Grounding to a metal case

[robbiemcm]

Yeah, I've read alot from topics, so don't tell me to use the search feature. I'm just trying to make sense of it without the seemingly conflicting information I get from just reading other topics.

1. The metal part of my jacks are touching the case, I've heard about ground loops and stuff, but what if I only have one stompbox... will this still be a problem?

2. I wanted a switch for power on/off instead of disconnecting the leads. The ground of my PCB is connected to the case, a wire from my switch is connected to the case, and a wire from my switch is connected to the (-) of my battery. Is this wrong?

[EDIT]

3. I see some people have plastic washers on there switches... is this to isolate  them? And if so... why would you do this?

Thanks for all help you can give me
Robbie

[puretube]

3.):  the washers are solely for protecting the case/paint/artwork from being scratched...

[octafish]

1. I didn't use to bother isolating jacks until I built my first big gain circuit (BMP) it had a hum that was driving me nuts. So I relented and isolated the out socket. The hum was reduced significantly. The rest of the hum is from my cables or guitar or something I think. So if your effect is humming you could try isolating one of the jacks.
2. Does it work? Sounds like it should. Common practice is to tie all ground to one point, call it star grounding. Its an amp building thing, probably not neccesary for stomps but a good practice anyway.
3. I think also the washers give the switches something to apsorb the impact of someones great big boot crashing down on them... a little...as well as protecting the paint.

In my practice I tie all my grounds to the input socket, and sometimes isolate the output if I'm having problems. But thats me.

[puretube]

ooops: now you say it,
that "impact-distribute" thing is a good reason for those large washers...
- haven`t thought about that before, coz I don`t like the "look" -

TNX

[robbiemcm]

Thanks for that, I've actually got other problems which I havn't figured out that's currently keeping my first build from not working. It's screeching, and the pitch can be set by the gain pot :S I was just trying to get this figured out for future builds, plus I find it painful when theory doesn't work and I can't figure something out in my head. Things I think I should know, that I don't understand make me extremely distracted and annoyed. That's probably a bad thing considering I have 7 exams in the next 2 weeks.

[gaussmarkov]

Yeah, I've read alot from topics, so don't tell me to use the search feature. I'm just trying to make sense of it without the seemingly conflicting information I get from just reading other topics.

+1   And I agree with what octafish and puretube say.

1. The metal part of my jacks are touching the case, I've heard about ground loops and stuff, but what if I only have one stompbox... will this still be a problem?

I think it could be in this case also.  But ... i interpret every FAQ that I have read says don't worry about this.  I have spent a fair amount of time trying to get this right and I put some quotes here.  So far that seems to have stood the forum test.  But maybe this thread will shed more insight.

2. I wanted a switch for power on/off instead of disconnecting the leads. The ground of my PCB is connected to the case, a wire from my switch is connected to the case, and a wire from my switch is connected to the (-) of my battery. Is this wrong?

I think best practice would remove one of these connections.  The logic of the star grounding system that is widely used for amps implies (to me) that best practice would be to use the ground on your output as the ground for the whole unit, because that is where the ground actually is.  Your guitar isn't grounded, the stompbox isn't grounded, but your amp is.  So, if you need to be careful, then isolate all other jacks but the output.  Run the grounds from the other jacks to a single grounding spot on your pcb, and run a connection from there to your output jack's sleeve.  The enclosure is grounded there too because it's not isolated from that jack.  With this arrangement everything grounds to that one spot.

[niftydog]

all the pedals I've ever peeked inside only ever have a single ground connection to the chassis, usually on the input jack. This means that the output jack can be contacting the chassis, but as it's not connected to the circuit ground you won't cause a ground loop. Just an observation that might help.

The switch thing sounds ok, provided the ONLY connection from the -ve battery terminal is to this switch.

[gaussmarkov]

all the pedals I've ever peeked inside only ever have a single ground connection to the chassis, usually on the input jack. This means that the output jack can be contacting the chassis, but as it's not connected to the circuit ground you won't cause a ground loop. Just an observation that might help.

niftydog, when you say "ground connection to the chassis," do you mean a wire running from the sleeve lug to a ground lug screwed into the chassis, or something similar?

your comment gave me the idea to go and open up some pedals and here's my little survey.  i looked at a loooper pedal (1 loop), a zvex super duper (dated 11/15/01), a and a barber direct drive ss.  i had already borrowed the first two from a friend to see what was inside.  i own the barber which, by the way, is gorgeous inside.  something to aspire to.

but i meander.  here are the results.  there are no insulated jacks--all contact the chassis.  and there are no other jack connections to the chassis, like to a ground lug.  the loooper pedal is passive (except for the led) and most of its jacks have no ground wires.  the super duper uses a stereo input plug in the usual way to connect the battery (there is no dc jack) and the ground for the circuit is on the input jack.  there is no ground wire on the output jack.  the ddss also has the stereo input jack and additionally has a dc jack.  both jacks run wires from ground lugs to the pcb.

not a lot of data, but at least an actual survey.   we must be careful not to extrapolate far beyond these few observations.  :?  i guess it's not surprising to find the only ground wire on the input jack when it's managing the battery connection.  probably common practice so that the input jack may typically ground the pcb.  but ... i gotta stop talking about this. :wink:

[niftydog]

what I meant was; only one jack in any one pedal has a ground wire connected between it and the circuit board.

The lug screwed to the chassis is not a bad idea, but to me it's overkill. I'm no mojohead.

My basic rule is this; any circuit with more than one connection to ground has the potential for causing ground loops.

