Electronic Circuit : 2 Watt Amplifier

An audio amplifier made from discrete components with 2 Watts audio power into an 8 ohm load. Carlos has used this amplifier on his AM radio for many years.

Notes
The transistors are all direct coupled for good low frequency response, DC input blocking is provided by C3 and C2 is the output capacitor. The output transistors Q1 and Q2 are complimentary and in emitter follower. Q5 is the first stage amplifier,  direct coupled to Q4. Q4 and active load Q3 provide the bias for the output pair Q1 and Q2. Overall gain is controlled by ratio R11 / R8.
Output power is about 1.5 watt into an 8 ohm load with 1.5% THD at audio frequencies. Supply voltage is 12V DC.


Bode Plot
The frequency response is shown below and is flat from 100Hz to 20kHz.

Bode Plot

Output Waveform
LTspice shows a very nice output waveform across resitive load R12. Output analysis can be performed in LTspice .