Understanding Milliamps (mA) in Guitar Pedal Power

Most people understand the voltage requirements of guitars pedals. The bulk of them require a 9V DC current, while some pedals can go up to 12 and even 18V, though these are not as common as the 9V variety. The definition of voltage is the amount of work energy required to move an electrical charge from point A to point B.

But in most guitar rigs, voltage ratings are pretty straightforward, even if we don't understand the science behind it.

The voltage rating of the output (on the power supply) must match the voltage rating of the input (on the guitar pedal). In other words, 9V to 9V, 12V to 12V, etc.

But milliamps are a little harder to pin down.

They're a second electrical issue that we need to consider when powering our guitar pedals.

Quick Definition of Milliamps in Guitar Pedals

A milliamp is a fraction of an ampere. When listed on a guitar pedal, or a guitar pedal power supply, it means the following:

• On a guitar pedal: The minimum mA rating required to power the pedal
• On a power supply output: The maximum amount of mA provided to a connected pedal

This means the mA rating is the amount of current required to power a particular guitar pedal, where the power output must have at least as much as the pedal requires. If it has more than what the pedal requires, that will work fine as well.

Typical Milliamp Ratings for Various Effects

The following list gives you some approximate mA ratings for a wide range of pedals. With so many effects pedals running less than 100 mA, there's usually no need to have a bunch of high mA outputs on a single power supply or guitar rig. The exact number of high mA rated outputs will depend on the power supply in question.

Read more: Best guitar pedal power supplies

Of course it also depends on which pedals you're trying to power.

Here's a broad look at how it breaks down:

• Gain effects (distortion, fuzz, etc.), wah pedals, tuners, simple modulation, simple ambient effects: Under 50 mA (sometimes as low as 4 mA)
• Older digital effects before year 2000: Under 80 mA (usually between 50 and 70)
• Digital effects after 2000 and MIDI controllers: 150 to 200 mA
• Larger, modern digital pedals (2010 and beyond): Between 200 and 500 mA depending on the brand

Some Examples

As you can see from the above list, most pedals require less than a 100 mA current, which almost all multi-source power supplies provide. But take this output on the Voodoo Lab ISO-5 for example:

This power output provides a 400 mA current, which you would need for a guitar pedal between, say, 200 mA and 400 mA. The Strymon BigSky, for example, requires a 9V DC 300 mA power source, thus would need the 400 mA output on the ISO-5 to operate. 

A pedal requiring a 300 mA power source would not work in the other 9V power supplies because they do not meet the minimum mA requirement.

The first three 9V power outs on the ISO-5 are rated at 100 mA.

Many modern pedals that are high-functioning will require between 200 and 300 mA or higher. Some brands, like Eventide, go up to 400 and 500 mA.

If the requirement were 450 mA, the ISO-5 400 mA power source would not be enough.

Pedals that require this amount of power often come with their own dedicated power supply.

The Eventide H90, for example, comes with a power supply included.

Is it okay if the power supply's output has a higher mA rating than the pedal requires?

If your pedal requires a 200 mA current and you plug it into a 300 mA rated power source, this will work fine and will not harm your pedal. In fact, it's difficult to match the mA ratings up perfectly between power supplies and guitar pedals all the time.

In other words, a 400 mA power source will work for any pedal requiring 400 mA or less.

Think of the mA rating on the pedal as a minimum requirement.

If you want to get into the weeds, Ohms law goes a lot deeper.

What happens if the mA rating on the power source is less than the pedal?

With a power source that doesn't meet the pedal's minimum mA requirement, the unit will likely just not power on when you click the bypass switch. 

What about voltage?

Voltage is a different story.

You should not mix and match voltage with your guitar pedals and power supplies. For example, do not plug a 9V pedal into a 12V power source. By the same logic, don't plug a 12V pedal into a 9V power source.

Always match them up.

In some cases they might power on, but prolonged use could end up frying electrical components in either the power brick or the pedal.

By the letter of the law, this can actually cause electrical fires.

While that's unlikely to happen, it's something we should keep in mind.

Conclusion

Not enough mA will often be the cause of a pedal not turning on when hooked up to a power supply, especially with larger and more complex digital pedals. Now that we've covered the basics, as it relates to guitar pedals, that's one of the first things you can check if you can't get a pedal to power on.

It will also help you plan your pedalboard and get the proper power source for the pedals you have.

If you have questions, jump into the comments section and leave it there.

We'll try and help out where we can.

Sources and External References

• Voltage and Pedal Power Needs
• Definition of an Ampere
• The Voodoo Lab ISO-5 User Manual

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