MOSFET based amplifiers as we all know are outstanding with their sound qualities and they can easily beat the performance of other counterparts based on power transistors or linear ICs.
Why use Mosfets in Amplifiers
Amplifiers based on mosfets are not always easy to design or make.
Moreover after assembling a prototype, testing to perfection always remains an issue with new electronic hobbyists.
You might have come across many hi-fi complex mosfet amplifier designs, but might have not dared making it just because of the above reasons.
The simple mosfet amplifier circuit diagram is super simple to build and yet will provide you with a crystal clear 100 watts of raw music power that all the listeners will cherish for a long time.
The idea was developed a long time ago by the Hitachi researchers and still it remains one of the favorite designs of all time considering the involved simplicity against quality.
How the Amplifier is designed to Function
Looking at the figure we can understand the circuit with the following points:
The involved simplicity would also certainly mean that some of the ideal features of the circuit was sacrificed in the design, for example it lacks a constant current source for the differential amplifier at the input stage of the amplifier.
But this has no serious impact on the design, whatsoever..
The differential amplifier makes sure that the input is sufficiently amplified to some reasonable levels suitable for feeding the next driver stage.
The driver stage consists of a well balanced high voltage transistor stage which are necessarily positioned for driving the output power mosfets.
The pot positioned in between the two sections of the driver stage is used for setting the quiescent current of the circuit.
The output stage is a common push pull type of mosfet stage which finally provides the boost for amplifying the fed low signal music into a 100 watt thumping music over a 8 Ohm speaker.
The shown parts might be obsolete today so may be replaced as follows:
The differential transistor may be replaced with BC556.
The driver transistors may be replaced with MJE350/MJE340.
The mosfets may be replaced with 2SJ162/2SK1058
The below given diagram is the original design from Hitachi, see the preset arrangement for setting up the quiescent current. You must adjust this preset to set the quiescent current to zer