Welcome fellow Quakelings to yet another entry to the Tube Town Blog. Last month we overindulged ourselves on overtones and harmonics. We are also featuring Mike Tolan, our assistant production manager, in this month's “Rigs of EarthQuaker Devices.” My aim this month is to share what I know about Power Supplies. So let’s dive in and get juicy.
Power Supplies vs. Batteries
In the days of yore, one simply bought a battery for your gizmo, and that would suffice as portable power. Batteries are great and serve up the Direct Current (DC) that most electronics need to perform their sonic wizardry. Batteries have limitations, though, both in terms of reliability and environmental sustainability. As a culture, we have become more conscious of our footprint and consumption of resources. That’s not to mention the shift in the gear industry to have huge pedalboards acting as our sonic palettes, allowing us the ability to tap into myriad of sounds at the click of a toe. These, among other issues, have led us to the External Power Supply. Plug this thing into a 120 volt wall outlet and power all the stuff you want. Eliminate the frustration of dead batteries and the piled up mountain of those we’ve laid waste to. Cool, I can live with that.
I was a late bloomer to the Power Supply movement, often pontificating about the tone being better with batteries. It is my opinion that there is some legitimacy to this belief.
Here’s an example: “Batteries sound better in my fuzz pedal than my ‘Wall Wart’ DC power supply.” I think this is due to the fact that Fuzz pedals often have germanium transistors that are sensitive to changes in temperature. This thermal instability affects the gain structure of the circuit. Pair that with a 9-volt battery that’s 8 months old and not crankin’ out the power it once did. In sonic terms, the lower voltage is what we hear and/or feel as “Sag."
Interestingly enough it is the combination of these two factors - environmental temperature and “Saggy” power, that creates the Fuzzy Bliss that we’re looking for. This fluctuation in temperature and current is not always consistently repeatable, though. With an external power supply, you lose the variation in voltage that a battery delivers during its lifespan, because power supplies deliver a consistent voltage. This is great for most effects pedals, but takes a bit of the magic out of many fuzzes. It’s not that it sounds bad, but you can hear a bit of a difference, albeit not one you’re likely to detect ripping up the stage with your band.
Let’s explore things a little deeper. What are some things to look for in a good Power Supply and, oh yeah, how the heck does it work?
Here’s what’s happening when you use a power supply: you are taking the power from the wall, which is Alternating Current (AC) and rectifying (or converting) it into Direct Current (DC) for your pedals. That’s it. But it's not quite so simple.
Imagine a dolphin jumping out of the water. This is AC current. The water represents 0 volts, or the “zero crossing.” As the dolphin jumps up out of the water, it reaches a peak in the air before falling toward the water’s surface (zero crossing) and diving down below the water. It repeats this pattern over and over again.
In the United States, our electricity flows at 120 Volts/60 Hertz. 120 Volts is indicative of how high the dolphin jumps. 60 Hertz is how many times the dolphin jumps up out of the water and back down below the water in the span on one second. Flipper is doing it 60 times a second. That’s one fast swimmer! This alternating above/below pattern is how we get the name Alternating Current.
Now let’s rectify the AC voltage to get the DC supply we need. The component that does the rectification is called a diode. Diodes are semiconductors which act like a one-way street, allowing current to pass in only one direction. When wired in series with the AC voltage from the wall, the diode takes the positive swing of the AC (when the "dolphin" is above the water) and passes it through the diode. These short bursts of positive AC voltage through the rectifying diode are the basis of a Direct Current (DC) power supply.
Why do we need DC if we already have that voltage coming from the positive side of the AC supply out of the wall you ask? Because DC is the voltage that the guts of our gear need to do what they do.
Once we have rectified AC voltage to DC, we have to comb out the irregularities to smooth the flow of electrons and create a steady voltage. This is where filtering and regulation come into play.
Filtering is done by a capacitor placed after the rectifying diode. This capacitor’s job is to act as a storage container for all the bursts of AC going through the diode. Think of this capacitor as a reservoir providing a constant and consistent voltage. As the circuit demands power to make sound, the capacitor delivers the voltage it has stored up. Once depleted, it refills itself from the rectifier diode.
This change of voltage is normal and natural, but the capacitor wants to be refilled with DC to keep the juice flowing. This charging and discharging is called Ripple. Ripple is the irregularity of voltage caused by the filling and depletion of the supply voltage in the cap. It happens really fast but consistently. This introduces noise into our sensitive audio circuits.
The audible effect of ripple is 60-cycle hum. The filter’s job is to keep 60-cycle hum out of the circuit we are trying to power. Trust me, you want a filtered power supply.
Transformer Isolated Regulation
You will often hear the term “transformer isolated” in the description while shopping for power supplies. This is pretty normal and kinda ol’ school. You might be wondering how do we get 9 volts DC (like batteries) from the 120v AC coming from the wall. The transformer’s job is to take the 120-volt AC from the wall and convert it to the lower voltage we need to power our gear. That’s why wall warts are so big - to make room for the transformer!
Switch Mode Power Supplies
Some cheaper power supplies are what is called a Switch Mode Power Supply (SMPS). These use a transformerless voltage circuit to supply the desired voltage. No isolation transformer means that these units are lighter weight and more cost efficient for fabrication and shipping. With proper design they can be solid supplies with little noise. However, these cost cutting measures can reduce performance and introduce noise into your signal.
That’s a lot of info! I hope it serves you well as you shop for a power supply, or re-evaluate your existing setup. Not all power supplies are created equal. And there are things you can’t control like low voltage coming out of the wall, etc. Them’s the breaks. At EQD, we always recommend Transformer Balanced Isolated Power Supplies for maximum performance. But if you have an SMPS, that’s okay, too.
Rigs of EQD
EarthQuaker Devices Assistant Production Manager Mike Tolan is in the spotlight this month for the Rigs of EQD showcase! He’s a rad Dad with a penchant for kindness, musicality, humor, and a calm demeanor that helps us all vibe out. I like him so much I gave him the first amp I ever built (after a few beers). Mike has played in countless projects lending his skills on all instruments. He was cool enough to detail his current guitar rig, and the cool gear he makes the jams with. Check out his music with his original solo project Talons'!
Here’s what’s in Mike’s stable:
I would love to hear some of your questions or comments on the Juice!
We’re all in this together!
Keep it crunchy Nuggets, till next time.
Joe Golden is a circuit builder and amp designer at EarthQuaker Devices. His touring and recording credits include Bernie Worrel (Parliament / Funkadelic, Talking Heads), Chrissy Hynde, and the Dirty Dozen Brass Band. He currently plays guitar in the Mark Leach band and is a Fender certified amp technician. Joe lives in Akron, Ohio.