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AC, DC currents and swimming pools

Sebastien Vezina

Before learning about another very important passive component, the capacitor, we will address another fundamental piece of the electronic puzzle that can also create a lot of confusion: alternating current (AC) vs direct current (DC) - queue Thunderstruck.

Not exactly!

Not exactly!

Electrical current comes in two forms: AC and DC. The main difference is pretty straightforward: AC changes amplitude over time and DC does not. Mathematically, DC has a frequency of 0 (which is not entirely true in the real world but we’ll talk about it later). 

If you live in North America, the current that you get from the wall warts has a frequency of about 60 Hz - thus, it is AC, just the same as your guitar signal, except at much more dangerous voltages so don’t go and try to figure out what it sounds like, you dingus.



Most household electronic devices, including pedals, amps, TVs, computers, etc, are powered by DC current. We use power supplies with our guitar pedals, most of them are set to supply 9 volts of DC power. We’ll see how that works later.

One very, very important thing to know about these two that has also caused me numerous headaches is that they don’t hate each other and are not mutually exclusive. AC and DC are actually bros and get along real well and this has very real uses in the realm of guitar effects and analog circuitry in general.

AC and DC currents (also called “components” of a same current) can both ride the same circuit paths and to help picture this - here’s an analogy: We can think of DC current as water in a pool. Let’s say our pool is 9 volts high. When it’s full, our pool contains 9 volts of DC current.

AC current can be pictured as ripples, or waves, riding the level of water. If you could cut your pool in half and look at a cross section of the water before your parents/significant other see you’ve ruined their summer, you would see the wave ride on top and it would look kind of like this:

Apologies, I play guitar, I don’t draw.

Apologies, I play guitar, I don’t draw.

What we see, is a wave riding the water, an AC current riding a DC current. There’s a word for the act of filling the pool with a certain level of water for the waves to ride on: biasing. It’s another very important principle that will be used over and over again in the future. We’ll have a blog post or ten specifically about biasing later.

For the moment, remember that AC current changes amplitude over time, DC current does not and that nothing prevents both to ride the same path, at the same time, except maybe the subject of the next post: capacitors. 


Sebastien Vezina

Hello! I certainly hope you did your homework and now know a little bit about voltage, current and resistance because today we’ll be digging a bit deeper into what does what in a basic electronic circuit.

You’ve seen their names and their little symbols on schematics, but have no idea what they really do. Passive components, resistors and capacitors (also inductors but we won’t really bother with them for now as they are much less often used in guitar pedals), are everywhere and are essential building blocks of all guitar effect circuits.

Today, we take a quick look at resistors.

As you should remember from reading about Ohm’s law, applying a voltage to a resistance will generate a current. There is no current without resistance. Actually, there’s is no such thing as “no resistance”. A perfect conducting medium does not exist and zero resistance would mean infinite current in any given amount of time which is physically impossible. There are things like “superconductors” and “perfect conductors” but these don’t apply to us and as such we’ll pretend they don’t exist. For all intents and purposes related to building guitar pedals: wires, guitar pickups, cables, jacks, PCB (Printed Circuit Board) traces, air, you, everything has resistance (and no, it is not futile… nerds).

While resistors have many different practical uses, it is safe to say that they are basically used to control the amount of current, in amperes, going through them. What does that mean for your guitar signal? Not much by itself, I’m afraid. But what if you were to put two resistors in series and take measurement right in between? You get a very simple, but very powerful arrangement: the voltage divider.

Here’s what it looks like:

Let’s say our typical Fender Telecaster with stock single coils and an average strum on the low E string generates a signal of about 100 mV of amplitude. That’s one tenth of a volt. Following the schematics, we can see that our 100mV signal will be applied across R1 and R2, generating current. Remembering Kirchoff’s Voltage Law (you did read about it, right?), we know that the sum of the voltage drops across all series resistor will amount to our source voltage. In plain English, that means that the amount of volts that will drop from R1 + the amount of volts that will drop from R2 will be equal to the amount of volts we put in, which is 100 mV.

Using Ohm’s law, we can deduce that the voltage drops for each resistor will be proportional to their values. What that means is that if we pick resistors of equal values, they will each drop about half of the voltage so, about 50 mV each, regardless of said value.

Now, what happens if we measure our voltage right in between our resistors? We read a voltage of 50 mV. Yup that’s right, we just made our guitar signal half as loud. Crazy. This is the basic principle behind the volume knob on your guitar, your amp and on almost every single pedal in the observable universe.

We will see many other uses for resistors, but for now that’s pretty much the gist of it.


What is ground? Baby, don't hurt me!

Sebastien Vezina

While I would very much like to talk about love, today we will discuss something else entirely. You’ve seen the name and the quirky little symbol, in our own branding, even. You can’t speak about electronics without mentioning ground and, in fact, any circuit by definition has a ground otherwise it’s just not a circuit.

