What do you think about this audio amplifier with 1 transistor. I intend to replace LM324 with TDA2030, any suggestions for the transistor are welcomed. There will be about "2V", "1A" power over the transistor, so a small iron is in order to cool it off? I think the OPAMP is good without an iron.

EDIT: It bothers me that the sinusoid has a very small margin (peak to peak), will that be ok? Will it be better to use 2 transistors (NPN and PNP), suggestions about transistors and orcad gives me bad results when I try to do it with 2 transistors? I think there should be "1.2V" pre-voltage for class AB work. But Orcad gives me a bad sinusoid, I will post the graphic when I can.

 

There are far better chips than the TDA2020 /50 series, that give better frequency response, the tda chips dont need a power transistor slave.

 

As you can see in both the current and voltage waveforms, there is increasing harmonic distortion in the positive half-cycles due to the gain of the transistor decreasing as its collector current increases.

This is a very poor amplifier design. There is over 1/2 amp of static current through the speaker. This is more than enough to cause its cone to be WAY off center in its travel range, almost certainly causing it to "bottom out". That is when the voice coil bangs into part of the magnet structure.

Consider replacing the entire circuit with an LM386.

R3 has no purpose and can be removed.

ak

 

Audio amplifiers have plenty of negative feedback from the output to the inverting input. The negative feedback causes the distortion to be so low it is hard to measure. Your circuit has no negative feedback.

 

Another problem is that you have a bipolar input signal but are using a single supply.

 

Hello ArakelTheDragon. Do not be offended, but what you painted is delirium. This is forgivable for beginners. Operational amplifiers are commonly used with feedback. The transmission ratio for combining the inverting and non-inverting inputs is the common-mode signal transfer coefficient. Some speakers will not like direct current. This current will greatly dislodge the membrane and this will cause large distortions. In real circuits, either separating capacitors or bipolar power are used. And further. Do not completely trust the results of the calculations. After all, the developer of the operational amplifier model, only in a terrible dream would you see your project.

 

See

 

Hello,

Did you already have a look at this thread?
Components Selection Guide
in post #7 there are all kinds of amplifiers mentioned.

Bertus

 

You never ever feed both inputs of an opamp with the same signal!
An opamp input must be biased at an input voltage so that it can swing equally up and down.
All audio amplifiers have negative feedback from the output to the (-) input of the opamp.
The LM324 (and its sister the LM358) have crossover distortion, too much noise and a poor high frequency slew rate to be used in an audio amplifier.
An audio amplifier almost always has two output transistors with one pulling the output up and the other pushing the output down called "push-pull". Then when there is no input signal they both do not conduct much current so they stay cool. But your amplifier with only one output transistor has a high current in the output transistor all the time so it will get hot and waste the battery power away.

 

You never ever feed both inputs of an opamp with the same signal!
An opamp input must be biased at an input voltage so that it can swing equally up and down.
All audio amplifiers have negative feedback from the output to the (-) input of the opamp.
The LM324 (and its sister the LM358) have crossover distortion, too much noise and a poor high frequency slew rate to be used in an audio amplifier.
An audio amplifier almost always has two output transistors with one pulling the output up and the other pushing the output down called "push-pull". Then when there is no input signal they both do not conduct much current so they stay cool. But your amplifier with only one output transistor has a high current in the output transistor all the time so it will get hot and waste the battery power away.

Entering the output stage into Class A mode with the help of an additional resistor (in this case 1 kΩ) removes cross distortion. I built a transistor model of these operational amplifiers. This model well imitates cross-distortion. Also, the addition of a resistor removes the cross distortion provided that the load current does not exceed the current of the additional resistor. At a load of 100 kΩ, no distortion gives an internal 50 μA current generator.

 

Connecting the two op amp inputs to the same signal is how you would test “common mode rejection” of the amplifier. Ideally it would be a zero output signal.

Why are you connecting the amplifier this way?

 

I know opamps are differential amplifiers. I wwill read the rest when I can.

 

I know opamps are differential amplifiers. I wwill read the rest when I can.

Op amps can be connected to create a differential amplifier.

 

Opamps amplify the difference between the positive and the negative input.

 

Opamps amplify the difference between the positive and the negative input.

 

Opamps amplify the difference between the positive and the negative input.

True, in theory but feedback to (-) input is needed to control how much it amplifies, and a voltage divider to the (+) input is needed to reference the output to some level.

 

Opamps amplify the difference between the positive and the negative input.

Yes, so why are you feeding the same signal into the + and - inputs, which results in a difference of zero?

Bob