Is String Grounding Necessary?

[Richard]

I'm not sure we're understanding each other.
I assumed it obvious that a TRS to TS cable would use 2 conductor shielded cable.
The guitar's innards would be wired as Mike outlined.

The cable connections would be:

Guitar End
T - SIG+
R - SIG-
S - SHD

Amp End
T - SIG+
S - SIG- and GND

If you swapped cable ends, you would tie SIG- to SHD at the guitar's TRS jack, defeating the separation of "signal ground" from shield.

If you used a two-conductor TRS-to-TRS cable and plugged it into an unmodified amp, SIG- would float at the amp's mono input jack.

Again, I'm not sure what you're saying.
Did you wire the guitar with a TRS jack (as Mike outlined), connect the guitar to an unmodified amp with a TRS-TS cable, and find no difference when you swapped cable ends?
I'm not questioning your observation- just confirming we're on the same page.

Thanks,
-rb

These are standard TS plugs, maybe if I used TRS and separated the shield from the ground on the guitar I would've noticed a difference. I specified 2 conductor cable because some cables are shield and conductor only. The cable I used to do this was 4 conductor but 2 color (white and blue if it matters) Canare 405. I read somewhere that lifting the shield helps. To be honest, the majority of my noise comes thought the pickups. Also I run through a pedalboard and don't have the ground separated so it would only be on the last run to the guitar.

While we're on the subject of cables, does anyone know what advantage there could be to having tandem conductors? The cable is obviously not intended for 4 conductor wiring.

[Richard]

I had google "why does the bridge have to be grounded?", and I got a different answer for every guitar forum that came up in the results, and yet I bet that book has the single, correct answer somewhere within its pages. It's funny that in the age of the Internet and self-publishing, quality information is suddenly so hard to find, while wild guesses aplenty are at our fingertips. It's like The Great Dumbening is upon us.

Don't the strings form a Faraday cage that absorbs stray EMF and directs it to ground?

[salvarsan]

It's only 12 pages, and even has a cartoon illustration.
http://www.rane.com/pdf/ranenotes/Gr...io_Devices.pdf

Figure 6 shows an RCA to NEMA-1-15 AC mains adapter. I like that guy.

[rjb]

These are standard TS plugs, maybe if I used TRS and separated the shield from the ground on the guitar I would've noticed a difference.

Oh, OK. Nevermind.

I specified 2 conductor cable because some cables are shield and conductor only.

"Some cables" AKA standard 1/4" instrument cables.

The cable I used to do this was 4 conductor but 2 color (white and blue if it matters) Canare 405.

That would be "star quad" mic cable.

I read somewhere that lifting the shield helps.

To eliminate ground loops in balanced systems?

While we're on the subject of cables, does anyone know what advantage there could be to having tandem conductors? The cable is obviously not intended for 4 conductor wiring.

Here's one explanation. For others, Google "star quad".
http://www.canare.com/UploadedDocuments/Cat11_p35.pdf

-rb

[Steve A.]

The thing about balanced cable though is that both conductors need to have equal impedance to ground. Plus then you'd need a bal/un transformer at the amp (or the first effects pedal) unless you're making a wholly balanced rig. Which would be impressive and commendable!

I have not yet read all of the posts here but what Mike suggested is NOT a balanced signal but just a better system for grounding a guitar. Too bad nobody thought of it 60 or 70 years because it *could* have become the industry standard for guitar cables. (With the existing standards Mike's scheme would end at the first pedal after his guitar... unless that was modified as well. And so on down the line...)

FWIW I have been promoting that wiring scheme for 5 or 10 years but haven't tried it out myself yet either.

Steve Ahola

P.S I see that Mike Sulzer came to his own defense in Post #16.

P.P.S. If anybody thinks that this thread should be moved to a different forum please chime in. I did at first but then I came to appreciate the answers by the people who frequent this forum. Maybe when it has run its course here I could move it to a different forum for a fresh take on things...

[rjb]

P.P.S. If anybody thinks that this thread should be moved to a different forum please chime in. I did at first but then I came to appreciate the answers by the people who frequent this forum. Maybe when it has run its course here I could move it to a different forum for a fresh take on things...

Maybe open & immediately close a one-message thread in another forum that "points" to this thread?

[rjb]

Dr. Obvious Sez

Post #2

There is a way around this, in principle, although I have not tried it. It involves using a stereo jack for the guitar and amp and two conductor shielded cable....

That's fine and dandy if you have a tube amp with chassis mounted input jack; easier said than done if you use FX pedals or a modern production amp with PCB mounted jacks.

