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Thread: Is String Grounding Necessary?

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    Is String Grounding Necessary?

    Folks -

    Even in high impedance situations I've often thought that getting as close to 100% shielding as possible (which includes things like forming a tube for traditional Tele jack tunnels) seemed to make string grounding unnecessary.

    Now I've found a situation in which this doesn't seem to be the case at all.

    Thoughts? Have I just been getting lucky all these years?

    Non-functional 3rd prongs in the wall socket (or deliberately lifting that ground) make for a good torture test, by the way.

    Bob Palmieri

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    Quote Originally Posted by fieldwrangler View Post
    Folks -

    Even in high impedance situations I've often thought that getting as close to 100% shielding as possible (which includes things like forming a tube for traditional Tele jack tunnels) seemed to make string grounding unnecessary.

    Now I've found a situation in which this doesn't seem to be the case at all.

    Thoughts? Have I just been getting lucky all these years?

    Non-functional 3rd prongs in the wall socket (or deliberately lifting that ground) make for a good torture test, by the way.

    Bob Palmieri
    Well, an EE or physicist will tell you that a perfect shield keeps out all electric fields, but that is not necessarily the whole story for preventing hum resulting from electric fields. For example, one potential problem is that the shield of the guitar cable is used to carry signal current. The problem is that there could be hum currents flowing on this shield as well, currents that are a result of the shield doing its job to neutralize electric fields. The resulting voltage in series with the input (because the shield has some resistance) is not very big, but on the other hand, guitarists sometimes play with a lot of gain.

    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. You then have two signal leads, call them high and low. The high signal is what it is, and it goes to the tip. The low signal is what people usually call ground, but you have to make sure that no actual shield is connected to it, and it goes to the ring. So all the copper foil, pot cases, etc. connect to the shield of the cable and at the other end it goes to the chassis of the amp. The low side of the signal runs directly to the bottom of the cathode biasing resistor of the first stage. (Yes, that point is at "ground" potential, but it is signal ground rather than chassis ground, and they can be a bit different.)

    Both guitar and amp should remain compatible with the normal world since with the use of mono cable and plugs, the ring contact on the jacks gets connected to the shield. As I said, I have never tried it, but a separate conductor for the shield is standard in some applications. (The amp might have more hum that it should when using a mono cable because the chassis and signal ground are connected together at a non-optimum point.)

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    Last edited by Mike Sulzer; 08-31-2016 at 06:15 PM.

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    Quote Originally Posted by Mike Sulzer View Post
    Well, an EE or physicist will tell you that a perfect shield keeps out all electric fields, but that is not necessarily the whole story for preventing hum resulting from electric fields. For example, one potential problem is that the shield of the guitar cable is used to carry signal current. The problem is that there could be hum currents flowing on this shield as well, currents that are a result of the shield doing its job to neutralize electric fields. The resulting voltage in series with the input (because the shield has some resistance) is not very big, but on the other hand, guitarists sometimes play with a lot of gain. 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. You then have two signal leads, call them high and low. The high signal is what it is, and it goes to the tip. The low signal what people usually call ground, but you have to make sure that no actual shield is connected to it, and it goes to the ring. So all the copper foil, pot cases, etc. connect to the shield of the cable and at the other end it goes to the chassis of the amp. The low side of the signal runs directly to the bottom of the cathode biasing resistor of the first stage. (Yes, that point is at "ground" potential, but it is signal ground rather than chassis ground, and they can be a bit different.)

    Both guitar and amp should remain compatible with the normal world since with the use of mono cable and plugs, the ring contact on the jacks gets connected to the shield. As I said, I have never tried it, but a separate conductor for the shield is standard in some applications.
    Mike -

    Thanks, as always, for specifying key aspects of the problem & solution. In this case I'll be "telescoping" the cable shield, using 2 conductor cable to carry the signal and attaching shield to ground at the guitar end only (unless someone thinks there's a good reason to attach it at the amp end.) However, I won't be able to take control of what will constitute the amp's input conditions; customers, after all, will be customers.

    While we're here, though, it might be a good time to clear up some odd info that often gets circulated regarding string grounds. I've read that the reason it's used is that the player's "body capacitance" is somehow sinking the high-z electrostatic buzz field. I always thought that it basically grounded the player's body, which seems to be a fine "source" for some of this noise.

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    Quote Originally Posted by fieldwrangler View Post
    Mike -

    Thanks, as always, for specifying key aspects of the problem & solution. In this case I'll be "telescoping" the cable shield, using 2 conductor cable to carry the signal and attaching shield to ground at the guitar end only (unless someone thinks there's a good reason to attach it at the amp end.) However, I won't be able to take control of what will constitute the amp's input conditions; customers, after all, will be customers.

