I am so used to using op-amps to do all my amplification, when would it be appropriate to actually do BJT etc.. transistor amplifiers?

 

You might find such an animal useful when driving speakers and not earbuds. Op amps have a hard time handling +/- 75 VDC @ 12 amps.

 

Op amps are more linear devices than BJTs and you can design easier. However, if you require high power outputs then you have to use transistors.

What is the application?

 

Just inquiring for future design knowledge.

So why not just op-amp into a buffer stage? i.e. emitter follower buffer etc..? Or a power push/pull?

The component footprint of an op-amp amplifier seems like it would almost always be less, so easier to stick with op-amp and just buffer output.

 

Yes, it would be better to amplify voltage using an op amp (if the voltage level permits) and then use a push-pull pair as buffer (amplify the current).

 

Just inquiring for future design knowledge.

So why not just op-amp into a buffer stage? i.e. emitter follower buffer etc..? Or a power push/pull?

The component footprint of an op-amp amplifier seems like it would almost always be less, so easier to stick with op-amp and just buffer output.

If possible, you should put the buffer inside the feedback loop. You will get better linearity (less distortion).

 

Aye, drives you through the cut-off regions. That is Class-AB yeah?

 

Aye, drives you through the cut-off regions. That is Class-AB yeah?

That seems to be the most popular choice.

 

Most common high power amplifiers these days use an op-amp or BJT preamp section and a Mosfet output stage. I am currently touring with amplifiers that will drive 2500 watts into 4 ohms. The mosfet power stage is easy to bias and drives massive current with minimal distortion.