar had a separate ground wire connected to a pipe or something, and also the output jack ground, than you might get a ground loop.

So my opinion is that star grounding serves no purpose in a guitar, but it's very useful in high voltage situations, like a tube amp.

Having said that, it's not a bad practice to keep your shields separate from your signal (common) ground as long as possible, but once again, look how it's been done for the past 50 years or so. I see no problem with the common practice of grounding wires to the back of pots, which are often sitting on the shield foil. Think of the guitar as an effects unit. An effects unit has an aluminum enclosure, and all the pots and switches and jacks are grounded to that case (usually... sometimes they use isolation jacks, etc.) So the shield in the control cavity is just an extension of the cans on the pots, and the shield in the coax, etc.

If you are using a cap on your string ground to block DC current, I would only use that on the wire to the bridge, and not on any shields, and certainly not on the signal ground.

So, if you are getting hum from a guitar, especially one with single coils, it's not from a ground loop. It's just electrical and magnetic field interference.

Hi all. I have a question to David Schwab:

To avoid noise what is a better practice,

that the input jack is in contact with the pickguard shield and then the signal star ground connected to that shield? (no ground cable connected to jack)
OR
that the jack is isolated first from the shield, cable from jack to star ground and from star ground to pickguard shield (through the safety cap)?

Many thanks in advance. Best,

Fernando


(I'm trying to avoid ground loops on a Gibson S-1 and getting nuts)

[fernando]

Thank you David, it's very enlightening!


About the safety cap or net:

Wich value and wattage for the suggested added resistor?
And, in series or in parallel with the capacitor?

On the linked article a value of 0.33 uF/400V is suggested as a good compromise for protection from AC and DC.
Do you like that value for this application?

[tubeswell]

I used 2 x .1uF in parallel (making .2uF) and it seems to sound okay. (The two caps in parallel also gives more voltage-handling capability).

[BlackAngusYoung]

I have similar problem with an acoustic...

I have an acoustic guitar with a magnetic pickup. It's a stacked humbucker, I believe.

There is a buzzing noise coming through the amp, which goes away when I touch metal on the cord or amp, or the wire going into the pickup. It seems like maybe the strings should be ground like on a solid-body, but I can't think of how that could be done.

I don't get the noise when I use a battery-powered amp.

Anyone have a problem like mine with an acoustic? I don't think acoustics with magnetic pickups are that common, and I can't find much info about similar guitars.

Any help would by much appreciated!

[Ronsonic]

I believe that string grounding has its effect mostly by grounding the player's body. If the guitar has a poorly shielded control cavity, then it will pick up capacitively coupled hum from your body, which in turn is picking it up from the mains wiring in the room. But once your body is grounded it turns from a big squishy antenna into a shield.

Pickups without metal covers can also pick up stuff capacitively, and the grounded strings help to shield them.

My latest "amp" design needs the best shielded guitar possible, not to mention a 30ft fibre optic guitar cord for personal safety.
YouTube - Tesla Guitar

Oh my. All that awesomeness and it sounds like a Gorilla amp.

[bbsailor]

I have an acoustic guitar with a magnetic pickup. It's a stacked humbucker, I believe.

There is a buzzing noise coming through the amp, which goes away when I touch metal on the cord or amp, or the wire going into the pickup. It seems like maybe the strings should be ground like on a solid-body, but I can't think of how that could be done.

I don't get the noise when I use a battery-powered amp.

Anyone have a problem like mine with an acoustic? I don't think acoustics with magnetic pickups are that common, and I can't find much info about similar guitars.

Any help would by much appreciated!

BlackAngusYoung,

To easily ground the strings go to the Stewart McDonald web site and obtain a PlateMate. This is a brass plaste with holes spaced to match the bridge pin spacing. Measure your pin spacing and obtain the correct version. Before you install, solder a flexible stranded wire (about 1 foot) to the metal plate mate and connect the other end to the output jack ground connection or metal braid of the pickup lead. This will ground your strings as the ball ends of the string will rest in the notch being grounded to prevent the ball end of the string from chewing up the wood under the bridge.

This is an undocumented use for the Platemate and works very well when using magnetic pickups on acoustic guitars.

Joseph Rogowski

[Steve Conner]

Oh my. All that awesomeness and it sounds like a Gorilla amp.

Yeah, unfortunately it sounds like crap (I've tried a Gorilla, and this thing is worse!) and there are serious physical reasons why it's always going to sound like that. The cool appearance of the sparks is mutually exclusive with improved tone.

If I wanted it to sound good, I'd gang it up with an ordinary guitar amp, but then the Youtube peanut gallery would accuse me of "cheating".

Ironically in spite of the terrible sound, it got me far more internet-famous than any of my efforts as a regular guitarist. My various musical Tesla coil videos have over a million views between them, and my boss now insists that I play the thing at open days.

[BlackAngusYoung]

That looks like a great idea. I could maybe even make something that would work in that way.
Thanks a lot for the help.

And, wow... my pictures showed up a lot bigger than I'd hoped!
(Sorry about that if anyone's annoyed. New to the forum.)