Sorry for asking a non-keil related question. I have a microcontroller that generates some noise by a PWM signal / speaker. I use three NPN transistors as audio boosters. My power source is momentarily a power supply of 9V 750mA (will be batteries on the end). Can you recommend a way to boost the volume and to generate very high frequency sounds? Is there an advantage to use an audio amplifier rather than NPN transistors if I don't care about sound quality?
Consider using an audio transformer, it's what they are designed for. They simplify matching the speaker impedance, block any DC, isolate the circuit 0v from the speaker -ve.