'standard' DC jack wiring for effects pedals.

[mikepukmel]

Hi All,
I have some pedal kits, have a few working with batteries. Getting ready to either build or buy a wall power supply, I went to double check the pedal wiring, and found I had put the + wire (power to the board) to the sleeve side of the DC power jack/plug. Thinking it didn't look right, I did a google search and found both: some diagrams are wired with the sleeve marked + and some the pin marked +.
So, i dug out a really old HP Printer power supply I salvaged from the garbage that I use for my also garbage salvaged Altec computer speakers, and was very surprised to find it is 18v positive on the pin, negative on the sleeve.

So, questions:
- are guitar effects pedals and power supplies typically wired backwards compared to e.g. printer power supplies?
- I read someplace that some older pedals with NPN transistors (some old fuzz boxes) have their power supplies wired "backwards" compared to most newer pedals.
- I don't have any commercial pedal power supply yet, was going to order one from Antique Electronic supply before i started looking into building one. Are these commercial units usually sleeve positive?

Thanks
Mike

PS Happy Holidays, whatever you celebrate.

[Justin Thomas]

I'm not SUPER-knowledgeable in pesals, but every pedal I've seen has been what they call "center-negative" when checking the polarity. I never thought about it until I got hold of my own Dunlop Power Brick, whose instructions told me to check the polarity before using it with my pedals.

Sure enough I found my oldwst pedal, a Boss Turbo Distortion, was the opposite of all my other pedals which dated from 1992 or newer. I found instructions online (possibly from Boss's website?) about how to rewire it so the polarity would line up with all my others. I don't remember the process, though... It was fairly simple, though.

I do believe the center-negative has become a sort of convention in the pedal world; there are probably those who do the opposite for some reason, though I would think that would discourage sales a bit. I certainly wouldn't want to have to purchase adapters or rewire my pedals unless it was a true vintage classic...

I'd be curious to know if I can build the "wall-wart" part of my Dunlop power supply, as the cable on mine was ripped out and sinply reattaching it didn't work... As I don't have a pedal board, I think I could make something a bit more roadworthy.

Justin

[Enzo]

There is no backwards. You can design a circuit either way. Note there is no ground connection, just plus and minus, and it really doesn;t matter which side of a connector you use for it as a designer.

here is why I think center negative is popular with designers. That way the negative can go right to ground, the sleeve usually has a switching contact in the jack, which allows simple battery clip wiring, that transfers over to wall wart when connected.

[galaxiex]

I do believe the center-negative has become a sort of convention in the pedal world

This ^^^

It is now quite rare to find a pedal with the power jack wired different from the "convention".

There are exceptions, of course.

I have an old-ish SansAmp pedal that uses a 3.5mm mono tip/sleeve phone jack for power.
I modified the pedal and installed the conventional 2.1mm barrel jack.
Saves confusion and lets me use a standard daisy chain power cable with that, and my other effects.

Edit; and what Enzo said.

Also, some pedal makers use a different jack to "force" you to use their power supply.
In some cases there is a good reason for that.
For example, digital pedals can draw relatively large current and you would not want to use an under rated supply.

Plus there can be noise issues.
EHX organ machine comes to mind.
If you daisy chain that pedal with others it introduces a digital "whine" on the power line.
The EHX uses the normal 2.1mm barrel jack but it really works better on it's own (included) wall wart.

I made a power line noise filter for mine, pi filter with a hand wound inductor and 2X 10,000uf caps.
It worked, but there was still a very faint whine if you really cranked the volume.

I went back to using the EHX wall wart...

[mikepukmel]

Cool, thanks everyone. So I better get the meter out and check the pedals I built and the store bought wall wart to make sure I don't toast anything.

Curious why it isn't common to put a 'protector' diode in line with the input power to protect against power supplies that are backwards? Is it OK do do that (put a diode in there)?

[galaxiex]

Cool, thanks everyone. So I better get the meter out and check the pedals I built and the store bought wall wart to make sure I don't toast anything.

Curious why it isn't common to put a 'protector' diode in line with the input power to protect against power supplies that are backwards? Is it OK do do that (put a diode in there)?

Yup, it's fine to put in a reverse polarity diode protection.
It is fairly common on a lot of the DIY pedal circuit boards.
Not all have it, but many do.

Commercial pedals don't usually have it (reverse protection) probably a cost thing.
Plus they warn you in the instructions to not plug in any supply other than their own.
So they cover their A$$ that way.

[Enzo]

A series diode works, but it costs you the voltage drop across the diode, which will be somewhere around half a volt to a whole volt.

[galaxiex]

Some other ideas on reverse polarity protection...

http://sound.whsites.net/appnotes/an013.htm