Electrical ignorance question

[cdaniel]

I have an old Ross Phaser pedal I may start using again. I need a power supply. It's rated at 9v 7.0ma, All of the power supply's I've seen are rated at several hundred ma. Would something like that over power the pedal or will the pedal only use what it requires?

[phatbass]

The pedal will quite happily live with an oversupply of mA.

As long as it's the correct polarity. And check it takes DC (most do, but there are some that need AC)

[cdaniel]

Definately DC as it has a 9v battery inside.

How can I verify polarity of a new to me wall wart?

[bongomania]

Best-case scenario it will be labeled on the "wart" part. There will be a small symbol like a dot inside a circle, and there will be a "+" pointed at either the dot or the circle, and a "-" pointed at the other one.

Do you have a multimeter?

[cdaniel]

Originally Posted by bongomania

Best-case scenario it will be labeled on the "wart" part. There will be a small symbol like a dot inside a circle, and there will be a "+" pointed at either the dot or the circle, and a "-" pointed at the other one.

Do you have a multimeter?

I do have a meter. And after further investigation, the supply I've found online is described has 1/8 plug tip positive, And I see the diagram you describe on the label.

I guess the next step is looking at the wiring from the internal battery to the power jack.

[DUC1098]

The difference between voltage and amperage is that voltage is a "constant", meaning that it is always at the level indicated. But amperage is an "as needed" value. The circuit will only pull as much amperage as it needs. So no matter how much the power supply "can" output, the circuit will only take what it needs.

Usually the power adapter end is ground on the outer section and positive in the center, this limits the possibility of shorting the supply if the plug touches ground.