Power amplififer design question

[hamsiii]

Hello everyone,
can anyone help me how to design this kind of power amplifier? hardware part is easy, i need just the schematic, or just how kind of transistors will be used with which resistors or capacitors?
This is the specifications of the amplifier:

Amplifier circuit must be 2 or 3 stage amplifier without feedback. Design a circuit which contains a BJT output stage.

Power amplifier:
• 1dB bandwidth: 25 – 35 KHz
• Input signal: 1 v p-p
• Output power: as large as possible, into 20 ohms
• Input impedance: 1 kOhms
• Adjustable gain
• +/- 12 volt supply
• Fuse connector for properly selected fuse
• Appropriate heat sinks must be incorporated
• To be built on a PCB
• Box connectors:
o Banana inputs (red and black) for +/-12V and ground (protected for reverse
voltage)
o 50 ohm BNC input
o 50ohm BNC output
• 60dB boxed attenuator (BNC input and output)

 

[audioguru]

You saved your schematic as a very fuzzy JPG file type instead of as a very clear PNG file type.
Your schematic drawing software makes wires all over the place and makes chicken pox dots all over the place.
I straightened some wires and added a few voltage measurements to the first transistor. It is biased wrong which makes it saturated. It cannot amplify anything. Since the resistors have very low values then the current is very high.

The bottom Mosfet looks like it is upside-down. It should be a P-channel Mosfet.

You cannot use diodes to bias Mosfets because each Mosfet has a different gate-source voltage.

 

[hamsiii]

ok first of all thanks for the constructive reply. Next time JPG will be PNGs
i have take this schematic from a working amplifier, i was told that this amp. meets the requirements. I understand what you are saying but i will ask one more thing, if I make this amp. not in saturation by the resistor values and bias it without the diodes, how can I adjust this requirement: • 1dB bandwidth: 25 – 35 KHz?

 

[audioguru]

I looked at your fuzzy schematic again and used different resistor values to make the transistor a linear amplifier that is not saturated.
I looked at the part numbers of the Mosfets and it looks like the top one is an N-channel and maybe the bottom one is correctly a P-channel.