In this post, I will go more into detail about the ins and outs of providing power to your effects pedals. But we’ll start with the humble battery 🙂
Battery or not?
There are two main ways to feed power to your pedals – either with an internal battery or with an external power source. I’ll come out straight off and say that the battery option is by far the best – at least when it comes to noise (or lack of it, rather). First off, no rectified AC power (as produced by your average AC->;DC adapter) will ever be as steady as the pure DC from a battery. There will always be remains of the alternating current there, ready to cause hum. These remnants – called ”ripple” – fluctuate at exactly twice the rate of the alternations in the mains power (if your mains power is 50Hz, the ripple will be at 100Hz). The ripple can be filtered out, but never completely. Let me borrow a couple of images from a techie site (credit at the bottom of the page), to illustrate. Let’s start with the simple transformer/rectifier combo:
The peak of the wave represents the 9 volts we want, but it’s not exactly steady… remember that a pure DC source (such as the one from a battery) would come up as a perfectly straight line here. If you fed this power to your pedals, you would hear a very loud low-frequency hum at all times. Not very nice. Well, with a little filtering, it’s possible to cancel out some of the ripple.
To the right, you’ll see what the output would look like with the added filter components. Basically, a capacitor is added across the DC rails, to smooth out the chop. The capacitor charges itself when the power is at its peak, and then discharges when the voltage drops (in between the peaks).
Now, why is this important? Well, simply put, most guitar pedals are very simple circuits that use the DC power more or less directly to generate sound, so if there’s a 100Hz (120Hz if you are in the US) ripple in the incoming DC, it will be there in the output signal as well. Most pedals have additional filtering to remove the ripple, which usually works just fine. But some (vintage-style fuzz pedals and older wah pedals come to mind) don’t, which can get noisy even with an otherwise quiet supply.
With all of that said, batteries aren’t always very convenient. Or cheap… If you play a lot, an adapter will pay for itself rather quickly. However, if your pedals (or rather, your wallet) need external power or not has a lot to do with how much power they consume – if a pedal eats batteries for breakfast, getting an adapter for it will be economically wise. If a pedal draws very little power, you might consider running it on batteries even if you get an adapter for other pedals – usually, the less pedals you give external power, the smaller the risk of getting annoying hum and noise.
I want external power!
Personally I don’t bother with adapters unless I have my pedals at least semi-permanently set up on a pedalboard, or if there’s a pedal that really needs it (either because it uses its own special adapter, or because it eats batteries for breakfast). But the premise of this article is that you want to use external power, so… There are two ways to go about it. Option #1 was covered in the ”beginners version” of this page, but here I’ll go into it in more detail. Now, to the options…
- ”Wall wart” or adapter with daisy chain
- Dedicated power supply unit
On the Power List page, you will find a run-through of the more common adapters/power supplies used, and what they can provide and not. Check that one over before you hand over the cash.
…come in all shapes and colours and some are good, some are bad. A generic ”Radio Shack-type” adapter is infinitely more likely to cause you grief through hum and noise than one that was designed specifically for audio use. Stay away from them – it’s not worth the gamble. But before you buy an adapter, you need to decide which pedals you’re going to power with it, and know their current draw. Then add the numbers up – the adapter’s max current output must never be exceeded! Again, there’s a list here, to help you out.
Also, be aware that not all pedals use 9vDC, so they will need their own power supply. Also, there are those that use 9vDC, but still can’t be run from the same power source as the others (they are called ”positive ground” pedals, and there will be a separate page on those later). So take care to study the specs on the pedals you want to power.
Anyway, the adapter has a plug that fits in the power jack of one of the pedals, but to power more than one you need some means of splitting the power. Enter the daisy chain cable. It’s a cable with several plugs on it (in general it has 4 to 6) that starts with a female connector. The adapter plug fits into the female connector, and the other plugs goes in the pedals. Easy!
(Note: some daisy chains – such as the one from Boss – have all male plugs, which obviously won’t work with a regular adapter. Make sure the one you get is meant for use with a regular adapter – the ”beginners” version of this page has a few suggestions.)
A possible problem with daisy chains is hum caused by ground loops. As your pedals will now have contact with ground not only through your signal cables, but also through the adapter cables, you are in danger of creating a ground loop. This manifests itself as hum. It can happen between pedals in a normal pedal chain, but the most common cause is when people power both pedals that go in front of the amp and pedals that go in the amp’s effects loop from the same source.
