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Ground Loops


psw
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Here's a quote from a recent thread

...Having all the grounds meet at one spot is just a good way to make sure you have all the grounds done right..
It also completely eliminates the chance for noisy ground loops, which are really easy to wire in if you don't have a clear-cut idea of how your grounding scheme works. It's not compulsory, but it is cheap insurance.

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A ground loop, in a guitar, I understand to mean any place where a grounded point has more than one route to get to the ground connection (the jack, in the case of a guitar). The idea is, that this creates a low resistance loop around the grounded connections in which noise signals can be induced of significant magnitude to be affecting the signal. 'Star grounding' is one to make sure this doesnt happen, since it ensures that only one route is available from each point to ground.

Thats the theory, But...

I can not figure out how these effects become significant enough to be a problem in a guitar (although they are a problem in assemblies of audio equipment where several may be plugged into the mains).

Also I cannot create a guitar ground loop to test it, and have tried with large loops of wire! I have a thread on 'Guitarnuts 2' on this, and am still looking for a definative answer:

http://guitarnuts2.proboards45.com/index.c...16477808&page=1

Anyone here able to help?

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I' can't explain it very well, so how's this?

A ground loop occurs when there is more than one ground connection path between two pieces of equipment. The duplicate ground paths form the equivalent of a loop antenna which very efficiently picks up interference currents. Lead resistance transforms these currents into voltage fluctuations. As a consequence of ground-loop induced voltages, the ground reference in the system is no longer a stable potential, so signals ride on the noise. The noise becomes part of the program signal.
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I think I like the first explanation best...so what's being said is that each "loop" of wire forms a mini antenna and these signals make the ground "unstable"...ie noisy

So in a guitar...where these tiny signals are being heavily amplified...the condition is worse...

OK...I guess I'm asking for two reasons...

First...Like my fellow Aussie JohnH (g'day mate, welcome to PG)...

I haven't had any problems with my "loopy" shielded guitars...in fact they're very quite...even the one I'm working with whith all those switches and such everywhere...

And of course...the Sustainer System...

This is possibly the real test as I'm now running cables through the wiring which I have no doubt sending out magnetic interferance...some of it high frequency noise...and this may be showing up the pitfalls of all these loops I've not experienced before...

Here's part of JohnH's original question from his link...

Our guitars are not affected by mains currents, the guitar has only one overall ground route, through the lead. Any ground loop effects can only be caused by induced currents in the control wires within the guitar. I could see that some small signals could be induced in a low resistance path around the ground connections of the guitar controls etc, but they are also mostly shorted out, because they are grounded.

I’ve tried to create a ground loop: I put a 33k resistor between ground and hot connection of a guitar lead (representing guitar pups, pots etc), with the ground connection to it being via two separate wires (either the same or different lengths), physically separated. I plugged in and cranked up the overdrive gain to get a nice buzz. Breaking the ‘ground loop’ by disconnecting one of those wires caused no change. Can anyone demonstrate a ground loop?

My guitar also has a ground loop in its circuitry. Since I’ve shielded it its been pretty quiet, but breaking the ground loop caused no change.

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(for a quick explanation)

I've always just thought of ground loops as places where the difference in ground potential between one ground spot and another is different. The difference can be caused by many things and create many different symptoms.

(long winded explanation of my understanding)

When wiring radio communications systems I have to make the ground lines as short as possible because if they are too long or too close to an antenna or coax line, the ground can actually act like an antenna and the signal picked up through the ground line raises the potential from ground. Can cause noisy audio or even speedometers and other gauges/computer controls to go nutz in cars and video equipment interference.

All ground lines need to be ground potential. If not, any signals that make there way into the ground line can cause unwanted noises and can even damage some circuitry.

I worked for Kurzweil Music Systems as a service tech for several years and after researching a recurring problem I found out that when customers plugged their audio cables into their synths they would blow their Flash ROM.

It would back-feed just enough current that made it's way to the sensitive Flash ROM and the diodes didn't block it fast enough.

It was because they didn't use a power conditioner and the audio equipment grounds and the synth grounds were at a different potential.

Sorry, too much confusing info. :D

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No, no...not at all...fonz!

My bigger adgenda...the sustainers wierd quirks in installation touch on this...

For instace I have a neck pickup that has it's hot disconnected when the sustainer is in operation yet it still effects performance and creates noise...untill the phase of this pickup is reversed...

Strange stuff...so what you're saying...am I right...that my pickup, even though not connected at one end may still be transmitting noise like an antenna...even though it's out of the loop?

For more syptoms...check out the sustainer thread...

Sustainer Thread Noise Problem Symptoms...

pete

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I know what it is Pete! Its a Northern Hemisphere effect, caused by residual radiation created when the US governement tinkered with alien spacecraft at Area 51.

In Australia, we are protected from it by extra solar UV rays which reach us through the hole in the ozone layer.

