I was designing an audio amp for a final project for an electronics course. We were given a very vague set of requirements and told almost nothing about our input signals or desired output minus relative gains.
This was our exact prompt:
- Design, build, and test a practical audio amplifier that would meet the following criteria(this portion is to be built in the lab).
Input signal: Audio frequencies
Voltage gain: 100 or higher
Input Impedance: > 1 M Ohms
Output Impedance: negligible
Load impedance: 8 Ohm speaker
State any assumptions you make, use discrete components (resistors, caps, diodes, transistors, op-amps), power supply use +/- 9 V
We've covered a fair set of transistor topologies, how to calculate gains and good design practices but we did essentially nothing on push-pull amplifiers, which is what my design is based on:
Reviewing some of the literature I came to realize this is more or less what a Class AB amp looks like, currently this design can do voltage gains of 1000 (something like 500-2500 if I put a variable pot 5k-15k) but one thing is bothering me. I have no idea how to calculate the current gain from the push pull, and I think that in this design there is a beta dependance on the output current. If so that's a pretty big problem since that means my current gain can wildly fluctuate and not even be the same between two transistors, and can scale unpredictably in different conditions.
My question is twofold:
- How do I calculate my current gain for this circuit?
- How can I modify this push-pull such that if there is a dependance on beta I can remove that dependence.