Buying Replacement Synth AC Power Supplies

Some Tips On Shopping For Replacement AC Power Adapters

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AC Adapters: Why we need them

Electronics devices can very rarely run off the power that comes straight out of your home's electrical outlets. That power has to be converted to something that more closely matches the needs of the electrical device you are trying to use. For one, the power that comes from your outlets is AC power and almost all electronics devices these days, need DC power. Lamps/light bulbs are about the only common consumer item that i can think of that uses AC power directly.

Now we will not get into why your outlets put out AC power when all your stuff actually needs DC. we'll leave that for the ghosts of Edison and Tesla to fight out. All you need to know now is that your house has AC and most of your devices will need DC. If you feed AC power to a device that wants DC, in most cases you will destroy it, or let out the “magic smoke” that makes the device work (as those in the electronics trade know it).

Designers of electronics devices have to always consider how power is going to get to their device. The best method is for the manufacturer to design and implement a separate internal power supply for each and every device that they make; a power supply that is perfectly suited to the electrical needs of that device. Unfortunately, this is also the most time consuming, parts consuming and money consuming method. If you have an electrical device that has just a bare cord that plugs into the wall, with no chunky black box somewhere on the cord or end of the cord, then that device has an internal power supply. A lot of electrical devices have internal supplies, but the more budget oriented the device (or smaller the device) the higher the chance that it will use an external AC power adapter a.k.a a “Wall Wort”, or a line “lump” if it's a black box in the middle of the power cord.

AC power adapters take the AC current coming from your home's outlet and convert (or “adapt” i suppose) it to DC current. Manufacturers like to use them because they can buy them in bulk, stick their name on them and not have to worry about paying someone to design custom power supplies for their devices. This is a big cost cut. That's why it's usually the lower cost electronics that get stuck with external AC adapters. Low cost or not however, many of our favorite devices use them. My Yamaha TG33, Boss SE-70, Roland CM-64 all use AC adapters (FYI: the SE-70 oddly uses one that converts AC to another type of AC).

AC Adapters: The Five Important Pieces of Information to Know

An AC adapters generally has five specs associated with it. All of these numbers with the exception of the connector size, should be written somewhere on the AC adapter itself.

  • Input Voltage
  • Output Voltage
  • Rated Current Draw
  • Polarity
  • Physical Size of the Adapter's Connector

Input Voltage

This indicates the voltage that the adapter itself needs to receive (or have “input” to it). In other words, the voltage that is coming out of your house's electrical outlet. In general you will not need to worry with this number much. As long as you are buying the adapter in the country that you plan to use it in you should have no problems. In North America the voltage coming out of the outlet will be 120, plus or minus 10%. In Japan it is 100 volts and in Europe it's 220 volts.

In short, make sure that the adapter you are buying was meant to be used in your country and it will be fine as far as input voltages are concerned.

Output Voltage

This designation has two parts, the actual number of volts that is output and whether or not those are AC volts or DC volts. This basically describes the voltage of the power that is leaving the AC adapter. In other words, the voltage of the power that will be going directly to your device and whether or not it will be AC current or DC current.

First AC and DC. This is extremely important. If you feed AC current to a device designed to work with DC, there is about a 99% chance that you will destroy the device. Do not get AC and DC mixed up. By far, most adapters are going to put out DC current, but occasionally some (such as the Boss BRA-100 or BRA-120) are designed to output AC, just at a much lower voltage than the AC that is coming directly out of the wall. Make sure that the replacement AC adapter that you buy puts out the correct AC or DC current for your device.

Look closely at the device you need the power adapter for. Somewhere, either just under or just above the power input port on the device there will be a listing that says the required voltage number and whether it needs AC or DC (most cases this will be DC). In this same location the device should indicate the polarity (positive/negative). We will cover that soon, but make a note of it now if you see it.

It is very important that you match the output voltage exactly to your device. If your device says 12V DC then it needs 12 volts. If it says 9V DC then it needs 9 volts DC, not 9 volts AC or 15 volts DC. Get this part right for sure.

Rated Current

Without getting into too much detail here, rated current is the rate at which an AC adapter can supply power. Said another way, rated current is the measurement of the maximum amount of electricity that this power adapter will be able to flow to your device. If your device needs more than this amount, it will try and pull it from the adapter anyway. Doing so can destroy both the adapter and the device by overheating. This is also a potential source of electrical fires.

When dealing with AC adapters, current is usually measured in milliamps (as in one one-thousandth of an amp) and uses the symbol mA. You will occasionally see an adapter rated at 1000mA. This is the same as 1A or one amp, but since adapters put out less than one amp, they stick with the milliamp measurement for consistency.

Your device is going to require a certain amount of power. If you give it less than it needs, it may actually still turn on, but it will strain the electrical components inside and in most cases the device will not work properly. An LCD screen full of unintelligible garbage is a common symptom on an under-powered device. Of course, if you severely under-power your device it simply will not turn on to begin with.

This is the area where a lot of people get confused. Most people think that the AC adapter will PUSH electricity out to the device and if the adapter it is rated at 900mA and your device is only asking for 500mA then it is going to push more power to your device than it can take and damage it. This is not how power works. In reality, your device will PULL power from the AC adapter and it will pull only the amount of power that it needs to operate, no more.

So that current rating on the AC adapter is not a measure of how much it will put out but rather a measure of how much it CAN put out if asked to do so. If your device needs 600mA and you give it an adapter rated at 1000mA, that is perfectly fine assuming that all the other parameters are correct If however, your device needs 600mA and you give it an adapter rated at only 350mA then your device will be under-powered and not work properly. You would need an adapter rated at at least 600mA (and a bit higher is always a safe bet).

