Any rules for grounding the box with plastic jacks? Weird grounding issue.

[midwayfair]

Technically this is a solved problem, but what I don't understand is WHY.

Project: Mysterioso this time, though it could be any box with plastic jacks.

Substitutions, etc: Not really relevant here, but the mids boost was on a foot switch.

Problem: Ran into a VERY peculiar issue. I built and boxed a Mysterioso and used plastic jacks, and I was getting some buzzing whenever I touched the box. Sounded like something wasn't grounded properly, or maybe something was grounding that shouldn't, so I opened it up and clamped one of my multimeter probes to the case and went over the entire board and every single lug of the switches, jacks, etc ... nothing. Well now I'm more than just a little curious ... why was my body causing any sound change when there was no contact of any sort between the circuit and the box?

Anyway, after poking and prodding a bit, and noticing that the issue "solved" itself when I touched my guitar strings at the same time, I decided that this particular box just really, really wanted to be grounded. So I ran a little wire to the enclosure and it completely solved the issue.

Nevertheless ... wtf.

Now I'm wondering, should I open up all my mini boxes and ground all the cases? They ALL use plastic jacks. And though I've never encountered anything like this in the past, maybe there's some sort of benefit to doing it?

I did realize while typing this that the layout involved running a ground wire along 75% of the perimeter of the box, and that the ground rail on the perf was most of the remaining 25% of the box, so maybe this had something to do with it, and that would be a lot more antenna than exists in a 1590A ground scheme.

[pappasmurfsharem]

Technically this is a solved problem, but what I don't understand is WHY.

Project: Mysterioso this time, though it could be any box with plastic jacks.

Substitutions, etc: Not really relevant here, but the mids boost was on a foot switch.

Problem: Ran into a VERY peculiar issue. I built and boxed a Mysterioso and used plastic jacks, and I was getting some buzzing whenever I touched the box. Sounded like something wasn't grounded properly, or maybe something was grounding that shouldn't, so I opened it up and clamped one of my multimeter probes to the case and went over the entire board and every single lug of the switches, jacks, etc ... nothing. Well now I'm more than just a little curious ... why was my body causing any sound change when there was no contact of any sort between the circuit and the box?

Anyway, after poking and prodding a bit, and noticing that the issue "solved" itself when I touched my guitar strings at the same time, I decided that this particular box just really, really wanted to be grounded. So I ran a little wire to the enclosure and it completely solved the issue.

Nevertheless ... wtf.

Now I'm wondering, should I open up all my mini boxes and ground all the cases? They ALL use plastic jacks. And though I've never encountered anything like this in the past, maybe there's some sort of benefit to doing it?

I did realize while typing this that the layout involved running a ground wire along 75% of the perimeter of the box, and that the ground rail on the perf was most of the remaining 25% of the box, so maybe this had something to do with it, and that would be a lot more antenna than exists in a 1590A ground scheme.

I'm quite the noob when is comes to this, but did you also ground the sleeve on your Output jack? Since a plastic jack doesn't ground with the enclosure

[midwayfair]

I'm quite the noob when is comes to this, but did you also ground the sleeve on your Output jack? Since a plastic jack doesn't ground with the enclosure

Yes, all my ground points, including both jacks, are tied together by a single wire. I usually do that even with metal jacks in case I need to remove the jacks from the box for troubleshooting.

[nzCdog]

Jon, the plastic insulated jacks shouldn't behave differently to the mica-insulated neutrik style, providing they aren't broke that is. 

On the face of it sounds to me like it might have been a grounding continuity issue inside the enclosure, where one of the ground points may have had poor connection due to oxidation, paint, dry joint etc...  Glad you fixed it tho

[midwayfair]

Jon, the plastic insulated jacks shouldn't behave differently to the mica-insulated neutrik style, providing they aren't broke that is. 

On the face of it sounds to me like it might have been a grounding continuity issue inside the enclosure, where one of the ground points may have had poor connection due to oxidation, paint, dry joint etc...  Glad you fixed it tho

I'll be the first to admit that my soldering is not always perfect, and in this case there was definitely the possibility of bad contact if I didn't scrape away the vinyl perfectly with my knife after melting it since I was soldering in the center of the wire. I also think it was excessive in this particular enclosure simply due to the ground wire being so long. Last night I went back and checked ALL the pedals I've ever built with isolated/plastic jacks, which includes almost all my 1590A builds. Now that I knew what I was looking for, they really did all displayed similar behavior: touching the switch with my finger while note holding the guitar made a very faint buzzing noise that disappeared when I lifted my finger. These did not make as much if any noise when handling the enclosure (could be the paint), and I had to turn the amp up to hear it, but it was definitely there. None of the metal jack-equipped builds did this at all that I could hear. Touching the guitar strings at the same time made the sound go away. And when I grounded the enclosures, they all stopped making the noise.

At any rate, I'll be doing this from now on just to be safe.

Here's a picture of the inside of the enclosure I the trouble with. The ground wire I added just goes from the xwing switch to the side of the box. It's a pain to get the solder to stick to the side, but it apparently doesn't have to be perfect to quiet things down.

[nzCdog]

Ah picture helps. Glad you found a fix

[murdog47]

Similar issue here, thought I would piggy back on this thread. Made a Timmy Clone and used plastic jacks.  I get hum from the effect that goes away when I either A:Touch the guitar strings B: touch the stomp switch. Figured that maybe the enclosure needed grounded? When I ran a alligator clip from ground to the enclosure the signal cuts out.  I don't get it.

[electricstorm]

Jon,

You may be experiencing a ground loop or floating ground. You can get weird noises or oscillations when this happens. As you have explained it, it sounds like the metal box was acting as an antenna and being picked up by the input side of the board. Seeing how grounding the case solved the problem for you, this is what I am guessing was the problem (and it is just a guess).

To save you some headaches in trying to find a soldering point in the box for a ground, you can do this one of two ways. If you are using metal pots (like Alpha, for example) that have a metal back and metal bushing, you can use a heavier soldering iron and solder a ground wire to the back of the pot like they do on the pots on a guitar volume or tone control.

You second, and easier option, would be to use ground lugs, These have a starred large ring and a smaller soldering ring and attach to the case where you screww the back cover on to the pedal.

Here is what they look like:



Hope this helps!

Jim

[midwayfair]

I had forgotten I posted this here, too. There were some interesting suggestions on DIYSB. My favorite (which I've now used and it works great) is to create a loop with a cut lead or stripped wire, wrap it around a jack, and then solder it to the ground. Works perfectly and costs nothing. I've decided to go with that moving forward.

Murdog, sounds like you could have a grounding issue elsewhere, too. Maybe post some pics or see what the multimeter tells you?

[electricstorm]

That's a cool solution Jon! I'll have to try it sometime.

Jim