Understanding what pedal power actually is
If you have any Boss style stomp box, you have the option of using a 9v battery (or two in some cases), or using external power. This external power is aptly known as a power supply.
Some people (ahem, Eric Johnson), swear by batteries. While we won’t be debating the highly subjective audio quality between batteries and power supplies, I think we can all agree that power supplies are way more convenient.
Using a power supply means that as long as your wall outlet has power, so do your pedals. Power supplies come in many flavors, with differing polarity and several voltage ratings. In this article we’re going to take a look at all of these differences to better understand what power supplies are, how they work, and what that means for your pedalboard.
How Do Guitar Pedal Power Supplies Works?
Boss Pedals is to thank for the standard 9v ratings of power supplies. Their pedals were originally powered with 9v batteries, and because they were ground (no pun intended!) breaking and successful, other companies followed suit.
A power supply (affectionately known as a wall wart) takes the AC (Alternating Current) power from you wall and literally transforms it into a nice steady dose of DC (Direct Current) power in your pedal.
The wall current travels through a transformer which reduces the voltage to the required rating of your pedal. After the current runs through the transformer, it goes through a rectifier to be converted into DC. From there, the DC current at the new voltage range is pumped into your pedal to power the electronics inside.
What Is Center Negative and Center Positive?
If you have a power supply that came with a pedal, take a look at the wall wart. It should have an indication that the power is either Center Negative or Center Positive. On many pedals you’ll also see this next to the power input jack on your pedals (it’s always listed in the manual).
This indicates the polarity on any DC (Direct Current) power. This next part is very important: You must match the polarity of the power supply with the polarity requirements of the pedal.
I’ll say it again. The polarity of the pedal must match the polarity of the power supply.
Absolute best case scenario using mismatched polarity is that your pedal wont power on. Worst case, you’re buying a new pedal and the manufacturer’s warranty won’t cover user error.
It’s actually pretty unique that guitar pedals have center negative polarity in general, since most electronic devices only have center positive. Some guitar pedals have center negative polarity because they work with both a battery and wall power.
In these pedals, the battery needs to be bypassed when plugged into a power source. This is achieved in the circuit by attaching the battery’s negative terminal to the sleeve of the power jack. When a power jack is plugged into the pedal, it breaks the chain to the battery’s positive terminal. The battery is bypassed and the pedal is powered by the external power.
Conversely, when there is no power jack plugged in but an instrument cable is inserted, it completes the circuit on the negative terminal of the battery.
(You can find pretty cheap polarity adapters that will convert the polarity from the power source)
Does Voltage Matter?
YES! By default, you should only use the voltage identified on the pedal. Underpowering or overpowering your pedals can result in performance issues, or even damage to the pedals.
Typical voltages you’ll see are 9v, 12v, 18v, and even 24v. 18v and 24v power usually utilizes different power supply cables or adapters. If your pedal requires these voltages it’s not uncommon that they’ll come with a unique power supply.
Most stomp boxes like Boss pedals are 9v or 12v. The larger pedals from Strymon and Eventide typically require a little more juice in the 18v to 24v range. But 9v and 12v are what you’ll see 90% of the time.
Some overdrive pedals thrive on higher voltages. In many cases, using 12v or 18v can give your overdrives more life. Before you experiment, just make sure your specific pedals can handle this. Most user manuals will tell you this and you can always contact the manufacturer.
Voltage vs (milli)Amps
In addition to voltage requirements it’s important to note the mA (milliamps) rating of power supplies. The general rule is to have equal or higher mA for your pedal. So if you have a 9v 100mA pedal, you’ll want a 9v power supply rated with at least 100mA. More is better. But more on that in a bit.
There are two different ways to power multiple pedals: Daisy Chains and Isolated Power Supplies.
Daisy chains take a single power source and run it into multiple pedals. You can have your single 9v wall wart and add a daisy chain to power your overdrive, wah, delay, reverb, etc .
The inherent problem with daisy chains, besides the obvious differing voltage requirements, is that any minor issue will be amplified exponentially throughout the chain. For example, if you have a noisy pedal in the middle of the chain, it’s going to be amplified by each pedal down the line.
Because they all share the same power circuit, you’re risking introducing ground loops between each pedal. Ground loops can cause excess hum that’s further amplified in each pedal.
The biggest roadblock of all is differing voltage requirements, and potentially polarity issues. If you’re running standard Boss style stomp box pedals that are all in good shape with the same polarity, you’ll be able to get away with daisy chains most of the time.
If you’re in this boat, here’s a great option. It’s 9v and rated at 1700mA (plenty of headroom for mA requirements), and comes with a daisy chain.
More About mA
If you decide to use a daisy chain, carefully review the mA requirements of every pedal in your chain in addition to the power supply you’re using with the daisy chain.
Every pedal is rated at a specific max mA current draw. This varies widely with pedals. If your pedal doesn’t show the ratings on the housing and you don’t have the manual, do a quick Google (or BING!) search. You need to calculate the max current draw from all of your pedals and make sure you have a power supply rated to at least that.
Let’s say you have 4 pedals with these ratings:
Pedal 1: 100mA
Pedal 2: 100mA
Pedal 3: 100mA
Pedal 4: 100mA
Pedal 5: 100mA
Pedal 6: 100mA
You need a power supply rated at 600mA or more. A 500mA power supply would under power your pedals. At best your tone is going to suffer. At worst you might need to buy new pedals.
But a 600mA power supply might not be enough either. The rule of thumb is to have a power supply at least 100mA more than the max draw. Stepping up to a 1000mA (or 1A) power supply gives you plenty of room with the ability to add pedals without getting a new power supply.
Remember, this is max current, so you don’t have to worry about overpowering your pedals based on mA ratings. The extra mA is basically headroom.
Here’s another example:
Pedal 1: 100mA
Pedal 2: 22mA
Pedal 3: 2mA
Pedal 4: 100mA
The total max current from your pedal board is 224mA, so you’re looking at a 300mA power supply (which are extremely common). Even though it’s less than 100mA over, it’s still enough headroom to ensure you’ll never reach the upper limit.
Isolated Power Supplies
Isolated power supplies are my preferred way to power pedals. Each power source is completely isolated from the rest, and each has its own ground. They use one or more transformers to keep each port completely electronically isolated.
Because of this, the operation is quieter and safer for your pedals. An issue with one pedal or power source wont impact anything else. Most of these “power brick” isolated power supplies have some sort of short circuit protection. Any power surges are handled by the power supply, not your pedal.
My favorite thing about them is they’re a clean way to power an entire pedal board. Most of the isolated power supplies are housed in a pretty small case that fits neatly on your pedalboard.
You might have heard the term “switching power supplies”. Avoid these at all cost. They’re a great way to charge your phone, but a horrible option for your pedals. They’ll give you random transients and excessive noise.
Since I’m big on these, here are a few of my favorites.
Voodoo Labs Pedal Power 2
Walrus Audio Phoenix
1 Spot PRO CS12
Has this article helped you understand power supplies? If it has, share it with a friend!