The electrical ground can usually be described as the point of least impedance (or resistance). If an electrical charge has a clear path to ground, you can be sure it’s going there and nowhere else. Mathematically speaking, that’s not true. Kirchoff’s law says current will go everywhere it can, but Ohm’s says that more current will go where there is less resistance. There is no such thing as “no resistance” so while most of the current will go straight to ground, a tiny wee bit of charge will still follow the other paths. We’ll get to this in a future post. For practical purposes, it’s true enough.

Why is it called “ground”, anyway? Way back when, in the days of yore when people used telegraphs instead of the Internet, they noticed that the actual earth worked as a current return path (for sciencey reasons) and it stuck. Your house probably has a connection to earth. Fortunately, that doesn’t quite mean you need to take a wire from your pedals and bury it or drop half a pound of dirt in your enclosures just yet.

Let’s take a look at what a voltage is. A voltage is not an absolute measure. You can’t say “that point right there has 9 volts” as if they were apples because it doesn’t mean anything. A voltage is a differential measure of potential energy between two points if they were connected. The resistance between those two points would define the amount of current developed by that voltage. Wait, that’s Ohm’s law again! Dude and his law are just everywhere. When we say a battery “has 9 volts” it means there is 9 volts of potential between the anode (positive pole) and the cathode (negative pole). Form a circuit between the two and you’ll get the full glory of its whole 9 volts until its charge is depleted. In that particular case, the point of least impedance is the cathode.

In a circuit, most potential measurements are made relative to ground, making it what we call a reference point. We say ground is 0 volts because, in reference to itself, there is indeed a potential of 0 volts but the same can be said of any point in a circuit. If you turn your measurement around and decide that the anode of your battery is your new reference point, your ground, the cathode will have a potential of negative (-)9 volts relative to it. That actually leads to a pretty neat trick we call a virtual ground, that has many uses in guitar pedals.

Most modern overdrive pedals use a standard 9 volts DC supply. Battery or wall wart, doesn’t matter. You might’ve heard that in some cases, using an 18 volts supply might give you more gain or more headroom (disclaimer: before sticking any power supply to a pedal, triple check with the pedal manufacturer if you can actually do that otherwise you just might fry it - we warned you). That’s great but what if you don’t have or want to buy an 18 volts power supply? We got you, bro.

Further down the line we’ll talk about a nifty little device called a voltage converter. These puppies use internal oscillators and filters to do simple operations on a DC voltage such as inverting or doubling. That might be hella confusing right now but that’s ok. 

Using a voltage converter, you can feed its input a 9vdc supply and on the output, get another voltage that has the same potential in reference to ground but with a reversed polarity: -9vdc. Knowing that, you can say that the potential between the supply and the voltage converter’s output is 9v - (-9v), so 18v! See where this is going? You can use that -9vdc supply as a virtual ground for your circuit, in which case the supply, in reference to ground, becomes 18v. 

Mind = blown.

Ground is a fundamental part of any electrical or electronic circuit and while it seems very simple at first - the subject can become quite complex. For the moment, remember these:

    - Ground is a reference point for measurements
    - Ground is where current wants to go

Questions and comments are more than welcome, just below!


Sound to electricity and back again

Sebastien Vezina

Hello aspiring builders. Today we won’t discuss volts and amperes - we’ll save that for later while it all sinks in a bit. Instead, we will discuss a process that tends to confuse a lot of newcomers: how does sound get turned into an electrical signal and back to sound again?

Basically, a sound and an electrical signal are one and the same. Both can be described with an amplitude and a frequency, and can represented on a two dimensional graph. That’s it, there’s no magic (not *actual* magic, at least).

Electric guitars have pickups. We already know and love these guys. Pickups are made of small magnetic cores, wrapped with many, many turns of fine copper wiring. Guitar strings are also made of metal ( \m/ ). When we hit a string, it vibrates and its movement disturbs the cores’ natural magnetic fields, inducing electron activity in the copper wiring. This induction generates an electrical current in the wiring at the exact same frequency as the vibrating string, at an amplitude that’s proportional to the amount of wiring wound around the cores. The result: our guitar sound turns into an electrical signal. Sorcery!

Now that we’ve figured that out, what about the other way around?

Our electrical signal has quite the adventure ahead of itself. It will travel through pickups, a long cable, some pedals, an amplifier and all the way to a couple of speakers, fighting its way through stray capacitance (keyword!), output and input impedance (more keywords!), losing some of its power (keywords for everybody!) along the way. We’ll worry about these eventually. For the time being, all you need to know is that when a signal finally reaches a speaker, it goes through the exact same process of induction, except in reverse.

Speakers are built upon the same principles as our pickups, with a magnetic core and copper wiring wrapped around it. The current from our signal will induce changes in the core’s magnetic field, again at the same frequency as the signal. Changes in the magnetic field will produce physical movement in a coil attached to our speaker cone, thus making the air around it vibrate, which translates to sound in our ears.

There we have it, we plucked a string, our guitar pickups turned the motion into electricity and a speaker did the exact opposite. Amazing.

Next time, we’ll get into the dirty stuff, promise.