TUTORIAL What Are All Those Symbols? - Intro to Schematic Reading

BuddytheReow

Breadboard Baker
You've got your breadboard, jumper wires, offboard components, and breadboard components in hand and are ready to go. You download a build doc from PedalPCB website, skip the pretty picture of the PCB, skip the components listing since your order came in the mail 3 and a half minutes ago, get to the schematic and all the anxiety in the world is telling you to run away and return everything you just bought because you see THIS...
1629312645778.png

Don't worry! We are here to help you!

For purposes of this thread I would rather talk about what the components are rather than the why/how they work. The why/how is more theory based and can/will be a separate thread once the basics are covered here.

Schematics in general are read from left to right with input on the left and output on the right. Schematics on PedalPCB generally break down a schematic into either 1 or 2 sections, the second section being the power section. You can see in the schematic above that there are 2 circuit blocks. The smaller section on the bottom is the power section. Your guitar/bass do not go into this section, but this section is needed in order to properly power the main circuit.

OK. Read it left to right. Power section is sometimes separated. Got it. But what are all those symbols?

Here is a basic list of the symbols needed to understand, IMO, 2/3 to 3/4 of the circuits on PedalPCB. Some of the more complex digital circuits have a basic block with all the pins numbered showing what connects to where. There are definitely other things to talk about here, such as the pinouts for transistors (what line does what), electrolytic capacitor polarity (the minus sign on the actual component corresponds to negative end and should go where the curved line in the symbol is connected to), diode polarity, potentiometer lug numbering, etc. But those are separate threads for another day. You should learn the basic circuit itself before you whip out your breadboard.
1629313521384.png

Squiggly line is resistor, triangle with a line on the tip is a diode, triangle with + and - is an IC or opamp. Got it. What about all those dots?

Dots you say? Oh you mean these?

1629313755521.png
Those dots represent a connection point between components. Looking at the top right hand corner, the schematic is telling me that the signal is coming out of pin one of an IC chip and into a resistor, labelled R6. Before it reaches the resistor a separate connection must also be made to a capacitor, a potentiometer, and a resistor before being fed into pin 2 of the IC chip. This is called a negative feedback loop in an opamp circuit and more will be talked about in (potentially) a separate post by someone who wants to share their circuit knowledge with the universe or anyone who cares to listen.

What about the Vcc and Vref I see in nearly every schematic?
1629314346092.png
VCC actually stands for Voltage Common Collector. Think of it as the main power input to the circuit after any preliminary tampering has been done via a couple of components. Since we're all building pedals here it will most likely be 9v (most common), 12v, or 18v depending on the power supply you have available.

Vref refers to a voltage reference. Think of this as after more tampering has been done to the supply voltage. From here, check the rest of the schematic to see where in the circuit this point connects to. Here, there are two points.
1629314873986.png

I get the power points after the "tampering" like you said, but where do I plug in my power source into?

Right here.
1629314796536.png
What about those ground points. Where do I connect those?

You mean like this resistor here? 1629315073117.png
You can do 1 of 2 things: either connect the lead of that resistor directly to the blue column on your breadboard OR you can put that lead in an unused or commonly used row with other components that should go to ground and THEN add a jumper wire to the blue column on your breadboard.

I think I understand now. Let me brainwash myself and learn these symbols even while I sleep.

Such a good little pedal builder...pretty soon you'll be starting your own company. They grow up so fast!
 

BuddytheReow

Breadboard Baker
One error @temol pointed out. The reference power symbol is upside down. It should look like this, but with the line coming out of the point. This is what you will see in PedalPCB schematics. My CAD software can't alter the little line.
1629376013926.png
 

Feral Feline

Well-known member
One error @temol pointed out. The reference power symbol is upside down. It should look like this, but with the line coming out of the point. This is what you will see in PedalPCB schematics. My CAD software can't alter the little line.
View attachment 15027


For anyone that somehow missed it (like me):
The VREF symbol in error is found in the lower left of the symbols graphic (2nd graphic in the OP).
Since there are a lot of VREF symbols amidst the many graphics/schematics in the OP, it took me a while to find the mentioned error as I was working from bottom to top...
 
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Coda

Well-known member
How about when you don't use all of the legs of the op amp. You know, those little mini-circles. What dat mean?
 

Coda

Well-known member
Can you provide an example?
Yes, though I should have clarified. When I first breadboarded with an op amp, I had no idea what to do with the legs that I didn’t use. I searched and searched and searched. It was only after reading an article about how an op amp works that I realized that you don’t do anything with the legs you don’t use…since you are no using them.
 

BuddytheReow

Breadboard Baker
Yes, though I should have clarified. When I first breadboarded with an op amp, I had no idea what to do with the legs that I didn’t use. I searched and searched and searched. It was only after reading an article about how an op amp works that I realized that you don’t do anything with the legs you don’t use…since you are no using them.
Exactly. Just make sure you're not plugging anything else into your breadboard on that row! Depending on the opamp you may want to simply ground out the unused pins to reduce noise
 

Jeff C

Active member
You've got your breadboard, jumper wires, offboard components, and breadboard components in hand and are ready to go. You download a build doc from PedalPCB website, skip the pretty picture of the PCB, skip the components listing since your order came in the mail 3 and a half minutes ago, get to the schematic and all the anxiety in the world is telling you to run away and return everything you just bought because you see THIS...
View attachment 14998

Don't worry! We are here to help you!

For purposes of this thread I would rather talk about what the components are rather than the why/how they work. The why/how is more theory based and can/will be a separate thread once the basics are covered here.

