300 watt MOSFET Power amplifier circuit class G

This is the Class G 300 watt MOSFET Power amplifier circuit with PCB MOSFET. which is high end for all your jobs. It have more feature,
– maximum RMS output power: 200 watts at load 8 ohms or 360 watts at the load 4 ohms.
– The frequency response range: 10Hz.-150kHz.
– Minimum harmonic distortion: 0.008%.

How it works

the complete circuit of this project
Figure 1 the complete circuit of this project.

The input signal is sent to C1 into base of Q1 that is connected with Q2 as the differential amplifier circuit. Then,this signal is increased to the section 2 (Q3,Q4). Next,the signal is sent to the transistors driver(Q12, Q13), to drive the output transistors (Q15, Q16). Finally, the output signal is drive to the loud speaker.

In lower signal range, both transistors Q14, Q15 will doesn’t works. But when is the peak signal rage,this signal is sent to D3, D4 to bias Q10, Q11 works. As a result, the mosfet Q14, Q17 also works. This cause the power supply 2 that have the higher voltage up to 100 volts to the amplifier section. This feature makes the peak signal aren’t trimmed like the general others amplifiers.

Here are the highlights of the class G amplifier. Because all transistors do not need to work hard all the time. So, Reduce energy loss and heat of the output power transistors better than the others high power amplifiers.

How to builds it

First of all,make the PCB as Figure 2 which is actual-size of Single-sided Copper PCB layout. Then, assemble the parts on the PCB as Figure 3 Should check carefully several times. Because this project have more details, If the error it would have been severely damaged.
the copper PCB layout of class G amplifier
Figure 2 the copper PCB layout

the components layout
Figure 3 the components layout

Next,screw the power transistors and power mosfet on the heat sink. By use of mica sheets and the silicone pad to aid cooling. It was attached to the heat sink, Tighten the screws firmly. Remmeber! Do not the body of transistor strictly short circuit to the heat sink.

When we finish assembling the project. Then,short circuit the input to the ground. Next,apply the power to the project. After that,measure current that flow through the positive of the 100 volts power supply. We should read maximum current about 20 mA. Then, measure current at the positive of the 40 volts supply and also have maximum current about 20 mA.

Use the voltmeter measure voltage between both base of Q11 and Q12, then adjust VR1 until read the voltage about 2.6-2.7volts.

Lastly,measure at the speaker terminal it must be zero only. Now this amplifiers ready to use.

The power supply

We should use the transformer minimum current 4 Amperes (per channel), and secondary coil must have center trap at 70 and 31 volts as Figure 4.

the power supply
Figure 4 the power supply

At the filter capacitors should connects the low capacitors to reduce the oscillation of circuit in high frequencies,we use about 0.033-0.1uF.

Power Supply
T1 (70-31-0-31-70V)__4A./CH.
D1, D2_____________BRIDGE 25A 200V
C1, C2_____________>8200uF 120V___Electrolytic Capacitors
C3, C4, C5, C6______0.033uF 250V____Polyester Capacitor
C7, C8_____________10000uF 50V___Electrolytic Capacitors

The parts you need
Q1, Q2, Q1______2SA872 or similar
Q3, Q4__________BC648 or similar
Q5, Q6, Q7, Q8___2SD668 or similar
Q9______________BD139 or similar
Q10_____________2SC1775 or similar
Q12_____________2SD669 or similar
Q13_____________2SB649 or similar
Q14_____________2SK176 or similar
Q15_____________2SD551, 2SC2608 or similar
Q16_____________2SB681, 2SA1117 or similar
Q17_____________2SJ56 or similar
C1, C6___________1uF 63V____Polyester Capacitor
C2_______________100pF 63V____Polyester Capacitor
C3_______________0.1uF 63V____Polyester Capacitor
C4_______________22pF 63V____Polyester Capacitor
C5_______________220uF 50V___Electrolytic Capacitors
C7, C22__________75pF 63V_Polyester Capacitor
C8_______________100uF 25V___Electrolytic Capacitors
C9, C13__________1pF 63V_Polyester Capacitor
C10______________4pF 63V_Polyester Capacitor
C11______________0.22uF 63V_Polyester Capacitor
C12______________390pF 63V_Polyester Capacitor
C14, C21_________0.47uF 63V_Polyester Capacitor
C15, C16_________0.0022uF 63V_Polyester Capacitor
C17, C18_________100uF 250V___
D1, D2, D3________1N4148_______75V 150mA Diodes
D4, D6____________1N5403____400V 3A Diodes
D5________________ZD 15V____1W Zener diodes
R1________________470K___1/2W Resistors tolerance: 1%
R2________________2.2K___1/2W Resistors tolerance: 1%
R3________________12K___1/2W Resistors tolerance: 1%
R4________________33K___1/2W Resistors tolerance: 1%
R5, R6, R7, R15_____68K___1/2W Resistors tolerance: 1%
R17, R18___________68K___1/2W Resistors tolerance: 1%
R8_________________56 ohms ___1/2W Resistors tolerance: 1%
R9, R10____________1.8K___1/2W Resistors tolerance: 1%
R11________________10K___1/2W Resistors tolerance: 1%
R12________________2.7K___1/2W Resistors tolerance: 1%
R13, R16___________1.2K___1/2W Resistors tolerance: 1%
R14________________270 ohms___1/2W Resistors tolerance: 1%
R19, R30, R32_______100 ohms___1/2W Resistors tolerance: 1%
R20________________200 ohms___1/2W Resistors tolerance: 1%
R21, R27____________470 ohms___1/2W Resistors tolerance: 1%
R22, R26____________150 ohms___1/2W Resistors tolerance: 1%
R24, R35____________0.3 ohms___5W Resistors tolerance: 5%
R25, R28____________220 ohms___1/2W Resistors tolerance: 1%
R29, R34____________10K____1W_Resistors tolerance: 1%
R31_________________33 ohms__5W Resistors tolerance: 5%
R33_________________39K___1/2W Resistors tolerance: 1%
R36_________________47 ohms__5W Resistors tolerance: 5%
VR1_________________1K PRESET


  1. Zelino September 11, 2014 Reply
  2. chayapon September 11, 2014 Reply
  3. Mr.newbie September 16, 2014 Reply
  4. k.r gopalakrishnan July 2, 2015 Reply
  5. Shubham chimurkar December 13, 2016 Reply
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