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The Zen of Power Adapters

Most effects pedals today come with a jack, which allows an AC adapter to run the effect instead of batteries.

While these jacks are mostly very similar – based on what Boss pedals use – plugging in the wrong adapter can damage your effect. Here’s the five critical items you need to look at before powering your pedals from an AC adapter.

1. AC or DC power?
Each of your pedals should have an inscription, usually on the bottom or at the power inlet jack, that tells you the kind of power you should feed the pedal. It is critical to look for whether the pedal expects AC (alternating current) or DC (direct current) power. Some well-known pedals require AC and come with a matching adapter that supplies it. If you accidentally plug the adapter for that pedal into an effect which is supposed to run on DC, it can kill the DC pedal, possibly beyond a reasonable repair price. A good example of this is the Line 6 adapter for the POD and the larger modeling pedals (DL4, etc.) which is 9V AC, not DC.

2. The Rated Voltage
If you put too little voltage into your effect, it may not work right. Put in too much and it may work great – or it may need a part transplant to work again. Pedals vary substantially in how much variation from their rated voltage the pedal will take. Pedals do exist that will run well from more than twice their rated voltage. However, many mass produced pedals are designed to run on 9V DC, and include parts that will be damaged at over 10V. Learning by experimentation is an expensive way to find this out.

3. What polarity is the DC plug?
Direct current (DC) is polarized. There is a positive and a negative contact to the power plug; most effects pedals have the center of the plug negative – but a few have center positive. If you plug in an adapter with the wrong polarity, your effect will not work. If your effect is older, with no polarity protection circuitry, this may damage the effect. The adapter will usually have the rated output voltage, current, and polarity printed on the label.

Another issue that gets raised at Visual Sound regarding the 1 SPOT power supply is the internal polarity of the pedal. Old germanium fuzz pedals use a “positive ground” which will conflict with more modern pedals, which are mostly “negative ground.” For example, most pedals these days use the “Boss standard,” which is a barrel plug 9V DC adapter with the center of the plug negative and internally having a negative ground. It’s perfectly fine to daisy-chain these to a single power supply, as long as there isn’t a positive ground pedal in the chain, like a Fuzz Face.

4. Is it regulated DC?
A “regulated” adapter will put out a nearly constant voltage. A regulated 9V DC output adapter will be about 9.0V if you don’t overload it.

Unregulated adapters also exist. These adapters will have a rating like “9V @ 200mA” printed on them. The correct way to read that is that the voltage will decline to 9V only if you load it down with 200mA of current. With a lower load, it will put out a higher voltage. How much higher? They usually don’t tell, but it can be as high as 15V.

Unregulated adapters have one more nasty surprise: they hum, due to a lack of electrical filtering components. So if you plug in your pedal and it hums, it could very well be that your adapter is unregulated. Radio Shack and so-called “universal” adapters are typically unregulated – not recommended for musicians.

5. Rated Power
(you know … that mA thing) You know how the adapter labels always have a mA rating? All that means is that the adapter will continue to work up to the mA rating on the label. So, if you have a 1 SPOT, for example, it will work up to 1700mA of current being drawn out of it. The average analog pedal consumes only about 10-20mA of current and a digital pedal uses anywhere from 50-150mA typically. You can do the math to figure out how many pedals that will power.

So before you hook up AC adapters to your pedal effects, do a little bit of homework. Look at each pedal, write down what voltage and current it needs, and note what kind of plug it takes. The pedals you save could be your own.

R.G. Keen
Cheif Engineer
Visual Sound