Schematics in general are read from left to right with input on the left and output on the right. Schematics on PedalPCB generally break down a schematic into either 1 or 2 sections, the second section being the power section. You can see in the schematic above that there are 2 circuit blocks. The smaller section on the bottom is the power section. Your guitar/bass do not go into this section, but this section is needed in order to properly power the main circuit.

OK. Read it left to right. Power section is sometimes separated. Got it. But what are all those symbols?

Here is a basic list of the symbols needed to understand, IMO, 2/3 to 3/4 of the circuits on PedalPCB. Some of the more complex digital circuits have a basic block with all the pins numbered showing what connects to where. There are definitely other things to talk about here, such as the pinouts for transistors (what line does what), electrolytic capacitor polarity (the minus sign on the actual component corresponds to negative end and should go where the curved line in the symbol is connected to), diode polarity, potentiometer lug numbering, etc. But those are separate threads for another day. You should learn the basic circuit itself before you whip out your breadboard.
View attachment 15000

Squiggly line is resistor, triangle with a line on the tip is a diode, triangle with + and - is an IC or opamp. Got it. What about all those dots?

Dots you say? Oh you mean these?

View attachment 15001
Those dots represent a connection point between components. Looking at the top right hand corner, the schematic is telling me that the signal is coming out of pin one of an IC chip and into a resistor, labelled R6. Before it reaches the resistor a separate connection must also be made to a capacitor, a potentiometer, and a resistor before being fed into pin 2 of the IC chip. This is called a negative feedback loop in an opamp circuit and more will be talked about in (potentially) a separate post by someone who wants to share their circuit knowledge with the universe or anyone who cares to listen.

What about the Vcc and Vref I see in nearly every schematic?
View attachment 15002
VCC actually stands for Voltage Common Collector. Think of it as the main power input to the circuit after any preliminary tampering has been done via a couple of components. Since we're all building pedals here it will most likely be 9v (most common), 12v, or 18v depending on the power supply you have available.

Vref refers to a voltage reference. Think of this as after more tampering has been done to the supply voltage. From here, check the rest of the schematic to see where in the circuit this point connects to. Here, there are two points.
View attachment 15004

I get the power points after the "tampering" like you said, but where do I plug in my power source into?

Right here.
View attachment 15003
What about those ground points. Where do I connect those?

You mean like this resistor here?View attachment 15005
You can do 1 of 2 things: either connect the lead of that resistor directly to the blue column on your breadboard OR you can put that lead in an unused or commonly used row with other components that should go to ground and THEN add a jumper wire to the blue column on your breadboard.

I think I understand now. Let me brainwash myself and learn these symbols even while I sleep.

Such a good little pedal builder...pretty soon you'll be starting your own company. They grow up so fast!
This was very helpful for a noob like me. But I’m still a little unclear on the path sequence I should use with my audio probe on the Cobalt Drive I‘m trying to build but get no signal through. I guess I could figure it out by trial and error but if you have some helpful suggestions, that would be awesome. https://docs.pedalpcb.com/project/CobaltDrive.pdf. Thanks!
 

Harry Klippton

Well-known member
This was very helpful for a noob like me. But I’m still a little unclear on the path sequence I should use with my audio probe on the Cobalt Drive I‘m trying to build but get no signal through. I guess I could figure it out by trial and error but if you have some helpful suggestions, that would be awesome. https://docs.pedalpcb.com/project/CobaltDrive.pdf. Thanks!
There's a little trial and error to it, especially on a board where the trace routing isnt in the build doc. When looking at the schematic, it's often but not always signal flow from left to right, ground connections going down, and power connections going up. Try and figure out how the signal is getting from the input to the output on the schematic, and then figure out how that corresponds to the components on the board. Best thing about an audio probe is you can pome around and figure out yup there's the signal! You can try it on a working circuit to practice
 

EGRENIER

Well-known member
There's a little trial and error to it, especially on a board where the trace routing isnt in the build doc. When looking at the schematic, it's often but not always signal flow from left to right, ground connections going down, and power connections going up. Try and figure out how the signal is getting from the input to the output on the schematic, and then figure out how that corresponds to the components on the board. Best thing about an audio probe is you can pome around and figure out yup there's the signal! You can try it on a working circuit to practice
I've been trying to help @Jeff C on his Cobalt drive issue... but the schematic includes stuff I have never seen and don't understand. There seems to be 2 JFET facing each other, clipping diodes going to ground ????

I think we need help, any volunteers the thread is here:

 

giovanni

Well-known member
I've been trying to help @Jeff C on his Cobalt drive issue... but the schematic includes stuff I have never seen and don't understand. There seems to be 2 JFET facing each other, clipping diodes going to ground ????

I think we need help, any volunteers the thread is here:

I responded on the thread. Check it out! It’s not rocket science, just electrical engineering ;)
 

Fizz

Active member
Those dots represent a connection point between components. Looking at the top right hand corner, the schematic is telling me that the signal is coming out of pin one of an IC chip and into a resistor, labelled R6. Before it reaches the resistor a separate connection must also be made to a capacitor, a potentiometer, and a resistor before being fed into pin 2 of the IC chip. This is called a negative feedback loop in an opamp circuit and more will be talked about in (potentially) a separate post by someone who wants to share their circuit knowledge with the universe or anyone who cares to listen.
I'd like to know more about this negative feedback loop. I would have thought the signal was coming from 2 and going to 1.
 

BuddytheReow

Breadboard Baker
I'd like to know more about this negative feedback loop. I would have thought the signal was coming from 2 and going to 1.
 
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