Audio Power Amplifier with tonal controls

[Yash_avengers]

The requirements are a minimum of 8W RMS power to 8Ω speakers with a maximum of 1% second harmonic distortion and 0.2% third harmonic distortion.
Can anyone help me decide the Class AB amplifier which fits the specifications! Also need help for tonal controls circuit design.

 

[Inquisitive]

Is this a homework assignment?

 

[Yash_avengers]

Yes, actually kinda project!

 

[alec_t]

Welcome to ETO!
I suggest you research 'Baxandall'.

 

[Yash_avengers]

Any suggestion for Amplifier?

 

[audioguru]

There are maybe 50 IC amplifiers available that are much better than the spec's you have. Or must you make an amplifier from transistors, resistors and capacitors and design the circuit yourself or find one in Google and simply copy it?
You might find a circuit that works or you might find a circuit that does not work.

 

[Yash_avengers]

Single chip integrated IC amplifiers are not allowed. BJT and MOSFETs in class A, AB, D or circlotron topology are recommended.

For the amplifier I tried building the EXACT circuit on this circuit. But apparently the signal got de-amplified instead of amplifying. http://hackaweek.com/hacks/?p=332

For tonal controls I am thinking of using this circuit on the below website link:
http://www.ecircuitcenter.com/Circuits/op_tone1/op_tone1.htm

 

[alec_t]

For the amplifier I tried building the EXACT circuit on this circuit. But apparently the signal got de-amplified instead of amplifying.

Read the datasheets for the transistors used in the hackaweek link. Consider that you want an 8W amp.

 

[audioguru]

The hackaweek amplifier is a horrible design:
1) The transistors are biased wrong so the output badly clips off the bottom of every waveform.
2) The poor weak output transistors have a maximum allowed current of 200mA and perform poorly above 50mA but in this circuit if the output is trying to be 7V peak-to-peak which is 3.5V peak then their current is 3.5V/8 ohms= 438mA.

The input impedance of that awful circuit is very low. If the signal source also has a low impedance then it shorts the negative feedback which causes the distortion to be much higher. So I added a series input resistor my R4.

I simulated it to show you and changed the output transistors to more powerful ones and fixed the bias point. My fixes produce low distortion and 7.3V p-p output. 7.3V p-p is 2.58V RMS then the power into the 8 ohm speaker is (2.58V squared)/8 ohms= 0.83W.
The amplifier output is only 1/10th what you need. It needs a higher supply voltage, more powerful output transistors and probably driver transistors.

 

[audioguru]

To see if you know how to do the simple arithmetic:
1) How much RMS output voltage is needed?
2) How much peak-to-peak output voltage is needed?
3) What supply voltage is needed for the 8W amplifier?