# 12watt audio amplifier

Discussion in 'Homework Help' started by Boltean, May 19, 2013.

1. ### Boltean Thread Starter New Member

May 19, 2013
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Hi!I have a project to do,a 12Watt audio amp.But I need a 30Kohm input resistance and 2ohm load resistance.The imput voltage being 1uV.Can you help me with an electric diagram?Thank you!

2. ### MrChips Moderator

Oct 2, 2009
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5,449
That is not how Homework Help works. You present your design ideas and we provide feedback.
We don't do your homework for you. Show us your circuit diagram.

3. ### Boltean Thread Starter New Member

May 19, 2013
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Well this is how far I've been working for so long.The only problem is that the imput voltage is to low to power the transitors,and I heard that I need to implement a preamplifier so that the voltage would be enough for the transitors to enter the conduction zone.Also I have to scale the whole electric diagram to fit to my project requirements.I'm not good at electronic,sorry for my reduced knowledge and my bad english.The project should be implemented in Orcad and not physical.This is the diagram I implemented in Ordac CaptureCIS http://postimg.org/image/m42ergws1/,following from this one https://sites.google.com/site/amplificatoare/12w-amplifier-using-741-op-amp
Thank you!

4. ### bountyhunter Well-Known Member

Sep 7, 2009
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why don't you post the specs like input signal amplitude.

5. ### tubeguy Well-Known Member

Nov 3, 2012
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Are you sure the input voltage is 1uV ( 1 micro-volt ) ? Is a frequency specified ?

6. ### Boltean Thread Starter New Member

May 19, 2013
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Yes,I'm sure that the imput voltage is 1 micro-volt.And there is no freqency specified.I think I can use any type of voltage source for different analysis.The hard part is to find a electric diagram and size it acording to my requirements.

7. ### THE_RB AAC Fanatic!

Feb 11, 2008
5,432
1,312
1uV sounds very unusual. A normal electret microphone will easily produce 50mV to 200mV directly.

An audio source will be 1v to 2v, similar for guitar pickups etc.

What makes 1uV, that you want to amplify REALLY loud ie 12W?

Even the RF noise etc from your circuit wiring will be many uV, so you are now talking about special construction and shielding techniques etc. This is sounding very weird.

8. ### Boltean Thread Starter New Member

May 19, 2013
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Because the profssor wanted it unusual.I think that the pshisically implementation of this circuit would serve to no end,but I need the simulation in Orcad of such a circuit.From what I heard is that I certainly need a preamplifier...so that the 1uV imput voltage would be amplified enough that the circuit will work properly and provide 12W.

9. ### bountyhunter Well-Known Member

Sep 7, 2009
2,498
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That's what I assumed when I read it. This is not a real project, just some computer exercise which is supposed to "illustrate" something.... in reality, there are no commercially available op amps which can amplify a 1uV signal with any kind of decent signal to noise ratio. The whole thing is just a waste of time.

10. ### Boltean Thread Starter New Member

May 19, 2013
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It seems that I noted wrong the imput voltage,it's 100uV instead of 1uV,however this is also a small voltage.I've been searching for another electric diagram and it looks like this:http://postimg.org/image/wfeztihf1/
http://postimg.org/image/7hu492i81/
I'm not sure if the imput resistance is formed of R7||R6||R5 and why the power on the load resistance is 0W.Do i need another Darlington connection(because the courrent doesn't seem to be amplified)?If so how do I implement it in the circuit?Thank you!

11. ### JoeJester AAC Fanatic!

Apr 26, 2005
3,949
1,758
You know if Boltean turned in an assignment with a single opamp with a gain of approx. 6 x 10^6, the professor would be all over them.

I can remember once my Operations Commander wanted a simplified diagram of a system on one of his tests. I drew a single box with titled UNIT and a Data line going in and out, and a Control line going in. He told me he expected a more detailed drawing, and I told him he should not have specified basic. I then offered to let him take a qualifying test used at the unit. He declined.

I do have a diagram of a perfect op amp accomplishing the task, but I'm sure Boltean's professor would not receive it well. Although, a simple functional block diagram showing that does answer the question sufficiently.

Of course, your professor could have given you the assignment in this manner ... leaving it up to you to design the innards anyway you saw fit, and show them.

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Last edited: May 20, 2013
12. ### bountyhunter Well-Known Member

Sep 7, 2009
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Except it is 100X times as much which puts it into reality range. There are good low noise preamps like TL072 and NE5532 that can handle signal levels of 100uV with decent signal to noise ratio.

You need to know the bandwidth (audio is typically 20 - 20 KHz).

But to do a design, there must be specs for:

signal-to-noise
harmonic distortion
slew rate

and the other relevant specs that define performance.

You also did not specify the available power rails: +/- 12V only?

Did the teacher say you could use integrated devices?

You could use a TDA2030 power amp with a TL072 pre amp stage.

Last edited: May 20, 2013
13. ### Boltean Thread Starter New Member

May 19, 2013
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He said we can't use integrated devices.We can only use devices from Orcad PsPice library.I asked about the power rails and he said the value of it would be irrelevant .I decided to go with the second diagram http://postimg.org/image/wfeztihf1/