About Powering Pedals

Powering pedals can be tricky. It is often not done properly, and becomes the prime source of noise in a rig. This page will help you design power for your pedals that is reliable, quiet, and economical, without resorting to expensive multi-isolated-output power supplies.

Use Good Power Supplies (yes, wall warts are fine)

Power Chaining is Fine (When Done Right)

How To Avoid Ground Loop Hum

Don't Overload

Pedal Voltages

Voltage Polarities

Power Supply Current Ratings

Power Plug Sizes

Other Helpful Resources

Use Good Power Supplies (yes...wall warts are fine)

Good power supplies are needed for quiet audio, but you do not have to spend $175 on a board-mounted, multi-output supply. If you can afford to do that, that is OK. They can solve a lot of problems for you, and save you time and effort. But they have a downside.

The downside is, apart from the unnecessarily high cost, is that an expensive board mounted supply will hog space and add weight to your pedalboard. But...and this is important...they force you to continue running the big AC power cord to your pedal area--even after you switch to PedalSnake. This prevents the ideal "one cable solution" achieved with PedalSnake's Low Voltage Method.

Contrary to popular belief, standard power supplies made for pedals are actually true isolated Class 2 Transformers (aka "wall warts") are as quiet as a battery when used properly.

Wall warts earn their funny name because of the size and weight of the transformer. But being big and clunky is a small price to pay for a quiet iron-core transformer. This is the only way to isolate power, and keep ground loop hum from sneaking in.

Supplies with many isolated outputs have essentially many small wall warts inside. The outputs come off a coil of wire on one large isolated transformer.

There are some good power supplies out there now that are smaller, and can put out lots of current (over 1000mA in some cases). But these are not true isolated transformers. They weigh a lot less than a true iron transformer, and can be a bit noisier than a transformer-based wall wart.

Here are some guidelines to follow to ensure that you use wall warts quietly:
  • Use a good designed-for-audio power supply, from a reputable pedal maker.

  • Do not place a wall wart right beside a pedal. If close enough, transformer noise can get into pedal electronics (see our demo at 0.26 in the video P-Lines and Power). Only 3-4" spacing is needed. And with PedalSnake, wall warts move all the way to the backline!...which is the quietest power solution you can have..

  • If you chain power from one wall wart to several pedals, follow the proper guidelines. See Power Chaining Is Fine (When Done Right) (below).

Most wall warts deliver 200mA or so, only enough power for 4-6 stompboxes (9V battery pedals) on a power chain.
To improve this situation, we introduced SnakePOWER . At 500mA, it is the most powerful isolated wall wart on the market. It will power a dozen or more 9V pedals, which can cut down on the number of P-Lines you need if and when you switch to PedalSnake.

How do you know how many pedals can be powered from one wall wart? See Don't Overload below.

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Power Chaining is Fine (When Done Right)

A good way to make efficient use of power supplies is to chain power to several pedals from one power supply.

Some guidelines to follow to ensure quiet, reliable power chains are:

  • Use a true isolated Class 2 Transformer (like most any good wall wart from a reputable pedal maker)

  • Don't place the power supply too close to a pedal. The transformer magnetic field could induce some noise. NOTE: PedalSnakes Low Voltage Method places power supplies at the backline, entirely off your pedalboard. This is the quietest solution.

  • See Don't Overload below.

  • See Avoid Ground Loop Hum below.

  • Isolate noisy digital pedals. This is rare, but if a digital pedal causes noise on the power chain, you may need to Isolate it with it's own power supply. See Isolating Digital Noise.

  • Don't leave unused plugs on the chain uncovered. f you have unused plugs on your power chain, they can short out the power if they touch any grounded metal, like a metal guitar plug. You can be worry-free with PedalSnake's Vari-Chain Power Chain System, the world's only power chain system with configurable length. You design it for the exact number of pedals you need to power, with no unused plugs left over. Vari-Chain also sports all spacing-saving right-angle plugs.

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How To Avoid Ground Loop Hum

In pedal rigs, ground loop hum can occur if the wrong things get hooked together without proper isolation.

Isolate Stereo Amps

Even if plugged into the same AC socket, two stereo amps can have slightly different ground potentials. This is caused by small voltages induced into the metal chassis by their power transformers. If the amps are connected together, ground loop hum can result (see Isolating Stereo Amps).

If driven with a stereo pedal whose outputs are not isolated, the grounds of both amps are tied together by two audio lines connected at the pedal. In this case, isolating power to the pedal will not help. One pedal output should use an audio isolation transformer. You can find these on the web. EbTech makes some good ones.

Isolate FX Loops

Although rare, some powerful all-tube amps with FX Loops can have different ground potentials with the same metal chassis!   So powering front end pedals and FX Loop pedals with the same power supply can sometimes result in a bit of ground loop hum.
Even though it doesn't make much difference with most amps, it is a good practice to use a separate isolated supply for Amp Input Pedals and FX Loop Pedals. For more about this, see Isolating Power Chains. This article is found on the page about general Isolation and Grounding.

