Class A amplifier circuits

These are simple Class A amplifier circuit. First circuit I used main part electronic is transistor only.
The main power transistor i used TIP41 or TIP31 or C1061 or MJE3055 and next part is TIP42 (PNP) or TIP32 or A761.
It is have power output 20W at 8ohm. and used volte of supply 22V to 28V at 4A.
Detail more please read in image.

Power Amplifier Class A by Transistor

5 watts Class A amplifier using NE5532 and MJ2955

Here is the 5 watts really class A amplifier using NE5532 and MJ2955 as based. This is best of quality sound.

We used popularly the many type of power amplifier. For example: Class A, Class B, Class AB etc. The Class A amplifier is the best of quality sound.

But the class A to the output power is low, just 20% only. When compared with a loss of power or consumption ratio approximately 5 times of the output power.

So we have a problem with the heat. Although there is no ?the input audio. However, despite the low wattage, it also provides crystal clear sound quality than class B and class AB.

How circuit works
The principle of the class A amplifier is IC1 will increase a positive halfcycle signal. Then, this signal will flow through to a capacitor C2 into both transistors Q1 and Q3 as darlington compound, to increase the audio signal up.

5 watts Class A amplifier using NE5532 and MJ2955

And the negative halfcycle signal will through C3. Then, the signal will be increased by both Q2 and Q4. Which is also the darlington.

Next, the output positive halfcycle signal will come out to lead E of Q3, and the negative halfcycle signal will through lead E of Q4.

Then, the signal will flow through R10 and R11, to protect output short circuit. Next, out to the speaker that output no more than 5 watts.

The diode D1-D4 acts as the rectifier to DC voltage to bias Q1 and Q2, and VR1 adjusted bias current is steady in working that, by Q1-Q4 will be screw to the heatsink. Especially in Q3 and Q4.

The heatsink is large because the circuit has lost high power.

The parts you will need
R1__________68K ¼ W
R2__________2.7K ¼ W
R3__________39K ¼ W
R4, R5_______1K¼ W
R6, R7_______1.5K ¼ W
R8, R9_______100 ohms ¼ W
R10, R11_____0.1 ohms 3W
VR1________470 ohms__Linear Potentiometer
C1__________Ceramic capacitors 0.82uF 50V or 1uF 50V
C2, C3______100uF 16V Electrolytic
Semiconductors and others
D1-D4______1N4003____1A 300V__Silicon Diode
Q1_________BD139 ___80V 1.5A NPN Transistor
Q2_________BD140 ___80V 1.5A PNP Transistor
Q3_________2N3055___100V, 15A, NPN transistor
Q4_________MJ2955___100V, 15A, PNP transistor
IC1_________NE5532__OP Amp Dual General Purpose ±20 Volt 8-Pin DIP
SP1_________Speaker 8 ohms 5W
T1_________6V-0-6V/ 5A_____Dual DC power supply
T2_______18V-0-18V, 1A ____Dual DC power supply



  1. Emmanuel April 7, 2014
  2. osdfghjk September 5, 2014

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