What a power supply’s numbers mean
Four numbers on the box decide whether a supply suits your board:
- Output voltage. Most pedals run on 9 V DC. Some need 12 V, 18 V or more, and some accept a range such as 9 to 18 V. A supply either has fixed outputs or outputs you can switch or adjust.
- Current per output, in mA. This is the ceiling for one jack. It does not add across jacks: eight 500 mA outputs are not a 4,000 mA output.
- Total current, if listed. Some supplies share a total across outputs. If yours does, everything you plug in together must stay under that total.
- Isolated or not. On isolated outputs each jack is electrically separate from the others, so noise made by one pedal cannot travel along the supply to the next.
Check polarity and connector as well. The usual standard is a 2.1 mm barrel plug with the centre pin negative, but a few pedals differ, and reverse-polarity cables exist. Never feed a pedal more voltage than it is rated for: too little can cause weak or dead behaviour, too much can destroy it. Read the label or manual.
How much current do pedals draw?
Current draw depends mostly on whether the pedal is analog or digital. Simple analog circuits sip current; anything with a processor, display or large delay buffer draws far more.
The label or manual figure is usually the maximum draw, so it is the safe number to plan with. If a pedal does not list one, the maker’s website usually does, and a DC ammeter or a multimeter in current mode, placed in series with the supply lead, will measure it.
Daisy chain or isolated outputs?
A daisy-chain cable runs several pedals from one output. It works, but every pedal on the chain shares that jack’s current and its electrical noise. An isolated supply gives each output its own path, which is why digital pedals, the noisiest and most current-hungry, belong on their own.
A daisy chain is fine when all of these hold: the pedals share a voltage, they are analog, and the combined draw times 1.3 stays under the output’s rating. Anything digital, or anything that needs a different voltage, gets its own output.
Size it in four steps
- List every pedal with its voltage and current. Use the label, the manual or the maker’s site. Group the list by voltage; each voltage is its own sum.
- Add each voltage’s current and multiply by 1.25. That is the minimum total capacity the supply needs on that voltage, with room for power-up inrush.
- Multiply your busiest pedal’s current by 1.3. That is the minimum rating of the output that feeds it.
- Assign outputs. Each digital pedal gets its own isolated output. Analog pedals of the same voltage can share one output until their combined draw times 1.3 reaches the output’s rating. Count the outputs and check the supply has enough, with the right voltages.
Here is a worked example, using example current values for a typical board. Your own pedals’ labels replace these numbers.
| Pedal | Draw | Output |
|---|---|---|
| Digital reverb | 150 mA | 1, on its own |
| Digital delay | 100 mA | 2, on its own |
| Tuner | 50 mA | 3, shared |
| Compressor | 25 mA | 3, shared |
| Overdrive | 10 mA | 3, shared |
| Fuzz | 10 mA | 3, shared |
| Chorus | 30 mA | 3, shared |
The total is 375 mA, so the supply needs at least 469 mA across the 9 V outputs. The busiest pedal draws 150 mA, so its output must be rated at least 195 mA. The shared output carries 125 mA, and 125 × 1.3 = 163 mA, comfortably inside a common 500 mA output. Three outputs of 500 mA each cover this board with room to add pedals.
Power-supply sizer
Enter how many of each kind of pedal you have and its current, then your supply’s output rating and count. The page address updates, so you can copy it and share the exact result.
Pedalboard power-supply sizer
Runs in your browserCommon power problems and what they mean
- Hum, buzz or a high-pitched whine. Often noise travelling along a shared supply or ground, and often worse when a digital pedal is on the same chain. Move digital pedals to their own isolated outputs and keep power cables away from signal cables.
- A pedal resets, cuts out or sounds dull when another switches on. The supply or output cannot deliver the current, or voltage is sagging. Use a higher-rated output and split the load.
- The supply runs hot or shuts down. It is overloaded. Recheck the total on each voltage against its capacity.
- A pedal will not turn on at all. Check polarity and voltage first: a reversed plug or the wrong voltage is the usual cause.
- A pedal that accepts 9 to 18 V. Some pedals are rated for the whole range and can give more headroom at 18 V. Only do this if the manual says so.
Questions people ask
How many mA does a guitar pedal need?
It depends on the type. Most analog pedals draw about 2 to 35 mA; digital delays and reverbs draw about 60 to 300 mA; loopers and multi-effects often 100 to 500 mA. The label or manual gives the exact figure for your pedal.
How many pedals can I run from one 500 mA output?
Up to about 385 mA of combined pedal draw (500 ÷ 1.3), which is a dozen or more analog pedals but only one or two digital ones. A single 300 mA pedal needs an output rated at least 390 mA.
Can I daisy-chain guitar pedals?
Yes, when the pedals share a voltage, are analog, and their combined draw times 1.3 stays under the output’s rating. Digital pedals and pedals at a different voltage should have their own outputs.
Do I need isolated power outputs?
Not strictly, but they are the most reliable way to avoid noise, particularly with digital pedals. If you hear hum or whine that changes with a digital pedal, isolating that pedal is the first fix to try.
What is the difference between a 9 V 1 A supply and 9 V 500 mA outputs?
1 A (1,000 mA) is a total, usually shared by everything you plug into one adapter. A 500 mA output rating is the limit for a single jack on a multi-output supply, with each jack separate. Check whether a supply’s figure is per output, a shared total or both.
Can I power a 9 V pedal with an 18 V supply?
Not unless the pedal is rated for it. Too much voltage can destroy a pedal. Use an output set to the voltage on the pedal’s label.
What does centre-negative mean?
It describes the plug’s polarity: the centre pin of the barrel connector is the negative terminal. It is the common standard for pedals, but check each pedal’s label, and use a polarity-reversing cable for the exceptions.
How do I find out how much current a pedal draws?
Look for the mA figure on the pedal’s label, in its manual or on the maker’s website. To measure it, put a DC ammeter or a multimeter in current mode in series with the supply lead and engage the pedal.
Put the plan to work
When comparing estimates or adding headroom, check which value is the baseline in our percentage change and difference guide. Use the Percentage Calculator to keep the arithmetic visible, and explore related planning workflows before choosing equipment.
Sources and method
- The 25% total headroom, the 1.3× per-output rule and the dedicated output for digital pedals follow the rules documented in the Pedalboard Planner, which also holds a library of pedals with typical current figures.
- Current ranges by pedal type are typical label values, not measurements of any one product. Always plan with the figure on your own pedal.