I've NEVER seen free wheel diodes in a hi-fi amplifier, MOSFET or Bipolar.

Power transistors often contain them, built-in.

I am not sure what your point on capacitors is. Aznar seemed to be talking about coupling the processor to the pin for DC blocking ?

Assume, you connect a loudspeaker to output of 74HCMOS gate, via capacitor. Then, if output toggles to high state, capacitor is charged. If after 50% duty cycle time output again toggles to low state, capacitor is discharged again. Across capacitor about Vcc/2 develops. But only, if impedance of PMOS and NMOS transistors are rather equally.

If you connect this circuit to an output, providing highly different impedance to Vcc and 0V, then Vcc/2 does not develop, but a much different voltage. So, connecting DC blocking capacitor to standard port pin of '51 micro can result in something unwanted.

Kai