Reversed polarity pedals - How would l I know?

[Marelton]

Hi,

I've just bought a Caline 5 power distribution pack for a pedal board and I read in the instructions (yes, I hear you, it's not normal to read the instructions first!) there is a potential risk of connecting up pedals with the opposite polarity to the power unit.

I'm still waiting for pedals to be delivered, but is it possible for me to connect up a reversed polarity pedal to the unit without realising it or is the Jack plug different? How would I know?

[fender3x]

Unfortunately there is no law that says that the plug must be different.

Most pedals are powered by a 9v battery when not plugged in. They don't always have the sort of universal symbol stenciled on them, but if they do that looks like this:



If the polarity is reversed it would look like this:



If there is no symbol, I would assume it's center negative, particularly if it can use a 9v battery.

Nice article about this stuff here:

https://neunaber.net/blogs/brian-s-n...l-power-basics

Mostly you don't have to worry about it, but I learned the hard way that sometimes you do. I bought a digital effects pedal on ebay that came without the "wall wart." It did not use a battery (dead giveaway that power is going to be different). Turned out to use 9v AC.

I don't use pedals much and all mine are 9v center negative except that one. I know there are 18v too, and I think the same rules should apply.

[Dedman]

the live terminal is the outside so you will see next to the socket a picture with + pointing to the outside C and - pointing to the centre O.

Fender beat me to it

[Marelton]

Great advice guys as ever, thanks.

As a rule of thumb (working on worst case that there are no instructions or markings on the pedal) I would go with, if the pedal has a battery it would be safe to wire up.
One interesting comment in the article is that most conventional 9V power supplies work on opposite polarity to that of a pedal power distribution pack.
Maybe would explain why a recently bought 'cheapo' secondhand pedal didn't work when I connected it to a generic power supply I had lying around.
Now I'm more educated on the subject I'll pay more attention to this detail.

Thanks again Fender & Dedman, very useful info.

[Dedman]

I have a Caline unit,it hums through my cordless headphones but not through my amp....weird. But it's powering Korg,Boss,Moer, Vox , Docs Fuzz Face and Joyo stuff no probs.

[fender3x]

It took a very patient EE to give me an idea about where hum comes from and how it gets eliminated. Wall warts are notorious for passing on the hum from wall current, but it can come from RF and probably other sources. Pedal board power supplies usually have some filters built in to lessen the effect of at least the wall current. That lessens but does not eliminate the noise. To complicate matters, a lot of pedals have a small amp in them. Sometimes these little amps can pretty dramatically increase the proportion of signal that comes from noise rather than your playing. That might be what is happening with the headphones. They could be amplifying some noise that your amp has filters for. That happened to me with a little pedal I built. It was originally designed to run only on battery power only. When I plugged it in to wall power, it turned out that a part of the IC amp chip that was basically unused when on DC power began amplifying the hum. My EE friend showed me how to bypass this, and the hum all but disappeared--which I now know means "became mostly inaudible, but still there."

[Dedman]

thanks for that! I don't use the head phones at the same time as the pedals very often so it's not an issue really, I only found out by accident :P