2N3055 amplifier circuit, 30w OCL integrated amp with PCB

When a friend of mine wanted The integrated amplifier that is smaller. For listening in a small room. Must have good the sound quality. Low noise and cheap.

I often recommend this project 2N3055 amplifier circuit diagram is a featured there are power 30 watts RMS. Using all transistors. Do not select the IC Because my friends do not like. Bored find that the ICs difficult. And he has a lot of power transistor. want to return conserve valuable antiques are and timeless.

If a will is comparing prices. Watt power and the sound quality well. Had to cede This 30 watts OCL amplifier projects This that. Actually superior because the circuit design is really perfect.

How this project works

As will see Figure 1 that they composed of the most 2 parts are:
1. The tone control circuit
2. The power amplifier circuit

The figure 1 circuit of the project

To begin with, the tone control section is determined as the feedback tone control type. Which is popular extensively at this time.

Then, you can adjust the bass sound up to +18dB at frequency 100Hz. And, can adjust the treble sound up to +18dB at frequency 10Khz.

In power amplifier circuit, you will see that input circuit is connected to differential amplifier type. To control the output of this circuit is zero volts. By using the feedback at the base of Q4 through the R16.

The gain of this circuit is R16/R15. Then, the signal from the collector of Q3 will pass to the base of Q6. Which, Q6 acts as pre-driver to amplifiers signal to the driver circuit that consists of Q5, Q7.

In setting, the last output section is determined by forming the Quasi-Complimentary. So, the saving than the direction the pair complimentary. Then, we use both 2N3055 transistors are pair output Q8, Q9.

How to builds the circuit

  • First of all, Build the PCB as Figure 2 and assemble correctly the components layout for the PCB as Figure 3.
  • Second, does not connect the power transistors Q8, Q9
  • Third, use the voltmeter set range DC Volt is 50 volts and then measures the voltage across between TP point compare with the ground. But must short circuit for the input to the ground before.

Figure 2 Actual-size, single-sided PCB layout for the circuit.

Figure 3. Component layout for the PCB

  • Next, connect power to this project Observed meter needle that reverses or not, if error to must switch the test leads immediately.
  • Then, adjust the potentiometer VR5 until the voltage is zero volts. You should reduce the range of meter to lower respectively, until the lowest, with the certainty that can read really is zero.
  • Then, insert correctly the output transistor to this project.
  • The main DC power supply of this project is + 24 volts up to 2 amperes. So, we use the transformer that has secondary coil is 18-0-18V at 2 amperes. Next, passing the bridge rectifier circuit and filter capacitors. Then, we will have the results as the DC volts + 24 volts for this circuit.
  • Next, The filter capacitor- should have over 4700uF 50V as characteristics the standard power supply circuit that uses in normal.

Detail of parts (Parts you will need.)
Q1, Q2 __________BC547___45V 100mA NPN Transistor
Q3, Q4 __________BC557___45V 100mA PNP Transistor
Q5, Q6 __________MPS3569___ 40V 1A PNP Transistor
Q7_____________MPS4355___60V 1A PNP Transistor
Q8, Q9 __________2N3055___100V, 15A, 115W, >2,5MHz NPN transistor
D1, D2 __________1N4148__ 75V 150mA Diodes
ZD1____________18V___1/2W Zener Diode

Linear Potentiometer
VR1, VR2____________100KB
VR5________________50K PRESET

Electrolytic Capacitors
C1, C2, C6, C8, C9____10uF 16V
C7________________100uF 10V
C10_______________100uF 25V
C11_______________47uF 16V
C13_______________47uF 25V

Polyester Capacitor
C3, C4____________0.047uF 50V
C5_______________0.0022uF 50V
C12______________33pF 63V

1/4W + 1% Resistors
R3, R10___________4.7K
R4, R5, R6_________8.2K
R7, R17___________3.3K
R11, R14, R16______1K
R19, R22__________15 ohms 0.5 watts
R20______________100 ohms 0.5 watts
R21, R23__________390 ohms 0.5 watts
R24, R25__________0.5 ohms 1 watts

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Domonation Corporation


El circuito dice unos valores para R17 a R23 y en la lista de materiales dice otros valores para estas resistencias.
Que valores son los correctos?



thankz bro


Does it work as a eletric guitar amplifier? Thank you.


@Gabriel: since the audio output from the guitar is so low, you’re going to need more gain. Slap a pre-amplifier circuit to the input of this stage, and you’ll be good to go.


is this amplifier work if i have 12 volts battery ??
please give the answer ??


Is this amplifier work if i have 12 volts battery ??
please give the answer


sir what is the replacement for the transistor mps4355 and mps3569


I need circuit diagram of NO55 & PO55 transistor amplifier circuit diagram with PCB.

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