Hi, I have a little question: in practically all circuits that i have seen, two voltages are present
3.3V used for DAC
5V used for audio amplifier (in Bridge-tied load configuration) Why?Is not possible to use the same voltage (3.3V) for DAC and amplifier? I don't think it is strictly related to speaker volume...or not? Thanks
Not knowing the DACs in question, I can't give a definitive answer, but modern integrated circuits do tend to be made with very small transistors with very thin insulators, which can't take 5V. It's not difficult to derive a 3.3V rail from a 5V rail, nor to boost the output from a 3.3V DAC to a level that is suitable for driving a loudspeaker.
The rail voltage you choose for the amplifier that drives the loudspeaker depends on the amount of power the loudspeaker can dissipate, and the thickness of the wire used to wind the speaker coils - manufacturers who produce in sufficinet volume to justify commisioning their own loudspeaker design do have more flexibility.