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Don't Overload

Every power supply has its limit, which is called its current rating. The average 9V stompbox draws about 20mA of current. But this varies widely, from 1mA to 75mA (we are talking about stompboxes that have the option for a 9V battery. These draw very little current.) If too many pedals are power chained from one supply, a supply can overload, causing hum, or have a shorter life from overheating.

A good conservative rule of thumb:
  • Two 9V pedals per 100mA of current rating for the supply

So a 200mA supply is usually good for 4 pedals. This is conservative. Usually a typical 200mA power supply will usually power 4-6 9V pedals safely and quietly. SnakePOWER is rated 500mA, and will power a dozen or more.

If you can get a reasonable estimate of how much current your pedals are drawing, then you can may be able to safely add more pedals. Basically, try not exceed 50% of the supply's current rating. If push comes to shove, 75% is fine with most supplies.

How do you know how much current is being drawn by a pedal?

You can try to find out from the manufacturer, but that can be a joke with some companies. Stinkfoot.se has a good website with a Power List. You can try to find your pedals on his list.

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Pedal Voltages

Every pedal has a specific operating voltage. The most popular operating voltage is 9VDC. Pedals that take 9V batteries operate at 9VDC, but they can usually be powered with a 9DVC power supply too.

A pedal's voltage is usually printed at it's power input connector, like "9VDC". Remember, "DC" voltage is different from "AC" voltage. If not on the pedal, look for the voltage on its power supply, like "OUTPUT: 9VDC". If it just says "9V", with no "DC" or "AC", it is probably DC.

  • If you have five (5) 9VDC pedals and one (1) 18VDC pedal, you can use MF2 Dual P-Line. It works on a 3wire or 5wire channel, and is best used with two isolated DC supplies, not AC.

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Voltage Polarities

The standard voltage polarity is "center-negative", which (unfortunately) was not a good idea for the industry to adopt (read why here).  A little diagram like this is usually printed on the power supply.

If you use a standard center-negative supply, and you wish to power-chain it to a center-positive pedal (that is +9VDC), you will need a 21RP Reverse Polarity adapter for that pedal.

NOTE Some pedals that say "center-positive" really have ground at the center, and run on -9VDC instead of +9VDC. We know this is confusing, and fortunately not many pedals run on -9VDC. They are mostly germanium fuzzes it seems. But if you have one, you can't add it to a power chain using 21RP. You must power it by itself with a separate supply. Use a center-positive supply, or use a center-negative supply with 21RP added to reverse the polarity.

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Power Supply Current Ratings

Sometimes this gets confused with how much current a pedal actually draws---that is usually only a fraction of the power supply's current rating.

You can usually see the current-rating printed on the power supply---look for something like "Output: ..200mA". This tell you how much current the supply can safely deliver before it starts to hum. But, before it starts to hum, it can overheat, which can shorten its life expectancy. See Don't Overload.

So, to not overload the supply when power-chaining pedals from one supply, it is good to know (or estimate) the real current draw of the pedals. They add up, and a good rule of thumb, to have your supply last a long time, is to not exceed 50% of the power supply's rating. If push comes to shove, you can go up to 75%, but just beware that the total current draw matters.

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Power Plug Sizes

The standard size for a pedal power jack is 2.1mm. Some pedals have other sizes. These are usually pedals that take some voltage other than 9V (but not always).

The 2 most common non-standard power plug sizes are 2.5mm (Digitech, Line 6, Eventide, etc.), and 3.5mm (1/8" miniphone plug, used by older DOD, Electro-Harmonix, etc.) PedalSnake offers Power Plug Adapters the for 2 non-standard sizes.

How to tell the difference is shown below.

2.1mm ( x 5.5 ) standard

This is the standard size used by stompboxes from Boss, Dunlop, etc. PedalSnake P-Lines, as well as most any power-chain cable, use the standard 2.1.

2.5mm ( x 5.5 )

2.5 is hard to tell from 2.1, but there are ways:

  • Check our Pedal Power Adapter List to see which power plug adapter your pedal (or supply) may need, or
  • Do your own test with a pedal and wall wart, knowing that:
    • The pin inside a 2.5 pedal's power-in jack won't fit into the hole of a 2.1 wall wart plug.
    • The hole in a wall wart's 2.5 plug fits easily over the pin inside a 2.1 pedal jack, but it makes little or no connection.
  • With PedalSnake, use 2125AR for 2.5 pedals, and 2521A for 2.5 power supplies.

3.5mm (1/8" mini-phone connector)

These are easy to see----the male plug is like the 1/8" miniphone plug on portable headphones, and unlike a female barrel connector, the 3.5 jack has no "pin" inside.

  • With PedalSnake, use 2135AR for 2.5 pedals, and 3521A for 2.5 supplies.

Other Helpful Resources

Guitar Noise Manual

Isolation and Grounding

Power Plug Adapters List

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PedalSnake® is the trademark name for Stage Magic's All-in-One Pedal Cabling Solution. Copyright © 2012 Stage Magic, Inc.