Batteries, Wall Warts, and the Future of Pedal Power Supplies
~ Or, when is 9 volts really 9 volts?
"GREAT SCOTT!" ~ Doctor Emmett Brown
When it comes to electronics, it's easy to overlook the importance of what supplies the power. When we buy an electronic thing we're attracted to all the shiny objects, the bells and whistles, what it does, etc… we at most only give a fleeting thought towards what powers the thing as we plug it in, and rarely think about power again unless there is a problem. In a way, your power source is not unlike the engine in a car; in the sense that your car can have all the best gadgets and features, but if you don't have a good engine, it won't get you very far.
When it comes to Musicians and Music Lovers, etc… having good, clean power is the foundation of pure audio. And, since we're always trying to chain gear together in different ways to make a signal path (for example: Guitar >> pedal 1 >>pedal 2 >> DI >> mixer >> EQ's >> Amps >> Speakers, and so on) it helps to understand a little about how the power supplies behave when they are connected through the ground wires in your patch cords. For the purposes of this article, I just want to focus on pedal power.
With Pedal Power, you usually have two choices… 9V batteries, or AC adapters ("wall warts", "line lumps" and "Pedal Power Bricks"). They all have some obvious pros and cons and your choice will probably depend on the pros outweighing the cons in a given situation. For instance, out on the road playing a live show, I'd hope I'm not going to be shut down by a dead battery, whereas in a recording studio, I'm going to want the cleanest possible sound. If I'm doing a lot of sessions and playing live, I might compromise a little for convenience being on the go.
Batteries come in lead, alkaline, lithium and rechargeable varieties to name a few. They generate 9V via chemical reactions. Once the chemicals are depleted the battery is discharged and dies. In the case of rechargeable batteries, chargers cause these chemical reactions to run in reverse so you can use the same battery again and again, they can be good for several hundred to thousands of charging cycles.
"Can different batteries really make a pedal sound different?"
You would think from a pedal's perspective, it shouldn't make much difference which kind of battery I use as long as it can deliver enough voltage and current. HOWEVER, it does make a difference DEPENDING on the pedal's design. You may ask, "Can different batteries really make a pedal sound different?" The answer is "YES!"
The battery's voltage may seem like an obvious answer… the voltage may be 9V or it may be 9.6V or it may be a weak 4.5V or whatever – voltage can effect most pedal's analog signal paths in terms of limiting headroom. You hear a lot about running some pedals at 18V for increased headroom (warning: not all pedals can handle it, so experiment at your own peril!). A lot of pedals fart-out and sound terrible if the voltage gets too low, but some other pedals, particularly analog fuzz pedals, sound better. I've done some limited testing, by no means extensive research, and the trend seems to favor pedals with discrete analog designs over pedals with digital circuits. One shining example is the classic Fuzz Face pedal which sounds differently as the battery dies; good, but different.
Another, not so obvious reason batteries can make pedals sound different is the battery's impedance. What does that mean? One way to describe this would be in terms of how "stiff" the 9V is. Does the voltage sag, dip or bounce? Actually, batteries do all this. Those chemical reactions which generate the voltage are not instantaneous, they can lag, and there is resistance, capacitance and inductance in the various parts that make up a battery – without getting into a science class, all this means is that in subtle ways, depending on how your pedal sucks the life from a battery (which may in turn depend on how you are playing your instrument) the battery's voltage may be swinging, sagging and rebounding – some chemistries more so than others. That can affect how your pedal sounds. If the battery is "stiff", your pedal will be more hard clipped when it runs out of headroom. On the other hand, if the battery is not "stiff", your pedal will have a softer clipping which can sometimes be described as a tube-like quality. Again, there are some pedals that don't care and other pedals that blow chunks – you'll have to experiment.
Besides being 9V, batteries will have a rating for milliamp hours, abbreviated "mAh". This is an indication of how long the battery should last. For example, a 9V 600 mAh battery should run a 60 mA pedal for 10 hours, and a 9V 1200 mAh battery should run the same pedal for 20 hours. I've tested a lot of batteries. In general, it seems the higher the mAh number, the "stiffer" the battery is; and the lower the mAh number the "softer" the battery is. Also, it is important to note that when a battery gets weaker, it also gets softer. I've found that as the battery gets weaker the voltage usually doesn't drop much at first, it can be putting out almost 9V but the swinging, sagging and rebounding starts getting more and more pronounced.