Post #19

Say you harness a guitar as outlined, but do not modify the amplifier....

I guess the answer to the question is that the effectiveness of my proposed shielding configuration would depend on the amp's grounding scheme. Theoretically, it would work great in a highly unlikely scenario where the amp is star-grounded from the input jack. Probably less effective if the amp is star grounded from the power supply output. Anybody's guess if the amp is not star grounded.

-rb

[Steve A.]

Post #2

There is a way around this, in principle, although I have not tried it. It involves using a stereo jack for the guitar and amp and two conductor shielded cable....

That's fine and dandy if you have a tube amp with chassis mounted input jack; easier said than done if you use FX pedals or a modern production amp with PCB mounted jacks.

Post #19

Say you harness a guitar as outlined, but do not modify the amplifier....

I guess the answer to my question is that the effectiveness of the proposed shielding configuration would depend on the amp's grounding scheme. Theoretically, it would work great in a highly unlikely scenario where the amp is star-grounded from the input jack. Probably less effective if the amp is star grounded from the power supply output. Anybody's guess if the amp is not star grounded.

For many years I have considered the advantages of using a stereo shielded cable between a guitar and an amp- even an unmodified amp- but alas, I have never conducted any experiments.

Scenario A. Modified guitar / unmodified amp / modified stereo shielded cable:
1.) Guitar would be rewired with a star ground scheme as suggested by the Guitar Nuts website in 1998 or 1999: signal returns from pickups and pots would be isolated from the shields throughout the guitar control circuitry and connected at a single point to the ground directly from the guitar cable.**
In this scenario we would keep the two separate, with the signal returns connected to the ring terminal and the grounds connected to the sleeve of a stereo output jack.
2.) With an unmodified amp the signal return lead of the modified stereo cable would be connected to the cable shield at the amp end mono plug. (You would need to indicate which end of the cable is connected to the amp.)

Scenario B. Modified guitar / modified tube amp / unmodified stereo shielded cable:
1.) Guitar modifications as spelled out in step #1 of Scenario A - and -
. a.) Tube amp would be modified with ring terminal of stereo input jack(s) connected to cathode ground of first tube stage.
. b.) If not feasible then the ring terminal would be connected to, preferably, the star ground point of the amp;
. c.) otherwise it would be connected to the shield terminal of the stereo input jack(s).
2.) If input jack(s) cannot be replaced then follow step #2 of Scenario A.

Many people in this discussion agree that Scenario B.1.a would help in a room with a lot of noise "picked up from the ether".*** The big question is whether the other scenarios would help in a room with "a lot of noise gremlins" (see ***).

I suspect that under those scenarios there would be some reduction of noise (see ***) as it would be captured by the cable shield and guitar grounds, and bled off to the amp chassis. It would be easy enough to test this in an "RF noisy" room by doing the modifications spelled out in Scenario #1 to a guitar and a modified stereo cable, and comparing the noise level to that of the modified guitar using a regular mono guitar cord.

Note to self: #1. Find one of my guitars that I wired with a star ground and connect the signal returns to the ring terminal of a stereo output jack.
#2. Get a shielded stereo cable with 1/4" plugs and replace one of them with a mono plug as spelled out in Scenario #1.B

** In the original webpages he suggested connecting the signal returns to ground through a capacitor- I used a huge 1.0uF or 2.2uF poly cap. He might have dropped that suggestion later because it has more to do with safety than noise. Either way you would typically connect the two at the back of a volume or tone pot.

*** I would call it "RF noise" but it is in fact quite audible. With single coil pickups you can often reduce this noise considerably by rotating the guitar on the vertical axis.

Steve Ahola

[Richard]

To eliminate ground loops in balanced systems?
http://www.canare.com/UploadedDocuments/Cat11_p35.pdf

-rb

I can't remember where I read it but (unless I misread) I don't think it was about ground loops, just that if the shield is grounded at the amp any interference has to travel farther to get to the input. Without separating the shielding and strings of a guitar, it's a negligible difference, at least in my experience. Perhaps if the cable were passing by the interference causing item it may help.

[Steve A.]

I can't remember where I read it but (unless I misread) I don't think it was about ground loops, just that if the shield is grounded at the amp any interference has to travel farther to get to the input. Without separating the shielding and strings of a guitar, it's a negligible difference, at least in my experience. Perhaps if the cable were passing by the interference causing item it may help.

FWIW before I read those articles on Guitar Nuts back around 1998 I had treated signal returns and grounds interchangeably in all of my custom wiring harnesses, thinking that the less wire connecting the various components, the quieter the guitar would be. Wrong!

