Audio amplifier design

[Ahacker]

Hey guys can you suggest a good audio amplifier circuit class d with standby and power 20 or 25W max.

 

[crutschow]

If you use a single supply, you will need a series output capacitor to block the DC to the speaker.
A value of about 1500μF is typically used.

You will also need to bias the input at 1/2 the supply voltage, such as with a 42kΩ resistor from V+ to the junction of R1 and R3, and changing R2 to 42kΩ.

 

[audioguru]

Hey guys can you suggest a good audio amplifier circuit class d with standby and power 20 or 25W max.

You do not say where on earth you are at so we don't know if you can buy a Texas Instruments class-D amplifier IC. Go to TI's website and select one from the many they make.
Amplifier power ratings are usually exaggerated so that the power number is high. The rated distortion is 10% that sounds awful because the amplifier is clipping like crazy so that the number is higher than with no clipping and very low distortion. The output power depends on the supply voltage and the speaker impedance. Many modern amplifier ICs use BTL which is Bridge Tied Load. A BTL amplifier connects the speaker between the outputs of 2 amplifiers that have opposite phase so that a supply that is about half the voltage can produce almost double the power in a speaker than an amplifier with only a normal single amplifier. Usually a BTL amplifier uses a single positive supply without using a negative supply. Since the speaker is directly connected to the outputs of amplifiers that have the same DC voltage, with a single positive supply then no output coupling capacitor is needed.