Pedal Power Failure When Plugged In

Frequently asked questions regarding powering your pedal.
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justicefreed
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Post by justicefreed »

I recently put in a switchable DC power jack into my cloned Fulltone OCD, and came across an odd issue.The pedal works 100% fine using just the battery, without an adapter plugged in. The LED also lights up when the adapter is plugged in, but turns off as soon as I plug in either the input or output of the pedal.

Since the input and output shouldn't affect the power state of the pedal, to me, it seems to be a grounding issue. Other pedals work on the power supply, the pedal is both expecting and receiving center pin negative 9V DC. Any thoughts on why this situation would occur?

The switchable power jack must be wired correctly because 1) The LED turns on via battery when not plugged in and still when plugged in and 2) The LED, by nature of being a diode, only accepts current in one direction, so the ground and + weren't switched. Its possible that some wire became disconnected, but I haven't yet found one, and that wouldn't explain the situation.

Thanks in advance! If any additional information would be helpful, let me know!
-Justice Reed

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Nocentelli
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Post by Nocentelli »

Maybe first check that you've wired the battery positive to the correct lug on the DC jack, and you've got the battery negative hooked up to the ring of the input or output stereo jack:

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modman wrote: Let's hope it's not a hit, because soldering up the same pedal everyday, is a sad life. It's that same ole devilish double bind again...

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justicefreed
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Post by justicefreed »

I currently don't have the pedal set up so that unplugging the input/out disconnects the ground. The ground is always connected, but my 3dpt switches the positive lead.

And, correct me if I'm wrong, but if the power jack was incorrectly soldered, wouldn't the LED not light up at all? Because the jack only ever connects two leads in one switched state, so it would not be possible for both to work if it was the jack.

Nonetheless, I will check again just in case I missed something.

Thanks,
Justice

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Post by Nocentelli »

Ok, how are the in/out jacks, dc jack, battery snap leads, LED and switch all hooked up together? Can you link to a diagram you've used or jot it out? It's rather hard to diagnose remotely, and there are plenty of different ways to hook up a pedal, and numerous different ways to make an unnoticed error.
modman wrote: Let's hope it's not a hit, because soldering up the same pedal everyday, is a sad life. It's that same ole devilish double bind again...

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Mr.Grumpy
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Post by Mr.Grumpy »

justicefreed wrote:I currently don't have the pedal set up so that unplugging the input/out disconnects the ground. The ground is always connected, but my 3dpt switches the positive lead.
What the heck? [smilie=wtf.gif]

I'm sure you thought you were being extra clever by having the footswitch turn the power off and on and save on those expensive 9v batteries. However, no production pedal is made this way, and there's several good reasons. There's a reason effects circuits are "always on" even when they're switched out of the circuit. Usually there's a split second delay as a circuit is powered up while capacitors charge and bias currents stabilize, so there would be a "thump"or "pop" sound every time you turned on your pedal.

In a modern effect pedal that can be powered by a batter or from a DC adaptor jack, there are actually TWO lines being switched. On the battery, the negative side is only connected to ground only when a guitar cable is inserted into the jack (almost always the input jack, but either one will work). Secondly, the power adapter jack has a switch inside that connects the battery's + terminal to the + terminal on the power adapter jack when NO plug is inserted. When a DC adaptor plug is inserted, the + terminal to the battery is disconnected.

There's no need to re-invent the wheel, use the diagram above.

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justicefreed
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Post by justicefreed »

You're absolutely right, that is a novice mistake (guilty). I will absolutely do it that way, thanks for explaining it, no else had.

I finally figured out the source of my issue. Turns out the power jack has a design flaw. The positive switchable lead, when plugged in, is pushed towards the outside of the jack, through a section that was cut out, coming into contact with the inside edge of the box, which in turn is connected to the input jack. Therefore, when I plugged in the input, the ring made contact with the sleeve (which was grounded) and therefore caused a short circuit!

I enlarged my power jack hole a little, wrapped electrical tape, stuck it back in, trimmed the excess, and put the nut back on. Now working perfectly. Thanks for the help and suggestions, and if anyone ends up having the same issue, I'll try my best to help!

-Justice

(From now on only buying jacks with plastic enclosures)

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