Thank you all, let me ask about a schematic design of a Class A amplifier schematic on internet. Please explain to me about how much voltage gain is obtained for the amplifier in this design? Is it 10x times or 100x times? How do we calculate the 10-14 watt power?
Please explain step by step.
This amplifier must crawl before it can walk. Your idle current is not well defined, thermal runaway is possible. The bottom NPN Darlington is not being driven in any way so it is trying to be a constant source. This means that the max efficiency if all the parts were ideal would be 25% instead of the normal 50% max. Your 680k seems really high so such a high prospective gain means little or no feedback. If you used say a 68k then there would of course be much less gain but lower distortion.
base voltage is about 3 volts
emitter voltage about 2 volts
emitter current = 2v/150 or 12mA
The reac thus is 2 ohms (transconductance is 0.48 amps/volt)
the gain of the transistor is 1.8K / 2 ohms or about 900x
this circuit also has huge input capacity caused by Miller multiplication of Cob * gain of the 2n3904; this will be about 10,000 picofarads
but this circuit also has global negative feedback, implemented right at the input
