Wall Wart Specs

Wall warts are those clunky black boxes that plug into a wall outlet to supply power to your gear.

When a wall wart burns out or gets lost you can often substitute a general purpose replacement but you have to know FOUR THINGS:

1. OUTPUT VOLTAGE

Wall warts reduce the input voltage from the wall (120 volts AC) to an output voltage, typically between 6 and 18 volts. The output might also be converted from alternating to direct current (AC to DC).

Be sure your replacement adapter puts out the right voltage and the right AC or DC.

The output voltage is printed on the adapter. A 9-volt, battery-operated pedal, for example, needs an adapter that reads "9 VDC" since all batteries are DC. If it says "9 VAC", it's the wrong adapter.

OUTPUT:
15 VAC, 320 mA

OUTPUT:
9 VDC, 300 mA
Center-positive

OUTPUT:
12 VDC, 300 mA
Center-negative

2. DC POLARITY

This photo shows a common wall-wart plug. There are two metal contacts: a center, female contact and an outer barrel. A black insulator separates them. This type of plug is called "co-ax", short for coaxial.

Some DC plugs have the positive side of the voltage connected to the center contact while others have the minus side in the center.

This is the symbol for a center-negative adapter. A center-positive adapter would have the plus and minus signs reversed.

The wrong wall wart polarity can damage your gear so be sure the polarity pictured on the adapter matches the polarity pictured on your gear.

If you must, you can reverse a plug's polarity. With the wall wart out of the wall, cut the 2-wire cord leading to the plug (cut it somewhere in the middle). Reconnect the wires in reverse. Have a tech do this if you're not comfortable repairing electrical cables.

3. PIN SIZE

Coax jacks, like the plugs, have two contacts: a center pin and an outer spring.

The jack's pin must fit snugly into the female contact of the wall wart plug. Common pin diameters are 2.1 mm and 2.5 mm. Plug barrel diameters also vary so, if you can, take your gear with you when you shop for an adapter, making sure the plug fits the jack without wobbling.

In some older gear, 1/8" phone plugs and jacks are used instead of co-ax connectors.

4. CURRENT RATING

The maximum current a wall adapter can supply is limited. The adapter will overheat and fail if it can't supply all the current your gear needs to operate. Make sure the replacement adapter can supply at least as much current as the original.

The current rating is listed on the wall wart in amps (A) or milliamps (mA). Fuzz boxes can draw as little as 10 mA of current, chorus and delay pedals can draw several hundred milliamps, and portable keyboards can draw 1500 mA (1.5 A).

The more current a wall wart has to supply the more it's voltage will sag. Wall warts are designed to supply their rated voltage at their rated current. The output voltage will be higher if less current is drawn. For example, a wall wart rated at 9 V, 1000 mA might output 12 V at 50 mA.

Even an alkaline 9V battery can make a fuzz tone sound different than it would with a carbon-zinc 9V battery. That's because alkaline batteries have a higher current rating than carbon-zinc and therefore less voltage sag.

NOTES:

Also available are universal adapters like those shown below. With them, you can select various output voltages, either polarity, and a variety of plug types and pin sizes.

Universal Adapter (500 mA)	Plug Types here include Battery Snaps and both 1/8" and 1/16" Phone Plugs.
Universal Adapter (800 mA)	This Adapter has lots of Coax Sizes

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