100w amplifier circuit with PCB

Imagine you have a small party. Turn on great music. Friends really appreciate your audio system. These 100W transistor power amplifier circuits may make it true.

Although these are Classical amplifier circuits for over 40 years ago.
But if people love music. They are not outdated.

We use only all-transistor, MJ15003 and MJ15004 are the main in circuits.  And the power supply +38V 0 -38V 3A. Because it is a style of OCL amplifier.


  • Power output : 105watts at 4 ohm load, 88watt at 8 ohms load
  • Input sensitivity : 0.5V
  • Frequency response : 10-10kHZ +/- 1dB
  • THD: 0.07% at 50 watt , 0.1% at 100 watt.
100w amplifier circuit with PCB - Electronic Projects

A circuit of  cheap 100 watts transistor power amplifier project

How it works

This 100W OCL power amplifier is excellent sound quality. In the circuit uses all direct coupling connection together. To cut-off frequency low-loss problems the super bass.


Because the details in the article are too less for beginners And it needs some skill like good quality soldering. However, if you accept any damage that happened later. Yes, you can. Let’s get started.

It is so hard that explain you understand how it works in simple ways.

Here is step its process.

  • First, enter a signal from the tone controls to the input. C1 passes the audio signal to the base of Q1.
  • Q1 and Q2 connect together as  the differential amplifier. To increase low audio with reducing noise input.
  • Then, the signal from the collector lead of Q1 flows to Q5.  It is a pre-driver amplifier circuit.
  • The transistor Q4 sets a level bias or act as to control Idle current in this circuit. Which we can adjust level idle current By adjusting the VR1.
  • The transistor Q3 acts as a boost trapping.
  • The output signal of Q5 comes in the base of Q8 and Q9.  Which they act as the driver circuit.  For the signal output to drive the output transistors Q10, Q11.
  • See both output transistors Q10 and Q11. We use MJ15003 and MJ15004. This couple can use up to 200W. So no problem in durability.

If you want to save.

Some use a pair of these output transistors to connect in parallel instead.

  • Two 2N3055 instead of MJ15003.
  • Two MJ2955 instead of MJ15004.
  • Two MJ802 instead of MJ15003.
  • Two MJ4502 instead of MJ15004.

Short datasheet

  • 2N3055: NPN, 60V(Vce), 15A(Ic), hFE 20-70
  • MJ2955: PNP, 60V(Vce), 15A(Ic), hFE 20-70
  • MJ802: NPN, 90V(Vce), 30A(Ic) 200W, hFE min 25
  • MJ4502: PNP, 90V(Vce), 30A(Ic) 200W, hFE min 25

100W amplifier Power supply

This circuit requires enough energy source.

Look at below.

It is a 100W amplifier Dual 38V power supply circuit diagram.

It can power output +38V Gnd and -38V at more than 3A current.

100W amplifier 38V dual power supply circuit diagram

How to build

You can assemble and set this project as step as follows:

Parts lists

Get all parts first:
Q1, Q2: MPS9632
Q3, Q6, Q9: MPSA06
Q4: BD139
Q5, Q7, Q8: MPSA56
Q10: MJ15004
Q11: MJ15003

0.5W Resistors, 1% tolerance
R1: 15K
R2: 5.6K
R3: 12K
R4: 470 ohms
R5: 30K
R6, R22, R23, R25: 1.2K
R7, R11, R12, R20, R21: 100 ohms
R8, R9: 560 ohms
R10, R13, R14: 10K
R15, R16: 330 ohms
R17, R18 0.25W 5W
R19: 10 ohms 1W

C1: 1uF 50V Electrolytic
C2: 47uF 16V Electrolytic
C3: 47pF 50V Ceramic
C4: 0.1uF 63V MKT Capacitor

L1 coil


Then, assemble all part on the PCB layout as Figure below.

PCB of The cheap 100 watt transistor power amplifier project

Setting and Testing

  • Check the assembly of all equipment to correct the circuit without the output transistors.
  • Use a voltmeter measure the voltage at the speaker terminals but without a speaker.
  • At the end of this process was completed and ready to operate immediately.
  • Put the power supply to the circuit.
  • Then to measure the voltage is 0V or not higher than 0.25V. If not same this, it means that the circuit failure, need to check first.

Note: All Amplifers Projects with PCB layout

  • Then a short input circuit. And measure the current of output power transistors with an ammeter. And, adjust VR1 until reading about the current 20-40 mA.
  • Should install transistor Q4 with the output power transistor heatsink. To help control the bias current output relative to the temperature change of the output transistor.
  • The power supply circuit is got by the power of transformer T1, which provides voltage to the coil in the secondary coil is 27-0-27 volts, 5A.
  • The Diodes Bridge rectifier should be not lower than 5 Amp 100V, The filter capacitor C7, C8 we used a 1,000uF 50V, the voltage at the capacitor after through the filter will can about 38V.

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

This circuit is very old. You may find it difficult to buy. We recommend the below kits.

Other 100W transistor OCL power amplifier

Keep reading: ‘2CH 100W stereo audio amplifier’ »


I always try to make Electronics Learning Easy.

Apichet Garaipoom

I love the electronic circuits. I will collect a lot of circuit electronics to teach my son and are useful for everyone.
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