I've been simulating with 40 Hz, could that be a problem?

Possibly. But it's easy to explore, isn't it. Increase the frequency to 400 Hz and then perhaps to 4 kHz and see if you see a significant difference. But also heed what #12 is telling you about discharging the coupling capacitor.

 

Possibly. But it's easy to explore, isn't it. Increase the frequency to 400 Hz and then perhaps to 4 kHz and see if you see a significant difference. But also heed what #12 is telling you about discharging the coupling capacitor.

My "aim" is to explore the use of this amp for audio applications, am I wrong by using it in this way?

 

My "aim" is to explore the use of this amp for audio applications, am I wrong by using it in this way?

I answered that in post #4
It has been done. It used to be the standard way to make a class A amplifier.
Who is going to tell you that you are wrong to do what has been done thousands of times before?

Now, if you want to put a modifier on that like, "good" or, "efficient" audio amplifier, you could receive a different answer.

 

I answered that in post #4
It has been done. It used to be the standard way to make a class A amplifier.
Who is going to tell you that you are wrong to do what has been done thousands of times before?

Now, if you want to put a modifier on that like, "good" or, "efficient" audio amplifier, you could receive a different answer.

Sorry i completely forgot that it was answered.

When you say "good" or "efficient", that points to op amps? or should i still explore discrete transistors?

 

should i still explore discrete transistors

Explore them for what? You never said anything except, "audio amplifier". You can make audio amplifiers several ways.
If you want to name any particular property of an audio amplifier, like frequency range, distortion, or power efficiency, there will be something to talk about.

 

Explore them for what? You never said anything except, "audio amplifier". You can make audio amplifiers several ways.
If you want to name any particular property of an audio amplifier, like frequency range, distortion, or power efficiency, there will be something to talk about.

well when i say explore them i mean understand deeper how they work, their properties and things like that. Remember that i'm a complete novice.

 

Class A is a great place to start. Then look at push-pull, then op-amp driven, then amplifiers that are essentially huge, discrete op-amps, then IC power audio amps, then fast switching audio amps. That's most of them.

 

Class A is a great place to start. Then look at push-pull, then op-amp driven, then amplifiers that are essentially huge, discrete op-amps, then IC power audio amps, then fast switching audio amps. That's most of them.

Interesting!

Playing around with this sim i'm using i saw a follower simple that it is biased at the center of the supply voltage at the base. where i "learned" it said that the base had to be 1/2 supply + 0.65 V. also this simple has a very Little (40 ohm) emitter resistor.

Could you give me a tip about biasing and about the emitter resistor?

 

Could you give me a tip about biasing and about the emitter resistor?

If you're going to charge the output capacitor through an 8 ohm speaker, you need to discharge it through an 8 ohm emitter resistor.

(This isn't exactly true, but it's close enough for a beginner.)

 

If you're going to charge the output capacitor through an 8 ohm speaker, you need to discharge it through an 8 ohm emitter resistor.

Requiring such a low emitter resistor value is the reason such a Class A amp is seldom used to generate any significant amounts of power into a speaker.

 

If you're going to charge the output capacitor through an 8 ohm speaker, you need to discharge it through an 8 ohm emitter resistor.

(This isn't exactly true, but it's close enough for a beginner.)

And looking the simulations a deep fried transistor too! I guess that's why class A are not chosen too much or have been displaced in favor of other classes.

 

If you are serious about driving a speaker, then you should look at push-pull Class B (or AB) circuits.

 

And looking the simulations a deep fried transistor too! I guess that's why class A are not chosen too much or have been displaced in favor of other classes.

It depends on the needs. For very good linearity it's hard to beat Class A, but it comes at a significant power cost. Remember that the reason there are different types of amplifiers is that they all have their pros and cons. If there was one, best, fits-all type, then that is all we would use. Engineering almost always comes down to compromises. So learn those pros and cons so that you can make reasonable and justifiable compromises -- your employers will love you.

 

If you are serious about driving a speaker, then you should look at push-pull Class B (or AB) circuits.

i'm moving to those ones next. any advice from your experience?

 

It depends on the needs. For very good linearity it's hard to beat Class A, but it comes at a significant power cost. Remember that the reason there are different types of amplifiers is that they all have their pros and cons. If there was one, best, fits-all type, then that is all we would use. Engineering almost always comes down to compromises. So learn those pros and cons so that you can make reasonable and justifiable compromises -- your employers will love you.

balance, balance & more balance...

 

i'm moving to those ones next. any advice from your experience?

Depends upon whether you are just learning or want to build a working circuit.

 

that means that if i want to drive a 8 ohm i need a smaller emitter resistor?

Yes, and that rapidly can turn into a real design problem. The smaller the emitter resistor, the larger the transistor has to be and the more power it has to dissipate. This is why the "push-pull" output stage was invented.

I've been simulating with 40 Hz, could that be a problem?

Depends on what you want the circuit to do. For telephone-quality voice signals you can get away with a low frequency corner of 300 Hz, but for even low quality audio you want that corner below 100 Hz.

ak

 

Yes, and that rapidly can turn into a real design problem. The smaller the emitter resistor, the larger the transistor has to be and the more power it has to dissipate. This is why the "push-pull" output stage was invented.

Depends on what you want the circuit to do. For telephone-quality voice signals you can get away with a low frequency corner of 300 Hz, but for even low quality audio you want that corner below 100 Hz.

ak

I will definitely read about push pull.

 

Depends upon whether you are just learning or want to build a working circuit.

well, first i would like to get familiar with it and then build some.

 

Your emitter resistor is way to large. When the transistor is off, this is the only path to ground for the speaker, so the negative half of the cycle is severely attenuated, giving you a very distorted output.

Change the emitter resistor to 8 Ohms and the output capacitor to 1000uF. According to my simulation, this gives you about 450mV on the output.

Bob