CLICK HERE to download 100 watt mosfet amplifier circuit diagram
Input Stage
Input stage works as a transconductance amplifier (voltage in - current out).
This stage consist of Long Tailed Pair (LTP) made of Q1 & Q2 working as differential amplifier.
Input signal received at the base of Q1 is amplified and sent to VAS from collector.
Negative feedback (NFB) received at the base of Q2 from output determines overall gain and balance of the amplifier. Current is supplied to the LTP by resistor R4.
In simple words input signal is amplified by the input pair Q1 & Q2 and sent to VAS for further amplification.
Voltage Amplification Stage (VAS)
As the name suggests, all the voltage gain of the amplifier is achieved in VA Stage.
Signal received from input stage at the base of Q5 is Voltage amplified and sent to the gate of mosfet Q7.
In simple words signal received from input stage is amplified by Q3 & sent to output stage.
Output Stage ( OPS )
This circuit has Class B output stage, so each half of the signal is amplified by each N-channel and P-channel mosfet.
Zobel Network - made of R15 & C6, provides protection against high frequency oscillations.
In simple words signal received from VAS is given to the output mosfets. Output mosfet conduct high current to drive the speakers load.