Pros, Batteries are inherently isolated sources of power, so they aren't going to create ground loops. And because they are not connected to the grid and develop voltage with chemistry they have a very good clean, almost nonexistent noise floor. The Con is that they die. Yeah, they do that… so you have to spend a bunch of money on spare batteries, and chances are you'll waste a lot of money changing out batteries before a show, batteries that might still be good, just in case they might die (or not). If you swear by batteries you probably have a box of half used batteries that you don't want to throw away, but you don't know if they can be trusted. Rechargeable batteries might be the solution, but you'll want two sets, one set in your pedals, and a back-up set on the chargers. That can get expensive. In a short time, you can easily spend more money on batteries than it would cost to buy AC power adapters.
Another inexpensive alternative is the pedaltrain VOLTO. We helped pedaltrain develop a rechargeable battery pack called the VOLTO. It is sort of like a pedal power brick in the sense that it is a stand-alone unit which you can use to power a small pedal board, rather than having to install batteries inside each pedal. We learned a lot in the development process. Lithium Ion batteries are currently the lightest and most power dense batteries by weight available in mass production. They come in 3.7V cells which can be stacked together for 7.4V or 11.1V. That means to get the battery pack to put out 9V, a regulator circuit is needed to convert the voltage. The design of this regulator circuit is extremely important so as not to pollute the chemically clean battery voltage. There are cheap knock-offs of the VOLTO that use switching regulators which pollute the power with a high noise floor. In the case of a genuine VOLTO we designed a hybrid circuit that uses an expensive linear regulator which preserves the almost nonexistent noise floor of the battery. Also, with the genuine VOLTO we made sure it would be possible to charge the battery while powering your pedals at the same time.
AC adapters ("wall warts", "line lumps" and "Pedal Power Bricks") come in all sorts. For this article I am going to limit the conversation to the DC variety. Acknowledging they can be from 5V up to 48V I want to focus on the 9V ones since that’s what most pedals use and for the purpose of comparing them with batteries.
Of the 9V DC wall wart options you can find regulated and unregulated varieties. Regulated means that no matter what the power company throws at you, the adapter will attempt to keep the output locked at 9V. They clean-up the noise and protect you from power spikes. On the other hand, Unregulated means if the power company voltage dips down or jumps up, the 9V will also dip down or jump up, and any noise coming from the power company will get through as well. These adapters are the cheapest you can find. But they risk being noisy, and won't protect you from power spikes.
"Linear regulation provides the cleanest power"
Of the regulated options you can choose from linear regulation or switch mode regulation. Linear regulation provides the cleanest power. A well designed linear power supply will have an almost nonexistent noise floor just like a battery. Linear regulators lock the output at 9V by burning off excess voltage in the form of heat. It's done in a brute force kind of way, so they do waste a little power. And usually, they only work in one country, so if you take an American version to Europe, you might be in for some troubles.
Due to government regulations companies are being forced to build adapters with Switch Mode regulation because they waste less electricity. Almost every new wall wart and line lump you find will be switch mode. These can also be made cheaper and put out more amperage for their size and weight. Another big advantage is that they can work in any country from 100VAC in Japan to 120VAC in North America and 240VAC elsewhere.
However, of all the switch mode adapters I've ever seen, they always have really high noise floors because of the way they work. Instead of burning off excess voltage, they lock the output at 9V by switching the power on and off really fast (being "off" part of the time saves electricity) then filtering the switched output with inductors and capacitors to get a somewhat clean 9V. This switching happens at about 100,000 to a million times a second. Although it happens at frequencies above what humans can hear, that noise still eats up headroom in your signal path and can sometimes alias against the sample rates of digital converter chips found in digital effect pedals, causing distortions we can hear and psycho-acoustic phenomena we can feel.
Pedal Power Bricks as far as I have seen, are always regulated, and most of them still have linear regulation. However, there are a few switch mode versions beginning to hit the market. Power Bricks are basically beefy adapters with multiple outlets that give you a variety of options. You can usually pick 9V or 12V, some have up to 18V, some you can adjust anywhere from 4.5 to 9V and some have both AC and DC outputs.