    While we're here, though, it might be a good time to clear up some odd info that often gets circulated regarding string grounds. I've read that the reason it's used is that the player's "body capacitance" is somehow sinking the high-z electrostatic buzz field. I always thought that it basically grounded the player's body, which seems to be a fine "source" for some of this noise.
    Yes, grounding the guitar shield separately from the amp ought to work just as well as to the amp chassis (or just as badly if the problem is something else).

    As for the string ground:

    The player is probably not normally grounded, but must be at some potential resulting from fields in the area or possibly contact with something else that is not at ground potential. So when the player touches ungrounded strings, they are raised to the same potential above ground. Thus a field develops across an imperfectly shielded pickup or other guitar component, causing hum. The voltage developed in the circuit is referred to the guitar ground: so put the strings at this ground potential, and the player touching them goes to the same potential, or almost so. Thus in summary, if the shielding is imperfect, get rid of nearby fields by grounding the player. Too bad if the player is also connected to another source at a different potential with some force behind it!

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    To cut electrical noise from the strings, many guitars have a wire connecting the bridge or string ends to the guitar electrical ground.

    I was apprehensive about using a straight wire.

    My luthier connected the bridge to the guitar ground by a parallel RC widget, 270k/0.02uF. Seemed plausible, worked, cost little. The 270k resistor was chosen as a generic value to limit current flow should the amp's 400VDC mysteriously short to the guitar ground while I stood in salt water playing my guitar. Yeah, it could happen. No, really.

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    Last edited by salvarsan; 09-01-2016 at 12:16 AM.
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    Quote Originally Posted by salvarsan View Post
    To cut electrical noise from the strings,
    So if your strings are not grounded, are they somehow acting as an antenna, even though they are not connected to the circuit? Is your body also acting as an antenna, even though it too is not connected to the circuit (considering the noise level drops when you touch grounded strings)?

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    Quote Originally Posted by John Kolbeck View Post
    So if your strings are not grounded, are they somehow acting as an antenna, even though they are not connected to the circuit? Is your body also acting as an antenna, even though it too is not connected to the circuit (considering the noise level drops when you touch grounded strings)?
    Personally, I hold to the theory that a subspecie of noise demons were attracted to that particular luthier's instrument strings, and that we provided them with an escape route through a pair of talismans that had been pre-incantated and graven in runes (red-purple-yellow, and 20nf-400V) by their creator. It's said to be a minor example of conservation of thaumaturgic aether, or so they tell me. I have no real understanding of this because I'm not a thaumaturgist. That said, I prefer Magic that works irrespective of my belief in it.

    There was string noise. We stopped it with 50 cents in parts used as described.

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    Quote Originally Posted by salvarsan View Post
    There was string noise. We stopped it with 50 cents in parts used as described.
    We'll have none of that pragmatism here, sir.
    We must know why, why, WHY?

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    Quote Originally Posted by rjb View Post
    We'll have none of that pragmatism here, sir.
    We must know why, why, WHY?
    Sir,

    I refuse to inject reproducible facts and rational thought into an on-topic discussion, for with those, it can't degenerate into personal invective and ignorant hand-waving arguments.

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    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!

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    Quote Originally Posted by salvarsan View Post
    Personally, I hold to the theory that a subspecie of noise demons were attracted to that particular luthier's instrument strings, and that we provided them with an escape route through a pair of talismans that had been pre-incantated and graven in runes (red-purple-yellow, and 20nf-400V) by their creator. It's said to be a minor example of conservation of thaumaturgic aether, or so they tell me. I have no real understanding of this because I'm not a thaumaturgist. That said, I prefer Magic that works irrespective of my belief in it.

    There was string noise. We stopped it with 50 cents in parts used as described.
    You pick up those parts at the shop on Perdido Street?

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    Quote Originally Posted by potatofarmer View Post
    The thing about balanced cable though is that both conductors need to have equal impedance to ground.
    Spoilsport.

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    You'd think a company like Fender, that produces at least one product somewhere along the entire signal chain, could introduce something like a balanced guitar rig more readily than anyone else, and exploit the selling point.

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    Quote Originally Posted by Jason Rodgers View Post
    You pick up those parts at the shop on Perdido Street?
    I wish, but no, it was across the bay from Tokyo in the Port of Chiba where ...

    the sky above the port was the color of television, tuned to a dead channel.

