As we are like to show you about audio and sound circuit ,I found the circuit which is good one for power amplifier with one MOSFET.
The output power of an operational amplifier is often increased by a complementary emiter follower.
20W power amp MOSFET
It can also be done with a MOSFET,but it is not a good idea to connect such a device as a complementary souce follower because the maximum output voltage of the opamp is then reduced appreciably by the gate-source control voltage of the MOSFET ,which can be a couple of volts.
Another approach is to connect two MOSFETs as a complementary drain follower.The (alternating) output current provided by the MOSFETs is limited by the level of the supply voltages and the saturateion voltages of T3 and T4 Resistor R8,together with R9,provides feedback for both the opamp and MOSFETs .
The open-loop amplification of the opampis,therefore,increased by (1+R8/R9).the closed-loop amplification of the complete amplifier is (1+R3/R2).
The current source formed by T1 and T2 is required for arreanging the quiescent current of T3 and T4 at 50 mA.The values of resistors R4 and R5 are such that,without the current source the voltage drop across the resistor resulting from the direct current through the opamp is not sufficient to switch on T3 and T4 .with the current source,and depending on the setting of P1,the voltages across R4 and R5 rise,which increases the quiescent current through T3 and T4.
In view of the temperature dependence of the quiescent current,T2 must be mounted on the common heat sink(c. 5 K/W) of the MOSFETs.
The output power is not less than 20 W into 8 ohm,at which level the harmonic distortion amounts to 0.075 per cent at 100 Hz to 0,135 per cent at 10 kHz.
