I will be designing a 30 watt audio amplifier. I read numerous stuff on the internet mostly about types/classes. Here are my observations

The requirement is that it should be transistor based: jfet,bjt,mosfets only (not allowed to use IC based design like the LMxxxx)

There will be 3 sections of the circuit, the powersupply pre amp and the power amp.

The signal that needs to.be pre amp is an mp3 player from mobile phones, those with 3.5 jack. The load will be a loud speaker around 8 ohms.

What is the real meaning of 30 watt amplifier, how do we make it 30 watt, what are the parameters? (as far as i know, 30 watt here means the maximum power.)

Now, for the preamp, i prefer to use class AB since its the best compromise between class a and class b. How can we reduce the noise in the pre amp so that it is very clean since the output signal will be fed to the power amp??

Also, for the power amp, we know it will be amplified here and current will be the main factor since we need heavy currents to drive the speaker. now isn't it just combining preamp and poweramp reduces the overall noise in the system? what are the factors do we need in desinging both pre amps and power amps?

Theres also one thing in my mind, how can we add bass and treble in the circuit? Will it make the circuit complicated?


closed as not a real question by Leon Heller, Olin Lathrop, embedded.kyle, Brian Carlton, W5VO Nov 16 '12 at 15:35

It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this question so that it can be reopened, visit the help center. If this question can be reworded to fit the rules in the help center, please edit the question.

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    \$\begingroup\$ you just opened a can of worms son \$\endgroup\$ – Nate Nov 15 '12 at 15:47
  • \$\begingroup\$ @Nate what do you mean \$\endgroup\$ – WantIt Nov 15 '12 at 15:48
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    \$\begingroup\$ Also, you should clarify your question a little bit. What is important in your amplifier? Is it an audio amplifier? What do you need for input and output impedance? You mention you want a preamp, why? What is the signal that you need the preamp? Microphones? Biodigital equipment? \$\endgroup\$ – Nate Nov 15 '12 at 15:49
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    \$\begingroup\$ Entropy is a terrible thing... and overall noise in a system doesn't reduce, it only multiplies! On a more serious note, noise outside the frequency band of interest can be attenuated by suitable filters. I'll try and put together an answer to address some of your queries in a bit, after you respond to @Nate's questions. \$\endgroup\$ – Anindo Ghosh Nov 15 '12 at 15:52
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    \$\begingroup\$ Why not allowed to use ICs? Is this homework? \$\endgroup\$ – Brian Carlton Nov 15 '12 at 16:58

It appears you want to make a audio amp that can take rougly line in levels and drive a 8 Ω speaker up to 30 W. Since the audio is already at usual preamp output levels, I don't understand why you need that.

To get 30 W into 8 Ω requires 15.5 V RMS, which means for a sine wave the peaks need to be ±22 V. That means about a ±24 V power supply, which leaves 2 V headroom at each end. The peak current this supply must be able to produce is 22V / 8Ω = 2.8A. It only needs to provide this in one rail at a time, although that's probably not of much use.

Tone controls, like separate volume for bass and treble, is something you do to the signal before the power stage.

There are various topologies you could use for the power stage, but we are not here just to do your homework for you. Explain what your strategy is, what you have tried, what the results were, and perhaps I can add to this answer with more information. You should ask yourself what is really important compared to other criteria. Is the driving factor good efficiency? Low distortion? Just need to show something working to the professor? Something else?


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