The problem with current draw is that while most devices list the voltage, AC or DC and the polarity (polarity is described below) they rarely list the current that they need. The easiest way to tell what your minimum rated current needs to be is to look at the AC adapter that came with your device. They are almost always listed on the black box portion of the adapter. Problem is, if you had the adapter in the first place you would probably not be reading this page. The next best thing is to ask around. If anyone you know has the same device then they can look on their AC adapter and tell you the current. Failing that you could try and contact the manufacturer for support. As a side note: I am still trying to find out what current my Korg S3 Rhythm Workstation needs. I know it wants 9V DC, negative center polarity but that's it, i have no info on the current draw. I gave it an adapter rated at 600mA but that was not quite enough. The S3 switched on but was not in any way happy. If you happen to know the required current for the Korg S3, please drop me a line.


Polarity is another one like AC/DC that absolutely, positively has to be correct. Get the polarity wrong and you are likely going to destroy the device.

Polarity refers to the positive and negative parts of the electrical charge. Think of a AAA battery. It has a positive end and a negative end, that is the polarity. When you put the batteries in your TV remote control, you have to make sure that you don't put them in backwards or it will not work. Now that happens fairly often with battery powered devices so they are usually built so that doing so will not harm them, but this is not the case with your AC adapter powered electronics.

If you look back at your device's power adapter port, where we found the required voltage last time, you will see a small symbol that has three circles connected by lines, one of the circles on the end will have a + positive symbol inside it and the circle on the other end will have have the — negative symbol inside. The important part is the circle in the middle. If you look closely, the lines from one circle will encapsulate the other. Keep this in mind for a moment while you read the next paragraph.

If you look at the connector end of most AC power adapters you will see what is called a “coaxial connector” or “barrel connector”. Some adapters may have a tiny headphone pin style connector (especially on older, very small electronics) or some other, proprietary style (such as on the Roland R5's AC adapter) but the coaxial connector has become the standard for AC power adapters for quite some time now. The coaxial connector looks like a metal sleeve and has an inside and an outside. One side is positive power and one side is negative power. The big question is which one is which? This is the polarity.

The circular symbols that we saw near the power port of your device are representations of the inside and outside parts of the sleeve. Look back at that symbol and you will see that one of the circles (probably the negative one) has a line that is leading to the center of the middle circle. If so, that means this device needs an adapter that is “center negative” polarity. On almost all newer devices and adapters, the inside part will be the negative and the outside will be positive, but on some older stuff that may be switched so please be sure to double check.

We mentioned it above but i will mention it again just in case, DO NOT GET THE POLARITY REVERSED. Doing so can ruin your electronics in a fraction of a second.

Physical Size of the Adapter Connection

As mentioned above, the coaxial connector is by far the most common AC adapter connector used these days so that is the one we will deal with. The coaxial connector does come in a selection of different sizes however. You may be asking your self, “Why in the hell would they make these things all different sizes?” Well it was a noble plan that didn't really pan out. At one point, and still technically today, the different connector sized relate to differing voltages and currents. That way, you would not physically be able to plug an incompatible AC adapter into your device and damage it, theoretically. Problem is that no one really stuck to that plan and now we just have a mess of different plug sizes to deal with.

A coaxial AC adapter connector's size is generally given in two measurements, an outside diameter and an inside diameter. The outside diameter is the diameter of the outer metal sleeve portion. The internal diameter is the diameter of the hole. The most common size today is 5.5mm/2.5mm (that's 5.5mm outside and 2.5mm inside), but of course you will need to check with your own device and see if the plug fits. I recommend looking around your home and finding any adapter that fits regardless of the voltage, polarity/ AC/DC or current but DO NOT PLUG IT INTO THE WALL! We are just trying to find a coaxial connector that physically fits so you can measure it and have those measurements on hand when shopping of the replacement adapter. Usually if the outside diameter fits, the inside will as well but this is not always the case.

It would be nice if device manufacturers would print the FULL AC adapter info in their owner's manuals, voltage DC and the polarity, but that's a pipe dream.

AC Adapters: The Short Version

This is the re-cap, or if, in a more probable scenario, you skipped all the stuff written above, this is the short version of the “How to find the right replacement AC adapter for my stuff”.

  1. Buy the replacement adapter in the country that you will use it in and the input voltage will likely be correct.
  2. Match the output voltage number and AC or DC EXACTLY to the device that you want to use.
  3. Make sure that the rated current is AT LEAST as much as the device needs to run, a larger rated current will not hurt your device at all. If you don't know the current your device needs, ask someone who has the original adapter to read it off the adapter.
  4. Match the polarity of the replacement AC adapter EXACTLY to that of the device that you want to use.
  5. Match the coaxial connector (or other connector if you are unlucky) size to the one that your device needs. This is largely trial and error unless you or someone you know has a fitting adapter that you can actually measure.
  6. You should now have a replacement AC adapter that will work just as well with your device as the original manufacturer supplied adapter did.

If anything in steps 1 through 5 above does not make sense to you, see the two miles of text just above the list.

PS: One last tip and this is a good one. Buy a metallic silver ink Sharpie marker and whenever you buy anything that comes with an external AC adapter as soon as you open the box take that Sharpie and write the name of the device on the side of the AC adapter. Do this for ALL your stuff but definitely do it for devices that use a generic, non-branded or replacement, AC adapter. You will be glad that you did this later on, trust me. Wait... last last tip, unlike most Sharpies, store the metallic silver ink versions tip down or it will not work well later on. It actually says to do so on the side of the marker but most people never notice it.