50W OCL main amplifier using LF351-2N3055-MJ2955 with PCB

This 50W OCL main amplifier circuit has high quality and economical. Because it is designed simple, It can be easily created in your friends, An electronics rookie. And cheap when compared to other speakers, the as same volume level.

The main power amp.
This circuit is designed in such a way “Direct Coupling All Complementary IC Drive” will be seen that, the heart of the circuit is IC1(LF351), are the differential amplifier and pre driver circuit.
Note: I chose LF351, because the noise reduction circuit. And high frequency response than IC741, or you may use a number TL071 or NE5534N is good quality as well.
The output signal of IC1 pass through two diodes D1,D2(both is 1N4148) to the transistor drivers Q1(BD139),Q2(BD140). Then, their current is entered to two main transistor output Q3(MJ2955),Q4(2N3055).
The small Potentiometer VR2-1K is fined the idle current of this amplifier circuit that easy to fine who not has an amp meter to do not need measure the IDLE current, you just fine the VR2 at middle only (very simple!)


The dc dual power supply +35V GND -35V, 3A for Mono and 5A for stereo system.

Instructions on how to create.
1. Check the completed of PCB that defective, short circuit or not.
2. First, do not connect to the output transistors(MJ2955,2N3055).
3. Use a voltmeter measure voltage at output speaker and ground point.
4. Supply to this circuit And must meter reading is zero volts. Or error must not exceed 0.5V.
5. put the output transistor into this circuit.
6. The voltage must be OV the same, If non-zero, indicating that the bad output transistors.
7. Connect speakers and input signal to this amplifier circuit. Let’s to listen the melodic music.


The Electronic parts.
ZD1,ZD2___15V 0.5W Zener diode
VR1______50K Potentiometer
VR2______1K pot
C1,C9____10uF 16V Electrolytic capacitors
C3,C4___47uF 25V Electrolytic capacitors
C2______100uF 16V Electrolytic capacitors
D1,D2____1N4148 Diode

The caution.
Holding the output transistors onto the heat sink you must sure that:
1. The screws tight, not fell, the loose easily.
2. Do not the short circuit between the collector Pin(transistor body) and heat sink, Due to the installation of mica insulation is not well.

And….. This circuit may be good for you!


Besides this, we introduce these projects sometimes, you may like them.

1. 55 watts rms classic OTL integrated amplifier easy to builds

2. The 30 watts rms integrated amplifier projects using cheap transistors.

3. Power Amplifier OCL 50W by Mosfet (K1058 + J162)


  1. werechai June 1, 2015
  2. Nokia70 July 24, 2015
  3. Alex August 29, 2015
  4. hakan January 13, 2016
  5. babool January 30, 2016
  6. msdava July 15, 2016
  7. jovan June 27, 2017
  8. S.abdulla July 20, 2017
  9. hermes belt August 5, 2017

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