300W – 1200W MOSFET Amplifier for professionals only

When you need a high power MOSFET amplifier. For use in applications such as a concert, theater, the festivals, etc. This circuit is the most suitable. Both Loudness and durability, that courage to try.

For this MOSFET Amplifier circuit, typically the maximum watt power at load 4Ω equal to 300 watts. or about 200 watts at load 8Ω. Which the watt power very much this level. If you are not satisfied. Also may add a higher power.

Note: Today I edit PCB layout to clear view.

For example: Increasing onto 1200 watts with the bridge adapter circuit. Or If will use a folkway that locals they made popularly are connected the output MOSFET transistors in several parallels. To can resist the higher currents. Then connects the speaker that also the several parallel utils the load is very low resistances, some time is internally OHM Now also called to as a 1000 watts!

Which would you prefer, you can choose as well.

As Figure 1 is shown the 300watt MOSFET amplifier schematic diagram, version of our standards.

How does it work

Base on the Figure1, which determine All complementary input form will consist of the differential circuit of two sets, the separate independent, responsible for driving directly both the positive and negative side output.

As it can see that the positive side signal will be entered pass through the resistor R4 to the differential amplifier circuit with two 2SC1775 transistors Q1, Q2, which there are Q3 acts as the constant current source.

The signal is amplified by the driver circuit consist of the Q7(2SA640), Q8(2SA640), Q9(2SA690) to as the signal voltage is high enough to drive the output 2SK1058 MOSFET Q14, Q15, Q16, Q17 for acts as the positive signal to the speaker. (2SJ162 MOSFET Q18, Q19, Q20, Q21 for the negative signal)

The resistors R43, R45, R47, R49 that is at the source pin to help the average current through the MOSFET equal to the function of a circuit more stable.
The capacitors C17, C18, C18, C20 protects the noise oscillator in this. Why we put it an only side MOSFET N Channel. Because normally. The capacitance between Gate-Source of N Channel will lower than P Channel of about 400pF (Normal the P-type will have a value of C=900pF, but N-type = 500pF)

The diodes D16, D17, D18, D19 acts as a protection to a gate of MOSFET, do not get too high voltage driver. It may cause damage through the gate. Typically, the maximum voltage will not exceed 15 volts.

The transistor Q10 is setting a bias voltage value of the circuit. With adjusting the idle current on VR1 for this circuit we should adjust the Idle current about 80-120 mA.

The total gain of the circuit is determined with feedback circuit R24, R25, R26, C11, C12 and for this circuit the growth rate of about 220 times.

The negative signal will enter to the below side differential circuit consisting of Q4, Q5 has the output signal from Q4 go to the driver circuit Q11, Q12, Q13 to driver power MOSFET works in a negative channel of a signal.

They R51, C23 are used to protect oscillator in high frequency since connecting the speaker wiring and speaker

The power supply
This voltage we use positive/negative 80 volt. We may use a 75 volt one. The features of the circuit is reduced, ostensibly. But lets you select the filter capacitors are quite a lot.

Please try to be to know that was true.
Characteristics power supply circuit. As shown in Figure 4. The transformer that use in this project we use a size of 58-0-58 volt 10A provide through the bridge rectifier and the filter capacitor about 22,000uF 100V , or 10,000uF 100V for 2 is connected in parallel instead.

We need to carefully use the transformer. It will help to produce high performance truly.

Let’s build this project

Those who think to build this mosfet amplifier project. Should have experience in the audio sufficient. This will require careful and skilled in soldering is higher. Otherwise, it throws money to breathtaking. Because the equipment is quite a lot expensive.

– Building start of the main board. Securely attached by soldering to a point. , Put it in the right position. And A polarized components such as the diode and electrolytic capacitors do not have to be an absolute.

– Check the position of the transistors pin, should be accurate as the circuit. And that same body must be not alternate.

– For transistors Q9,Q13 should correctly the heat sink before install to the PCB.

Figure 2 the PCB layout

Figure 3 The layout of PCB

-The assembly the power MOSFET, prohibited, pin S touch the heat sink is strictly prohibited. And for good cooling. We apply silicone between the MOSFET and the heatsink.

This is reason the copper pin Source and pin drain of MOSFET current can not get high. Use copper wire number 18, soldered copper pattern is pressed on it.

Then, connect the cable from the output mosfet board. Onto the motherboard. Do not switch the switch positions is strictly prohibited. The wires must be large. And not broken or easily broken.

The testing project

When the project is complete. To check the accuracy with the eye again. The previous experimental input voltage to the circuit.

– Using a voltmeter to measure the voltage at the speaker, while Short the input to ground should be zero volts. If it does not show that. circuit malfunction. Immediately turn off the power and check again.

If the voltage is zero. The next step is to adjust Idle current of the circuit. Using an ammeter. The power of the positive or negative voltage. VR1 adjusts to the current 80-100 mA.

Turn off the power supply to this Mosfet amplifier. Remove the ammeter and the Short Line Input out. Power supply to the circuit again with the input signal to the point. input will be heard from the speakers as you need.

When used with a full load and continuous for a long time. We should install the proper cooling fans to the Power MOSFET. The key is indispensable. Another possibility is speaker protection. Which must use it alway with the high power amplifier. The relay contacts are big as well.

Caution! This project needs to use the speaker protection circuit. Otherwise, your speaker may be damaged.

More MOSFET Amplifiers

  1. First simple mosfet amplifier circuit by K134+J49
  2. 100 watt DC servo amplifier circuit by Power MOSFET
  3. 50w mosfet amplifier circuit OCL using K1058 + J162
  4. 300 watt MOSFET Power amplifier circuit class G

If this is hard or you can find the parts or others. Please look these projects below.
Mosfet power amplifier Kit on Amazon

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I always try to make Electronics Learning Easy.


I love electronic circuit. I will collect a lot circuit electronic for teach my son and are useful for everyone.
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