power amplifier

[rajenbesu]

why is a power amplifier always preceded by a voltage amplifier???

[R1Geezer]

Can you be more specific. A voltage amplifier is a transformer, by definition it is also a power amplifier, so perhaps you could expand a bit on your question.

[mibn2cweus]

Keeping in mind that P(Watts)=VI and P=V�/R (or Z) . . .

For a given load (such as a loudspeaker) the power delivered is in proportion to the voltage pushing the current through a given impedance.

The preamp stage typically operates at a lower voltage to reduce thermal noise generation that would adversely effect the signal to noise ratio.

Using an audio amplifier driving a speaker as an example:

The output stage is typically designed around a low impedance constant voltage power supply with the voltage modulated proportionately to correspond to a varying audio signal reference voltage.

Although speakers typically present a relatively low (4-8 ohm) impedance to the power amp driving them, the voltage required to push the large currents necessary to drive speakers to the highest sound levels often exceeds twenty volts or more.

Twenty volts will deliver 50W of power to an 8Ω speaker.
W = V� / Z

[Theland1]

Merry Xmas Mibs

[mibn2cweus]

forgot the link

[mibn2cweus]

Thanks Theland! Boxing Day Greetings and I wish you the best for the New Year.