Powering your Guitar Effect Pedals
So you got yourself a nice guitar effect pedal, great! But you don't want to accidentally fry the unit, do you? So you carefully check the specifications... But what does voltage, polarity and current mean?! GuitarFX is here to help!
Some basic background regarding electricity is required to understand why some power supplies will work, why some won't, and why some will destroy your pedal. Electricity is the flow of electrons, and this process creates a charge. So when connecting the power supply to a guitar effect pedal, the electrons flow through the circuit board and components, powering the device. We can refer to this flow of electrons as seeing them as individual "energy packages", containing an amount of energy, at a specific rate at which it runs through your guitar effect.
The amount of charge (or difference between + and - pole) is called voltage. You will be familiar with the 9 volt battery, which means each "energy package" has 9 volts in it, when comparing between both lugs of the battery. An AAA battery has 1.5 volt. Now, a power supply can provide various voltages. It converts 230 volt to e.g. 9 volt, or 12 volt, or 18 volt, or whichever amount the power supply is designed to be. Here you will see that it often shows 230 V AC (or 110 V AC in the USA) and 9 V DC. AC stands for Alternating Current, and DC for Direct Current. Alternating current comes from the wall socket, and is converted to direct current by the adapter. If there is a polarity sign on your pedal, you have direct current. Sometimes you will also see pedals where a squiggle (~) or 9VAC is indicated instead of the polarity symbol as below; then the pedal needs AC voltage. This is not very common.
The next important thing to keep in mind is the polarity of the power supply. This is where most accidents happen. People will see "9 volt" and figure, "yep, that's what my pedal needs". However, there is a 50-50 chance you get it wrong! Most electronic devices are designed to have a fixed polarity as an input, which means that e.g. the outside of the plug should be positive (+) and the inside of the plug should be negative (-). This indicates which way the electrons, or "energy packages", flow through your device. If they go the wrong way, well, if there aren't any safety measures installed in the pedal, you'll start smelling a burning scent... Therefore, always triple check the power supply diagram before connecting up a pedal. Most guitar effects use outside positive (+), inside negative (-)!
The rate of which the electrons pass through the guitar pedal is called current. Some pedals require more current to work than others; they are thirsty for energy. The power supply connected should keep up with this thirst, or the pedal will refuse to work (properly). The unit for this is called Ampere or amps (not to be confused with amplifiers). Simple overdrive pedals are roughly requiring 10 to 40 mA (milliamps), where digital pedals require more, upwards to 500 mA even. In contrast to voltage, it is perfectly fine to power up a pedal which has plenty of Ampere to deliver. It just means that the power supply is up for the job; it can provide more than enough juice to the pedals, more than it needs. It does not send it however, it only sends what the pedal needs. If you are connecting more pedals on your board using a daisy chain, the current required will increase with the sum of all the pedals. A default Boss power supply provides roughly 200mA. Therefore, if you run, say 5 different 50mA pedals in one daisy chain, the pedals will not work: 250mA is more than 200mA. It cannot keep up with the required flow of electrons. That's why TrueTone (Visual Sound) 1-spot, or Godlyke PowerAll power supplies exist, as they provide up to 2000mA (= 2 Ampere)! There is no risk in beefing up your power supply in terms of Amperes. When in doubt of purchasing a wall wart, bigger is better when running a large board.
Isolated power supplies
On a final note, perhaps you have heard of isolated power supplies, This means that each output is independent of another, and each output will be rated for a certain amount of current. Therefore, usually each output is connected to an individual pedal, decreasing noise or interference via the power line. All parameters mentioned above still hold true; ensure the output of the isolated power supply brick is the specified voltage for the pedal (usually 9 volt), the polarity is correct, and it can deliver enough current for the connected pedal.