Offboard wiring issue on multiple pedals

[eve-the-frog]

Hi,
I feel dumb. I'm sure this is a minor (and stupid) issue but I can't figure out what's happening...

When I built my first FX pedals I wired all of them with negative sleeve and positive tip, because I have an old wall-wart 9V power supply wired this way.

I've decided a few weeks ago to build a 9V regulated power supply and wired it with negative tip and postive sleeve, because I learned its the common way to do it with FX pedals.

This power supply works perfectly with the build I wired since.
All my board are wired following the off-board wiring schematic found here.


But if I take an older build and just switch power wires inside the box (I swap + and - on the DC power socket) there is a short when I press the footswitch to turn the effect on.
I've spent hours looking inside these pedals to understand... But I don't !

It should be an obvious thing right in front of my eyes that I don't see.

Any idea ?

This is not really a board's debugging, but I don't know where to post it. Sorry if I'm at the wrong place.

[Hozy31]

Is it possible you have wired one of the wires to  your battery connection on your dc socket, thats all i can think of.

[eve-the-frog]

No battery on my pedals, only DC socket...

Can I check if the problem come from my regulated power supply ?
When the short occur the LED turn off and turn on again as soon as I turn off the pedal (with footswitch).

[PMowdes]

Post a picture of one of the builds please, i've got an idea but before i say anything stupid i want an example.

[eve-the-frog]

Here is an example :


And more investigations show me that : it works if I disconnect power supply and solder a battery box to the DC socket lugs, and it works again if I connect the pedal to the power supply via a plastic DC socket not mounted in the enclosure.

I guess the problem is the metallic DC socket I use ?
But I still don't understand why...

[kirshman]

My understanding is if you used a metal power jack that'll ground out on the box.  Because we use center negative wiring with pedals the positive will ground on the case.  Someone who knows more can explain better or correct me if I'm wrong.

[Travis]

Kirshman is right. If you use a metal jack with center negative wiring, the sleeve portion of the jack is carrying the positive voltage. Since the sleeve is part of the metal frame of the jack, which contacts the grounded metal enclosure, you short out the power supply. You will need to use plastic or insulated DC jacks for center negative operation in a typical pedal

[rocket88]

correct. but, if he's using a center positive power supply then the DC jack ground is directly connected to the enclosure, so that shouldn't be an issue. in fact that's what i've done when i've made my power bricks. the DC in is center positive into a metal DC jack. it looks though as though he's using a plastic DC jack, correct me if i'm wrong. but based on the fact that the jack out of the enclosure it works tells me it's grounding out to the enclosure some how.

[eve-the-frog]

I think I got it.
The black wires on the DC socket tip goes to the sleeve of the jack, and these sleeves are obviously connected to enclosures ground. The short is between this jack ground (sleeve is ground on the jack) and the DC socket ground (sleeve is +9V on the DC socket).

It works on another pedal because it's a painted one, I suppose paint act as an insulation.
I still don't understand why on another pedal the short only occur when I switch on the FX...

Is there a trick to mod the metal DC socket (or something else) or do I have to replace all of them with plastic's ones ?

[PMowdes]

The trick would be to use the correct power supply and wire everything in the conventional way.

Negative pin power supplies are relatively cheap, get one and save yourself lots of hassle.

[eve-the-frog]

Already built mine a few weeks ago ;o)


So I use the correct power supply and the proper offboard wiring layout...

It's the non-insulated chassis mount DC socket that causes my problem. Am I right ?