# Who Understands Ground Loops?



## david henman (Feb 3, 2006)

...okay, so you've got your pedal board set up. effects like compression, overdrive and distortion go in the front end (guitar input) of your amp. time-based effects (delay, reverb, chorus etc) are routed through the effects loop. done!

but wait, what is that loud hum, which gets even louder when you kick in your high gain distortion pedal?

that, according to ALL of the experts i have polled, is a "ground loop".

there are, apparently, devices that will "mask" it, and maybe that is the way to go, but i would like to think that there is a way to solve this problem "at the source" as it were.

anyone?

-dh


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## bolero (Oct 11, 2006)

same here, no expert, but if you reverse the FX plugs in the outlet you may find the offender & get rid of it. 

from what I understand *ground* has to be the same for each unit...so if one has a circuit that differs or inverts the ground reference in relation to the others ( or the 2 prong plug is backwards in relation to the other FX ) it will hum.

same thing with multiple amps, but it gets a bit dangerous as the voltages are higher. ground lift switches will kill the hum, but can also kill you....or make you dance like a banana :banana:


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## PaulS (Feb 27, 2006)

Also from the not an expert section, I have seen on some schematics the reference to positive ground circuit and negative ground circuit. If one was to have a mix of these could they be the culprit ????? :confused-smiley-010


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## Coustfan'01 (Sep 27, 2006)

I have a couple of electronic classes in my field of study . I don't remember all that much about it , but I remember it's when there's current going from one ground to the other(duh ) . I also remember there are ways to get rid of it , by separating the grounds from one another , like by using optocoupler(if that's the same word in english) , optic fiber , or, more likely in your case , the ground lift switch . Don't think I'm an expert...But I'm almost sure there are ways to solve that other than lowering the gain , putting a nosie gate or a smart ass answers along those lines .


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## david henman (Feb 3, 2006)

...yeah, i forgot to mention that the ground loop is caused by the fact that both chains of effects are plugged into the same power bar. at least, that's what the experts tell me. a cheater (ground lift, or two-prong plug) might fix the hum, but i refuse to go that route.

at the moment i'm running ALL of the effects into the front end (guitar input) and that has reduced the hum somewhat.

mainly, i'm curious to see if any of you have run into the same problem, to find out what you learned and how you addressed it.

-dh


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## Ripper (Jul 1, 2006)

ground loops are a fairly common thing, both with effects and causing noise in amps and electronics circuits. David it might be something as simple as a haloed/cold solder joint on a ground in one of your pedals causing the offending hum. It can also be caused by poor power bars. On my pedal boards I use a switching power supply (from an old laptop, those power supplies work great and most have a pot inside to adjust the voltage. They also put out enough amperage to power alot of pedals). Since going this route I have never had a problem with ground hum.

Faulty guitar cables can also be a culprit in the situation. The easiest place to start is to see if you can isolate it to one offending pedal. If so, then that pedal can be taken a look at. Are your pedals each powered by a separate wall-wart/adapter? One of those could be causing the issue as well.


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## Wild Bill (May 3, 2006)

*"What he said..."*



Ripper said:


> ground loops are a fairly common thing, both with effects and causing noise in amps and electronics circuits. David it might be something as simple as a haloed/cold solder joint on a ground in one of your pedals causing the offending hum. It can also be caused by poor power bars. On my pedal boards I use a switching power supply (from an old laptop, those power supplies work great and most have a pot inside to adjust the voltage. They also put out enough amperage to power alot of pedals). Since going this route I have never had a problem with ground hum.
> 
> Faulty guitar cables can also be a culprit in the situation. The easiest place to start is to see if you can isolate it to one offending pedal. If so, then that pedal can be taken a look at. Are your pedals each powered by a separate wall-wart/adapter? One of those could be causing the issue as well.


Ripper is right in his suggestions. I would add a bit, however.

Ground loops causing hum in audio installations have nothing to do with a power supply using negative or positive as ground. They are caused by a hum signal having multiple paths to ground. Hum is an AC signal and you can't think of ground like with a car, where any metal anywhere is a good ground.

The change to 3-prong power wiring was actually the biggest pain in the ass ever given to audio technicians. The problem of ground loops increased a hundred fold.

Consider that any audio device (including pedals run from a wall-wart supply) grounds the outside shield of the in/out patch cords. In the old days you could simply wire all the units with a separate ground wire to a common ground in the system, usually a rack in the studio. All hum was routed to one ground point. The AC supply was 2-wire. True, one side of the power from the wall was grounded but if one unit added some hum you could simply flip the plug over at the wall and that would likely fix it. If you got ground loops you could move the ground wires to run in a "daisy chain" from unit to unit and then grounded at the end.

