# 2.1mm DC Power polarity



## MikeT (Jul 23, 2019)

Pardon the super newb question but I haven't used one of these jacks before. Is the longer leg + or -? I'm wrapping up an Awful Waffle and don't want to get this part wrong. 

Thanks!


----------



## Nostradoomus (Jul 23, 2019)




----------



## MikeT (Jul 23, 2019)

Sorry! I should've provided this pic. This is what I got since it fit the Tayda enclosure w/o drilling the hole out


----------



## Nostradoomus (Jul 23, 2019)

Oh those little guys haha, short pin should be ground


----------



## MikeT (Jul 23, 2019)

Awesome, Thanks! I was guessing correctly.  Now to just wait on a few missing parts...


----------



## Nostradoomus (Jul 23, 2019)

If you have a multimeter check continuity from the center pin inside the jack to one of the legs. The center pin is ground. Sometimes, but not very often, those jacks are wired for positive center.


----------



## Chuck D. Bones (Jul 23, 2019)

Or plug your power adapter into the jack and measure the voltage on the pins.  _Before _wiring it into your pedal!


----------



## phi1 (Jul 23, 2019)

For anyone who's used both types, are there any disadvantages to the smaller one (like does the male jack nest all the way in it)?  Of course the larger one nostrodoomus posted a pic of (which I always use) has the switch, but I almost never need it.


----------



## Chuck D. Bones (Jul 23, 2019)

I have used both.  They both work well.  The power plug fully engages in both.  The little one actually protrudes a bit more outside the box because the lip is thicker.


----------



## MikeT (Jul 23, 2019)

I'm doing this at work between emails. The beauty of tech support. I got shorted a cap and an led by a supplier so I have time to double check it before fully assembly


----------



## abucior (Aug 22, 2019)

Nostradoomus said:


> If you have a multimeter check continuity from the center pin inside the jack to one of the legs. The center pin is ground. Sometimes, but not very often, those jacks are wired for positive center.


Sorry to come in late here, but I'm curious about this comment. I was just wiring up my first board, grabbed a 9V power supply from my stack of old power supplies and did a quick multimeter sanity check before I wired up the plug. I have three 9V supplies from random manufacturers and all three of them have center positive polarity. I did a bit of google'ing and found a Banggood page about "How to choose the right AC adapter for your project" and even they state:  "The most common is center positive (+) connectors. There is also the less popular center negative (-) connector."
Is center negative perhaps just more of a standard in the pedal world?


----------



## abucior (Aug 22, 2019)

Answering my own question, I was looking on Amazon for "pedal power supply" and sure enough, they all seem to be negative center.
That's a really interesting difference between pedal power supplies and what's "normal" for the most consumer devices.
So let this be a warning to anyone building their first pedal and hoping to re-use one of the 9V power supplies they may have lying around: Check your polarity: It's likely backwards from what the circuit expects, and you'll have to reverse the wiring when connecting the power plug.
Edit: Some good info here: http://stinkfoot.se/archives/532
"Well, this is all Boss’ fault… before they started using the barrel type plug, almost all pedals had the 3.5mm (1/8″) mini plug instead. That plug is still used on some Electro-Harmonix pedals and the RAT, by the way. But Boss chose the 2.1mm barrel plug/jack for their compact pedal line, and others have since followed (for instance, Ibanez started using them in ’83, when the 9 series was released). Like the 3.5mm (1/8″) jacks, the 2.1mm jacks had a switch function, which was (and still is) used to switch the battery positive out when a plug is inserted in the jack. On the 3.5mm jacks, that switch function was located on the tip connection, while on the 2.1mm jacks it is located on the sleeve connection. So the positive voltage needed to go on the outside of the plug. Simple as that."


----------



## the_grumpy_gnome (Aug 22, 2019)

Nostradoomus said:


> If you have a multimeter check continuity from the center pin inside the jack to one of the legs. The center pin is ground. Sometimes, but not very often, those jacks are wired for positive center.


I actually have that picture printed out above my bench.  I rarely use the little (2-prong) jacks anymore and when I do, so still use the multimeter to check.  Don't believe all the pictures online, esp LED legs)


----------



## Chuck D. Bones (Aug 22, 2019)

Good thing PedalPCB puts series protection diodes on the boards.


----------

