Many Electronic circuit projects in simple ways of learning

100w amplifier circuit with PCB

This Power Amp OCL 100 watt circuit by transistors. They have been old circuits, but very well amplifier schematic.

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.


A circuit of  cheap 100 watts transistor power amplifier project

This power amp OCL 100w is a very excellent sound quality. We provide a circuit in all direct coupling connection join together. To cut-off frequency low-loss problems the super bass really does not tell who.

The signal Input of the tone controls enter via C1 to the base pin of transistor Q1, which together with the Q2 is the differential amplifier, the signal from the collection pin of Q1 supplied to the bas pin of the Q5, which it acts as the pre-driver circuit.

– The transistor Q4 is setting level bias or act as to control Idle current in this circuit. Which we can adjust level idle current by By adjusting the VR1.

– The transistor Q3 acts as a boost trapping.

– The output signal from the Q5 will enter to base pin of Q8,Q9. which acts as the driver circuit. For the signal output to drive the output transistors Q10, Q11.

– Both output transistors Q10, Q11, we used the number on the circuit are MJ15003, MJ15004. This couple can use up to 200W, so not problem in durability.

If you want to save. May be represented by a pair of output are 2N3055, MJ2955 each of the two parallels each other instead.

-Check the assembly of all equipment to correct the circuit, without the output transistors, Using a voltmeter measure the voltage at the speaker. By also does not have 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 in this means that the circuit failure, need to check first.

Note: All Amplifers Projects with PCB layout

PCB of The cheap 100 watt transistor power amplifier project
-The later, on output transistors, and then use an ammeter to measure the current is supplied with short input circuit. Measuring that positive or negative wire. Then, adjust VR1 until reading about the current 20-40 mA.

– For transistor Q4, when the device successfully. Should be installed on the cooling pad. Which installation of the output transistor. 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 volt, 5 amp.

– 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.

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

This Post Has 15 Comments

  1. Hi!
    Can anybody send me pcb project of this amp in better quality?

  2. hi I assemble this circuit it working good but it get too much of heat even without load the output transistors get too hot i use 2sc3855 &2sa1492

  3. Hi,Elekros90
    Thanks for feedback. Now I cannot show you good better than this image PCB.
    I am sorry for my error.
    Hope you come back to see again.

  4. Hi,kanagaraj
    Thanks your feedback. I am happy that you build this project in long time ago (than 20 years) I use this dual transistor so old circuit.

    Thanks for sharing.

  5. I want to amplify 10mW (10V over 1k ohm output impedance) to about 100W over the frequency range 10kHhz – 500kHz. Linearity is not at all critical since the signal is pure sine wave or possibly square wave. Would you for a fee design a suitable circuit for this? It would be an advantage but not neccessary if the output could be varied.

  6. what transistor should i place in Q1 and Q2

  7. I like this circuit, very simple and straight forward.

  8. I am extremely interested in building my own 100W RMS power amp and power supply.
    The one I’d love to do as a project Is the one shown in the schematic diagram. Please let me know the prices involved and how I can purchase it….thanks a ton

  9. I was Constructed a 30W+30W Cassette Deck very long ago, using N055 & P055 Transistor in Golden PCB. Recently all Transistors are burnt out but, I want to repair the Amplifier. I have lost the book. I did not find the Transistor or Circuit Diagram anywhere. Please give me the circuit diagram of the amplifier of N055-P055. And suggest me where can I find the Transistor or its substitute.
    Thanks in advance.

  10. pls I want detail journal on the 100watt OCL power transistor audio amplifier with PCB thanks.

  11. hi
    i am new in to design and planning to assemble this amplifier. i have one question here is. what is the use of Q6 and Q7 transistor here. what is role of this two transistor.


    1. Hi Suhas,
      I am happy you love music to build the power amplifier.
      Both transistors are protection for power transistors when overload.

  12. Hey, What dimensions are the PBC ?

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.

Close Menu