With a 3-wire system every unit's power cord is a path to ground but hum signals can also "loop" between units by running along the outer ground of the patch cords. There are no ground wires you can move and besides, there's now a ground through the power cords that's "cast in stone" that defeats the purpose of dedicated ground wires.

You should understand that the electricity companies never even thought about ground loops with a 3-prong system causing problems in audio studios or stages. They cared only about power safety. An electric skilsaw can be a shock hazard. Audio hum is somebody else's problem.

So what can one do about it? Well, cleaning up the usual rat's nest of wires and pedals in front of the guitarist is the first start. You can start with one common power bar if each pedal has it's own supply. Sometimes adding the pedal supplies one at a time will identify a specific culprit. Try flipping this one around in the plug. Having just one master supply for all the pedals is a great idea! Most pedal makers will have such a solution but it rarely works for the one different brand you just had to add to the mix!

Using batteries will often quiet things down enormously as well but it can get expensive.

There's more but if you're not a techie then you're not likely to understand it well enough to implement it. Odds are these tips will be enough anyway.

Me, I believe in a Les Paul plugged straight into a 100 watt JMP feeding a stack of vintage Celestions. If you want a boost then use heavier strings and dig in with your pick over the bridge pickup! The only extra hum will be coming from forgetting your RightGuard...


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## david henman (Feb 3, 2006)

...i should also mention that i have tried isolating each individual pedal. no one pedal is the culprit, unfortunately.

the hum is deep and low, not a "buzz".

i'm doing a lot of research on this, and i intend to report back if and when i am able to determine the specific cause.

-dh


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## sysexguy (Mar 5, 2006)

I like to think I know a thing or two about ground loops. The only way to get rid of them is to assure that all possible ground loops are eliminated. If there is one gl, you have 1 problem, but then it becomes a series as every possible alternate path to ground is an alternate for all previous paths.

The first thing is that the effects loop comes from the amp (send) and eventually goes back (return) so as those cables are grounded via the shields, you start with a ground loop by default. On some amps, they have forseen this and isolated one of these jacks but they likely haven't.

A simple test, plug 2 working 1/4 guitar cables into the loop and simply touch the two tips together without connecting the sleeve. If there is no hum, you now have one ground loop localized. Options are either to telescope the shield on one of the loop wires or get an isolation transformer in line in the loop. I'd start with a cable with the shield telescoped from the send ie. not connected on the first effect input. Cost the time it takes to open the jack and open the sleeve connection on one side. I usually don't cut it but rather desolder it, bend it back and cover it with heatshrink. That way the cable can be returned to normal in seconds. Labeling the cable is good practice.

Next possible problem are any effects with a 3 prong plug, either in the effect loop or before the input. The quick and easy, but less safe method is to eliminate the third pin via grey ground lifts or (don't) breaking the ground pin. I'd recommend using the grey ground lifts only as a last resort and not on anything big and powerful (like an amp) but they can be helpful in diagnosing the problem. Remove all pedals that don't have an Ac plug and add grey ground lifts to all of the AC plugs except the amp. Now go about replacing the grey ground lift (one unit at a time) with a ground lifted audio cable from that unit's output to the next effect or amp input (input or fx return). If this doesn't cure a unit, you will likely need an audio isolation transformer.....(note, this is a tiny transformer like the inside of a DI not a power transformer) or you may need a technician to clean up a dirty ground (circuit ground/chassis ground problem). Racks can also provide a nasty ground loop path so start with all units un-racked and not touching (magazines work well here, use tywraps to keep the units from sliding around when patching). Then, once the system is noise free, introduce each unit, one at a time into the rack. Stepped plastic washers (front and back) will assure a ground loop free install (Raxess/Mid Atlantic).....don't get the non stepped ones. 

Finally, connect the pedals and their power supplies. Daisy chain power supplies like Powerall or Boss cause ground loops especially if power is distributed to both effects loop and input effect simultaneously. A better choice is something like a Pedal Power II which has 8 isolated outputs or better yet a DNA unit that is actually supplying 8 runs of battery power.

If the setup involves any effects in stereo, you should start by getting one side perfect before even thinking out the second side. If you are using a stereo power amp, use identical length cables for stereo runs. If two distinct amps are used, an isolation box like the Lehle P Split will be essential in assuring everything works noise free.

Be sure to test each step one step at a time or you'll be starting all over from step one.....there are no shortcuts.

or you can pay Pete Cornish his rate:bow: 

Andy


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## Brian G (Aug 17, 2006)

Sounds like your problem is in all likelihood caused by a ground loop, but if it proves not to be, and depending on how it actually sounds (e.g. 60Hz or a 
1st harmonic of that at 120Hz), it's possible to be an artifact of dirty power that your system is sensitive to.

