How Do I Interpret Circuit Schematics for Building a Pocket Amplifier?

[KingNothing]

Hi, I am just getting into building circuits. I have found a nice page with all the symbols: http://library.thinkquest.org/10784/circuit_symbols.html which has helped me some but I still get confused. The circuit I am talking in regards to is this: http://tangentsoft.net/audio/cmoy-tutorial/misc/cmoy-tangent-sch.pdf . As a reference, here is the page for the pocket amplifier.

It is a pocket amplifier for headphones. I hope to be able to make a small amplifier for a guitar, and I figure this is a start.

First of all, on the far left side, those symbols where it says 9V are for grounding right? What exactly is being grounded. I understand that there is a 9V battery used but doesn't that just have positive and negative terminals (shown on the far right)? What exactly is being grounded?

Also, Capacitor 1 (C1). Having a plus or minus means it is polarized right? Since the positive is connected to the negative by a line, doesn't this mean that the two terminals are directly connected? Should that be a concern?

What does the SW 1 \ 2 mean along the top? My guess is that it is a switch that will either connect the circuit there or disconnect it there. (I am only referring to the first schematic in the document for all the preceding questions)

On the second schematic, I see the potentiometer is being used as a volume control because it is a voltage divider. If I already have a volume control that controls the volume of the input signal (this is an amplifier circuit), do I still want the pot? If not, how would I get rid of it and keep the amp at full power always?

The capacitor 2 in the second schematic appears as though it is unpolarized and is just connected in series there, is that correct? What is the purpose of this? To prevent some sort of overload or other hazard?

It also appears as though R3 and R2 are just kinda connected off to the side and then grounded. What is the purpose of this? is this to decrease current in a proportional sort of way as the potentiometer is adjusted?

It also looks like there is an integrated circuit there, how do those work? This is the op-amp, right? It looks as though tehre are five different terminals.

Please excuse me if my questions seem stupid or very novice, because I haven't taken any classes on this, and haven't built anything yet.

 

[dlgoff]

First of all, on the far left side, those symbols where it says 9V are for grounding right?

These are the two 9 volt batteries. No grounding here. The +9V, -9V, and ground symbols on the power section connect to the same symbol points on the amplifier section.

What exactly is being grounded.

This ground symbol is not an Earth ground. It's just a reference or common for the circuits

Also, Capacitor 1 (C1). Having a plus or minus means it is polarized right?

right.

Since the positive is connected to the negative by a line, doesn't this mean that the two terminals are directly connected?

yes, there are two capacitors called C1 connected together. This is the common reference point.

What does the SW 1 \ 2 mean along the top? My guess is that it is a switch that will either connect the circuit there or disconnect it there.

This is the power-on switch. The 1 and 2 refer to the switch terminal number.

If I already have a volume control that controls the volume of the input signal (this is an amplifier circuit), do I still want the pot?

I would keep it.

The capacitor 2 in the second schematic appears as though it is unpolarized and is just connected in series there, is that correct? What is the purpose of this? To prevent some sort of overload or other hazard?

The capacitor feeds the AC signal to the amplifer and prevents DC from your source from getting through. It along with R2 provides a little load. R3 and R4 determines the gain on the amplifier.

This is the op-amp, right?

yes. You should research a little to find out how op amps work. This circuit show your two inputs, one output, and the two power terminals(+ & -).

Regards

 

[ravenprp]

Hi there,

First of all, don't worry about your questions being "stupid" or "novice." Everyone starts somewhere and it's great that you're taking the initiative to learn about circuits and schematics.

To answer your first question, yes, the symbols on the far left side of the schematic represent the ground connection. This is where all the components that require a ground connection will be connected to. The 9V battery has a positive and negative terminal, but it still needs a ground connection for the circuit to work properly.

Regarding Capacitor 1 (C1), you are correct that the plus and minus signs indicate that it is a polarized capacitor. The line connecting the two terminals indicates that they are directly connected, but this is not a concern. This is just how the capacitor is represented on the schematic.

You are also correct about SW 1 \ 2 being a switch that will either connect or disconnect the circuit. In this case, it is a double-pole double-throw (DPDT) switch, which means it can control two separate circuits at the same time. In this circuit, it is being used to switch between two different input sources.

In the second schematic, the potentiometer is being used as a volume control, but if you already have a volume control for the input signal, you may not need it. You can simply remove it from the circuit and connect the input signal directly to the op-amp. This will keep the amp at full power.

Capacitor 2 in the second schematic is indeed an unpolarized capacitor and is being used to filter out any unwanted noise or interference from the input signal. It is not there to prevent any hazards.

R3 and R2 are connected to the potentiometer to help control the gain of the amplifier. As you adjust the potentiometer, the resistance changes, which affects the amount of gain in the circuit.

Lastly, the integrated circuit (IC) is the op-amp. It is a small electronic component that amplifies the input signal and outputs a larger signal. The five terminals represent the power supply connections (V+ and V-), the input signal (IN), and the output signal (OUT). The fifth terminal is not used in this circuit.

I hope this helps to clarify some of your questions. Keep exploring and learning about circuits and schematics, and don't be afraid to ask more questions. Good luck with your pocket amplifier project!