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40W transistor audio amplifier circuit with PCB

The 40W transistor audio amplifier circuit OCL 2N3055+MJ2955 is easy to build,and very inexpensive. To use Power Supply +35V -35V 2A. Transistor 2N3055+MJ2955 must be mounted on heatsink. Can be directly connected to CD players, tuners and tape recorders.

This circuit is one that stands out for ages over 40 years, with sound quality that is hard to find compared be other circuits. If you experimental build or ask people who try already built. Will believe that this is not as exaggerated statement more than true.

This power amplifier series circuit, be able to output of up to 40 watt on load 8 ohm, and will provide output capacity of up to 60 watt load 4 ohm.
The circuit design an All complementary all direct coupling (except the input), Making low frequency response of the circuit well.

Power Amplifier OCL 40W by 2N3055+MJ2955


Figure 1 :The OCL 40W transistor audio amplifier circuit  using 2N3055+MJ2955

The transistor(MPS9632) Q1, Q2 together to as a differential amplifier, By has R10,R4 and C2 together constitute the feed back circuit and defined an all gain ratio of circuit. At emitter circuit has zener diode is connected as maintain a constant voltage 15V.

The transistor Q5 is the part second amplifier circuit, by has C3 is to feedback between pin base and collector, for prevent procreation oscillator way high frequency

Q8,Q9 acting as the driver circuit to drives the power transistor Q10(MJ2955),Q11(2N3055).
For Q6, Q7 acts as the output transistor protection circuit from damage. Because the current flowing through the load too much such as a speaker cable short-circuited, by will acts as short the bias circuit of the output transistor is reduced so that it not works.

Q3 serves limit current, the general bootstrapped circuit that use the RC. for Q4 acts as setting bias level of the output transistor which which be instead Diodes same the normal amplifier circuit. This connection reduces the crossover distortion as well.
VR1 serves as to adjust a bias voltage the idle current to the circuit.

35V OCL amplifier Dual DC power supply

Here is a power supply circuit of 40W-50W OCL amplifier. It is a 35V 4A Dual DC power supply circuit. The output is +35V, GND, -35V terminal. A circuit Designer set in an unregulated power supply pattern. Which this is enough for this case.

35V Dual power supply for amplifier

How it works
First of all, the AC voltage comes to a step-down transformer T1 through S1 on-off switch and Fuse F1. The T1 changes AC220V—120VAC in the USA—into about 24V+24V = 48V.

Parts You will need

Q1,Q2,Q3: MPS9632_Transistors, Bipolar, Si NPN Low-Power Audio Frequency Small Signal Transistors or…
Replace Part is BC167, BC171, BC182, BC237, BC547

Q3,Q6,Q9: MPSA06_NPN general purpose transistor or
Replace Part : BC 639, 2SD667, 2SD1226, 2SD1616A

Q5,Q7,Q8: MPSA56_Small Signal General Purpose PNP or
Replace Part : BC 640, 2SB647, 2SB910, 2SB1116A
Q10: MJ2955
Q9: 2N3055
ZD1: 15V 0.5W_zener diode
D1,D2: 1N4148_75V 150mA Diodes

0.25W Resistors  tolerance: ±5%
R1,R10,R13,R14: 10K
R2: 7.5K
R3: 3.3K
R4: 470Ω
R5: 27K
R6,R8: 1.2K
R7: 150Ω
R9: 680Ω
R11, R12: 100Ω
R15, R16: 220Ω
R17, R18: 0.5Ω 2W Resistor
R19: 10Ω 1W Resistor
P1: 1K Potentiometer

Electrolytic Capacitors
C1: 10uF 16V
C2: 47uF 16V
C5,C6: 47uF 50V

Polyester Capacitor
C3: 680pF 50V, Polyester Capacitor
C4: 0.1uF 63V, Polyester Capacitor

L1 use #24 copper wire on air coil 5mm.

2SA1248=2SA1249=SAB649
2SC3116=2SC3116=2SC3117=2SD669

PCB layout 40W Amplifier OCL 2N3055 MJ2955
PCB layout

Component Layout 40W Amplifier OCL 2N3055-MJ2955

Component layout

Customization this circuit.
When this project is done, not to the speaker cable, adjust VR1 at the center. And then power supply to the circuit, to measure at output point as the loud speaker with the ground Should be less than 0V or 0.1V.

Then uses the voltmeter to measure the voltage across R17, as with adjust the VR1 slowly until you read 0.01V Or may be adjusted by measuring the Idle current is about 15-30mA.
And then, connect the speakers, and input single to use work immediately.

Keep reading: 100W OCL Power Amplifier

Do no see if you like small!

This Post Has 13 Comments

  1. need computation for 40 watts amplifier…..asap

  2. hi!
    Is This stereo, or only for 1 channel??

  3. Hi,rafael
    thank your comment,this is ocl 40watts use transistors.
    old circuit but worked well. nice sound.

  4. Hi, Ritvars.
    This is mono system. If you need to use stereo, you must make them on two sets.(next one)

  5. i compiled it,but give noise

  6. but sound is good and have less base

  7. ok.very good.
    ahmad.from iran

  8. Yes ,
    This is very very good circuit,
    No noise
    High base
    High sound quality

  9. Hi, just followed the circuit but when tested on a 24V dual phase power, the C5 capacitor is burnt… it’s working on 12-V though… please help me how to fix it… thanks.

  10. could not complete due to p0wer supply

  11. Hello May I Ask for the Computations of this Circuit . thank you so much

  12. hi
    I noticed that are differences between schematic and pcb. I couldn’t find the 100k resistor in the schematic. There are four 0.5 R resistors on the pcb but only two in the schematic. I’ve made the pcb but I don’t know now what should I follow: schematic or pcb. Please give me a little help with this

  13. Sir, how can I get 2 PCBs for the – 40W Amp OCL 2N3055 +MJ2955 ?

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