Making the chassis - ground connection

[JFace]

Many pedal makers either ignore grounding the enclosure, or use metal bushing instrument jacks to mechanically make the connection. The common convention for proper grounding, however, is grounding the enclosure at one point only. Using the input and output jacks to ground the enclosure causes two connections, and the potential for ground loops. This may be problematic for high gain circuits, or in my experience, connecting high current digital pedals to the "culprit" dual ground pedal.

My question is, what are some good methods to make the chassis grounded at only one point?

Some ideas:

• The input jack is metal bushing, the output jack is plastic bushing. Increases the bill of materials and doesn't look "pro", but it would work
• Solder a ground wire to the back of a pot. I haven't had much success doing this with alpha pots.
• Here's one I've done once...use a piece of copper foil from guitar shielding to connect the pcb ground to the enclosure. The tape overlapped the lip of the box so the lid would make a solid connection when closed.
• Use 9mm right angle pots with the snap-in pins...are these pins connected to the bushing of the pot? If so, one could use one of these pins as the connection to ground
• Other ideas?

[GibsonGM]

Those are all good ideas, and have been done, but I do wonder about the mechanical stability of using something like a pot or jack for the "one true ground".    Many of us fudge it, and do have more than one ground point (I typically ground both input AND output jack with a WIRE, and 'get away with it', but there sure IS the potential for a loop if it's a high gain circuit, or whatnot).   

The risk is small, but a loop COULD happen by doing this.  What is avoided is the eventual loosening of the output jack, and the horrible noise that will create on stage     Other than this horrible way I tend to do it, I'd go for the 'metal input jack/plastic output jack' as well.


So, the best thing I could throw in here based on many builds would be, if you're worried about it, to do what amp makers do with their safety grounds:   Use an actual very small BOLT thru the side of your enclosure, and connect to it via a dedicated ground wire from the PCB or whatever single point you're calling your main star.   Use a wire lug soldered to that wire, and one of those "chewy nuts" with the teeth that will bite in and make a solid ground.   Then make everything else floating (plastic jacks, no grounds on pot bodies - all grounds must go to the star).   All of your grounding/jack switching must happen very close to that bolt point to avoid ground currents.    I've seen rack gear that used this method - it works, and hey - gives you a first place to look if it peters out!  I've found more than one non-working reverb that had its ground come off this tie point.

In practice, I haven't had any issues with grounding, but you say you have and I believe it, as it's always 'lurking' and enough ppl mention it.  So, maybe one would try out some conventional things before going all the way like this, but the option is always there!   It's just a small screw head on the side of the box, so no big deal...hope that is useful.

[electrosonic]

This has come up before - I have seen the use of a battery spring terminal on the pcb which is pressed against the bare metal of the inside of the enclosure to give a single point of contact.




Andrew.

[slacker]

I use plastic jacks, these normally come with washers so I strip a couple of inches of wire and wrap it round one of the washers and connect it to the ground lug of the jack. Connect this to the rest of your grounds using whatever method you prefer, this gives one ground connection to the enclosure. It's still susceptible to coming loose through use/abuse but you don't loose your signal ground like you would relying on the enclosure to provide the ground between metal jacks.

[mth5044]

What if you use two metal jacks and only ground one of them?

[vigilante397]

What if you use two metal jacks and only ground one of them?

That's a pretty common method as well.

[pupil]

What if you use two metal jacks and only ground one of them?

That's a pretty common method as well.

but like GibsonGM noted, if two non-insulated jacks connect at ground through the enclosure by their sleeves and are not actually wired together, then if the output jack is loose and becomes ungrounded it will make a very startling noise. I think.

[davent]

If you want to isolate your metal jacks from the enclosure you can get nylon shoulder washers for the job, you just need to be sure you have enough bushing length to accommodate the added thickness of those washers.

[canman]

I must be missing something here.  Why is "grounding the enclosure at one point only" considered "proper grounding?"  Is something wrong with having a couple different grounding points?

(Not trying to be a butthead here, I'm genuinely wondering.)

[JFace]

I must be missing something here.  Why is "grounding the enclosure at one point only" considered "proper grounding?"  Is something wrong with having a couple different grounding points?

(Not trying to be a butthead here, I'm genuinely wondering.)

Basically having two grounding points causes a ground loop, which is a no-no. Here are some articles (there are many more):

http://www.rane.com/note151.html
http://valvewizard.co.uk/Grounding.html

[canman]

So essentially, any time you mount an input and output jack to the enclosure, you're creating a ground loop?  I now understand what you guys are talking about...seems like it's difficult to avoid that problem.

