I do get the problem, but I still have some questions:
- why would I use just a potentionmeter? This indeed is usefull to control the volume of the sound, however turning the sound to loud might saturate the transistors. So wouldn't it be better to have one resistor making sure that the transistors will not saturate at the lowest resistence of the potentiometer, and then add a potentiomenter to control the volume?
Well.. yes and no. Both are valid solutions. The reason I put a potentiometer here is because it's much easier to adjust the 'volume' knob than to pull out a resistor and put a new one in. Personal preference though, both solutions will work just fine
I did look at the link you send, but I didn't really understand their circuit. This is probably because they use two rails instead of a battery, I'm not really used to this type of notation yet.
However, I did make a new (improved circuit).
It's easy enough to get the hang of, and it looks like you have a decent handle on it already.
In this circuit the values of R1 and R3 shoud be the same to give both transistors the same 'lift' in input signal.
I had to create a negative signal to add to the input signal of the NPN. I didn't really know how to do this, so I came up with a quite complicated sollution. I wondered if there's something easer to do to create a negative signal.
Well... two things, R1 and R3 most certainly will be the same, but the value also depends on R2. The goal here isn't to give them the 'same' lift, but a specific lift of roughly 0.7v on each transistor... (So R2 would need to have 1.4v across it)
You don't actually have to do anything here regarding making a signal negative. The signal current is centred at 0v and swings positive and negative by itself. There is a bit of a flaw in your current drawing though... you are missing the capacitors used in the Class B Transformerless and Class AB designs, this is important or you will be shorting out R2 and both transistors will no longer be lifted.
Also i realised that this signal has one impurity; The extra voltage I add (or substract) form the imput signal to overcome the lack in voltage in some parts of the curve, is absolute and not relative to the curve, causing the shape of the curve to change. Also it kind of rips apart the curve like shown in the picture below the circuit.
The way to make it relative is to add an other transistor, but this has the same lack in voltage in some parts of the curve.
Meaning this is an infinite problem....
Is their any way to solve this, or is this a not so significant problem?
There sure is
The thing is, it's already taken care of with the class AB design and a properly tuned Class B on the link I shared.
You see... the voltage you add or subtract is setup so that you add 0.7v to the top transistor, and take 0.7v away from the bottom transistor. This means that both transistors are on the brink of conducting and all it takes is a 'tiny' amount to push it over the edge to conduct. As soon as the signal goes positive what happens?
The top transistor conducts right away, and the bottom transistor stops conducting completely. The problem you are thinking of would only apply if you didn't setup the 'float' voltage to the transistors first... or if you applied the wrong float voltage to the transistors. Remember the voltage is added/subtracted for each transistor... NOT the signal itself.
And I had one more question:
When connecting your circuit to the ground this is often illustrated with the tree stripes, but what does this look like in real life.
A treat toutching the ground litteraly is namely not so practical ....
Haha. that little tree icon is commonly called 'ground' but there is nothing so special with it.
The best way to think of 'ground' is how it's used. For example, in a car the 'ground' is attached to the body of the vehicle. This ground is almost always attached to the negative side of the battery, but some cars actually use the positive instead. Both options are fine, and both options use the car body as a 'common' return path. So they only really need to run one wire from the battery to something, then they use the body to go back. In things like the amplifier you are building, the 'ground' is considered to be the 'common' path. You have a pair of batteries making the positive and negative voltages, and as you had drawn the 'ground' is in-between them. To actually build it, the ground is simply a shortcut when drawing the circuit and can be replaced by drawing a line to connect each ground symbol to each other.
Now... that said, some 'ground' connections have more meaning... like in home appliances. The ground it actually connected to 'Earth ground', which is also connected to the body of the appliance. The reason here is that if something goes wrong inside the appliance, the current will go to the ground wire instead of going through a person who touches the appliance. This only works because the power plant also has an 'Earth' ground... so much like the car body being used in the previous example, our Earth can behave the same way as a return path for electricity back to the power plant. This is only used for emergency purposes though because earth is not a perfect conductor.
(Remember that electricity flows in a circle... so a battery operated devices will almost always gain nothing at all from using any kind of 'earth' ground.)
