Is this a ground loop?

[fuzzy645]

Lets consider the particular circuit in question a "black box" for the purpose of my question.  Imagine any fully functional fuzz or overdrive or booster circuit board with 4 color coded leads: input (white), output (blue), power rail (red), and ground (black).  Assume the circuit has been fully tested and is perfect.  Also (for the sake of simplicity and to stay focused on the topic of ground loops), assume we will not be using any kind of on/off foot switch, no LED and no DC jack.   

• I solder the circuit board's red wire to a battery snap's red lead.  No problem.


• I solder the circuit board's white wire to the input jack tip. No problem.


• I solder the circuit board's Blue wire to the output jack tip.  All is good.


• I then solder a new wire to the input jack ground lug (lets call this wire A).  I solder yet another wire to the output jack ground lug (lets call this wire B).  I then take A and B, and solder them to the circuit board's black wire (that is, to the circuit ground), along with the battery snap's black wire to form a common ground.  All should be good.  Lets say this tests out 100% perfect when not mounted into an enclosure.


• OK, here's where it gets dicey.  If I mount this whole thing into a metal enclosure, would this now form a ground loop given the way I have described the connections? The reason I ask, is both the input jack and the output jack ground lugs connect to the metal box, and therefore form an additional path to ground.  In other words.  You have the input jack's ground lug soldered to ground via wire A.  You have the output jack's ground lug soldered to ground via wire B.  These input and output jack's ground lugs happen to come together a 2nd time due to the enclosure being conductive and therefore connecting them.
  

Has anyone had problems with this?  What is the common solution?  Would it be to use plastic jacks?   Is there some other solution?

Thanks in advance.

[armdnrdy]

Without spending too much time wrapping my head around your "Ins and Outs",

The best practice is to bring all of the "grounds" back to one location. (star ground)

You want to keep separate paths for signal and power.

IN/out jacks and board power ground should all go back to a common point.

[GGBB]

From what I've gathered elsewhere on this forum, yes it is a ground loop.  A problem?  Not necessarily - depends on the circuit and what else is connected etc.  Typically, this is avoided via either plastic jack housings (but you then need to deliberately ground the box) or - how many DIYers and boutique/custom builders do it - simply not connecting the output jack's ground lug (let the box take care of it).

[fuzzy645]

From what I've gathered elsewhere on this forum, yes it is a ground loop.  A problem?  Not necessarily - depends on the circuit and what else is connected etc.  Typically, this is avoided via either plastic jack housings (but you then need to deliberately ground the box) or - how many DIYers and boutique/custom builders do it - simply not connecting the output jack's ground lug (let the box take care of it).

That does indeed sound like an elegant solution, thanks!  So by not connecting the ground lug of the output jack directly to ground via way of an explicit wire, it gets grounded via way of the metal enclosure which is connected to ground lug of the input jack which is explicitly grounded by a wire.  Got it.  Thank you!!

[armdnrdy]

That does indeed sound like an elegant solution, thanks!  So by not connecting the ground lug of the output jack directly to ground via way of an explicit wire, it gets grounded via way of the metal enclosure which is connected to ground lug of the input jack which is explicitly grounded by a wire.  Got it.  Thank you!!

I actually have never seen grounding the In/out jacks via the enclosure referred to as "elegant".

This is how some pedal manufacturers used to ground the jacks to save time. (time = money)

The major problem with this arrangement is if the jack nut comes loose.......and they do.......you have lost signal ground.

I would ground the jacks using the enclosure only if I were held at gunpoint!

[fuzzy645]

That does indeed sound like an elegant solution, thanks!  So by not connecting the ground lug of the output jack directly to ground via way of an explicit wire, it gets grounded via way of the metal enclosure which is connected to ground lug of the input jack which is explicitly grounded by a wire.  Got it.  Thank you!!

I actually have never seen grounding the In/out jacks via the enclosure referred to as "elegant".

This is how some pedal manufacturers used to ground the jacks to save time. (time = money)

The major problem with this arrangement is if the jack nut comes loose.......and they do.......you have lost signal ground.

I would ground the jacks using the enclosure only if I were held at gunpoint!

Armdnrdy - Appreciate the advise, thanks!  That is a good point too.  So how would you then avoid the ground loop?  Do you use plastic jacks, and then explicitly ground the metal enclosure via way of a wire?  Or rather, do you not worry about the ground loop?

I fully realize that on many circuits the ground loop is not an issue, but on some it might very well be an issue.

[armdnrdy]

It depends on the circuit,

I star ground things with clocks, LFOs, and the like, but for less complicated "dirt boxes", I don't think that it's as much of an issue.

[GGBB]

The major problem with this arrangement is if the jack nut comes loose.......and they do.......you have lost signal ground.

It's a trade off I suppose - easy solution vs. potential vulnerability.  Even if it comes loose, there is usually still a connection due to connector weight and gravity etc. although it is not at all a secure one.  At least its very easy and quick to fix.  For my purposes it doesn't worry me at all.

[DIMstompboxes]

For usual negative ground, I just use 4pcs black wire all connected to input lug and for those other end on:
1. negative (power input jack)
2. (one)circuit board ground
3. output lug
4. (one on the) 3pdt

for LED supply
1. (black)neg wire from 3pdt lug to LED
2. (red)positive wire with resistor to LED connected to positive power supply

I don't use battery no more.

[pinkjimiphoton]

yes, it's a ground loop and may or may not cause hum.

i use open frame stereo metal headphone jacks for input, and them plastic ones for the outputs and do exactly what you do, but there's only one ground, at the input jack that way. works great.

[PRR]

A ground-loop, INside a box, NOT siting on high-power wiring, is often not a problem.

And I know you probably are not working around hi-power wires because your guitar pickup is like 5,000 ground-loops stacked-up and only partially enclosed. If the guitar isn't hum/buzzing like mad, the ground-loop inside the pedal is probably not gonna spoil your gig.

[pinkjimiphoton]

the shielding is effectively a box anyways, innit? and vice-versa... as long as both are connected to ground, they form a faraday cage around the circuit, right?

[johngreene]

While technically you could say this is a ground loop, it isn't likely to be a problem because the Chassis ground is completely surrounding the inside ground path (i.e. a 'shield'). Because the chassis ground is such a low impedance it would be quite unlikely any voltage could develop across it. If you are concerned about it the solution would be to use a plastic isolated output jack that gets its ground from the circuit board only. Personally I like to have a continuous outside shield all along the signal path. Internal loops inside the effects should not be a problem if you use good design practices.