In terms of chaining together effect pedals, what you will run into is choosing power with isolated vs. non-isolated outputs. Whereas batteries are inherently isolated, when you start daisy chaining power to have multiple pedals sharing the same source you could get ground loops and noise problems. Often, digital pedals will pollute a power supply with clocking and switching noise which can resurface as excessive noise floor in a high gain analog pedal sharing the same source. Ideally, you would love for each pedal to have its own isolated power supply but that can get expensive and messy (try fitting a dozen wall warts under your pedaltrain). Some pedals will play nice together, for instance you can usually daisy chain analog pedals, as long as you keep digital pedals on their own separate power adapters. A lot of power bricks will have individually isolated outputs. Think of each output as if it was its own separate battery. Aside from fixing noise problems, when you have isolated outputs you can stack them together to get 18V or run them in parallel to get more amperage by using special Y cables.
Bricks vs. Batteries - Perhaps in an attempt to satisfy battery advocates, some power bricks offer a "sag" control which is just a variable output so you can adjust the voltage down to 4.5V. Although this will affect the headroom in your pedals, the power supply is still putting out very stiff voltages. As discussed above in the section on batteries, sometimes having power that's not so stiff helps your pedal have a softer, tube-like clipping quality. Almost all adapters and power bricks put out very stiff voltages, which means your pedals will experience hard clipping.
There is one exception, we helped design a pedal power brick for pedaltrain. Our powertrain 1250 (PT1250) uses a novel circuit that lets you adjust the impedance of the output power - allowing the voltage to lag, swing, dip and rebound just like a real battery. We didn't know what sort of cool name to give it, so we just called it by what it technically does, "LDV" or "Load Dependent Voltage ". You can adjust the LDV trim pot and go from emulating a fresh, new, stiff battery to emulating a weak, old, soft battery, and any sort of battery in-between. You can play through your pedal and adjust the power supply to get the best sound of a semi-soft battery, then not have to worry about an actual battery that would continue to die off. We made sure those outputs would be isolated and used the best linear regulators on the market so that it has the same almost nonexistent noise floor as if it was really just a battery. In addition, we made sure to give it a 115/230V switch so you can take it to other countries as well as an extra AC outlet so that you can daisy chain power to use multiple powertrain 1250's, get power to an amplifier or some other gear.
"The powertrain 1250 is really the best of both worlds, you get everything good about a battery; isolation, low noise floor and a way to simulate that chemistry between a battery and a pedal that makes some pedals sound so good, but without the worry that the battery is going to die, or the expense of constantly replacing batteries…" ~ John Chandler
A quick search shows that you could spend about $180 to get twenty 9V Ultra Life Lithium batteries… But, for a lot less money you can get a powertrain 1250 to power those same 20 pedals forever… hmmm, math is fun, isn't it!
We've done a lot of homework on batteries and power supplies. In the next 10 years or less, you should be able to pick up a rechargeable power brick that can run 30 pedals for days between charges. Already existing today in university laboratories are rechargeable batteries based on carbon nano tubes that can hold twice as much power in half the space, and they are able to fully charge in minutes. They will be cheap, safe and easy to produce – but there are still years of bureaucratic red tape that must be navigated to get them to market. I hope we will see new pedals produced with these batteries integrated right inside, not unlike an iPhone, so you will never have another issue with dirty power, ground noises or isolation ever again. One laboratory I read about has tested a diamond battery made from recycled nuclear waste that they say can power a watch for thousands of years… read Forbes Article. I mean it's great to be alive now, seeing the birth of so much incredible technology, but man, to see what will be possible in another 100 years, that would be something!
Alex “Skip” Welti is currently the V.P. of Research at Creation Audio Labs, Inc. a Nashville based pro audio service facility which also designs custom circuits and upgrades for pro audio gear and manufactures a line of products for guitar and bass. Skip is an abbreviation of "Skipper", a nickname Alex earned as National Service Manager for Soundcraft USA where he worked for 10 years before opening Creation Audio Labs. Prior to Soundcraft, he was with Westlake Audio in Los Angeles for eight years. As Technical Supervisor there, Alex helped out on projects such as Michael Jackson’s “Bad” and Paul Simon’s “Graceland”, among many, many others. A true techno-wizard, Skip the mad scientist is ever at work in his laboratory; dreaming about cheap clean energy, zero noise and even-order harmonic distortion.