Multi-stage audio amp help

Thread Starter


Joined Mar 11, 2015
Hello all,
Me and my group are doing a design project right now and we are a little stuck on the question, ok very stuck. The question is to:

Design a multi-stage audio amplifier for delivering an average power of a minimum of 200 mW to an 8 Ohm speaker from a microphone that produces a 10 mV peak-peak sinusoidal signal and has a source resistance of 1 kW. Use commercial NPN transistors available in our lab for your design. Analyze the frequency response for the amplifier as well. Design such that the upper 3 dB frequency is at least 50 kHz, and lower cutoff frequency below 25 Hz. Show your design, calculations, as well as simulation results in your report. Use base-emitter junction capacitance and base collector junction capacitance values from the device spec sheet.

We are not very sure on where to start so any help would be very appreciated.
Thanks alot.


Joined Jan 3, 2011
You're given load power and impedance, which means you can figure out the voltage and current needed to drive the load to the required power level.

- You'll need voltage amplification between the source and the load. Figure out the necessary load voltage and amplify accordingly.
- You'll need an output stage that can drive enough current to reach the desired load power. Figure out the necessary load current and design accordingly.
- You'll need to use input impedance calculations together with the junction capacitances mentioned to calculate high frequency cutoff. Do you know how to calculate that?

If your project doesn't state any distortion or efficiency specifications it can be pretty simple.