Sadly, this means most pedals have the potential to cause ground loops by virtue of the fact that the ground is connected to the signal input as well as the DC power jack.  

[aron]

I've made so many pedals and none of them have had hum issues from grounding jacks. Mostly hi-gain pedals - none have had hum.

Almost all commercial pedals ground their jacks. If you solve your hum problem by isolating and star grounding your pedal, then great. Until you get the hum, I would simply ground my jacks and not worry about it.

[ESPguitar]

What can i use to isolate 11 and jacks from switchcraft?

Thanks,

RB

[robbiemcm]

Alright three new things that have popped up for me.

1. What is star grounding? Is that all things that are to be grounded are connected at the same point? If so is that what all the problems grounding the jacks is about, because they will be connected at different points (I have them connected to the circuit board, but they touch the case aswell).

2. What's the deal with A/B boxes... I thought they were simple and needed no battery other than for LED? Couldn't you just do it (well this is for no LED) by getting a DPDT stomp switch, all jacks grounded to the metal case, signal is switched to one jack, the other jacks tip is grounded at that time using the other pole-ness of the DPDT switch?

3. What's the difference between an A/B and an A/B/Y ?

[JimRayden]

3. I think the "Y" stands for the method it connects. It connects an input into either of the two outputs or vice versa. The connection looks kinda like a "y". So I see no difference between A/B and A/B/Y.

Or, the A/B/Y could be a new kinda box I haven't heard of yet.  :?

-----------
Jimbo

[robbiemcm]

That makes a fair amount of sense... on top of the other 2 questions, what happens if you don't ground the input?

[gaussmarkov]

Alright three new things that have popped up for me.

1. What is star grounding? Is that all things that are to be grounded are connected at the same point? If so is that what all the problems grounding the jacks is about, because they will be connected at different points (I have them connected to the circuit board, but they touch the case aswell).

See the Aiken Amps explanation.  I think a better name would've been "tree" or "river" grounding.  The routes to ground are supposed to look like a system of tributaries running into one final connection to ground.

2. What's the deal with A/B boxes... I thought they were simple and needed no battery other than for LED? Couldn't you just do it (well this is for no LED) by getting a DPDT stomp switch, all jacks grounded to the metal case, signal is switched to one jack, the other jacks tip is grounded at that time using the other pole-ness of the DPDT switch?

3. What's the difference between an A/B and an A/B/Y ?

A/B boxes switch between two channels, labelled A and B.  A/B/Y boxes have a third option, both channels at once.  These boxes are passive and only need volts for LEDs.  But they have potential grounding problems that cause either audible pops when the channels are switched or hums from ground loops that come from hooking up two (grounded) amps to the same stompbox.   The latter is a violation of star grounding because there are two routes/rivers to ground, the two amps.

[gaussmarkov]

That makes a fair amount of sense... on top of the other 2 questions, what happens if you don't ground the input?

Depends on whether there is a ground connection somewhere else.  For my first A/B box, I insulated all of the jacks (input and output).  So the signal ground did not contact the metal enclosure.  The result was that the stompbox hummed.  Letting one jack ground contact the enclosure removed the problem because it grounded the enclosure.  It does not matter which jack you use for the ground.

By the way, I have the impression that there is some confusion about whether the enclosure is the ground or a jack is grounded by the enclosure.  What makes sense to me is to say that the enclosure can provide a route to ground for a jack but that the ground for a stompbox is the ground of the output jack, which connects directly to the ground wire in the output cable which connects to the ground of the amp which really goes to earth.  Naturally, this gets abbreviated in discussions among the knowing so that sometimes it sounds like the enclosure is where you ground your stompbox.

What can i use to isolate 11 and jacks from switchcraft?

I used the washers mentioned in the  FAQ:

How do I isolate my jacks from the enclosure?

From R.G.

Two choices:
(a) get insulated bushing jacks like the Switchcraft N1xx typesor the ReAn nylon body ones (excellent choice, that). Mouser has both.
(b) buy the white nylon bushings that Mouser offers. These fit a 1/2" hole and have a 3/8" hole for a standard jack.They're used a lot in isolating input jacks for tube amp hum reduction.

From JD

If you want to go with the nylon washers, here are the Mouserpart numbers for the washers that work with Switchcraft jacks

561-SW375 - Nylon Shoulder Washer
561-D37562 - Nylon Flat Washer[/list:u]

[robbiemcm]

Thanks this answers a lot of questions I have. But if one only one jack is touching the metal case, say the output jack... then if the input jack isn't touching the metal case, won't there be no grounding for whatever your input is?

[gaussmarkov]

Thanks this answers a lot of questions I have. But if one only one jack is touching the metal case, say the output jack... then if the input jack isn't touching the metal case, won't there be no grounding for whatever your input is?

That's right, unless you run a wire connecting the ground lug of your input jack to the ground trace on your pcb.  That's part of "general practice."  Run wires from each jack's ground/sleeve lug to grounded points on your pcb so that all jacks are grounded.

Now if one jack (say the output) touches the enclosure, the enclosure will be grounded through that jack.

You may have noticed that on pcb's from GGG the various ground connections are all in one spot.  This is clear pcb design and it makes a "star ground" for the circuit/stompbox.  Here's a couple of examples from the Boosters/Routers section of Effects Projects: the Brian May Treble Booster and the the LPB2.  Notice how all the jack's have ground wires running to points that line up together on the same corner of the pcb.  And that's where all the other ground wires are going, too, like the volume pot ground for the LPB2 and the DC jack ground for the Brian May.