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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.

Dingus

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.