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    Quote Originally Posted by John Kolbeck View Post
    You'd think a company like Fender, that produces at least one product somewhere along the entire signal chain, could introduce something like a balanced guitar rig more readily than anyone else, and exploit the selling point.
    It'd be good engineering and a good product but you'd still have guitarists, seldom the sharpest tools in the shed, using them.

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    Quote Originally Posted by potatofarmer View Post
    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!
    A separate conductor for the low side of the signal does not imply an attempt to make a balanced system. It is just good grounding practice.

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    Quote Originally Posted by John Kolbeck View Post
    You'd think a company like Fender, that produces at least one product somewhere along the entire signal chain, could introduce something like a balanced guitar rig more readily than anyone else, and exploit the selling point.
    Gibson had some Les Paul guitars & basses with balanced outputs. Never caught on much. Still needed a transformer at the amp end. And if "going direct" guess what's in the mix console, just on the other side of those balanced inputs. A transformer again. It's a bit disheartening to see all those studio gadgets with balanced inputs, each and every one processes signals in a "one sided" circuit so there's transformers or the op amp equivalent at inputs & outputs. There was a notion for a long time "get the iron out of the signal path" - no transformers please - but in actuality practically all the recorded music we enjoy has passed thru many of them. And somehow we still manage to enjoy it.

    Can you imagine the size and expense of a pedal board where all the effects have balanced ins & outs? All to no good effect really, just makes everything bigger and raises the price a lot. I'm sure there are some people for whom that would be an attraction.

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    Quote Originally Posted by salvarsan View Post
    I wish, but no, it was across the bay from Tokyo in the Port of Chiba where ...

    the sky above the port was the color of television, tuned to a dead channel.
    Please tell us the truth, the guitar hum was just an excuse, you were shopping for illegal synthetic body parts

    FWIW IŽd be interested in an aftermarket pancreas

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    Quote Originally Posted by Mike Sulzer View Post
    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. You then have two signal leads, call them high and low. The high signal is what it is, and it goes to the tip. The low signal is what people usually call ground, but you have to make sure that no actual shield is connected to it, and it goes to the ring. So all the copper foil, pot cases, etc. connect to the shield of the cable and at the other end it goes to the chassis of the amp. The low side of the signal runs directly to the bottom of the cathode biasing resistor of the first stage. (Yes, that point is at "ground" potential, but it is signal ground rather than chassis ground, and they can be a bit different.)
    Question:
    Say you harness a guitar as outlined, but do not modify the amplifier.
    Build an instrument cable with TRS on one end, TS on the other (SIG- and SHD tied together).
    Plug the TRS end into the guitar, TS end into the amp.
    Would (might) this configuration offer some advantage over using a mono cable?
    If the answer is "it depends", what are the considerations?

    -rb

    EDIT:
    My guess is that hum induced in the cable and guitar shields would be largely eliminated from the signal, but hum induced on the amp chassis would remain.

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    Last edited by rjb; 09-01-2016 at 10:05 PM. Reason: EDIT 2: Added "and guitar" shields
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    Quote Originally Posted by J M Fahey View Post
    Please tell us the truth, the guitar hum was just an excuse, you were shopping for illegal synthetic body parts
    working title: "Neuromantic Lyttony"

    Fortified wines from Portugal are named accordingly -- port. Inside Texas, a port is only a fortified wine when export sales are involved. Sometimes, a port-style vinified in Texas or 'Tejas' is euphemistically called "portejas" and seldom leaves the state.

    Enoch's Stomp's first harvest was Texas Black Spanish or Lenoir grapes, known to thrive despite threat of Pierce's Disease in the weather extremes of East Texas. The Lenoir must, they fermented, fortified, and aged in barrel for 4 years. It waited another 4 years in bottles labeled "Dark Portejas". Upon release, it won double gold and Grand Star at the 2015 Lone Star International. Competing well in the $$$ category, it is inexplicably underpriced at $40/btl.

    Dark Portejas, a rare and fine thing, is available only over the winery's tasting room counter.

    When I finally arrived at Enoch's for a tasting, the day was dusk, warm, and wet. Electing to enjoy the weather on the patio, I carried the Portejas snifter outside, sank into a chair beneath an umbrella. I filled my head with the wine's cloyed cedar-and-oak aroma and reflected on the weather.

    A dark sky met the darker horizon while outdoor lights obliquely lit the gentle rain to give the air a chrome-and-black speckle like monochrome video noise. On a whim, I lifted my snifter to eye level and brought the dark wine meniscus even with the black horizon.

    The sky above the port was the color of television, tuned to a dead channel.

