Colorless writings, part 23 – Learn to read

What now?

I think the title says it pretty well. I was thinking about going through the basics of reading schematics, but that is more or less useless. I will talk about it a bit nevertheless. And get to the bigger picture in a while.

If we take a look at any analog guitar effect circuit’s schematic, we notice that there are the same symbols in use all over. Saw line represents the resistor, capacitors are represented by two parallel lines that do not connect in the middle. These are the two main ingredients found in every single schematic. Other important ones are the semiconductors. Bipolar Junction Transistors with either NPN or PNP configuration and Field Effect Transistors that come in N-channel and P-channel types – these can be standard silicon or metal oxide semiconductor (or MOS). Then we have our Operational amplifier blocks of various types.. And let’s not forget the diodes. Sometimes, in contrast to mechanical switching, switching can be handled with CMOS (complimentary metal oxide semiconductor) switches like CD4066 and many others. Some special chips may be used as well. These usually mean regulators (positive and negative), power amps (i.e. LM386), BBD (Bucket Brigade Device) analogue delay chips and timers or DC to DC conversion chips like MAX1044 or ICL7660S. In some relatively rare cases the bypass could be configured with a mechanical relay. This is a quite common way to achieve “clickless” true bypass. In addition to those there could be inductors, but usually very few of anything else. Let it sink in. I know i just listed more than twelve different component types with their own symbols that you need to visualize for yourself.

Next, you need to ask yourself what is a schematic. If you don’t know it as an easy answer, i’ll tell you. It’s a drawing of how the components listed above connect to each other. Once you are familiar with the symbols, you should quite easily get the point of the lines between the terminals on them. All the others have their own symbols, except for the “special” chips. Those are usually depicted as the chip itself, in a manner that the symbol looks just like the actual chip on in the circuit. Sure, sometimes these special chips can be depicted as square blocks with just a number next to the line that connects to the block. This method seems to be quite standard to, lets say for an example, NE571 compander. And yes. Regulator is a “chip”, even though it physically appears and looks like a common transistor. These are commonly depicted as blocks as well.

Then there are potentiometers that are in the simplest terms, variable resistors. Also jacks for the inputs, outputs and the power.

The things above are the components every single circuit is made of. In addition to those, we have couple of more things that are found in every single circuit ever made. The power supply and the ground. Most designs take advantage of switching between a battery and a supply that transforms the wall AC voltage to the 9V we usually want. These connections should be in the schematic for the drawing to be whole. Sometimes we see drawings of the signal path and power supply only. The jacks need to be there in your guitar effect unit, whether they are actually drawn in the schematic or not. Obviously.

I can think of two different types of power supply sections. Once you’ve read enough schematics you’ll spot these out easily. First, the basic 9V and ground supply method. Seen in simple, classic designs, such as Fuzz Face. There isn’t anything else in there but the 9V and the ground. Second, a bipolar supply. In essence this means that there are +9V and -9V voltages present. This equals in our amplifiers seeing 18V. Bipolar supplies must be used with the basic supply on some of the designs. Take a Tubescreamer for an example. The operational amplifier needs the supply voltage and a reference voltage for it to operate properly. We can divide the original supply voltage in half with just two resistors, which will work great as a reference voltage. Note that these both are referenced with ground, being 0 volts. If we don’t divide the voltage, we’ll need +/- voltages present, and the ground will act as a reference for the operational amplifiers. Let this sink in for a while too…

Then there’s the most important thing. Signal path. As some of you probably know, the “signal” your guitar sends is nothing more but an alternating current (AC) signal. This signal basically vibrates in voltage between the ground and the signal path. Faster the vibration, higher the pitch in tone. It’ll pass through of all our capacitors with little trouble and it’ll make its way through our filters and amplifiers too.

With a well drawn schematic, you’ll be able to follow where the signal should be travelling and where the power supply sets the voltage. With this tiny piece of information one could basically learn everything there is to know about any analog guitar effect circuit. Just remember, capacitors block DC voltage by not letting it pass.

Now, if you were able to follow my thought through all the way to here, there are two choices. Either you know all this already and found the text rather boring. Or. You really tried to visualize things and learned something. You probably noticed that i didn’t use any images in describing things. It was surprisingly hard for me to go through these things and explain them as i just did. Words in certain order can teach a lot, but i wrote this from my memories and gut feelings. Both of which i’ve gained from tinkering with guitar effects for nearly five years on a daily basis. The internet is good, but it is also evil. Anyone can write anything they want and if you read just bits and pieces from here and there, you might very well get a picture that’s broken. So please. Learn to read. And more importantly, learn to think about what you just read. There may be two opposing views on any subject. It’s up to you to determine what is true, what is false and what is XOR.