Im happier now :D

John

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Just what I thought when I saw Chris Kinman quoted...plus we live in the future...it's already tomorrow while america sleeps.... :D ....in the future we wont have ground loops...

Plus we have our hole in the ozone layer...that's got to help...not to mention all that empty space...eptied by English Atomic tests of course so that they stay empty...and what are the Yanks up to at Pine Gap...only the hippies seem to know.... :D

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If a pickup is disconnected at one end and not, then, grounded or "killed" it CAN bring in noise OR cancel some signals to a small extent. I have never tried to recreate a problematic ground loop but I have made several by accident. I think that is why some of us have just made star grounding an integral part of design and construction. Got enough trouble getting it to LOOK decent. I see a lot of REALLY crappy wiring jobs with grounds going all over the place that don't have a noise problem. Go figure.

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If a pickup is disconnected at one end and not, then, grounded or "killed" it CAN bring in noise OR cancel some signals to a small extent.

I agree with the Doc there. Sometimes, when working out a complex switching arrangement, it is easier to disconnect a coil at one end rather than both ends, to make the switching more practical. That is generally enough to take it out as far as its contribution to the tone goes. But if one end is still connected, I always make sure it is grounded, rather than hanging off the hot connection, or halfway along a chain of coils in series. That way any noise it picks up as an antennae is taken away to ground.

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Thanks JohnH...but...

So, with my Sustainer Device where I've got effectively got speaker wires (carrying AC to the driver and putting out EMI) I've likely got some extreme electro-magnetic interferance happening...

When the phase switch is in one position in the half connected coil, it's switching it to ground perhaps killing the noise...But hang on...all the phase switch is doing is switching which end ot the coil is connected to ground...it's never "ungrounded"!!? :D

I still don't get why the phase of the coil (ie which end is grounded) should make such a difference....hmmmm

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Can you relate this to the symptoms experienced with the sustainer...the guitar is very quiet, ground loops included, but the symptoms are a little bizare...

For instance, the neck pickup is connected to ground...the phase switch will alter which end of the pickup coil is grounded, but it isn't a "loop" as one end is always free...yet...it does make a significant difference...and alternates with the driver's phase (harmonic switch)...

On the other hand, rolling the tone control pretty much all the way down nix's the noise and the device comes to life...

I've tried rigging a RC tone control of similar values to various places with mixed success so as to have this tone roll off occur only when the sustainer is activated...the problem seems to be in the disconnected electronics so attenuating the signal from the bridge pickup to the sustainer and the output seems not to quite be the answer...

Of course it may not be a stricktly ground loop problem...

pete

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Pete,

I havnt followed the sustainier thread - I figure I should start at page 1 when I do that, but thats a long read!

This single pickup, with the reversed phase. I cant see that there is a ground loop problem there. You did say however that it is connected with a single core plus shield. In that case, you might expect less noise when the shield is grounded than when the shield is hot and the core is grounded. Is that too simple?

John

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I havnt followed the sustainier thread - I figure I should start at page 1 when I do that, but thats a long read!

:D No go back a few pages say to fifty and read forward...or to get the gist check out G'Mikes pictorial in the tutorial section....

Here's a pick of the pickup....

pup-driver1b.jpg

And here it is out of it's cover...

pup-driver1a.jpg

The blue edged part is the driver coil, the black the PUp coil, a magnet under that...

You did say however that it is connected with a single core plus shield.

No, I use two core from the pickup (+ shield) so all shields are always ground...the phase switch may change which end of the coil is connected but one end alway's is grounded...

I use single core after the phase switches when the ground has been detirminded by the phase switch...

Is that too simple?

I'm afraid it might be, John. The symptoms are a bit wierd but I'm slowly getting there...for instance, once the high frequency noise is filtered out (with the tone control) it works beautifully....

pete

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I see a lot of REALLY crappy wiring jobs with grounds going all over the place that don't have a noise problem. Go figure.

Ain't that the darndest thing?! :D

I'm not an expert on this, but in a passive pickup guitar, I would think that ground loops are a non-issue compared to EMI being picked up by the pickups. It's the amplifier that amplifies the heck out of the guitar (and the hum picked up by pickups) and the amp itself can have some healthy ground currents - this is where ground loops really show up. Hence, star grounding...

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Exactly...in amplifier's and other equipment it's completely understandable...

With my sustainer guitar, I have got a small amplifier with the -ve to ground so that's why I'm looking into ground loops as a potential source...might have nothing to do with it 'course.... :D

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Exactly...in amplifier's and other equipment it's completely understandable...

With my sustainer guitar, I have got a small amplifier with the -ve to ground so that's why I'm looking into ground loops as a potential source...might have nothing to do with it 'course.... :D

Oh yeah, I forgot about that. I was thinking about conventional guitar electronics. :D

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