However 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.
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.
However that doesn't induce any serious problems though.
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
All resistors are 1/4 watt, CFR 5%, unless otherwise stated.
100 Ohm = 7nos
100k = 1no
47k = 1no
5.1k = 2nos
62k = 1no
22k = 1no
2.2k = 1no
12k = 1no
1k = 1no
4.7 ohm = 1no
0.2 ohm / 5 watts = 4nos
All capacitors must be minimum 100V rated
1uF = 1no Electrolytic
100uF = 3nos Electrolytic
15pF = 1no Polyester
30pF = 1no Polyester
0.22uF = 3nos Polyester
0.0068uF = 1no Polyester
Q1, Q2 = BC546
Q3 = MJE350
Q4, Q5 = MJE340
Q6, Q7 = 2SK1058
Q8, Q9 = 2SJ162
1N4148 = 2nos
Inductor = 1uH, 20 turns of close wound 1mm super enameled copper wire, with 10mm diameter (air core)
Note: The resistor, and capacitor values are not critical, slight up and down will do, and will not cause any harm to the performance of the amplifier