9V jack polarity question

[notneb]

I'm wiring up my first overdrive and doing the power jack and battery as shown here http://www.generalguitargadgets.com/pdf/ggg_sgo_lo_wiring.pdf which makes the center pin negative. All the power supllies, 6 in all, I just tested are center pin positive.  What am I missing here? Thx.

[xorophone]

I'm wiring up my first overdrive and doing the power jack and battery as shown here http://www.generalguitargadgets.com/pdf/ggg_sgo_lo_wiring.pdf which makes the center pin negative. All the power supllies, 6 in all, I just tested are center pin positive.  What am I missing here? Thx.

On guitar pedals the center pin usually is negative. That's the standard. For most other electronics the center pin is positive, so most power supplies will be center positive. If you have a universal power supply you might be able to flip the adapter part (the part you plug in to the pedal) around to make it center negative. I guess you could also just flip the polarity around in your pedal (use the lug connected to the center pin as positive), but be sure to remember that in the future if you switch power supply. Reverse polarity is bad, you know.

If you decide you want to just buy a new power supply, make sure it has the icon on the right printed on it:

That means the center pin is negative.

Good luck!


Edit: Just realised that I don't know if flipping the polarity around inside the pedal is a good idea, because I don't know how the switch pin (which is connected to the battery) on the jacks work. Someone else will have to answer that part.

Edit2: Thanks GibsonGM for confirming that it indeed isn't a good idea to flip the polarity around inside the pedal. Don't do it!

[GibsonGM]

You can, of course, cut the plug of a 'donor wall wart' (you know, you find them at the "dump store" sometimes) and reverse it for stompbox use.   

Not all of 'em are good for audio use, but some sure are!

~~Good call on the internal jack switching, X.  It's not a good idea, no.

[a2music]

The center pin is almost always negative for modern pedals. Are these power supplies made by (labeled by) a pedal manufacturer? In other words, are they intended for use with pedals?


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[Ice-9]

I would suggest just to buy a decent power supply which is suitable for guitar/audio use. ie a cheap boss psa230 or 1-spot adapter. it will save a lot of future trouble shooting when you might experience hum or whine in your pedal which could possibly end up being caused by a cheap multi purpose adapter rather than the pedal.

[Mark Hammer]

(I have to make this a sticky some day)

Why are there two kinds of polarities?

If one was thinking solely in terms of safety, you'd want the part of the plug that a person is most likely to be in contact with to be ground, in case they're also touching something else that is ground.  And that means that the shaft would be ground, rather than the part of the plug you can barely touch.

But what happens if you need to switch from internal battery to external supply when you insert that plug?  Phone plugs and jacks have the advantage of a tip which can push a contact out of the way and do the switching between battery and external supply.  Barrel plugs do not, so any "pushing" has to be done by the shaft of the plug, because there IS no tip to do it.  And the way jacks do that switching is by the power connection to the board being a piece of spring steel.  When nothing is inserted in the jack, that spring piece touches another contact connected to the battery lead.  Insert the plug and you nudge the spring out of the way and out of contact.

So, for anything that aspires to be battery-operated, you have to make the shaft/outside "hot" and the center pin ground.

What has happened over time is that outside-pos became the standard for appropriately-regulated supplies.  So, even though fewer and fewer pedals are using batteries - whether because they're digital and require too much current, or because they use 1590A boxes and have no room for a battery - outside pos became the standard so that whatever you were using for your vintage battery-operable pedals worked fine with your mini-Mooers or Strymons or whatever. 

There are plenty of wall warts that permit polarity-flipping, although my experience is that many are maybe not as well-regulated as they could/should be for audio purposes.  I know it's hard for some to wrap their heads around but there WAS a time when people used calculators and those calculators used outside power which did not have to be especially well-regulated.  I still have wallwarts left over from that era.  Some are polarity-flippable, but many are outside ground.

[notneb]

Wow... and might I add, ouch. Actually these were old walwarts, not pedal specific, I had lying around and didn't realize power supplies for pedals had the negative in the center. Glad ya'll cleared that up before I plugged into the pedal.