[davent]

So essentially, any time you mount an input and output jack to the enclosure, you're creating a ground loop?  I now understand what you guys are talking about...seems like it's difficult to avoid that problem.

You only need to connect one of the jack's grounds to the circuit if the jacks are metal and they make good contact with a metal enclosure.  Quality jacks you can properly tighten and an inner-toothed lock washer on each jack you should be good to go.
dave

[mth5044]

Also make sure there is no paint in the jack holes.



Jack holes.

[kaycee]

I really don't like soldering a ground wire to the back of a pot as a lot of people seem to do. I find it takes a fair bit of heat to get the solder to take, even if you give the back of the pot a rub down and degrease. It boils the grease inside if you are not quick enough.

I now use a small nut and bolt, and solder tag for my chassis ground, drilling through at a convenient point. Cost a few pence each build. I know that there is a possibility of the nut working loose so I stop it with a dab of hot glue.

[anotherjim]

Once upon a time it was really easy to solder a wire onto the back of a pot, but there are some now, Alpha included, that are plated with something that doesn't like solder. Solution is to file off the plating at a spot near an edge and get some solder on quick before it can oxidise - but you need a powerful iron that will heat the spot up quickly before everything else does. Sometimes there's a tab on the pot case (not the cast tabs like Alpha have) meant to go in an anti-turn hole, and you can bend that out and solder a ground wire to that.

My take on ground arrangement is a star connection from the output jack ground.

[bool]

Jacks will do it for free ... (in low power stompboxes at least).


... "This is the house that Jack built" ...

[GibsonGM]

I always connect a REAL ground wire to in/out jacks. Had 1 bad experience where an output jack came loose on stage and sounded like total @ss, lol.  To me, any savings in hiss are minor compared to looking like a tool when your main pedal is now out until you can open it to tighten the jack up    

As always, the extent you need to go to is really variable, and kind of personal....my builds seem to require very little attention to this.    So I'm looking at this as an academic exercise      One point of contact, SOLID, that will not come loose, is the ideal ground and what is aimed for in amps.    Ground connections made to things like pots that could spin loose aren't really considered to be a good idea. 

In the end, the currents flowing around MOST stomp boxes aren't going to be great enough to generate big noise voltages on short wire runs, except for the odd very high gain monster pedal...which is already putting out monster sound, IMO....   So, try a couple of things and see what works for you!

I get TWO connections because i typically have the input jack grounded to enclosure, and include the output jack's 'dead man' wire.  Never an issue.    Maybe if I did true star grounding, 1 point only, I could make things quieter, but have not had noise apparent much above my amp's noise floor....I'm one who NEVER leaves a distortion on between songs, tho...I don't expect them to be "quiet", don't require it of them, and know it's almost mystical to think they WILL be hiss-free at gain of 10...

[vigilante397]

As always, the extent you need to go to is really variable, and kind of personal....my builds seem to require very little attention to this.    So I'm looking at this as an academic exercise

You perfectly summed up my feelings on the subject. I have never had an issue with ground loop noise on any build, even the couple high-gain monsters I've built. I ground both jacks simply because it seems "safe."

[JFace]

I am designing a mixer pedal that has input, output, send, and return jacks. If all four jacks are chassis grounded, and I connect a fuzz pedal (that also has chassis connected jacks) in the send/return path, this seems like a potential noisy situation. I am contemplating leaving all jack grounds unwired except one, and make sure they are really tight, with the possibility of loctite in the threads to keep them secure.

Interestingly, however, the boss LS2 is similar in concept and I believe all their jacks are chassis grounded.

[GGBB]

In the end, the currents flowing around MOST stomp boxes aren't going to be great enough to generate big noise voltages on short wire runs, except for the odd very high gain monster pedal...which is already putting out monster sound, IMO....   So, try a couple of things and see what works for you!

+1

One thing we've left out here is that a greater risk of ground loops in pedal boards stems from the power supply ground, not the chassis/shield/signal ground. When you have multiple pedals sharing the same non-isolated supply (such as with daisy-chain cables or multiple regulated outputs from the same transformer/secondary), the power cable grounds are all forming ground loops with the signal cable shields that are probably somewhat larger than any loop you might have within a pedal. And yet even these are often not problematic. The other big opportunity for ground loops is your amp's effects loop. With the cable shields connected to the grounds of both the input and output of the loop which share the amp's ground, you are creating a big loop unless your amp lifts one of the grounds (unlikely). If you also have effects in front of the amp, and they share the power supply ground with the loop's effects, you create another big loop formed by the input section effects and cable, loop send cable, and power supply ground. Fun , eh? That's why some players resort to using batteries instead of power supplies, and that's also why we have multiple isolated output power supplies.

IMO, loops inside pedals are the least of our problems.