2. Dedicated power supplies…
…also come in many flavours. Some are more or less a splitter unit (like a daisy chain, but with all the splits inside a box, and a separate cable to each pedal), while others are more involved. The splitter type often runs from its own adapter, which means that it receives 9v power and feeds it to the outputs. Some of them have internal transformers, and can be connected to the mains system directly. Now, some of these units are pretty good – they provide stable power while preventing ground loops – while others are utter crap. As always, you need to know the max current output available, and read the fine print. For instance, the Dunlop DC Brick has gotten good rewiews, and seem to work fine for most people. But while the adapter that powers it can provide 1000mA total, you are limited to 375mA on the 9vDC outputs (the remaining 625mA can be had from the three 18vDC outputs).
At the higher end of the market you’ll find units that not only split the power, but also isolate the outputs from each other. This will prevent any ground loops, as the pedals all think they are alone. Clever stuff, and quite pricey. But if you have problems with noise, it might just be the ticket. Some units use isolated groups (like having two separate power supplies and daisy chains), so you can partner pedals that can live together and isolate those that can’t. Other units isolate ALL outputs separately, which means that unless you daisy-chain several pedals from a single output (which you can do, as long as you don’t exceed the max capacity of that output), all pedals will think they are alone. As always, you need to know the current draw of your pedals, and the max current output of each output/group of outputs. You’ll find a comprehensive list of power supplies in the Power List section, where you can also see which ones have isolated outputs.
But hey… my Boss TU-2 can power pedals!
No… it can not. Let’s put that issue firmly to rest. The TU-2 (and the other Boss pedals with power output) has a link output that will let you daisy-chain from it, rather than straight from the adapter. It is a ”power through” jack, but it’s still the adapter that does the powering… The only difference is that you plug the adapter cable into the TU-2 rather than into a female cable connector, and then you need a special daisy chain cable (as the link output on the pedal is the same type as the input). I’ve found that when people use this setup and have noise problems, the issues often disappear when the TU-2 is removed either from the signal chain or the power chain. As it usually sits at the front of the effects chain (where the signal is most vulnerable to picking up hum), to me it seems like a daft idea to pass signal as well as all the power through it… Treat it as you would any other pedal, and things will usually be fine.
But if you do use the power through jack, please note that Boss only guarantees this connection for up to 200 mA, including whatever current the pedal itself draws – no matter what your adapter can deliver. This is because even though the power input and output jacks are simply wired in parallel, the connection between them is made through thin copper traces on a small circuit board. Running large amounts of current through there can cause the traces to overheat and lift from the board… So, be advised that 200mA (including the 35mA the TU-2 itself uses) is to be viewed as an actual physical limit for this type of jack. If you plan on using the ”power through” jack on one of these Boss pedals, make sure the total current draw doesn’t exceed 200mA or so. Or just get a regular daisy-chain cable (like the one pictured earlier) and add the TU-2 to it like you would any other pedal – which is what I’d do.
Keep in mind that we’ve actually only discussed pedals that use DC (direct current) power – the same type of power you get from a battery. There are pedals out there that use AC (alternating current) power – the same type of power as found in the wall outlet. You have to be very careful about this, as the two types are not compatible. There usually is a figure on the pedal itself, by the adapter jack, which tells you what kind of power it wants. AC is indicated either with the letters ”AC” or a wiggly line like ”~”. DC will be indicated either by the plain ”DC” or a straight line, often with a dotted one underneath. Some of the pedals that use AC (in various voltages) are from DigiTech’s floor pedal line (Whammy 1-4, XP pedals etc), FoxRox CC2/TZF, Hughes&Kettner and a host of others. If you only have one pedal that wants AC power, your best bet will in many cases be to simply use the adapter that came with it. If you haven’t already made arrangements for your regular DC supply, you might want to look into one of the multi supplies at the higher end of the market – some of them can provide AC voltages as well as DC, but you need to check that it is the proper voltage (some can only do 9 or 12 volts AC, and your 9vAC pedal might not like the extra voltage), and that the current capacity is enough. If you have more than one AC pedal, the Voodoo Lab Pedal Power AC is dedicated to providing this type of power, and can provide a total of 4 separate outputs at any given time.
There are also pedals that use 12vDC or 18vDC, which – if you have any such pedals – you need to take into account when shopping for an adapter/power supply. And then there are those that are positive ground, which need a separate power source from normal negative ground pedals. These are mostly germanium fuzz/octavia type pedals, so they’re not too common. But still…
Now, 95% of the guitar pedals out there do use plain old 9vDC power, so most of this will be academic for a lot of people. But don’t guess which pedals are which – it’s far better to know, before you try. Again, go visit the Power List, where you will find current draw figures and voltage requirements of many common and uncommon pedals. There you will also find an overview of the more popular adapters/power supplies available, and what they can and can’t provide.