Audio Power Amplifier



Project Name: Designing an Audio power Amplifier.

Objective: To show high output gain from a low audio signal. Input can be taken from mobile or laptop. And taking output from a Speaker.


  1. Transistor (D718)
  2. Resistor
  3. Battery (9V, 8.5V available)
  4. Speaker
  5. Capacitor.
  6. Dip trace app
  7. Ferric chloride etc.


Working procedure: First we implemented the circuit on the breadboard then connected with power, the amplifier worked. Then we designed the PCB using Dip trace Software, printed the design on a glossy paper then marked the designed circuit on a copper board using iron (cloth iron). Then wash the board by ferric chloride liquid. We got the circuit designed on the copper board.  Then we soldered the component on the circuit board. Again we supplied power. Circuit implemented on

PCB board also worked. So now we are confirm that our project is alright.

Determining  and  using Q-point:

We select the position of Q point is about middle of the active region. Because middle point of active region is the best area for audio quality. So we keep our design here stable.If we change vale of input or Rc the Q point shift. But when the Q point is near to saturation region or cut off region, there are noise in the Audio quality. We investigated this curse in lab and found that when the Q point is close to saturation of cut off region then portion of output signal is clipped off. For this clip-off audio suffer from distortion. Shown in the picture below.


Now we determine the value of resistor and Vcc using the KVL in the output.

Vce= Vcc- IcRc                      …  ….  …. ….. (i)

But for Q-point  Ic=0;

Vce=Vcc=8.5V              (We used biasing voltage Vcc=8.5V)

Now drawing a vertical line from Q-point we get Ic=2.125A

Again from in Eqn. (i) for Q-point Vce=0;


IcRc=Vcc    Or,  Rc= Vcc/Ic=8.5V/2.125A=4ohm

We used these Vcc and Rc  in the circuit.

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