I'm currently reading Designing Audio Power Amplifiers by Bob Cordell. After seeing the "Basic 50W Amplifier" that he shows in the beginning of chapter 2, I now am trying to use the same building blocks to design an amp to specifications I've chosen to help me understand things.
I've chosen an output power of 5W through an 8ohm load (Which should at least be audible I hope), this means I am going to need a peak output voltage of about 9V. I'm assuming my input signal is coming from something like a phone, and I'm making an educated guess that its peak voltage is 1v. This means I'm going to need a total gain of about 9.
The building blocks of his circuit are as follows:
Stage 1 of 3 (Input Amplification Stage): Constant Current Driven Differential Long Tailed Pair
- Rejects noise well, and negative feedback is easy to achieve from the final output of the amplifier with a simple voltage divider
Stage 2 of 3 (Voltage Amplification Stage): Constant Current Driven Common Emitter Amplifier
- Easy to get a really high gain from what I understand
Stage 3 of 3 (Output Amplification Stage): Triple Emitter Follower
- High input impedance, with a decent amount of output capability.
This is basically an op-amp I think, but with higher power capabilities. What I'm really struggling with is the input stage.
What I've been taught in my Electronics 1 class so far about BJTs is that for these amplifier configurations, the gain usually is a ratio of the resistors used (and maybe includes the base-emitter resistance). I have no idea where the gain is coming from in this schematic. I basically just fiddled with the resistor values until I got an output that looked alright-ish.
Is a source out there that goes through the design process of this type of configuration, or can anyone can help me out? Thanks!