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    Quote Originally Posted by salvarsan View Post
    working title: "Neuromantic Lyttony"....
    The sky above the port was the color of television, tuned to a dead channel.
    It appears this forum needs a new category: "Writer's Colony".

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    Quote Originally Posted by rjb View Post
    Question:
    Say you harness a guitar as outlined, but do not modify the amplifier.
    Build an instrument cable with TRS on one end, TS on the other (SIG- and SHD tied together).
    Plug the TRS end into the guitar, TS end into the amp.
    Would (might) this configuration offer some advantage over using a mono cable?
    If the answer is "it depends", what are the considerations?

    -rb

    EDIT:
    My guess is that hum induced on the cable shield would be largely eliminated from the signal, but hum induced on the amp chassis would remain.
    You can just connect the shield at the amp end provided you have 2 conductor cable. I've done this but didn't notice a difference. I suppose the RFI is "further" from the amp input by whatever the resistance of you conductor (would we call it ground still?) is but with 5+K of pickup impedance, I dont thing that half ohm is much of a factor. I swapped ends and didn't notice a difference.

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    Is that yours?

    VERY good !!!!!!!

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    Quote Originally Posted by Richard View Post
    You can just connect the shield at the amp end provided you have 2 conductor cable.... I swapped ends and didn't notice a difference.
    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- from the guitar 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

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    Last edited by rjb; 09-02-2016 at 01:51 AM.

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    Quote Originally Posted by rjb View Post
    It appears this forum needs a new category: "Writer's Colony".
    Hey! That quip about "Perdido Street Station" started it.

    The "Lyttony" in the title should have clued you to its aggressive competition in bad writing, i.e., the Bulwer-Lytton Fiction Contest in which contestants compete against the original "it was a dark and stormy night . . ."

    So, if there's a writing category, it should explicitly be "Bad Writing".

    You mooks, fix the damn guitar ground awreddy. That horse is dead and rotting.

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    Senior Member salvarsan's Avatar
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    Quote Originally Posted by J M Fahey View Post
    Is that yours?
    Yes. It's a documentary, accurate but for the last sentence.

    Enoch's Stomp Dark Portejas is real, good enough that you shouldn't leave the bottle unattended among company. (*sigh!*)

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    Quote Originally Posted by salvarsan View Post
    You mooks, fix the damn guitar ground awreddy. That horse is dead and rotting.
    But how can we know we've chosen the best fix, without exhausting all possibilities?

    Seriously, as a concrete-skulled ignoramus, I can sometimes benefit from being told "Don't waste your time trying that. It won't work because yadda, yadda, yadda."

    -rb

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    Senior Member salvarsan's Avatar
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    A good reference is Ralph Morrison's laconic 146 page "Grounding and Shielding Techniques in Instrumentation, Second Edition", published 1977, ISBN-13: 978-0471029922.

    It's practical physics written for electrical engineering types. Used hardcover copies are about $5 shipped but later editions are stupid money expensive.

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    Last edited by salvarsan; 09-01-2016 at 10:35 PM. Reason: pub. date, isbn added
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    Quote Originally Posted by salvarsan View Post
    A good reference is Ralph Morrison's laconic 146 page "Grounding and Shielding Techniques in Instrumentation, Second Edition"
    Laconic sounds good. 146 pages may exceed my attention span.
    Maybe I'll warm up with this.
    (Haven't read it in a few years. Maybe more will sink in this time).
    It's only 12 pages, and even has a cartoon illustration.
    http://www.rane.com/pdf/ranenotes/Gr...io_Devices.pdf

    -rb

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    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.

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    Quote Originally Posted by rjb View Post
    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.

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  32. #32
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    Quote Originally Posted by John Kolbeck View Post
    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?

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  33. #33
    Senior Member salvarsan's Avatar
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    Quote Originally Posted by rjb View Post
    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.

    Click image for larger version. 

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    The lofted fewmet doth soon hew close to the whirling blades.

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    Quote Originally Posted by Richard View Post
    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.
    Quote Originally Posted by Richard View Post
    I specified 2 conductor cable because some cables are shield and conductor only.
    "Some cables" AKA standard 1/4" instrument cables.

    Quote Originally Posted by Richard View Post
    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.

    Quote Originally Posted by Richard View Post
    I read somewhere that lifting the shield helps.
    To eliminate ground loops in balanced systems?

    Quote Originally Posted by Richard View Post
    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

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  35. #35
    Supporting Member Steve A.'s Avatar
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    Quote Originally Posted by potatofarmer View Post
    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...

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    Last edited by Steve A.; 09-02-2016 at 12:09 AM.

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