Keeping the signal returns separate from ground up until the star ground point made my guitars much quieter. The various grounds and shielding would pick up the "RF gremlins", with some of it cancelling out and some of it going straight to the amp chassis while the signal returns were not molested quite as much. Connecting the signal returns to ground through a 1.0 to 2.2uF poly cap might have isolated the signal returns even better for less noise but that was a long time ago and I forget which of my guitars had the isolating caps.

As you said its not about ground loops because there is hardly any current involved. But I always figured that if I could keep the signal returns separated from chassis ground all of the way to the first stage of a tube amp it would be even quieter. BTW I live in a 4-plex condo with all sorts of crap on the electrical lines and floating around the air so I am always looking for ways to eliminate it... and I usually play well-shielded guitars with humbuckers!

Steve A.

P.S. As for SS amps it seems like many of them introduce a lot less hum and buzz than a tube amp so no special measures need to be taken, at least inside the guitar amp.

[David Schwab]

FWIW before I read those articles on Guitar Nuts back around 1998 I had treated signal returns and grounds interchangeably in all of my custom wiring harnesses, thinking that the less wire connecting the various components, the quieter the guitar would be. Wrong!

Everything on the website is pure crap. And that's being polite. Two of the biggest are star grounding, and wrapping pickups in foil.

You only have one ground point in a guitar, so star grounding does nothing. You can't have a ground loop. But I have found that redundant ground paths often help, which goes against the idea of star grounding. If you have a buzz you can't get rid of, run two ground wires to the jack! Shouldn't matter, but it does.

As far as string grounding, obviously you can get noise if you don't. But you can get a shock if you do. EMG showed that with a well shielded pickup (which also uses differential noise reduction) you can do away with string grounds.

Back in the early 80s I had totally shielded one of my Rickenbacker basses with copper foil tape. Every inch of the control and pickup cavities was covered, as well as the back of the pick guard. Then I had Hi-A and Gibson "mud bucker" humbucking pickups. The bass was dead quiet, even around usual noise sources, like light dimmers. I did not have the strings grounded.

So it is possible.

[John Kolbeck]

The bass was dead quiet, even around usual noise sources, like light dimmers. I did not have the strings grounded.

So it is possible.

Don't light dimmers emit the 60Hz hum that can't be thwarted by shielding alone, due to the low frequency?

[Richard]

I just remembered I have a guitar with a stereo jack (used to have active pickups). I need to rewire it anyway and I have the proper cables to separate the shield from the signal ground. All I need is a stereo jack and some motivation. Building the amp with the appropriate input wiring might not happen soon but I can test the guitar end of things. Would having a small resistor in the signal ground provide further separation from interference? I'm thinking that if I have 0 Ohms from shield to ground and then 10 Ohms from signal ground to ground that any RFI picked up would have a significantly better path to ground than through the signal circuit. Does anyone know if grounding a pickup through a small resistor has any effect on tone?

Is my terminology clear? I'm not sure if I'm using the correct language so my message is clear. Also is RFI the correct term for the noise or should it be EMF?

David, when you shielded your bass did it have any effect on the tone? Some say that the shielding adds capacitance. I think I hear a difference sometimes with different cables, my pedal board and volume pedal definitely take a slice of brilliance out and I want as much brilliance as I can get.

[John Kolbeck]

Is my terminology clear? I'm not sure if I'm using the correct language so my message is clear. Also is RFI the correct term for the noise or should it be EMF?

EMI is what afflicts electric guitars. EMF just means "electromagnetic field" and RFI refers to radio frequency interference that is way beyond human hearing.

David, when you shielded your bass did it have any effect on the tone? Some say that the shielding adds capacitance. I think I hear a difference sometimes with different cables, my pedal board and volume pedal definitely take a slice of brilliance out and I want as much brilliance as I can get.

If the lead wires touch the shielding, they will be close enough to capacitively couple, but will do so less than even a foot worth of guitar cable, so the sort of difference you hear if you swap an 8ft for a 9ft cable, which is to say, no audible difference.

The pedal board and volume pedal probably add a more significant amount of capacitance, as well as the extra length of cable that extends from the pedals to the amplifier, add together to create an amount of capacitance that will have an audible effect.

[Richard]

I think the biggest issue is the 250K pot in the volume pedal loading the signal but plugging straight in with my least capacitive and shortest cable to plugging in with my longest an most capacitive cable is a difference. About the smallest noticeable difference but a difference. The pedal board is definitely audible especially at the sparkly end of the spectrum.