30 watt OCL amplifier circuit diagram with PCB using 2N3055

Imagine you want to listen to great music in your room. You may have many choices. Before seeing others. Let’s see this 30w amplifier circuit. Why you should see it?

If your small room is small. And, you like to listen to great music that nice quality, low noise, full option adjusting. Also, it is cheap and easy to find the parts in any store.

30 watts RMS amplifier using 2N3055

What is more?

I often recommend this project. It is one of the timeless amplifiers. With the power of 30 watts RMS amplifier circuit diagram with PCB. It is suitable for you.

In the circuit uses all transistors like 2N3055 and small transistors.
So, low noise and easy to buy them. Though it is a too old circuit. But we want to return conserve valuable antiques.

If we will compare it with others in the same watts. This 30W amplifier is the best, quality sound. Because it is an OCL amplifier. So, responds to bass and treble well.

Thanks, designer, he designs the circuit is really perfect.

Read next: Video amplifier splitter using transistor

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 main amplifier circuit
30W RMS Integrated Amplifier circuit using transistors

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.

Read also: TDA2020 OCL HI-FI Power Amplifier, 20W to 80W

In the power amplifier circuit, you will see that the input circuit is connected to the 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.

See other 30W amplifier circuits list

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 points compare with the ground. But must short circuit for the input to the ground before.
PCB of 30W RMS OCL Amplifier
PCB Layout of 30 watts amplifier circuit

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

Here are a few related articles you may want to read:


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.
    Related: NE5532 Pinout Datasheet Dual low noise op-amp
  • 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 a 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.
    Read other sites: 30 Watt Amplifier Circuit using Transistors
  • Next, The filter capacitor- should have over 4700uF 50V as characteristics the standard power supply circuit that uses in normal.
24V power supply for 30w amplifier circuit

Selecting and substituting components.

I believe you understand basic equipment usage and can do it. We can use various components of the 30watts amplifier circuit.

The Small transistor. Look at Their Pinout of TO-92:

Sometimes, you may not buy MPS3569 or MPS4355. You can use:

  • C9013 is instead of MPS3569
  • C9012 is instead of MPS4355
  • BC547, BC548, BC549, BC546
  • BC557, BC558, BC559
Pinout of small transistors, CS9013, BC547 and, etc.
Pinout of small transistors, CS9013, BC547 and, etc.

Power transistor 2N3055. Look at the pinout of the TO-3 transistor.

If you want full power output, cheap. You should use a 2N3055 NPN transistor. But it may be better if uses TIP3055(TO-3P). We easily install it on the heatsink.

Pinout of 2N3055 and TIP3055
Pinout of 2N3055 and TIP3055

Listen to a lower volume. But still, sound good.

If you especially like treble or mid-range music. You can switch to a smaller power transistor instead of 2N3055. Like TIP41 with the shape of TO-220.

TIP41 pinout TO-220

Read next: Learning electronics for beginners for review.

Detail of parts list

  • Q1, Q2: BC547, 45V 100mA NPN Transistor
  • Q3, Q4: BC557, 45V 100mA PNP Transistor
  • Q5, Q6: MPS3569 or C9013, 40V 0.5A, NPN Transistor
  • Q7: MPS4355 or C9012, 40V 0.5A, 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
  • VR3, 50KACT
  • VR4, 100KMN
  • 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

Recommended: What is capacitor? Principle working, types and how it works

1/4W + 1% Resistors
R1: 560K
R2: 220K
R3, R10: 4.7K
R4, R5, R6: 8.2K
R7, R17: 3.3K
R8: 100K
R9: 470K
R11, R14, R16: 1K
R12: 47K
R13: 2K
R15: 56K
R18: 10K
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

Power supply parts list
(As the circuit diagram above)

  • C6, C7: 4,700uF 50V, Electrolytic Capacitors
  • C8, C9: 0.1uF 50V, Ceramic Capacitor
  • T1: 117V/230V AC primary to 18V-0-18V, 2A secondary transformer
  • D1-D4: Diode 5A, 100V
  • S1: ON-OFF Switch
  • F1: 0.5A Fuse

Check out these related articles, too:

Related Posts


I always try to make Electronics Learning Easy.

Notify of

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

Inline Feedbacks
View all comments
Close Menu