Short circuit in dc-jack.

[VPIF]

Hi.

General guitar gadgets Big Muff, Russian version.

Works with a battery, though it's not as gainy as it's supposed to be. Works with power supply when the (metal) dc-jack isn't mounted in the enclosure. When I touch the dc-jack to the enclosure there are visible sparks, and the power supply cut the power.

I have checked the circuit board and the wiering, and it seems to be matching the layout/wiering diagram. With a battery I get a voltage reading between the + on the battery and the screen of the output jack, that is close to the battery voltage. But I also get a voltage reading of about 3v between the + on the battery and the tip of the output jack.

Any ideas will be greatly appreciated.

[R O Tiree]

Get an isolated dc jack.  Don't mess with the one you have any more.

Here's the reason... You've connected GND to the centre-pin contact of the socket (as per the diagrams) and +9V is connected to the "barrel" terminal.  Sadly, that is also connected to the metal dc jack casing.  So, every time you touch the jack to the enclosure, you are connecting the 9V supply directly to GND, hence the sparks and the power supply shutting down to protect itself.

Something like this will do the trick nicely.

[haveyouseenhim]

If you don't have those on hand, you could use a center positive power supply so the barrel is negative. Be sure to swap the wires around though.(this is just a temporary fix)

What R O said is correct.

[VPIF]

OMG! Is it really that simple. I have been trying to locate a short circuit for the past few days

Thanks a lot, guys.

[blue_tokai]

The answers are mostly correct Sometimes the simplest answers are the most annoying ones to troubleshoot lol

[rutabaga bob]

I've used a rubber grommet to isolate a metal jack before, but it's just less hassle to get a regular plastic one...

[armdnrdy]

I made this mistake on my very first build!


I wanted the MANLY, INDUSTRIAL, METAL jack instead of the cheapo, kid's toy quality plastic jack.......

I use only plastic jacks now!

[Paul Marossy]

I made this mistake on my very first build!

Same here. And have never made that mistake ever again. 

[davent]

If you really want to use those metal jacks, Small Bear sell one with a long bushing plus isolating shoulder washers. http://www.smallbearelec.com/servlet/Detail?no=1216

There also is/was(?) a tutorial on Small Bear on drilling an over-size power jack hole, patching it with Bondo then redrilling a correct sized hole through the Bondo patch.

dave

[Paul Marossy]

I used those metal RadioShack ones for a while. I would wrap electrical tape around the barrel and use a pair of O-rings to isolate it from the enclosure. But it's a LOT easier to just buy some plastic ones and be done with it.