Is this in a home, and do you have exactly the same problem in a different location, e.g. another room, or is it in a practice space or similar? All our power is "dirty" from the grid, and problems are exacerbated by certain kinds of motors, dimmers, lighting controllers, switching power supplies, and on and on. That's why some very top-end audio systems use power isolation transformers, which can block common-mode noise that adversely affects the performance potential of the system, allowing audibly lower noise floors, a greater sense of sounds coming out of "black backgrounds", etc. and increasing perceived transparency.

One comment above is that a small, signal-level isolation transformer can often "break" a loop, because the transformer passes signal except at DC, which severs the loop. Jensen (not the speaker company) is one manufacturer of this type of transformer designed to solve ground loop problems for both audio and video. These are solutions when it's not practical or possible to resolve the problem at it's source.

(If you've already identified the problem as a loop, please ignore the above.)

Brian


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## david henman (Feb 3, 2006)

sysexguy said:


> Daisy chain power supplies like Powerall or Boss cause ground loops especially if power is distributed to both effects loop and input effect simultaneously. A better choice is something like a Pedal Power II which has 8 isolated outputs or better yet a DNA unit that is actually supplying 8 runs of battery power. Andy


...my pedalboard has exactly that: a powerall power supply connected "to both effects loop and input effect simultaneously."

what is a "DNA unit"?

-dh


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## sysexguy (Mar 5, 2006)

http://www.godlyke.com/shopping/pgm...scat=28&frompage=Online_Store&page_num=1&=SID

Might be MOL Marketing in Canada in which case call "the Arts"

Andy


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## david henman (Feb 3, 2006)

sysexguy said:


> http://www.godlyke.com/shopping/pgm...scat=28&frompage=Online_Store&page_num=1&=SID
> Might be MOL Marketing in Canada in which case call "the Arts"
> Andy


...yikes! pricey! nonetheless, if that's what it takes...

i should mention that i currently have everything running into the front end (guitar input) of the amp, and this does reduce the noice by about one third. 

i am continuing to experiment. for example, i'll try running each pedal from its own power supply. i may try running all the pedals on battery power, just to see what that tells me. i'll also test each power supply separately - i've read that the godlyke powerall can be noisy.

-dh


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## sysexguy (Mar 5, 2006)

btw, Burkhard Lehle insisted I get a Pedal Power II...which I did...for myself and several boards I built for studio clients live rigs (pics posted elsewhere on this board). I posted my post over at the gear page as well.....breaking off ground prongs is a macgyverism at its worst.

Some other sources of ground loop advice include the Rane tech FAQ's, Soundon Sound online and Gear****z. 

Andy

ps.....moderators? I didn't post those "****" it may be a bad word in your forum dictionary however I was refering to one of the most respected pro audio discussion forums, rhymes with.....putz


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## Ripper (Jul 1, 2006)

Just out of curiousity does it do it with any amp you plug it into??


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## david henman (Feb 3, 2006)

Ripper said:


> Just out of curiousity does it do it with any amp you plug it into??


...yup. even if i plug straight into the tascam portastudio.

-dh


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## gproud (Mar 2, 2006)

I have one of these (the small one) http://www.ebtechaudio.com/he-2des.html 
that I'm not using. If you think you might be interested I'll sell. I bought it because I was having hum problems, but most of the issue revolved around my amp. I have a Ceriatone amp that I bought from Nik and when I installed it in the headbox, didn't put any shielding on the case where the open part of the chassis sits. That was the issue. Let me know if this floats your boat.


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## david henman (Feb 3, 2006)

gproud said:


> I have one of these (the small one) http://www.ebtechaudio.com/he-2des.html
> that I'm not using. If you think you might be interested I'll sell. I bought it because I was having hum problems, but most of the issue revolved around my amp. I have a Ceriatone amp that I bought from Nik and when I installed it in the headbox, didn't put any shielding on the case where the open part of the chassis sits. That was the issue. Let me know if this floats your boat.


... i am defintely interested!

[email protected]

i have resolved most of the noise issues, so using one of these would probably be appropriate.

thanks!

i also plan to get a pedal power II - that should pretty much take care of any noise issues.

-dh


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## gproud (Mar 2, 2006)

david henman said:


> ... i am defintely interested!
> 
> [email protected]
> 
> ...


You have been emailed'd :wave:


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## david henman (Feb 3, 2006)

...i am very happy to report that the ebtech hum eliminator that the gentleman above (geoff proud) sold me has resolved ALL the noise issues coming from my pedal board!

it even quieted my very noisy tonebone hot british pedal!

thank you, my friend!

-dh


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## gproud (Mar 2, 2006)

david henman said:


> ...i am very happy to report that the ebtech hum eliminator that the gentleman above (geoff proud) sold me has resolved ALL the noise issues coming from my pedal board!
> 
> it even quieted my very noisy tonebone hot british pedal!
> 
> ...


My pleasure. It's nice to make someone's day with their gear. :banana:


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