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.